Merge remote-tracking branch 'origin/master' into handle-missing-gc-socket

.clang-format

@@ -0,0 +1,30 @@
+BasedOnStyle: LLVM
+IndentWidth: 4
+BreakBeforeBraces: Custom
+BraceWrapping:
+  AfterStruct: true
+  AfterClass: true
+  AfterFunction: true
+  AfterUnion: true
+  SplitEmptyRecord: false
+PointerAlignment: Middle
+FixNamespaceComments: false
+SortIncludes: Never
+#IndentPPDirectives: BeforeHash
+SpaceAfterCStyleCast: true
+SpaceAfterTemplateKeyword: false
+AccessModifierOffset: -4
+AlignAfterOpenBracket: AlwaysBreak
+AlignEscapedNewlines: DontAlign
+ColumnLimit: 120
+BreakStringLiterals: false
+BitFieldColonSpacing: None
+AllowShortFunctionsOnASingleLine: Empty
+AlwaysBreakTemplateDeclarations: Yes
+BinPackParameters: false
+BreakConstructorInitializers: BeforeComma
+EmptyLineAfterAccessModifier: Leave # change to always/never later?
+EmptyLineBeforeAccessModifier: Leave
+#PackConstructorInitializers: BinPack
+BreakBeforeBinaryOperators: NonAssignment
+AlwaysBreakBeforeMultilineStrings: true

.editorconfig

@@ -17,7 +17,7 @@ indent_style = space
 indent_size = 2
 
 # Match c++/shell/perl, set indent to spaces with width of four
-[*.{hpp,cc,hh,sh,pl}]
+[*.{hpp,cc,hh,sh,pl,xs}]
 indent_style = space
 indent_size = 4
 

.github/CODEOWNERS

@@ -10,9 +10,8 @@
 # This file
 .github/CODEOWNERS @edolstra
 
-# Public documentation
+# Documentation of built-in functions
-/doc @fricklerhandwerk
+src/libexpr/primops.cc @roberth
-*.md @fricklerhandwerk
 
 # Libstore layer
 /src/libstore @thufschmitt

.github/PULL_REQUEST_TEMPLATE.md

@@ -10,24 +10,8 @@
 
 <!-- Large change: Provide instructions to reviewers how to read the diff. -->
 
-# Checklist for maintainers
+# Priorities and Process
-
-<!-- Contributors: please leave this as is -->
-
-Maintainers: tick if completed or explain if not relevant
-
- - [ ] agreed on idea
- - [ ] agreed on implementation strategy
- - [ ] tests, as appropriate
-   - functional tests - `tests/**.sh`
-   - unit tests - `src/*/tests`
-   - integration tests - `tests/nixos/*`
- - [ ] documentation in the manual
- - [ ] documentation in the internal API docs
- - [ ] code and comments are self-explanatory
- - [ ] commit message explains why the change was made
- - [ ] new feature or incompatible change: updated release notes
-
-# Priorities
 
 Add :+1: to [pull requests you find important](https://github.com/NixOS/nix/pulls?q=is%3Aopen+sort%3Areactions-%2B1-desc).
+
+The Nix maintainer team uses a [GitHub project board](https://github.com/orgs/NixOS/projects/19) to [schedule and track reviews](https://github.com/NixOS/nix/tree/master/maintainers#project-board-protocol). 

.github/labeler.yml

@@ -1,23 +1,30 @@
 "documentation":
-  - doc/manual/*
+  - changed-files:
-  - src/nix/**/*.md
+    - any-glob-to-any-file: "doc/manual/*"
+    - any-glob-to-any-file: "src/nix/**/*.md"
 
 "store":
-  - src/libstore/store-api.*
+  - changed-files:
-  - src/libstore/*-store.*
+    - any-glob-to-any-file: "src/libstore/store-api.*"
+    - any-glob-to-any-file: "src/libstore/*-store.*"
 
 "fetching":
-  - src/libfetchers/**/*
+  - changed-files:
+    - any-glob-to-any-file: "src/libfetchers/**/*"
 
 "repl":
-  - src/libcmd/repl.*
+  - changed-files:
-  - src/nix/repl.*
+    - any-glob-to-any-file: "src/libcmd/repl.*"
+    - any-glob-to-any-file: "src/nix/repl.*"
 
 "new-cli":
-  - src/nix/**/*
+  - changed-files:
+    - any-glob-to-any-file: "src/nix/**/*"
+
+"with-tests":
+  - changed-files:
+    # Unit tests
+    - any-glob-to-any-file: "src/*/tests/**/*"
+    # Functional and integration tests
+    - any-glob-to-any-file: "tests/functional/**/*"
     
-"tests":
-  # Unit tests
-  - src/*/tests/**/*
-  # Functional and integration tests
-  - tests/**/*

.github/workflows/backport.yml

@@ -14,14 +14,14 @@ jobs:
     if: github.repository_owner == 'NixOS' && github.event.pull_request.merged == true && (github.event_name != 'labeled' || startsWith('backport', github.event.label.name))
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.sha }}
           # required to find all branches
           fetch-depth: 0
       - name: Create backport PRs
         # should be kept in sync with `version`
-        uses: zeebe-io/backport-action@v1.3.1
+        uses: zeebe-io/backport-action@v2.3.0
         with:
           # Config README: https://github.com/zeebe-io/backport-action#backport-action
           github_token: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/ci.yml

@@ -17,15 +17,15 @@ jobs:
     runs-on: ${{ matrix.os }}
     timeout-minutes: 60
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v24
       with:
         # The sandbox would otherwise be disabled by default on Darwin
         extra_nix_config: "sandbox = true"
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
-    - uses: cachix/cachix-action@v12
+    - uses: cachix/cachix-action@v13
       if: needs.check_secrets.outputs.cachix == 'true'
       with:
         name: '${{ env.CACHIX_NAME }}'
@@ -58,14 +58,14 @@ jobs:
     outputs:
       installerURL: ${{ steps.prepare-installer.outputs.installerURL }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v24
       with:
         install_url: https://releases.nixos.org/nix/nix-2.13.3/install
-    - uses: cachix/cachix-action@v12
+    - uses: cachix/cachix-action@v13
       with:
         name: '${{ env.CACHIX_NAME }}'
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
@@ -82,9 +82,9 @@ jobs:
         os: [ubuntu-latest, macos-latest]
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v24
       with:
         install_url: '${{needs.installer.outputs.installerURL}}'
         install_options: "--tarball-url-prefix https://${{ env.CACHIX_NAME }}.cachix.org/serve"
@@ -101,6 +101,9 @@ jobs:
 
   docker_push_image:
     needs: [check_secrets, tests]
+    permissions:
+      contents: read
+      packages: write
     if: >-
       github.event_name == 'push' &&
       github.ref_name == 'master' &&
@@ -108,15 +111,15 @@ jobs:
       needs.check_secrets.outputs.docker == 'true'
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v24
       with:
         install_url: https://releases.nixos.org/nix/nix-2.13.3/install
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
     - run: echo NIX_VERSION="$(nix --experimental-features 'nix-command flakes' eval .\#default.version | tr -d \")" >> $GITHUB_ENV
-    - uses: cachix/cachix-action@v12
+    - uses: cachix/cachix-action@v13
       if: needs.check_secrets.outputs.cachix == 'true'
       with:
         name: '${{ env.CACHIX_NAME }}'
@@ -126,10 +129,30 @@ jobs:
     - run: docker load -i ./result/image.tar.gz
     - run: docker tag nix:$NIX_VERSION nixos/nix:$NIX_VERSION
     - run: docker tag nix:$NIX_VERSION nixos/nix:master
+    # We'll deploy the newly built image to both Docker Hub and Github Container Registry.
+    #
+    # Push to Docker Hub first
     - name: Login to Docker Hub
-      uses: docker/login-action@v2
+      uses: docker/login-action@v3
       with:
         username: ${{ secrets.DOCKERHUB_USERNAME }}
         password: ${{ secrets.DOCKERHUB_TOKEN }}
     - run: docker push nixos/nix:$NIX_VERSION
     - run: docker push nixos/nix:master
+    # Push to GitHub Container Registry as well
+    - name: Login to GitHub Container Registry
+      uses: docker/login-action@v3
+      with:
+        registry: ghcr.io
+        username: ${{ github.actor }}
+        password: ${{ secrets.GITHUB_TOKEN }}
+    - name: Push image
+      run: |
+        IMAGE_ID=ghcr.io/${{ github.repository_owner }}/nix
+        # Change all uppercase to lowercase
+        IMAGE_ID=$(echo $IMAGE_ID | tr '[A-Z]' '[a-z]')
+
+        docker tag nix:$NIX_VERSION $IMAGE_ID:$NIX_VERSION
+        docker tag nix:$NIX_VERSION $IMAGE_ID:master
+        docker push $IMAGE_ID:$NIX_VERSION
+        docker push $IMAGE_ID:master

.github/workflows/hydra_status.yml

@@ -13,7 +13,7 @@ jobs:
     if: github.repository_owner == 'NixOS'
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
     - run: bash scripts/check-hydra-status.sh

.github/workflows/labels.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.repository_owner == 'NixOS'
     steps:
-    - uses: actions/labeler@v4
+    - uses: actions/labeler@v5
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
-        sync-labels: true
+        sync-labels: false

.gitignore

@@ -18,14 +18,19 @@ perl/Makefile.config
 /doc/manual/generated/*
 /doc/manual/nix.json
 /doc/manual/conf-file.json
-/doc/manual/builtins.json
+/doc/manual/language.json
 /doc/manual/xp-features.json
 /doc/manual/src/SUMMARY.md
+/doc/manual/src/SUMMARY-rl-next.md
+/doc/manual/src/store/types/*
+!/doc/manual/src/store/types/index.md.in
 /doc/manual/src/command-ref/new-cli
 /doc/manual/src/command-ref/conf-file.md
 /doc/manual/src/command-ref/experimental-features-shortlist.md
 /doc/manual/src/contributing/experimental-feature-descriptions.md
 /doc/manual/src/language/builtins.md
+/doc/manual/src/language/builtin-constants.md
+/doc/manual/src/release-notes/rl-next.md
 
 # /scripts/
 /scripts/nix-profile.sh
@@ -40,18 +45,18 @@ perl/Makefile.config
 /src/libexpr/parser-tab.hh
 /src/libexpr/parser-tab.output
 /src/libexpr/nix.tbl
-/src/libexpr/tests/libnixexpr-tests
+/tests/unit/libexpr/libnixexpr-tests
 
 # /src/libstore/
 *.gen.*
-/src/libstore/tests/libnixstore-tests
+/tests/unit/libstore/libnixstore-tests
 
 # /src/libutil/
-/src/libutil/tests/libnixutil-tests
+/tests/unit/libutil/libnixutil-tests
 
 /src/nix/nix
 
-/src/nix/doc
+/src/nix/generated-doc
 
 # /src/nix-env/
 /src/nix-env/nix-env
@@ -78,23 +83,24 @@ perl/Makefile.config
 
 /src/build-remote/build-remote
 
-# /tests/
+# /tests/functional/
-/tests/test-tmp
+/tests/functional/test-tmp
-/tests/common/vars-and-functions.sh
+/tests/functional/common/vars-and-functions.sh
-/tests/result*
+/tests/functional/result*
-/tests/restricted-innocent
+/tests/functional/restricted-innocent
-/tests/shell
+/tests/functional/shell
-/tests/shell.drv
+/tests/functional/shell.drv
-/tests/config.nix
+/tests/functional/config.nix
-/tests/ca/config.nix
+/tests/functional/ca/config.nix
-/tests/dyn-drv/config.nix
+/tests/functional/dyn-drv/config.nix
-/tests/repl-result-out
+/tests/functional/repl-result-out
-/tests/test-libstoreconsumer/test-libstoreconsumer
+/tests/functional/test-libstoreconsumer/test-libstoreconsumer
 
-# /tests/lang/
+# /tests/functional/lang/
-/tests/lang/*.out
+/tests/functional/lang/*.out
-/tests/lang/*.out.xml
+/tests/functional/lang/*.out.xml
-/tests/lang/*.ast
+/tests/functional/lang/*.err
+/tests/functional/lang/*.ast
 
 /perl/lib/Nix/Config.pm
 /perl/lib/Nix/Store.cc
@@ -135,5 +141,14 @@ compile_commands.json
 nix-rust/target
 
 result
+result-*
 
+# IDE
 .vscode/
+.idea/
+
+# clangd and possibly more
+.cache/
+
+# Mac OS
+.DS_Store

.version

@@ -1 +1 @@
-2.17.0
+2.20.0

CONTRIBUTING.md

@@ -24,30 +24,51 @@ Check out the [security policy](https://github.com/NixOS/nix/security/policy).
 
 ## Making changes to Nix
 
-1. Check for [pull requests](https://github.com/NixOS/nix/pulls) that might already cover the contribution you are about to make.
+1. Search for related issues that cover what you're going to work on.
-   There are many open pull requests that might already do what you intent to work on.
+   It could help to mention there that you will work on the issue.
+
+   Issues labeled [good first issue](https://github.com/NixOS/nix/labels/good%20first%20issue) should be relatively easy to fix and are likely to get merged quickly.
+   Pull requests addressing issues labeled [idea approved](https://github.com/NixOS/nix/labels/idea%20approved) or [RFC](https://github.com/NixOS/nix/labels/RFC) are especially welcomed by maintainers and will receive prioritised review.
+
+   If you are proficient with C++, addressing one of the [popular issues](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc) will be highly appreciated by maintainers and Nix users all over the world.
+   For far-reaching changes, please investigate possible blockers and design implications, and coordinate with maintainers before investing too much time in writing code that may not end up getting merged.
+
+   If there is no relevant issue yet and you're not sure whether your change is likely to be accepted, [open an issue](https://github.com/NixOS/nix/issues/new/choose) yourself.
+
+2. Check for [pull requests](https://github.com/NixOS/nix/pulls) that might already cover the contribution you are about to make.
+   There are many open pull requests that might already do what you intend to work on.
    You can use [labels](https://github.com/NixOS/nix/labels) to filter for relevant topics.
 
-2. Search for related issues that cover what you're going to work on. It could help to mention there that you will work on the issue.
-
-   Issues labeled ["good first issue"](https://github.com/NixOS/nix/labels/good-first-issue) should be relatively easy to fix and are likely to get merged quickly.
-   Pull requests addressing issues labeled ["idea approved"](https://github.com/NixOS/nix/labels/idea%20approved) are especially welcomed by maintainers and will receive prioritised review.
-
 3. Check the [Nix reference manual](https://nixos.org/manual/nix/unstable/contributing/hacking.html) for information on building Nix and running its tests.
 
    For contributions to the command line interface, please check the [CLI guidelines](https://nixos.org/manual/nix/unstable/contributing/cli-guideline.html).
 
-4. Make your changes!
+4. Make your change!
 
 5. [Create a pull request](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request) for your changes.
-   * [Mark the pull request as draft](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request) if you're not done with the changes.
+   * Clearly explain the problem that you're solving.
+
+     Link related issues to inform interested parties and future contributors about your change.
+     If your pull request closes one or multiple issues, mention that in the description using `Closes: #<number>`, as it will then happen automatically when your change is merged.
    * Make sure to have [a clean history of commits on your branch by using rebase](https://www.digitalocean.com/community/tutorials/how-to-rebase-and-update-a-pull-request).
-   * Link related issues in your pull request to inform interested parties and future contributors about your change.
+   * [Mark the pull request as draft](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request) if you're not done with the changes.
-     If your pull request closes one or multiple issues, note that in the description using `Closes: #<number>`, as it will then happen automatically when your change is merged.
 
 6. Do not expect your pull request to be reviewed immediately.
    Nix maintainers follow a [structured process for reviews and design decisions](https://github.com/NixOS/nix/tree/master/maintainers#project-board-protocol), which may or may not prioritise your work.
 
+   Following this checklist will make the process smoother for everyone:
+
+   - [ ] Fixes an [idea approved](https://github.com/NixOS/nix/labels/idea%20approved) issue
+   - [ ] Tests, as appropriate:
+     - Functional tests – [`tests/functional/**.sh`](./tests/functional)
+     - Unit tests – [`src/*/tests`](./src/)
+     - Integration tests – [`tests/nixos/*`](./tests/nixos)
+   - [ ] User documentation in the [manual](..doc/manual/src)
+   - [ ] API documentation in header files
+   - [ ] Code and comments are self-explanatory
+   - [ ] Commit message explains **why** the change was made
+   - [ ] New feature or incompatible change: updated [release notes](./doc/manual/src/release-notes/rl-next.md)
+
 7. If you need additional feedback or help to getting pull request into shape, ask other contributors using [@mentions](https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#mentioning-people-and-teams).
 
 ## Making changes to the Nix manual

Makefile

@@ -1,3 +1,13 @@
+# External build directory support
+
+include mk/build-dir.mk
+
+-include $(buildprefix)Makefile.config
+clean-files += $(buildprefix)Makefile.config
+
+# List makefiles
+
+ifeq ($(ENABLE_BUILD), yes)
 makefiles = \
   mk/precompiled-headers.mk \
   local.mk \
@@ -15,25 +25,30 @@ makefiles = \
   misc/zsh/local.mk \
   misc/systemd/local.mk \
   misc/launchd/local.mk \
-  misc/upstart/local.mk \
+  misc/upstart/local.mk
-  doc/manual/local.mk \
-  doc/internal-api/local.mk
-
--include Makefile.config
-
-ifeq ($(tests), yes)
-makefiles += \
-  src/libutil/tests/local.mk \
-  src/libstore/tests/local.mk \
-  src/libexpr/tests/local.mk \
-  tests/local.mk \
-  tests/test-libstoreconsumer/local.mk \
-  tests/plugins/local.mk
-else
-makefiles += \
-  mk/disable-tests.mk
 endif
 
+ifeq ($(ENABLE_UNIT_TESTS), yes)
+makefiles += \
+  tests/unit/libutil/local.mk \
+  tests/unit/libutil-support/local.mk \
+  tests/unit/libstore/local.mk \
+  tests/unit/libstore-support/local.mk \
+  tests/unit/libexpr/local.mk \
+  tests/unit/libexpr-support/local.mk
+endif
+
+ifeq ($(ENABLE_FUNCTIONAL_TESTS), yes)
+makefiles += \
+  tests/functional/local.mk \
+  tests/functional/ca/local.mk \
+  tests/functional/dyn-drv/local.mk \
+  tests/functional/test-libstoreconsumer/local.mk \
+  tests/functional/plugins/local.mk
+endif
+
+# Miscellaneous global Flags
+
 OPTIMIZE = 1
 
 ifeq ($(OPTIMIZE), 1)
@@ -43,6 +58,63 @@ else
   GLOBAL_CXXFLAGS += -O0 -U_FORTIFY_SOURCE
 endif
 
+include mk/platform.mk
+
+ifdef HOST_WINDOWS
+  # Windows DLLs are stricter about symbol visibility than Unix shared
+  # objects --- see https://gcc.gnu.org/wiki/Visibility for details.
+  # This is a temporary sledgehammer to export everything like on Unix,
+  # and not detail with this yet.
+  #
+  # TODO do not do this, and instead do fine-grained export annotations.
+  GLOBAL_LDFLAGS += -Wl,--export-all-symbols
+endif
+
+GLOBAL_CXXFLAGS += -g -Wall -include $(buildprefix)config.h -std=c++2a -I src
+
+# Include the main lib, causing rules to be defined
+
 include mk/lib.mk
 
-GLOBAL_CXXFLAGS += -g -Wall -include config.h -std=c++2a -I src
+# Fallback stub rules for better UX when things are disabled
+#
+# These must be defined after `mk/lib.mk`. Otherwise the first rule
+# incorrectly becomes the default target.
+
+ifneq ($(ENABLE_UNIT_TESTS), yes)
+.PHONY: check
+check:
+	@echo "Unit tests are disabled. Configure without '--disable-unit-tests', or avoid calling 'make check'."
+	@exit 1
+endif
+
+ifneq ($(ENABLE_FUNCTIONAL_TESTS), yes)
+.PHONY: installcheck
+installcheck:
+	@echo "Functional tests are disabled. Configure without '--disable-functional-tests', or avoid calling 'make installcheck'."
+	@exit 1
+endif
+
+# Documentation or else fallback stub rules.
+#
+# The documentation makefiles be included after `mk/lib.mk` so rules
+# refer to variables defined by `mk/lib.mk`. Rules are not "lazy" like
+# variables, unfortunately.
+
+ifeq ($(ENABLE_DOC_GEN), yes)
+$(eval $(call include-sub-makefile, doc/manual/local.mk))
+else
+.PHONY: manual-html manpages
+manual-html manpages:
+	@echo "Generated docs are disabled. Configure without '--disable-doc-gen', or avoid calling 'make manpages' and 'make manual-html'."
+	@exit 1
+endif
+
+ifeq ($(ENABLE_INTERNAL_API_DOCS), yes)
+$(eval $(call include-sub-makefile, doc/internal-api/local.mk))
+else
+.PHONY: internal-api-html
+internal-api-html:
+	@echo "Internal API docs are disabled. Configure with '--enable-internal-api-docs', or avoid calling 'make internal-api-html'."
+	@exit 1
+endif

Makefile.config.in

@@ -8,15 +8,22 @@ CXX = @CXX@
 CXXFLAGS = @CXXFLAGS@
 CXXLTO = @CXXLTO@
 EDITLINE_LIBS = @EDITLINE_LIBS@
+ENABLE_BUILD = @ENABLE_BUILD@
+ENABLE_DOC_GEN = @ENABLE_DOC_GEN@
+ENABLE_FUNCTIONAL_TESTS = @ENABLE_FUNCTIONAL_TESTS@
+ENABLE_INTERNAL_API_DOCS = @ENABLE_INTERNAL_API_DOCS@
 ENABLE_S3 = @ENABLE_S3@
+ENABLE_UNIT_TESTS = @ENABLE_UNIT_TESTS@
 GTEST_LIBS = @GTEST_LIBS@
 HAVE_LIBCPUID = @HAVE_LIBCPUID@
 HAVE_SECCOMP = @HAVE_SECCOMP@
 HOST_OS = @host_os@
+INSTALL_UNIT_TESTS = @INSTALL_UNIT_TESTS@
 LDFLAGS = @LDFLAGS@
 LIBARCHIVE_LIBS = @LIBARCHIVE_LIBS@
 LIBBROTLI_LIBS = @LIBBROTLI_LIBS@
 LIBCURL_LIBS = @LIBCURL_LIBS@
+LIBGIT2_LIBS = @LIBGIT2_LIBS@
 LIBSECCOMP_LIBS = @LIBSECCOMP_LIBS@
 LOWDOWN_LIBS = @LOWDOWN_LIBS@
 OPENSSL_LIBS = @OPENSSL_LIBS@
@@ -28,9 +35,10 @@ SODIUM_LIBS = @SODIUM_LIBS@
 SQLITE3_LIBS = @SQLITE3_LIBS@
 bash = @bash@
 bindir = @bindir@
+checkbindir = @checkbindir@
+checklibdir = @checklibdir@
 datadir = @datadir@
 datarootdir = @datarootdir@
-doc_generate = @doc_generate@
 docdir = @docdir@
 embedded_sandbox_shell = @embedded_sandbox_shell@
 exec_prefix = @exec_prefix@
@@ -46,5 +54,3 @@ sandbox_shell = @sandbox_shell@
 storedir = @storedir@
 sysconfdir = @sysconfdir@
 system = @system@
-tests = @tests@
-internal_api_docs = @internal_api_docs@

README.md

@@ -7,21 +7,20 @@ Nix is a powerful package manager for Linux and other Unix systems that makes pa
 management reliable and reproducible. Please refer to the [Nix manual](https://nixos.org/nix/manual)
 for more details.
 
-## Installation
+## Installation and first steps
 
-On Linux and macOS the easiest way to install Nix is to run the following shell command
+Visit [nix.dev](https://nix.dev) for [installation instructions](https://nix.dev/tutorials/install-nix) and [beginner tutorials](https://nix.dev/tutorials/first-steps).
-(as a user other than root):
 
-```console
+Full reference documentation can be found in the [Nix manual](https://nixos.org/nix/manual).
-$ curl -L https://nixos.org/nix/install | sh
-```
-
-Information on additional installation methods is available on the [Nix download page](https://nixos.org/download.html).
 
 ## Building And Developing
 
 See our [Hacking guide](https://nixos.org/manual/nix/unstable/contributing/hacking.html) in our manual for instruction on how to
-to set up a development environment and build Nix from source.
+ set up a development environment and build Nix from source.
+
+## Contributing
+
+Check the [contributing guide](./CONTRIBUTING.md) if you want to get involved with developing Nix.
 
 ## Additional Resources
 
@@ -29,7 +28,6 @@ to set up a development environment and build Nix from source.
 - [Nix jobsets on hydra.nixos.org](https://hydra.nixos.org/project/nix)
 - [NixOS Discourse](https://discourse.nixos.org/)
 - [Matrix - #nix:nixos.org](https://matrix.to/#/#nix:nixos.org)
-- [IRC - #nixos on libera.chat](irc://irc.libera.chat/#nixos)
 
 ## License
 

boehmgc-coroutine-sp-fallback.diff

@@ -59,12 +59,18 @@ index b5d71e62..aed7b0bf 100644
      GC_bool found_me = FALSE;
      size_t nthreads = 0;
      int i;
-@@ -851,6 +853,31 @@ GC_INNER void GC_push_all_stacks(void)
+@@ -851,6 +853,37 @@ GC_INNER void GC_push_all_stacks(void)
            hi = p->altstack + p->altstack_size;
            /* FIXME: Need to scan the normal stack too, but how ? */
            /* FIXME: Assume stack grows down */
 +        } else {
-+          if (pthread_getattr_np(p->id, &pattr)) {
++#ifdef HAVE_PTHREAD_ATTR_GET_NP
++          if (!pthread_attr_init(&pattr)
++              || !pthread_attr_get_np(p->id, &pattr))
++#else /* HAVE_PTHREAD_GETATTR_NP */
++          if (pthread_getattr_np(p->id, &pattr))
++#endif
++          {
 +            ABORT("GC_push_all_stacks: pthread_getattr_np failed!");
 +          }
 +          if (pthread_attr_getstacksize(&pattr, &stack_limit)) {

boehmgc-traceable_allocator-public.diff

@@ -0,0 +1,12 @@
+diff --git a/include/gc_allocator.h b/include/gc_allocator.h
+index 597c7f13..587286be 100644
+--- a/include/gc_allocator.h
++++ b/include/gc_allocator.h
+@@ -312,6 +312,7 @@ public:
+ 
+ template<>
+ class traceable_allocator<void> {
++public:
+   typedef size_t      size_type;
+   typedef ptrdiff_t   difference_type;
+   typedef void*       pointer;

bootstrap.sh

@@ -1,4 +0,0 @@
-#! /bin/sh -e
-rm -f aclocal.m4
-mkdir -p config
-exec autoreconf -vfi

configure.ac

@@ -5,7 +5,14 @@ AC_CONFIG_AUX_DIR(config)
 
 AC_PROG_SED
 
-# Construct a Nix system name (like "i686-linux").
+# Construct a Nix system name (like "i686-linux"):
+# https://www.gnu.org/software/autoconf/manual/html_node/Canonicalizing.html#index-AC_005fCANONICAL_005fHOST-1
+# The inital value is produced by the `config/config.guess` script:
+# upstream: https://git.savannah.gnu.org/cgit/config.git/tree/config.guess
+# It has the following form, which is not documented anywhere:
+# <cpu>-<vendor>-<os>[<version>][-<abi>]
+# If `./configure` is passed any of the `--host`, `--build`, `--target` options, the value comes from `config/config.sub` instead:
+# upstream: https://git.savannah.gnu.org/cgit/config.git/tree/config.sub
 AC_CANONICAL_HOST
 AC_MSG_CHECKING([for the canonical Nix system name])
 
@@ -61,6 +68,9 @@ case "$host_os" in
 esac
 
 
+ENSURE_NO_GCC_BUG_80431
+
+
 # Check for pubsetbuf.
 AC_MSG_CHECKING([for pubsetbuf])
 AC_LANG_PUSH(C++)
@@ -112,7 +122,6 @@ AC_PATH_PROG(flex, flex, false)
 AC_PATH_PROG(bison, bison, false)
 AC_PATH_PROG(dot, dot)
 AC_PATH_PROG(lsof, lsof, lsof)
-NEED_PROG(jq, jq)
 
 
 AC_SUBST(coreutils, [$(dirname $(type -p cat))])
@@ -123,6 +132,48 @@ AC_ARG_WITH(store-dir, AS_HELP_STRING([--with-store-dir=PATH],[path of the Nix s
 AC_SUBST(storedir)
 
 
+# Running the functional tests without building Nix is useful for testing
+# different pre-built versions of Nix against each other.
+AC_ARG_ENABLE(build, AS_HELP_STRING([--disable-build],[Do not build nix]),
+  ENABLE_BUILD=$enableval, ENABLE_BUILD=yes)
+AC_SUBST(ENABLE_BUILD)
+
+# Building without unit tests is useful for bootstrapping with a smaller footprint
+# or running the tests in a separate derivation. Otherwise, we do compile and
+# run them.
+
+AC_ARG_ENABLE(unit-tests, AS_HELP_STRING([--disable-unit-tests],[Do not build the tests]),
+  ENABLE_UNIT_TESTS=$enableval, ENABLE_UNIT_TESTS=$ENABLE_BUILD)
+AC_SUBST(ENABLE_UNIT_TESTS)
+
+AS_IF(
+  [test "$ENABLE_BUILD" == "no" && test "$ENABLE_UNIT_TESTS" == "yes"],
+  [AC_MSG_ERROR([Cannot enable unit tests when building overall is disabled. Please do not pass '--enable-unit-tests' or do not pass '--disable-build'.])])
+
+AC_ARG_ENABLE(functional-tests, AS_HELP_STRING([--disable-functional-tests],[Do not build the tests]),
+  ENABLE_FUNCTIONAL_TESTS=$enableval, ENABLE_FUNCTIONAL_TESTS=yes)
+AC_SUBST(ENABLE_FUNCTIONAL_TESTS)
+
+# documentation generation switch
+AC_ARG_ENABLE(doc-gen, AS_HELP_STRING([--disable-doc-gen],[disable documentation generation]),
+  ENABLE_DOC_GEN=$enableval, ENABLE_DOC_GEN=$ENABLE_BUILD)
+AC_SUBST(ENABLE_DOC_GEN)
+
+AS_IF(
+  [test "$ENABLE_BUILD" == "no" && test "$ENABLE_DOC_GEN" == "yes"],
+  [AC_MSG_ERROR([Cannot enable generated docs when building overall is disabled. Please do not pass '--enable-doc-gen' or do not pass '--disable-build'.])])
+
+# Building without API docs is the default as Nix' C++ interfaces are internal and unstable.
+AC_ARG_ENABLE(internal-api-docs, AS_HELP_STRING([--enable-internal-api-docs],[Build API docs for Nix's internal unstable C++ interfaces]),
+  ENABLE_INTERNAL_API_DOCS=$enableval, ENABLE_INTERNAL_API_DOCS=no)
+AC_SUBST(ENABLE_INTERNAL_API_DOCS)
+
+AS_IF(
+  [test "$ENABLE_FUNCTIONAL_TESTS" == "yes" || test "$ENABLE_DOC_GEN" == "yes"],
+  [NEED_PROG(jq, jq)])
+
+AS_IF([test "$ENABLE_BUILD" == "yes"],[
+
 # Look for boost, a required dependency.
 # Note that AX_BOOST_BASE only exports *CPP* BOOST_CPPFLAGS, no CXX flags,
 # and CPPFLAGS are not passed to the C++ compiler automatically.
@@ -145,17 +196,17 @@ if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
     LDFLAGS="-latomic $LDFLAGS"
 fi
 
-# Building without tests is useful for bootstrapping with a smaller footprint
+AC_ARG_ENABLE(install-unit-tests, AS_HELP_STRING([--enable-install-unit-tests],[Install the unit tests for running later (default no)]),
-# or running the tests in a separate derivation. Otherwise, we do compile and
+  INSTALL_UNIT_TESTS=$enableval, INSTALL_UNIT_TESTS=no)
-# run them.
+AC_SUBST(INSTALL_UNIT_TESTS)
-AC_ARG_ENABLE(tests, AS_HELP_STRING([--disable-tests],[Do not build the tests]),
-  tests=$enableval, tests=yes)
-AC_SUBST(tests)
 
-# Building without API docs is the default as Nix' C++ interfaces are internal and unstable.
+AC_ARG_WITH(check-bin-dir, AS_HELP_STRING([--with-check-bin-dir=PATH],[path to install unit tests for running later (defaults to $libexecdir/nix)]),
-AC_ARG_ENABLE(internal_api_docs, AS_HELP_STRING([--enable-internal-api-docs],[Build API docs for Nix's internal unstable C++ interfaces]),
+  checkbindir=$withval, checkbindir=$libexecdir/nix)
-  internal_api_docs=$enableval, internal_api_docs=no)
+AC_SUBST(checkbindir)
-AC_SUBST(internal_api_docs)
+
+AC_ARG_WITH(check-lib-dir, AS_HELP_STRING([--with-check-lib-dir=PATH],[path to install unit tests for running later (defaults to $libdir)]),
+  checklibdir=$withval, checklibdir=$libdir)
+AC_SUBST(checklibdir)
 
 # LTO is currently broken with clang for unknown reasons; ld segfaults in the llvm plugin
 AC_ARG_ENABLE(lto, AS_HELP_STRING([--enable-lto],[Enable LTO (only supported with GCC) [default=no]]),
@@ -200,17 +251,25 @@ PKG_CHECK_MODULES([SQLITE3], [sqlite3 >= 3.6.19], [CXXFLAGS="$SQLITE3_CFLAGS $CX
 # Look for libcurl, a required dependency.
 PKG_CHECK_MODULES([LIBCURL], [libcurl], [CXXFLAGS="$LIBCURL_CFLAGS $CXXFLAGS"])
 
-# Look for editline, a required dependency.
+# Look for editline or readline, a required dependency.
 # The the libeditline.pc file was added only in libeditline >= 1.15.2,
 # see https://github.com/troglobit/editline/commit/0a8f2ef4203c3a4a4726b9dd1336869cd0da8607,
-# but e.g. Ubuntu 16.04 has an older version, so we fall back to searching for
+# Older versions are no longer supported.
-# editline.h when the pkg-config approach fails.
+AC_ARG_WITH(
-PKG_CHECK_MODULES([EDITLINE], [libeditline], [CXXFLAGS="$EDITLINE_CFLAGS $CXXFLAGS"], [
+  [readline-flavor],
-  AC_CHECK_HEADERS([editline.h], [true],
+  AS_HELP_STRING([--with-readline-flavor],[Which library to use for nice line editting with the Nix language REPL" [default=editline]]),
-    [AC_MSG_ERROR([Nix requires libeditline; it was found neither via pkg-config nor its normal header.])])
+  [readline_flavor=$withval],
-  AC_SEARCH_LIBS([readline read_history], [editline], [],
+  [readline_flavor=editline])
-    [AC_MSG_ERROR([Nix requires libeditline; it was not found via pkg-config, but via its header, but required functions do not work. Maybe it is too old? >= 1.14 is required.])])
+AS_CASE(["$readline_flavor"],
-])
+  [editline], [
+    readline_flavor_pc=libeditline
+  ],
+  [readline], [
+    readline_flavor_pc=readline
+    AC_DEFINE([USE_READLINE], [1], [Use readline instead of editline])
+  ],
+  [AC_MSG_ERROR([bad value "$readline_flavor" for --with-readline-flavor, must be one of: editline, readline])])
+PKG_CHECK_MODULES([EDITLINE], [$readline_flavor_pc], [CXXFLAGS="$EDITLINE_CFLAGS $CXXFLAGS"])
 
 # Look for libsodium.
 PKG_CHECK_MODULES([SODIUM], [libsodium], [CXXFLAGS="$SODIUM_CFLAGS $CXXFLAGS"])
@@ -255,6 +314,14 @@ case "$host_os" in
 esac
 AC_SUBST(HAVE_SECCOMP, [$have_seccomp])
 
+# Optional dependencies for better normalizing file system data
+AC_CHECK_HEADERS([sys/xattr.h])
+AS_IF([test "$ac_cv_header_sys_xattr_h" = "yes"],[
+  AC_CHECK_FUNCS([llistxattr lremovexattr])
+  AS_IF([test "$ac_cv_func_llistxattr" = "yes" && test "$ac_cv_func_lremovexattr" = "yes"],[
+    AC_DEFINE([HAVE_ACL_SUPPORT], [1], [Define if we can manipulate file system Access Control Lists])
+  ])
+])
 
 # Look for aws-cpp-sdk-s3.
 AC_LANG_PUSH(C++)
@@ -281,8 +348,7 @@ if test "$gc" = yes; then
   AC_DEFINE(HAVE_BOEHMGC, 1, [Whether to use the Boehm garbage collector.])
 fi
 
-
+AS_IF([test "$ENABLE_UNIT_TESTS" == "yes"],[
-if test "$tests" = yes; then
 
 # Look for gtest.
 PKG_CHECK_MODULES([GTEST], [gtest_main])
@@ -309,19 +375,32 @@ AC_LINK_IFELSE([
   [AC_MSG_ERROR([librapidcheck is not found.])])
 AC_LANG_POP(C++)
 
-fi
+])
 
 # Look for nlohmann/json.
 PKG_CHECK_MODULES([NLOHMANN_JSON], [nlohmann_json >= 3.9])
 
 
-# documentation generation switch
-AC_ARG_ENABLE(doc-gen, AS_HELP_STRING([--disable-doc-gen],[disable documentation generation]),
-  doc_generate=$enableval, doc_generate=yes)
-AC_SUBST(doc_generate)
-
 # Look for lowdown library.
-PKG_CHECK_MODULES([LOWDOWN], [lowdown >= 0.9.0], [CXXFLAGS="$LOWDOWN_CFLAGS $CXXFLAGS"])
+AC_ARG_ENABLE([markdown], AS_HELP_STRING([--enable-markdown], [Enable Markdown rendering in the Nix binary (requires lowdown) [default=auto]]),
+  enable_markdown=$enableval, enable_markdown=auto)
+AS_CASE(["$enable_markdown"],
+  [yes | auto], [
+    PKG_CHECK_MODULES([LOWDOWN], [lowdown >= 0.9.0], [
+      CXXFLAGS="$LOWDOWN_CFLAGS $CXXFLAGS"
+      have_lowdown=1
+      AC_DEFINE(HAVE_LOWDOWN, 1, [Whether lowdown is available and should be used for Markdown rendering.])
+    ], [
+      AS_IF([test "x$enable_markdown" == "xyes"], [AC_MSG_ERROR([--enable-markdown was specified, but lowdown was not found.])])
+    ])
+  ],
+  [no], [have_lowdown=],
+  [AC_MSG_ERROR([bad value "$enable_markdown" for --enable-markdown, must be one of: yes, no, auto])])
+
+
+# Look for libgit2.
+PKG_CHECK_MODULES([LIBGIT2], [libgit2])
+
 
 # Setuid installations.
 AC_CHECK_FUNCS([setresuid setreuid lchown])
@@ -353,6 +432,8 @@ if test "$embedded_sandbox_shell" = yes; then
   AC_DEFINE(HAVE_EMBEDDED_SANDBOX_SHELL, 1, [Include the sandbox shell in the Nix binary.])
 fi
 
+])
+
 
 # Expand all variables in config.status.
 test "$prefix" = NONE && prefix=$ac_default_prefix

doc/internal-api/doxygen.cfg.in

@@ -39,21 +39,42 @@ INPUT                  = \
   src/libcmd \
   src/libexpr \
   src/libexpr/flake \
-  src/libexpr/tests \
+  tests/unit/libexpr \
-  src/libexpr/tests/value \
+  tests/unit/libexpr/value \
+  tests/unit/libexpr/test \
+  tests/unit/libexpr/test/value \
   src/libexpr/value \
   src/libfetchers \
   src/libmain \
   src/libstore \
   src/libstore/build \
   src/libstore/builtins \
-  src/libstore/tests \
+  tests/unit/libstore \
+  tests/unit/libstore/test \
   src/libutil \
-  src/libutil/tests \
+  tests/unit/libutil \
+  tests/unit/libutil/test \
   src/nix \
   src/nix-env \
   src/nix-store
 
+# If the MACRO_EXPANSION tag is set to YES, doxygen will expand all macro names
+# in the source code. If set to NO, only conditional compilation will be
+# performed. Macro expansion can be done in a controlled way by setting
+# EXPAND_ONLY_PREDEF to YES.
+# The default value is: NO.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+MACRO_EXPANSION        = YES
+
+# If the EXPAND_ONLY_PREDEF and MACRO_EXPANSION tags are both set to YES then
+# the macro expansion is limited to the macros specified with the PREDEFINED and
+# EXPAND_AS_DEFINED tags.
+# The default value is: NO.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+EXPAND_ONLY_PREDEF     = YES
+
 # The INCLUDE_PATH tag can be used to specify one or more directories that
 # contain include files that are not input files but should be processed by the
 # preprocessor. Note that the INCLUDE_PATH is not recursive, so the setting of
@@ -61,3 +82,16 @@ INPUT                  = \
 # This tag requires that the tag SEARCH_INCLUDES is set to YES.
 
 INCLUDE_PATH           = @RAPIDCHECK_HEADERS@
+
+# If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
+# tag can be used to specify a list of macro names that should be expanded. The
+# macro definition that is found in the sources will be used. Use the PREDEFINED
+# tag if you want to use a different macro definition that overrules the
+# definition found in the source code.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+EXPAND_AS_DEFINED      = \
+  DECLARE_COMMON_SERIALISER \
+  DECLARE_WORKER_SERIALISER \
+  DECLARE_SERVE_SERIALISER \
+  LENGTH_PREFIXED_PROTO_HELPER

doc/internal-api/local.mk

@@ -1,19 +1,7 @@
-.PHONY: internal-api-html
-
-ifeq ($(internal_api_docs), yes)
-
 $(docdir)/internal-api/html/index.html $(docdir)/internal-api/latex: $(d)/doxygen.cfg
 	mkdir -p $(docdir)/internal-api
 	{ cat $< ; echo "OUTPUT_DIRECTORY=$(docdir)/internal-api" ; } | doxygen -
 
 # Generate the HTML API docs for Nix's unstable internal interfaces.
+.PHONY: internal-api-html
 internal-api-html: $(docdir)/internal-api/html/index.html
-
-else
-
-# Make a nicer error message
-internal-api-html:
-	@echo "Internal API docs are disabled. Configure with '--enable-internal-api-docs', or avoid calling 'make internal-api-html'."
-	@exit 1
-
-endif

doc/manual/_redirects

@@ -0,0 +1,40 @@
+# redirect rules for paths (server-side) to prevent link rot.
+# see ./redirects.js for redirects based on URL fragments (client-side)
+#
+# concrete user story this supports:
+# - user finds URL to the manual for Nix x.y
+# - Nix x.z (z > y) is the most recent release
+# - updating the version in the URL will show the right thing
+#
+# format documentation:
+# - https://docs.netlify.com/routing/redirects/#syntax-for-the-redirects-file
+# - https://docs.netlify.com/routing/redirects/redirect-options/
+#
+# conventions:
+# - always force (<CODE>!) since this allows re-using file names
+# - group related paths to ease readability
+# - keep in alphabetical/wildcards-last order, which will reduce version control conflicts
+# - redirects that should have been there but are missing can be inserted where they belong
+
+/advanced-topics/advanced-topics /advanced-topics 301!
+
+/command-ref/command-ref /command-ref 301!
+
+/contributing/contributing /contributing 301!
+
+/expressions/expression-language /language/ 301!
+/expressions/language-constructs /language/constructs 301!
+/expressions/language-operators /language/operators 301!
+/expressions/language-values /language/values 301!
+/expressions/* /language/:splat 301!
+
+/installation/installation /installation 301!
+
+/package-management/basic-package-mgmt /command-ref/nix-env 301!
+/package-management/channels /command-ref/nix-channel 301!
+/package-management/package-management /package-management 301!
+/package-management/s3-substituter /store/types/s3-binary-cache-store 301!
+
+/protocols/protocols /protocols 301!
+
+/release-notes/release-notes /release-notes 301!

doc/manual/generate-builtin-constants.nix

@@ -0,0 +1,31 @@
+let
+  inherit (builtins) concatStringsSep attrValues mapAttrs;
+  inherit (import <nix/utils.nix>) optionalString squash;
+in
+
+builtinsInfo:
+let
+  showBuiltin = name: { doc, type, impure-only }:
+    let
+      type' = optionalString (type != null) " (${type})";
+
+      impureNotice = optionalString impure-only ''
+        > **Note**
+        >
+        > Not available in [pure evaluation mode](@docroot@/command-ref/conf-file.md#conf-pure-eval).
+      '';
+    in
+    squash ''
+      <dt id="builtins-${name}">
+        <a href="#builtins-${name}"><code>${name}</code></a>${type'}
+      </dt>
+      <dd>
+
+      ${doc}
+
+      ${impureNotice}
+
+      </dd>
+    '';
+in
+concatStringsSep "\n" (attrValues (mapAttrs showBuiltin builtinsInfo))

doc/manual/generate-builtins.nix

@@ -1,24 +1,35 @@
 let
-  inherit (builtins) concatStringsSep attrNames;
+  inherit (builtins) concatStringsSep attrValues mapAttrs;
+  inherit (import <nix/utils.nix>) optionalString squash;
 in
 
 builtinsInfo:
 let
-  showBuiltin = name:
+  showBuiltin = name: { doc, args, arity, experimental-feature }:
     let
-      inherit (builtinsInfo.${name}) doc args;
+      experimentalNotice = optionalString (experimental-feature != null) ''
+        > **Note**
+        >
+        > This function is only available if the [`${experimental-feature}` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-${experimental-feature}) is enabled.
+        >
+        > For example, include the following in [`nix.conf`](@docroot@/command-ref/conf-file.md):
+        >
+        > ```
+        > extra-experimental-features = ${experimental-feature}
+        > ```
+      '';
     in
-    ''
+    squash ''
       <dt id="builtins-${name}">
         <a href="#builtins-${name}"><code>${name} ${listArgs args}</code></a>
       </dt>
       <dd>
 
-        ${doc}
+      ${experimentalNotice}
 
+      ${doc}
       </dd>
     '';
   listArgs = args: concatStringsSep " " (map (s: "<var>${s}</var>") args);
 in
-concatStringsSep "\n" (map showBuiltin (attrNames builtinsInfo))
+concatStringsSep "\n" (attrValues (mapAttrs showBuiltin builtinsInfo))
-

doc/manual/generate-manpage.nix

@@ -1,11 +1,32 @@
 let
   inherit (builtins)
-    attrNames attrValues fromJSON listToAttrs mapAttrs
+    attrNames
-    concatStringsSep concatMap length lessThan replaceStrings sort;
+    attrValues
-  inherit (import ./utils.nix) concatStrings optionalString filterAttrs trim squash unique showSettings;
+    concatMap
+    concatStringsSep
+    fromJSON
+    groupBy
+    length
+    lessThan
+    listToAttrs
+    mapAttrs
+    match
+    replaceStrings
+    sort
+    ;
+  inherit (import <nix/utils.nix>)
+    attrsToList
+    concatStrings
+    filterAttrs
+    optionalString
+    squash
+    trim
+    unique
+    ;
+  showStoreDocs = import <nix/generate-store-info.nix>;
 in
 
-commandDump:
+inlineHTML: commandDump:
 
 let
 
@@ -30,7 +51,7 @@ let
 
         ${maybeSubcommands}
 
-        ${maybeDocumentation}
+        ${maybeProse}
 
         ${maybeOptions}
       '';
@@ -40,15 +61,15 @@ let
           showArgument = arg: "*${arg.label}*" + optionalString (! arg ? arity) "...";
           arguments = concatStringsSep " " (map showArgument args);
         in ''
-         `${command}` [*option*...] ${arguments}
+          `${command}` [*option*...] ${arguments}
         '';
 
       maybeSubcommands = optionalString (details ? commands && details.commands != {})
-         ''
+        ''
-           where *subcommand* is one of the following:
+          where *subcommand* is one of the following:
 
-           ${subcommands}
+          ${subcommands}
-         '';
+        '';
 
       subcommands = if length categories > 1
         then listCategories
@@ -70,40 +91,88 @@ let
         * [`${command} ${name}`](./${appendName filename name}.md) - ${subcmd.description}
       '';
 
-      maybeDocumentation = optionalString
+      maybeProse =
-        (details ? doc)
+        # FIXME: this is a horrible hack to keep `nix help-stores` working.
-        (replaceStrings ["@stores@"] [storeDocs] details.doc);
+        # the correct answer to this is to remove that command and replace it
-
+        # by statically generated manpages or the output of something like `nix
-      maybeOptions = optionalString (details.flags != {}) ''
+        # store info <store type>`.
-        # Options
-
-        ${showOptions details.flags toplevel.flags}
-      '';
-
-      showOptions = options: commonOptions:
         let
-          allOptions = options // commonOptions;
+          help-stores = ''
-          showCategory = cat: ''
+            ${index}
-            ${optionalString (cat != "") "**${cat}:**"}
 
-            ${listOptions (filterAttrs (n: v: v.category == cat) allOptions)}
+            ${allStores}
-            '';
+          '';
-          listOptions = opts: concatStringsSep "\n" (attrValues (mapAttrs showOption opts));
+          index = replaceStrings
+            [ "@store-types@" "./local-store.md" "./local-daemon-store.md" ]
+            [ storesOverview "#local-store" "#local-daemon-store" ]
+            details.doc;
+          storesOverview =
+            let
+              showEntry = store:
+                "- [${store.name}](#${store.slug})";
+            in
+            concatStringsSep "\n" (map showEntry storesList) + "\n";
+          allStores = concatStringsSep "\n" (attrValues storePages);
+          storePages = listToAttrs
+            (map (s: { name = s.filename; value = s.page; }) storesList);
+          storesList = showStoreDocs {
+            storeInfo = commandInfo.stores;
+            inherit inlineHTML;
+          };
+        in
+        optionalString (details ? doc) (
+          if match "@store-types@" details.doc != [ ]
+          then help-stores
+          else details.doc
+        );
+
+      maybeOptions =
+        let
+          allVisibleOptions = filterAttrs
+            (_: o: ! o.hiddenCategory)
+            (details.flags // toplevel.flags);
+        in
+        optionalString (allVisibleOptions != { }) ''
+          # Options
+
+          ${showOptions inlineHTML allVisibleOptions}
+
+          > **Note**
+          >
+          > See [`man nix.conf`](@docroot@/command-ref/conf-file.md#command-line-flags) for overriding configuration settings with command line flags.
+        '';
+
+      showOptions = inlineHTML: allOptions:
+        let
+          showCategory = cat: opts: ''
+            ${optionalString (cat != "") "## ${cat}"}
+
+            ${concatStringsSep "\n" (attrValues (mapAttrs showOption opts))}
+          '';
           showOption = name: option:
             let
+              result = trim ''
+                - ${item}
+
+                  ${option.description}
+              '';
+              item = if inlineHTML
+                then ''<span id="opt-${name}">[`--${name}`](#opt-${name})</span> ${shortName} ${labels}''
+                else "`--${name}` ${shortName} ${labels}";
               shortName = optionalString
                 (option ? shortName)
                 ("/ `-${option.shortName}`");
               labels = optionalString
                 (option ? labels)
                 (concatStringsSep " " (map (s: "*${s}*") option.labels));
-            in trim ''
+            in result;
-              - `--${name}` ${shortName} ${labels}
+          categories = mapAttrs
-
+            # Convert each group from a list of key-value pairs back to an attrset
-                ${option.description}
+            (_: listToAttrs)
-            '';
+            (groupBy
-          categories = sort lessThan (unique (map (cmd: cmd.category) (attrValues allOptions)));
+              (cmd: cmd.value.category)
-        in concatStrings (map showCategory categories);
+              (attrsToList allOptions));
+        in concatStrings (attrValues (mapAttrs showCategory categories));
     in squash result;
 
   appendName = filename: name: (if filename == "nix" then "nix3" else filename) + "-" + name;
@@ -135,18 +204,4 @@ let
       "    - [${page.command}](command-ref/new-cli/${page.name})";
     in concatStringsSep "\n" (map showEntry manpages) + "\n";
 
-  storeDocs =
-    let
-      showStore = name: { settings, doc }:
-        ''
-          ## ${name}
-
-          ${doc}
-
-          **Settings**:
-
-          ${showSettings { useAnchors = false; } settings}
-        '';
-    in concatStrings (attrValues (mapAttrs showStore commandInfo.stores));
-
 in (listToAttrs manpages) // { "SUMMARY.md" = tableOfContents; }

doc/manual/generate-settings.nix

@@ -0,0 +1,67 @@
+let
+  inherit (builtins) attrValues concatStringsSep isAttrs isBool mapAttrs;
+  inherit (import <nix/utils.nix>) concatStrings indent optionalString squash;
+in
+
+# `inlineHTML` is a hack to accommodate inconsistent output from `lowdown`
+{ prefix, inlineHTML ? true }: settingsInfo:
+
+let
+
+  showSetting = prefix: setting: { description, documentDefault, defaultValue, aliases, value, experimentalFeature }:
+    let
+      result = squash ''
+          - ${item}
+
+          ${indent "  " body}
+        '';
+      item = if inlineHTML
+        then ''<span id="${prefix}-${setting}">[`${setting}`](#${prefix}-${setting})</span>''
+        else "`${setting}`";
+      # separate body to cleanly handle indentation
+      body = ''
+          ${experimentalFeatureNote}
+
+          ${description}
+
+          **Default:** ${showDefault documentDefault defaultValue}
+
+          ${showAliases aliases}
+        '';
+
+      experimentalFeatureNote = optionalString (experimentalFeature != null) ''
+          > **Warning**
+          >
+          > This setting is part of an
+          > [experimental feature](@docroot@/contributing/experimental-features.md).
+          >
+          > To change this setting, make sure the
+          > [`${experimentalFeature}` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-${experimentalFeature})
+          > is enabled.
+          > For example, include the following in [`nix.conf`](@docroot@/command-ref/conf-file.md):
+          >
+          > ```
+          > extra-experimental-features = ${experimentalFeature}
+          > ${setting} = ...
+          > ```
+        '';
+
+      showDefault = documentDefault: defaultValue:
+        if documentDefault then
+          # a StringMap value type is specified as a string, but
+          # this shows the value type. The empty stringmap is `null` in
+          # JSON, but that converts to `{ }` here.
+          if defaultValue == "" || defaultValue == [] || isAttrs defaultValue
+            then "*empty*"
+            else if isBool defaultValue then
+              if defaultValue then "`true`" else "`false`"
+            else "`${toString defaultValue}`"
+        else "*machine-specific*";
+
+      showAliases = aliases:
+          optionalString (aliases != [])
+            "**Deprecated alias:** ${(concatStringsSep ", " (map (s: "`${s}`") aliases))}";
+
+    in result;
+
+in concatStrings (attrValues (mapAttrs (showSetting prefix) settingsInfo))

doc/manual/generate-store-info.nix

@@ -0,0 +1,57 @@
+let
+  inherit (builtins) attrNames listToAttrs concatStringsSep readFile replaceStrings;
+  inherit (import <nix/utils.nix>) optionalString filterAttrs trim squash toLower unique indent;
+  showSettings = import <nix/generate-settings.nix>;
+in
+
+{
+  # data structure describing all stores and their parameters
+  storeInfo,
+  # whether to add inline HTML tags
+  # `lowdown` does not eat those for one of the output modes
+  inlineHTML,
+}:
+
+let
+
+  showStore = { name, slug }: { settings, doc, experimentalFeature }:
+    let
+      result = squash ''
+        # ${name}
+
+        ${experimentalFeatureNote}
+
+        ${doc}
+
+        ## Settings
+
+        ${showSettings { prefix = "store-${slug}"; inherit inlineHTML; } settings}
+      '';
+
+      experimentalFeatureNote = optionalString (experimentalFeature != null) ''
+        > **Warning**
+        >
+        > This store is part of an
+        > [experimental feature](@docroot@/contributing/experimental-features.md).
+        >
+        > To use this store, make sure the
+        > [`${experimentalFeature}` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-${experimentalFeature})
+        > is enabled.
+        > For example, include the following in [`nix.conf`](@docroot@/command-ref/conf-file.md):
+        >
+        > ```
+        > extra-experimental-features = ${experimentalFeature}
+        > ```
+      '';
+    in result;
+
+  storesList = map
+    (name: rec {
+      inherit name;
+      slug = replaceStrings [ " " ] [ "-" ] (toLower name);
+      filename = "${slug}.md";
+      page = showStore { inherit name slug; } storeInfo.${name};
+    })
+    (attrNames storeInfo);
+
+in storesList

doc/manual/generate-store-types.nix

@@ -0,0 +1,39 @@
+let
+  inherit (builtins) attrNames listToAttrs concatStringsSep readFile replaceStrings;
+  showSettings = import <nix/generate-settings.nix>;
+  showStoreDocs = import <nix/generate-store-info.nix>;
+in
+
+storeInfo:
+
+let
+  storesList = showStoreDocs {
+    inherit storeInfo;
+    inlineHTML = true;
+  };
+
+  index =
+    let
+      showEntry = store:
+        "- [${store.name}](./${store.filename})";
+    in
+    concatStringsSep "\n" (map showEntry storesList);
+
+  "index.md" = replaceStrings
+    [ "@store-types@" ] [ index ]
+    (readFile ./src/store/types/index.md.in);
+
+  tableOfContents =
+    let
+      showEntry = store:
+        "    - [${store.name}](store/types/${store.filename})";
+    in
+    concatStringsSep "\n" (map showEntry storesList) + "\n";
+
+  "SUMMARY.md" = tableOfContents;
+
+  storePages = listToAttrs
+    (map (s: { name = s.filename; value = s.page; }) storesList);
+
+in
+storePages // { inherit "index.md" "SUMMARY.md"; }

doc/manual/generate-xp-features-shortlist.nix

@@ -1,5 +1,5 @@
 with builtins;
-with import ./utils.nix;
+with import <nix/utils.nix>;
 
 let
   showExperimentalFeature = name: doc:

doc/manual/generate-xp-features.nix

@@ -1,5 +1,5 @@
 with builtins;
-with import ./utils.nix;
+with import <nix/utils.nix>;
 
 let
   showExperimentalFeature = name: doc:
@@ -8,4 +8,6 @@ let
 
       ${doc}
     '';
-in xps: (concatStringsSep "\n" (attrValues (mapAttrs showExperimentalFeature xps)))
+in
+
+xps: (concatStringsSep "\n" (attrValues (mapAttrs showExperimentalFeature xps)))

doc/manual/local.mk

@@ -1,4 +1,7 @@
-ifeq ($(doc_generate),yes)
+# The version of Nix used to generate the doc. Can also be
+# `$(nix_INSTALL_PATH)` or just `nix` (to grap ambient from the `PATH`),
+# if one prefers.
+doc_nix = $(nix_PATH)
 
 MANUAL_SRCS := \
 	$(call rwildcard, $(d)/src, *.md) \
@@ -24,7 +27,7 @@ man-pages += $(foreach subcommand, \
 clean-files += $(d)/*.1 $(d)/*.5 $(d)/*.8
 
 # Provide a dummy environment for nix, so that it will not access files outside the macOS sandbox.
-# Set cores to 0 because otherwise nix show-config resolves the cores based on the current machine
+# Set cores to 0 because otherwise `nix config show` resolves the cores based on the current machine
 dummy-env = env -i \
 	HOME=/dummy \
 	NIX_CONF_DIR=/dummy \
@@ -32,7 +35,7 @@ dummy-env = env -i \
 	NIX_STATE_DIR=/dummy \
 	NIX_CONFIG='cores = 0'
 
-nix-eval = $(dummy-env) $(bindir)/nix eval --experimental-features nix-command -I nix/corepkgs=corepkgs --store dummy:// --impure --raw
+nix-eval = $(dummy-env) $(doc_nix) eval --experimental-features nix-command -I nix=doc/manual --store dummy:// --impure --raw
 
 # re-implement mdBook's include directive to make it usable for terminal output and for proper @docroot@ substitution
 define process-includes
@@ -92,58 +95,91 @@ $(d)/nix-profiles.5: $(d)/src/command-ref/files/profiles.md
 	$(trace-gen) lowdown -sT man --nroff-nolinks -M section=5 $^.tmp -o $@
 	@rm $^.tmp
 
-$(d)/src/SUMMARY.md: $(d)/src/SUMMARY.md.in $(d)/src/command-ref/new-cli $(d)/src/contributing/experimental-feature-descriptions.md
+$(d)/src/SUMMARY.md: $(d)/src/SUMMARY.md.in $(d)/src/SUMMARY-rl-next.md $(d)/src/store/types $(d)/src/command-ref/new-cli $(d)/src/contributing/experimental-feature-descriptions.md
 	@cp $< $@
 	@$(call process-includes,$@,$@)
 
-$(d)/src/command-ref/new-cli: $(d)/nix.json $(d)/utils.nix $(d)/generate-manpage.nix $(bindir)/nix
+$(d)/src/store/types: $(d)/nix.json $(d)/utils.nix $(d)/generate-store-info.nix  $(d)/generate-store-types.nix $(d)/src/store/types/index.md.in $(doc_nix)
+	@# FIXME: build out of tree!
+	@rm -rf $@.tmp
+	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-store-types.nix (builtins.fromJSON (builtins.readFile $<)).stores'
+	@# do not destroy existing contents
+	@mv $@.tmp/* $@/
+
+$(d)/src/command-ref/new-cli: $(d)/nix.json $(d)/utils.nix $(d)/generate-manpage.nix $(d)/generate-settings.nix $(d)/generate-store-info.nix $(doc_nix)
 	@rm -rf $@ $@.tmp
-	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-manpage.nix (builtins.readFile $<)'
+	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-manpage.nix true (builtins.readFile $<)'
 	@mv $@.tmp $@
 
-$(d)/src/command-ref/conf-file.md: $(d)/conf-file.json $(d)/utils.nix $(d)/src/command-ref/conf-file-prefix.md $(d)/src/command-ref/experimental-features-shortlist.md $(bindir)/nix
+$(d)/src/command-ref/conf-file.md: $(d)/conf-file.json $(d)/utils.nix $(d)/generate-settings.nix $(d)/src/command-ref/conf-file-prefix.md $(d)/src/command-ref/experimental-features-shortlist.md $(doc_nix)
 	@cat doc/manual/src/command-ref/conf-file-prefix.md > $@.tmp
-	$(trace-gen) $(nix-eval) --expr '(import doc/manual/utils.nix).showSettings { useAnchors = true; } (builtins.fromJSON (builtins.readFile $<))' >> $@.tmp;
+	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-settings.nix { prefix = "conf"; } (builtins.fromJSON (builtins.readFile $<))' >> $@.tmp;
 	@mv $@.tmp $@
 
-$(d)/nix.json: $(bindir)/nix
+$(d)/nix.json: $(doc_nix)
-	$(trace-gen) $(dummy-env) $(bindir)/nix __dump-cli > $@.tmp
+	$(trace-gen) $(dummy-env) $(doc_nix) __dump-cli > $@.tmp
 	@mv $@.tmp $@
 
-$(d)/conf-file.json: $(bindir)/nix
+$(d)/conf-file.json: $(doc_nix)
-	$(trace-gen) $(dummy-env) $(bindir)/nix show-config --json --experimental-features nix-command > $@.tmp
+	$(trace-gen) $(dummy-env) $(doc_nix) config show --json --experimental-features nix-command > $@.tmp
 	@mv $@.tmp $@
 
-$(d)/src/contributing/experimental-feature-descriptions.md: $(d)/xp-features.json $(d)/utils.nix $(d)/generate-xp-features.nix $(bindir)/nix
+$(d)/src/contributing/experimental-feature-descriptions.md: $(d)/xp-features.json $(d)/utils.nix $(d)/generate-xp-features.nix $(doc_nix)
 	@rm -rf $@ $@.tmp
 	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-xp-features.nix (builtins.fromJSON (builtins.readFile $<))'
 	@mv $@.tmp $@
 
-$(d)/src/command-ref/experimental-features-shortlist.md: $(d)/xp-features.json $(d)/utils.nix $(d)/generate-xp-features-shortlist.nix $(bindir)/nix
+$(d)/src/command-ref/experimental-features-shortlist.md: $(d)/xp-features.json $(d)/utils.nix $(d)/generate-xp-features-shortlist.nix $(doc_nix)
 	@rm -rf $@ $@.tmp
 	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-xp-features-shortlist.nix (builtins.fromJSON (builtins.readFile $<))'
 	@mv $@.tmp $@
 
-$(d)/xp-features.json: $(bindir)/nix
+$(d)/xp-features.json: $(doc_nix)
-	$(trace-gen) $(dummy-env) NIX_PATH=nix/corepkgs=corepkgs $(bindir)/nix __dump-xp-features > $@.tmp
+	$(trace-gen) $(dummy-env) $(doc_nix) __dump-xp-features > $@.tmp
 	@mv $@.tmp $@
 
-$(d)/src/language/builtins.md: $(d)/builtins.json $(d)/generate-builtins.nix $(d)/src/language/builtins-prefix.md $(bindir)/nix
+$(d)/src/language/builtins.md: $(d)/language.json $(d)/generate-builtins.nix $(d)/src/language/builtins-prefix.md $(doc_nix)
 	@cat doc/manual/src/language/builtins-prefix.md > $@.tmp
-	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-builtins.nix (builtins.fromJSON (builtins.readFile $<))' >> $@.tmp;
+	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-builtins.nix (builtins.fromJSON (builtins.readFile $<)).builtins' >> $@.tmp;
 	@cat doc/manual/src/language/builtins-suffix.md >> $@.tmp
 	@mv $@.tmp $@
 
-$(d)/builtins.json: $(bindir)/nix
+$(d)/src/language/builtin-constants.md: $(d)/language.json $(d)/generate-builtin-constants.nix $(d)/src/language/builtin-constants-prefix.md $(doc_nix)
-	$(trace-gen) $(dummy-env) NIX_PATH=nix/corepkgs=corepkgs $(bindir)/nix __dump-builtins > $@.tmp
+	@cat doc/manual/src/language/builtin-constants-prefix.md > $@.tmp
+	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-builtin-constants.nix (builtins.fromJSON (builtins.readFile $<)).constants' >> $@.tmp;
+	@cat doc/manual/src/language/builtin-constants-suffix.md >> $@.tmp
 	@mv $@.tmp $@
 
+$(d)/language.json: $(doc_nix)
+	$(trace-gen) $(dummy-env) $(doc_nix) __dump-language > $@.tmp
+	@mv $@.tmp $@
+
+# Generate "Upcoming release" notes (or clear it and remove from menu)
+$(d)/src/release-notes/rl-next.md: $(d)/rl-next $(d)/rl-next/*
+	@if type -p changelog-d > /dev/null; then \
+		echo "  GEN   " $@; \
+		changelog-d doc/manual/rl-next > $@; \
+	else \
+		echo "  NULL  " $@; \
+		true > $@; \
+	fi
+
+$(d)/src/SUMMARY-rl-next.md: $(d)/src/release-notes/rl-next.md
+	$(trace-gen) true
+	@if [ -s $< ]; then \
+		echo '  - [Upcoming release](release-notes/rl-next.md)' > $@; \
+	else \
+	  true > $@; \
+	fi
+
 # Generate the HTML manual.
 .PHONY: manual-html
 manual-html: $(docdir)/manual/index.html
 install: $(docdir)/manual/index.html
 
 # Generate 'nix' manpages.
+.PHONY: manpages
+manpages: $(mandir)/man1/nix3-manpages
 install: $(mandir)/man1/nix3-manpages
 man: doc/manual/generated/man1/nix3-manpages
 all: doc/manual/generated/man1/nix3-manpages
@@ -167,14 +203,18 @@ doc/manual/generated/man1/nix3-manpages: $(d)/src/command-ref/new-cli
 	done
 	@touch $@
 
-$(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/anchors.jq $(d)/custom.css $(d)/src/SUMMARY.md $(d)/src/command-ref/new-cli $(d)/src/contributing/experimental-feature-descriptions.md $(d)/src/command-ref/conf-file.md $(d)/src/language/builtins.md
+# the `! -name 'contributing.md'` filter excludes the one place where
+# `@docroot@` is to be preserved for documenting the mechanism
+# FIXME: maybe contributing guides should live right next to the code
+# instead of in the manual
+$(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/anchors.jq $(d)/custom.css $(d)/src/SUMMARY.md $(d)/src/store/types $(d)/src/command-ref/new-cli $(d)/src/contributing/experimental-feature-descriptions.md $(d)/src/command-ref/conf-file.md $(d)/src/language/builtins.md $(d)/src/language/builtin-constants.md $(d)/src/release-notes/rl-next.md
 	$(trace-gen) \
 		tmp="$$(mktemp -d)"; \
 		cp -r doc/manual "$$tmp"; \
 		find "$$tmp" -name '*.md' | while read -r file; do \
 			$(call process-includes,$$file,$$file); \
 		done; \
-		find "$$tmp" -name '*.md' | while read -r file; do \
+		find "$$tmp" -name '*.md' ! -name 'documentation.md' | while read -r file; do \
 			docroot="$$(realpath --relative-to="$$(dirname "$$file")" $$tmp/manual/src)"; \
 			sed -i "s,@docroot@,$$docroot,g" "$$file"; \
 		done; \
@@ -185,5 +225,3 @@ $(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/anchors.jq $(d)/
 	@rm -rf $(DESTDIR)$(docdir)/manual
 	@mv $(DESTDIR)$(docdir)/manual.tmp/html $(DESTDIR)$(docdir)/manual
 	@rm -rf $(DESTDIR)$(docdir)/manual.tmp
-
-endif

doc/manual/redirects.js

@@ -1,7 +1,9 @@
-// redirect rules for anchors ensure backwards compatibility of URLs.
+// redirect rules for URL fragments (client-side) to prevent link rot.
-// this must be done on the client side, as web servers do not see the anchor part of the URL.
+// this must be done on the client side, as web servers do not see the fragment part of the URL.
+// it will only work with JavaScript enabled in the browser, but this is the best we can do here.
+// see ./_redirects for path redirects (client-side)
 
-// redirections are declared as follows:
+// redirects are declared as follows:
 // each entry has as its key a path matching the requested URL path, relative to the mdBook document root.
 //
 //     IMPORTANT: it must specify the full path with file name and suffix
@@ -19,6 +21,7 @@ const redirects = {
     "chap-distributed-builds": "advanced-topics/distributed-builds.html",
     "chap-post-build-hook": "advanced-topics/post-build-hook.html",
     "chap-post-build-hook-caveats": "advanced-topics/post-build-hook.html#implementation-caveats",
+    "chap-writing-nix-expressions": "language/index.html",
     "part-command-ref": "command-ref/command-ref.html",
     "conf-allow-import-from-derivation": "command-ref/conf-file.html#conf-allow-import-from-derivation",
     "conf-allow-new-privileges": "command-ref/conf-file.html#conf-allow-new-privileges",
@@ -281,7 +284,7 @@ const redirects = {
     "chap-introduction": "introduction.html",
     "ch-basic-package-mgmt": "package-management/basic-package-mgmt.html",
     "ssec-binary-cache-substituter": "package-management/binary-cache-substituter.html",
-    "sec-channels": "package-management/channels.html",
+    "sec-channels": "command-ref/nix-channel.html",
     "ssec-copy-closure": "package-management/copy-closure.html",
     "sec-garbage-collection": "package-management/garbage-collection.html",
     "ssec-gc-roots": "package-management/garbage-collector-roots.html",
@@ -330,17 +333,31 @@ const redirects = {
     "ssec-relnotes-2.0": "release-notes/rl-2.0.html",
     "ssec-relnotes-2.1": "release-notes/rl-2.1.html",
     "ssec-relnotes-2.2": "release-notes/rl-2.2.html",
-    "ssec-relnotes-2.3": "release-notes/rl-2.3.html"
+    "ssec-relnotes-2.3": "release-notes/rl-2.3.html",
   },
   "language/values.html": {
     "simple-values": "#primitives",
     "lists": "#list",
     "strings": "#string",
-    "lists": "#list",
+    "attribute-sets": "#attribute-set",
-    "attribute-sets": "#attribute-set"
   },
   "installation/installing-binary.html": {
-    "uninstalling": "uninstall.html"
+    "linux": "uninstall.html#linux",
+    "macos": "uninstall.html#macos",
+    "uninstalling": "uninstall.html",
+  },
+  "contributing/hacking.html": {
+    "nix-with-flakes": "#building-nix-with-flakes",
+    "classic-nix": "#building-nix",
+    "running-tests": "testing.html#running-tests",
+    "unit-tests": "testing.html#unit-tests",
+    "functional-tests": "testing.html#functional-tests",
+    "debugging-failing-functional-tests": "testing.html#debugging-failing-functional-tests",
+    "integration-tests": "testing.html#integration-tests",
+    "installer-tests": "testing.html#installer-tests",
+    "one-time-setup": "testing.html#one-time-setup",
+    "using-the-ci-generated-installer-for-manual-testing": "testing.html#using-the-ci-generated-installer-for-manual-testing",
+    "characterization-testing": "#characterisation-testing-unit",
   }
 };
 

doc/manual/rl-next/allowed-uris-can-now-match-whole-schemes.md

@@ -0,0 +1,7 @@
+---
+synopsis: Option `allowed-uris` can now match whole schemes in URIs without slashes
+prs: 9547
+---
+
+If a scheme, such as `github:` is specified in the `allowed-uris` option, all URIs starting with `github:` are allowed.
+Previously this only worked for schemes whose URIs used the `://` syntax.

doc/manual/rl-next/cgroup-stats.md

@@ -0,0 +1,8 @@
+---
+synopsis: Include cgroup stats when building through the daemon
+prs: 9598
+---
+
+Nix now also reports cgroup statistics when building through the nix daemon and when doing remote builds using ssh-ng,
+if both sides of the connection are this version of Nix or newer. 
+

doc/manual/rl-next/config

@@ -0,0 +1,2 @@
+organization: NixOS
+repository: nix

doc/manual/rl-next/drv-string-parse-hang.md

@@ -0,0 +1,6 @@
+---
+synopsis: Fix handling of truncated `.drv` files.
+prs: 9673
+---
+
+Previously a `.drv` that was truncated in the middle of a string would case nix to enter an infinite loop, eventually exhausting all memory and crashing.

doc/manual/rl-next/env-size-reduction.md

@@ -0,0 +1,7 @@
+---
+synopsis: Reduce eval memory usage and wall time
+prs: 9658
+---
+
+Reduce the size of the `Env` struct used in the evaluator by a pointer, or 8 bytes on most modern machines.
+This reduces memory usage during eval by around 2% and wall time by around 3%.

doc/manual/rl-next/eval-system.md

@@ -0,0 +1,12 @@
+---
+synopsis: Add new `eval-system` setting
+prs: 4093
+---
+
+Add a new `eval-system` option.
+Unlike `system`, it just overrides the value of `builtins.currentSystem`.
+This is more useful than overriding `system`, because you can build these derivations on remote builders which can work on the given system.
+In contrast, `system` also effects scheduling which will cause Nix to build those derivations locally even if that doesn't make sense.
+
+`eval-system` only takes effect if it is non-empty.
+If empty (the default) `system` is used as before, so there is no breakage.

doc/manual/rl-next/hash-format-nix32.md

@@ -0,0 +1,23 @@
+---
+synopsis: Rename hash format `base32` to `nix32`
+prs: 9452
+---
+
+Hash format `base32` was renamed to `nix32` since it used a special nix-specific character set for 
+[Base32](https://en.wikipedia.org/wiki/Base32).
+
+## Deprecation: Use `nix32` instead of `base32` as `toHashFormat`
+
+For the builtin `convertHash`, the `toHashFormat` parameter now accepts the same hash formats as the `--to`/`--from`
+parameters of the `nix hash conert` command: `"base16"`, `"nix32"`, `"base64"`, and `"sri"`. The former `"base32"` value
+remains as a deprecated alias for `"base32"`. Please convert your code from:
+
+```nix
+builtins.convertHash { inherit hash hashAlgo; toHashFormat = "base32";}
+```
+
+to
+
+```nix
+builtins.convertHash { inherit hash hashAlgo; toHashFormat = "nix32";}
+```

doc/manual/rl-next/ifd-eval-store.md

@@ -0,0 +1,8 @@
+---
+synopsis: import-from-derivation builds the derivation in the build store
+prs: 9661
+---
+
+When using `--eval-store`, `import`ing from a derivation will now result in the derivation being built on the build store, i.e. the store specified in the `store` Nix option.
+
+Because the resulting Nix expression must be copied back to the eval store in order to be imported, this requires the eval store to trust the build store's signatures.

doc/manual/rl-next/mounted-ssh-store.md

@@ -0,0 +1,8 @@
+---
+synopsis: Mounted SSH Store
+issues: 7890
+prs: 7912
+---
+
+Introduced the store [`mounted-ssh-ng://`](@docroot@/command-ref/new-cli/nix3-help-stores.md).
+This store allows full access to a Nix store on a remote machine and additionally requires that the store be mounted in the local filesystem.

doc/manual/rl-next/nix-config-show.md

@@ -0,0 +1,7 @@
+---
+synopsis: Rename to `nix config show`
+issues: 7672
+prs: 9477
+---
+
+`nix show-config` was renamed to `nix config show`, and `nix doctor` was renamed to `nix config check`, to be more consistent with the rest of the command-line interface.

doc/manual/rl-next/nix-env-json-drv-path.md

@@ -0,0 +1,6 @@
+---
+synopsis: Fix `nix-env --query --drv-path --json`
+prs: 9257
+---
+
+Fixed a bug where `nix-env --query` ignored `--drv-path` when `--json` was set.

doc/manual/rl-next/nix-hash-convert.md

@@ -0,0 +1,47 @@
+---
+synopsis: Add `nix hash convert`
+prs: 9452
+---
+
+New [`nix hash convert`](https://github.com/NixOS/nix/issues/8876) sub command with a fast track
+to stabilization! Examples:
+
+- Convert the hash to `nix32`.
+
+  ```bash
+  $ nix hash convert --algo "sha1" --to nix32 "800d59cfcd3c05e900cb4e214be48f6b886a08df"
+  vw46m23bizj4n8afrc0fj19wrp7mj3c0
+  ```
+  `nix32` is a base32 encoding with a nix-specific character set.
+  Explicitly specify the hashing algorithm (optional with SRI hashes) but detect hash format by the length of the input
+  hash.
+- Convert the hash to the `sri` format that includes an algorithm specification:
+  ```bash
+  nix hash convert --algo "sha1" "800d59cfcd3c05e900cb4e214be48f6b886a08df"
+  sha1-gA1Zz808BekAy04hS+SPa4hqCN8=
+  ```
+  or with an explicit `-to` format:
+  ```bash
+  nix hash convert --algo "sha1" --to sri "800d59cfcd3c05e900cb4e214be48f6b886a08df"
+  sha1-gA1Zz808BekAy04hS+SPa4hqCN8=
+  ```
+- Assert the input format of the hash:
+  ```bash
+  nix hash convert --algo "sha256" --from nix32 "ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0="
+  error: input hash 'ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=' does not have the expected format '--from nix32'
+  nix hash convert --algo "sha256" --from nix32 "1b8m03r63zqhnjf7l5wnldhh7c134ap5vpj0850ymkq1iyzicy5s"
+  sha256-ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=
+  ```
+
+The `--to`/`--from`/`--algo` parameters have context-sensitive auto-completion.
+
+## Related Deprecations
+
+The following commands are still available but will emit a deprecation warning. Please convert your code to
+`nix hash convert`:
+
+- `nix hash to-base16 $hash1 $hash2`: Use `nix hash convert --to base16 $hash1 $hash2` instead.
+- `nix hash to-base32 $hash1 $hash2`: Use `nix hash convert --to nix32 $hash1 $hash2` instead.
+- `nix hash to-base64 $hash1 $hash2`: Use `nix hash convert --to base64 $hash1 $hash2` instead.
+- `nix hash to-sri $hash1 $hash2`: : Use `nix hash convert --to sri $hash1 $hash2`
+  or even just `nix hash convert $hash1 $hash2` instead.

doc/manual/rl-next/nix-profile-names.md

@@ -0,0 +1,6 @@
+---
+synopsis: "`nix profile` now allows referring to elements by human-readable name"
+prs: 8678
+---
+
+[`nix profile`](@docroot@/command-ref/new-cli/nix3-profile.md) now uses names to refer to installed packages when running [`list`](@docroot@/command-ref/new-cli/nix3-profile-list.md), [`remove`](@docroot@/command-ref/new-cli/nix3-profile-remove.md) or [`upgrade`](@docroot@/command-ref/new-cli/nix3-profile-upgrade.md) as opposed to indices. Indices are deprecated and will be removed in a future version.

doc/manual/rl-next/source-positions-in-errors.md

@@ -0,0 +1,42 @@
+---
+synopsis: Source locations are printed more consistently in errors
+issues: 561
+prs: 9555
+---
+
+Source location information is now included in error messages more
+consistently. Given this code:
+
+```nix
+let
+  attr = {foo = "bar";};
+  key = {};
+in
+  attr.${key}
+```
+
+Previously, Nix would show this unhelpful message when attempting to evaluate
+it:
+
+```
+error:
+       … while evaluating an attribute name
+
+       error: value is a set while a string was expected
+```
+
+Now, the error message displays where the problematic value was found:
+
+```
+error:
+       … while evaluating an attribute name
+
+         at bad.nix:4:11:
+
+            3|   key = {};
+            4| in attr.${key}
+             |           ^
+            5|
+
+       error: value is a set while a string was expected
+```

doc/manual/rl-next/stack-overflow-segfaults.md

@@ -0,0 +1,32 @@
+---
+synopsis: Some stack overflow segfaults are fixed
+issues: 9616
+prs: 9617
+---
+
+The number of nested function calls has been restricted, to detect and report
+infinite function call recursions. The default maximum call depth is 10,000 and
+can be set with [the `max-call-depth`
+option](@docroot@/command-ref/conf-file.md#conf-max-call-depth).
+
+This fixes segfaults or the following unhelpful error message in many cases:
+
+    error: stack overflow (possible infinite recursion)
+
+Before:
+
+```
+$ nix-instantiate --eval --expr '(x: x x) (x: x x)'
+Segmentation fault: 11
+```
+
+After:
+
+```
+$ nix-instantiate --eval --expr '(x: x x) (x: x x)'
+error: stack overflow
+
+       at «string»:1:14:
+            1| (x: x x) (x: x x)
+             |              ^
+```

doc/manual/rl-next/with-error-reporting.md

@@ -0,0 +1,31 @@
+---
+synopsis: Better error reporting for `with` expressions
+prs: 9658
+---
+
+`with` expressions using non-attrset values to resolve variables are now reported with proper positions.
+
+Previously an incorrect `with` expression would report no position at all, making it hard to determine where the error originated:
+
+```
+nix-repl> with 1; a  
+error:
+       … <borked>
+
+         at «none»:0: (source not available)
+
+       error: value is an integer while a set was expected
+```
+
+Now position information is preserved and reported as with most other errors:
+
+```
+nix-repl> with 1; a
+error:
+       … while evaluating the first subexpression of a with expression
+         at «string»:1:1:
+            1| with 1; a
+             | ^
+
+       error: value is an integer while a set was expected
+```

doc/manual/src/SUMMARY.md.in

@@ -2,7 +2,7 @@
 
 - [Introduction](introduction.md)
 - [Quick Start](quick-start.md)
-- [Installation](installation/installation.md)
+- [Installation](installation/index.md)
   - [Supported Platforms](installation/supported-platforms.md)
   - [Installing a Binary Distribution](installation/installing-binary.md)
   - [Installing Nix from Source](installation/installing-source.md)
@@ -16,32 +16,38 @@
   - [Environment Variables](installation/env-variables.md)
   - [Upgrading Nix](installation/upgrading.md)
   - [Uninstalling Nix](installation/uninstall.md)
-- [Package Management](package-management/package-management.md)
+- [Nix Store](store/index.md)
-  - [Basic Package Management](package-management/basic-package-mgmt.md)
+  - [File System Object](store/file-system-object.md)
+  - [Store Object](store/store-object.md)
+  - [Store Path](store/store-path.md)
+  - [Store Types](store/types/index.md)
+{{#include ./store/types/SUMMARY.md}}
+- [Nix Language](language/index.md)
+  - [Data Types](language/values.md)
+  - [Language Constructs](language/constructs.md)
+    - [String interpolation](language/string-interpolation.md)
+    - [Lookup path](language/constructs/lookup-path.md)
+  - [Operators](language/operators.md)
+  - [Derivations](language/derivations.md)
+    - [Advanced Attributes](language/advanced-attributes.md)
+    - [Import From Derivation](language/import-from-derivation.md)
+  - [Built-in Constants](language/builtin-constants.md)
+  - [Built-in Functions](language/builtins.md)
+- [Package Management](package-management/index.md)
   - [Profiles](package-management/profiles.md)
   - [Garbage Collection](package-management/garbage-collection.md)
     - [Garbage Collector Roots](package-management/garbage-collector-roots.md)
-  - [Channels](package-management/channels.md)
+- [Advanced Topics](advanced-topics/index.md)
   - [Sharing Packages Between Machines](package-management/sharing-packages.md)
     - [Serving a Nix store via HTTP](package-management/binary-cache-substituter.md)
     - [Copying Closures via SSH](package-management/copy-closure.md)
     - [Serving a Nix store via SSH](package-management/ssh-substituter.md)
     - [Serving a Nix store via S3](package-management/s3-substituter.md)
-- [Nix Language](language/index.md)
-  - [Data Types](language/values.md)
-  - [Language Constructs](language/constructs.md)
-    - [String interpolation](language/string-interpolation.md)
-  - [Operators](language/operators.md)
-  - [Derivations](language/derivations.md)
-    - [Advanced Attributes](language/advanced-attributes.md)
-  - [Built-in Constants](language/builtin-constants.md)
-  - [Built-in Functions](language/builtins.md)
-- [Advanced Topics](advanced-topics/advanced-topics.md)
   - [Remote Builds](advanced-topics/distributed-builds.md)
   - [Tuning Cores and Jobs](advanced-topics/cores-vs-jobs.md)
   - [Verifying Build Reproducibility](advanced-topics/diff-hook.md)
   - [Using the `post-build-hook`](advanced-topics/post-build-hook.md)
-- [Command Reference](command-ref/command-ref.md)
+- [Command Reference](command-ref/index.md)
   - [Common Options](command-ref/opt-common.md)
   - [Common Environment Variables](command-ref/env-common.md)
   - [Main Commands](command-ref/main-commands.md)
@@ -98,16 +104,22 @@
     - [Channels](command-ref/files/channels.md)
     - [Default Nix expression](command-ref/files/default-nix-expression.md)
 - [Architecture and Design](architecture/architecture.md)
-  - [File System Object](architecture/file-system-object.md)
+- [Protocols](protocols/index.md)
-- [Protocols](protocols/protocols.md)
   - [Serving Tarball Flakes](protocols/tarball-fetcher.md)
+  - [Derivation "ATerm" file format](protocols/derivation-aterm.md)
 - [Glossary](glossary.md)
-- [Contributing](contributing/contributing.md)
+- [Contributing](contributing/index.md)
   - [Hacking](contributing/hacking.md)
+  - [Testing](contributing/testing.md)
+  - [Documentation](contributing/documentation.md)
   - [Experimental Features](contributing/experimental-features.md)
   - [CLI guideline](contributing/cli-guideline.md)
-- [Release Notes](release-notes/release-notes.md)
+  - [C++ style guide](contributing/cxx.md)
-  - [Release X.Y (202?-??-??)](release-notes/rl-next.md)
+- [Release Notes](release-notes/index.md)
+{{#include ./SUMMARY-rl-next.md}}
+  - [Release 2.19 (2023-11-17)](release-notes/rl-2.19.md)
+  - [Release 2.18 (2023-09-20)](release-notes/rl-2.18.md)
+  - [Release 2.17 (2023-07-24)](release-notes/rl-2.17.md)
   - [Release 2.16 (2023-05-31)](release-notes/rl-2.16.md)
   - [Release 2.15 (2023-04-11)](release-notes/rl-2.15.md)
   - [Release 2.14 (2023-02-28)](release-notes/rl-2.14.md)

doc/manual/src/advanced-topics/advanced-topics.md

@@ -1 +0,0 @@
-

doc/manual/src/advanced-topics/distributed-builds.md

@@ -12,14 +12,14 @@ machine is accessible via SSH and that it has Nix installed. You can
 test whether connecting to the remote Nix instance works, e.g.
 
 ```console
-$ nix store ping --store ssh://mac
+$ nix store info --store ssh://mac
 ```
 
 will try to connect to the machine named `mac`. It is possible to
 specify an SSH identity file as part of the remote store URI, e.g.
 
 ```console
-$ nix store ping --store ssh://mac?ssh-key=/home/alice/my-key
+$ nix store info --store ssh://mac?ssh-key=/home/alice/my-key
 ```
 
 Since builds should be non-interactive, the key should not have a

doc/manual/src/advanced-topics/index.md

@@ -0,0 +1 @@
+This section lists advanced topics related to builds and builds performance

doc/manual/src/advanced-topics/post-build-hook.md

@@ -17,9 +17,8 @@ the build loop.
 
 # Prerequisites
 
-This tutorial assumes you have [configured an S3-compatible binary
+This tutorial assumes you have configured an [S3-compatible binary cache](@docroot@/command-ref/new-cli/nix3-help-stores.md#s3-binary-cache-store) as a [substituter](../command-ref/conf-file.md#conf-substituters),
-cache](../package-management/s3-substituter.md), and that the `root`
+and that the `root` user's default AWS profile can upload to the bucket.
-user's default AWS profile can upload to the bucket.
 
 # Set up a Signing Key
 
@@ -69,6 +68,8 @@ exec nix copy --to "s3://example-nix-cache" $OUT_PATHS
 > store sign`. Nix guarantees the paths will not contain any spaces,
 > however a store path might contain glob characters. The `set -f`
 > disables globbing in the shell.
+> If you want to upload the `.drv` file too, the `$DRV_PATH` variable
+> is also defined for the script and works just like `$OUT_PATHS`.
 
 Then make sure the hook program is executable by the `root` user:
 

doc/manual/src/architecture/architecture.md

@@ -52,17 +52,18 @@ The following [concept map] shows its main components (rectangles), the objects
                                             '---------------'
 ```
 
-At the top is the [command line interface](../command-ref/command-ref.md) that drives the underlying layers.
+At the top is the [command line interface](../command-ref/index.md) that drives the underlying layers.
 
 The [Nix language](../language/index.md) evaluator transforms Nix expressions into self-contained *build plans*, which are used to derive *build results* from referenced *build inputs*.
 
 The command line interface and Nix expressions are what users deal with most.
 
 > **Note**
+>
 > The Nix language itself does not have a notion of *packages* or *configurations*.
 > As far as we are concerned here, the inputs and results of a build plan are just data.
 
-Underlying the command line interface and the Nix language evaluator is the [Nix store](../glossary.md#gloss-store), a mechanism to keep track of build plans, data, and references between them.
+Underlying the command line interface and the Nix language evaluator is the [Nix store](../store/index.md), a mechanism to keep track of build plans, data, and references between them.
 It can also execute build plans to produce new data, which are made available to the operating system as files.
 
 A build plan itself is a series of *build tasks*, together with their build inputs.

doc/manual/src/command-ref/conf-file-prefix.md

@@ -4,49 +4,67 @@
 
 # Description
 
-By default Nix reads settings from the following places:
+Nix supports a variety of configuration settings, which are read from configuration files or taken as command line flags.
 
-  - The system-wide configuration file `sysconfdir/nix/nix.conf` (i.e.
+## Configuration file
-    `/etc/nix/nix.conf` on most systems), or `$NIX_CONF_DIR/nix.conf` if
-    `NIX_CONF_DIR` is set. Values loaded in this file are not forwarded
-    to the Nix daemon. The client assumes that the daemon has already
-    loaded them.
 
-  - If `NIX_USER_CONF_FILES` is set, then each path separated by `:`
+By default Nix reads settings from the following places, in that order:
-    will be loaded in reverse order.
 
-    Otherwise it will look for `nix/nix.conf` files in `XDG_CONFIG_DIRS`
+1. The system-wide configuration file `sysconfdir/nix/nix.conf` (i.e. `/etc/nix/nix.conf` on most systems), or `$NIX_CONF_DIR/nix.conf` if [`NIX_CONF_DIR`](./env-common.md#env-NIX_CONF_DIR) is set.
-    and `XDG_CONFIG_HOME`. If unset, `XDG_CONFIG_DIRS` defaults to
-    `/etc/xdg`, and `XDG_CONFIG_HOME` defaults to `$HOME/.config`
-    as per [XDG Base Directory Specification](https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html).
 
-  - If `NIX_CONFIG` is set, its contents is treated as the contents of
+   Values loaded in this file are not forwarded to the Nix daemon.
-    a configuration file.
+   The client assumes that the daemon has already loaded them.
 
-The configuration files consist of `name = value` pairs, one per
+1. If [`NIX_USER_CONF_FILES`](./env-common.md#env-NIX_USER_CONF_FILES) is set, then each path separated by `:` will be loaded in reverse order.
-line. Other files can be included with a line like `include path`,
-where *path* is interpreted relative to the current conf file and a
-missing file is an error unless `!include` is used instead. Comments
-start with a `#` character. Here is an example configuration file:
 
-    keep-outputs = true       # Nice for developers
+   Otherwise it will look for `nix/nix.conf` files in `XDG_CONFIG_DIRS` and [`XDG_CONFIG_HOME`](./env-common.md#env-XDG_CONFIG_HOME).
-    keep-derivations = true   # Idem
+   If unset, `XDG_CONFIG_DIRS` defaults to `/etc/xdg`, and `XDG_CONFIG_HOME` defaults to `$HOME/.config` as per [XDG Base Directory Specification](https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html).
 
-You can override settings on the command line using the `--option`
+1. If [`NIX_CONFIG`](./env-common.md#env-NIX_CONFIG) is set, its contents are treated as the contents of a configuration file.
-flag, e.g. `--option keep-outputs false`. Every configuration setting
-also has a corresponding command line flag, e.g. `--max-jobs 16`; for
-Boolean settings, there are two flags to enable or disable the setting
-(e.g. `--keep-failed` and `--no-keep-failed`).
 
-A configuration setting usually overrides any previous value. However,
+### File format
-you can prefix the name of the setting by `extra-` to *append* to the
-previous value. For instance,
 
-    substituters = a b
+Configuration files consist of `name = value` pairs, one per line.
-    extra-substituters = c d
+Comments start with a `#` character.
 
-defines the `substituters` setting to be `a b c d`. This is also
+Example:
-available as a command line flag (e.g. `--extra-substituters`).
 
-The following settings are currently available:
+```
+keep-outputs = true       # Nice for developers
+keep-derivations = true   # Idem
+```
+
+Other files can be included with a line like `include <path>`, where `<path>` is interpreted relative to the current configuration file.
+A missing file is an error unless `!include` is used instead.
+
+A configuration setting usually overrides any previous value.
+However, for settings that take a list of items, you can prefix the name of the setting by `extra-` to *append* to the previous value.
+
+For instance,
+
+```
+substituters = a b
+extra-substituters = c d
+```
+
+defines the `substituters` setting to be `a b c d`.
+
+Unknown option names are not an error, and are simply ignored with a warning.
+
+## Command line flags
+
+Configuration options can be set on the command line, overriding the values set in the [configuration file](#configuration-file):
+
+- Every configuration setting has corresponding command line flag (e.g. `--max-jobs 16`).
+  Boolean settings do not need an argument, and can be explicitly disabled with the `no-` prefix (e.g. `--keep-failed` and `--no-keep-failed`).
+
+  Unknown option names are invalid flags (unless there is already a flag with that name), and are rejected with an error.
+
+- The flag `--option <name> <value>` is interpreted exactly like a `<name> = <value>` in a setting file.
+
+  Unknown option names are ignored with a warning.
+
+The `extra-` prefix is supported for settings that take a list of items (e.g. `--extra-trusted users alice` or `--option extra-trusted-users alice`).
+
+# Available settings
 

doc/manual/src/command-ref/env-common.md

@@ -2,109 +2,124 @@
 
 Most Nix commands interpret the following environment variables:
 
-  - <span id="env-IN_NIX_SHELL">[`IN_NIX_SHELL`](#env-IN_NIX_SHELL)</span>\
+- <span id="env-IN_NIX_SHELL">[`IN_NIX_SHELL`](#env-IN_NIX_SHELL)</span>
-    Indicator that tells if the current environment was set up by
-    `nix-shell`. It can have the values `pure` or `impure`.
 
-  - <span id="env-NIX_PATH">[`NIX_PATH`](#env-NIX_PATH)</span>\
+  Indicator that tells if the current environment was set up by
-    A colon-separated list of directories used to look up the location of Nix
+  `nix-shell`. It can have the values `pure` or `impure`.
-    expressions using [paths](@docroot@/language/values.md#type-path)
-    enclosed in angle brackets (i.e., `<path>`),
-    e.g. `/home/eelco/Dev:/etc/nixos`. It can be extended using the
-    [`-I` option](@docroot@/command-ref/opt-common.md#opt-I).
 
-    If `NIX_PATH` is not set at all, Nix will fall back to the following list in [impure](@docroot@/command-ref/conf-file.md#conf-pure-eval) and [unrestricted](@docroot@/command-ref/conf-file.md#conf-restrict-eval) evaluation mode:
+- <span id="env-NIX_PATH">[`NIX_PATH`](#env-NIX_PATH)</span>
 
-      1. `$HOME/.nix-defexpr/channels`
+  A colon-separated list of directories used to look up the location of Nix
-      2. `nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixpkgs`
+  expressions using [paths](@docroot@/language/values.md#type-path)
-      3. `/nix/var/nix/profiles/per-user/root/channels`
+  enclosed in angle brackets (i.e., `<path>`),
+  e.g. `/home/eelco/Dev:/etc/nixos`. It can be extended using the
+  [`-I` option](@docroot@/command-ref/opt-common.md#opt-I).
 
-    If `NIX_PATH` is set to an empty string, resolving search paths will always fail.
+  If `NIX_PATH` is not set at all, Nix will fall back to the following list in [impure](@docroot@/command-ref/conf-file.md#conf-pure-eval) and [unrestricted](@docroot@/command-ref/conf-file.md#conf-restrict-eval) evaluation mode:
-    For example, attempting to use `<nixpkgs>` will produce:
 
-        error: file 'nixpkgs' was not found in the Nix search path
+  1. `$HOME/.nix-defexpr/channels`
+  2. `nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixpkgs`
+  3. `/nix/var/nix/profiles/per-user/root/channels`
 
-  - <span id="env-NIX_IGNORE_SYMLINK_STORE">[`NIX_IGNORE_SYMLINK_STORE`](#env-NIX_IGNORE_SYMLINK_STORE)</span>\
+  If `NIX_PATH` is set to an empty string, resolving search paths will always fail.
-    Normally, the Nix store directory (typically `/nix/store`) is not
+  For example, attempting to use `<nixpkgs>` will produce:
-    allowed to contain any symlink components. This is to prevent
-    “impure” builds. Builders sometimes “canonicalise” paths by
-    resolving all symlink components. Thus, builds on different machines
-    (with `/nix/store` resolving to different locations) could yield
-    different results. This is generally not a problem, except when
-    builds are deployed to machines where `/nix/store` resolves
-    differently. If you are sure that you’re not going to do that, you
-    can set `NIX_IGNORE_SYMLINK_STORE` to `1`.
 
-    Note that if you’re symlinking the Nix store so that you can put it
+      error: file 'nixpkgs' was not found in the Nix search path
-    on another file system than the root file system, on Linux you’re
-    better off using `bind` mount points, e.g.,
 
-    ```console
+- <span id="env-NIX_IGNORE_SYMLINK_STORE">[`NIX_IGNORE_SYMLINK_STORE`](#env-NIX_IGNORE_SYMLINK_STORE)</span>
-    $ mkdir /nix
-    $ mount -o bind /mnt/otherdisk/nix /nix
-    ```
 
-    Consult the mount 8 manual page for details.
+  Normally, the Nix store directory (typically `/nix/store`) is not
+  allowed to contain any symlink components. This is to prevent
+  “impure” builds. Builders sometimes “canonicalise” paths by
+  resolving all symlink components. Thus, builds on different machines
+  (with `/nix/store` resolving to different locations) could yield
+  different results. This is generally not a problem, except when
+  builds are deployed to machines where `/nix/store` resolves
+  differently. If you are sure that you’re not going to do that, you
+  can set `NIX_IGNORE_SYMLINK_STORE` to `1`.
 
-  - <span id="env-NIX_STORE_DIR">[`NIX_STORE_DIR`](#env-NIX_STORE_DIR)</span>\
+  Note that if you’re symlinking the Nix store so that you can put it
-    Overrides the location of the Nix store (default `prefix/store`).
+  on another file system than the root file system, on Linux you’re
+  better off using `bind` mount points, e.g.,
 
-  - <span id="env-NIX_DATA_DIR">[`NIX_DATA_DIR`](#env-NIX_DATA_DIR)</span>\
+  ```console
-    Overrides the location of the Nix static data directory (default
+  $ mkdir /nix
-    `prefix/share`).
+  $ mount -o bind /mnt/otherdisk/nix /nix
+  ```
 
-  - <span id="env-NIX_LOG_DIR">[`NIX_LOG_DIR`](#env-NIX_LOG_DIR)</span>\
+  Consult the mount 8 manual page for details.
-    Overrides the location of the Nix log directory (default
-    `prefix/var/log/nix`).
 
-  - <span id="env-NIX_STATE_DIR">[`NIX_STATE_DIR`](#env-NIX_STATE_DIR)</span>\
+- <span id="env-NIX_STORE_DIR">[`NIX_STORE_DIR`](#env-NIX_STORE_DIR)</span>
-    Overrides the location of the Nix state directory (default
-    `prefix/var/nix`).
 
-  - <span id="env-NIX_CONF_DIR">[`NIX_CONF_DIR`](#env-NIX_CONF_DIR)</span>\
+  Overrides the location of the Nix store (default `prefix/store`).
-    Overrides the location of the system Nix configuration directory
-    (default `prefix/etc/nix`).
 
-  - <span id="env-NIX_CONFIG">[`NIX_CONFIG`](#env-NIX_CONFIG)</span>\
+- <span id="env-NIX_DATA_DIR">[`NIX_DATA_DIR`](#env-NIX_DATA_DIR)</span>
-    Applies settings from Nix configuration from the environment.
-    The content is treated as if it was read from a Nix configuration file.
-    Settings are separated by the newline character.
 
-  - <span id="env-NIX_USER_CONF_FILES">[`NIX_USER_CONF_FILES`](#env-NIX_USER_CONF_FILES)</span>\
+  Overrides the location of the Nix static data directory (default
-    Overrides the location of the Nix user configuration files to load from.
+  `prefix/share`).
 
-    The default are the locations according to the [XDG Base Directory Specification].
+- <span id="env-NIX_LOG_DIR">[`NIX_LOG_DIR`](#env-NIX_LOG_DIR)</span>
-    See the [XDG Base Directories](#xdg-base-directories) sub-section for details.
 
-    The variable is treated as a list separated by the `:` token.
+  Overrides the location of the Nix log directory (default
+  `prefix/var/log/nix`).
 
-  - <span id="env-TMPDIR">[`TMPDIR`](#env-TMPDIR)</span>\
+- <span id="env-NIX_STATE_DIR">[`NIX_STATE_DIR`](#env-NIX_STATE_DIR)</span>
-    Use the specified directory to store temporary files. In particular,
-    this includes temporary build directories; these can take up
-    substantial amounts of disk space. The default is `/tmp`.
 
-  - <span id="env-NIX_REMOTE">[`NIX_REMOTE`](#env-NIX_REMOTE)</span>\
+  Overrides the location of the Nix state directory (default
-    This variable should be set to `daemon` if you want to use the Nix
+  `prefix/var/nix`).
-    daemon to execute Nix operations. This is necessary in [multi-user
-    Nix installations](@docroot@/installation/multi-user.md). If the Nix
-    daemon's Unix socket is at some non-standard path, this variable
-    should be set to `unix://path/to/socket`. Otherwise, it should be
-    left unset.
 
-  - <span id="env-NIX_SHOW_STATS">[`NIX_SHOW_STATS`](#env-NIX_SHOW_STATS)</span>\
+- <span id="env-NIX_CONF_DIR">[`NIX_CONF_DIR`](#env-NIX_CONF_DIR)</span>
-    If set to `1`, Nix will print some evaluation statistics, such as
-    the number of values allocated.
 
-  - <span id="env-NIX_COUNT_CALLS">[`NIX_COUNT_CALLS`](#env-NIX_COUNT_CALLS)</span>\
+  Overrides the location of the system Nix configuration directory
-    If set to `1`, Nix will print how often functions were called during
+  (default `prefix/etc/nix`).
-    Nix expression evaluation. This is useful for profiling your Nix
-    expressions.
 
-  - <span id="env-GC_INITIAL_HEAP_SIZE">[`GC_INITIAL_HEAP_SIZE`](#env-GC_INITIAL_HEAP_SIZE)</span>\
+- <span id="env-NIX_CONFIG">[`NIX_CONFIG`](#env-NIX_CONFIG)</span>
-    If Nix has been configured to use the Boehm garbage collector, this
+
-    variable sets the initial size of the heap in bytes. It defaults to
+  Applies settings from Nix configuration from the environment.
-    384 MiB. Setting it to a low value reduces memory consumption, but
+  The content is treated as if it was read from a Nix configuration file.
-    will increase runtime due to the overhead of garbage collection.
+  Settings are separated by the newline character.
+
+- <span id="env-NIX_USER_CONF_FILES">[`NIX_USER_CONF_FILES`](#env-NIX_USER_CONF_FILES)</span>
+
+  Overrides the location of the Nix user configuration files to load from.
+
+  The default are the locations according to the [XDG Base Directory Specification].
+  See the [XDG Base Directories](#xdg-base-directories) sub-section for details.
+
+  The variable is treated as a list separated by the `:` token.
+
+- <span id="env-TMPDIR">[`TMPDIR`](#env-TMPDIR)</span>
+
+  Use the specified directory to store temporary files. In particular,
+  this includes temporary build directories; these can take up
+  substantial amounts of disk space. The default is `/tmp`.
+
+- <span id="env-NIX_REMOTE">[`NIX_REMOTE`](#env-NIX_REMOTE)</span>
+
+  This variable should be set to `daemon` if you want to use the Nix
+  daemon to execute Nix operations. This is necessary in [multi-user
+  Nix installations](@docroot@/installation/multi-user.md). If the Nix
+  daemon's Unix socket is at some non-standard path, this variable
+  should be set to `unix://path/to/socket`. Otherwise, it should be
+  left unset.
+
+- <span id="env-NIX_SHOW_STATS">[`NIX_SHOW_STATS`](#env-NIX_SHOW_STATS)</span>
+
+  If set to `1`, Nix will print some evaluation statistics, such as
+  the number of values allocated.
+
+- <span id="env-NIX_COUNT_CALLS">[`NIX_COUNT_CALLS`](#env-NIX_COUNT_CALLS)</span>
+
+  If set to `1`, Nix will print how often functions were called during
+  Nix expression evaluation. This is useful for profiling your Nix
+  expressions.
+
+- <span id="env-GC_INITIAL_HEAP_SIZE">[`GC_INITIAL_HEAP_SIZE`](#env-GC_INITIAL_HEAP_SIZE)</span>
+
+  If Nix has been configured to use the Boehm garbage collector, this
+  variable sets the initial size of the heap in bytes. It defaults to
+  384 MiB. Setting it to a low value reduces memory consumption, but
+  will increase runtime due to the overhead of garbage collection.
 
 ## XDG Base Directories
 

doc/manual/src/command-ref/nix-build.md

@@ -51,8 +51,9 @@ derivation).
 
 # Options
 
-All options not listed here are passed to `nix-store --realise`,
+All options not listed here are passed to
-except for `--arg` and `--attr` / `-A` which are passed to `nix-instantiate`.
+[`nix-store --realise`](nix-store/realise.md),
+except for `--arg` and `--attr` / `-A` which are passed to [`nix-instantiate`](nix-instantiate.md).
 
   - <span id="opt-no-out-link">[`--no-out-link`](#opt-no-out-link)<span>
 
@@ -69,6 +70,8 @@ except for `--arg` and `--attr` / `-A` which are passed to `nix-instantiate`.
     Change the name of the symlink to the output path created from
     `result` to *outlink*.
 
+{{#include ./status-build-failure.md}}
+
 {{#include ./opt-common.md}}
 
 {{#include ./env-common.md}}

doc/manual/src/command-ref/nix-channel.md

@@ -8,36 +8,46 @@
 
 # Description
 
-A Nix channel is a mechanism that allows you to automatically stay
+Channels are a mechanism for referencing remote Nix expressions and conveniently retrieving their latest version.
-up-to-date with a set of pre-built Nix expressions. A Nix channel is
-just a URL that points to a place containing a set of Nix expressions.
 
-To see the list of official NixOS channels, visit
+The moving parts of channels are:
-<https://nixos.org/channels>.
+- The official channels listed at <https://nixos.org/channels>
+- The user-specific list of [subscribed channels](#subscribed-channels)
+- The [downloaded channel contents](#channels)
+- The [Nix expression search path](@docroot@/command-ref/conf-file.md#conf-nix-path), set with the [`-I` option](#opt-i) or the [`NIX_PATH` environment variable](#env-NIX_PATH)
+
+> **Note**
+>
+> The state of a subscribed channel is external to the Nix expressions relying on it.
+> This may limit reproducibility.
+>
+> Dependencies on other Nix expressions can be declared explicitly with:
+> - [`fetchurl`](@docroot@/language/builtins.md#builtins-fetchurl), [`fetchTarball`](@docroot@/language/builtins.md#builtins-fetchTarball), or [`fetchGit`](@docroot@/language/builtins.md#builtins-fetchGit) in Nix expressions
+> - the [`-I` option](@docroot@/command-ref/opt-common.md#opt-I) in command line invocations
 
 This command has the following operations:
 
   - `--add` *url* \[*name*\]\
-    Adds a channel named *name* with URL *url* to the list of subscribed
+    Add a channel *name* located at *url* to the list of subscribed channels.
-    channels. If *name* is omitted, it defaults to the last component of
+    If *name* is omitted, default to the last component of *url*, with the suffixes `-stable` or `-unstable` removed.
-    *url*, with the suffixes `-stable` or `-unstable` removed.
+
+    > **Note**
+    >
+    > `--add` does not automatically perform an update.
+    > Use `--update` explicitly.
 
     A channel URL must point to a directory containing a file `nixexprs.tar.gz`.
     At the top level, that tarball must contain a single directory with a `default.nix` file that serves as the channel’s entry point.
 
   - `--remove` *name*\
-    Removes the channel named *name* from the list of subscribed
+    Remove the channel *name* from the list of subscribed channels.
-    channels.
 
   - `--list`\
-    Prints the names and URLs of all subscribed channels on standard
+    Print the names and URLs of all subscribed channels on standard output.
-    output.
 
   - `--update` \[*names*…\]\
-    Downloads the Nix expressions of all subscribed channels (or only
+    Download the Nix expressions of subscribed channels and create a new generation.
-    those included in *names* if specified) and makes them the default
+    Update all channels if none is specified, and only those included in *names* otherwise.
-    for `nix-env` operations (by symlinking them from the directory
-    `~/.nix-defexpr`).
 
   - `--list-generations`\
     Prints a list of all the current existing generations for the
@@ -49,13 +59,8 @@ This command has the following operations:
     ```
 
   - `--rollback` \[*generation*\]\
-    Reverts the previous call to `nix-channel
+    Revert channels to the state before the last call to `nix-channel --update`.
-                    --update`. Optionally, you can specify a specific channel generation
+    Optionally, you can specify a specific channel *generation* number to restore.
-    number to restore.
-
-Note that `--add` does not automatically perform an update.
-
-The list of subscribed channels is stored in `~/.nix-channels`.
 
 {{#include ./opt-common.md}}
 
@@ -69,23 +74,33 @@ The list of subscribed channels is stored in `~/.nix-channels`.
 
 # Examples
 
-To subscribe to the Nixpkgs channel and install the GNU Hello package:
+Subscribe to the Nixpkgs channel and run `hello` from the GNU Hello package:
 
 ```console
 $ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
+$ nix-channel --list
+nixpkgs https://nixos.org/channels/nixpkgs
 $ nix-channel --update
-$ nix-env --install --attr nixpkgs.hello
+$ nix-shell -p hello --run hello
+hello
 ```
 
-You can revert channel updates using `--rollback`:
+Revert channel updates using `--rollback`:
 
 ```console
-$ nix-instantiate --eval --expr '(import <nixpkgs> {}).lib.version'
+$ nix-instantiate --eval '<nixpkgs>' --attr lib.version
-"14.04.527.0e935f1"
+"22.11pre296212.530a53dcbc9"
 
 $ nix-channel --rollback
 switching from generation 483 to 482
 
-$ nix-instantiate --eval --expr '(import <nixpkgs> {}).lib.version'
+$ nix-instantiate --eval '<nixpkgs>' --attr lib.version
-"14.04.526.dbadfad"
+"22.11pre281526.d0419badfad"
+```
+
+Remove a channel:
+
+```console
+$ nix-channel --remove nixpkgs
+$ nix-channel --list
 ```

doc/manual/src/command-ref/nix-collect-garbage.md

@@ -57,7 +57,7 @@ These options are for deleting old [profiles] prior to deleting unreachable [sto
   Delete all generations of profiles older than the specified amount (except for the generations that were active at that point in time).
   *period* is a value such as `30d`, which would mean 30 days.
 
-  This is the equivalent of invoking [`nix-env --delete-generations <period>`](@docroot@/command-ref/nix-env/delete-generations.md#generations-days) on each found profile.
+  This is the equivalent of invoking [`nix-env --delete-generations <period>`](@docroot@/command-ref/nix-env/delete-generations.md#generations-time) on each found profile.
   See the documentation of that command for additional information about the *period* argument.
 
 {{#include ./opt-common.md}}

doc/manual/src/command-ref/nix-env/delete-generations.md

@@ -20,22 +20,30 @@ This operation deletes the specified generations of the current profile.
 
 - The special value <span id="generations-old">`old`</span>
 
-  Delete all generations older than the current one.
+  Delete all generations except the current one.
 
-- <span id="generations-days">`<days>d`</span>:\
+  > **WARNING**
-  The last *days* days
+  >
+  > Older *and newer* generations will be deleted by this operation.
+  >
+  > One might expect this to just delete older generations than the curent one, but that is only true if the current generation is also the latest.
+  > Because one can roll back to a previous generation, it is possible to have generations newer than the current one.
+  > They will also be deleted.
+
+- <span id="generations-time">`<number>d`</span>:\
+  The last *number* days
 
   *Example*: `30d`
 
-  Delete all generations older than *days* days.
+  Delete all generations created more than *number* days ago, except the most recent one of them.
-  The generation that was active at that point in time is excluded, and will not be deleted.
+  This allows rolling back to generations that were available within the specified period.
 
-- <span id="generations-count">`+<count>`</span>:\
+- <span id="generations-count">`+<number>`</span>:\
-  The last *count* generations up to the present
+  The last *number* generations up to the present
 
   *Example*: `+5`
 
-  Keep the last *count* generations, along with any newer than current.
+  Keep the last *number* generations, along with any newer than current.
 
 Periodically deleting old generations is important to make garbage collection
 effective.
@@ -61,7 +69,7 @@ $ nix-env --delete-generations 3 4 8
 
 Delete the generations numbered 3, 4, and 8, so long as the current active generation is not any of those.
 
-## Keep most-recent by count count
+## Keep most-recent by count (number of generations)
 
 ```console
 $ nix-env --delete-generations +5
@@ -72,7 +80,7 @@ Suppose `30` is the current generation, and we currently have generations number
 Then this command will delete generations `20` through `25` (`<= 30 - 5`),
 and keep generations `26` through `31` (`> 30 - 5`).
 
-## Keep most-recent in days
+## Keep most-recent by time (number of days)
 
 ```console
 $ nix-env --delete-generations 30d

doc/manual/src/command-ref/nix-env/install.md

@@ -14,23 +14,28 @@
 
 # Description
 
-The install operation creates a new user environment, based on the
+The install operation creates a new user environment.
-current generation of the active profile, to which a set of store paths
+It is based on the current generation of the active [profile](@docroot@/command-ref/files/profiles.md), to which a set of [store paths] described by *args* is added.
-described by *args* is added. The arguments *args* map to store paths in
-a number of possible ways:
 
-  - By default, *args* is a set of derivation names denoting derivations
+[store paths]: @docroot@/glossary.md#gloss-store-path
-    in the active Nix expression. These are realised, and the resulting
+
-    output paths are installed. Currently installed derivations with a
+The arguments *args* map to store paths in a number of possible ways:
-    name equal to the name of a derivation being added are removed
+
-    unless the option `--preserve-installed` is specified.
+
+  - By default, *args* is a set of [derivation] names denoting derivations in the [default Nix expression].
+    These are [realised], and the resulting output paths are installed.
+    Currently installed derivations with a name equal to the name of a derivation being added are removed unless the option `--preserve-installed` is specified.
+
+    [derivation]: @docroot@/glossary.md#gloss-derivation
+    [default Nix expression]: @docroot@/command-ref/files/default-nix-expression.md
+    [realised]: @docroot@/glossary.md#gloss-realise
 
     If there are multiple derivations matching a name in *args* that
     have the same name (e.g., `gcc-3.3.6` and `gcc-4.1.1`), then the
     derivation with the highest *priority* is used. A derivation can
     define a priority by declaring the `meta.priority` attribute. This
     attribute should be a number, with a higher value denoting a lower
-    priority. The default priority is `0`.
+    priority. The default priority is `5`.
 
     If there are multiple matching derivations with the same priority,
     then the derivation with the highest version will be installed.
@@ -40,44 +45,90 @@ a number of possible ways:
     gcc-3.3.6 gcc-4.1.1` will install both version of GCC (and will
     probably cause a user environment conflict\!).
 
-  - If `--attr` (`-A`) is specified, the arguments are *attribute
+  - If [`--attr`](#opt-attr) / `-A` is specified, the arguments are *attribute paths* that select attributes from the [default Nix expression].
-    paths* that select attributes from the top-level Nix
+    This is faster than using derivation names and unambiguous.
-    expression. This is faster than using derivation names and
+    Show the attribute paths of available packages with [`nix-env --query`](./query.md):
-    unambiguous. To find out the attribute paths of available
+
-    packages, use `nix-env --query --available --attr-path `.
+    ```console
+    nix-env --query --available --attr-path`
+    ```
 
   - If `--from-profile` *path* is given, *args* is a set of names
-    denoting installed store paths in the profile *path*. This is an
+    denoting installed [store paths] in the profile *path*. This is an
     easy way to copy user environment elements from one profile to
     another.
 
-  - If `--from-expression` is given, *args* are Nix
+  - If `--from-expression` is given, *args* are [Nix language functions](@docroot@/language/constructs.md#functions) that are called with the [default Nix expression] as their single argument.
-    [functions](@docroot@/language/constructs.md#functions)
+    The derivations returned by those function calls are installed.
-    that are called with the active Nix expression as their single
+    This allows derivations to be specified in an unambiguous way, which is necessary if there are multiple derivations with the same name.
-    argument. The derivations returned by those function calls are
-    installed. This allows derivations to be specified in an
-    unambiguous way, which is necessary if there are multiple
-    derivations with the same name.
 
-  - If *args* are [store derivations](@docroot@/glossary.md#gloss-store-derivation), then these are
+  - If *args* are [store derivations](@docroot@/glossary.md#gloss-store-derivation), then these are [realised], and the resulting output paths are installed.
-    [realised](@docroot@/command-ref/nix-store/realise.md), and the resulting output paths
-    are installed.
 
-  - If *args* are store paths that are not store derivations, then these
+  - If *args* are [store paths] that are not store derivations, then these are [realised] and installed.
-    are [realised](@docroot@/command-ref/nix-store/realise.md) and installed.
 
-  - By default all outputs are installed for each derivation. That can
+  - By default all [outputs](@docroot@/language/derivations.md#attr-outputs) are installed for each [derivation].
-    be reduced by setting `meta.outputsToInstall`.
+    This can be overridden by adding a `meta.outputsToInstall` attribute on the derivation listing a subset of the output names.
 
-# Flags
+    Example:
+
+    The file `example.nix` defines a derivation with two outputs `foo` and `bar`, each containing a file.
+
+    ```nix
+    # example.nix
+    let
+      pkgs = import <nixpkgs> {};
+      command = ''
+        ${pkgs.coreutils}/bin/mkdir -p $foo $bar
+        echo foo > $foo/foo-file
+        echo bar > $bar/bar-file
+      '';
+    in
+    derivation {
+      name = "example";
+      builder = "${pkgs.bash}/bin/bash";
+      args = [ "-c" command ];
+      outputs = [ "foo" "bar" ];
+      system = builtins.currentSystem;
+    }
+    ```
+
+    Installing from this Nix expression will make files from both outputs appear in the current profile.
+
+    ```console
+    $ nix-env --install --file example.nix
+    installing 'example'
+    $ ls ~/.nix-profile
+    foo-file
+    bar-file
+    manifest.nix
+    ```
+
+    Adding `meta.outputsToInstall` to that derivation will make `nix-env` only install files from the specified outputs.
+
+    ```nix
+    # example-outputs.nix
+    import ./example.nix // { meta.outputsToInstall = [ "bar" ]; }
+    ```
+
+    ```console
+    $ nix-env --install --file example-outputs.nix
+    installing 'example'
+    $ ls ~/.nix-profile
+    bar-file
+    manifest.nix
+    ```
+
+# Options
+
+  - `--prebuilt-only` / `-b`
 
-  - `--prebuilt-only` / `-b`\
     Use only derivations for which a substitute is registered, i.e.,
     there is a pre-built binary available that can be downloaded in lieu
     of building the derivation. Thus, no packages will be built from
     source.
 
-  - `--preserve-installed` / `-P`\
+  - `--preserve-installed` / `-P`
+
     Do not remove derivations with a name matching one of the
     derivations being installed. Usually, trying to have two versions of
     the same package installed in the same generation of a profile will
@@ -85,7 +136,8 @@ a number of possible ways:
     clashes between the two versions. However, this is not the case for
     all packages.
 
-  - `--remove-all` / `-r`\
+  - `--remove-all` / `-r`
+
     Remove all previously installed packages first. This is equivalent
     to running `nix-env --uninstall '.*'` first, except that everything happens
     in a single transaction.

doc/manual/src/command-ref/nix-prefetch-url.md

@@ -31,15 +31,18 @@ store already contains a file with the same hash and base name.
 Otherwise, the file is downloaded, and an error is signaled if the
 actual hash of the file does not match the specified hash.
 
-This command prints the hash on standard output. Additionally, if the
+This command prints the hash on standard output.
-option `--print-path` is used, the path of the downloaded file in the
+The hash is printed using base-32 unless `--type md5` is specified,
-Nix store is also printed.
+in which case it's printed using base-16.
+Additionally, if the option `--print-path` is used,
+the path of the downloaded file in the Nix store is also printed.
 
 # Options
 
   - `--type` *hashAlgo*\
-    Use the specified cryptographic hash algorithm, which can be one of
+    Use the specified cryptographic hash algorithm,
-    `md5`, `sha1`, `sha256`, and `sha512`.
+    which can be one of `md5`, `sha1`, `sha256`, and `sha512`.
+    The default is `sha256`.
 
   - `--print-path`\
     Print the store path of the downloaded file on standard output.

doc/manual/src/command-ref/nix-shell.md

@@ -235,14 +235,14 @@ package like Terraform:
 
 ```bash
 #! /usr/bin/env nix-shell
-#! nix-shell -i bash --packages "terraform.withPlugins (plugins: [ plugins.openstack ])"
+#! nix-shell -i bash --packages 'terraform.withPlugins (plugins: [ plugins.openstack ])'
 
 terraform apply
 ```
 
 > **Note**
 >
-> You must use double quotes (`"`) when passing a simple Nix expression
+> You must use single or double quotes (`'`, `"`) when passing a simple Nix expression
 > in a nix-shell shebang.
 
 Finally, using the merging of multiple nix-shell shebangs the following
@@ -251,7 +251,7 @@ branch):
 
 ```haskell
 #! /usr/bin/env nix-shell
-#! nix-shell -i runghc --packages "haskellPackages.ghcWithPackages (ps: [ps.download-curl ps.tagsoup])"
+#! nix-shell -i runghc --packages 'haskellPackages.ghcWithPackages (ps: [ps.download-curl ps.tagsoup])'
 #! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-20.03.tar.gz
 
 import Network.Curl.Download

doc/manual/src/command-ref/nix-store/query.md

@@ -5,8 +5,8 @@
 # Synopsis
 
 `nix-store` {`--query` | `-q`}
-  {`--outputs` | `--requisites` | `-R` | `--references` |
+  {`--outputs` | `--requisites` | `-R` | `--references` | `--referrers` |
-  `--referrers` | `--referrers-closure` | `--deriver` | `-d` |
+  `--referrers-closure` | `--deriver` | `-d` | `--valid-derivers` |
   `--graph` | `--tree` | `--binding` *name* | `-b` *name* | `--hash` |
   `--size` | `--roots`}
   [`--use-output`] [`-u`] [`--force-realise`] [`-f`]
@@ -82,13 +82,21 @@ symlink.
     in the Nix store that are dependent on *paths*.
 
   - `--deriver`; `-d`\
-    Prints the [deriver] of the store paths *paths*. If
+    Prints the [deriver] that was used to build the store paths *paths*. If
     the path has no deriver (e.g., if it is a source file), or if the
     deriver is not known (e.g., in the case of a binary-only
     deployment), the string `unknown-deriver` is printed.
+    The returned deriver is not guaranteed to exist in the local store, for
+    example when *paths* were substituted from a binary cache.
+    Use `--valid-derivers` instead to obtain valid paths only.
 
     [deriver]: ../../glossary.md#gloss-deriver
 
+  - `--valid-derivers`\
+    Prints a set of derivation files (`.drv`) which are supposed produce
+    said paths when realized. Might print nothing, for example for source paths
+    or paths subsituted from a binary cache.
+
   - `--graph`\
     Prints the references graph of the store paths *paths* in the format
     of the `dot` tool of AT\&T's [Graphviz

doc/manual/src/command-ref/nix-store/realise.md

@@ -1,6 +1,6 @@
 # Name
 
-`nix-store --realise` - realise specified store paths
+`nix-store --realise` - build or fetch store objects
 
 # Synopsis
 
@@ -8,33 +8,39 @@
 
 # Description
 
-The operation `--realise` essentially “builds” the specified store
-paths. Realisation is a somewhat overloaded term:
 
-  - If the store path is a *derivation*, realisation ensures that the
+Each of *paths* is processed as follows:
-    output paths of the derivation are [valid] (i.e.,
-    the output path and its closure exist in the file system). This
-    can be done in several ways. First, it is possible that the
-    outputs are already valid, in which case we are done
-    immediately. Otherwise, there may be [substitutes]
-    that produce the outputs (e.g., by downloading them). Finally, the
-    outputs can be produced by running the build task described
-    by the derivation.
 
-  - If the store path is not a derivation, realisation ensures that the
+- If the path leads to a [store derivation]:
-    specified path is valid (i.e., it and its closure exist in the file
+  1. If it is not [valid], substitute the store derivation file itself.
-    system). If the path is already valid, we are done immediately.
+  2. Realise its [output paths]:
-    Otherwise, the path and any missing paths in its closure may be
+    - Try to fetch from [substituters] the [store objects] associated with the output paths in the store derivation's [closure].
-    produced through substitutes. If there are no (successful)
+      - With [content-addressed derivations] (experimental):
-    substitutes, realisation fails.
+        Determine the output paths to realise by querying content-addressed realisation entries in the [Nix database].
+    - For any store paths that cannot be substituted, produce the required store objects:
+      1. Realise all outputs of the derivation's dependencies
+      2. Run the derivation's [`builder`](@docroot@/language/derivations.md#attr-builder) executable
+         <!-- TODO: Link to build process page #8888 -->
+- Otherwise, and if the path is not already valid: Try to fetch the associated [store objects] in the path's [closure] from [substituters].
 
+If no substitutes are available and no store derivation is given, realisation fails.
+
+[store paths]: @docroot@/glossary.md#gloss-store-path
 [valid]: @docroot@/glossary.md#gloss-validity
-[substitutes]: @docroot@/glossary.md#gloss-substitute
+[store derivation]: @docroot@/glossary.md#gloss-store-derivation
+[output paths]: @docroot@/glossary.md#gloss-output-path
+[store objects]: @docroot@/glossary.md#gloss-store-object
+[closure]: @docroot@/glossary.md#gloss-closure
+[substituters]: @docroot@/command-ref/conf-file.md#conf-substituters
+[content-addressed derivations]: @docroot@/contributing/experimental-features.md#xp-feature-ca-derivations
+[Nix database]: @docroot@/glossary.md#gloss-nix-database
 
-The output path of each derivation is printed on standard output. (For
+The resulting paths are printed on standard output.
-non-derivations argument, the argument itself is printed.)
+For non-derivation arguments, the argument itself is printed.
 
-The following flags are available:
+{{#include ../status-build-failure.md}}
+
+# Options
 
   - `--dry-run`\
     Print on standard error a description of what packages would be
@@ -54,37 +60,6 @@ The following flags are available:
     previous build, the new output path is left in
     `/nix/store/name.check.`
 
-Special exit codes:
-
-  - `100`\
-    Generic build failure, the builder process returned with a non-zero
-    exit code.
-
-  - `101`\
-    Build timeout, the build was aborted because it did not complete
-    within the specified `timeout`.
-
-  - `102`\
-    Hash mismatch, the build output was rejected because it does not
-    match the [`outputHash` attribute of the
-    derivation](@docroot@/language/advanced-attributes.md).
-
-  - `104`\
-    Not deterministic, the build succeeded in check mode but the
-    resulting output is not binary reproducible.
-
-With the `--keep-going` flag it's possible for multiple failures to
-occur, in this case the 1xx status codes are or combined using binary
-or.
-
-    1100100
-       ^^^^
-       |||`- timeout
-       ||`-- output hash mismatch
-       |`--- build failure
-       `---- not deterministic
-
-
 {{#include ./opt-common.md}}
 
 {{#include ../opt-common.md}}
@@ -96,8 +71,6 @@ or.
 This operation is typically used to build [store derivation]s produced by
 [`nix-instantiate`](@docroot@/command-ref/nix-instantiate.md):
 
-[store derivation]: @docroot@/glossary.md#gloss-store-derivation
-
 ```console
 $ nix-store --realise $(nix-instantiate ./test.nix)
 /nix/store/31axcgrlbfsxzmfff1gyj1bf62hvkby2-aterm-2.3.1

doc/manual/src/command-ref/opt-common-syn.md

@@ -1,57 +0,0 @@
-\--help
-
-\--version
-
-\--verbose
-
-\-v
-
-\--quiet
-
-\--log-format
-
-format
-
-\--no-build-output
-
-\-Q
-
-\--max-jobs
-
-\-j
-
-number
-
-\--cores
-
-number
-
-\--max-silent-time
-
-number
-
-\--timeout
-
-number
-
-\--keep-going
-
-\-k
-
-\--keep-failed
-
-\-K
-
-\--fallback
-
-\--readonly-mode
-
-\-I
-
-path
-
-\--option
-
-name
-
-value

doc/manual/src/command-ref/opt-common.md

@@ -2,217 +2,208 @@
 
 Most Nix commands accept the following command-line options:
 
-  - <span id="opt-help">[`--help`](#opt-help)</span>\
+- <span id="opt-help">[`--help`](#opt-help)</span>
-    Prints out a summary of the command syntax and exits.
 
-  - <span id="opt-version">[`--version`](#opt-version)</span>\
+  Prints out a summary of the command syntax and exits.
-    Prints out the Nix version number on standard output and exits.
 
-  - <span id="opt-verbose">[`--verbose`](#opt-verbose)</span> / `-v`\
+- <span id="opt-version">[`--version`](#opt-version)</span>
-    Increases the level of verbosity of diagnostic messages printed on
-    standard error. For each Nix operation, the information printed on
-    standard output is well-defined; any diagnostic information is
-    printed on standard error, never on standard output.
 
-    This option may be specified repeatedly. Currently, the following
+  Prints out the Nix version number on standard output and exits.
-    verbosity levels exist:
 
-      - 0\
+- <span id="opt-verbose">[`--verbose`](#opt-verbose)</span> / `-v`
-        “Errors only”: only print messages explaining why the Nix
-        invocation failed.
 
-      - 1\
+  Increases the level of verbosity of diagnostic messages printed on standard error.
-        “Informational”: print *useful* messages about what Nix is
+  For each Nix operation, the information printed on standard output is well-defined;
-        doing. This is the default.
+  any diagnostic information is printed on standard error, never on standard output.
 
-      - 2\
+  This option may be specified repeatedly.
-        “Talkative”: print more informational messages.
+  Currently, the following verbosity levels exist:
 
-      - 3\
+  - `0` “Errors only”
-        “Chatty”: print even more informational messages.
 
-      - 4\
+    Only print messages explaining why the Nix invocation failed.
-        “Debug”: print debug information.
 
-      - 5\
+  - `1` “Informational”
-        “Vomit”: print vast amounts of debug information.
 
-  - <span id="opt-quiet">[`--quiet`](#opt-quiet)</span>\
+    Print *useful* messages about what Nix is doing.
-    Decreases the level of verbosity of diagnostic messages printed on
+    This is the default.
-    standard error. This is the inverse option to `-v` / `--verbose`.
 
-    This option may be specified repeatedly. See the previous verbosity
+  - `2` “Talkative”
-    levels list.
 
-  - <span id="opt-log-format">[`--log-format`](#opt-log-format)</span> *format*\
+    Print more informational messages.
-    This option can be used to change the output of the log format, with
-    *format* being one of:
 
-      - raw\
+  - `3` “Chatty”
-        This is the raw format, as outputted by nix-build.
 
-      - internal-json\
+    Print even more informational messages.
-        Outputs the logs in a structured manner.
 
-        > **Warning**
+  - `4` “Debug”
-        >
-        > While the schema itself is relatively stable, the format of
-        > the error-messages (namely of the `msg`-field) can change
-        > between releases.
    
-      - bar\
+    Print debug information.
-        Only display a progress bar during the builds.
 
-      - bar-with-logs\
+  - `5` “Vomit”
-        Display the raw logs, with the progress bar at the bottom.
 
-  - <span id="opt-no-build-output">[`--no-build-output`](#opt-no-build-output)</span> / `-Q`\
+    Print vast amounts of debug information.
-    By default, output written by builders to standard output and
-    standard error is echoed to the Nix command's standard error. This
-    option suppresses this behaviour. Note that the builder's standard
-    output and error are always written to a log file in
-    `prefix/nix/var/log/nix`.
 
-  - <span id="opt-max-jobs">[`--max-jobs`](#opt-max-jobs)</span> / `-j` *number*\
+- <span id="opt-quiet">[`--quiet`](#opt-quiet)</span>
-    Sets the maximum number of build jobs that Nix will perform in
-    parallel to the specified number. Specify `auto` to use the number
-    of CPUs in the system. The default is specified by the `max-jobs`
-    configuration setting, which itself defaults to `1`. A higher
-    value is useful on SMP systems or to exploit I/O latency.
 
-    Setting it to `0` disallows building on the local machine, which is
+  Decreases the level of verbosity of diagnostic messages printed on standard error.
-    useful when you want builds to happen only on remote builders.
+  This is the inverse option to `-v` / `--verbose`.
 
-  - <span id="opt-cores">[`--cores`](#opt-cores)</span>\
+  This option may be specified repeatedly.
-    Sets the value of the `NIX_BUILD_CORES` environment variable in
+  See the previous verbosity levels list.
-    the invocation of builders. Builders can use this variable at
-    their discretion to control the maximum amount of parallelism. For
-    instance, in Nixpkgs, if the derivation attribute
-    `enableParallelBuilding` is set to `true`, the builder passes the
-    `-jN` flag to GNU Make. It defaults to the value of the `cores`
-    configuration setting, if set, or `1` otherwise. The value `0`
-    means that the builder should use all available CPU cores in the
-    system.
 
-  - <span id="opt-max-silent-time">[`--max-silent-time`](#opt-max-silent-time)</span>\
+- <span id="opt-log-format">[`--log-format`](#opt-log-format)</span> *format*
-    Sets the maximum number of seconds that a builder can go without
-    producing any data on standard output or standard error. The
-    default is specified by the `max-silent-time` configuration
-    setting. `0` means no time-out.
 
-  - <span id="opt-timeout">[`--timeout`](#opt-timeout)</span>\
+  This option can be used to change the output of the log format, with *format* being one of:
-    Sets the maximum number of seconds that a builder can run. The
-    default is specified by the `timeout` configuration setting. `0`
-    means no timeout.
 
-  - <span id="opt-keep-going">[`--keep-going`](#opt-keep-going)</span> / `-k`\
+  - `raw`
-    Keep going in case of failed builds, to the greatest extent
-    possible. That is, if building an input of some derivation fails,
-    Nix will still build the other inputs, but not the derivation
-    itself. Without this option, Nix stops if any build fails (except
-    for builds of substitutes), possibly killing builds in progress (in
-    case of parallel or distributed builds).
 
-  - <span id="opt-keep-failed">[`--keep-failed`](#opt-keep-failed)</span> / `-K`\
+    This is the raw format, as outputted by nix-build.
-    Specifies that in case of a build failure, the temporary directory
-    (usually in `/tmp`) in which the build takes place should not be
-    deleted. The path of the build directory is printed as an
-    informational message.
 
-  - <span id="opt-fallback">[`--fallback`](#opt-fallback)</span>\
+  - `internal-json`
-    Whenever Nix attempts to build a derivation for which substitutes
-    are known for each output path, but realising the output paths
-    through the substitutes fails, fall back on building the derivation.
 
-    The most common scenario in which this is useful is when we have
+    Outputs the logs in a structured manner.
-    registered substitutes in order to perform binary distribution from,
-    say, a network repository. If the repository is down, the
-    realisation of the derivation will fail. When this option is
-    specified, Nix will build the derivation instead. Thus, installation
-    from binaries falls back on installation from source. This option is
-    not the default since it is generally not desirable for a transient
-    failure in obtaining the substitutes to lead to a full build from
-    source (with the related consumption of resources).
 
-  - <span id="opt-readonly-mode">[`--readonly-mode`](#opt-readonly-mode)</span>\
+    > **Warning**
-    When this option is used, no attempt is made to open the Nix
+    >
-    database. Most Nix operations do need database access, so those
+    > While the schema itself is relatively stable, the format of
-    operations will fail.
+    > the error-messages (namely of the `msg`-field) can change
+    > between releases.
 
-  - <span id="opt-arg">[`--arg`](#opt-arg)</span> *name* *value*\
+  - `bar`
-    This option is accepted by `nix-env`, `nix-instantiate`,
-    `nix-shell` and `nix-build`. When evaluating Nix expressions, the
-    expression evaluator will automatically try to call functions that
-    it encounters. It can automatically call functions for which every
-    argument has a [default
-    value](@docroot@/language/constructs.md#functions) (e.g.,
-    `{ argName ?  defaultValue }: ...`). With `--arg`, you can also
-    call functions that have arguments without a default value (or
-    override a default value). That is, if the evaluator encounters a
-    function with an argument named *name*, it will call it with value
-    *value*.
 
-    For instance, the top-level `default.nix` in Nixpkgs is actually a
+    Only display a progress bar during the builds.
-    function:
 
-    ```nix
+  - `bar-with-logs`
-    { # The system (e.g., `i686-linux') for which to build the packages.
-      system ? builtins.currentSystem
-      ...
-    }: ...
-    ```
 
-    So if you call this Nix expression (e.g., when you do `nix-env --install --attr
+    Display the raw logs, with the progress bar at the bottom.
-    pkgname`), the function will be called automatically using the
-    value [`builtins.currentSystem`](@docroot@/language/builtins.md) for
-    the `system` argument. You can override this using `--arg`, e.g.,
-    `nix-env --install --attr pkgname --arg system \"i686-freebsd\"`. (Note that
-    since the argument is a Nix string literal, you have to escape the
-    quotes.)
 
-  - <span id="opt-argstr">[`--argstr`](#opt-argstr)</span> *name* *value*\
+- <span id="opt-no-build-output">[`--no-build-output`](#opt-no-build-output)</span> / `-Q`
-    This option is like `--arg`, only the value is not a Nix
-    expression but a string. So instead of `--arg system
-    \"i686-linux\"` (the outer quotes are to keep the shell happy) you
-    can say `--argstr system i686-linux`.
 
-  - <span id="opt-attr">[`--attr`](#opt-attr)</span> / `-A` *attrPath*\
+  By default, output written by builders to standard output and standard error is echoed to the Nix command's standard error.
-    Select an attribute from the top-level Nix expression being
+  This option suppresses this behaviour.
-    evaluated. (`nix-env`, `nix-instantiate`, `nix-build` and
+  Note that the builder's standard output and error are always written to a log file in `prefix/nix/var/log/nix`.
-    `nix-shell` only.) The *attribute path* *attrPath* is a sequence
-    of attribute names separated by dots. For instance, given a
-    top-level Nix expression *e*, the attribute path `xorg.xorgserver`
-    would cause the expression `e.xorg.xorgserver` to be used. See
-    [`nix-env --install`](@docroot@/command-ref/nix-env/install.md) for some
-    concrete examples.
 
-    In addition to attribute names, you can also specify array indices.
+- <span id="opt-max-jobs">[`--max-jobs`](#opt-max-jobs)</span> / `-j` *number*
-    For instance, the attribute path `foo.3.bar` selects the `bar`
-    attribute of the fourth element of the array in the `foo` attribute
-    of the top-level expression.
 
-  - <span id="opt-expr">[`--expr`](#opt-expr)</span> / `-E`\
+  Sets the maximum number of build jobs that Nix will perform in parallel to the specified number.
-    Interpret the command line arguments as a list of Nix expressions to
+  Specify `auto` to use the number of CPUs in the system.
-    be parsed and evaluated, rather than as a list of file names of Nix
+  The default is specified by the `max-jobs` configuration setting, which itself defaults to `1`.
-    expressions. (`nix-instantiate`, `nix-build` and `nix-shell` only.)
+  A higher value is useful on SMP systems or to exploit I/O latency.
 
-    For `nix-shell`, this option is commonly used to give you a shell in
+  Setting it to `0` disallows building on the local machine, which is useful when you want builds to happen only on remote builders.
-    which you can build the packages returned by the expression. If you
-    want to get a shell which contain the *built* packages ready for
-    use, give your expression to the `nix-shell --packages ` convenience flag
-    instead.
 
-  - <span id="opt-I">[`-I`](#opt-I)</span> *path*\
+- <span id="opt-cores">[`--cores`](#opt-cores)</span>
-    Add an entry to the [Nix expression search path](@docroot@/command-ref/conf-file.md#conf-nix-path).
-    This option may be given multiple times.
-    Paths added through `-I` take precedence over [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH).
 
-  - <span id="opt-option">[`--option`](#opt-option)</span> *name* *value*\
+  Sets the value of the `NIX_BUILD_CORES` environment variable in the invocation of builders.
-    Set the Nix configuration option *name* to *value*. This overrides
+  Builders can use this variable at their discretion to control the maximum amount of parallelism.
-    settings in the Nix configuration file (see nix.conf5).
+  For instance, in Nixpkgs, if the derivation attribute `enableParallelBuilding` is set to `true`, the builder passes the `-jN` flag to GNU Make.
+  It defaults to the value of the `cores` configuration setting, if set, or `1` otherwise.
+  The value `0` means that the builder should use all available CPU cores in the system.
 
-  - <span id="opt-repair">[`--repair`](#opt-repair)</span>\
+- <span id="opt-max-silent-time">[`--max-silent-time`](#opt-max-silent-time)</span>
-    Fix corrupted or missing store paths by redownloading or rebuilding
+
-    them. Note that this is slow because it requires computing a
+  Sets the maximum number of seconds that a builder can go without producing any data on standard output or standard error.
-    cryptographic hash of the contents of every path in the closure of
+  The default is specified by the `max-silent-time` configuration setting.
-    the build. Also note the warning under `nix-store --repair-path`.
+  `0` means no time-out.
+
+- <span id="opt-timeout">[`--timeout`](#opt-timeout)</span>
+
+  Sets the maximum number of seconds that a builder can run.
+  The default is specified by the `timeout` configuration setting.
+  `0` means no timeout.
+
+- <span id="opt-keep-going">[`--keep-going`](#opt-keep-going)</span> / `-k`
+
+  Keep going in case of failed builds, to the greatest extent possible.
+  That is, if building an input of some derivation fails, Nix will still build the other inputs, but not the derivation itself.
+  Without this option, Nix stops if any build fails (except for builds of substitutes), possibly killing builds in progress (in case of parallel or distributed builds).
+
+- <span id="opt-keep-failed">[`--keep-failed`](#opt-keep-failed)</span> / `-K`
+
+  Specifies that in case of a build failure, the temporary directory (usually in `/tmp`) in which the build takes place should not be deleted.
+  The path of the build directory is printed as an informational message.
+
+- <span id="opt-fallback">[`--fallback`](#opt-fallback)</span>
+
+  Whenever Nix attempts to build a derivation for which substitutes are known for each output path, but realising the output paths through the substitutes fails, fall back on building the derivation.
+
+  The most common scenario in which this is useful is when we have registered substitutes in order to perform binary distribution from, say, a network repository.
+  If the repository is down, the realisation of the derivation will fail.
+  When this option is specified, Nix will build the derivation instead.
+  Thus, installation from binaries falls back on installation from source.
+  This option is not the default since it is generally not desirable for a transient failure in obtaining the substitutes to lead to a full build from source (with the related consumption of resources).
+
+- <span id="opt-readonly-mode">[`--readonly-mode`](#opt-readonly-mode)</span>
+
+  When this option is used, no attempt is made to open the Nix database.
+  Most Nix operations do need database access, so those operations will fail.
+
+- <span id="opt-arg">[`--arg`](#opt-arg)</span> *name* *value*
+
+  This option is accepted by `nix-env`, `nix-instantiate`, `nix-shell` and `nix-build`.
+  When evaluating Nix expressions, the expression evaluator will automatically try to call functions that it encounters.
+  It can automatically call functions for which every argument has a [default value](@docroot@/language/constructs.md#functions) (e.g., `{ argName ?  defaultValue }: ...`).
+
+  With `--arg`, you can also call functions that have arguments without a default value (or override a default value).
+  That is, if the evaluator encounters a function with an argument named *name*, it will call it with value *value*.
+
+  For instance, the top-level `default.nix` in Nixpkgs is actually a function:
+
+  ```nix
+  { # The system (e.g., `i686-linux') for which to build the packages.
+    system ? builtins.currentSystem
+    ...
+  }: ...
+  ```
+
+  So if you call this Nix expression (e.g., when you do `nix-env --install --attr pkgname`), the function will be called automatically using the value [`builtins.currentSystem`](@docroot@/language/builtins.md) for the `system` argument.
+  You can override this using `--arg`, e.g., `nix-env --install --attr pkgname --arg system \"i686-freebsd\"`.
+  (Note that since the argument is a Nix string literal, you have to escape the quotes.)
+
+- <span id="opt-argstr">[`--argstr`](#opt-argstr)</span> *name* *value*
+
+  This option is like `--arg`, only the value is not a Nix expression but a string.
+  So instead of `--arg system \"i686-linux\"` (the outer quotes are to keep the shell happy) you can say `--argstr system i686-linux`.
+
+- <span id="opt-attr">[`--attr`](#opt-attr)</span> / `-A` *attrPath*
+
+  Select an attribute from the top-level Nix expression being evaluated.
+  (`nix-env`, `nix-instantiate`, `nix-build` and `nix-shell` only.)
+  The *attribute path* *attrPath* is a sequence of attribute names separated by dots.
+  For instance, given a top-level Nix expression *e*, the attribute path `xorg.xorgserver` would cause the expression `e.xorg.xorgserver` to be used.
+  See [`nix-env --install`](@docroot@/command-ref/nix-env/install.md) for some concrete examples.
+
+  In addition to attribute names, you can also specify array indices.
+  For instance, the attribute path `foo.3.bar` selects the `bar`
+  attribute of the fourth element of the array in the `foo` attribute
+  of the top-level expression.
+
+- <span id="opt-expr">[`--expr`](#opt-expr)</span> / `-E`
+
+  Interpret the command line arguments as a list of Nix expressions to be parsed and evaluated, rather than as a list of file names of Nix expressions.
+  (`nix-instantiate`, `nix-build` and `nix-shell` only.)
+
+  For `nix-shell`, this option is commonly used to give you a shell in which you can build the packages returned by the expression.
+  If you want to get a shell which contain the *built* packages ready for use, give your expression to the `nix-shell --packages ` convenience flag instead.
+
+- <span id="opt-I">[`-I`](#opt-I)</span> *path*
+
+  Add an entry to the [Nix expression search path](@docroot@/command-ref/conf-file.md#conf-nix-path).
+  This option may be given multiple times.
+  Paths added through `-I` take precedence over [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH).
+
+- <span id="opt-option">[`--option`](#opt-option)</span> *name* *value*
+
+  Set the Nix configuration option *name* to *value*.
+  This overrides settings in the Nix configuration file (see nix.conf5).
+
+- <span id="opt-repair">[`--repair`](#opt-repair)</span>
+
+  Fix corrupted or missing store paths by redownloading or rebuilding them.
+  Note that this is slow because it requires computing a cryptographic hash of the contents of every path in the closure of the build.
+  Also note the warning under `nix-store --repair-path`.
+
+> **Note**
+>
+> See [`man nix.conf`](@docroot@/command-ref/conf-file.md#command-line-flags) for overriding configuration settings with command line flags.

doc/manual/src/command-ref/opt-inst-syn.md

@@ -1,15 +0,0 @@
-\--prebuilt-only
-
-\-b
-
-\--attr
-
-\-A
-
-\--from-expression
-
-\-E
-
-\--from-profile
-
-path

doc/manual/src/command-ref/status-build-failure.md

@@ -0,0 +1,34 @@
+# Special exit codes for build failure
+
+1xx status codes are used when requested builds failed.
+The following codes are in use:
+
+- `100` Generic build failure
+
+  The builder process returned with a non-zero exit code.
+
+- `101` Build timeout
+
+  The build was aborted because it did not complete within the specified `timeout`.
+
+- `102` Hash mismatch
+
+  The build output was rejected because it does not match the
+  [`outputHash` attribute of the derivation](@docroot@/language/advanced-attributes.md).
+
+- `104` Not deterministic
+
+  The build succeeded in check mode but the resulting output is not binary reproducible.
+
+With the `--keep-going` flag it's possible for multiple failures to occur.
+In this case the 1xx status codes are or combined using
+[bitwise OR](https://en.wikipedia.org/wiki/Bitwise_operation#OR).
+
+```
+0b1100100
+     ^^^^
+     |||`- timeout
+     ||`-- output hash mismatch
+     |`--- build failure
+     `---- not deterministic
+```

doc/manual/src/contributing/cli-guideline.md

@@ -87,7 +87,7 @@ impacted the most by bad user experience.
       and [aligning of text](#text-alignment).
     - [Autocomplete](#shell-completion) of options.
 
-  Examples of such commands: `nix doctor`, `nix edit`, `nix eval`, ...
+  Examples of such commands: `nix edit`, `nix eval`, ...
 
 - **Utility and scripting commands**
 
@@ -426,7 +426,7 @@ This leads to the following guidelines:
 ### Examples
 
 
-This is bad, because all keys must be assumed to be store implementations:
+This is bad, because all keys must be assumed to be store types:
 
 ```json
 {

doc/manual/src/contributing/contributing.md

@@ -1 +0,0 @@
-# Contributing

doc/manual/src/contributing/cxx.md

@@ -0,0 +1,28 @@
+# C++ style guide
+
+Some miscellaneous notes on how we write C++.
+Formatting we hope to eventually normalize automatically, so this section is free to just discuss higher-level concerns.
+
+## The `*-impl.hh` pattern
+
+Let's start with some background info first.
+Headers, are supposed to contain declarations, not definitions.
+This allows us to change a definition without changing the declaration, and have a very small rebuild during development.
+Templates, however, need to be specialized to use-sites.
+Absent fancier techniques, templates require that the definition, not just mere declaration, must be available at use-sites in order to make that specialization on the fly as part of compiling those use-sites.
+Making definitions available like that means putting them in headers, but that is unfortunately means we get all the extra rebuilds we want to avoid by just putting declarations there as described above.
+
+The `*-impl.hh` pattern is a ham-fisted partial solution to this problem.
+It constitutes:
+
+- Declaring items only in the main `foo.hh`, including templates.
+
+- Putting template definitions in a companion `foo-impl.hh` header.
+
+Most C++ developers would accompany this by having `foo.hh` include `foo-impl.hh`, to ensure any file getting the template declarations also got the template definitions.
+But we've found not doing this has some benefits and fewer than imagined downsides.
+The fact remains that headers are rarely as minimal as they could be;
+there is often code that needs declarations from the headers but not the templates within them.
+With our pattern where `foo.hh` doesn't include `foo-impl.hh`, that means they can just include `foo.hh`
+Code that needs both just includes `foo.hh` and `foo-impl.hh`.
+This does make linking error possible where something forgets to include `foo-impl.hh` that needs it, but those are build-time only as easy to fix.

doc/manual/src/contributing/documentation.md

@@ -0,0 +1,210 @@
+# Contributing documentation
+
+Improvements to documentation are very much appreciated, and a good way to start out with contributing to Nix.
+
+This is how you can help:
+- Address [open issues with documentation](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+label%3Adocumentation)
+- Review [pull requests concerning documentation](https://github.com/NixOS/nix/pulls?q=is%3Apr+is%3Aopen+label%3Adocumentation)
+
+Incremental refactorings of the documentation build setup to make it faster or easier to understand and maintain are also welcome.
+
+## Building the manual
+
+Build the manual from scratch:
+
+```console
+nix-build $(nix-instantiate)'!doc'
+```
+
+or
+
+```console
+nix build .#^doc
+```
+
+and open `./result-doc/share/doc/nix/manual/index.html`.
+
+To build the manual incrementally, [enter the development shell](./hacking.md) and run:
+
+```console
+make manual-html -j $NIX_BUILD_CORES
+```
+
+and open `./outputs/out/share/doc/nix/manual/language/index.html`.
+
+In order to reflect changes to the [Makefile for the manual], clear all generated files before re-building:
+
+[Makefile for the manual]: https://github.com/NixOS/nix/blob/master/doc/manual/local.mk
+
+```console
+rm $(git ls-files doc/manual/ -o | grep -F '.md') && rmdir doc/manual/src/command-ref/new-cli && make manual-html -j $NIX_BUILD_CORES
+```
+
+## Style guide
+
+The goal of this style guide is to make it such that
+- The manual is easy to search and skim for relevant information
+- Documentation sources are easy to edit
+- Changes to documentation are easy to review
+
+You will notice that this is not implemented consistently yet.
+Please follow the guide when making additions or changes to existing documentation.
+Do not make sweeping changes, unless they are programmatic and can be validated easily.
+
+### Language
+
+This manual is [reference documentation](https://diataxis.fr/reference/).
+The typical usage pattern is to look up isolated pieces of information.
+It should therefore aim to be correct, consistent, complete, and easy to navigate at a glance.
+
+- Aim for clarity and brevity.
+
+  Please take the time to read the [plain language guidelines](https://www.plainlanguage.gov/guidelines/) for details.
+
+- Describe the subject factually.
+
+  In particular, do not make value judgements or recommendations.
+  Check the code or add tests if in doubt.
+
+- Provide complete, minimal examples, and explain them.
+
+  Readers should be able to try examples verbatim and get the same results as shown in the manual.
+  Always describe in words what a given example does.
+
+  Non-trivial examples may need additional explanation, especially if they use concepts from outside the given context.
+
+- Always explain code examples in the text.
+
+  Use comments in code samples very sparingly, for instance to highlight a particular aspect.
+  Readers tend to glance over large amounts of code when scanning for information.
+
+  Especially beginners will likely find reading more complex-looking code strenuous and may therefore avoid it altogether.
+
+  If a code sample appears to require a lot of inline explanation, consider replacing it with a simpler one.
+  If that's not possible, break the example down into multiple parts, explain them separately, and then show the combined result at the end.
+  This should be a last resort, as that would amount to writing a [tutorial](https://diataxis.fr/tutorials/) on the given subject.
+
+- Use British English.
+
+  This is a somewhat arbitrary choice to force consistency, and accounts for the fact that a majority of Nix users and developers are from Europe.
+
+### Links and anchors
+
+Reference documentation must be readable in arbitrary order.
+Readers cannot be expected to have any particular prerequisite knowledge about Nix.
+While the table of contents can provide guidance and full-text search can help, they are most likely to find what they need by following sensible cross-references.
+
+- Link to technical terms
+
+  When mentioning Nix-specific concepts, commands, options, settings, etc., link to appropriate documentation.
+  Also link to external tools or concepts, especially if their meaning may be ambiguous.
+  You may also want to link to definitions of less common technical terms.
+
+  Then readers won't have to actively search for definitions and are more likely to discover relevant information on their own.
+
+  > **Note**
+  >
+  > `man` and `--help` pages don't display links.
+  > Use appropriate link texts such that readers of terminal output can infer search terms.
+
+- Do not break existing URLs between releases.
+
+  There are countless links in the wild pointing to old versions of the manual.
+  We want people to find up-to-date documentation when following popular advice.
+
+  - When moving files, update [redirects on nixos.org](https://github.com/NixOS/nixos-homepage/blob/master/netlify.toml).
+
+    This is especially important when moving information out of the Nix manual to other resources.
+
+  - When changing anchors, update [client-side redirects](https://github.com/NixOS/nix/blob/master/doc/manual/redirects.js)
+
+  The current setup is cumbersome, and help making better automation is appreciated.
+
+The build checks for broken internal links with.
+This happens late in the process, so [building the whole manual](#building-the-manual) is not suitable for iterating quickly.
+[`mdbook-linkcheck`] does not implement checking [URI fragments] yet.
+
+[`mdbook-linkcheck`]: https://github.com/Michael-F-Bryan/mdbook-linkcheck
+[URI fragments]: https://en.wikipedia.org/wiki/URI_fragment
+
+### Markdown conventions
+
+The manual is written in markdown, and rendered with [mdBook](https://github.com/rust-lang/mdBook) for the web and with [lowdown](https://github.com/kristapsdz/lowdown) for `man` pages and `--help` output.
+
+For supported markdown features, refer to:
+- [mdBook documentation](https://rust-lang.github.io/mdBook/format/markdown.html)
+- [lowdown documentation](https://kristaps.bsd.lv/lowdown/)
+
+Please observe these guidelines to ease reviews:
+
+- Write one sentence per line.
+
+  This makes long sentences immediately visible, and makes it easier to review changes and make direct suggestions.
+
+- Use reference links – sparingly – to ease source readability.
+  Put definitions close to their first use.
+
+  Example:
+
+  ```
+  A [store object] contains a [file system object] and [references] to other store objects.
+
+  [store object]: @docroot@/glossary.md#gloss-store-object
+  [file system object]: @docroot@/architecture/file-system-object.md
+  [references]: @docroot@/glossary.md#gloss-reference
+  ```
+
+- Use admonitions of the following form:
+
+  ```
+  > **Note**
+  >
+  > This is a note.
+  ```
+
+  Highlight examples as such:
+
+  ````
+  > **Example**
+  >
+  > ```console
+  > $ nix --version
+  > ```
+  ````
+
+  Highlight syntax definiions as such, using [EBNF](https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form) notation:
+
+  ````
+  > **Syntax**
+  >
+  > *attribute-set* = `{` [ *attribute-name* `=` *expression* `;` ... ] `}`
+  ````
+
+### The `@docroot@` variable
+
+`@docroot@` provides a base path for links that occur in reusable snippets or other documentation that doesn't have a base path of its own.
+
+If a broken link occurs in a snippet that was inserted into multiple generated files in different directories, use `@docroot@` to reference the `doc/manual/src` directory.
+
+If the `@docroot@` literal appears in an error message from the [`mdbook-linkcheck`] tool, the `@docroot@` replacement needs to be applied to the generated source file that mentions it.
+See existing `@docroot@` logic in the [Makefile for the manual].
+Regular markdown files used for the manual have a base path of their own and they can use relative paths instead of `@docroot@`.
+
+## API documentation
+
+[Doxygen API documentation] is available online.
+You can also build and view it yourself:
+
+[Doxygen API documentation]: https://hydra.nixos.org/job/nix/master/internal-api-docs/latest/download-by-type/doc/internal-api-docs
+
+```console
+# nix build .#hydraJobs.internal-api-docs
+# xdg-open ./result/share/doc/nix/internal-api/html/index.html
+```
+
+or inside `nix-shell` or `nix develop`:
+
+```
+# make internal-api-html
+# xdg-open ./outputs/doc/share/doc/nix/internal-api/html/index.html
+```

doc/manual/src/contributing/hacking.md

@@ -10,16 +10,17 @@ $ cd nix
 
 The following instructions assume you already have some version of Nix installed locally, so that you can use it to set up the development environment. If you don't have it installed, follow the [installation instructions].
 
-[installation instructions]: ../installation/installation.md
+[installation instructions]: ../installation/index.md
 
-## Nix with flakes
+## Building Nix with flakes
 
-This section assumes you are using Nix with [flakes] enabled. See the [next section](#classic-nix) for equivalent instructions which don't require flakes.
+This section assumes you are using Nix with the [`flakes`] and [`nix-command`] experimental features enabled.
+See the [Building Nix](#building-nix) section for equivalent instructions using stable Nix interfaces.
 
-[flakes]: ../command-ref/new-cli/nix3-flake.md#description
+[`flakes`]: @docroot@/contributing/experimental-features.md#xp-feature-flakes
+[`nix-command`]: @docroot@/contributing/experimental-features.md#xp-nix-command
 
-To build all dependencies and start a shell in which all environment
+To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:
-variables are set up so that those dependencies can be found:
 
 ```console
 $ nix develop
@@ -30,7 +31,7 @@ This shell also adds `./outputs/bin/nix` to your `$PATH` so you can run `nix` im
 To get a shell with one of the other [supported compilation environments](#compilation-environments):
 
 ```console
-$ nix develop .#native-clang11StdenvPackages
+$ nix develop .#native-clangStdenvPackages
 ```
 
 > **Note**
@@ -41,8 +42,8 @@ $ nix develop .#native-clang11StdenvPackages
 To build Nix itself in this shell:
 
 ```console
-[nix-shell]$ ./bootstrap.sh
+[nix-shell]$ autoreconfPhase
-[nix-shell]$ ./configure $configureFlags --prefix=$(pwd)/outputs/out
+[nix-shell]$ configurePhase
 [nix-shell]$ make -j $NIX_BUILD_CORES
 ```
 
@@ -55,20 +56,38 @@ To install it in `$(pwd)/outputs` and test it:
 nix (Nix) 2.12
 ```
 
-To build a release version of Nix:
+To build a release version of Nix for the current operating system and CPU architecture:
 
 ```console
 $ nix build
 ```
 
-You can also build Nix for one of the [supported target platforms](#target-platforms).
+You can also build Nix for one of the [supported platforms](#platforms).
 
-## Classic Nix
+## Makefile variables
 
-This section is for Nix without [flakes].
+You may need `profiledir=$out/etc/profile.d` and `sysconfdir=$out/etc` to run
+`make install`.
 
-To build all dependencies and start a shell in which all environment
+You may want to set `MAKEFLAGS="-e -j $NIX_BUILD_CORES"` to allow environment
-variables are set up so that those dependencies can be found:
+variables to override `Makefile` variables.
+
+- `ENABLE_BUILD=yes` to enable building the C++ code.
+- `ENABLE_DOC_GEN=yes` to enable building the documentation (manual, man pages, etc.).
+
+  The docs can take a while to build, so you may want to disable this for local development.
+- `ENABLE_FUNCTIONAL_TESTS=yes` to enable building the functional tests.
+- `ENABLE_UNIT_TESTS=yes` to enable building the unit tests.
+- `OPTIMIZE=1` to enable optimizations.
+- `libraries=libutil programs=` to only build a specific library (this will
+  fail in the linking phase if you don't have the other libraries built, but is
+  useful for checking types).
+- `libraries= programs=nix` to only build a specific program (this will not, in
+  general, work, because the programs need the libraries).
+
+## Building Nix
+
+To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:
 
 ```console
 $ nix-shell
@@ -77,7 +96,7 @@ $ nix-shell
 To get a shell with one of the other [supported compilation environments](#compilation-environments):
 
 ```console
-$ nix-shell --attr devShells.x86_64-linux.native-clang11StdenvPackages
+$ nix-shell --attr devShells.x86_64-linux.native-clangStdenvPackages
 ```
 
 > **Note**
@@ -88,7 +107,7 @@ $ nix-shell --attr devShells.x86_64-linux.native-clang11StdenvPackages
 To build Nix itself in this shell:
 
 ```console
-[nix-shell]$ ./bootstrap.sh
+[nix-shell]$ autoreconfPhase
 [nix-shell]$ ./configure $configureFlags --prefix=$(pwd)/outputs/out
 [nix-shell]$ make -j $NIX_BUILD_CORES
 ```
@@ -102,51 +121,107 @@ To install it in `$(pwd)/outputs` and test it:
 nix (Nix) 2.12
 ```
 
-To build Nix for the current operating system and CPU architecture use
+To build a release version of Nix for the current operating system and CPU architecture:
 
 ```console
 $ nix-build
 ```
 
-You can also build Nix for one of the [supported target platforms](#target-platforms).
+You can also build Nix for one of the [supported platforms](#platforms).
 
 ## Platforms
 
-As specified in [`flake.nix`], Nix can be built for various platforms:
+Nix can be built for various platforms, as specified in [`flake.nix`]:
-
-- `aarch64-linux`
-- `i686-linux`
-- `x86_64-darwin`
-- `x86_64-linux`
 
 [`flake.nix`]: https://github.com/nixos/nix/blob/master/flake.nix
 
+- `x86_64-linux`
+- `x86_64-darwin`
+- `i686-linux`
+- `aarch64-linux`
+- `aarch64-darwin`
+- `armv6l-linux`
+- `armv7l-linux`
+
 In order to build Nix for a different platform than the one you're currently
-on, you need to have some way for your system Nix to build code for that
+on, you need a way for your current Nix installation to build code for that
-platform. Common solutions include [remote builders] and [binfmt emulation]
+platform. Common solutions include [remote builders] and [binary format emulation]
 (only supported on NixOS).
 
 [remote builders]: ../advanced-topics/distributed-builds.md
-[binfmt emulation]: https://nixos.org/manual/nixos/stable/options.html#opt-boot.binfmt.emulatedSystems
+[binary format emulation]: https://nixos.org/manual/nixos/stable/options.html#opt-boot.binfmt.emulatedSystems
 
-These solutions let Nix perform builds as if you're on the native platform, so
+Given such a setup, executing the build only requires selecting the respective attribute.
-executing the build is as simple as
+For example, to compile for `aarch64-linux`:
-
-```console
-$ nix build .#packages.aarch64-linux.default
-```
-
-for flake-enabled Nix, or
 
 ```console
 $ nix-build --attr packages.aarch64-linux.default
 ```
 
-for classic Nix.
+or for Nix with the [`flakes`] and [`nix-command`] experimental features enabled:
 
-You can use any of the other supported platforms in place of `aarch64-linux`.
+```console
+$ nix build .#packages.aarch64-linux.default
+```
 
-Cross-compiled builds are available for ARMv6 and ARMv7, and Nix on unsupported platforms can be bootstrapped by adding more `crossSystems` in `flake.nix`.
+Cross-compiled builds are available for ARMv6 (`armv6l-linux`) and ARMv7 (`armv7l-linux`).
+Add more [system types](#system-type) to `crossSystems` in `flake.nix` to bootstrap Nix on unsupported platforms.
+
+### Building for multiple platforms at once
+
+It is useful to perform multiple cross and native builds on the same source tree,
+for example to ensure that better support for one platform doesn't break the build for another.
+In order to facilitate this, Nix has some support for being built out of tree – that is, placing build artefacts in a different directory than the source code:
+
+1. Create a directory for the build, e.g.
+
+   ```bash
+   mkdir build
+   ```
+
+2. Run the configure script from that directory, e.g.
+
+   ```bash
+   cd build
+   ../configure <configure flags>
+   ```
+
+3. Run make from the source directory, but with the build directory specified, e.g.
+
+   ```bash
+   make builddir=build <make flags>
+   ```
+
+## System type
+
+Nix uses a string with he following format to identify the *system type* or *platform* it runs on:
+
+```
+<cpu>-<os>[-<abi>]
+```
+
+It is set when Nix is compiled for the given system, and based on the output of [`config.guess`](https://github.com/nixos/nix/blob/master/config/config.guess) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.guess)):
+
+```
+<cpu>-<vendor>-<os>[<version>][-<abi>]
+```
+
+When Nix is built such that `./configure` is passed any of the `--host`, `--build`, `--target` options, the value is based on the output of [`config.sub`](https://github.com/nixos/nix/blob/master/config/config.sub) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.sub)):
+
+```
+<cpu>-<vendor>[-<kernel>]-<os>
+```
+
+For historic reasons and backward-compatibility, some CPU and OS identifiers are translated from the GNU Autotools naming convention in [`configure.ac`](https://github.com/nixos/nix/blob/master/configure.ac) as follows:
+
+| `config.guess`             | Nix                 |
+|----------------------------|---------------------|
+| `amd64`                    | `x86_64`            |
+| `i*86`                     | `i686`              |
+| `arm6`                     | `arm6l`             |
+| `arm7`                     | `arm7l`             |
+| `linux-gnu*`               | `linux`             |
+| `linux-musl*`              | `linux`             |
 
 ## Compilation environments
 
@@ -181,7 +256,7 @@ See [supported compilation environments](#compilation-environments) and instruct
 To use the LSP with your editor, you first need to [set up `clangd`](https://clangd.llvm.org/installation#project-setup) by running:
 
 ```console
-make clean && bear -- make -j$NIX_BUILD_CORES install
+make clean && bear -- make -j$NIX_BUILD_CORES default check install
 ```
 
 Configure your editor to use the `clangd` from the shell, either by running it inside the development shell, or by using [nix-direnv](https://github.com/nix-community/nix-direnv) and [the appropriate editor plugin](https://github.com/direnv/direnv/wiki#editor-integration).
@@ -192,232 +267,81 @@ Configure your editor to use the `clangd` from the shell, either by running it i
 > Some other editors (e.g. Emacs, Vim) need a plugin to support LSP servers in general (e.g. [lsp-mode](https://github.com/emacs-lsp/lsp-mode) for Emacs and [vim-lsp](https://github.com/prabirshrestha/vim-lsp) for vim).
 > Editor-specific setup is typically opinionated, so we will not cover it here in more detail.
 
-## Running tests
+## Add a release note
 
-### Unit-tests
+`doc/manual/rl-next` contains release notes entries for all unreleased changes.
 
-The unit-tests for each Nix library (`libexpr`, `libstore`, etc..) are defined
+User-visible changes should come with a release note.
-under `src/{library_name}/tests` using the
-[googletest](https://google.github.io/googletest/) and
-[rapidcheck](https://github.com/emil-e/rapidcheck) frameworks.
 
-You can run the whole testsuite with `make check`, or the tests for a specific component with `make libfoo-tests_RUN`. Finer-grained filtering is also possible using the [--gtest_filter](https://google.github.io/googletest/advanced.html#running-a-subset-of-the-tests) command-line option.
+### Add an entry
 
-### Functional tests
+Here's what a complete entry looks like. The file name is not incorporated in the document.
-
-The functional tests reside under the `tests` directory and are listed in `tests/local.mk`.
-Each test is a bash script.
-
-The whole test suite can be run with:
-
-```shell-session
-$ make install && make installcheck
-ran test tests/foo.sh... [PASS]
-ran test tests/bar.sh... [PASS]
-...
-```
-
-Individual tests can be run with `make`:
-
-```shell-session
-$ make tests/${testName}.sh.test
-ran test tests/${testName}.sh... [PASS]
-```
-
-or without `make`:
-
-```shell-session
-$ ./mk/run-test.sh tests/${testName}.sh
-ran test tests/${testName}.sh... [PASS]
-```
-
-To see the complete output, one can also run:
-
-```shell-session
-$ ./mk/debug-test.sh tests/${testName}.sh
-+ foo
-output from foo
-+ bar
-output from bar
-...
-```
-
-The test script will then be traced with `set -x` and the output displayed as it happens, regardless of whether the test succeeds or fails.
-
-#### Debugging failing functional tests
-
-When a functional test fails, it usually does so somewhere in the middle of the script.
-
-To figure out what's wrong, it is convenient to run the test regularly up to the failing `nix` command, and then run that command with a debugger like GDB.
-
-For example, if the script looks like:
-
-```bash
-foo
-nix blah blub
-bar
-```
-edit it like so:
-
-```diff
- foo
--nix blah blub
-+gdb --args nix blah blub
- bar
-```
-
-Then, running the test with `./mk/debug-test.sh` will drop you into GDB once the script reaches that point:
-
-```shell-session
-$ ./mk/debug-test.sh tests/${testName}.sh
-...
-+ gdb blash blub
-GNU gdb (GDB) 12.1
-...
-(gdb)
-```
-
-One can debug the Nix invocation in all the usual ways.
-For example, enter `run` to start the Nix invocation.
-
-### Integration tests
-
-The integration tests are defined in the Nix flake under the `hydraJobs.tests` attribute.
-These tests include everything that needs to interact with external services or run Nix in a non-trivial distributed setup.
-Because these tests are expensive and require more than what the standard github-actions setup provides, they only run on the master branch (on <https://hydra.nixos.org/jobset/nix/master>).
-
-You can run them manually with `nix build .#hydraJobs.tests.{testName}` or `nix-build -A hydraJobs.tests.{testName}`
-
-### Installer tests
-
-After a one-time setup, the Nix repository's GitHub Actions continuous integration (CI) workflow can test the installer each time you push to a branch.
-
-Creating a Cachix cache for your installer tests and adding its authorization token to GitHub enables [two installer-specific jobs in the CI workflow](https://github.com/NixOS/nix/blob/88a45d6149c0e304f6eb2efcc2d7a4d0d569f8af/.github/workflows/ci.yml#L50-L91):
-
-- The `installer` job generates installers for the platforms below and uploads them to your Cachix cache:
-  - `x86_64-linux`
-  - `armv6l-linux`
-  - `armv7l-linux`
-  - `x86_64-darwin`
-
-- The `installer_test` job (which runs on `ubuntu-latest` and `macos-latest`) will try to install Nix with the cached installer and run a trivial Nix command.
-
-#### One-time setup
-
-1. Have a GitHub account with a fork of the [Nix repository](https://github.com/NixOS/nix).
-2. At cachix.org:
-    - Create or log in to an account.
-    - Create a Cachix cache using the format `<github-username>-nix-install-tests`.
-    - Navigate to the new cache > Settings > Auth Tokens.
-    - Generate a new Cachix auth token and copy the generated value.
-3. At github.com:
-    - Navigate to your Nix fork > Settings > Secrets > Actions > New repository secret.
-    - Name the secret `CACHIX_AUTH_TOKEN`.
-    - Paste the copied value of the Cachix cache auth token.
-
-#### Using the CI-generated installer for manual testing
-
-After the CI run completes, you can check the output to extract the installer URL:
-1. Click into the detailed view of the CI run.
-2. Click into any `installer_test` run (the URL you're here to extract will be the same in all of them).
-3. Click into the `Run cachix/install-nix-action@v...` step and click the detail triangle next to the first log line (it will also be `Run cachix/install-nix-action@v...`)
-4. Copy the value of `install_url`
-5. To generate an install command, plug this `install_url` and your GitHub username into this template:
-
-    ```console
-    curl -L <install_url> | sh -s -- --tarball-url-prefix https://<github-username>-nix-install-tests.cachix.org/serve
-    ```
-
-<!-- #### Manually generating test installers
-
-There's obviously a manual way to do this, and it's still the only way for
-platforms that lack GA runners.
-
-I did do this back in Fall 2020 (before the GA approach encouraged here). I'll
-sketch what I recall in case it encourages someone to fill in detail, but: I
-didn't know what I was doing at the time and had to fumble/ask around a lot--
-so I don't want to uphold any of it as "right". It may have been dumb or
-the _hard_ way from the getgo. Fundamentals may have changed since.
-
-Here's the build command I used to do this on and for x86_64-darwin:
-nix build --out-link /tmp/foo ".#checks.x86_64-darwin.binaryTarball"
-
-I used the stable out-link to make it easier to script the next steps:
-link=$(readlink /tmp/foo)
-cp $link/*-darwin.tar.xz ~/somewheres
-
-I've lost the last steps and am just going from memory:
-
-From here, I think I had to extract and modify the `install` script to point
-it at this tarball (which I scped to my own site, but it might make more sense
-to just share them locally). I extracted this script once and then just
-search/replaced in it for each new build.
-
-The installer now supports a `--tarball-url-prefix` flag which _may_ have
-solved this need?
--->
-
-### Checking links in the manual
-
-The build checks for broken internal links.
-This happens late in the process, so `nix build` is not suitable for iterating.
-To build the manual incrementally, run:
-
-```console
-make html -j $NIX_BUILD_CORES
-```
-
-In order to reflect changes to the [Makefile], clear all generated files before re-building:
-
-[Makefile]: https://github.com/NixOS/nix/blob/master/doc/manual/local.mk
-
-```console
-rm $(git ls-files doc/manual/ -o | grep -F '.md') && rmdir doc/manual/src/command-ref/new-cli && make html -j $NIX_BUILD_CORES
-```
-
-[`mdbook-linkcheck`] does not implement checking [URI fragments] yet.
-
-[`mdbook-linkcheck`]: https://github.com/Michael-F-Bryan/mdbook-linkcheck
-[URI fragments]: https://en.wikipedia.org/wiki/URI_fragment
-
-#### `@docroot@` variable
-
-`@docroot@` provides a base path for links that occur in reusable snippets or other documentation that doesn't have a base path of its own.
-
-If a broken link occurs in a snippet that was inserted into multiple generated files in different directories, use `@docroot@` to reference the `doc/manual/src` directory.
-
-If the `@docroot@` literal appears in an error message from the `mdbook-linkcheck` tool, the `@docroot@` replacement needs to be applied to the generated source file that mentions it.
-See existing `@docroot@` logic in the [Makefile].
-Regular markdown files used for the manual have a base path of their own and they can use relative paths instead of `@docroot@`.
-
-## API documentation
-
-Doxygen API documentation is [available
-online](https://hydra.nixos.org/job/nix/master/internal-api-docs/latest/download-by-type/doc/internal-api-docs). You
-can also build and view it yourself:
-
-```console
-# nix build .#hydraJobs.internal-api-docs
-# xdg-open ./result/share/doc/nix/internal-api/html/index.html
-```
-
-or inside a `nix develop` shell by running:
 
 ```
-# make internal-api-html
+---
-# xdg-open ./outputs/doc/share/doc/nix/internal-api/html/index.html
+synopsis: Basically a title
+issues: 1234
+prs: 1238
+---
+
+Here's one or more paragraphs that describe the change.
+
+- It's markdown
+- Add references to the manual using @docroot@
 ```
 
-## Coverage analysis
+Significant changes should add the following header, which moves them to the top.
-
-A coverage analysis report is [available
-online](https://hydra.nixos.org/job/nix/master/coverage/latest/download-by-type/report/coverage). You
-can build it yourself:
 
 ```
-# nix build .#hydraJobs.coverage
+significance: significant
-# xdg-open ./result/coverage/index.html
 ```
 
-Metrics about the change in line/function coverage over time are also
+<!-- Keep an eye on https://codeberg.org/fgaz/changelog-d/issues/1 -->
-[available](https://hydra.nixos.org/job/nix/master/coverage#tabs-charts).
+See also the [format documentation](https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md#changelog).
+
+### Build process
+
+Releases have a precomputed `rl-MAJOR.MINOR.md`, and no `rl-next.md`.
+Set `buildUnreleasedNotes = true;` in `flake.nix` to build the release notes on the fly.
+
+## Branches
+
+- [`master`](https://github.com/NixOS/nix/commits/master)
+
+  The main development branch. All changes are approved and merged here.
+  When developing a change, create a branch based on the latest `master`.
+
+  Maintainers try to [keep it in a release-worthy state](#reverting).
+
+- [`maintenance-*.*`](https://github.com/NixOS/nix/branches/all?query=maintenance)
+
+  These branches are the subject of backports only, and are
+  also [kept](#reverting) in a release-worthy state.
+
+  See [`maintainers/backporting.md`](https://github.com/NixOS/nix/blob/master/maintainers/backporting.md)
+
+- [`latest-release`](https://github.com/NixOS/nix/tree/latest-release)
+
+  The latest patch release of the latest minor version.
+
+  See [`maintainers/release-process.md`](https://github.com/NixOS/nix/blob/master/maintainers/release-process.md)
+
+- [`backport-*-to-*`](https://github.com/NixOS/nix/branches/all?query=backport)
+
+  Generally branches created by the backport action.
+
+  See [`maintainers/backporting.md`](https://github.com/NixOS/nix/blob/master/maintainers/backporting.md)
+
+- [_other_](https://github.com/NixOS/nix/branches/all)
+
+  Branches that do not conform to the above patterns should be feature branches.
+
+## Reverting
+
+If a change turns out to be merged by mistake, or contain a regression, it may be reverted.
+A revert is not a rejection of the contribution, but merely part of an effective development process.
+It makes sure that development keeps running smoothly, with minimal uncertainty, and less overhead.
+If maintainers have to worry too much about avoiding reverts, they would not be able to merge as much.
+By embracing reverts as a good part of the development process, everyone wins.
+
+However, taking a step back may be frustrating, so maintainers will be extra supportive on the next try.

doc/manual/src/contributing/index.md

@@ -0,0 +1,8 @@
+# Development
+
+Nix is developed on GitHub.
+Check the [contributing guide](https://github.com/NixOS/nix/blob/master/CONTRIBUTING.md) if you want to get involved.
+
+This chapter is a collection of guides for making changes to the code and documentation.
+
+If you're not sure where to start, try to [compile Nix from source](./hacking.md) and consider [making improvements to documentation](./documentation.md).

doc/manual/src/contributing/testing.md

@@ -0,0 +1,333 @@
+# Running tests
+
+## Coverage analysis
+
+A [coverage analysis report] is available online
+You can build it yourself:
+
+[coverage analysis report]: https://hydra.nixos.org/job/nix/master/coverage/latest/download-by-type/report/coverage
+
+```
+# nix build .#hydraJobs.coverage
+# xdg-open ./result/coverage/index.html
+```
+
+[Extensive records of build metrics](https://hydra.nixos.org/job/nix/master/coverage#tabs-charts), such as test coverage over time, are also available online.
+
+## Unit-tests
+
+The unit tests are defined using the [googletest] and [rapidcheck] frameworks.
+
+[googletest]: https://google.github.io/googletest/
+[rapidcheck]: https://github.com/emil-e/rapidcheck
+[property testing]: https://en.wikipedia.org/wiki/Property_testing
+
+### Source and header layout
+
+> An example of some files, demonstrating much of what is described below
+>
+> ```
+> src
+> ├── libexpr
+> │   ├── local.mk
+> │   ├── value/context.hh
+> │   ├── value/context.cc
+> │   …
+> │
+> ├── tests
+> │   │
+> │   …
+> │   └── unit
+> │       ├── libutil
+> │       │   ├── local.mk
+> │       │   …
+> │       │   └── data
+> │       │       ├── git/tree.txt
+> │       │       …
+> │       │
+> │       ├── libexpr-support
+> │       │   ├── local.mk
+> │       │   └── tests
+> │       │       ├── value/context.hh
+> │       │       ├── value/context.cc
+> │       │       …
+> │       │
+> │       ├── libexpr
+> │       …   ├── local.mk
+> │           ├── value/context.cc
+> │           …
+> …
+> ```
+
+The tests for each Nix library (`libnixexpr`, `libnixstore`, etc..) live inside a directory `tests/unit/${library_name_without-nix}`.
+Given a interface (header) and implementation pair in the original library, say, `src/libexpr/value/context.{hh,cc}`, we write tests for it in `tests/unit/libexpr/tests/value/context.cc`, and (possibly) declare/define additional interfaces for testing purposes in `tests/unit/libexpr-support/tests/value/context.{hh,cc}`.
+
+Data for unit tests is stored in a `data` subdir of the directory for each unit test executable.
+For example, `libnixstore` code is in `src/libstore`, and its test data is in `tests/unit/libstore/data`.
+The path to the `tests/unit/data` directory is passed to the unit test executable with the environment variable `_NIX_TEST_UNIT_DATA`.
+Note that each executable only gets the data for its tests.
+
+The unit test libraries are in `tests/unit/${library_name_without-nix}-lib`.
+All headers are in a `tests` subdirectory so they are included with `#include "tests/"`.
+
+The use of all these separate directories for the unit tests might seem inconvenient, as for example the tests are not "right next to" the part of the code they are testing.
+But organizing the tests this way has one big benefit:
+there is no risk of any build-system wildcards for the library accidentally picking up test code that should not built and installed as part of the library.
+
+### Running tests
+
+You can run the whole testsuite with `make check`, or the tests for a specific component with `make libfoo-tests_RUN`.
+Finer-grained filtering is also possible using the [--gtest_filter](https://google.github.io/googletest/advanced.html#running-a-subset-of-the-tests) command-line option, or the `GTEST_FILTER` environment variable.
+
+### Characterisation testing { #characaterisation-testing-unit }
+
+See [functional characterisation testing](#characterisation-testing-functional) for a broader discussion of characterisation testing.
+
+Like with the functional characterisation, `_NIX_TEST_ACCEPT=1` is also used.
+For example:
+```shell-session
+$ _NIX_TEST_ACCEPT=1 make libstore-tests_RUN
+...
+[  SKIPPED ] WorkerProtoTest.string_read
+[  SKIPPED ] WorkerProtoTest.string_write
+[  SKIPPED ] WorkerProtoTest.storePath_read
+[  SKIPPED ] WorkerProtoTest.storePath_write
+...
+```
+will regenerate the "golden master" expected result for the `libnixstore` characterisation tests.
+The characterisation tests will mark themselves "skipped" since they regenerated the expected result instead of actually testing anything.
+
+### Unit test support libraries
+
+There are headers and code which are not just used to test the library in question, but also downstream libraries.
+For example, we do [property testing] with the [rapidcheck] library.
+This requires writing `Arbitrary` "instances", which are used to describe how to generate values of a given type for the sake of running property tests.
+Because types contain other types, `Arbitrary` "instances" for some type are not just useful for testing that type, but also any other type that contains it.
+Downstream types frequently contain upstream types, so it is very important that we share arbitrary instances so that downstream libraries' property tests can also use them.
+
+It is important that these testing libraries don't contain any actual tests themselves.
+On some platforms they would be run as part of every test executable that uses them, which is redundant.
+On other platforms they wouldn't be run at all.
+
+## Functional tests
+
+The functional tests reside under the `tests/functional` directory and are listed in `tests/functional/local.mk`.
+Each test is a bash script.
+
+### Running the whole test suite
+
+The whole test suite can be run with:
+
+```shell-session
+$ make install && make installcheck
+ran test tests/functional/foo.sh... [PASS]
+ran test tests/functional/bar.sh... [PASS]
+...
+```
+
+### Grouping tests
+
+Sometimes it is useful to group related tests so they can be easily run together without running the entire test suite.
+Each test group is in a subdirectory of `tests`.
+For example, `tests/functional/ca/local.mk` defines a `ca` test group for content-addressed derivation outputs.
+
+That test group can be run like this:
+
+```shell-session
+$ make ca.test-group -j50
+ran test tests/functional/ca/nix-run.sh... [PASS]
+ran test tests/functional/ca/import-derivation.sh... [PASS]
+...
+```
+
+The test group is defined in Make like this:
+```makefile
+$(test-group-name)-tests := \
+  $(d)/test0.sh \
+  $(d)/test1.sh \
+  ...
+
+install-tests-groups += $(test-group-name)
+```
+
+### Running individual tests
+
+Individual tests can be run with `make`:
+
+```shell-session
+$ make tests/functional/${testName}.sh.test
+ran test tests/functional/${testName}.sh... [PASS]
+```
+
+or without `make`:
+
+```shell-session
+$ ./mk/run-test.sh tests/functional/${testName}.sh tests/functional/init.sh
+ran test tests/functional/${testName}.sh... [PASS]
+```
+
+To see the complete output, one can also run:
+
+```shell-session
+$ ./mk/debug-test.sh tests/functional/${testName}.sh tests/functional/init.sh
++(${testName}.sh:1) foo
+output from foo
++(${testName}.sh:2) bar
+output from bar
+...
+```
+
+The test script will then be traced with `set -x` and the output displayed as it happens, regardless of whether the test succeeds or fails.
+
+### Debugging failing functional tests
+
+When a functional test fails, it usually does so somewhere in the middle of the script.
+
+To figure out what's wrong, it is convenient to run the test regularly up to the failing `nix` command, and then run that command with a debugger like GDB.
+
+For example, if the script looks like:
+
+```bash
+foo
+nix blah blub
+bar
+```
+edit it like so:
+
+```diff
+ foo
+-nix blah blub
++gdb --args nix blah blub
+ bar
+```
+
+Then, running the test with `./mk/debug-test.sh` will drop you into GDB once the script reaches that point:
+
+```shell-session
+$ ./mk/debug-test.sh tests/functional/${testName}.sh tests/functional/init.sh
+...
++ gdb blash blub
+GNU gdb (GDB) 12.1
+...
+(gdb)
+```
+
+One can debug the Nix invocation in all the usual ways.
+For example, enter `run` to start the Nix invocation.
+
+### Troubleshooting
+
+Sometimes running tests in the development shell may leave artefacts in the local repository.
+To remove any traces of that:
+
+```console
+git clean -x --force tests
+```
+
+### Characterisation testing { #characterisation-testing-functional }
+
+Occasionally, Nix utilizes a technique called [Characterisation Testing](https://en.wikipedia.org/wiki/Characterization_test) as part of the functional tests.
+This technique is to include the exact output/behavior of a former version of Nix in a test in order to check that Nix continues to produce the same behavior going forward.
+
+For example, this technique is used for the language tests, to check both the printed final value if evaluation was successful, and any errors and warnings encountered.
+
+It is frequently useful to regenerate the expected output.
+To do that, rerun the failed test(s) with `_NIX_TEST_ACCEPT=1`.
+For example:
+```bash
+_NIX_TEST_ACCEPT=1 make tests/functional/lang.sh.test
+```
+This convention is shared with the [characterisation unit tests](#characterisation-testing-unit) too.
+
+An interesting situation to document is the case when these tests are "overfitted".
+The language tests are, again, an example of this.
+The expected successful output of evaluation is supposed to be highly stable – we do not intend to make breaking changes to (the stable parts of) the Nix language.
+However, the errors and warnings during evaluation (successful or not) are not stable in this way.
+We are free to change how they are displayed at any time.
+
+It may be surprising that we would test non-normative behavior like diagnostic outputs.
+Diagnostic outputs are indeed not a stable interface, but they still are important to users.
+By recording the expected output, the test suite guards against accidental changes, and ensure the *result* (not just the code that implements it) of the diagnostic code paths are under code review.
+Regressions are caught, and improvements always show up in code review.
+
+To ensure that characterisation testing doesn't make it harder to intentionally change these interfaces, there always must be an easy way to regenerate the expected output, as we do with `_NIX_TEST_ACCEPT=1`.
+
+## Integration tests
+
+The integration tests are defined in the Nix flake under the `hydraJobs.tests` attribute.
+These tests include everything that needs to interact with external services or run Nix in a non-trivial distributed setup.
+Because these tests are expensive and require more than what the standard github-actions setup provides, they only run on the master branch (on <https://hydra.nixos.org/jobset/nix/master>).
+
+You can run them manually with `nix build .#hydraJobs.tests.{testName}` or `nix-build -A hydraJobs.tests.{testName}`
+
+## Installer tests
+
+After a one-time setup, the Nix repository's GitHub Actions continuous integration (CI) workflow can test the installer each time you push to a branch.
+
+Creating a Cachix cache for your installer tests and adding its authorisation token to GitHub enables [two installer-specific jobs in the CI workflow](https://github.com/NixOS/nix/blob/88a45d6149c0e304f6eb2efcc2d7a4d0d569f8af/.github/workflows/ci.yml#L50-L91):
+
+- The `installer` job generates installers for the platforms below and uploads them to your Cachix cache:
+  - `x86_64-linux`
+  - `armv6l-linux`
+  - `armv7l-linux`
+  - `x86_64-darwin`
+
+- The `installer_test` job (which runs on `ubuntu-latest` and `macos-latest`) will try to install Nix with the cached installer and run a trivial Nix command.
+
+### One-time setup
+
+1. Have a GitHub account with a fork of the [Nix repository](https://github.com/NixOS/nix).
+2. At cachix.org:
+    - Create or log in to an account.
+    - Create a Cachix cache using the format `<github-username>-nix-install-tests`.
+    - Navigate to the new cache > Settings > Auth Tokens.
+    - Generate a new Cachix auth token and copy the generated value.
+3. At github.com:
+    - Navigate to your Nix fork > Settings > Secrets > Actions > New repository secret.
+    - Name the secret `CACHIX_AUTH_TOKEN`.
+    - Paste the copied value of the Cachix cache auth token.
+
+## Working on documentation
+
+### Using the CI-generated installer for manual testing
+
+After the CI run completes, you can check the output to extract the installer URL:
+1. Click into the detailed view of the CI run.
+2. Click into any `installer_test` run (the URL you're here to extract will be the same in all of them).
+3. Click into the `Run cachix/install-nix-action@v...` step and click the detail triangle next to the first log line (it will also be `Run cachix/install-nix-action@v...`)
+4. Copy the value of `install_url`
+5. To generate an install command, plug this `install_url` and your GitHub username into this template:
+
+    ```console
+    curl -L <install_url> | sh -s -- --tarball-url-prefix https://<github-username>-nix-install-tests.cachix.org/serve
+    ```
+
+<!-- #### Manually generating test installers
+
+There's obviously a manual way to do this, and it's still the only way for
+platforms that lack GA runners.
+
+I did do this back in Fall 2020 (before the GA approach encouraged here). I'll
+sketch what I recall in case it encourages someone to fill in detail, but: I
+didn't know what I was doing at the time and had to fumble/ask around a lot--
+so I don't want to uphold any of it as "right". It may have been dumb or
+the _hard_ way from the getgo. Fundamentals may have changed since.
+
+Here's the build command I used to do this on and for x86_64-darwin:
+nix build --out-link /tmp/foo ".#checks.x86_64-darwin.binaryTarball"
+
+I used the stable out-link to make it easier to script the next steps:
+link=$(readlink /tmp/foo)
+cp $link/*-darwin.tar.xz ~/somewheres
+
+I've lost the last steps and am just going from memory:
+
+From here, I think I had to extract and modify the `install` script to point
+it at this tarball (which I scped to my own site, but it might make more sense
+to just share them locally). I extracted this script once and then just
+search/replaced in it for each new build.
+
+The installer now supports a `--tarball-url-prefix` flag which _may_ have
+solved this need?
+-->
+

doc/manual/src/glossary.md

@@ -1,236 +1,284 @@
 # Glossary
 
-  - [derivation]{#gloss-derivation}\
+- [derivation]{#gloss-derivation}
-    A description of a build task. The result of a derivation is a
-    store object. Derivations are typically specified in Nix expressions
-    using the [`derivation` primitive](./language/derivations.md). These are
-    translated into low-level *store derivations* (implicitly by
-    `nix-env` and `nix-build`, or explicitly by `nix-instantiate`).
 
-    [derivation]: #gloss-derivation
+  A description of a build task. The result of a derivation is a
+  store object. Derivations are typically specified in Nix expressions
+  using the [`derivation` primitive](./language/derivations.md). These are
+  translated into low-level *store derivations* (implicitly by
+  `nix-env` and `nix-build`, or explicitly by `nix-instantiate`).
 
-  - [store derivation]{#gloss-store-derivation}\
+  [derivation]: #gloss-derivation
-    A [derivation] represented as a `.drv` file in the [store].
-    It has a [store path], like any [store object].
 
-    Example: `/nix/store/g946hcz4c8mdvq2g8vxx42z51qb71rvp-git-2.38.1.drv`
+- [store derivation]{#gloss-store-derivation}
 
-    See [`nix derivation show`](./command-ref/new-cli/nix3-derivation-show.md) (experimental) for displaying the contents of store derivations.
+  A [derivation] represented as a `.drv` file in the [store].
+  It has a [store path], like any [store object].
 
-    [store derivation]: #gloss-store-derivation
+  Example: `/nix/store/g946hcz4c8mdvq2g8vxx42z51qb71rvp-git-2.38.1.drv`
 
-  - [instantiate]{#gloss-instantiate}, instantiation\
+  See [`nix derivation show`](./command-ref/new-cli/nix3-derivation-show.md) (experimental) for displaying the contents of store derivations.
-    Translate a [derivation] into a [store derivation].
 
-    See [`nix-instantiate`](./command-ref/nix-instantiate.md).
+  [store derivation]: #gloss-store-derivation
 
-    [instantiate]: #gloss-instantiate
+- [instantiate]{#gloss-instantiate}, instantiation
 
-  - [realise]{#gloss-realise}, realisation\
+  Translate a [derivation] into a [store derivation].
-    Ensure a [store path] is [valid][validity].
 
-    This means either running the `builder` executable as specified in the corresponding [derivation] or fetching a pre-built [store object] from a [substituter].
+  See [`nix-instantiate`](./command-ref/nix-instantiate.md).
 
-    See [`nix-build`](./command-ref/nix-build.md) and [`nix-store --realise`](@docroot@/command-ref/nix-store/realise.md).
+  [instantiate]: #gloss-instantiate
 
-    See [`nix build`](./command-ref/new-cli/nix3-build.md) (experimental).
+- [realise]{#gloss-realise}, realisation
 
-    [realise]: #gloss-realise
+  Ensure a [store path] is [valid][validity].
 
-  - [content-addressed derivation]{#gloss-content-addressed-derivation}\
+  This can be achieved by:
-    A derivation which has the
+  - Fetching a pre-built [store object] from a [substituter]
-    [`__contentAddressed`](./language/advanced-attributes.md#adv-attr-__contentAddressed)
+  - Running the [`builder`](@docroot@/language/derivations.md#attr-builder) executable as specified in the corresponding [derivation]
-    attribute set to `true`.
+  - Delegating to a [remote builder](@docroot@/advanced-topics/distributed-builds.html) and retrieving the outputs
+  <!-- TODO: link [running] to build process page, #8888 -->
 
-  - [fixed-output derivation]{#gloss-fixed-output-derivation}\
+  See [`nix-store --realise`](@docroot@/command-ref/nix-store/realise.md) for a detailed description of the algorithm.
-    A derivation which includes the
-    [`outputHash`](./language/advanced-attributes.md#adv-attr-outputHash) attribute.
 
-  - [store]{#gloss-store}\
+  See also [`nix-build`](./command-ref/nix-build.md) and [`nix build`](./command-ref/new-cli/nix3-build.md) (experimental).
-    The location in the file system where store objects live. Typically
-    `/nix/store`.
 
-    From   the  perspective   of   the  location   where  Nix   is
+  [realise]: #gloss-realise
-    invoked, the  Nix store can be  referred to
-    as a "_local_" or a "_remote_" one:
 
-    + A [local store]{#gloss-local-store} exists on the filesystem of
+- [content-addressed derivation]{#gloss-content-addressed-derivation}
-      the machine where Nix is  invoked. You can use other
-      local stores  by passing  the `--store` flag  to the
-      `nix` command.  Local stores can be used for building derivations.
 
-    + A  *remote store*  exists  anywhere  other than  the
+  A derivation which has the
-      local  filesystem. One  example is  the `/nix/store`
+  [`__contentAddressed`](./language/advanced-attributes.md#adv-attr-__contentAddressed)
-      directory on another machine,  accessed via `ssh` or
+  attribute set to `true`.
-      served by the `nix-serve` Perl script.
 
-    [store]: #gloss-store
+- [fixed-output derivation]{#gloss-fixed-output-derivation}
-    [local store]: #gloss-local-store
 
-  - [chroot store]{#gloss-chroot-store}\
+  A derivation which includes the
-    A [local store] whose canonical path is anything other than `/nix/store`.
+  [`outputHash`](./language/advanced-attributes.md#adv-attr-outputHash) attribute.
 
-  - [binary cache]{#gloss-binary-cache}\
+- [store]{#gloss-store}
-    A *binary cache* is a Nix store which uses a different format: its
-    metadata and signatures are kept in `.narinfo` files rather than in a
-    [Nix database]. This different format simplifies serving store objects
-    over the network, but cannot host builds. Examples of binary caches
-    include S3 buckets and the [NixOS binary cache](https://cache.nixos.org).
 
-  - [store path]{#gloss-store-path}\
+  A collection of store objects, with operations to manipulate that collection.
-    The location of a [store object] in the file system, i.e., an
+  See [Nix store](./store/index.md) for details.
-    immediate child of the Nix store directory.
 
-    Example: `/nix/store/a040m110amc4h71lds2jmr8qrkj2jhxd-git-2.38.1`
+  There are many types of stores.
+  See [`nix help-stores`](@docroot@/command-ref/new-cli/nix3-help-stores.md) for a complete list.
 
-    [store path]: #gloss-store-path
+  From the perspective of the location where Nix is invoked, the Nix store can be  referred to _local_ or _remote_.
+  Only a [local store]{#gloss-local-store} exposes a location in the file system of the machine where Nix is invoked that allows access to store objects, typically `/nix/store`.
+  Local stores can be used for building [derivations](#derivation).
+  See [Local Store](@docroot@/command-ref/new-cli/nix3-help-stores.md#local-store) for details.
 
-  - [file system object]{#gloss-store-object}\
+  [store]: #gloss-store
-    The Nix data model for representing simplified file system data.
+  [local store]: #gloss-local-store
 
-    See [File System Object](@docroot@/architecture/file-system-object.md) for details.
+- [chroot store]{#gloss-chroot-store}
 
-    [file system object]: #gloss-file-system-object
+  A [local store] whose canonical path is anything other than `/nix/store`.
 
-  - [store object]{#gloss-store-object}\
+- [binary cache]{#gloss-binary-cache}
 
-    A store object consists of a [file system object], [reference]s to other store objects, and other metadata.
+  A *binary cache* is a Nix store which uses a different format: its
-    It can be referred to by a [store path].
+  metadata and signatures are kept in `.narinfo` files rather than in a
+  [Nix database]. This different format simplifies serving store objects
+  over the network, but cannot host builds. Examples of binary caches
+  include S3 buckets and the [NixOS binary cache](https://cache.nixos.org).
 
-    [store object]: #gloss-store-object
+- [store path]{#gloss-store-path}
 
-  - [input-addressed store object]{#gloss-input-addressed-store-object}\
+  The location of a [store object](@docroot@/store/index.md#store-object) in the file system, i.e., an immediate child of the Nix store directory.
-    A store object produced by building a
-    non-[content-addressed](#gloss-content-addressed-derivation),
-    non-[fixed-output](#gloss-fixed-output-derivation)
-    derivation.
 
-  - [output-addressed store object]{#gloss-output-addressed-store-object}\
+  > **Example**
-    A [store object] whose [store path] is determined by its contents.
+  >
-    This includes derivations, the outputs of [content-addressed derivations](#gloss-content-addressed-derivation), and the outputs of [fixed-output derivations](#gloss-fixed-output-derivation).
+  > `/nix/store/a040m110amc4h71lds2jmr8qrkj2jhxd-git-2.38.1`
 
-  - [substitute]{#gloss-substitute}\
+  See [Store Path](@docroot@/store/store-path.md) for details.
-    A substitute is a command invocation stored in the [Nix database] that
-    describes how to build a store object, bypassing the normal build
-    mechanism (i.e., derivations). Typically, the substitute builds the
-    store object by downloading a pre-built version of the store object
-    from some server.
 
-  - [substituter]{#gloss-substituter}\
+  [store path]: #gloss-store-path
-    An additional [store]{#gloss-store} from which Nix can obtain store objects instead of building them.
-    Often the substituter is a [binary cache](#gloss-binary-cache), but any store can serve as substituter.
 
-    See the [`substituters` configuration option](./command-ref/conf-file.md#conf-substituters) for details.
+- [file system object]{#gloss-store-object}
 
-    [substituter]: #gloss-substituter
+  The Nix data model for representing simplified file system data.
 
-  - [purity]{#gloss-purity}\
+  See [File System Object](@docroot@/store/file-system-object.md) for details.
-    The assumption that equal Nix derivations when run always produce
-    the same output. This cannot be guaranteed in general (e.g., a
-    builder can rely on external inputs such as the network or the
-    system time) but the Nix model assumes it.
 
-  - [Nix database]{#gloss-nix-database}\
+  [file system object]: #gloss-file-system-object
-    An SQlite database to track [reference]s between [store object]s.
-    This is an implementation detail of the [local store].
 
-    Default location: `/nix/var/nix/db`.
+- [store object]{#gloss-store-object}
 
-    [Nix database]: #gloss-nix-database
+  Part of the contents of a [store].
 
-  - [Nix expression]{#gloss-nix-expression}\
+  A store object consists of a [file system object], [references][reference] to other store objects, and other metadata.
-    A high-level description of software packages and compositions
+  It can be referred to by a [store path].
-    thereof. Deploying software using Nix entails writing Nix
-    expressions for your packages. Nix expressions are translated to
-    derivations that are stored in the Nix store. These derivations can
-    then be built.
 
-  - [reference]{#gloss-reference}\
+  See [Store Object](@docroot@/store/index.md#store-object) for details.
-    A [store object] `O` is said to have a *reference* to a store object `P` if a [store path] to `P` appears in the contents of `O`.
 
-    Store objects can refer to both other store objects and themselves.
+  [store object]: #gloss-store-object
-    References from a store object to itself are called *self-references*.
-    References other than a self-reference must not form a cycle.
 
-    [reference]: #gloss-reference
+- [IFD]{#gloss-ifd}
 
-  - [reachable]{#gloss-reachable}\
+  [Import From Derivation](./language/import-from-derivation.md)
-    A store path `Q` is reachable from another store path `P` if `Q`
-    is in the *closure* of the *references* relation.
 
-  - [closure]{#gloss-closure}\
+- [input-addressed store object]{#gloss-input-addressed-store-object}
-    The closure of a store path is the set of store paths that are
-    directly or indirectly “reachable” from that store path; that is,
-    it’s the closure of the path under the *references* relation. For
-    a package, the closure of its derivation is equivalent to the
-    build-time dependencies, while the closure of its output path is
-    equivalent to its runtime dependencies. For correct deployment it
-    is necessary to deploy whole closures, since otherwise at runtime
-    files could be missing. The command `nix-store --query --requisites ` prints out
-    closures of store paths.
 
-    As an example, if the [store object] at path `P` contains a [reference]
+  A store object produced by building a
-    to a store object at path `Q`, then `Q` is in the closure of `P`. Further, if `Q`
+  non-[content-addressed](#gloss-content-addressed-derivation),
-    references `R` then `R` is also in the closure of `P`.
+  non-[fixed-output](#gloss-fixed-output-derivation)
+  derivation.
 
-    [closure]: #gloss-closure
+- [output-addressed store object]{#gloss-output-addressed-store-object}
 
-  - [output path]{#gloss-output-path}\
+  A [store object] whose [store path] is determined by its contents.
-    A [store path] produced by a [derivation].
+  This includes derivations, the outputs of [content-addressed derivations](#gloss-content-addressed-derivation), and the outputs of [fixed-output derivations](#gloss-fixed-output-derivation).
 
-    [output path]: #gloss-output-path
+- [substitute]{#gloss-substitute}
 
-  - [deriver]{#gloss-deriver}\
+  A substitute is a command invocation stored in the [Nix database] that
-    The [store derivation] that produced an [output path].
+  describes how to build a store object, bypassing the normal build
+  mechanism (i.e., derivations). Typically, the substitute builds the
+  store object by downloading a pre-built version of the store object
+  from some server.
 
-  - [validity]{#gloss-validity}\
+- [substituter]{#gloss-substituter}
-    A store path is valid if all [store object]s in its [closure] can be read from the [store].
 
-    For a [local store], this means:
+  An additional [store]{#gloss-store} from which Nix can obtain store objects instead of building them.
-    - The store path leads to an existing [store object] in that [store].
+  Often the substituter is a [binary cache](#gloss-binary-cache), but any store can serve as substituter.
-    - The store path is listed in the [Nix database] as being valid.
-    - All paths in the store path's [closure] are valid.
 
-    [validity]: #gloss-validity
+  See the [`substituters` configuration option](./command-ref/conf-file.md#conf-substituters) for details.
 
-  - [user environment]{#gloss-user-env}\
+  [substituter]: #gloss-substituter
-    An automatically generated store object that consists of a set of
-    symlinks to “active” applications, i.e., other store paths. These
-    are generated automatically by
-    [`nix-env`](./command-ref/nix-env.md). See *profiles*.
 
-  - [profile]{#gloss-profile}\
+- [purity]{#gloss-purity}
-    A symlink to the current *user environment* of a user, e.g.,
-    `/nix/var/nix/profiles/default`.
 
-  - [installable]{#gloss-installable}\
+  The assumption that equal Nix derivations when run always produce
-    Something that can be realised in the Nix store.
+  the same output. This cannot be guaranteed in general (e.g., a
+  builder can rely on external inputs such as the network or the
+  system time) but the Nix model assumes it.
 
-    See [installables](./command-ref/new-cli/nix.md#installables) for [`nix` commands](./command-ref/new-cli/nix.md) (experimental) for details.
+- [Nix database]{#gloss-nix-database}
 
-  - [NAR]{#gloss-nar}\
+  An SQlite database to track [reference]s between [store object]s.
-    A *N*ix *AR*chive. This is a serialisation of a path in the Nix
+  This is an implementation detail of the [local store].
-    store. It can contain regular files, directories and symbolic
-    links.  NARs are generated and unpacked using `nix-store --dump`
-    and `nix-store --restore`.
 
-  - [`∅`]{#gloss-emtpy-set}\
+  Default location: `/nix/var/nix/db`.
-    The empty set symbol. In the context of profile history, this denotes a package is not present in a particular version of the profile.
 
-  - [`ε`]{#gloss-epsilon}\
+  [Nix database]: #gloss-nix-database
-    The epsilon symbol. In the context of a package, this means the version is empty. More precisely, the derivation does not have a version attribute.
 
-  - [string interpolation]{#gloss-string-interpolation}\
+- [Nix expression]{#gloss-nix-expression}
-    Expanding expressions enclosed in `${ }` within a [string], [path], or [attribute name].
 
-    See [String interpolation](./language/string-interpolation.md) for details.
+  A high-level description of software packages and compositions
+  thereof. Deploying software using Nix entails writing Nix
+  expressions for your packages. Nix expressions are translated to
+  derivations that are stored in the Nix store. These derivations can
+  then be built.
 
-    [string]: ./language/values.md#type-string
+- [reference]{#gloss-reference}
-    [path]: ./language/values.md#type-path
-    [attribute name]: ./language/values.md#attribute-set
 
-  - [experimental feature]{#gloss-experimental-feature}\
+  A [store object] `O` is said to have a *reference* to a store object `P` if a [store path] to `P` appears in the contents of `O`.
-    Not yet stabilized functionality guarded by named experimental feature flags.
-    These flags are enabled or disabled with the [`experimental-features`](./command-ref/conf-file.html#conf-experimental-features) setting.
 
-    See the contribution guide on the [purpose and lifecycle of experimental feaures](@docroot@/contributing/experimental-features.md).
+  Store objects can refer to both other store objects and themselves.
+  References from a store object to itself are called *self-references*.
+  References other than a self-reference must not form a cycle.
+
+  [reference]: #gloss-reference
+
+- [reachable]{#gloss-reachable}
+
+  A store path `Q` is reachable from another store path `P` if `Q`
+  is in the *closure* of the *references* relation.
+
+- [closure]{#gloss-closure}
+
+  The closure of a store path is the set of store paths that are
+  directly or indirectly “reachable” from that store path; that is,
+  it’s the closure of the path under the *references* relation. For
+  a package, the closure of its derivation is equivalent to the
+  build-time dependencies, while the closure of its output path is
+  equivalent to its runtime dependencies. For correct deployment it
+  is necessary to deploy whole closures, since otherwise at runtime
+  files could be missing. The command `nix-store --query --requisites ` prints out
+  closures of store paths.
+
+  As an example, if the [store object] at path `P` contains a [reference]
+  to a store object at path `Q`, then `Q` is in the closure of `P`. Further, if `Q`
+  references `R` then `R` is also in the closure of `P`.
+
+  [closure]: #gloss-closure
+
+- [output]{#gloss-output}
+
+  A [store object] produced by a [derivation].
+  See [the `outputs` argument to the `derivation` function](@docroot@/language/derivations.md#attr-outputs) for details.
+
+  [output]: #gloss-output
+
+- [output path]{#gloss-output-path}
+
+  The [store path] to the [output] of a [derivation].
+
+  [output path]: #gloss-output-path
+
+- [deriver]{#gloss-deriver}
+
+  The [store derivation] that produced an [output path].
+
+- [validity]{#gloss-validity}
+
+  A store path is valid if all [store object]s in its [closure] can be read from the [store].
+
+  For a [local store], this means:
+  - The store path leads to an existing [store object] in that [store].
+  - The store path is listed in the [Nix database] as being valid.
+  - All paths in the store path's [closure] are valid.
+
+  [validity]: #gloss-validity
+
+- [user environment]{#gloss-user-env}
+
+  An automatically generated store object that consists of a set of
+  symlinks to “active” applications, i.e., other store paths. These
+  are generated automatically by
+  [`nix-env`](./command-ref/nix-env.md). See *profiles*.
+
+- [profile]{#gloss-profile}
+
+  A symlink to the current *user environment* of a user, e.g.,
+  `/nix/var/nix/profiles/default`.
+
+- [installable]{#gloss-installable}
+
+  Something that can be realised in the Nix store.
+
+  See [installables](./command-ref/new-cli/nix.md#installables) for [`nix` commands](./command-ref/new-cli/nix.md) (experimental) for details.
+
+- [NAR]{#gloss-nar}
+
+  A *N*ix *AR*chive. This is a serialisation of a path in the Nix
+  store. It can contain regular files, directories and symbolic
+  links.  NARs are generated and unpacked using `nix-store --dump`
+  and `nix-store --restore`.
+
+- [`∅`]{#gloss-emtpy-set}
+
+  The empty set symbol. In the context of profile history, this denotes a package is not present in a particular version of the profile.
+
+- [`ε`]{#gloss-epsilon}
+
+  The epsilon symbol. In the context of a package, this means the version is empty. More precisely, the derivation does not have a version attribute.
+
+- [string interpolation]{#gloss-string-interpolation}
+
+  Expanding expressions enclosed in `${ }` within a [string], [path], or [attribute name].
+
+  See [String interpolation](./language/string-interpolation.md) for details.
+
+  [string]: ./language/values.md#type-string
+  [path]: ./language/values.md#type-path
+  [attribute name]: ./language/values.md#attribute-set
+
+- [experimental feature]{#gloss-experimental-feature}
+
+  Not yet stabilized functionality guarded by named experimental feature flags.
+  These flags are enabled or disabled with the [`experimental-features`](./command-ref/conf-file.html#conf-experimental-features) setting.
+
+  See the contribution guide on the [purpose and lifecycle of experimental feaures](@docroot@/contributing/experimental-features.md).

doc/manual/src/installation/building-source.md

@@ -3,7 +3,7 @@
 After cloning Nix's Git repository, issue the following commands:
 
 ```console
-$ ./bootstrap.sh
+$ autoreconf -vfi
 $ ./configure options...
 $ make
 $ make install

doc/manual/src/installation/installing-binary.md

@@ -1,26 +1,60 @@
 # Installing a Binary Distribution
 
-The easiest way to install Nix is to run the following command:
+To install the latest version Nix, run the following command:
 
 ```console
 $ curl -L https://nixos.org/nix/install | sh
 ```
 
-This will run the installer interactively (causing it to explain what
+This performs the default type of installation for your platform:
-it is doing more explicitly), and perform the default "type" of install
-for your platform:
-- single-user on Linux
-- multi-user on macOS
 
-  > **Notes on read-only filesystem root in macOS 10.15 Catalina +**
+- [Multi-user](#multi-user-installation):
-  >
+  - Linux with systemd and without SELinux
-  > - It took some time to support this cleanly. You may see posts,
+  - macOS
-  >   examples, and tutorials using obsolete workarounds.
+- [Single-user](#single-user-installation):
-  > - Supporting it cleanly made macOS installs too complex to qualify
+  - Linux without systemd
-  >   as single-user, so this type is no longer supported on macOS.
+  - Linux with SELinux
 
-We recommend the multi-user install if it supports your platform and
+We recommend the multi-user installation if it supports your platform and you can authenticate with `sudo`.
-you can authenticate with `sudo`.
+
+The installer can configured with various command line arguments and environment variables.
+To show available command line flags:
+
+```console
+$ curl -L https://nixos.org/nix/install | sh -s -- --help
+```
+
+To check what it does and how it can be customised further, [download and edit the second-stage installation script](#installing-from-a-binary-tarball).
+
+# Installing a pinned Nix version from a URL
+
+Version-specific installation URLs for all Nix versions since 1.11.16 can be found at [releases.nixos.org](https://releases.nixos.org/?prefix=nix/).
+The directory for each version contains the corresponding SHA-256 hash.
+
+All installation scripts are invoked the same way:
+
+```console
+$ export VERSION=2.19.2 
+$ curl -L https://releases.nixos.org/nix/nix-$VERSION/install | sh
+```
+
+# Multi User Installation
+
+The multi-user Nix installation creates system users and a system service for the Nix daemon.
+
+Supported systems:
+
+- Linux running systemd, with SELinux disabled
+- macOS
+
+To explicitly instruct the installer to perform a multi-user installation on your system:
+
+```console
+$ curl -L https://nixos.org/nix/install | sh -s -- --daemon
+```
+
+You can run this under your usual user account or `root`.
+The script will invoke `sudo` as needed.
 
 # Single User Installation
 
@@ -30,60 +64,48 @@ To explicitly select a single-user installation on your system:
 $ curl -L https://nixos.org/nix/install | sh -s -- --no-daemon
 ```
 
-This will perform a single-user installation of Nix, meaning that `/nix`
+In a single-user installation, `/nix` is owned by the invoking user.
-is owned by the invoking user. You can run this under your usual user
+The script will invoke `sudo` to create `/nix` if it doesn’t already exist.
-account or root. The script will invoke `sudo` to create `/nix`
+If you don’t have `sudo`, manually create `/nix` as `root`:
-if it doesn’t already exist. If you don’t have `sudo`, you should
-manually create `/nix` first as root, e.g.:
 
 ```console
-$ mkdir /nix
+$ su root
-$ chown alice /nix
+# mkdir /nix
+# chown alice /nix
 ```
 
-The install script will modify the first writable file from amongst
+# Installing from a binary tarball
-`.bash_profile`, `.bash_login` and `.profile` to source
-`~/.nix-profile/etc/profile.d/nix.sh`. You can set the
-`NIX_INSTALLER_NO_MODIFY_PROFILE` environment variable before executing
-the install script to disable this behaviour.
 
-# Multi User Installation
+You can also download a binary tarball that contains Nix and all its dependencies:
+- Choose a [version](https://releases.nixos.org/?prefix=nix/) and [system type](../contributing/hacking.md#platforms)
+- Download and unpack the tarball
+- Run the installer
 
-The multi-user Nix installation creates system users, and a system
+> **Example**
-service for the Nix daemon.
-
-**Supported Systems**
-- Linux running systemd, with SELinux disabled
-- macOS
-
-You can instruct the installer to perform a multi-user installation on
-your system:
-
-```console
-$ curl -L https://nixos.org/nix/install | sh -s -- --daemon
-```
-
-The multi-user installation of Nix will create build users between the
-user IDs 30001 and 30032, and a group with the group ID 30000. You
-can run this under your usual user account or root. The script
-will invoke `sudo` as needed.
-
-> **Note**
 >
-> If you need Nix to use a different group ID or user ID set, you will
+> ```console
-> have to download the tarball manually and [edit the install
+> $ pushd $(mktemp -d)
-> script](#installing-from-a-binary-tarball).
+> $ export VERSION=2.19.2
+> $ export SYSTEM=x86_64-linux
+> $ curl -LO https://releases.nixos.org/nix/nix-$VERSION/nix-$VERSION-$SYSTEM.tar.xz
+> $ tar xfj nix-$VERSION-$SYSTEM.tar.xz
+> $ cd nix-$VERSION-$SYSTEM
+> $ ./install
+> $ popd
+> ```
 
-The installer will modify `/etc/bashrc`, and `/etc/zshrc` if they exist.
+The installer can be customised with the environment variables declared in the file named `install-multi-user`.
-The installer will first back up these files with a `.backup-before-nix`
+
-extension. The installer will also create `/etc/profile.d/nix.sh`.
+## Native packages for Linux distributions
+
+The Nix community maintains installers for some Linux distributions in their native packaging format(https://nix-community.github.io/nix-installers/).
 
 # macOS Installation
 
+<!-- anchors to catch existing links -->
 []{#sect-macos-installation-change-store-prefix}[]{#sect-macos-installation-encrypted-volume}[]{#sect-macos-installation-symlink}[]{#sect-macos-installation-recommended-notes}
-<!-- Note: anchors above to catch permalinks to old explanations -->
 
-We believe we have ironed out how to cleanly support the read-only root
+We believe we have ironed out how to cleanly support the read-only root file system
 on modern macOS. New installs will do this automatically.
 
 This section previously detailed the situation, options, and trade-offs,
@@ -126,33 +148,3 @@ this to run the installer, but it may help if you run into trouble:
   boot process to avoid problems loading or restoring any programs that
   need access to your Nix store
 
-# Installing a pinned Nix version from a URL
-
-Version-specific installation URLs for all Nix versions
-since 1.11.16 can be found at [releases.nixos.org](https://releases.nixos.org/?prefix=nix/).
-The corresponding SHA-256 hash can be found in the directory for the given version.
-
-These install scripts can be used the same as usual:
-
-```console
-$ curl -L https://releases.nixos.org/nix/nix-<version>/install | sh
-```
-
-# Installing from a binary tarball
-
-You can also download a binary tarball that contains Nix and all its
-dependencies. (This is what the install script at
-<https://nixos.org/nix/install> does automatically.) You should unpack
-it somewhere (e.g. in `/tmp`), and then run the script named `install`
-inside the binary tarball:
-
-```console
-$ cd /tmp
-$ tar xfj nix-1.8-x86_64-darwin.tar.bz2
-$ cd nix-1.8-x86_64-darwin
-$ ./install
-```
-
-If you need to edit the multi-user installation script to use different
-group ID or a different user ID range, modify the variables set in the
-file named `install-multi-user`.

doc/manual/src/installation/installing-docker.md

@@ -3,14 +3,14 @@
 To run the latest stable release of Nix with Docker run the following command:
 
 ```console
-$ docker run -ti nixos/nix
+$ docker run -ti ghcr.io/nixos/nix
-Unable to find image 'nixos/nix:latest' locally
+Unable to find image 'ghcr.io/nixos/nix:latest' locally
-latest: Pulling from nixos/nix
+latest: Pulling from ghcr.io/nixos/nix
 5843afab3874: Pull complete
 b52bf13f109c: Pull complete
 1e2415612aa3: Pull complete
 Digest: sha256:27f6e7f60227e959ee7ece361f75d4844a40e1cc6878b6868fe30140420031ff
-Status: Downloaded newer image for nixos/nix:latest
+Status: Downloaded newer image for ghcr.io/nixos/nix:latest
 35ca4ada6e96:/# nix --version
 nix (Nix) 2.3.12
 35ca4ada6e96:/# exit

doc/manual/src/installation/prerequisites-source.md

@@ -72,7 +72,7 @@
     This is an optional dependency and can be disabled
     by providing a `--disable-cpuid` to the `configure` script.
 
-  - Unless `./configure --disable-tests` is specified, GoogleTest (GTest) and
+  - Unless `./configure --disable-unit-tests` is specified, GoogleTest (GTest) and
     RapidCheck are required, which are available at
     <https://google.github.io/googletest/> and
     <https://github.com/emil-e/rapidcheck> respectively.

doc/manual/src/installation/upgrading.md

@@ -1,5 +1,40 @@
 # Upgrading Nix
 
+> **Note**
+>
+> These upgrade instructions apply for regular Linux distributions where Nix was installed following the [installation instructions in this manual](./index.md).
+
+First, find the name of the current [channel](@docroot@/command-ref/nix-channel.md) through which Nix is distributed:
+
+```console
+$ nix-channel --list
+```
+
+By default this should return an entry for Nixpkgs:
+
+```console
+nixpkgs https://nixos.org/channels/nixpkgs-23.05
+```
+
+Check which Nix version will be installed:
+
+```console
+$ nix-shell -p nix -I nixpkgs=channel:nixpkgs-23.11 --run "nix --version"
+nix (Nix) 2.18.1
+```
+
+> **Warning**
+>
+> Writing to the [local store](@docroot@/store/types/local-store.md) with a newer version of Nix, for example by building derivations with `nix-build` or `nix-store --realise`, may change the database schema!
+> Reverting to an older version of Nix may therefore require purging the store database before it can be used.
+
+Update the channel entry:
+
+```console
+$ nix-channel --remove nixpkgs
+$ nix-channel --add https://nixos.org/channels/nixpkgs-23.11 nixpkgs
+```
+
 Multi-user Nix users on macOS can upgrade Nix by running: `sudo -i sh -c
 'nix-channel --update &&
 nix-env --install --attr nixpkgs.nix &&

doc/manual/src/language/advanced-attributes.md

@@ -112,6 +112,13 @@ Derivations can declare some infrequently used optional attributes.
     > environmental variables come from the environment of the
     > `nix-build`.
 
+    If the [`configurable-impure-env` experimental
+    feature](@docroot@/contributing/experimental-features.md#xp-feature-configurable-impure-env)
+    is enabled, these environment variables can also be controlled
+    through the
+    [`impure-env`](@docroot@/command-ref/conf-file.md#conf-impure-env)
+    configuration setting.
+
   - [`outputHash`]{#adv-attr-outputHash}; [`outputHashAlgo`]{#adv-attr-outputHashAlgo}; [`outputHashMode`]{#adv-attr-outputHashMode}\
     These attributes declare that the derivation is a so-called
     *fixed-output derivation*, which means that a cryptographic hash of
@@ -229,6 +236,8 @@ Derivations can declare some infrequently used optional attributes.
     [`outputHashAlgo`](#adv-attr-outputHashAlgo)
     like for *fixed-output derivations* (see above).
 
+    It also implicitly requires that the machine to build the derivation must have the `ca-derivations` [system feature](@docroot@/command-ref/conf-file.md#conf-system-features).
+
   - [`passAsFile`]{#adv-attr-passAsFile}\
     A list of names of attributes that should be passed via files rather
     than environment variables. For example, if you have
@@ -248,41 +257,36 @@ Derivations can declare some infrequently used optional attributes.
     of the environment (typically, a few hundred kilobyte).
 
   - [`preferLocalBuild`]{#adv-attr-preferLocalBuild}\
-    If this attribute is set to `true` and [distributed building is
+    If this attribute is set to `true` and [distributed building is enabled](../advanced-topics/distributed-builds.md), then, if possible, the derivation will be built locally instead of being forwarded to a remote machine.
-    enabled](../advanced-topics/distributed-builds.md), then, if
+    This is useful for derivations that are cheapest to build locally.
-    possible, the derivation will be built locally instead of forwarded
-    to a remote machine. This is appropriate for trivial builders
-    where the cost of doing a download or remote build would exceed
-    the cost of building locally.
 
   - [`allowSubstitutes`]{#adv-attr-allowSubstitutes}\
-    If this attribute is set to `false`, then Nix will always build this
+    If this attribute is set to `false`, then Nix will always build this derivation (locally or remotely); it will not try to substitute its outputs.
-    derivation; it will not try to substitute its outputs. This is
+    This is useful for derivations that are cheaper to build than to substitute.
-    useful for very trivial derivations (such as `writeText` in Nixpkgs)
+
-    that are cheaper to build than to substitute from a binary cache.
+    This attribute can be ignored by setting [`always-allow-substitutes`](@docroot@/command-ref/conf-file.md#conf-always-allow-substitutes) to `true`.
 
     > **Note**
     >
-    > You need to have a builder configured which satisfies the
+    > If set to `false`, the [`builder`](./derivations.md#attr-builder) should be able to run on the system type specified in the [`system` attribute](./derivations.md#attr-system), since the derivation cannot be substituted.
-    > derivation’s `system` attribute, since the derivation cannot be
-    > substituted. Thus it is usually a good idea to align `system` with
-    > `builtins.currentSystem` when setting `allowSubstitutes` to
-    > `false`. For most trivial derivations this should be the case.
 
   - [`__structuredAttrs`]{#adv-attr-structuredAttrs}\
     If the special attribute `__structuredAttrs` is set to `true`, the other derivation
-    attributes are serialised in JSON format and made available to the
+    attributes are serialised into a file in JSON format. The environment variable
-    builder via the file `.attrs.json` in the builder’s temporary
+    `NIX_ATTRS_JSON_FILE` points to the exact location of that file both in a build
-    directory. This obviates the need for [`passAsFile`](#adv-attr-passAsFile) since JSON files
+    and a [`nix-shell`](../command-ref/nix-shell.md). This obviates the need for
-    have no size restrictions, unlike process environments.
+    [`passAsFile`](#adv-attr-passAsFile) since JSON files have no size restrictions,
+    unlike process environments.
 
     It also makes it possible to tweak derivation settings in a structured way; see
     [`outputChecks`](#adv-attr-outputChecks) for example.
 
     As a convenience to Bash builders,
-    Nix writes a script named `.attrs.sh` to the builder’s directory
+    Nix writes a script that initialises shell variables
-    that initialises shell variables corresponding to all attributes
+    corresponding to all attributes that are representable in Bash. The
-    that are representable in Bash. This includes non-nested
+    environment variable `NIX_ATTRS_SH_FILE` points to the exact
+    location of the script, both in a build and a
+    [`nix-shell`](../command-ref/nix-shell.md). This includes non-nested
     (associative) arrays. For example, the attribute `hardening.format = true`
     ends up as the Bash associative array element `${hardening[format]}`.
 
@@ -320,16 +324,6 @@ Derivations can declare some infrequently used optional attributes.
     ```
 
   - [`unsafeDiscardReferences`]{#adv-attr-unsafeDiscardReferences}\
-    > **Warning**
-    > This attribute is part of an [experimental feature](@docroot@/contributing/experimental-features.md).
-    >
-    > To use this attribute, you must enable the
-    > [`discard-references`](@docroot@/contributing/experimental-features.md#xp-feature-discard-references) experimental feature.
-    > For example, in [nix.conf](../command-ref/conf-file.md) you could add:
-    >
-    > ```
-    > extra-experimental-features = discard-references
-    > ```
 
     When using [structured attributes](#adv-attr-structuredAttrs), the
     attribute `unsafeDiscardReferences` is an attribute set with a boolean value for each output name.
@@ -345,3 +339,15 @@ Derivations can declare some infrequently used optional attributes.
     This is useful, for example, when generating self-contained filesystem images with
     their own embedded Nix store: hashes found inside such an image refer
     to the embedded store and not to the host's Nix store.
+
+- [`requiredSystemFeatures`]{#adv-attr-requiredSystemFeatures}\
+
+  If a derivation has the `requiredSystemFeatures` attribute, then Nix will only build it on a machine that has the corresponding features set in its [`system-features` configuration](@docroot@/command-ref/conf-file.md#conf-system-features).
+
+  For example, setting
+
+  ```nix
+  requiredSystemFeatures = [ "kvm" ];
+  ```
+
+  ensures that the derivation can only be built on a machine with the `kvm` feature.

doc/manual/src/language/builtin-constants-prefix.md

@@ -0,0 +1,5 @@
+# Built-in Constants
+
+These constants are built into the Nix language evaluator:
+
+<dl>

doc/manual/src/language/builtin-constants-suffix.md

@@ -0,0 +1 @@
+</dl>

doc/manual/src/language/builtin-constants.md

@@ -1,43 +0,0 @@
-# Built-in Constants
-
-These constants are built into the Nix language evaluator:
-
-- [`builtins`]{#builtins-builtins} (attribute set)
-
-  Contains all the [built-in functions](./builtins.md) and values, in order to avoid polluting the global scope.
-
-  Since built-in functions were added over time, [testing for attributes](./operators.md#has-attribute) in `builtins` can be used for graceful fallback on older Nix installations:
-
-  ```nix
-  if builtins ? getEnv then builtins.getEnv "PATH" else ""
-  ```
-
-- [`builtins.currentSystem`]{#builtins-currentSystem} (string)
-
-  The built-in value `currentSystem` evaluates to the Nix platform
-  identifier for the Nix installation on which the expression is being
-  evaluated, such as `"i686-linux"` or `"x86_64-darwin"`.
-
-  Not available in [pure evaluation mode](@docroot@/command-ref/conf-file.md#conf-pure-eval).
-
-- [`builtins.currentTime`]{#builtins-currentTime} (integer)
-
-  Return the [Unix time](https://en.wikipedia.org/wiki/Unix_time) at first evaluation.
-  Repeated references to that name will re-use the initially obtained value.
-
-  Example:
-
-  ```console
-  $ nix repl
-  Welcome to Nix 2.15.1 Type :? for help.
-
-  nix-repl> builtins.currentTime
-  1683705525
-
-  nix-repl> builtins.currentTime
-  1683705525
-  ```
-
-  The [store path](@docroot@/glossary.md#gloss-store-path) of a derivation depending on `currentTime` will differ for each evaluation.
-
-  Not available in [pure evaluation mode](@docroot@/command-ref/conf-file.md#conf-pure-eval).

doc/manual/src/language/builtins-prefix.md

@@ -3,7 +3,7 @@
 This section lists the functions built into the Nix language evaluator.
 All built-in functions are available through the global [`builtins`](./builtin-constants.md#builtins-builtins) constant.
 
-For convenience, some built-ins are can be accessed directly:
+For convenience, some built-ins can be accessed directly:
 
 - [`derivation`](#builtins-derivation)
 - [`import`](#builtins-import)

doc/manual/src/language/constructs.md

@@ -92,10 +92,10 @@ In this fragment from `all-packages.nix`,
 ```nix
 graphviz = (import ../tools/graphics/graphviz) {
   inherit fetchurl stdenv libpng libjpeg expat x11 yacc;
-  inherit (xlibs) libXaw;
+  inherit (xorg) libXaw;
 };
 
-xlibs = {
+xorg = {
   libX11 = ...;
   libXaw = ...;
   ...
@@ -109,7 +109,7 @@ libjpg = ...;
 the set used in the function call to the function defined in
 `../tools/graphics/graphviz` inherits a number of variables from the
 surrounding scope (`fetchurl` ... `yacc`), but also inherits `libXaw`
-(the X Athena Widgets) from the `xlibs` (X11 client-side libraries) set.
+(the X Athena Widgets) from the `xorg` set.
 
 Summarizing the fragment
 
@@ -132,6 +132,32 @@ a = src-set.a; b = src-set.b; c = src-set.c;
 when used while defining local variables in a let-expression or while
 defining a set.
 
+In a `let` expression, `inherit` can be used to selectively bring specific attributes of a set into scope. For example
+
+
+```nix
+let
+  x = { a = 1; b = 2; };
+  inherit (builtins) attrNames;
+in
+{
+  names = attrNames x;
+}
+```
+
+is equivalent to
+
+```nix
+let
+  x = { a = 1; b = 2; };
+in
+{
+  names = builtins.attrNames x;
+}
+```
+
+both evaluate to `{ names = [ "a" "b" ]; }`.
+
 ## Functions
 
 Functions have the following form:
@@ -209,29 +235,40 @@ three kinds of patterns:
     { x, y, z, ... } @ args: z + y + x + args.a
     ```
 
-    Here `args` is bound to the entire argument, which is further
+    Here `args` is bound to the argument *as passed*, which is further
-    matched against the pattern `{ x, y, z,
+    matched against the pattern `{ x, y, z, ... }`.
-            ... }`. `@`-pattern makes mainly sense with an ellipsis(`...`) as
+    The `@`-pattern makes mainly sense with an ellipsis(`...`) as
     you can access attribute names as `a`, using `args.a`, which was
     given as an additional attribute to the function.
 
     > **Warning**
     >
-    > The `args@` expression is bound to the argument passed to the
+    > `args@` binds the name `args` to the attribute set that is passed to the function.
-    > function which means that attributes with defaults that aren't
+    > In particular, `args` does *not* include any default values specified with `?` in the function's set pattern.
-    > explicitly specified in the function call won't cause an
-    > evaluation error, but won't exist in `args`.
     >
     > For instance
     >
     > ```nix
     > let
-    >   function = args@{ a ? 23, ... }: args;
+    >   f = args@{ a ? 23, ... }: [ a args ];
     > in
-    >   function {}
+    >   f {}
-    > ````
+    > ```
     >
-    > will evaluate to an empty attribute set.
+    > is equivalent to
+    >
+    > ```nix
+    > let
+    >   f = args @ { ... }: [ (args.a or 23) args ];
+    > in
+    >   f {}
+    > ```
+    >
+    > and both expressions will evaluate to:
+    >
+    > ```nix
+    > [ 23 {} ]
+    > ```
 
 Note that functions do not have names. If you want to give them a name,
 you can bind them to an attribute, e.g.,

doc/manual/src/language/constructs/lookup-path.md

@@ -0,0 +1,27 @@
+# Lookup path
+
+> **Syntax**
+>
+> *lookup-path* = `<` *identifier* [ `/` *identifier* ]... `>`
+
+A lookup path is an identifier with an optional path suffix that resolves to a [path value](@docroot@/language/values.md#type-path) if the identifier matches a search path entry.
+
+The value of a lookup path is determined by [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath).
+
+See [`builtins.findFile`](@docroot@/language/builtins.md#builtins-findFile) for details on lookup path resolution.
+
+> **Example**
+>
+> ```nix
+> <nixpkgs>
+>```
+>
+>     /nix/var/nix/profiles/per-user/root/channels/nixpkgs
+
+> **Example**
+>
+> ```nix
+> <nixpkgs/nixos>
+>```
+>
+>     /nix/var/nix/profiles/per-user/root/channels/nixpkgs/nixos

doc/manual/src/language/derivations.md

@@ -1,161 +1,315 @@
 # Derivations
 
-The most important built-in function is `derivation`, which is used to
+The most important built-in function is `derivation`, which is used to describe a single derivation:
-describe a single derivation (a build task). It takes as input a set,
+a specification for running an executable on precisely defined input files to repeatably produce output files at uniquely determined file system paths.
-the attributes of which specify the inputs of the build.
 
-  - There must be an attribute named [`system`]{#attr-system} whose value must be a
+It takes as input an attribute set, the attributes of which specify the inputs to the process.
-    string specifying a Nix system type, such as `"i686-linux"` or
+It outputs an attribute set, and produces a [store derivation] as a side effect of evaluation.
-    `"x86_64-darwin"`. (To figure out your system type, run `nix -vv
-    --version`.) The build can only be performed on a machine and
-    operating system matching the system type. (Nix can automatically
-    [forward builds for other
-    platforms](../advanced-topics/distributed-builds.md) by forwarding
-    them to other machines.)
 
-  - There must be an attribute named `name` whose value must be a
+[store derivation]: @docroot@/glossary.md#gloss-store-derivation
-    string. This is used as a symbolic name for the package by
-    `nix-env`, and it is appended to the output paths of the derivation.
 
-  - There must be an attribute named `builder` that identifies the
+## Input attributes
-    program that is executed to perform the build. It can be either a
-    derivation or a source (a local file reference, e.g.,
-    `./builder.sh`).
 
-  - Every attribute is passed as an environment variable to the builder.
+### Required
-    Attribute values are translated to environment variables as follows:
 
-      - Strings and numbers are just passed verbatim.
+- [`name`]{#attr-name} ([String](@docroot@/language/values.md#type-string))
 
-      - A *path* (e.g., `../foo/sources.tar`) causes the referenced file
+  A symbolic name for the derivation.
-        to be copied to the store; its location in the store is put in
+  It is added to the [store path] of the corresponding [store derivation] as well as to its [output paths](@docroot@/glossary.md#gloss-output-path).
-        the environment variable. The idea is that all sources should
-        reside in the Nix store, since all inputs to a derivation should
-        reside in the Nix store.
 
-      - A *derivation* causes that derivation to be built prior to the
+  [store path]: @docroot@/glossary.md#gloss-store-path
-        present derivation; its default output path is put in the
-        environment variable.
 
-      - Lists of the previous types are also allowed. They are simply
+  > **Example**
-        concatenated, separated by spaces.
+  >
+  > ```nix
+  > derivation {
+  >   name = "hello";
+  >   # ...
+  > }
+  > ```
+  >
+  > The store derivation's path will be `/nix/store/<hash>-hello.drv`.
+  > The [output](#attr-outputs) paths will be of the form `/nix/store/<hash>-hello[-<output>]`
 
-      - `true` is passed as the string `1`, `false` and `null` are
+- [`system`]{#attr-system} ([String](@docroot@/language/values.md#type-string))
-        passed as an empty string.
 
-  - The optional attribute `args` specifies command-line arguments to be
+  The system type on which the [`builder`](#attr-builder) executable is meant to be run.
-    passed to the builder. It should be a list.
 
-  - The optional attribute `outputs` specifies a list of symbolic
+  A necessary condition for Nix to build derivations locally is that the `system` attribute matches the current [`system` configuration option].
-    outputs of the derivation. By default, a derivation produces a
+  It can automatically [build on other platforms](../advanced-topics/distributed-builds.md) by forwarding build requests to other machines.
-    single output path, denoted as `out`. However, derivations can
-    produce multiple output paths. This is useful because it allows
-    outputs to be downloaded or garbage-collected separately. For
-    instance, imagine a library package that provides a dynamic library,
-    header files, and documentation. A program that links against the
-    library doesn’t need the header files and documentation at runtime,
-    and it doesn’t need the documentation at build time. Thus, the
-    library package could specify:
 
-    ```nix
+  [`system` configuration option]: @docroot@/command-ref/conf-file.md#conf-system
-    outputs = [ "lib" "headers" "doc" ];
-    ```
 
-    This will cause Nix to pass environment variables `lib`, `headers`
+  > **Example**
-    and `doc` to the builder containing the intended store paths of each
+  >
-    output. The builder would typically do something like
+  > Declare a derivation to be built on a specific system type:
+  >
+  > ```nix
+  > derivation {
+  >   # ...
+  >   system = "x86_64-linux";
+  >   # ...
+  > }
+  > ```
 
-    ```bash
+  > **Example**
-    ./configure \
+  >
-      --libdir=$lib/lib \
+  > Declare a derivation to be built on the system type that evaluates the expression:
-      --includedir=$headers/include \
+  >
-      --docdir=$doc/share/doc
+  > ```nix
-    ```
+  > derivation {
+  >   # ...
+  >   system = builtins.currentSystem;
+  >   # ...
+  > }
+  > ```
+  >
+  > [`builtins.currentSystem`](@docroot@/language/builtin-constants.md#builtins-currentSystem) has the value of the [`system` configuration option], and defaults to the system type of the current Nix installation.
 
-    for an Autoconf-style package. You can refer to each output of a
+- [`builder`]{#attr-builder} ([Path](@docroot@/language/values.md#type-path) | [String](@docroot@/language/values.md#type-string))
-    derivation by selecting it as an attribute, e.g.
 
-    ```nix
+  Path to an executable that will perform the build.
-    buildInputs = [ pkg.lib pkg.headers ];
-    ```
 
-    The first element of `outputs` determines the *default output*.
+  > **Example**
-    Thus, you could also write
+  >
+  > Use the file located at `/bin/bash` as the builder executable:
+  >
+  > ```nix
+  > derivation {
+  >   # ...
+  >   builder = "/bin/bash";
+  >   # ...
+  > };
+  > ```
 
-    ```nix
+  <!-- -->
-    buildInputs = [ pkg pkg.headers ];
-    ```
 
-    since `pkg` is equivalent to `pkg.lib`.
+  > **Example**
+  >
+  > Copy a local file to the Nix store for use as the builder executable:
+  >
+  > ```nix
+  > derivation {
+  >   # ...
+  >   builder = ./builder.sh;
+  >   # ...
+  > };
+  > ```
 
-The function `mkDerivation` in the Nixpkgs standard environment is a
+  <!-- -->
-wrapper around `derivation` that adds a default value for `system` and
-always uses Bash as the builder, to which the supplied builder is passed
-as a command-line argument. See the Nixpkgs manual for details.
 
-The builder is executed as follows:
+  > **Example**
+  >
+  > Use a file from another derivation as the builder executable:
+  >
+  > ```nix
+  > let pkgs = import <nixpkgs> {}; in
+  > derivation {
+  >   # ...
+  >   builder = "${pkgs.python}/bin/python";
+  >   # ...
+  > };
+  > ```
 
-  - A temporary directory is created under the directory specified by
+### Optional
-    `TMPDIR` (default `/tmp`) where the build will take place. The
-    current directory is changed to this directory.
 
-  - The environment is cleared and set to the derivation attributes, as
+- [`args`]{#attr-args} ([List](@docroot@/language/values.md#list) of [String](@docroot@/language/values.md#type-string))
-    specified above.
 
-  - In addition, the following variables are set:
+  Default: `[ ]`
 
-      - `NIX_BUILD_TOP` contains the path of the temporary directory for
+  Command-line arguments to be passed to the [`builder`](#attr-builder) executable.
-        this build.
 
-      - Also, `TMPDIR`, `TEMPDIR`, `TMP`, `TEMP` are set to point to the
+  > **Example**
-        temporary directory. This is to prevent the builder from
+  >
-        accidentally writing temporary files anywhere else. Doing so
+  > Pass arguments to Bash to interpret a shell command:
-        might cause interference by other processes.
+  >
+  > ```nix
+  > derivation {
+  >   # ...
+  >   builder = "/bin/bash";
+  >   args = [ "-c" "echo hello world > $out" ];
+  >   # ...
+  > };
+  > ```
 
-      - `PATH` is set to `/path-not-set` to prevent shells from
+- [`outputs`]{#attr-outputs} ([List](@docroot@/language/values.md#list) of [String](@docroot@/language/values.md#type-string))
-        initialising it to their built-in default value.
 
-      - `HOME` is set to `/homeless-shelter` to prevent programs from
+  Default: `[ "out" ]`
-        using `/etc/passwd` or the like to find the user's home
-        directory, which could cause impurity. Usually, when `HOME` is
-        set, it is used as the location of the home directory, even if
-        it points to a non-existent path.
 
-      - `NIX_STORE` is set to the path of the top-level Nix store
+  Symbolic outputs of the derivation.
-        directory (typically, `/nix/store`).
+  Each output name is passed to the [`builder`](#attr-builder) executable as an environment variable with its value set to the corresponding [store path].
 
-      - For each output declared in `outputs`, the corresponding
+  By default, a derivation produces a single output called `out`.
-        environment variable is set to point to the intended path in the
+  However, derivations can produce multiple outputs.
-        Nix store for that output. Each output path is a concatenation
+  This allows the associated [store objects](@docroot@/glossary.md#gloss-store-object) and their [closures](@docroot@/glossary.md#gloss-closure) to be copied or garbage-collected separately.
-        of the cryptographic hash of all build inputs, the `name`
-        attribute and the output name. (The output name is omitted if
-        it’s `out`.)
 
-  - If an output path already exists, it is removed. Also, locks are
+  > **Example**
-    acquired to prevent multiple Nix instances from performing the same
+  >
-    build at the same time.
+  > Imagine a library package that provides a dynamic library, header files, and documentation.
+  > A program that links against such a library doesn’t need the header files and documentation at runtime, and it doesn’t need the documentation at build time.
+  > Thus, the library package could specify:
+  >
+  > ```nix
+  > derivation {
+  >   # ...
+  >   outputs = [ "lib" "dev" "doc" ];
+  >   # ...
+  > }
+  > ```
+  >
+  > This will cause Nix to pass environment variables `lib`, `dev`, and `doc` to the builder containing the intended store paths of each output.
+  > The builder would typically do something like
+  >
+  > ```bash
+  > ./configure \
+  >   --libdir=$lib/lib \
+  >   --includedir=$dev/include \
+  >   --docdir=$doc/share/doc
+  > ```
+  >
+  > for an Autoconf-style package.
 
-  - A log of the combined standard output and error is written to
+  The name of an output is combined with the name of the derivation to create the name part of the output's store path, unless it is `out`, in which case just the name of the derivation is used.
-    `/nix/var/log/nix`.
 
-  - The builder is executed with the arguments specified by the
+  > **Example**
-    attribute `args`. If it exits with exit code 0, it is considered to
+  >
-    have succeeded.
+  >
+  > ```nix
+  > derivation {
+  >   name = "example";
+  >   outputs = [ "lib" "dev" "doc" "out" ];
+  >   # ...
+  > }
+  > ```
+  >
+  > The store derivation path will be `/nix/store/<hash>-example.drv`.
+  > The output paths will be
+  > - `/nix/store/<hash>-example-lib`
+  > - `/nix/store/<hash>-example-dev`
+  > - `/nix/store/<hash>-example-doc`
+  > - `/nix/store/<hash>-example`
 
-  - The temporary directory is removed (unless the `-K` option was
+  You can refer to each output of a derivation by selecting it as an attribute.
-    specified).
+  The first element of `outputs` determines the *default output* and ends up at the top-level.
 
-  - If the build was successful, Nix scans each output path for
+  > **Example**
-    references to input paths by looking for the hash parts of the input
+  >
-    paths. Since these are potential runtime dependencies, Nix registers
+  > Select an output by attribute name:
-    them as dependencies of the output paths.
+  >
+  > ```nix
+  > let
+  >   myPackage = derivation {
+  >     name = "example";
+  >     outputs = [ "lib" "dev" "doc" "out" ];
+  >     # ...
+  >   };
+  > in myPackage.dev
+  > ```
+  >
+  > Since `lib` is the first output, `myPackage` is equivalent to `myPackage.lib`.
 
-  - After the build, Nix sets the last-modified timestamp on all files
+  <!-- FIXME: refer to the output attributes when we have one -->
-    in the build result to 1 (00:00:01 1/1/1970 UTC), sets the group to
+
-    the default group, and sets the mode of the file to 0444 or 0555
+- See [Advanced Attributes](./advanced-attributes.md) for more, infrequently used, optional attributes.
-    (i.e., read-only, with execute permission enabled if the file was
+
-    originally executable). Note that possible `setuid` and `setgid`
+  <!-- FIXME: This should be moved here -->
-    bits are cleared. Setuid and setgid programs are not currently
+
-    supported by Nix. This is because the Nix archives used in
+- Every other attribute is passed as an environment variable to the builder.
-    deployment have no concept of ownership information, and because it
+  Attribute values are translated to environment variables as follows:
-    makes the build result dependent on the user performing the build.
+
+    - Strings are passed unchanged.
+
+    - Integral numbers are converted to decimal notation.
+
+    - Floating point numbers are converted to simple decimal or scientific notation with a preset precision.
+
+    - A *path* (e.g., `../foo/sources.tar`) causes the referenced file
+      to be copied to the store; its location in the store is put in
+      the environment variable. The idea is that all sources should
+      reside in the Nix store, since all inputs to a derivation should
+      reside in the Nix store.
+
+    - A *derivation* causes that derivation to be built prior to the
+      present derivation. The environment variable is set to the [store path] of the derivation's default [output](#attr-outputs).
+
+    - Lists of the previous types are also allowed. They are simply
+      concatenated, separated by spaces.
+
+    - `true` is passed as the string `1`, `false` and `null` are
+      passed as an empty string.
+
+<!-- FIXME: add a section on output attributes -->
+
+## Builder execution
+
+The [`builder`](#attr-builder) is executed as follows:
+
+- A temporary directory is created under the directory specified by
+  `TMPDIR` (default `/tmp`) where the build will take place. The
+  current directory is changed to this directory.
+
+- The environment is cleared and set to the derivation attributes, as
+  specified above.
+
+- In addition, the following variables are set:
+
+  - `NIX_BUILD_TOP` contains the path of the temporary directory for
+    this build.
+
+  - Also, `TMPDIR`, `TEMPDIR`, `TMP`, `TEMP` are set to point to the
+    temporary directory. This is to prevent the builder from
+    accidentally writing temporary files anywhere else. Doing so
+    might cause interference by other processes.
+
+  - `PATH` is set to `/path-not-set` to prevent shells from
+    initialising it to their built-in default value.
+
+  - `HOME` is set to `/homeless-shelter` to prevent programs from
+    using `/etc/passwd` or the like to find the user's home
+    directory, which could cause impurity. Usually, when `HOME` is
+    set, it is used as the location of the home directory, even if
+    it points to a non-existent path.
+
+  - `NIX_STORE` is set to the path of the top-level Nix store
+    directory (typically, `/nix/store`).
+
+  - `NIX_ATTRS_JSON_FILE` & `NIX_ATTRS_SH_FILE` if `__structuredAttrs`
+    is set to `true` for the derivation. A detailed explanation of this
+    behavior can be found in the
+    [section about structured attrs](./advanced-attributes.md#adv-attr-structuredAttrs).
+
+  - For each output declared in `outputs`, the corresponding
+    environment variable is set to point to the intended path in the
+    Nix store for that output. Each output path is a concatenation
+    of the cryptographic hash of all build inputs, the `name`
+    attribute and the output name. (The output name is omitted if
+    it’s `out`.)
+
+- If an output path already exists, it is removed. Also, locks are
+  acquired to prevent multiple Nix instances from performing the same
+  build at the same time.
+
+- A log of the combined standard output and error is written to
+  `/nix/var/log/nix`.
+
+- The builder is executed with the arguments specified by the
+  attribute `args`. If it exits with exit code 0, it is considered to
+  have succeeded.
+
+- The temporary directory is removed (unless the `-K` option was
+  specified).
+
+- If the build was successful, Nix scans each output path for
+  references to input paths by looking for the hash parts of the input
+  paths. Since these are potential runtime dependencies, Nix registers
+  them as dependencies of the output paths.
+
+- After the build, Nix sets the last-modified timestamp on all files
+  in the build result to 1 (00:00:01 1/1/1970 UTC), sets the group to
+  the default group, and sets the mode of the file to 0444 or 0555
+  (i.e., read-only, with execute permission enabled if the file was
+  originally executable). Note that possible `setuid` and `setgid`
+  bits are cleared. Setuid and setgid programs are not currently
+  supported by Nix. This is because the Nix archives used in
+  deployment have no concept of ownership information, and because it
+  makes the build result dependent on the user performing the build.

doc/manual/src/language/import-from-derivation.md

@@ -0,0 +1,139 @@
+# Import From Derivation
+
+The value of a Nix expression can depend on the contents of a [store object](@docroot@/glossary.md#gloss-store-object).
+
+Passing an expression `expr` that evaluates to a [store path](@docroot@/glossary.md#gloss-store-path) to any built-in function which reads from the filesystem constitutes Import From Derivation (IFD):
+
+- [`import`](./builtins.md#builtins-import)` expr`
+- [`builtins.readFile`](./builtins.md#builtins-readFile)` expr`
+- [`builtins.readFileType`](./builtins.md#builtins-readFileType)` expr`
+- [`builtins.readDir`](./builtins.md#builtins-readDir)` expr`
+- [`builtins.pathExists`](./builtins.md#builtins-pathExists)` expr`
+- [`builtins.filterSource`](./builtins.md#builtins-filterSource)` f expr`
+- [`builtins.path`](./builtins.md#builtins-path)` { path = expr; }`
+- [`builtins.hashFile`](./builtins.md#builtins-hashFile)` t expr`
+- `builtins.scopedImport x drv`
+
+When the store path needs to be accessed, evaluation will be paused, the corresponding store object [realised], and then evaluation resumed.
+
+[realised]: @docroot@/glossary.md#gloss-realise
+
+This has performance implications:
+Evaluation can only finish when all required store objects are realised.
+Since the Nix language evaluator is sequential, it only finds store paths to read from one at a time.
+While realisation is always parallel, in this case it cannot be done for all required store paths at once, and is therefore much slower than otherwise.
+
+Realising store objects during evaluation can be disabled by setting [`allow-import-from-derivation`](../command-ref/conf-file.md#conf-allow-import-from-derivation) to `false`.
+Without IFD it is ensured that evaluation is complete and Nix can produce a build plan before starting any realisation.
+
+## Example
+
+In the following Nix expression, the inner derivation `drv` produces a file with contents `hello`.
+
+```nix
+# IFD.nix
+let
+  drv = derivation {
+    name = "hello";
+    builder = "/bin/sh";
+    args = [ "-c" "echo -n hello > $out" ];
+    system = builtins.currentSystem;
+  };
+in "${builtins.readFile drv} world"
+```
+
+```shellSession
+nix-instantiate IFD.nix --eval --read-write-mode
+```
+
+```
+building '/nix/store/348q1cal6sdgfxs8zqi9v8llrsn4kqkq-hello.drv'...
+"hello world"
+```
+
+The contents of the derivation's output have to be [realised] before they can be read with [`readFile`](./builtins.md#builtins-readFile).
+Only then evaluation can continue to produce the final result.
+
+## Illustration
+
+As a first approximation, the following data flow graph shows how evaluation and building are interleaved, if the value of a Nix expression depends on realising a [store object].
+Boxes are data structures, arrow labels are transformations.
+
+```
++----------------------+             +------------------------+
+| Nix evaluator        |             | Nix store              |
+|  .----------------.  |             |                        |
+|  | Nix expression |  |             |                        |
+|  '----------------'  |             |                        |
+|          |           |             |                        |
+|       evaluate       |             |                        |
+|          |           |             |                        |
+|          V           |             |                        |
+|    .------------.    |             |  .------------------.  |
+|    | derivation |----|-instantiate-|->| store derivation |  |
+|    '------------'    |             |  '------------------'  |
+|                      |             |           |            |
+|                      |             |        realise         |
+|                      |             |           |            |
+|                      |             |           V            |
+|  .----------------.  |             |    .--------------.    |
+|  | Nix expression |<-|----read-----|----| store object |    |
+|  '----------------'  |             |    '--------------'    |
+|          |           |             |                        |
+|       evaluate       |             |                        |
+|          |           |             |                        |
+|          V           |             |                        |
+|    .------------.    |             |                        |
+|    |   value    |    |             |                        |
+|    '------------'    |             |                        |
++----------------------+             +------------------------+
+```
+
+In more detail, the following sequence diagram shows how the expression is evaluated step by step, and where evaluation is blocked to wait for the build output to appear.
+
+```
+.-------.     .-------------.                        .---------.
+|Nix CLI|     |Nix evaluator|                        |Nix store|
+'-------'     '-------------'                        '---------'
+    |                |                                    |
+    |evaluate IFD.nix|                                    |
+    |--------------->|                                    |
+    |                |                                    |
+    |  evaluate `"${readFile drv} world"`                 |
+    |                |                                    |
+    |    evaluate `readFile drv`                          |
+    |                |                                    |
+    |   evaluate `drv` as string                          |
+    |                |                                    |
+    |                |instantiate /nix/store/...-hello.drv|
+    |                |----------------------------------->|
+    |                :                                    |
+    |                :  realise /nix/store/...-hello.drv  |
+    |                :----------------------------------->|
+    |                :                                    |
+    |                                                     |--------.
+    |                :                                    |        |
+    |      (evaluation blocked)                           |  echo hello > $out
+    |                :                                    |        |
+    |                                                     |<-------'
+    |                :        /nix/store/...-hello        |
+    |                |<-----------------------------------|
+    |                |                                    |
+    |  resume `readFile /nix/store/...-hello`             |
+    |                |                                    |
+    |                |   readFile /nix/store/...-hello    |
+    |                |----------------------------------->|
+    |                |                                    |
+    |                |               hello                |
+    |                |<-----------------------------------|
+    |                |                                    |
+    |      resume `"${"hello"} world"`                    |
+    |                |                                    |
+    |        resume `"hello world"`                       |
+    |                |                                    |
+    | "hello world"  |                                    |
+    |<---------------|                                    |
+.-------.     .-------------.                        .---------.
+|Nix CLI|     |Nix evaluator|                        |Nix store|
+'-------'     '-------------'                        '---------'
+```

doc/manual/src/language/index.md

@@ -83,7 +83,8 @@ This is an incomplete overview of language features, by example.
   </td>
   <td>
 
-   A multi-line string. Strips common prefixed whitespace. Evaluates to `"multi\n line\n  string"`.
+   <!-- FIXME: using two no-break spaces, because apparently mdBook swallows the second regular space! -->
+   A multi-line string. Strips common prefixed whitespace. Evaluates to `"multi\n line\n  string"`.
 
   </td>
  </tr>

doc/manual/src/language/operators.md

@@ -25,7 +25,7 @@
 | Inequality                             | *expr* `!=` *expr*                         | none          | 11         |
 | Logical conjunction (`AND`)            | *bool* `&&` *bool*                         | left          | 12         |
 | Logical disjunction (`OR`)             | *bool* <code>\|\|</code> *bool*            | left          | 13         |
-| [Logical implication]                  | *bool* `->` *bool*                         | none          | 14         |
+| [Logical implication]                  | *bool* `->` *bool*                         | right         | 14         |
 
 [string]: ./values.md#type-string
 [path]: ./values.md#type-path
@@ -35,6 +35,8 @@
 
 ## Attribute selection
 
+> **Syntax**
+>
 > *attrset* `.` *attrpath* \[ `or` *expr* \]
 
 Select the attribute denoted by attribute path *attrpath* from [attribute set] *attrset*.
@@ -42,21 +44,29 @@ If the attribute doesn’t exist, return the *expr* after `or` if provided, othe
 
 An attribute path is a dot-separated list of [attribute names](./values.md#attribute-set).
 
+> **Syntax**
+>
 > *attrpath* = *name* [ `.` *name* ]...
 
 [Attribute selection]: #attribute-selection
 
 ## Has attribute
 
+> **Syntax**
+>
 > *attrset* `?` *attrpath*
 
 Test whether [attribute set] *attrset* contains the attribute denoted by *attrpath*.
 The result is a [Boolean] value.
 
+See also: [`builtins.hasAttr`](@docroot@/language/builtins.md#builtins-hasAttr)
+
 [Boolean]: ./values.md#type-boolean
 
 [Has attribute]: #has-attribute
 
+After evaluating *attrset* and *attrpath*, the computational complexity is O(log(*n*)) for *n* attributes in the *attrset*
+
 ## Arithmetic
 
 Numbers are type-compatible:
@@ -70,6 +80,8 @@ The `+` operator is overloaded to also work on strings and paths.
 
 ## String concatenation
 
+> **Syntax**
+>
 > *string* `+` *string*
 
 Concatenate two [string]s and merge their string contexts.
@@ -78,6 +90,8 @@ Concatenate two [string]s and merge their string contexts.
 
 ## Path concatenation
 
+> **Syntax**
+>
 > *path* `+` *path*
 
 Concatenate two [path]s.
@@ -87,6 +101,8 @@ The result is a path.
 
 ## Path and string concatenation
 
+> **Syntax**
+>
 > *path* + *string*
 
 Concatenate *[path]* with *[string]*.
@@ -100,6 +116,8 @@ The result is a path.
 
 ## String and path concatenation
 
+> **Syntax**
+>
 > *string* + *path*
 
 Concatenate *[string]* with *[path]*.
@@ -117,6 +135,8 @@ The result is a string.
 
 ## Update
 
+> **Syntax**
+>
 > *attrset1* // *attrset2*
 
 Update [attribute set] *attrset1* with names and values from *attrset2*.

doc/manual/src/language/string-interpolation.md

@@ -1,19 +1,12 @@
 # String interpolation
 
-String interpolation is a language feature where a [string], [path], or [attribute name] can contain expressions enclosed in `${ }` (dollar-sign with curly brackets).
+String interpolation is a language feature where a [string], [path], or [attribute name][attribute set] can contain expressions enclosed in `${ }` (dollar-sign with curly brackets).
 
-Such a string is an *interpolated string*, and an expression inside is an *interpolated expression*.
+Such a construct is called *interpolated string*, and the expression inside is an [interpolated expression](#interpolated-expression).
-
-Interpolated expressions must evaluate to one of the following:
-
-- a [string]
-- a [path]
-- a [derivation]
 
 [string]: ./values.md#type-string
 [path]: ./values.md#type-path
-[attribute name]: ./values.md#attribute-set
+[attribute set]: ./values.md#attribute-set
-[derivation]: ../glossary.md#gloss-derivation
 
 ## Examples
 
@@ -70,13 +63,136 @@ you can instead write
 
 ### Attribute name
 
-Attribute names can be created dynamically with string interpolation:
+<!--
+FIXME: these examples are redundant with the main page on attribute sets.
+figure out what to do about that
+-->
 
-```nix
+Attribute names can be interpolated strings.
-let name = "foo"; in
-{
-  ${name} = "bar";
-}
-```
 
-    { foo = "bar"; }
+> **Example**
+>
+> ```nix
+> let name = "foo"; in
+> { ${name} = 123; }
+> ```
+>
+>     { foo = 123; }
+
+Attributes can be selected with interpolated strings.
+
+> **Example**
+>
+> ```nix
+> let name = "foo"; in
+> { foo = 123; }.${name}
+> ```
+>
+>     123
+
+# Interpolated expression
+
+An expression that is interpolated must evaluate to one of the following:
+
+- a [string]
+- a [path]
+- an [attribute set] that has a `__toString` attribute or an `outPath` attribute
+
+  - `__toString` must be a function that takes the attribute set itself and returns a string
+  - `outPath` must be a string
+
+  This includes [derivations](./derivations.md) or [flake inputs](@docroot@/command-ref/new-cli/nix3-flake.md#flake-inputs) (experimental).
+
+A string interpolates to itself.
+
+A path in an interpolated expression is first copied into the Nix store, and the resulting string is the [store path] of the newly created [store object](../glossary.md#gloss-store-object).
+
+[store path]: ../glossary.md#gloss-store-path
+
+> **Example**
+>
+> ```console
+> $ mkdir foo
+> ```
+>
+> Reference the empty directory in an interpolated expression:
+>
+> ```nix
+> "${./foo}"
+> ```
+>
+>     "/nix/store/2hhl2nz5v0khbn06ys82nrk99aa1xxdw-foo"
+
+A derivation interpolates to the [store path] of its first [output](./derivations.md#attr-outputs).
+
+> **Example**
+>
+> ```nix
+> let
+>   pkgs = import <nixpkgs> {};
+> in
+> "${pkgs.hello}"
+> ```
+>
+>     "/nix/store/4xpfqf29z4m8vbhrqcz064wfmb46w5r7-hello-2.12.1"
+
+An attribute set interpolates to the return value of the function in the `__toString` applied to the attribute set itself.
+
+> **Example**
+>
+> ```nix
+> let
+>   a = {
+>     value = 1;
+>     __toString = self: toString (self.value + 1);
+>   };
+> in
+> "${a}"
+> ```
+>
+>     "2"
+
+An attribute set also interpolates to the value of its `outPath` attribute.
+
+> **Example**
+>
+> ```nix
+> let
+>   a = { outPath = "foo"; };
+> in
+> "${a}"
+> ```
+>
+>     "foo"
+
+If both `__toString` and `outPath` are present in an attribute set, `__toString` takes precedence.
+
+> **Example**
+>
+> ```nix
+> let
+>   a = { __toString = _: "yes"; outPath = throw "no"; };
+> in
+> "${a}"
+> ```
+>
+>     "yes"
+
+If neither is present, an error is thrown.
+
+> **Example**
+>
+> ```nix
+> let
+>   a = {};
+> in
+> "${a}"
+> ```
+>
+>     error: cannot coerce a set to a string
+>
+>            at «string»:4:2:
+>
+>                 3| in
+>                 4| "${a}"
+>                  |  ^

doc/manual/src/language/values.md

@@ -107,29 +107,25 @@
   e.g. `~/foo` would be equivalent to `/home/edolstra/foo` for a user
   whose home directory is `/home/edolstra`.
 
-  Paths can also be specified between angle brackets, e.g.
-  `<nixpkgs>`. This means that the directories listed in the
-  environment variable `NIX_PATH` will be searched for the given file
-  or directory name.
-
-  When an [interpolated string][string interpolation] evaluates to a path, the path is first copied into the Nix store and the resulting string is the [store path] of the newly created [store object].
-
-  [store path]: ../glossary.md#gloss-store-path
-  [store object]: ../glossary.md#gloss-store-object
-
   For instance, evaluating `"${./foo.txt}"` will cause `foo.txt` in the current directory to be copied into the Nix store and result in the string `"/nix/store/<hash>-foo.txt"`.
 
   Note that the Nix language assumes that all input files will remain _unchanged_ while  evaluating a Nix expression.
   For example, assume you used a file path in an interpolated string during a `nix repl` session.
-  Later in the same session, after having changed the file contents, evaluating the interpolated string with the file path again might not return a new store path, since Nix might not re-read the file contents.
+  Later in the same session, after having changed the file contents, evaluating the interpolated string with the file path again might not return a new [store path], since Nix might not re-read the file contents.
 
-  Paths themselves, except those in angle brackets (`< >`), support [string interpolation].
+  [store path]: ../glossary.md#gloss-store-path
+
+  Paths can include [string interpolation] and can themselves be [interpolated in other expressions].
+
+  [interpolated in other expressions]: ./string-interpolation.md#interpolated-expressions
 
   At least one slash (`/`) must appear *before* any interpolated expression for the result to be recognized as a path.
 
   `a.${foo}/b.${bar}` is a syntactically valid division operation.
   `./a.${foo}/b.${bar}` is a path.
 
+  [Lookup paths](./constructs/lookup-path.md) such as `<nixpkgs>` resolve to path values.
+
 - <a id="type-boolean" href="#type-boolean">Boolean</a>
 
   *Booleans* with values `true` and `false`.
@@ -167,13 +163,17 @@ An attribute set is a collection of name-value-pairs (called *attributes*) enclo
 An attribute name can be an identifier or a [string](#string).
 An identifier must start with a letter (`a-z`, `A-Z`) or underscore (`_`), and can otherwise contain letters (`a-z`, `A-Z`), numbers (`0-9`), underscores (`_`), apostrophes (`'`), or dashes (`-`).
 
+> **Syntax**
+>
 > *name* = *identifier* | *string* \
 > *identifier* ~ `[a-zA-Z_][a-zA-Z0-9_'-]*`
 
 Names and values are separated by an equal sign (`=`).
 Each value is an arbitrary expression terminated by a semicolon (`;`).
 
-> *attrset* = `{` [ *name* `=` *expr* `;` `]`... `}`
+> **Syntax**
+>
+> *attrset* = `{` [ *name* `=` *expr* `;` ]... `}`
 
 Attributes can appear in any order.
 An attribute name may only occur once.

doc/manual/src/package-management/basic-package-mgmt.md

@@ -1,179 +0,0 @@
-# Basic Package Management
-
-The main command for package management is
-[`nix-env`](../command-ref/nix-env.md).  You can use it to install,
-upgrade, and erase packages, and to query what packages are installed
-or are available for installation.
-
-In Nix, different users can have different “views” on the set of
-installed applications. That is, there might be lots of applications
-present on the system (possibly in many different versions), but users
-can have a specific selection of those active — where “active” just
-means that it appears in a directory in the user’s `PATH`. Such a view
-on the set of installed applications is called a *user environment*,
-which is just a directory tree consisting of symlinks to the files of
-the active applications.
-
-Components are installed from a set of *Nix expressions* that tell Nix
-how to build those packages, including, if necessary, their
-dependencies. There is a collection of Nix expressions called the
-Nixpkgs package collection that contains packages ranging from basic
-development stuff such as GCC and Glibc, to end-user applications like
-Mozilla Firefox. (Nix is however not tied to the Nixpkgs package
-collection; you could write your own Nix expressions based on Nixpkgs,
-or completely new ones.)
-
-You can manually download the latest version of Nixpkgs from
-<https://github.com/NixOS/nixpkgs>. However, it’s much more
-convenient to use the Nixpkgs [*channel*](channels.md), since it makes
-it easy to stay up to date with new versions of Nixpkgs. Nixpkgs is
-automatically added to your list of “subscribed” channels when you
-install Nix. If this is not the case for some reason, you can add it
-as follows:
-
-```console
-$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
-$ nix-channel --update
-```
-
-> **Note**
-> 
-> On NixOS, you’re automatically subscribed to a NixOS channel
-> corresponding to your NixOS major release (e.g.
-> <http://nixos.org/channels/nixos-21.11>). A NixOS channel is identical
-> to the Nixpkgs channel, except that it contains only Linux binaries
-> and is updated only if a set of regression tests succeed.
-
-You can view the set of available packages in Nixpkgs:
-
-```console
-$ nix-env --query --available --attr-path
-nixpkgs.aterm                       aterm-2.2
-nixpkgs.bash                        bash-3.0
-nixpkgs.binutils                    binutils-2.15
-nixpkgs.bison                       bison-1.875d
-nixpkgs.blackdown                   blackdown-1.4.2
-nixpkgs.bzip2                       bzip2-1.0.2
-…
-```
-
-The flag `-q` specifies a query operation, `-a` means that you want
-to show the “available” (i.e., installable) packages, as opposed to the
-installed packages, and `-P` prints the attribute paths that can be used
-to unambiguously select a package for installation (listed in the first column).
-If you downloaded Nixpkgs yourself, or if you checked it out from GitHub,
-then you need to pass the path to your Nixpkgs tree using the `-f` flag:
-
-```console
-$ nix-env --query --available --attr-path --file /path/to/nixpkgs
-aterm                               aterm-2.2
-bash                                bash-3.0
-…
-```
-
-where */path/to/nixpkgs* is where you’ve unpacked or checked out
-Nixpkgs.
-
-You can filter the packages by name:
-
-```console
-$ nix-env --query --available --attr-path firefox
-nixpkgs.firefox-esr                 firefox-91.3.0esr
-nixpkgs.firefox                     firefox-94.0.1
-```
-
-and using regular expressions:
-
-```console
-$ nix-env --query --available --attr-path 'firefox.*'
-```
-
-It is also possible to see the *status* of available packages, i.e.,
-whether they are installed into the user environment and/or present in
-the system:
-
-```console
-$ nix-env --query --available --attr-path --status
-…
--PS  nixpkgs.bash                bash-3.0
---S  nixpkgs.binutils            binutils-2.15
-IPS  nixpkgs.bison               bison-1.875d
-…
-```
-
-The first character (`I`) indicates whether the package is installed in
-your current user environment. The second (`P`) indicates whether it is
-present on your system (in which case installing it into your user
-environment would be a very quick operation). The last one (`S`)
-indicates whether there is a so-called *substitute* for the package,
-which is Nix’s mechanism for doing binary deployment. It just means that
-Nix knows that it can fetch a pre-built package from somewhere
-(typically a network server) instead of building it locally.
-
-You can install a package using `nix-env --install --attr `. For instance,
-
-```console
-$ nix-env --install --attr nixpkgs.subversion
-```
-
-will install the package called `subversion` from `nixpkgs` channel (which is, of course, the
-[Subversion version management system](http://subversion.tigris.org/)).
-
-> **Note**
-> 
-> When you ask Nix to install a package, it will first try to get it in
-> pre-compiled form from a *binary cache*. By default, Nix will use the
-> binary cache <https://cache.nixos.org>; it contains binaries for most
-> packages in Nixpkgs. Only if no binary is available in the binary
-> cache, Nix will build the package from source. So if `nix-env
-> -iA nixpkgs.subversion` results in Nix building stuff from source, then either
-> the package is not built for your platform by the Nixpkgs build
-> servers, or your version of Nixpkgs is too old or too new. For
-> instance, if you have a very recent checkout of Nixpkgs, then the
-> Nixpkgs build servers may not have had a chance to build everything
-> and upload the resulting binaries to <https://cache.nixos.org>. The
-> Nixpkgs channel is only updated after all binaries have been uploaded
-> to the cache, so if you stick to the Nixpkgs channel (rather than
-> using a Git checkout of the Nixpkgs tree), you will get binaries for
-> most packages.
-
-Naturally, packages can also be uninstalled. Unlike when installing, you will
-need to use the derivation name (though the version part can be omitted),
-instead of the attribute path, as `nix-env` does not record which attribute
-was used for installing:
-
-```console
-$ nix-env --uninstall subversion
-```
-
-Upgrading to a new version is just as easy. If you have a new release of
-Nix Packages, you can do:
-
-```console
-$ nix-env --upgrade --attr nixpkgs.subversion
-```
-
-This will *only* upgrade Subversion if there is a “newer” version in the
-new set of Nix expressions, as defined by some pretty arbitrary rules
-regarding ordering of version numbers (which generally do what you’d
-expect of them). To just unconditionally replace Subversion with
-whatever version is in the Nix expressions, use `-i` instead of `-u`;
-`-i` will remove whatever version is already installed.
-
-You can also upgrade all packages for which there are newer versions:
-
-```console
-$ nix-env --upgrade
-```
-
-Sometimes it’s useful to be able to ask what `nix-env` would do, without
-actually doing it. For instance, to find out what packages would be
-upgraded by `nix-env --upgrade `, you can do
-
-```console
-$ nix-env --upgrade --dry-run
-(dry run; not doing anything)
-upgrading `libxslt-1.1.0' to `libxslt-1.1.10'
-upgrading `graphviz-1.10' to `graphviz-1.12'
-upgrading `coreutils-5.0' to `coreutils-5.2.1'
-```

doc/manual/src/package-management/channels.md

@@ -1,50 +0,0 @@
-# Channels
-
-If you want to stay up to date with a set of packages, it’s not very
-convenient to manually download the latest set of Nix expressions for
-those packages and upgrade using `nix-env`. Fortunately, there’s a
-better way: *Nix channels*.
-
-A Nix channel is just a URL that points to a place that contains a set
-of Nix expressions and a manifest. Using the command
-[`nix-channel`](../command-ref/nix-channel.md) you can automatically
-stay up to date with whatever is available at that URL.
-
-To see the list of official NixOS channels, visit
-<https://nixos.org/channels>.
-
-You can “subscribe” to a channel using `nix-channel --add`, e.g.,
-
-```console
-$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
-```
-
-subscribes you to a channel that always contains that latest version of
-the Nix Packages collection. (Subscribing really just means that the URL
-is added to the file `~/.nix-channels`, where it is read by subsequent
-calls to `nix-channel
---update`.) You can “unsubscribe” using `nix-channel
---remove`:
-
-```console
-$ nix-channel --remove nixpkgs
-```
-
-To obtain the latest Nix expressions available in a channel, do
-
-```console
-$ nix-channel --update
-```
-
-This downloads and unpacks the Nix expressions in every channel
-(downloaded from `url/nixexprs.tar.bz2`). It also makes the union of
-each channel’s Nix expressions available by default to `nix-env`
-operations (via the symlink `~/.nix-defexpr/channels`). Consequently,
-you can then say
-
-```console
-$ nix-env --upgrade
-```
-
-to upgrade all packages in your profile to the latest versions available
-in the subscribed channels.