Merge remote-tracking branch 'upstream/master' into overlayfs-store

.github/CODEOWNERS

@@ -14,4 +14,4 @@
 src/libexpr/primops.cc @roberth
 
 # Libstore layer
-/src/libstore @thufschmitt
+/src/libstore @thufschmitt @ericson2314

.github/workflows/backport.yml

@@ -21,7 +21,7 @@ jobs:
           fetch-depth: 0
       - name: Create backport PRs
         # should be kept in sync with `version`
-        uses: zeebe-io/backport-action@v2.4.1
+        uses: zeebe-io/backport-action@v2.5.0
         with:
           # Config README: https://github.com/zeebe-io/backport-action#backport-action
           github_token: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/ci.yml

@@ -159,3 +159,11 @@ jobs:
         # deprecated 2024-02-24
         docker tag nix:$NIX_VERSION $IMAGE_ID:master
         docker push $IMAGE_ID:master
+
+  vm_tests:
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - run: nix build -L .#hydraJobs.tests.githubFlakes .#hydraJobs.tests.tarballFlakes

.gitignore

@@ -49,6 +49,9 @@ perl/Makefile.config
 /src/libexpr/tests
 /tests/unit/libexpr/libnixexpr-tests
 
+# /src/libfetchers
+/tests/unit/libfetchers/libnixfetchers-tests
+
 # /src/libstore/
 *.gen.*
 /src/libstore/tests
@@ -142,6 +145,7 @@ GTAGS
 
 # auto-generated compilation database
 compile_commands.json
+*.compile_commands.json
 
 nix-rust/target
 

Makefile

@@ -18,6 +18,9 @@ makefiles = \
   src/libexpr/local.mk \
   src/libcmd/local.mk \
   src/nix/local.mk \
+  src/libutil-c/local.mk \
+  src/libstore-c/local.mk \
+  src/libexpr-c/local.mk \
   src/resolve-system-dependencies/local.mk \
   scripts/local.mk \
   misc/bash/local.mk \
@@ -34,6 +37,7 @@ makefiles += \
   tests/unit/libutil-support/local.mk \
   tests/unit/libstore/local.mk \
   tests/unit/libstore-support/local.mk \
+  tests/unit/libfetchers/local.mk \
   tests/unit/libexpr/local.mk \
   tests/unit/libexpr-support/local.mk
 endif
@@ -60,6 +64,10 @@ ifeq ($(ENABLE_INTERNAL_API_DOCS), yes)
 makefiles-late += doc/internal-api/local.mk
 endif
 
+ifeq ($(ENABLE_EXTERNAL_API_DOCS), yes)
+makefiles-late += doc/external-api/local.mk
+endif
+
 # Miscellaneous global Flags
 
 OPTIMIZE = 1
@@ -124,3 +132,10 @@ 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
+
+ifneq ($(ENABLE_EXTERNAL_API_DOCS), yes)
+.PHONY: external-api-html
+external-api-html:
+	@echo "External API docs are disabled. Configure with '--enable-external-api-docs', or avoid calling 'make external-api-html'."
+	@exit 1
+endif

Makefile.config.in

@@ -12,6 +12,7 @@ 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_EXTERNAL_API_DOCS = @ENABLE_EXTERNAL_API_DOCS@
 ENABLE_S3 = @ENABLE_S3@
 ENABLE_UNIT_TESTS = @ENABLE_UNIT_TESTS@
 GTEST_LIBS = @GTEST_LIBS@

configure.ac

@@ -150,6 +150,11 @@ AC_ARG_ENABLE(unit-tests, AS_HELP_STRING([--disable-unit-tests],[Do not build th
   ENABLE_UNIT_TESTS=$enableval, ENABLE_UNIT_TESTS=$ENABLE_BUILD)
 AC_SUBST(ENABLE_UNIT_TESTS)
 
+# Build external API docs by default
+AC_ARG_ENABLE(external_api_docs, AS_HELP_STRING([--enable-external-api-docs],[Build API docs for Nix's C interface]),
+  external_api_docs=$enableval, external_api_docs=yes)
+AC_SUBST(external_api_docs)
+
 AS_IF(
   [test "$ENABLE_BUILD" == "no" && test "$ENABLE_UNIT_TESTS" == "yes"],
   [AC_MSG_ERROR([Cannot enable unit tests when building overall is disabled. Please do not pass '--enable-unit-tests' or do not pass '--disable-build'.])])
@@ -172,6 +177,10 @@ AC_ARG_ENABLE(internal-api-docs, AS_HELP_STRING([--enable-internal-api-docs],[Bu
   ENABLE_INTERNAL_API_DOCS=$enableval, ENABLE_INTERNAL_API_DOCS=no)
 AC_SUBST(ENABLE_INTERNAL_API_DOCS)
 
+AC_ARG_ENABLE(external-api-docs, AS_HELP_STRING([--enable-external-api-docs],[Build API docs for Nix's external unstable C interfaces]),
+  ENABLE_EXTERNAL_API_DOCS=$enableval, ENABLE_EXTERNAL_API_DOCS=no)
+AC_SUBST(ENABLE_EXTERNAL_API_DOCS)
+
 AS_IF(
   [test "$ENABLE_FUNCTIONAL_TESTS" == "yes" || test "$ENABLE_DOC_GEN" == "yes"],
   [NEED_PROG(jq, jq)])

doc/external-api/.gitignore

@@ -0,0 +1,3 @@
+/doxygen.cfg
+/html
+/latex

doc/external-api/README.md

@@ -0,0 +1,108 @@
+# Getting started
+
+> **Warning** These bindings are **experimental**, which means they can change
+> at any time or be removed outright; nevertheless the plan is to provide a
+> stable external C API to the Nix language and the Nix store.
+
+The language library allows evaluating Nix expressions and interacting with Nix
+language values. The Nix store API is still rudimentary, and only allows
+initialising and connecting to a store for the Nix language evaluator to
+interact with.
+
+Currently there are two ways to interface with the Nix language evaluator
+programmatically:
+
+1. Embedding the evaluator
+2. Writing language plug-ins
+
+Embedding means you link the Nix C libraries in your program and use them from
+there. Adding a plug-in means you make a library that gets loaded by the Nix
+language evaluator, specified through a configuration option.
+
+Many of the components and mechanisms involved are not yet documented, therefore
+please refer to the [Nix source code](https://github.com/NixOS/nix/) for
+details. Additions to in-code documentation and the reference manual are highly
+appreciated.
+
+The following examples, for simplicity, don't include error handling. See the
+[Handling errors](@ref errors) section for more information.
+
+# Embedding the Nix Evaluator
+
+In this example we programmatically start the Nix language evaluator with a
+dummy store (that has no store paths and cannot be written to), and evaluate the
+Nix expression `builtins.nixVersion`.
+
+**main.c:**
+
+```C
+#include <nix_api_util.h>
+#include <nix_api_expr.h>
+#include <nix_api_value.h>
+#include <stdio.h>
+
+// NOTE: This example lacks all error handling. Production code must check for
+// errors, as some return values will be undefined.
+int main() {
+   nix_libexpr_init(NULL);
+
+   Store* store = nix_store_open(NULL, "dummy://", NULL);
+   EvalState* state = nix_state_create(NULL, NULL, store); // empty search path (NIX_PATH)
+   Value *value = nix_alloc_value(NULL, state);
+
+   nix_expr_eval_from_string(NULL, state, "builtins.nixVersion", ".", value);
+   nix_value_force(NULL, state, value);
+   printf("Nix version: %s\n", nix_get_string(NULL, value));
+
+   nix_gc_decref(NULL, value);
+   nix_state_free(state);
+   nix_store_free(store);
+   return 0;
+}
+```
+
+**Usage:**
+
+```ShellSession
+$ gcc main.c $(pkg-config nix-expr-c --libs --cflags) -o main
+$ ./main
+Nix version: 2.17
+```
+
+# Writing a Nix language plug-in
+
+In this example we add a custom primitive operation (_primop_) to `builtins`. It
+will increment the argument if it is an integer and throw an error otherwise.
+
+**plugin.c:**
+
+```C
+#include <nix_api_util.h>
+#include <nix_api_expr.h>
+#include <nix_api_value.h>
+
+void increment(void* user_data, nix_c_context* ctx, EvalState* state, Value** args, Value* v) {
+    nix_value_force(NULL, state, args[0]);
+    if (nix_get_type(NULL, args[0]) == NIX_TYPE_INT) {
+      nix_init_int(NULL, v, nix_get_int(NULL, args[0]) + 1);
+    } else {
+      nix_set_err_msg(ctx, NIX_ERR_UNKNOWN, "First argument should be an integer.");
+    }
+}
+
+void nix_plugin_entry() {
+  const char* args[] = {"n", NULL};
+  PrimOp *p = nix_alloc_primop(NULL, increment, 1, "increment", args, "Example custom built-in function: increments an integer", NULL);
+  nix_register_primop(NULL, p);
+  nix_gc_decref(NULL, p);
+}
+```
+
+**Usage:**
+
+```ShellSession
+$ gcc plugin.c $(pkg-config nix-expr-c --libs --cflags) -shared -o plugin.so
+$ nix --plugin-files ./plugin.so repl
+nix-repl> builtins.increment 1
+2
+```

doc/external-api/doxygen.cfg.in

@@ -0,0 +1,57 @@
+# Doxyfile 1.9.5
+
+# The PROJECT_NAME tag is a single word (or a sequence of words surrounded by
+# double-quotes, unless you are using Doxywizard) that should identify the
+# project for which the documentation is generated. This name is used in the
+# title of most generated pages and in a few other places.
+# The default value is: My Project.
+
+PROJECT_NAME           = "Nix"
+
+# The PROJECT_NUMBER tag can be used to enter a project or revision number. This
+# could be handy for archiving the generated documentation or if some version
+# control system is used.
+
+PROJECT_NUMBER         = @PACKAGE_VERSION@
+
+# Using the PROJECT_BRIEF tag one can provide an optional one line description
+# for a project that appears at the top of each page and should give viewer a
+# quick idea about the purpose of the project. Keep the description short.
+
+PROJECT_BRIEF          = "Nix, the purely functional package manager: C API (experimental)"
+
+# If the GENERATE_LATEX tag is set to YES, doxygen will generate LaTeX output.
+# The default value is: YES.
+
+GENERATE_LATEX         = NO
+
+# The INPUT tag is used to specify the files and/or directories that contain
+# documented source files. You may enter file names like myfile.cpp or
+# directories like /usr/src/myproject. Separate the files or directories with
+# spaces. See also FILE_PATTERNS and EXTENSION_MAPPING
+# Note: If this tag is empty the current directory is searched.
+
+# FIXME Make this list more maintainable somehow. We could maybe generate this
+# in the Makefile, but we would need to change how `.in` files are preprocessed
+# so they can expand variables despite configure variables.
+
+INPUT                  = \
+  src/libutil-c \
+  src/libexpr-c \
+  src/libstore-c \
+  doc/external-api/README.md
+
+FILE_PATTERNS = nix_api_*.h *.md
+
+# 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
+# RECURSIVE has no effect here.
+# This tag requires that the tag SEARCH_INCLUDES is set to YES.
+
+INCLUDE_PATH           = @RAPIDCHECK_HEADERS@
+EXCLUDE_PATTERNS = *_internal.h
+GENERATE_TREEVIEW = YES
+OPTIMIZE_OUTPUT_FOR_C  = YES
+
+USE_MDFILE_AS_MAINPAGE = doc/external-api/README.md

doc/external-api/local.mk

@@ -0,0 +1,7 @@
+$(docdir)/external-api/html/index.html $(docdir)/external-api/latex: $(d)/doxygen.cfg
+	mkdir -p $(docdir)/external-api
+	{ cat $< ; echo "OUTPUT_DIRECTORY=$(docdir)/external-api" ; } | doxygen -
+
+# Generate the HTML API docs for Nix's unstable C bindings
+.PHONY: external-api-html
+external-api-html: $(docdir)/external-api/html/index.html

doc/manual/custom.css

@@ -1,3 +1,25 @@
+:root {
+    --sidebar-width: 23em;
+}
+
+h1.menu-title::before {
+  content: "";
+  background-image: url("./favicon.svg");
+  padding: 1.25em;
+  background-position: center center;
+  background-size: 2em;
+  background-repeat: no-repeat;
+}
+
+
+h1.menu-title {
+  padding: 0.5em;
+}
+
+.sidebar .sidebar-scrollbox {
+  padding: 1em;
+}
+
 h1:not(:first-of-type) {
     margin-top: 1.3em;
 }

doc/manual/local.mk

@@ -175,6 +175,16 @@ $(d)/src/SUMMARY-rl-next.md: $(d)/src/release-notes/rl-next.md
 # Generate the HTML manual.
 .PHONY: manual-html
 manual-html: $(docdir)/manual/index.html
+
+# Open the built HTML manual in the default browser.
+manual-html-open: $(docdir)/manual/index.html
+	@echo "  OPEN  " $<; \
+	  xdg-open $< \
+		  || open $< \
+			|| { \
+		echo "Could not open the manual in a browser. Please open '$<'" >&2; \
+		false; \
+		}
 install: $(docdir)/manual/index.html
 
 # Generate 'nix' manpages.
@@ -207,7 +217,7 @@ doc/manual/generated/man1/nix3-manpages: $(d)/src/command-ref/new-cli
 # `@docroot@` is to be preserved for documenting the mechanism
 # FIXME: maybe contributing guides should live right next to the code
 # instead of in the manual
-$(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 $(d)/src/release-notes/rl-next.md
+$(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 $(d)/src/figures $(d)/src/favicon.png $(d)/src/favicon.svg
 	$(trace-gen) \
 		tmp="$$(mktemp -d)"; \
 		cp -r doc/manual "$$tmp"; \

doc/manual/rl-next/remove-repl-flake.md

@@ -0,0 +1,8 @@
+---
+synopsis: Remove experimental repl-flake
+significance: significant
+issues: 10103
+prs: 10299
+---
+
+The `repl-flake` experimental feature has been removed. The `nix repl` command now works like the rest of the new CLI in that `nix repl {path}` now tries to load a flake at `{path}` (or fails if the `flakes` experimental feature isn't enabled).*

doc/manual/src/SUMMARY.md.in

@@ -119,7 +119,7 @@
   - [Experimental Features](contributing/experimental-features.md)
   - [CLI guideline](contributing/cli-guideline.md)
   - [C++ style guide](contributing/cxx.md)
-- [Release Notes](release-notes/index.md)
+- [Releases](release-notes/index.md)
 {{#include ./SUMMARY-rl-next.md}}
   - [Release 2.21 (2024-03-11)](release-notes/rl-2.21.md)
   - [Release 2.20 (2024-01-29)](release-notes/rl-2.20.md)

doc/manual/src/contributing/documentation.md

@@ -27,11 +27,9 @@ 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
+make manual-html-open -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

doc/manual/src/contributing/hacking.md

@@ -258,10 +258,10 @@ 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 default check install
+make compile_commands.json
 ```
 
-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).
+Configure your editor to use the `clangd` from the `.#native-clangStdenvPackages` shell. You can do that 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).
 
 > **Note**
 >

doc/manual/src/favicon.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="587.11" height="516.604" viewBox="0 0 550.416 484.317"><defs><linearGradient id="a"><stop offset="0" style="stop-color:#699ad7;stop-opacity:1"/><stop offset=".243" style="stop-color:#7eb1dd;stop-opacity:1"/><stop offset="1" style="stop-color:#7ebae4;stop-opacity:1"/></linearGradient><linearGradient id="b"><stop offset="0" style="stop-color:#415e9a;stop-opacity:1"/><stop offset=".232" style="stop-color:#4a6baf;stop-opacity:1"/><stop offset="1" style="stop-color:#5277c3;stop-opacity:1"/></linearGradient><linearGradient xlink:href="#a" id="c" x1="200.597" x2="290.087" y1="351.411" y2="506.188" gradientTransform="translate(70.65 -1055.151)" gradientUnits="userSpaceOnUse"/><linearGradient xlink:href="#b" id="e" x1="-584.199" x2="-496.297" y1="782.336" y2="937.714" gradientTransform="translate(864.696 -1491.34)" gradientUnits="userSpaceOnUse"/></defs><g style="display:inline;opacity:1" transform="translate(-132.651 958.04)"><path id="d" d="m309.549-710.388 122.197 211.675-56.157.527-32.624-56.87-32.856 56.566-27.903-.011-14.29-24.69 46.81-80.49-33.23-57.826z" style="opacity:1;fill:url(#c);fill-opacity:1;fill-rule:evenodd;stroke:none;stroke-width:3;stroke-linecap:butt;stroke-linejoin:round;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1"/><use xlink:href="#d" width="100%" height="100%" transform="rotate(60 407.112 -715.787)"/><use xlink:href="#d" width="100%" height="100%" transform="rotate(-60 407.312 -715.7)"/><use xlink:href="#d" width="100%" height="100%" transform="rotate(180 407.419 -715.756)"/><path id="f" d="m309.549-710.388 122.197 211.675-56.157.527-32.624-56.87-32.856 56.566-27.903-.011-14.29-24.69 46.81-80.49-33.23-57.826z" style="color:#000;clip-rule:nonzero;display:inline;overflow:visible;visibility:visible;opacity:1;isolation:auto;mix-blend-mode:normal;color-interpolation:sRGB;color-interpolation-filters:linearRGB;solid-color:#000;solid-opacity:1;fill:url(#e);fill-opacity:1;fill-rule:evenodd;stroke:none;stroke-width:3;stroke-linecap:butt;stroke-linejoin:round;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1;color-rendering:auto;image-rendering:auto;shape-rendering:auto;text-rendering:auto;enable-background:accumulate"/><use xlink:href="#f" width="100%" height="100%" style="display:inline" transform="rotate(120 407.34 -716.084)"/><use xlink:href="#f" width="100%" height="100%" style="display:inline" transform="rotate(-120 407.288 -715.87)"/></g></svg>

doc/manual/src/installation/upgrading.md

@@ -28,7 +28,7 @@ $ sudo su
 ## macOS multi-user
 
 ```console
-$ sudo nix-env --install --file '<nixpkgs>' --attr nix -I nixpkgs=channel:nixpkgs-unstable
+$ sudo nix-env --install --file '<nixpkgs>' --attr nix cacert -I nixpkgs=channel:nixpkgs-unstable
 $ sudo launchctl remove org.nixos.nix-daemon
 $ sudo launchctl load /Library/LaunchDaemons/org.nixos.nix-daemon.plist
 ```

doc/manual/src/language/index.md

@@ -1,7 +1,13 @@
 # Nix Language
 
 The Nix language is designed for conveniently creating and composing *derivations* – precise descriptions of how contents of existing files are used to derive new files.
-It is:
+
+> **Tip**
+>
+> These pages are written as a reference.
+> If you are learning Nix, nix.dev has a good [introduction to the Nix language](https://nix.dev/tutorials/nix-language).
+
+The language is:
 
 - *domain-specific*
 

doc/manual/src/release-notes/index.md

@@ -1,12 +1,13 @@
 # Nix Release Notes
 
+The Nix release cycle is calendar-based as follows:
+
 Nix has a release cycle of roughly 6 weeks.
 Notable changes and additions are announced in the release notes for each version.
 
-Bugfixes can be backported on request to previous Nix releases.
-We typically backport only as far back as the Nix version used in the latest NixOS release, which is announced in the [NixOS release notes](https://nixos.org/manual/nixos/stable/release-notes.html#ch-release-notes).
-
-Backports never skip releases.
-If a feature is backported to version `x.y`, it must also be available in version `x.(y+1)`.
-This ensures that upgrading from an older version with backports is still safe and no backported functionality will go missing.
+The supported Nix versions are:
+- The latest release
+- The version used in the stable NixOS release, which is announced in the [NixOS release notes](https://nixos.org/manual/nixos/stable/release-notes.html#ch-release-notes).
 
+Bugfixes and security issues are backported to every supported version.
+Patch releases are published as needed.

flake.nix

@@ -285,6 +285,13 @@
           enableInternalAPIDocs = true;
         };
 
+        # API docs for Nix's C bindings.
+        external-api-docs = nixpkgsFor.x86_64-linux.native.callPackage ./package.nix {
+          inherit fileset;
+          doBuild = false;
+          enableExternalAPIDocs = true;
+        };
+
         # System tests.
         tests = import ./tests/nixos { inherit lib nixpkgs nixpkgsFor; } // {
 

local.mk

@@ -2,9 +2,14 @@ GLOBAL_CXXFLAGS += -Wno-deprecated-declarations -Werror=switch
 # Allow switch-enum to be overridden for files that do not support it, usually because of dependency headers.
 ERROR_SWITCH_ENUM = -Werror=switch-enum
 
-$(foreach i, config.h $(wildcard src/lib*/*.hh), \
+$(foreach i, config.h $(wildcard src/lib*/*.hh) $(wildcard src/lib*/*.h $(filter-out %_internal.h, $(wildcard src/lib*c/*.h))), \
   $(eval $(call install-file-in, $(i), $(includedir)/nix, 0644)))
 
+ifdef HOST_UNIX
+  $(foreach i, $(wildcard src/lib*/unix/*.hh), \
+    $(eval $(call install-file-in, $(i), $(includedir)/nix, 0644)))
+endif
+
 $(GCH): src/libutil/util.hh config.h
 
-GCH_CXXFLAGS = -I src/libutil
+GCH_CXXFLAGS = $(INCLUDE_libutil)

mk/compilation-database.mk

@@ -0,0 +1,11 @@
+compile-commands-json-files :=
+
+define write-compile-commands
+  _srcs := $$(sort $$(foreach src, $$($(1)_SOURCES), $$(src)))
+
+  $(1)_COMPILE_COMMANDS_JSON := $$(addprefix $(buildprefix), $$(addsuffix .compile_commands.json, $$(basename $$(_srcs))))
+
+  compile-commands-json-files += $$($(1)_COMPILE_COMMANDS_JSON)
+
+  clean-files += $$($(1)_COMPILE_COMMANDS_JSON)
+endef

mk/lib.mk

@@ -68,6 +68,7 @@ include mk/patterns.mk
 include mk/templates.mk
 include mk/cxx-big-literal.mk
 include mk/tests.mk
+include mk/compilation-database.mk
 
 
 # Include all sub-Makefiles.
@@ -97,6 +98,13 @@ $(foreach test-group, $(install-tests-groups), \
     $(eval $(call run-test,$(test),$(install_test_init))) \
     $(eval $(test-group).test-group: $(test).test)))
 
+# Compilation database.
+$(foreach lib, $(libraries), $(eval $(call write-compile-commands,$(lib))))
+$(foreach prog, $(programs), $(eval $(call write-compile-commands,$(prog))))
+
+compile_commands.json: $(compile-commands-json-files)
+	@jq --slurp '.' $^ >$@
+
 # Include makefiles requiring built programs.
 $(foreach mf, $(makefiles-late), $(eval $(call include-sub-makefile,$(mf))))
 

mk/patterns.mk

@@ -1,11 +1,41 @@
+
+# These are the complete command lines we use to compile C and C++ files.
+# - $< is the source file.
+# - $1 is the object file to create.
+CC_CMD=$(CC) -o $1 -c $< $(CPPFLAGS) $(GLOBAL_CFLAGS) $(CFLAGS) $($1_CFLAGS) -MMD -MF $(call filename-to-dep,$1) -MP
+CXX_CMD=$(CXX) -o $1 -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($1_CXXFLAGS) $(ERROR_SWITCH_ENUM) -MMD -MF $(call filename-to-dep,$1) -MP
+
+# We use COMPILE_COMMANDS_JSON_CMD to turn a compilation command (like CC_CMD
+# or CXX_CMD above) into a comple_commands.json file. We rely on bash native
+# word splitting to define the positional arguments.
+# - $< is the source file being compiled.
+COMPILE_COMMANDS_JSON_CMD=jq --null-input '{ directory: $$ENV.PWD, file: "$<", arguments: $$ARGS.positional }' --args --
+
+
 $(buildprefix)%.o: %.cc
 	@mkdir -p "$(dir $@)"
-	$(trace-cxx) $(CXX) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($@_CXXFLAGS) $(ERROR_SWITCH_ENUM) -MMD -MF $(call filename-to-dep, $@) -MP
+	$(trace-cxx) $(call CXX_CMD,$@)
 
 $(buildprefix)%.o: %.cpp
 	@mkdir -p "$(dir $@)"
-	$(trace-cxx) $(CXX) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($@_CXXFLAGS) $(ERROR_SWITCH_ENUM) -MMD -MF $(call filename-to-dep, $@) -MP
+	$(trace-cxx) $(call CXX_CMD,$@)
 
 $(buildprefix)%.o: %.c
 	@mkdir -p "$(dir $@)"
-	$(trace-cc) $(CC) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CFLAGS) $(CFLAGS) $($@_CFLAGS) -MMD -MF $(call filename-to-dep, $@) -MP
+	$(trace-cc) $(call CC_CMD,$@)
+
+# In the following we need to replace the .compile_commands.json extension in $@ with .o
+# to make the object file. This is needed because CC_CMD and CXX_CMD do further expansions
+# based on the object file name (i.e. *_CXXFLAGS and filename-to-dep).
+
+$(buildprefix)%.compile_commands.json: %.cc
+	@mkdir -p "$(dir $@)"
+	$(trace-jq) $(COMPILE_COMMANDS_JSON_CMD) $(call CXX_CMD,$(@:.compile_commands.json=.o)) > $@
+
+$(buildprefix)%.compile_commands.json: %.cpp
+	@mkdir -p "$(dir $@)"
+	$(trace-jq) $(COMPILE_COMMANDS_JSON_CMD) $(call CXX_CMD,$(@:.compile_commands.json=.o)) > $@
+
+$(buildprefix)%.compile_commands.json: %.c
+	@mkdir -p "$(dir $@)"
+	$(trace-jq) $(COMPILE_COMMANDS_JSON_CMD) $(call CC_CMD,$(@:.compile_commands.json=.o)) > $@

mk/tracing.mk

@@ -10,6 +10,8 @@ ifeq ($(V), 0)
   trace-install = @echo "  INST  " $@;
   trace-mkdir   = @echo "  MKDIR " $@;
   trace-test    = @echo "  TEST  " $@;
+  trace-sh      = @echo "  SH    " $@;
+  trace-jq      = @echo "  JQ    " $@;
 
   suppress  = @
 

package.nix

@@ -5,6 +5,7 @@
 , autoreconfHook
 , aws-sdk-cpp
 , boehmgc
+, buildPackages
 , nlohmann_json
 , bison
 , boost
@@ -75,7 +76,10 @@
 # sounds so long as evaluation just takes places within short-lived
 # processes. (When the process exits, the memory is reclaimed; it is
 # only leaked *within* the process.)
-, enableGC ? true
+#
+# Temporarily disabled on Windows because the `GC_throw_bad_alloc`
+# symbol is missing during linking.
+, enableGC ? !stdenv.hostPlatform.isWindows
 
 # Whether to enable Markdown rendering in the Nix binary.
 , enableMarkdown ? !stdenv.hostPlatform.isWindows
@@ -88,9 +92,10 @@
 # - readline
 , readlineFlavor ? if stdenv.hostPlatform.isWindows then "readline" else "editline"
 
-# Whether to build the internal API docs, can be done separately from
+# Whether to build the internal/external API docs, can be done separately from
 # everything else.
 , enableInternalAPIDocs ? false
+, enableExternalAPIDocs ? false
 
 # Whether to install unit tests. This is useful when cross compiling
 # since we cannot run them natively during the build, but can do so
@@ -179,6 +184,9 @@ in {
           ./doc/manual
         ] ++ lib.optionals enableInternalAPIDocs [
           ./doc/internal-api
+        ] ++ lib.optionals enableExternalAPIDocs [
+          ./doc/external-api
+        ] ++ lib.optionals (enableInternalAPIDocs || enableExternalAPIDocs) [
           # Source might not be compiled, but still must be available
           # for Doxygen to gather comments.
           ./src
@@ -196,7 +204,7 @@ in {
     ++ lib.optional doBuild "dev"
     # If we are doing just build or just docs, the one thing will use
     # "out". We only need additional outputs if we are doing both.
-    ++ lib.optional (doBuild && (enableManual || enableInternalAPIDocs)) "doc"
+    ++ lib.optional (doBuild && (enableManual || enableInternalAPIDocs || enableExternalAPIDocs)) "doc"
     ++ lib.optional installUnitTests "check";
 
   nativeBuildInputs = [
@@ -218,7 +226,7 @@ in {
   ] ++ lib.optionals (doInstallCheck || enableManual) [
     jq # Also for custom mdBook preprocessor.
   ] ++ lib.optional stdenv.hostPlatform.isLinux util-linux
-    ++ lib.optional enableInternalAPIDocs doxygen
+    ++ lib.optional (enableInternalAPIDocs || enableExternalAPIDocs) doxygen
   ;
 
   buildInputs = lib.optionals doBuild [
@@ -282,6 +290,7 @@ in {
     (lib.enableFeature buildUnitTests "unit-tests")
     (lib.enableFeature doInstallCheck "functional-tests")
     (lib.enableFeature enableInternalAPIDocs "internal-api-docs")
+    (lib.enableFeature enableExternalAPIDocs "external-api-docs")
     (lib.enableFeature enableManual "doc-gen")
     (lib.enableFeature enableGC "gc")
     (lib.enableFeature enableMarkdown "markdown")
@@ -306,7 +315,8 @@ in {
   makeFlags = "profiledir=$(out)/etc/profile.d PRECOMPILE_HEADERS=1";
 
   installTargets = lib.optional doBuild "install"
-    ++ lib.optional enableInternalAPIDocs "internal-api-html";
+    ++ lib.optional enableInternalAPIDocs "internal-api-html"
+    ++ lib.optional enableExternalAPIDocs "external-api-html";
 
   installFlags = "sysconfdir=$(out)/etc";
 
@@ -333,6 +343,16 @@ in {
   '' + lib.optionalString enableInternalAPIDocs ''
     mkdir -p ''${!outputDoc}/nix-support
     echo "doc internal-api-docs $out/share/doc/nix/internal-api/html" >> ''${!outputDoc}/nix-support/hydra-build-products
+  ''
+    + lib.optionalString enableExternalAPIDocs ''
+    mkdir -p ''${!outputDoc}/nix-support
+    echo "doc external-api-docs $out/share/doc/nix/external-api/html" >> ''${!outputDoc}/nix-support/hydra-build-products
+  '';
+
+  # So the check output gets links for DLLs in the out output.
+  preFixup = lib.optionalString (stdenv.hostPlatform.isWindows && builtins.elem "check" finalAttrs.outputs) ''
+    ln -s "$check/lib/"*.dll "$check/bin"
+    ln -s "$out/bin/"*.dll "$check/bin"
   '';
 
   doInstallCheck = attrs.doInstallCheck;

scripts/nix-profile-daemon.fish.in

@@ -28,7 +28,7 @@ else
 end
 
 # Set $NIX_SSL_CERT_FILE so that Nixpkgs applications like curl work.
-if test -n "$NIX_SSH_CERT_FILE"
+if test -n "$NIX_SSL_CERT_FILE"
   : # Allow users to override the NIX_SSL_CERT_FILE
 else if test -e /etc/ssl/certs/ca-certificates.crt # NixOS, Ubuntu, Debian, Gentoo, Arch
   set --export NIX_SSL_CERT_FILE /etc/ssl/certs/ca-certificates.crt
@@ -44,7 +44,7 @@ else if test -e "$NIX_LINK/etc/ca-bundle.crt" # old cacert in Nix profile
   set --export NIX_SSL_CERT_FILE "$NIX_LINK/etc/ca-bundle.crt"
 else
   # Fall back to what is in the nix profiles, favouring whatever is defined last.
-  for i in $NIX_PROFILES
+  for i in (string split ' ' $NIX_PROFILES)
     if test -e "$i/etc/ssl/certs/ca-bundle.crt"
       set --export NIX_SSL_CERT_FILE "$i/etc/ssl/certs/ca-bundle.crt"
     end

src/build-remote/build-remote.cc

@@ -202,7 +202,7 @@ static int main_build_remote(int argc, char * * argv)
                         else
                             drvstr = "<unknown>";
 
-                        auto error = HintFmt(errorText);
+                        auto error = HintFmt::fromFormatString(errorText);
                         error
                             % drvstr
                             % neededSystem

src/libcmd/local.mk

@@ -6,7 +6,7 @@ libcmd_DIR := $(d)
 
 libcmd_SOURCES := $(wildcard $(d)/*.cc)
 
-libcmd_CXXFLAGS += -I src/libutil -I src/libstore -I src/libexpr -I src/libmain -I src/libfetchers
+libcmd_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libexpr) $(INCLUDE_libmain)
 
 libcmd_LDFLAGS = $(EDITLINE_LIBS) $(LOWDOWN_LIBS) $(THREAD_LDFLAGS)
 

src/libcmd/markdown.cc

@@ -50,7 +50,7 @@ std::string renderMarkdownToTerminal(std::string_view markdown)
     if (!rndr_res)
         throw Error("allocation error while rendering Markdown");
 
-    return filterANSIEscapes(std::string(buf->data, buf->size), !shouldANSI());
+    return filterANSIEscapes(std::string(buf->data, buf->size), !isTTY());
 #else
     return std::string(markdown);
 #endif

src/libcmd/repl-interacter.cc

@@ -0,0 +1,186 @@
+#include <cstdio>
+
+#ifdef USE_READLINE
+#include <readline/history.h>
+#include <readline/readline.h>
+#else
+// editline < 1.15.2 don't wrap their API for C++ usage
+// (added in https://github.com/troglobit/editline/commit/91398ceb3427b730995357e9d120539fb9bb7461).
+// This results in linker errors due to to name-mangling of editline C symbols.
+// For compatibility with these versions, we wrap the API here
+// (wrapping multiple times on newer versions is no problem).
+extern "C" {
+#include <editline.h>
+}
+#endif
+
+#include "signals.hh"
+#include "finally.hh"
+#include "repl-interacter.hh"
+#include "file-system.hh"
+#include "libcmd/repl.hh"
+
+namespace nix {
+
+namespace {
+// Used to communicate to NixRepl::getLine whether a signal occurred in ::readline.
+volatile sig_atomic_t g_signal_received = 0;
+
+void sigintHandler(int signo)
+{
+    g_signal_received = signo;
+}
+};
+
+static detail::ReplCompleterMixin * curRepl; // ugly
+
+static char * completionCallback(char * s, int * match)
+{
+    auto possible = curRepl->completePrefix(s);
+    if (possible.size() == 1) {
+        *match = 1;
+        auto * res = strdup(possible.begin()->c_str() + strlen(s));
+        if (!res)
+            throw Error("allocation failure");
+        return res;
+    } else if (possible.size() > 1) {
+        auto checkAllHaveSameAt = [&](size_t pos) {
+            auto & first = *possible.begin();
+            for (auto & p : possible) {
+                if (p.size() <= pos || p[pos] != first[pos])
+                    return false;
+            }
+            return true;
+        };
+        size_t start = strlen(s);
+        size_t len = 0;
+        while (checkAllHaveSameAt(start + len))
+            ++len;
+        if (len > 0) {
+            *match = 1;
+            auto * res = strdup(std::string(*possible.begin(), start, len).c_str());
+            if (!res)
+                throw Error("allocation failure");
+            return res;
+        }
+    }
+
+    *match = 0;
+    return nullptr;
+}
+
+static int listPossibleCallback(char * s, char *** avp)
+{
+    auto possible = curRepl->completePrefix(s);
+
+    if (possible.size() > (INT_MAX / sizeof(char *)))
+        throw Error("too many completions");
+
+    int ac = 0;
+    char ** vp = nullptr;
+
+    auto check = [&](auto * p) {
+        if (!p) {
+            if (vp) {
+                while (--ac >= 0)
+                    free(vp[ac]);
+                free(vp);
+            }
+            throw Error("allocation failure");
+        }
+        return p;
+    };
+
+    vp = check((char **) malloc(possible.size() * sizeof(char *)));
+
+    for (auto & p : possible)
+        vp[ac++] = check(strdup(p.c_str()));
+
+    *avp = vp;
+
+    return ac;
+}
+
+ReadlineLikeInteracter::Guard ReadlineLikeInteracter::init(detail::ReplCompleterMixin * repl)
+{
+    // Allow nix-repl specific settings in .inputrc
+    rl_readline_name = "nix-repl";
+    try {
+        createDirs(dirOf(historyFile));
+    } catch (SystemError & e) {
+        logWarning(e.info());
+    }
+#ifndef USE_READLINE
+    el_hist_size = 1000;
+#endif
+    read_history(historyFile.c_str());
+    auto oldRepl = curRepl;
+    curRepl = repl;
+    Guard restoreRepl([oldRepl] { curRepl = oldRepl; });
+#ifndef USE_READLINE
+    rl_set_complete_func(completionCallback);
+    rl_set_list_possib_func(listPossibleCallback);
+#endif
+    return restoreRepl;
+}
+
+static constexpr const char * promptForType(ReplPromptType promptType)
+{
+    switch (promptType) {
+    case ReplPromptType::ReplPrompt:
+        return "nix-repl> ";
+    case ReplPromptType::ContinuationPrompt:
+        return "          ";
+    }
+    assert(false);
+}
+
+bool ReadlineLikeInteracter::getLine(std::string & input, ReplPromptType promptType)
+{
+    struct sigaction act, old;
+    sigset_t savedSignalMask, set;
+
+    auto setupSignals = [&]() {
+        act.sa_handler = sigintHandler;
+        sigfillset(&act.sa_mask);
+        act.sa_flags = 0;
+        if (sigaction(SIGINT, &act, &old))
+            throw SysError("installing handler for SIGINT");
+
+        sigemptyset(&set);
+        sigaddset(&set, SIGINT);
+        if (sigprocmask(SIG_UNBLOCK, &set, &savedSignalMask))
+            throw SysError("unblocking SIGINT");
+    };
+    auto restoreSignals = [&]() {
+        if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr))
+            throw SysError("restoring signals");
+
+        if (sigaction(SIGINT, &old, 0))
+            throw SysError("restoring handler for SIGINT");
+    };
+
+    setupSignals();
+    char * s = readline(promptForType(promptType));
+    Finally doFree([&]() { free(s); });
+    restoreSignals();
+
+    if (g_signal_received) {
+        g_signal_received = 0;
+        input.clear();
+        return true;
+    }
+
+    if (!s)
+        return false;
+    input += s;
+    input += '\n';
+    return true;
+}
+
+ReadlineLikeInteracter::~ReadlineLikeInteracter()
+{
+    write_history(historyFile.c_str());
+}
+
+};

src/libcmd/repl-interacter.hh

@@ -0,0 +1,48 @@
+#pragma once
+/// @file
+
+#include "finally.hh"
+#include "types.hh"
+#include <functional>
+#include <string>
+
+namespace nix {
+
+namespace detail {
+/** Provides the completion hooks for the repl, without exposing its complete
+ * internals. */
+struct ReplCompleterMixin {
+    virtual StringSet completePrefix(const std::string & prefix) = 0;
+};
+};
+
+enum class ReplPromptType {
+    ReplPrompt,
+    ContinuationPrompt,
+};
+
+class ReplInteracter
+{
+public:
+    using Guard = Finally<std::function<void()>>;
+
+    virtual Guard init(detail::ReplCompleterMixin * repl) = 0;
+    /** Returns a boolean of whether the interacter got EOF */
+    virtual bool getLine(std::string & input, ReplPromptType promptType) = 0;
+    virtual ~ReplInteracter(){};
+};
+
+class ReadlineLikeInteracter : public virtual ReplInteracter
+{
+    std::string historyFile;
+public:
+    ReadlineLikeInteracter(std::string historyFile)
+        : historyFile(historyFile)
+    {
+    }
+    virtual Guard init(detail::ReplCompleterMixin * repl) override;
+    virtual bool getLine(std::string & input, ReplPromptType promptType) override;
+    virtual ~ReadlineLikeInteracter() override;
+};
+
+};

src/libcmd/repl.cc

@@ -3,32 +3,17 @@
 #include <cstring>
 #include <climits>
 
-#include <setjmp.h>
-
-#ifdef USE_READLINE
-#include <readline/history.h>
-#include <readline/readline.h>
-#else
-// editline < 1.15.2 don't wrap their API for C++ usage
-// (added in https://github.com/troglobit/editline/commit/91398ceb3427b730995357e9d120539fb9bb7461).
-// This results in linker errors due to to name-mangling of editline C symbols.
-// For compatibility with these versions, we wrap the API here
-// (wrapping multiple times on newer versions is no problem).
-extern "C" {
-#include <editline.h>
-}
-#endif
-
+#include "libcmd/repl-interacter.hh"
 #include "repl.hh"
 
 #include "ansicolor.hh"
-#include "signals.hh"
 #include "shared.hh"
 #include "eval.hh"
 #include "eval-cache.hh"
 #include "eval-inline.hh"
 #include "eval-settings.hh"
 #include "attr-path.hh"
+#include "signals.hh"
 #include "store-api.hh"
 #include "log-store.hh"
 #include "common-eval-args.hh"
@@ -38,7 +23,6 @@ extern "C" {
 #include "flake/flake.hh"
 #include "flake/lockfile.hh"
 #include "users.hh"
-#include "terminal.hh"
 #include "editor-for.hh"
 #include "finally.hh"
 #include "markdown.hh"
@@ -75,6 +59,7 @@ enum class ProcessLineResult {
 
 struct NixRepl
     : AbstractNixRepl
+    , detail::ReplCompleterMixin
     #if HAVE_BOEHMGC
     , gc
     #endif
@@ -90,17 +75,16 @@ struct NixRepl
     int displ;
     StringSet varNames;
 
-    const Path historyFile;
+    std::unique_ptr<ReplInteracter> interacter;
 
     NixRepl(const SearchPath & searchPath, nix::ref<Store> store,ref<EvalState> state,
             std::function<AnnotatedValues()> getValues);
-    virtual ~NixRepl();
+    virtual ~NixRepl() = default;
 
     ReplExitStatus mainLoop() override;
     void initEnv() override;
 
-    StringSet completePrefix(const std::string & prefix);
-    bool getLine(std::string & input, const std::string & prompt);
+    virtual StringSet completePrefix(const std::string & prefix) override;
     StorePath getDerivationPath(Value & v);
     ProcessLineResult processLine(std::string line);
 
@@ -144,16 +128,10 @@ NixRepl::NixRepl(const SearchPath & searchPath, nix::ref<Store> store, ref<EvalS
     , debugTraceIndex(0)
     , getValues(getValues)
     , staticEnv(new StaticEnv(nullptr, state->staticBaseEnv.get()))
-    , historyFile(getDataDir() + "/nix/repl-history")
+    , interacter(make_unique<ReadlineLikeInteracter>(getDataDir() + "/nix/repl-history"))
 {
 }
 
-
-NixRepl::~NixRepl()
-{
-    write_history(historyFile.c_str());
-}
-
 void runNix(Path program, const Strings & args,
     const std::optional<std::string> & input = {})
 {
@@ -170,79 +148,6 @@ void runNix(Path program, const Strings & args,
     return;
 }
 
-static NixRepl * curRepl; // ugly
-
-static char * completionCallback(char * s, int *match) {
-  auto possible = curRepl->completePrefix(s);
-  if (possible.size() == 1) {
-    *match = 1;
-    auto *res = strdup(possible.begin()->c_str() + strlen(s));
-    if (!res) throw Error("allocation failure");
-    return res;
-  } else if (possible.size() > 1) {
-    auto checkAllHaveSameAt = [&](size_t pos) {
-      auto &first = *possible.begin();
-      for (auto &p : possible) {
-        if (p.size() <= pos || p[pos] != first[pos])
-          return false;
-      }
-      return true;
-    };
-    size_t start = strlen(s);
-    size_t len = 0;
-    while (checkAllHaveSameAt(start + len)) ++len;
-    if (len > 0) {
-      *match = 1;
-      auto *res = strdup(std::string(*possible.begin(), start, len).c_str());
-      if (!res) throw Error("allocation failure");
-      return res;
-    }
-  }
-
-  *match = 0;
-  return nullptr;
-}
-
-static int listPossibleCallback(char *s, char ***avp) {
-  auto possible = curRepl->completePrefix(s);
-
-  if (possible.size() > (INT_MAX / sizeof(char*)))
-    throw Error("too many completions");
-
-  int ac = 0;
-  char **vp = nullptr;
-
-  auto check = [&](auto *p) {
-    if (!p) {
-      if (vp) {
-        while (--ac >= 0)
-          free(vp[ac]);
-        free(vp);
-      }
-      throw Error("allocation failure");
-    }
-    return p;
-  };
-
-  vp = check((char **)malloc(possible.size() * sizeof(char*)));
-
-  for (auto & p : possible)
-    vp[ac++] = check(strdup(p.c_str()));
-
-  *avp = vp;
-
-  return ac;
-}
-
-namespace {
-    // Used to communicate to NixRepl::getLine whether a signal occurred in ::readline.
-    volatile sig_atomic_t g_signal_received = 0;
-
-    void sigintHandler(int signo) {
-        g_signal_received = signo;
-    }
-}
-
 static std::ostream & showDebugTrace(std::ostream & out, const PosTable & positions, const DebugTrace & dt)
 {
     if (dt.isError)
@@ -282,24 +187,7 @@ ReplExitStatus NixRepl::mainLoop()
 
     loadFiles();
 
-    // Allow nix-repl specific settings in .inputrc
-    rl_readline_name = "nix-repl";
-    try {
-        createDirs(dirOf(historyFile));
-    } catch (SystemError & e) {
-        logWarning(e.info());
-    }
-#ifndef USE_READLINE
-    el_hist_size = 1000;
-#endif
-    read_history(historyFile.c_str());
-    auto oldRepl = curRepl;
-    curRepl = this;
-    Finally restoreRepl([&] { curRepl = oldRepl; });
-#ifndef USE_READLINE
-    rl_set_complete_func(completionCallback);
-    rl_set_list_possib_func(listPossibleCallback);
-#endif
+    auto _guard = interacter->init(static_cast<detail::ReplCompleterMixin *>(this));
 
     std::string input;
 
@@ -308,7 +196,7 @@ ReplExitStatus NixRepl::mainLoop()
         logger->pause();
         // When continuing input from previous lines, don't print a prompt, just align to the same
         // number of chars as the prompt.
-        if (!getLine(input, input.empty() ? "nix-repl> " : "          ")) {
+        if (!interacter->getLine(input, input.empty() ? ReplPromptType::ReplPrompt : ReplPromptType::ContinuationPrompt)) {
             // Ctrl-D should exit the debugger.
             state->debugStop = false;
             logger->cout("");
@@ -351,51 +239,6 @@ ReplExitStatus NixRepl::mainLoop()
     }
 }
 
-
-bool NixRepl::getLine(std::string & input, const std::string & prompt)
-{
-    struct sigaction act, old;
-    sigset_t savedSignalMask, set;
-
-    auto setupSignals = [&]() {
-        act.sa_handler = sigintHandler;
-        sigfillset(&act.sa_mask);
-        act.sa_flags = 0;
-        if (sigaction(SIGINT, &act, &old))
-            throw SysError("installing handler for SIGINT");
-
-        sigemptyset(&set);
-        sigaddset(&set, SIGINT);
-        if (sigprocmask(SIG_UNBLOCK, &set, &savedSignalMask))
-            throw SysError("unblocking SIGINT");
-    };
-    auto restoreSignals = [&]() {
-        if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr))
-            throw SysError("restoring signals");
-
-        if (sigaction(SIGINT, &old, 0))
-            throw SysError("restoring handler for SIGINT");
-    };
-
-    setupSignals();
-    char * s = readline(prompt.c_str());
-    Finally doFree([&]() { free(s); });
-    restoreSignals();
-
-    if (g_signal_received) {
-        g_signal_received = 0;
-        input.clear();
-        return true;
-    }
-
-    if (!s)
-      return false;
-    input += s;
-    input += '\n';
-    return true;
-}
-
-
 StringSet NixRepl::completePrefix(const std::string & prefix)
 {
     StringSet completions;
@@ -514,7 +357,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
     if (line.empty())
         return ProcessLineResult::PromptAgain;
 
-    _isInterrupted = false;
+    setInterrupted(false);
 
     std::string command, arg;
 

src/libcmd/repl.hh

@@ -3,11 +3,6 @@
 
 #include "eval.hh"
 
-#if HAVE_BOEHMGC
-#define GC_INCLUDE_NEW
-#include <gc/gc_cpp.h>
-#endif
-
 namespace nix {
 
 struct AbstractNixRepl

src/libexpr-c/local.mk

@@ -0,0 +1,25 @@
+libraries += libexprc
+
+libexprc_NAME = libnixexprc
+
+libexprc_DIR := $(d)
+
+libexprc_SOURCES := \
+  $(wildcard $(d)/*.cc) \
+
+# Not just for this library itself, but also for downstream libraries using this library
+
+INCLUDE_libexprc := -I $(d)
+libexprc_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libutilc) \
+                     $(INCLUDE_libfetchers) \
+                     $(INCLUDE_libstore) $(INCLUDE_libstorec) \
+                     $(INCLUDE_libexpr) $(INCLUDE_libexprc)
+
+libexprc_LIBS = libutil libutilc libstore libstorec libexpr
+
+libexprc_LDFLAGS += $(THREAD_LDFLAGS)
+
+$(eval $(call install-file-in, $(d)/nix-expr-c.pc, $(libdir)/pkgconfig, 0644))
+
+libexprc_FORCE_INSTALL := 1
+

src/libexpr-c/nix-expr-c.pc.in

@@ -0,0 +1,10 @@
+prefix=@prefix@
+libdir=@libdir@
+includedir=@includedir@
+
+Name: Nix
+Description: Nix Language Evaluator - C API
+Version: @PACKAGE_VERSION@
+Requires: nix-store-c
+Libs: -L${libdir} -lnixexprc
+Cflags: -I${includedir}/nix

src/libexpr-c/nix_api_expr.cc

@@ -0,0 +1,178 @@
+#include <cstring>
+#include <iostream>
+#include <stdexcept>
+#include <string>
+
+#include "config.hh"
+#include "eval.hh"
+#include "globals.hh"
+#include "util.hh"
+
+#include "nix_api_expr.h"
+#include "nix_api_expr_internal.h"
+#include "nix_api_store.h"
+#include "nix_api_store_internal.h"
+#include "nix_api_util.h"
+#include "nix_api_util_internal.h"
+
+#ifdef HAVE_BOEHMGC
+#include <mutex>
+#define GC_INCLUDE_NEW 1
+#include "gc_cpp.h"
+#endif
+
+nix_err nix_libexpr_init(nix_c_context * context)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    {
+        auto ret = nix_libutil_init(context);
+        if (ret != NIX_OK)
+            return ret;
+    }
+    {
+        auto ret = nix_libstore_init(context);
+        if (ret != NIX_OK)
+            return ret;
+    }
+    try {
+        nix::initGC();
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_expr_eval_from_string(
+    nix_c_context * context, EvalState * state, const char * expr, const char * path, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        nix::Expr * parsedExpr = state->state.parseExprFromString(expr, state->state.rootPath(nix::CanonPath(path)));
+        state->state.eval(parsedExpr, *(nix::Value *) value);
+        state->state.forceValue(*(nix::Value *) value, nix::noPos);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_value_call(nix_c_context * context, EvalState * state, Value * fn, Value * arg, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        state->state.callFunction(*(nix::Value *) fn, *(nix::Value *) arg, *(nix::Value *) value, nix::noPos);
+        state->state.forceValue(*(nix::Value *) value, nix::noPos);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_value_force(nix_c_context * context, EvalState * state, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        state->state.forceValue(*(nix::Value *) value, nix::noPos);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        state->state.forceValueDeep(*(nix::Value *) value);
+    }
+    NIXC_CATCH_ERRS
+}
+
+EvalState * nix_state_create(nix_c_context * context, const char ** searchPath_c, Store * store)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        nix::Strings searchPath;
+        if (searchPath_c != nullptr)
+            for (size_t i = 0; searchPath_c[i] != nullptr; i++)
+                searchPath.push_back(searchPath_c[i]);
+
+        return new EvalState{nix::EvalState(nix::SearchPath::parse(searchPath), store->ptr)};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+void nix_state_free(EvalState * state)
+{
+    delete state;
+}
+
+#ifdef HAVE_BOEHMGC
+std::unordered_map<
+    const void *,
+    unsigned int,
+    std::hash<const void *>,
+    std::equal_to<const void *>,
+    traceable_allocator<std::pair<const void * const, unsigned int>>>
+    nix_refcounts;
+
+std::mutex nix_refcount_lock;
+
+nix_err nix_gc_incref(nix_c_context * context, const void * p)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        std::scoped_lock lock(nix_refcount_lock);
+        auto f = nix_refcounts.find(p);
+        if (f != nix_refcounts.end()) {
+            f->second++;
+        } else {
+            nix_refcounts[p] = 1;
+        }
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_gc_decref(nix_c_context * context, const void * p)
+{
+
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        std::scoped_lock lock(nix_refcount_lock);
+        auto f = nix_refcounts.find(p);
+        if (f != nix_refcounts.end()) {
+            if (--f->second == 0)
+                nix_refcounts.erase(f);
+        } else
+            throw std::runtime_error("nix_gc_decref: object was not referenced");
+    }
+    NIXC_CATCH_ERRS
+}
+
+void nix_gc_now()
+{
+    GC_gcollect();
+}
+
+#else
+nix_err nix_gc_incref(nix_c_context * context, const void *)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    return NIX_OK;
+}
+nix_err nix_gc_decref(nix_c_context * context, const void *)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    return NIX_OK;
+}
+void nix_gc_now() {}
+#endif
+
+void nix_gc_register_finalizer(void * obj, void * cd, void (*finalizer)(void * obj, void * cd))
+{
+#ifdef HAVE_BOEHMGC
+    GC_REGISTER_FINALIZER(obj, finalizer, cd, 0, 0);
+#endif
+}

src/libexpr-c/nix_api_expr.h

@@ -0,0 +1,213 @@
+#ifndef NIX_API_EXPR_H
+#define NIX_API_EXPR_H
+/** @defgroup libexpr libexpr
+ * @brief Bindings to the Nix language evaluator
+ *
+ * Example (without error handling):
+ * @code{.c}
+ * int main() {
+ *    nix_libexpr_init(NULL);
+ *
+ *    Store* store = nix_store_open(NULL, "dummy", NULL);
+ *    EvalState* state = nix_state_create(NULL, NULL, store); // empty nix path
+ *    Value *value = nix_alloc_value(NULL, state);
+ *
+ *    nix_expr_eval_from_string(NULL, state, "builtins.nixVersion", ".", value);
+ *    nix_value_force(NULL, state, value);
+ *    printf("nix version: %s\n", nix_get_string(NULL, value));
+ *
+ *    nix_gc_decref(NULL, value);
+ *    nix_state_free(state);
+ *    nix_store_free(store);
+ *    return 0;
+ *    }
+ * @endcode
+ * @{
+ */
+/** @file
+ * @brief Main entry for the libexpr C bindings
+ */
+
+#include "nix_api_store.h"
+#include "nix_api_util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+// Type definitions
+/**
+ * @brief Represents a state of the Nix language evaluator.
+ *
+ * Multiple states can be created for multi-threaded
+ * operation.
+ * @struct EvalState
+ * @see nix_state_create
+ */
+typedef struct EvalState EvalState; // nix::EvalState
+/**
+ * @brief Represents a value in the Nix language.
+ *
+ * Owned by the garbage collector.
+ * @struct Value
+ * @see value_manip
+ */
+typedef void Value; // nix::Value
+
+// Function prototypes
+/**
+ * @brief Initialize the Nix language evaluator.
+ *
+ * This function must be called at least once,
+ * at some point before constructing a EvalState for the first time.
+ * This function can be called multiple times, and is idempotent.
+ *
+ * @param[out] context Optional, stores error information
+ * @return NIX_OK if the initialization was successful, an error code otherwise.
+ */
+nix_err nix_libexpr_init(nix_c_context * context);
+
+/**
+ * @brief Parses and evaluates a Nix expression from a string.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] state The state of the evaluation.
+ * @param[in] expr The Nix expression to parse.
+ * @param[in] path The file path to associate with the expression.
+ * This is required for expressions that contain relative paths (such as `./.`) that are resolved relative to the given
+ * directory.
+ * @param[out] value The result of the evaluation. You must allocate this
+ * yourself.
+ * @return NIX_OK if the evaluation was successful, an error code otherwise.
+ */
+nix_err nix_expr_eval_from_string(
+    nix_c_context * context, EvalState * state, const char * expr, const char * path, Value * value);
+
+/**
+ * @brief Calls a Nix function with an argument.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] state The state of the evaluation.
+ * @param[in] fn The Nix function to call.
+ * @param[in] arg The argument to pass to the function.
+ * @param[out] value The result of the function call.
+ * @return NIX_OK if the function call was successful, an error code otherwise.
+ */
+nix_err nix_value_call(nix_c_context * context, EvalState * state, Value * fn, Value * arg, Value * value);
+
+/**
+ * @brief Forces the evaluation of a Nix value.
+ *
+ * The Nix interpreter is lazy, and not-yet-evaluated Values can be
+ * of type NIX_TYPE_THUNK instead of their actual value.
+ *
+ * This function converts these Values into their final type.
+ *
+ * @note You don't need this function for basic API usage, since all functions
+ * that return a value call it for you. The only place you will see a
+ * NIX_TYPE_THUNK is in the arguments that are passed to a PrimOp function
+ * you supplied to nix_alloc_primop.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] state The state of the evaluation.
+ * @param[in,out] value The Nix value to force.
+ * @post value is not of type NIX_TYPE_THUNK
+ * @return NIX_OK if the force operation was successful, an error code
+ * otherwise.
+ */
+nix_err nix_value_force(nix_c_context * context, EvalState * state, Value * value);
+
+/**
+ * @brief Forces the deep evaluation of a Nix value.
+ *
+ * Recursively calls nix_value_force
+ *
+ * @see nix_value_force
+ * @warning Calling this function on a recursive data structure will cause a
+ * stack overflow.
+ * @param[out] context Optional, stores error information
+ * @param[in] state The state of the evaluation.
+ * @param[in,out] value The Nix value to force.
+ * @return NIX_OK if the deep force operation was successful, an error code
+ * otherwise.
+ */
+nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, Value * value);
+
+/**
+ * @brief Create a new Nix language evaluator state.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] searchPath Array of strings corresponding to entries in NIX_PATH.
+ * @param[in] store The Nix store to use.
+ * @return A new Nix state or NULL on failure.
+ */
+EvalState * nix_state_create(nix_c_context * context, const char ** searchPath, Store * store);
+
+/**
+ * @brief Frees a Nix state.
+ *
+ * Does not fail.
+ *
+ * @param[in] state The state to free.
+ */
+void nix_state_free(EvalState * state);
+
+/** @addtogroup GC
+ * @brief Reference counting and garbage collector operations
+ *
+ * The Nix language evaluator uses a garbage collector. To ease C interop, we implement
+ * a reference counting scheme, where objects will be deallocated
+ * when there are no references from the Nix side, and the reference count kept
+ * by the C API reaches `0`.
+ *
+ * Functions returning a garbage-collected object will automatically increase
+ * the refcount for you. You should make sure to call `nix_gc_decref` when
+ * you're done with a value returned by the evaluator.
+ * @{
+ */
+/**
+ * @brief Increment the garbage collector reference counter for the given object.
+ *
+ * The Nix language evaluator C API keeps track of alive objects by reference counting.
+ * When you're done with a refcounted pointer, call nix_gc_decref().
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] object The object to keep alive
+ */
+nix_err nix_gc_incref(nix_c_context * context, const void * object);
+/**
+ * @brief Decrement the garbage collector reference counter for the given object
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] object The object to stop referencing
+ */
+nix_err nix_gc_decref(nix_c_context * context, const void * object);
+
+/**
+ * @brief Trigger the garbage collector manually
+ *
+ * You should not need to do this, but it can be useful for debugging.
+ */
+void nix_gc_now();
+
+/**
+ * @brief Register a callback that gets called when the object is garbage
+ * collected.
+ * @note Objects can only have a single finalizer. This function overwrites existing values
+ * silently.
+ * @param[in] obj the object to watch
+ * @param[in] cd the data to pass to the finalizer
+ * @param[in] finalizer the callback function, called with obj and cd
+ */
+void nix_gc_register_finalizer(void * obj, void * cd, void (*finalizer)(void * obj, void * cd));
+
+/** @} */
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+
+/** @} */
+
+#endif // NIX_API_EXPR_H

src/libexpr-c/nix_api_expr_internal.h

@@ -0,0 +1,38 @@
+#ifndef NIX_API_EXPR_INTERNAL_H
+#define NIX_API_EXPR_INTERNAL_H
+
+#include "eval.hh"
+#include "attr-set.hh"
+#include "nix_api_value.h"
+
+struct EvalState
+{
+    nix::EvalState state;
+};
+
+struct BindingsBuilder
+{
+    nix::BindingsBuilder builder;
+};
+
+struct ListBuilder
+{
+    nix::ListBuilder builder;
+};
+
+struct nix_string_return
+{
+    std::string str;
+};
+
+struct nix_printer
+{
+    std::ostream & s;
+};
+
+struct nix_string_context
+{
+    nix::NixStringContext & ctx;
+};
+
+#endif // NIX_API_EXPR_INTERNAL_H

src/libexpr-c/nix_api_external.cc

@@ -0,0 +1,198 @@
+#include "attr-set.hh"
+#include "config.hh"
+#include "eval.hh"
+#include "globals.hh"
+#include "value.hh"
+
+#include "nix_api_expr.h"
+#include "nix_api_expr_internal.h"
+#include "nix_api_external.h"
+#include "nix_api_util.h"
+#include "nix_api_util_internal.h"
+#include "nix_api_value.h"
+#include "value/context.hh"
+
+#include <nlohmann/json.hpp>
+
+#ifdef HAVE_BOEHMGC
+# include "gc/gc.h"
+# define GC_INCLUDE_NEW 1
+# include "gc_cpp.h"
+#endif
+
+void nix_set_string_return(nix_string_return * str, const char * c)
+{
+    str->str = c;
+}
+
+nix_err nix_external_print(nix_c_context * context, nix_printer * printer, const char * c)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        printer->s << c;
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_external_add_string_context(nix_c_context * context, nix_string_context * ctx, const char * c)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto r = nix::NixStringContextElem::parse(c);
+        ctx->ctx.insert(r);
+    }
+    NIXC_CATCH_ERRS
+}
+
+class NixCExternalValue : public nix::ExternalValueBase
+{
+    NixCExternalValueDesc & desc;
+    void * v;
+
+public:
+    NixCExternalValue(NixCExternalValueDesc & desc, void * v)
+        : desc(desc)
+        , v(v){};
+    void * get_ptr()
+    {
+        return v;
+    }
+    /**
+     * Print out the value
+     */
+    virtual std::ostream & print(std::ostream & str) const override
+    {
+        nix_printer p{str};
+        desc.print(v, &p);
+        return str;
+    }
+
+    /**
+     * Return a simple string describing the type
+     */
+    virtual std::string showType() const override
+    {
+        nix_string_return res;
+        desc.showType(v, &res);
+        return std::move(res.str);
+    }
+
+    /**
+     * Return a string to be used in builtins.typeOf
+     */
+    virtual std::string typeOf() const override
+    {
+        nix_string_return res;
+        desc.typeOf(v, &res);
+        return std::move(res.str);
+    }
+
+    /**
+     * Coerce the value to a string.
+     */
+    virtual std::string coerceToString(
+        nix::EvalState & state,
+        const nix::PosIdx & pos,
+        nix::NixStringContext & context,
+        bool copyMore,
+        bool copyToStore) const override
+    {
+        if (!desc.coerceToString) {
+            return nix::ExternalValueBase::coerceToString(state, pos, context, copyMore, copyToStore);
+        }
+        nix_string_context ctx{context};
+        nix_string_return res{""};
+        // todo: pos, errors
+        desc.coerceToString(v, &ctx, copyMore, copyToStore, &res);
+        if (res.str.empty()) {
+            return nix::ExternalValueBase::coerceToString(state, pos, context, copyMore, copyToStore);
+        }
+        return std::move(res.str);
+    }
+
+    /**
+     * Compare to another value of the same type.
+     */
+    virtual bool operator==(const ExternalValueBase & b) const override
+    {
+        if (!desc.equal) {
+            return false;
+        }
+        auto r = dynamic_cast<const NixCExternalValue *>(&b);
+        if (!r)
+            return false;
+        return desc.equal(v, r->v);
+    }
+
+    /**
+     * Print the value as JSON.
+     */
+    virtual nlohmann::json printValueAsJSON(
+        nix::EvalState & state, bool strict, nix::NixStringContext & context, bool copyToStore = true) const override
+    {
+        if (!desc.printValueAsJSON) {
+            return nix::ExternalValueBase::printValueAsJSON(state, strict, context, copyToStore);
+        }
+        nix_string_context ctx{context};
+        nix_string_return res{""};
+        desc.printValueAsJSON(v, (EvalState *) &state, strict, &ctx, copyToStore, &res);
+        if (res.str.empty()) {
+            return nix::ExternalValueBase::printValueAsJSON(state, strict, context, copyToStore);
+        }
+        return nlohmann::json::parse(res.str);
+    }
+
+    /**
+     * Print the value as XML.
+     */
+    virtual void printValueAsXML(
+        nix::EvalState & state,
+        bool strict,
+        bool location,
+        nix::XMLWriter & doc,
+        nix::NixStringContext & context,
+        nix::PathSet & drvsSeen,
+        const nix::PosIdx pos) const override
+    {
+        if (!desc.printValueAsXML) {
+            return nix::ExternalValueBase::printValueAsXML(state, strict, location, doc, context, drvsSeen, pos);
+        }
+        nix_string_context ctx{context};
+        desc.printValueAsXML(
+            v, (EvalState *) &state, strict, location, &doc, &ctx, &drvsSeen,
+            *reinterpret_cast<const uint32_t *>(&pos));
+    }
+
+    virtual ~NixCExternalValue() override{};
+};
+
+ExternalValue * nix_create_external_value(nix_c_context * context, NixCExternalValueDesc * desc, void * v)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto ret = new
+#ifdef HAVE_BOEHMGC
+            (GC)
+#endif
+                NixCExternalValue(*desc, v);
+        nix_gc_incref(nullptr, ret);
+        return (ExternalValue *) ret;
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+void * nix_get_external_value_content(nix_c_context * context, ExternalValue * b)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto r = dynamic_cast<NixCExternalValue *>((nix::ExternalValueBase *) b);
+        if (r)
+            return r->get_ptr();
+        return nullptr;
+    }
+    NIXC_CATCH_ERRS_NULL
+}

src/libexpr-c/nix_api_external.h

@@ -0,0 +1,196 @@
+#ifndef NIX_API_EXTERNAL_H
+#define NIX_API_EXTERNAL_H
+/** @ingroup libexpr
+ * @addtogroup Externals
+ * @brief Deal with external values
+ * @{
+ */
+/** @file
+ * @brief libexpr C bindings dealing with external values
+ */
+
+#include "nix_api_expr.h"
+#include "nix_api_util.h"
+#include "nix_api_value.h"
+#include "stdbool.h"
+#include "stddef.h"
+#include "stdint.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+/**
+ * @brief Represents a string owned by the Nix language evaluator.
+ * @see nix_set_owned_string
+ */
+typedef struct nix_string_return nix_string_return;
+/**
+ * @brief Wraps a stream that can output multiple string pieces.
+ */
+typedef struct nix_printer nix_printer;
+/**
+ * @brief A list of string context items
+ */
+typedef struct nix_string_context nix_string_context;
+
+/**
+ * @brief Sets the contents of a nix_string_return
+ *
+ * Copies the passed string.
+ * @param[out] str the nix_string_return to write to
+ * @param[in]  c   The string to copy
+ */
+void nix_set_string_return(nix_string_return * str, const char * c);
+
+/**
+ * Print to the nix_printer
+ *
+ * @param[out] context Optional, stores error information
+ * @param printer The nix_printer to print to
+ * @param[in] str The string to print
+ * @returns NIX_OK if everything worked
+ */
+nix_err nix_external_print(nix_c_context * context, nix_printer * printer, const char * str);
+
+/**
+ * Add string context to the nix_string_context object
+ * @param[out] context Optional, stores error information
+ * @param[out] string_context The nix_string_context to add to
+ * @param[in] c The context string to add
+ * @returns NIX_OK if everything worked
+ */
+nix_err nix_external_add_string_context(nix_c_context * context, nix_string_context * string_context, const char * c);
+
+/**
+ * @brief Definition for a class of external values
+ *
+ * Create and implement one of these, then pass it to nix_create_external_value
+ * Make sure to keep it alive while the external value lives.
+ *
+ * Optional functions can be set to NULL
+ *
+ * @see nix_create_external_value
+ */
+typedef struct NixCExternalValueDesc
+{
+    /**
+     * @brief Called when printing the external value
+     *
+     * @param[in] self the void* passed to nix_create_external_value
+     * @param[out] printer The printer to print to, pass to nix_external_print
+     */
+    void (*print)(void * self, nix_printer * printer);
+    /**
+     * @brief Called on :t
+     * @param[in] self the void* passed to nix_create_external_value
+     * @param[out] res the return value
+     */
+    void (*showType)(void * self, nix_string_return * res);
+    /**
+     * @brief Called on `builtins.typeOf`
+     * @param self the void* passed to nix_create_external_value
+     * @param[out] res the return value
+     */
+    void (*typeOf)(void * self, nix_string_return * res);
+    /**
+     * @brief Called on "${str}" and builtins.toString.
+     *
+     * The latter with coerceMore=true
+     * Optional, the default is to throw an error.
+     * @param[in] self the void* passed to nix_create_external_value
+     * @param[out] c writable string context for the resulting string
+     * @param[in] coerceMore boolean, try to coerce to strings in more cases
+     * instead of throwing an error
+     * @param[in] copyToStore boolean, whether to copy referenced paths to store
+     * or keep them as-is
+     * @param[out] res the return value. Not touching this, or setting it to the
+     * empty string, will make the conversion throw an error.
+     */
+    void (*coerceToString)(
+        void * self, nix_string_context * c, int coerceMore, int copyToStore, nix_string_return * res);
+    /**
+     * @brief Try to compare two external values
+     *
+     * Optional, the default is always false.
+     * If the other object was not a Nix C external value, this comparison will
+     * also return false
+     * @param[in] self the void* passed to nix_create_external_value
+     * @param[in] other the void* passed to the other object's
+     * nix_create_external_value
+     * @returns true if the objects are deemed to be equal
+     */
+    int (*equal)(void * self, void * other);
+    /**
+     * @brief Convert the external value to json
+     *
+     * Optional, the default is to throw an error
+     * @param[in] self the void* passed to nix_create_external_value
+     * @param[in] state The evaluator state
+     * @param[in] strict boolean Whether to force the value before printing
+     * @param[out] c writable string context for the resulting string
+     * @param[in] copyToStore whether to copy referenced paths to store or keep
+     * them as-is
+     * @param[out] res the return value. Gets parsed as JSON. Not touching this,
+     * or setting it to the empty string, will make the conversion throw an error.
+     */
+    void (*printValueAsJSON)(
+        void * self, EvalState *, bool strict, nix_string_context * c, bool copyToStore, nix_string_return * res);
+    /**
+     * @brief Convert the external value to XML
+     *
+     * Optional, the default is to throw an error
+     * @todo The mechanisms for this call are incomplete. There are no C
+     *       bindings to work with XML, pathsets and positions.
+     * @param[in] self the void* passed to nix_create_external_value
+     * @param[in] state The evaluator state
+     * @param[in] strict boolean Whether to force the value before printing
+     * @param[in] location boolean Whether to include position information in the
+     * xml
+     * @param[out] doc XML document to output to
+     * @param[out] c writable string context for the resulting string
+     * @param[in,out] drvsSeen a path set to avoid duplicating derivations
+     * @param[in] pos The position of the call.
+     */
+    void (*printValueAsXML)(
+        void * self,
+        EvalState *,
+        int strict,
+        int location,
+        void * doc,
+        nix_string_context * c,
+        void * drvsSeen,
+        int pos);
+} NixCExternalValueDesc;
+
+/**
+ * @brief Create an external value, that can be given to nix_init_external
+ *
+ * Owned by the GC. Use nix_gc_decref when you're done with the pointer.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] desc a NixCExternalValueDesc, you should keep this alive as long
+ * as the ExternalValue lives
+ * @param[in] v the value to store
+ * @returns external value, owned by the garbage collector
+ * @see nix_init_external
+ */
+ExternalValue * nix_create_external_value(nix_c_context * context, NixCExternalValueDesc * desc, void * v);
+
+/**
+ * @brief Extract the pointer from a nix c external value.
+ * @param[out] context Optional, stores error information
+ * @param[in] b The external value
+ * @returns The pointer, or null if the external value was not from nix c.
+ * @see nix_get_external
+ */
+void * nix_get_external_value_content(nix_c_context * context, ExternalValue * b);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+/** @} */
+
+#endif // NIX_API_EXTERNAL_H

src/libexpr-c/nix_api_value.cc

@@ -0,0 +1,530 @@
+#include "attr-set.hh"
+#include "config.hh"
+#include "eval.hh"
+#include "globals.hh"
+#include "primops.hh"
+#include "value.hh"
+
+#include "nix_api_expr.h"
+#include "nix_api_expr_internal.h"
+#include "nix_api_util.h"
+#include "nix_api_util_internal.h"
+#include "nix_api_value.h"
+
+#ifdef HAVE_BOEHMGC
+# include "gc/gc.h"
+# define GC_INCLUDE_NEW 1
+# include "gc_cpp.h"
+#endif
+
+// Helper function to throw an exception if value is null
+static const nix::Value & check_value_not_null(const Value * value)
+{
+    if (!value) {
+        throw std::runtime_error("Value is null");
+    }
+    return *((const nix::Value *) value);
+}
+
+static nix::Value & check_value_not_null(Value * value)
+{
+    if (!value) {
+        throw std::runtime_error("Value is null");
+    }
+    return *((nix::Value *) value);
+}
+
+/**
+ * Helper function to convert calls from nix into C API.
+ *
+ * Deals with errors and converts arguments from C++ into C types.
+ */
+static void nix_c_primop_wrapper(
+    PrimOpFun f, void * userdata, nix::EvalState & state, const nix::PosIdx pos, nix::Value ** args, nix::Value & v)
+{
+    nix_c_context ctx;
+    f(userdata, &ctx, (EvalState *) &state, (Value **) args, (Value *) &v);
+    /* TODO: In the future, this should throw different errors depending on the error code */
+    if (ctx.last_err_code != NIX_OK)
+        state.error<nix::EvalError>("Error from builtin function: %s", *ctx.last_err).atPos(pos).debugThrow();
+}
+
+PrimOp * nix_alloc_primop(
+    nix_c_context * context,
+    PrimOpFun fun,
+    int arity,
+    const char * name,
+    const char ** args,
+    const char * doc,
+    void * user_data)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        using namespace std::placeholders;
+        auto p = new
+#ifdef HAVE_BOEHMGC
+            (GC)
+#endif
+                nix::PrimOp{
+                    .name = name,
+                    .args = {},
+                    .arity = (size_t) arity,
+                    .doc = doc,
+                    .fun = std::bind(nix_c_primop_wrapper, fun, user_data, _1, _2, _3, _4)};
+        if (args)
+            for (size_t i = 0; args[i]; i++)
+                p->args.emplace_back(*args);
+        nix_gc_incref(nullptr, p);
+        return (PrimOp *) p;
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+nix_err nix_register_primop(nix_c_context * context, PrimOp * primOp)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        nix::RegisterPrimOp r(std::move(*((nix::PrimOp *) primOp)));
+    }
+    NIXC_CATCH_ERRS
+}
+
+Value * nix_alloc_value(nix_c_context * context, EvalState * state)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        Value * res = state->state.allocValue();
+        nix_gc_incref(nullptr, res);
+        return res;
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+ValueType nix_get_type(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        using namespace nix;
+        switch (v.type()) {
+        case nThunk:
+            return NIX_TYPE_THUNK;
+        case nInt:
+            return NIX_TYPE_INT;
+        case nFloat:
+            return NIX_TYPE_FLOAT;
+        case nBool:
+            return NIX_TYPE_BOOL;
+        case nString:
+            return NIX_TYPE_STRING;
+        case nPath:
+            return NIX_TYPE_PATH;
+        case nNull:
+            return NIX_TYPE_NULL;
+        case nAttrs:
+            return NIX_TYPE_ATTRS;
+        case nList:
+            return NIX_TYPE_LIST;
+        case nFunction:
+            return NIX_TYPE_FUNCTION;
+        case nExternal:
+            return NIX_TYPE_EXTERNAL;
+        }
+        return NIX_TYPE_NULL;
+    }
+    NIXC_CATCH_ERRS_RES(NIX_TYPE_NULL);
+}
+
+const char * nix_get_typename(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        auto s = nix::showType(v);
+        return strdup(s.c_str());
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+bool nix_get_bool(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nBool);
+        return v.boolean;
+    }
+    NIXC_CATCH_ERRS_RES(false);
+}
+
+const char * nix_get_string(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nString);
+        return v.c_str();
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+const char * nix_get_path_string(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nPath);
+        // NOTE (from @yorickvP)
+        // v._path.path should work but may not be how Eelco intended it.
+        // Long-term this function should be rewritten to copy some data into a
+        // user-allocated string.
+        // We could use v.path().to_string().c_str(), but I'm concerned this
+        // crashes. Looks like .path() allocates a CanonPath with a copy of the
+        // string, then it gets the underlying data from that.
+        return v._path.path;
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+unsigned int nix_get_list_size(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nList);
+        return v.listSize();
+    }
+    NIXC_CATCH_ERRS_RES(0);
+}
+
+unsigned int nix_get_attrs_size(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nAttrs);
+        return v.attrs->size();
+    }
+    NIXC_CATCH_ERRS_RES(0);
+}
+
+double nix_get_float(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nFloat);
+        return v.fpoint;
+    }
+    NIXC_CATCH_ERRS_RES(0.0);
+}
+
+int64_t nix_get_int(nix_c_context * context, const Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nInt);
+        return v.integer;
+    }
+    NIXC_CATCH_ERRS_RES(0);
+}
+
+ExternalValue * nix_get_external(nix_c_context * context, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nExternal);
+        return (ExternalValue *) v.external;
+    }
+    NIXC_CATCH_ERRS_NULL;
+}
+
+Value * nix_get_list_byidx(nix_c_context * context, const Value * value, EvalState * state, unsigned int ix)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nList);
+        auto * p = v.listElems()[ix];
+        nix_gc_incref(nullptr, p);
+        if (p != nullptr)
+            state->state.forceValue(*p, nix::noPos);
+        return (Value *) p;
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+Value * nix_get_attr_byname(nix_c_context * context, const Value * value, EvalState * state, const char * name)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nAttrs);
+        nix::Symbol s = state->state.symbols.create(name);
+        auto attr = v.attrs->get(s);
+        if (attr) {
+            nix_gc_incref(nullptr, attr->value);
+            state->state.forceValue(*attr->value, nix::noPos);
+            return attr->value;
+        }
+        nix_set_err_msg(context, NIX_ERR_KEY, "missing attribute");
+        return nullptr;
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+bool nix_has_attr_byname(nix_c_context * context, const Value * value, EvalState * state, const char * name)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        assert(v.type() == nix::nAttrs);
+        nix::Symbol s = state->state.symbols.create(name);
+        auto attr = v.attrs->get(s);
+        if (attr)
+            return true;
+        return false;
+    }
+    NIXC_CATCH_ERRS_RES(false);
+}
+
+Value *
+nix_get_attr_byidx(nix_c_context * context, const Value * value, EvalState * state, unsigned int i, const char ** name)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        const nix::Attr & a = (*v.attrs)[i];
+        *name = ((const std::string &) (state->state.symbols[a.name])).c_str();
+        nix_gc_incref(nullptr, a.value);
+        state->state.forceValue(*a.value, nix::noPos);
+        return a.value;
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+const char * nix_get_attr_name_byidx(nix_c_context * context, const Value * value, EvalState * state, unsigned int i)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        const nix::Attr & a = (*v.attrs)[i];
+        return ((const std::string &) (state->state.symbols[a.name])).c_str();
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+nix_err nix_init_bool(nix_c_context * context, Value * value, bool b)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkBool(b);
+    }
+    NIXC_CATCH_ERRS
+}
+
+// todo string context
+nix_err nix_init_string(nix_c_context * context, Value * value, const char * str)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkString(std::string_view(str));
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_init_path_string(nix_c_context * context, EvalState * s, Value * value, const char * str)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkPath(s->state.rootPath(nix::CanonPath(str)));
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_init_float(nix_c_context * context, Value * value, double d)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkFloat(d);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_init_int(nix_c_context * context, Value * value, int64_t i)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkInt(i);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_init_null(nix_c_context * context, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkNull();
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_init_external(nix_c_context * context, Value * value, ExternalValue * val)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        auto r = (nix::ExternalValueBase *) val;
+        v.mkExternal(r);
+    }
+    NIXC_CATCH_ERRS
+}
+
+ListBuilder * nix_make_list_builder(nix_c_context * context, EvalState * state, size_t capacity)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto builder = state->state.buildList(capacity);
+        return new
+#if HAVE_BOEHMGC
+            (NoGC)
+#endif
+                ListBuilder{std::move(builder)};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+nix_err nix_list_builder_insert(nix_c_context * context, ListBuilder * list_builder, unsigned int index, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & e = check_value_not_null(value);
+        list_builder->builder[index] = &e;
+    }
+    NIXC_CATCH_ERRS
+}
+
+void nix_list_builder_free(ListBuilder * list_builder)
+{
+#if HAVE_BOEHMGC
+    GC_FREE(list_builder);
+#else
+    delete list_builder;
+#endif
+}
+
+nix_err nix_make_list(nix_c_context * context, ListBuilder * list_builder, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkList(list_builder->builder);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_init_primop(nix_c_context * context, Value * value, PrimOp * p)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkPrimOp((nix::PrimOp *) p);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_copy_value(nix_c_context * context, Value * value, Value * source)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        auto & s = check_value_not_null(source);
+        v = s;
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_make_attrs(nix_c_context * context, Value * value, BindingsBuilder * b)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        v.mkAttrs(b->builder);
+    }
+    NIXC_CATCH_ERRS
+}
+
+BindingsBuilder * nix_make_bindings_builder(nix_c_context * context, EvalState * state, size_t capacity)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto bb = state->state.buildBindings(capacity);
+        return new
+#if HAVE_BOEHMGC
+            (NoGC)
+#endif
+                BindingsBuilder{std::move(bb)};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+nix_err nix_bindings_builder_insert(nix_c_context * context, BindingsBuilder * bb, const char * name, Value * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto & v = check_value_not_null(value);
+        nix::Symbol s = bb->builder.state.symbols.create(name);
+        bb->builder.insert(s, &v);
+    }
+    NIXC_CATCH_ERRS
+}
+
+void nix_bindings_builder_free(BindingsBuilder * bb)
+{
+#if HAVE_BOEHMGC
+    GC_FREE((nix::BindingsBuilder *) bb);
+#else
+    delete (nix::BindingsBuilder *) bb;
+#endif
+}

src/libexpr-c/nix_api_value.h

@@ -0,0 +1,434 @@
+#ifndef NIX_API_VALUE_H
+#define NIX_API_VALUE_H
+
+/** @addtogroup libexpr
+ * @{
+ */
+/** @file
+ * @brief libexpr C bindings dealing with values
+ */
+
+#include "nix_api_util.h"
+#include "stdbool.h"
+#include "stddef.h"
+#include "stdint.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+// Type definitions
+typedef enum {
+    NIX_TYPE_THUNK,
+    NIX_TYPE_INT,
+    NIX_TYPE_FLOAT,
+    NIX_TYPE_BOOL,
+    NIX_TYPE_STRING,
+    NIX_TYPE_PATH,
+    NIX_TYPE_NULL,
+    NIX_TYPE_ATTRS,
+    NIX_TYPE_LIST,
+    NIX_TYPE_FUNCTION,
+    NIX_TYPE_EXTERNAL
+} ValueType;
+
+// forward declarations
+typedef void Value;
+typedef struct EvalState EvalState;
+// type defs
+/** @brief Stores an under-construction set of bindings
+ * @ingroup value_manip
+ *
+ * Do not reuse.
+ * @see nix_make_bindings_builder, nix_bindings_builder_free, nix_make_attrs
+ * @see nix_bindings_builder_insert
+ */
+typedef struct BindingsBuilder BindingsBuilder;
+
+/** @brief Stores an under-construction list
+ * @ingroup value_manip
+ *
+ * Do not reuse.
+ * @see nix_make_list_builder, nix_list_builder_free, nix_make_list
+ * @see nix_list_builder_insert
+ */
+typedef struct ListBuilder ListBuilder;
+
+/** @brief PrimOp function
+ * @ingroup primops
+ *
+ * Owned by the GC
+ * @see nix_alloc_primop, nix_init_primop
+ */
+typedef struct PrimOp PrimOp;
+/** @brief External Value
+ * @ingroup Externals
+ *
+ * Owned by the GC
+ */
+typedef struct ExternalValue ExternalValue;
+
+/** @defgroup primops
+ * @brief Create your own primops
+ * @{
+ */
+/** @brief Function pointer for primops
+ * When you want to return an error, call nix_set_err_msg(context, NIX_ERR_UNKNOWN, "your error message here").
+ *
+ * @param[in] user_data Arbitrary data that was initially supplied to nix_alloc_primop
+ * @param[out] context Stores error information.
+ * @param[in] state Evaluator state
+ * @param[in] args list of arguments. Note that these can be thunks and should be forced using nix_value_force before
+ * use.
+ * @param[out] ret return value
+ * @see nix_alloc_primop, nix_init_primop
+ */
+typedef void (*PrimOpFun)(void * user_data, nix_c_context * context, EvalState * state, Value ** args, Value * ret);
+
+/** @brief Allocate a PrimOp
+ *
+ * Owned by the garbage collector.
+ * Use nix_gc_decref() when you're done with the returned PrimOp.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] fun callback
+ * @param[in] arity expected number of function arguments
+ * @param[in] name function name
+ * @param[in] args array of argument names, NULL-terminated
+ * @param[in] doc optional, documentation for this primop
+ * @param[in] user_data optional, arbitrary data, passed to the callback when it's called
+ * @return primop, or null in case of errors
+ * @see nix_init_primop
+ */
+PrimOp * nix_alloc_primop(
+    nix_c_context * context,
+    PrimOpFun fun,
+    int arity,
+    const char * name,
+    const char ** args,
+    const char * doc,
+    void * user_data);
+
+/** @brief add a primop to the `builtins` attribute set
+ *
+ * Only applies to States created after this call.
+ *
+ * Moves your PrimOp content into the global evaluator
+ * registry, meaning your input PrimOp pointer is no longer usable.
+ * You are free to remove your references to it,
+ * after which it will be garbage collected.
+ *
+ * @param[out] context Optional, stores error information
+ * @return primop, or null in case of errors
+ *
+ */
+nix_err nix_register_primop(nix_c_context * context, PrimOp * primOp);
+/** @} */
+
+// Function prototypes
+
+/** @brief Allocate a Nix value
+ *
+ * Owned by the GC. Use nix_gc_decref() when you're done with the pointer
+ * @param[out] context Optional, stores error information
+ * @param[in] state nix evaluator state
+ * @return value, or null in case of errors
+ *
+ */
+Value * nix_alloc_value(nix_c_context * context, EvalState * state);
+
+/** @addtogroup value_manip Manipulating values
+ * @brief Functions to inspect and change Nix language values, represented by Value.
+ * @{
+ */
+/** @name Getters
+ */
+/**@{*/
+/** @brief Get value type
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return type of nix value
+ */
+ValueType nix_get_type(nix_c_context * context, const Value * value);
+
+/** @brief Get type name of value as defined in the evaluator
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return type name, owned string
+ * @todo way to free the result
+ */
+const char * nix_get_typename(nix_c_context * context, const Value * value);
+
+/** @brief Get boolean value
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return true or false, error info via context
+ */
+bool nix_get_bool(nix_c_context * context, const Value * value);
+
+/** @brief Get string
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return string
+ * @return NULL in case of error.
+ */
+const char * nix_get_string(nix_c_context * context, const Value * value);
+
+/** @brief Get path as string
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return string
+ * @return NULL in case of error.
+ */
+const char * nix_get_path_string(nix_c_context * context, const Value * value);
+
+/** @brief Get the length of a list
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return length of list, error info via context
+ */
+unsigned int nix_get_list_size(nix_c_context * context, const Value * value);
+
+/** @brief Get the element count of an attrset
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return attrset element count, error info via context
+ */
+unsigned int nix_get_attrs_size(nix_c_context * context, const Value * value);
+
+/** @brief Get float value in 64 bits
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return float contents, error info via context
+ */
+double nix_get_float(nix_c_context * context, const Value * value);
+
+/** @brief Get int value
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return int contents, error info via context
+ */
+int64_t nix_get_int(nix_c_context * context, const Value * value);
+
+/** @brief Get external reference
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @return reference to external, NULL in case of error
+ */
+ExternalValue * nix_get_external(nix_c_context * context, Value *);
+
+/** @brief Get the ix'th element of a list
+ *
+ * Owned by the GC. Use nix_gc_decref when you're done with the pointer
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] state nix evaluator state
+ * @param[in] ix list element to get
+ * @return value, NULL in case of errors
+ */
+Value * nix_get_list_byidx(nix_c_context * context, const Value * value, EvalState * state, unsigned int ix);
+
+/** @brief Get an attr by name
+ *
+ * Owned by the GC. Use nix_gc_decref when you're done with the pointer
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] state nix evaluator state
+ * @param[in] name attribute name
+ * @return value, NULL in case of errors
+ */
+Value * nix_get_attr_byname(nix_c_context * context, const Value * value, EvalState * state, const char * name);
+
+/** @brief Check if an attribute name exists on a value
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] state nix evaluator state
+ * @param[in] name attribute name
+ * @return value, error info via context
+ */
+bool nix_has_attr_byname(nix_c_context * context, const Value * value, EvalState * state, const char * name);
+
+/** @brief Get an attribute by index in the sorted bindings
+ *
+ * Also gives you the name.
+ *
+ * Owned by the GC. Use nix_gc_decref when you're done with the pointer
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] state nix evaluator state
+ * @param[in] i attribute index
+ * @param[out] name will store a pointer to the attribute name
+ * @return value, NULL in case of errors
+ */
+Value *
+nix_get_attr_byidx(nix_c_context * context, const Value * value, EvalState * state, unsigned int i, const char ** name);
+
+/** @brief Get an attribute name by index in the sorted bindings
+ *
+ * Useful when you want the name but want to avoid evaluation.
+ *
+ * Owned by the nix EvalState
+ * @param[out] context Optional, stores error information
+ * @param[in] value Nix value to inspect
+ * @param[in] state nix evaluator state
+ * @param[in] i attribute index
+ * @return name, NULL in case of errors
+ */
+const char * nix_get_attr_name_byidx(nix_c_context * context, const Value * value, EvalState * state, unsigned int i);
+
+/**@}*/
+/** @name Initializers
+ *
+ * Values are typically "returned" by initializing already allocated memory that serves as the return value.
+ * For this reason, the construction of values is not tied their allocation.
+ * Nix is a language with immutable values. Respect this property by only initializing Values once; and only initialize
+ * Values that are meant to be initialized by you. Failing to adhere to these rules may lead to undefined behavior.
+ */
+/**@{*/
+/** @brief Set boolean value
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] b the boolean value
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_init_bool(nix_c_context * context, Value * value, bool b);
+
+/** @brief Set a string
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] str the string, copied
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_init_string(nix_c_context * context, Value * value, const char * str);
+
+/** @brief Set a path
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] str the path string, copied
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_init_path_string(nix_c_context * context, EvalState * s, Value * value, const char * str);
+
+/** @brief Set a float
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] d the float, 64-bits
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_init_float(nix_c_context * context, Value * value, double d);
+
+/** @brief Set an int
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] i the int
+ * @return error code, NIX_OK on success.
+ */
+
+nix_err nix_init_int(nix_c_context * context, Value * value, int64_t i);
+/** @brief Set null
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @return error code, NIX_OK on success.
+ */
+
+nix_err nix_init_null(nix_c_context * context, Value * value);
+/** @brief Set an external value
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] val the external value to set. Will be GC-referenced by the value.
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_init_external(nix_c_context * context, Value * value, ExternalValue * val);
+
+/** @brief Create a list from a list builder
+ * @param[out] context Optional, stores error information
+ * @param[in] list_builder list builder to use. Make sure to unref this afterwards.
+ * @param[out] value Nix value to modify
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_make_list(nix_c_context * context, ListBuilder * list_builder, Value * value);
+
+/** @brief Create a list builder
+ * @param[out] context Optional, stores error information
+ * @param[in] state nix evaluator state
+ * @param[in] capacity how many bindings you'll add. Don't exceed.
+ * @return owned reference to a list builder. Make sure to unref when you're done.
+ */
+ListBuilder * nix_make_list_builder(nix_c_context * context, EvalState * state, size_t capacity);
+
+/** @brief Insert bindings into a builder
+ * @param[out] context Optional, stores error information
+ * @param[in] list_builder ListBuilder to insert into
+ * @param[in] index index to manipulate
+ * @param[in] value value to insert
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_list_builder_insert(nix_c_context * context, ListBuilder * list_builder, unsigned int index, Value * value);
+
+/** @brief Free a list builder
+ *
+ * Does not fail.
+ * @param[in] builder the builder to free
+ */
+void nix_list_builder_free(ListBuilder * list_builder);
+
+/** @brief Create an attribute set from a bindings builder
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] b bindings builder to use. Make sure to unref this afterwards.
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_make_attrs(nix_c_context * context, Value * value, BindingsBuilder * b);
+
+/** @brief Set primop
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] op primop, will be gc-referenced by the value
+ * @see nix_alloc_primop
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_init_primop(nix_c_context * context, Value * value, PrimOp * op);
+/** @brief Copy from another value
+ * @param[out] context Optional, stores error information
+ * @param[out] value Nix value to modify
+ * @param[in] source value to copy from
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_copy_value(nix_c_context * context, Value * value, Value * source);
+/**@}*/
+
+/** @brief Create a bindings builder
+* @param[out] context Optional, stores error information
+* @param[in] state nix evaluator state
+* @param[in] capacity how many bindings you'll add. Don't exceed.
+* @return owned reference to a bindings builder. Make sure to unref when you're
+done.
+*/
+BindingsBuilder * nix_make_bindings_builder(nix_c_context * context, EvalState * state, size_t capacity);
+
+/** @brief Insert bindings into a builder
+ * @param[out] context Optional, stores error information
+ * @param[in] builder BindingsBuilder to insert into
+ * @param[in] name attribute name, copied into the symbol store
+ * @param[in] value value to give the binding
+ * @return error code, NIX_OK on success.
+ */
+nix_err
+nix_bindings_builder_insert(nix_c_context * context, BindingsBuilder * builder, const char * name, Value * value);
+
+/** @brief Free a bindings builder
+ *
+ * Does not fail.
+ * @param[in] builder the builder to free
+ */
+void nix_bindings_builder_free(BindingsBuilder * builder);
+/**@}*/
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+
+/** @} */
+#endif // NIX_API_VALUE_H

src/libexpr/eval-cache.cc

@@ -581,7 +581,7 @@ std::string AttrCursor::getString()
     auto & v = forceValue();
 
     if (v.type() != nString && v.type() != nPath)
-        root->state.error<TypeError>("'%s' is not a string but %s", getAttrPathStr()).debugThrow();
+        root->state.error<TypeError>("'%s' is not a string but %s", getAttrPathStr(), showType(v)).debugThrow();
 
     return v.type() == nString ? v.c_str() : v.path().to_string();
 }
@@ -630,7 +630,7 @@ string_t AttrCursor::getStringWithContext()
     else if (v.type() == nPath)
         return {v.path().to_string(), {}};
     else
-        root->state.error<TypeError>("'%s' is not a string but %s", getAttrPathStr()).debugThrow();
+        root->state.error<TypeError>("'%s' is not a string but %s", getAttrPathStr(), showType(v)).debugThrow();
 }
 
 bool AttrCursor::getBool()

src/libexpr/eval-settings.hh

@@ -76,9 +76,10 @@ struct EvalSettings : Config
 
           - Restrict file system and network access to files specified by cryptographic hash
           - Disable impure constants:
-            - [`bultins.currentSystem`](@docroot@/language/builtin-constants.md#builtins-currentSystem)
+            - [`builtins.currentSystem`](@docroot@/language/builtin-constants.md#builtins-currentSystem)
             - [`builtins.currentTime`](@docroot@/language/builtin-constants.md#builtins-currentTime)
             - [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath)
+            - [`builtins.storePath`](@docroot@/language/builtin-constants.md#builtins-storePath)
         )"
         };
 

src/libexpr/eval.cc

@@ -435,7 +435,14 @@ EvalState::EvalState(
 
     static_assert(sizeof(Env) <= 16, "environment must be <= 16 bytes");
 
-    vEmptyList.mkList(0);
+    vEmptyList.mkList(buildList(0));
+    vNull.mkNull();
+    vTrue.mkBool(true);
+    vFalse.mkBool(false);
+    vStringRegular.mkString("regular");
+    vStringDirectory.mkString("directory");
+    vStringSymlink.mkString("symlink");
+    vStringUnknown.mkString("unknown");
 
     /* Initialise the Nix expression search path. */
     if (!evalSettings.pureEval) {
@@ -890,7 +897,6 @@ void Value::mkStringMove(const char * s, const NixStringContext & context)
     copyContextToValue(*this, context);
 }
 
-
 void Value::mkPath(const SourcePath & path)
 {
     mkPath(&*path.accessor, makeImmutableString(path.path.abs()));
@@ -923,14 +929,16 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
     }
 }
 
-void EvalState::mkList(Value & v, size_t size)
+ListBuilder::ListBuilder(EvalState & state, size_t size)
+    : size(size)
+    , elems(size <= 2 ? inlineElems : (Value * *) allocBytes(size * sizeof(Value *)))
 {
-    v.mkList(size);
-    if (size > 2)
-        v.bigList.elems = (Value * *) allocBytes(size * sizeof(Value *));
-    nrListElems += size;
+    state.nrListElems += size;
 }
 
+Value * EvalState::getBool(bool b) {
+    return b ? &vTrue : &vFalse;
+}
 
 unsigned long nrThunks = 0;
 
@@ -1353,9 +1361,10 @@ void ExprLet::eval(EvalState & state, Env & env, Value & v)
 
 void ExprList::eval(EvalState & state, Env & env, Value & v)
 {
-    state.mkList(v, elems.size());
-    for (auto [n, v2] : enumerate(v.listItems()))
-        const_cast<Value * &>(v2) = elems[n]->maybeThunk(state, env);
+    auto list = state.buildList(elems.size());
+    for (const auto & [n, v2] : enumerate(list))
+        v2 = elems[n]->maybeThunk(state, env);
+    v.mkList(list);
 }
 
 
@@ -1655,6 +1664,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                 try {
                     fn->fun(*this, vCur.determinePos(noPos), args, vCur);
                 } catch (Error & e) {
+                    if (fn->addTrace)
                         addErrorTrace(e, pos, "while calling the '%1%' builtin", fn->name);
                     throw;
                 }
@@ -1703,6 +1713,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                     //    so the debugger allows to inspect the wrong parameters passed to the builtin.
                     fn->fun(*this, vCur.determinePos(noPos), vArgs, vCur);
                 } catch (Error & e) {
+                    if (fn->addTrace)
                         addErrorTrace(e, pos, "while calling the '%1%' builtin", fn->name);
                     throw;
                 }
@@ -1945,7 +1956,7 @@ void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v)
 }
 
 
-void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos, std::string_view errorCtx)
+void EvalState::concatLists(Value & v, size_t nrLists, Value * const * lists, const PosIdx pos, std::string_view errorCtx)
 {
     nrListConcats++;
 
@@ -1963,14 +1974,15 @@ void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const Po
         return;
     }
 
-    mkList(v, len);
-    auto out = v.listElems();
+    auto list = buildList(len);
+    auto out = list.elems;
     for (size_t n = 0, pos = 0; n < nrLists; ++n) {
         auto l = lists[n]->listSize();
         if (l)
             memcpy(out + pos, lists[n]->listElems(), l * sizeof(Value *));
         pos += l;
     }
+    v.mkList(list);
 }
 
 

src/libexpr/eval.hh

@@ -17,6 +17,7 @@
 #include <optional>
 #include <unordered_map>
 #include <mutex>
+#include <functional>
 
 namespace nix {
 
@@ -69,10 +70,17 @@ struct PrimOp
      */
     const char * doc = nullptr;
 
+    /**
+     * Add a trace item, `while calling the '<name>' builtin`
+     *
+     * This is used to remove the redundant item for `builtins.addErrorContext`.
+     */
+    bool addTrace = true;
+
     /**
      * Implementation of the primop.
      */
-    PrimOpFun fun;
+    std::function<std::remove_pointer<PrimOpFun>::type> fun;
 
     /**
      * Optional experimental for this to be gated on.
@@ -186,6 +194,36 @@ public:
      */
     Value vEmptyList;
 
+    /**
+     * `null` constant.
+     *
+     * This is _not_ a singleton. Pointer equality is _not_ sufficient.
+     */
+    Value vNull;
+
+    /**
+     * `true` constant.
+     *
+     * This is _not_ a singleton. Pointer equality is _not_ sufficient.
+     */
+    Value vTrue;
+
+    /**
+     * `true` constant.
+     *
+     * This is _not_ a singleton. Pointer equality is _not_ sufficient.
+     */
+    Value vFalse;
+
+    /** `"regular"` */
+    Value vStringRegular;
+    /** `"directory"` */
+    Value vStringDirectory;
+    /** `"symlink"` */
+    Value vStringSymlink;
+    /** `"unknown"` */
+    Value vStringUnknown;
+
     /**
      * The accessor for the root filesystem.
      */
@@ -615,7 +653,16 @@ public:
         return BindingsBuilder(*this, allocBindings(capacity));
     }
 
-    void mkList(Value & v, size_t length);
+    ListBuilder buildList(size_t size)
+    {
+        return ListBuilder(*this, size);
+    }
+
+    /**
+     * Return a boolean `Value *` without allocating.
+     */
+    Value *getBool(bool b);
+
     void mkThunk_(Value & v, Expr * expr);
     void mkPos(Value & v, PosIdx pos);
 
@@ -662,7 +709,7 @@ public:
         const SingleDerivedPath & p,
         Value & v);
 
-    void concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos, std::string_view errorCtx);
+    void concatLists(Value & v, size_t nrLists, Value * const * lists, const PosIdx pos, std::string_view errorCtx);
 
     /**
      * Print statistics, if enabled.
@@ -756,6 +803,7 @@ private:
     friend void prim_split(EvalState & state, const PosIdx pos, Value * * args, Value & v);
 
     friend struct Value;
+    friend class ListBuilder;
 };
 
 struct DebugTraceStacker {

src/libexpr/flake/flake.cc

@@ -10,6 +10,7 @@
 #include "finally.hh"
 #include "fetch-settings.hh"
 #include "value-to-json.hh"
+#include "local-fs-store.hh"
 
 namespace nix {
 
@@ -755,7 +756,17 @@ void callFlake(EvalState & state,
 
         auto lockedNode = node.dynamic_pointer_cast<const LockedNode>();
 
-        auto [storePath, subdir] = state.store->toStorePath(sourcePath.path.abs());
+        // FIXME: This is a hack to support chroot stores. Remove this
+        // once we can pass a sourcePath rather than a storePath to
+        // call-flake.nix.
+        auto path = sourcePath.path.abs();
+        if (auto store = state.store.dynamic_pointer_cast<LocalFSStore>()) {
+            auto realStoreDir = store->getRealStoreDir();
+            if (isInDir(path, realStoreDir))
+                path = store->storeDir + path.substr(realStoreDir.size());
+        }
+
+        auto [storePath, subdir] = state.store->toStorePath(path);
 
         emitTreeAttrs(
             state,

src/libexpr/json-to-value.cc

@@ -57,11 +57,10 @@ class JSONSax : nlohmann::json_sax<json> {
         ValueVector values;
         std::unique_ptr<JSONState> resolve(EvalState & state) override
         {
-            Value & v = parent->value(state);
-            state.mkList(v, values.size());
-            for (size_t n = 0; n < values.size(); ++n) {
-                v.listElems()[n] = values[n];
-            }
+            auto list = state.buildList(values.size());
+            for (const auto & [n, v2] : enumerate(list))
+                v2 = values[n];
+            parent->value(state).mkList(list);
             return std::move(parent);
         }
         void add() override {

src/libexpr/local.mk

@@ -11,8 +11,11 @@ libexpr_SOURCES := \
   $(wildcard $(d)/flake/*.cc) \
   $(d)/lexer-tab.cc \
   $(d)/parser-tab.cc
+# Not just for this library itself, but also for downstream libraries using this library
 
-libexpr_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libmain -I src/libexpr
+INCLUDE_libexpr := -I $(d)
+
+libexpr_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libmain) $(INCLUDE_libexpr)
 
 libexpr_LIBS = libutil libstore libfetchers
 

src/libexpr/primops.cc

@@ -187,13 +187,13 @@ static void import(EvalState & state, const PosIdx pos, Value & vPath, Value * v
             NixStringContextElem::DrvDeep { .drvPath = *storePath },
         });
         attrs.alloc(state.sName).mkString(drv.env["name"]);
-        auto & outputsVal = attrs.alloc(state.sOutputs);
-        state.mkList(outputsVal, drv.outputs.size());
 
+        auto list = state.buildList(drv.outputs.size());
         for (const auto & [i, o] : enumerate(drv.outputs)) {
             mkOutputString(state, attrs, *storePath, o);
-            (outputsVal.listElems()[i] = state.allocValue())->mkString(o.first);
+            (list[i] = state.allocValue())->mkString(o.first);
         }
+        attrs.alloc(state.sOutputs).mkList(list);
 
         auto w = state.allocValue();
         w->mkAttrs(attrs);
@@ -694,10 +694,10 @@ static void prim_genericClosure(EvalState & state, const PosIdx pos, Value * * a
     }
 
     /* Create the result list. */
-    state.mkList(v, res.size());
-    unsigned int n = 0;
-    for (auto & i : res)
-        v.listElems()[n++] = i;
+    auto list = state.buildList(res.size());
+    for (const auto & [n, i] : enumerate(res))
+        list[n] = i;
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_genericClosure(PrimOp {
@@ -826,7 +826,7 @@ static void prim_addErrorContext(EvalState & state, const PosIdx pos, Value * *
         auto message = state.coerceToString(pos, *args[0], context,
                 "while evaluating the error message passed to builtins.addErrorContext",
                 false, false).toOwned();
-        e.addTrace(nullptr, HintFmt(message));
+        e.addTrace(nullptr, HintFmt(message), TracePrint::Always);
         throw;
     }
 }
@@ -834,6 +834,8 @@ static void prim_addErrorContext(EvalState & state, const PosIdx pos, Value * *
 static RegisterPrimOp primop_addErrorContext(PrimOp {
     .name = "__addErrorContext",
     .arity = 2,
+    // The normal trace item is redundant
+    .addTrace = false,
     .fun = prim_addErrorContext,
 });
 
@@ -896,10 +898,11 @@ static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Va
     try {
         state.forceValue(*args[0], pos);
         attrs.insert(state.sValue, args[0]);
-        attrs.alloc("success").mkBool(true);
+        attrs.insert(state.symbols.create("success"), &state.vTrue);
     } catch (AssertionError & e) {
-        attrs.alloc(state.sValue).mkBool(false);
-        attrs.alloc("success").mkBool(false);
+        // `value = false;` is unfortunate but removing it is a breaking change.
+        attrs.insert(state.sValue, &state.vFalse);
+        attrs.insert(state.symbols.create("success"), &state.vFalse);
     }
 
     // restore the debugRepl pointer if we saved it earlier.
@@ -1124,7 +1127,7 @@ drvName, Bindings * attrs, Value & v)
     bool contentAddressed = false;
     bool isImpure = false;
     std::optional<std::string> outputHash;
-    std::string outputHashAlgo;
+    std::optional<HashAlgorithm> outputHashAlgo;
     std::optional<ContentAddressMethod> ingestionMethod;
 
     StringSet outputs;
@@ -1223,7 +1226,7 @@ drvName, Bindings * attrs, Value & v)
                     else if (i->name == state.sOutputHash)
                         outputHash = state.forceStringNoCtx(*i->value, pos, context_below);
                     else if (i->name == state.sOutputHashAlgo)
-                        outputHashAlgo = state.forceStringNoCtx(*i->value, pos, context_below);
+                        outputHashAlgo = parseHashAlgoOpt(state.forceStringNoCtx(*i->value, pos, context_below));
                     else if (i->name == state.sOutputHashMode)
                         handleHashMode(state.forceStringNoCtx(*i->value, pos, context_below));
                     else if (i->name == state.sOutputs) {
@@ -1241,7 +1244,7 @@ drvName, Bindings * attrs, Value & v)
                     if (i->name == state.sBuilder) drv.builder = std::move(s);
                     else if (i->name == state.sSystem) drv.platform = std::move(s);
                     else if (i->name == state.sOutputHash) outputHash = std::move(s);
-                    else if (i->name == state.sOutputHashAlgo) outputHashAlgo = std::move(s);
+                    else if (i->name == state.sOutputHashAlgo) outputHashAlgo = parseHashAlgoOpt(s);
                     else if (i->name == state.sOutputHashMode) handleHashMode(s);
                     else if (i->name == state.sOutputs)
                         handleOutputs(tokenizeString<Strings>(s));
@@ -1324,7 +1327,7 @@ drvName, Bindings * attrs, Value & v)
                 "multiple outputs are not supported in fixed-output derivations"
             ).atPos(v).debugThrow();
 
-        auto h = newHashAllowEmpty(*outputHash, parseHashAlgoOpt(outputHashAlgo));
+        auto h = newHashAllowEmpty(*outputHash, outputHashAlgo);
 
         auto method = ingestionMethod.value_or(FileIngestionMethod::Flat);
 
@@ -1344,7 +1347,7 @@ drvName, Bindings * attrs, Value & v)
             state.error<EvalError>("derivation cannot be both content-addressed and impure")
                 .atPos(v).debugThrow();
 
-        auto ha = parseHashAlgoOpt(outputHashAlgo).value_or(HashAlgorithm::SHA256);
+        auto ha = outputHashAlgo.value_or(HashAlgorithm::SHA256);
         auto method = ingestionMethod.value_or(FileIngestionMethod::Recursive);
 
         for (auto & i : outputs) {
@@ -1567,23 +1570,50 @@ static RegisterPrimOp primop_pathExists({
     .fun = prim_pathExists,
 });
 
+// Ideally, all trailing slashes should have been removed, but it's been like this for
+// almost a decade as of writing. Changing it will affect reproducibility.
+static std::string_view legacyBaseNameOf(std::string_view path)
+{
+    if (path.empty())
+        return "";
+
+    auto last = path.size() - 1;
+    if (path[last] == '/' && last > 0)
+        last -= 1;
+
+    auto pos = path.rfind('/', last);
+    if (pos == path.npos)
+        pos = 0;
+    else
+        pos += 1;
+
+    return path.substr(pos, last - pos + 1);
+}
+
 /* Return the base name of the given string, i.e., everything
    following the last slash. */
 static void prim_baseNameOf(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     NixStringContext context;
-    v.mkString(baseNameOf(*state.coerceToString(pos, *args[0], context,
+    v.mkString(legacyBaseNameOf(*state.coerceToString(pos, *args[0], context,
             "while evaluating the first argument passed to builtins.baseNameOf",
             false, false)), context);
 }
 
 static RegisterPrimOp primop_baseNameOf({
     .name = "baseNameOf",
-    .args = {"s"},
+    .args = {"x"},
     .doc = R"(
-      Return the *base name* of the string *s*, that is, everything
-      following the final slash in the string. This is similar to the GNU
-      `basename` command.
+      Return the *base name* of either a [path value](@docroot@/language/values.md#type-path) *x* or a string *x*, depending on which type is passed, and according to the following rules.
+
+      For a path value, the *base name* is considered to be the part of the path after the last directory separator, including any file extensions.
+      This is the simple case, as path values don't have trailing slashes.
+
+      When the argument is a string, a more involved logic applies. If the string ends with a `/`, only this one final slash is removed.
+
+      After this, the *base name* is returned as previously described, assuming `/` as the directory separator. (Note that evaluation must be platform independent.)
+
+      This is somewhat similar to the [GNU `basename`](https://www.gnu.org/software/coreutils/manual/html_node/basename-invocation.html) command, but GNU `basename` will strip any number of trailing slashes.
     )",
     .fun = prim_baseNameOf,
 });
@@ -1775,20 +1805,20 @@ static RegisterPrimOp primop_hashFile({
     .fun = prim_hashFile,
 });
 
-static std::string_view fileTypeToString(InputAccessor::Type type)
+static Value * fileTypeToString(EvalState & state, InputAccessor::Type type)
 {
     return
-        type == InputAccessor::Type::tRegular ? "regular" :
-        type == InputAccessor::Type::tDirectory ? "directory" :
-        type == InputAccessor::Type::tSymlink ? "symlink" :
-        "unknown";
+        type == InputAccessor::Type::tRegular ? &state.vStringRegular :
+        type == InputAccessor::Type::tDirectory ? &state.vStringDirectory :
+        type == InputAccessor::Type::tSymlink ? &state.vStringSymlink :
+        &state.vStringUnknown;
 }
 
 static void prim_readFileType(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     auto path = realisePath(state, pos, *args[0], std::nullopt);
     /* Retrieve the directory entry type and stringize it. */
-    v.mkString(fileTypeToString(path.lstat().type));
+    v = *fileTypeToString(state, path.lstat().type);
 }
 
 static RegisterPrimOp primop_readFileType({
@@ -1819,8 +1849,8 @@ static void prim_readDir(EvalState & state, const PosIdx pos, Value * * args, Va
     Value * readFileType = nullptr;
 
     for (auto & [name, type] : entries) {
-        auto & attr = attrs.alloc(name);
         if (!type) {
+            auto & attr = attrs.alloc(name);
             // Some filesystems or operating systems may not be able to return
             // detailed node info quickly in this case we produce a thunk to
             // query the file type lazily.
@@ -1832,7 +1862,7 @@ static void prim_readDir(EvalState & state, const PosIdx pos, Value * * args, Va
         } else {
             // This branch of the conditional is much more likely.
             // Here we just stringize the directory entry type.
-            attr.mkString(fileTypeToString(*type));
+            attrs.insert(state.symbols.create(name), fileTypeToString(state, *type));
         }
     }
 
@@ -2193,11 +2223,8 @@ bool EvalState::callPathFilter(
     Value arg1;
     arg1.mkString(pathArg);
 
-    Value arg2;
     // assert that type is not "unknown"
-    arg2.mkString(fileTypeToString(st.type));
-
-    Value * args []{&arg1, &arg2};
+    Value * args []{&arg1, fileTypeToString(*this, st.type)};
     Value res;
     callFunction(*filterFun, 2, args, res, pos);
 
@@ -2423,14 +2450,15 @@ static void prim_attrNames(EvalState & state, const PosIdx pos, Value * * args,
 {
     state.forceAttrs(*args[0], pos, "while evaluating the argument passed to builtins.attrNames");
 
-    state.mkList(v, args[0]->attrs->size());
+    auto list = state.buildList(args[0]->attrs->size());
 
-    size_t n = 0;
-    for (auto & i : *args[0]->attrs)
-        (v.listElems()[n++] = state.allocValue())->mkString(state.symbols[i.name]);
+    for (const auto & [n, i] : enumerate(*args[0]->attrs))
+        (list[n] = state.allocValue())->mkString(state.symbols[i.name]);
 
-    std::sort(v.listElems(), v.listElems() + n,
+    std::sort(list.begin(), list.end(),
               [](Value * v1, Value * v2) { return strcmp(v1->c_str(), v2->c_str()) < 0; });
+
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_attrNames({
@@ -2450,21 +2478,22 @@ static void prim_attrValues(EvalState & state, const PosIdx pos, Value * * args,
 {
     state.forceAttrs(*args[0], pos, "while evaluating the argument passed to builtins.attrValues");
 
-    state.mkList(v, args[0]->attrs->size());
+    auto list = state.buildList(args[0]->attrs->size());
 
-    unsigned int n = 0;
-    for (auto & i : *args[0]->attrs)
-        v.listElems()[n++] = (Value *) &i;
+    for (const auto & [n, i] : enumerate(*args[0]->attrs))
+        list[n] = (Value *) &i;
 
-    std::sort(v.listElems(), v.listElems() + n,
+    std::sort(list.begin(), list.end(),
         [&](Value * v1, Value * v2) {
             std::string_view s1 = state.symbols[((Attr *) v1)->name],
                 s2 = state.symbols[((Attr *) v2)->name];
             return s1 < s2;
         });
 
-    for (unsigned int i = 0; i < n; ++i)
-        v.listElems()[i] = ((Attr *) v.listElems()[i])->value;
+    for (auto & v : list)
+        v = ((Attr *) v)->value;
+
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_attrValues({
@@ -2805,9 +2834,10 @@ static void prim_catAttrs(EvalState & state, const PosIdx pos, Value * * args, V
             res[found++] = i->value;
     }
 
-    state.mkList(v, found);
+    auto list = state.buildList(found);
     for (unsigned int n = 0; n < found; ++n)
-        v.listElems()[n] = res[n];
+        list[n] = res[n];
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_catAttrs({
@@ -2844,8 +2874,7 @@ static void prim_functionArgs(EvalState & state, const PosIdx pos, Value * * arg
 
     auto attrs = state.buildBindings(args[0]->lambda.fun->formals->formals.size());
     for (auto & i : args[0]->lambda.fun->formals->formals)
-        // !!! should optimise booleans (allocate only once)
-        attrs.alloc(i.name, i.pos).mkBool(i.def);
+        attrs.insert(i.name, state.getBool(i.def), i.pos);
     v.mkAttrs(attrs);
 }
 
@@ -2908,43 +2937,50 @@ static void prim_zipAttrsWith(EvalState & state, const PosIdx pos, Value * * arg
     // attribute with the merge function application. this way we need not
     // use (slightly slower) temporary storage the GC does not know about.
 
-    std::map<Symbol, std::pair<size_t, Value * *>> attrsSeen;
+    struct Item
+    {
+        size_t size = 0;
+        size_t pos = 0;
+        std::optional<ListBuilder> list;
+    };
+
+    std::map<Symbol, Item> attrsSeen;
 
     state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.zipAttrsWith");
     state.forceList(*args[1], pos, "while evaluating the second argument passed to builtins.zipAttrsWith");
-    const auto listSize = args[1]->listSize();
-    const auto listElems = args[1]->listElems();
+    const auto listItems = args[1]->listItems();
 
-    for (unsigned int n = 0; n < listSize; ++n) {
-        Value * vElem = listElems[n];
+    for (auto & vElem : listItems) {
         state.forceAttrs(*vElem, noPos, "while evaluating a value of the list passed as second argument to builtins.zipAttrsWith");
         for (auto & attr : *vElem->attrs)
-            attrsSeen[attr.name].first++;
+            attrsSeen.try_emplace(attr.name).first->second.size++;
+    }
+
+    for (auto & [sym, elem] : attrsSeen)
+        elem.list.emplace(state.buildList(elem.size));
+
+    for (auto & vElem : listItems) {
+        for (auto & attr : *vElem->attrs) {
+            auto & item = attrsSeen.at(attr.name);
+            (*item.list)[item.pos++] = attr.value;
+        }
     }
 
     auto attrs = state.buildBindings(attrsSeen.size());
+
     for (auto & [sym, elem] : attrsSeen) {
-        auto & list = attrs.alloc(sym);
-        state.mkList(list, elem.first);
-        elem.second = list.listElems();
-    }
-    v.mkAttrs(attrs.alreadySorted());
-
-    for (unsigned int n = 0; n < listSize; ++n) {
-        Value * vElem = listElems[n];
-        for (auto & attr : *vElem->attrs)
-            *attrsSeen[attr.name].second++ = attr.value;
-    }
-
-    for (auto & attr : *v.attrs) {
         auto name = state.allocValue();
-        name->mkString(state.symbols[attr.name]);
+        name->mkString(state.symbols[sym]);
         auto call1 = state.allocValue();
         call1->mkApp(args[0], name);
         auto call2 = state.allocValue();
-        call2->mkApp(call1, attr.value);
-        attr.value = call2;
+        auto arg = state.allocValue();
+        arg->mkList(*elem.list);
+        call2->mkApp(call1, arg);
+        attrs.insert(sym, call2);
     }
+
+    v.mkAttrs(attrs.alreadySorted());
 }
 
 static RegisterPrimOp primop_zipAttrsWith({
@@ -3055,9 +3091,10 @@ static void prim_tail(EvalState & state, const PosIdx pos, Value * * args, Value
     if (args[0]->listSize() == 0)
         state.error<EvalError>("'tail' called on an empty list").atPos(pos).debugThrow();
 
-    state.mkList(v, args[0]->listSize() - 1);
-    for (unsigned int n = 0; n < v.listSize(); ++n)
-        v.listElems()[n] = args[0]->listElems()[n + 1];
+    auto list = state.buildList(args[0]->listSize() - 1);
+    for (const auto & [n, v] : enumerate(list))
+        v = args[0]->listElems()[n + 1];
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_tail({
@@ -3088,10 +3125,11 @@ static void prim_map(EvalState & state, const PosIdx pos, Value * * args, Value
 
     state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.map");
 
-    state.mkList(v, args[1]->listSize());
-    for (unsigned int n = 0; n < v.listSize(); ++n)
-        (v.listElems()[n] = state.allocValue())->mkApp(
+    auto list = state.buildList(args[1]->listSize());
+    for (const auto & [n, v] : enumerate(list))
+        (v = state.allocValue())->mkApp(
             args[0], args[1]->listElems()[n]);
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_map({
@@ -3140,8 +3178,9 @@ static void prim_filter(EvalState & state, const PosIdx pos, Value * * args, Val
     if (same)
         v = *args[1];
     else {
-        state.mkList(v, k);
-        for (unsigned int n = 0; n < k; ++n) v.listElems()[n] = vs[n];
+        auto list = state.buildList(k);
+        for (const auto & [n, v] : enumerate(list)) v = vs[n];
+        v.mkList(list);
     }
 }
 
@@ -3316,12 +3355,13 @@ static void prim_genList(EvalState & state, const PosIdx pos, Value * * args, Va
     // as evaluating map without accessing any values makes little sense.
     state.forceFunction(*args[0], noPos, "while evaluating the first argument passed to builtins.genList");
 
-    state.mkList(v, len);
-    for (unsigned int n = 0; n < (unsigned int) len; ++n) {
+    auto list = state.buildList(len);
+    for (const auto & [n, v] : enumerate(list)) {
         auto arg = state.allocValue();
         arg->mkInt(n);
-        (v.listElems()[n] = state.allocValue())->mkApp(args[0], arg);
+        (v = state.allocValue())->mkApp(args[0], arg);
     }
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_genList({
@@ -3355,19 +3395,20 @@ static void prim_sort(EvalState & state, const PosIdx pos, Value * * args, Value
 
     state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.sort");
 
-    state.mkList(v, len);
-    for (unsigned int n = 0; n < len; ++n) {
-        state.forceValue(*args[1]->listElems()[n], pos);
-        v.listElems()[n] = args[1]->listElems()[n];
-    }
+    auto list = state.buildList(len);
+    for (const auto & [n, v] : enumerate(list))
+        state.forceValue(*(v = args[1]->listElems()[n]), pos);
 
     auto comparator = [&](Value * a, Value * b) {
         /* Optimization: if the comparator is lessThan, bypass
            callFunction. */
         /* TODO: (layus) this is absurd. An optimisation like this
            should be outside the lambda creation */
-        if (args[0]->isPrimOp() && args[0]->primOp->fun == prim_lessThan)
+        if (args[0]->isPrimOp()) {
+            auto ptr = args[0]->primOp->fun.target<decltype(&prim_lessThan)>();
+            if (ptr && *ptr == prim_lessThan)
                 return CompareValues(state, noPos, "while evaluating the ordering function passed to builtins.sort")(a, b);
+        }
 
         Value * vs[] = {a, b};
         Value vBool;
@@ -3378,7 +3419,9 @@ static void prim_sort(EvalState & state, const PosIdx pos, Value * * args, Value
     /* FIXME: std::sort can segfault if the comparator is not a strict
        weak ordering. What to do? std::stable_sort() seems more
        resilient, but no guarantees... */
-    std::stable_sort(v.listElems(), v.listElems() + len, comparator);
+    std::stable_sort(list.begin(), list.end(), comparator);
+
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_sort({
@@ -3424,17 +3467,17 @@ static void prim_partition(EvalState & state, const PosIdx pos, Value * * args,
 
     auto attrs = state.buildBindings(2);
 
-    auto & vRight = attrs.alloc(state.sRight);
     auto rsize = right.size();
-    state.mkList(vRight, rsize);
+    auto rlist = state.buildList(rsize);
     if (rsize)
-        memcpy(vRight.listElems(), right.data(), sizeof(Value *) * rsize);
+        memcpy(rlist.elems, right.data(), sizeof(Value *) * rsize);
+    attrs.alloc(state.sRight).mkList(rlist);
 
-    auto & vWrong = attrs.alloc(state.sWrong);
     auto wsize = wrong.size();
-    state.mkList(vWrong, wsize);
+    auto wlist = state.buildList(wsize);
     if (wsize)
-        memcpy(vWrong.listElems(), wrong.data(), sizeof(Value *) * wsize);
+        memcpy(wlist.elems, wrong.data(), sizeof(Value *) * wsize);
+    attrs.alloc(state.sWrong).mkList(wlist);
 
     v.mkAttrs(attrs);
 }
@@ -3481,10 +3524,10 @@ static void prim_groupBy(EvalState & state, const PosIdx pos, Value * * args, Va
     auto attrs2 = state.buildBindings(attrs.size());
 
     for (auto & i : attrs) {
-        auto & list = attrs2.alloc(i.first);
         auto size = i.second.size();
-        state.mkList(list, size);
-        memcpy(list.listElems(), i.second.data(), sizeof(Value *) * size);
+        auto list = state.buildList(size);
+        memcpy(list.elems, i.second.data(), sizeof(Value *) * size);
+        attrs2.alloc(i.first).mkList(list);
     }
 
     v.mkAttrs(attrs2.alreadySorted());
@@ -3531,14 +3574,15 @@ static void prim_concatMap(EvalState & state, const PosIdx pos, Value * * args,
         len += lists[n].listSize();
     }
 
-    state.mkList(v, len);
-    auto out = v.listElems();
+    auto list = state.buildList(len);
+    auto out = list.elems;
     for (unsigned int n = 0, pos = 0; n < nrLists; ++n) {
         auto l = lists[n].listSize();
         if (l)
             memcpy(out + pos, lists[n].listElems(), l * sizeof(Value *));
         pos += l;
     }
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_concatMap({
@@ -3820,7 +3864,7 @@ static RegisterPrimOp primop_stringLength({
     .name = "__stringLength",
     .args = {"e"},
     .doc = R"(
-      Return the length of the string *e*. If *e* is not a string,
+      Return the number of bytes of the string *e*. If *e* is not a string,
       evaluation is aborted.
     )",
     .fun = prim_stringLength,
@@ -3986,14 +4030,13 @@ void prim_match(EvalState & state, const PosIdx pos, Value * * args, Value & v)
         }
 
         // the first match is the whole string
-        const size_t len = match.size() - 1;
-        state.mkList(v, len);
-        for (size_t i = 0; i < len; ++i) {
+        auto list = state.buildList(match.size() - 1);
+        for (const auto & [i, v2] : enumerate(list))
             if (!match[i + 1].matched)
-                (v.listElems()[i] = state.allocValue())->mkNull();
+                v2 = &state.vNull;
             else
-                (v.listElems()[i] = state.allocValue())->mkString(match[i + 1].str());
-        }
+                (v2 = state.allocValue())->mkString(match[i + 1].str());
+        v.mkList(list);
 
     } catch (std::regex_error & e) {
         if (e.code() == std::regex_constants::error_space) {
@@ -4062,11 +4105,12 @@ void prim_split(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 
         // Any matches results are surrounded by non-matching results.
         const size_t len = std::distance(begin, end);
-        state.mkList(v, 2 * len + 1);
+        auto list = state.buildList(2 * len + 1);
         size_t idx = 0;
 
         if (len == 0) {
-            v.listElems()[idx++] = args[1];
+            list[0] = args[1];
+            v.mkList(list);
             return;
         }
 
@@ -4075,28 +4119,31 @@ void prim_split(EvalState & state, const PosIdx pos, Value * * args, Value & v)
             auto match = *i;
 
             // Add a string for non-matched characters.
-            (v.listElems()[idx++] = state.allocValue())->mkString(match.prefix().str());
+            (list[idx++] = state.allocValue())->mkString(match.prefix().str());
 
             // Add a list for matched substrings.
             const size_t slen = match.size() - 1;
-            auto elem = v.listElems()[idx++] = state.allocValue();
 
             // Start at 1, beacause the first match is the whole string.
-            state.mkList(*elem, slen);
-            for (size_t si = 0; si < slen; ++si) {
+            auto list2 = state.buildList(slen);
+            for (const auto & [si, v2] : enumerate(list2)) {
                 if (!match[si + 1].matched)
-                    (elem->listElems()[si] = state.allocValue())->mkNull();
+                    v2 = &state.vNull;
                 else
-                    (elem->listElems()[si] = state.allocValue())->mkString(match[si + 1].str());
+                    (v2 = state.allocValue())->mkString(match[si + 1].str());
             }
 
+            (list[idx++] = state.allocValue())->mkList(list2);
+
             // Add a string for non-matched suffix characters.
             if (idx == 2 * len)
-                (v.listElems()[idx++] = state.allocValue())->mkString(match.suffix().str());
+                (list[idx++] = state.allocValue())->mkString(match.suffix().str());
         }
 
         assert(idx == 2 * len + 1);
 
+        v.mkList(list);
+
     } catch (std::regex_error & e) {
         if (e.code() == std::regex_constants::error_space) {
             // limit is _GLIBCXX_REGEX_STATE_LIMIT for libstdc++
@@ -4316,9 +4363,10 @@ static void prim_splitVersion(EvalState & state, const PosIdx pos, Value * * arg
             break;
         components.emplace_back(component);
     }
-    state.mkList(v, components.size());
+    auto list = state.buildList(components.size());
     for (const auto & [n, component] : enumerate(components))
-        (v.listElems()[n] = state.allocValue())->mkString(std::move(component));
+        (list[n] = state.allocValue())->mkString(std::move(component));
+    v.mkList(list);
 }
 
 static RegisterPrimOp primop_splitVersion({
@@ -4411,8 +4459,7 @@ void EvalState::createBaseEnv()
         )",
     });
 
-    v.mkNull();
-    addConstant("null", v, {
+    addConstant("null", &vNull, {
         .type = nNull,
         .doc = R"(
           Primitive value.
@@ -4559,14 +4606,14 @@ void EvalState::createBaseEnv()
     });
 
     /* Add a value containing the current Nix expression search path. */
-    mkList(v, searchPath.elements.size());
-    int n = 0;
-    for (auto & i : searchPath.elements) {
+    auto list = buildList(searchPath.elements.size());
+    for (const auto & [n, i] : enumerate(searchPath.elements)) {
         auto attrs = buildBindings(2);
         attrs.alloc("path").mkString(i.path.s);
         attrs.alloc("prefix").mkString(i.prefix.s);
-        (v.listElems()[n++] = allocValue())->mkAttrs(attrs);
+        (list[n] = allocValue())->mkAttrs(attrs);
     }
+    v.mkList(list);
     addConstant("__nixPath", v, {
         .type = nList,
         .doc = R"(

src/libexpr/primops/context.cc

@@ -207,10 +207,10 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args,
         if (info.second.allOutputs)
             infoAttrs.alloc(sAllOutputs).mkBool(true);
         if (!info.second.outputs.empty()) {
-            auto & outputsVal = infoAttrs.alloc(state.sOutputs);
-            state.mkList(outputsVal, info.second.outputs.size());
+            auto list = state.buildList(info.second.outputs.size());
             for (const auto & [i, output] : enumerate(info.second.outputs))
-                (outputsVal.listElems()[i] = state.allocValue())->mkString(output);
+                (list[i] = state.allocValue())->mkString(output);
+            infoAttrs.alloc(state.sOutputs).mkList(list);
         }
         attrs.alloc(state.store->printStorePath(info.first)).mkAttrs(infoAttrs);
     }

src/libexpr/primops/fromTOML.cc

@@ -38,10 +38,10 @@ static void prim_fromTOML(EvalState & state, const PosIdx pos, Value * * args, V
                 {
                     auto array = toml::get<std::vector<toml::value>>(t);
 
-                    size_t size = array.size();
-                    state.mkList(v, size);
-                    for (size_t i = 0; i < size; ++i)
-                        visit(*(v.listElems()[i] = state.allocValue()), array[i]);
+                    auto list = state.buildList(array.size());
+                    for (const auto & [n, v] : enumerate(list))
+                        visit(*(v = state.allocValue()), array[n]);
+                    v.mkList(list);
                 }
                 break;;
             case toml::value_t::boolean:

src/libexpr/search-path.cc

@@ -44,7 +44,7 @@ SearchPath::Elem SearchPath::Elem::parse(std::string_view rawElem)
 }
 
 
-SearchPath parseSearchPath(const Strings & rawElems)
+SearchPath SearchPath::parse(const Strings & rawElems)
 {
     SearchPath res;
     for (auto & rawElem : rawElems)

src/libexpr/value.hh

@@ -18,6 +18,7 @@
 
 namespace nix {
 
+struct Value;
 class BindingsBuilder;
 
 
@@ -134,6 +135,34 @@ class ExternalValueBase
 std::ostream & operator << (std::ostream & str, const ExternalValueBase & v);
 
 
+class ListBuilder
+{
+    const size_t size;
+    Value * inlineElems[2] = {nullptr, nullptr};
+public:
+    Value * * elems;
+    ListBuilder(EvalState & state, size_t size);
+
+    ListBuilder(ListBuilder && x)
+        : size(x.size)
+        , inlineElems{x.inlineElems[0], x.inlineElems[1]}
+        , elems(size <= 2 ? inlineElems : x.elems)
+    { }
+
+    Value * & operator [](size_t n)
+    {
+        return elems[n];
+    }
+
+    typedef Value * * iterator;
+
+    iterator begin() { return &elems[0]; }
+    iterator end() { return &elems[size]; }
+
+    friend struct Value;
+};
+
+
 struct Value
 {
 private:
@@ -217,7 +246,7 @@ public:
         Bindings * attrs;
         struct {
             size_t size;
-            Value * * elems;
+            Value * const * elems;
         } bigList;
         Value * smallList[2];
         ClosureThunk thunk;
@@ -299,6 +328,7 @@ public:
     }
 
     void mkPath(const SourcePath & path);
+    void mkPath(std::string_view path);
 
     inline void mkPath(InputAccessor * accessor, const char * path)
     {
@@ -323,16 +353,20 @@ public:
 
     Value & mkAttrs(BindingsBuilder & bindings);
 
-    inline void mkList(size_t size)
+    void mkList(const ListBuilder & builder)
     {
         clearValue();
-        if (size == 1)
+        if (builder.size == 1) {
+            smallList[0] = builder.inlineElems[0];
             internalType = tList1;
-        else if (size == 2)
+        } else if (builder.size == 2) {
+            smallList[0] = builder.inlineElems[0];
+            smallList[1] = builder.inlineElems[1];
             internalType = tList2;
-        else {
+        } else {
+            bigList.size = builder.size;
+            bigList.elems = builder.elems;
             internalType = tListN;
-            bigList.size = size;
         }
     }
 
@@ -392,7 +426,7 @@ public:
         return internalType == tList1 || internalType == tList2 || internalType == tListN;
     }
 
-    Value * * listElems()
+    Value * const * listElems()
     {
         return internalType == tList1 || internalType == tList2 ? smallList : bigList.elems;
     }

src/libfetchers/fetch-settings.hh

@@ -78,7 +78,6 @@ struct FetchSettings : public Config
         )",
         {}, true, Xp::Flakes};
 
-
     Setting<bool> useRegistries{this, true, "use-registries",
         "Whether to use flake registries to resolve flake references.",
         {}, true, Xp::Flakes};
@@ -94,6 +93,22 @@ struct FetchSettings : public Config
           empty, the summary is generated based on the action performed.
         )",
         {}, true, Xp::Flakes};
+
+    Setting<bool> trustTarballsFromGitForges{
+        this, true, "trust-tarballs-from-git-forges",
+        R"(
+          If enabled (the default), Nix will consider tarballs from
+          GitHub and similar Git forges to be locked if a Git revision
+          is specified,
+          e.g. `github:NixOS/patchelf/7c2f768bf9601268a4e71c2ebe91e2011918a70f`.
+          This requires Nix to trust that the provider will return the
+          correct contents for the specified Git revision.
+
+          If disabled, such tarballs are only considered locked if a
+          `narHash` attribute is specified,
+          e.g. `github:NixOS/patchelf/7c2f768bf9601268a4e71c2ebe91e2011918a70f?narHash=sha256-PPXqKY2hJng4DBVE0I4xshv/vGLUskL7jl53roB8UdU%3D`.
+        )"};
+
 };
 
 // FIXME: don't use a global variable.

src/libfetchers/git-utils.cc

@@ -21,6 +21,7 @@
 #include <git2/refs.h>
 #include <git2/remote.h>
 #include <git2/repository.h>
+#include <git2/revparse.h>
 #include <git2/status.h>
 #include <git2/submodule.h>
 #include <git2/tree.h>
@@ -199,27 +200,10 @@ struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
 
     Hash resolveRef(std::string ref) override
     {
-        // Handle revisions used as refs.
-        {
-            git_oid oid;
-            if (git_oid_fromstr(&oid, ref.c_str()) == 0)
-                return toHash(oid);
-        }
-
-        // Resolve short names like 'master'.
-        Reference ref2;
-        if (!git_reference_dwim(Setter(ref2), *this, ref.c_str()))
-            ref = git_reference_name(ref2.get());
-
-        // Resolve full references like 'refs/heads/master'.
-        Reference ref3;
-        if (git_reference_lookup(Setter(ref3), *this, ref.c_str()))
+        Object object;
+        if (git_revparse_single(Setter(object), *this, ref.c_str()))
             throw Error("resolving Git reference '%s': %s", ref, git_error_last()->message);
-
-        auto oid = git_reference_target(ref3.get());
-        if (!oid)
-            throw Error("cannot get OID for Git reference '%s'", git_reference_name(ref3.get()));
-
+        auto oid = git_object_id(object.get());
         return toHash(*oid);
     }
 
@@ -364,7 +348,7 @@ struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
     {
         auto act = (Activity *) payload;
         act->result(resFetchStatus, trim(std::string_view(str, len)));
-        return _isInterrupted ? -1 : 0;
+        return getInterrupted() ? -1 : 0;
     }
 
     static int transferProgressCallback(const git_indexer_progress * stats, void * payload)
@@ -377,7 +361,7 @@ struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
                 stats->indexed_deltas,
                 stats->total_deltas,
                 stats->received_bytes / (1024.0 * 1024.0)));
-        return _isInterrupted ? -1 : 0;
+        return getInterrupted() ? -1 : 0;
     }
 
     void fetch(

src/libfetchers/github.cc

@@ -294,7 +294,9 @@ struct GitArchiveInputScheme : InputScheme
            Git revision alone, we also require a NAR hash for
            locking. FIXME: in the future, we may want to require a Git
            tree hash instead of a NAR hash. */
-        return input.getRev().has_value() && input.getNarHash().has_value();
+        return input.getRev().has_value()
+            && (fetchSettings.trustTarballsFromGitForges ||
+                input.getNarHash().has_value());
     }
 
     std::optional<ExperimentalFeature> experimentalFeature() const override

src/libfetchers/local.mk

@@ -5,8 +5,18 @@ libfetchers_NAME = libnixfetchers
 libfetchers_DIR := $(d)
 
 libfetchers_SOURCES := $(wildcard $(d)/*.cc)
+ifdef HOST_UNIX
+  libfetchers_SOURCES += $(wildcard $(d)/unix/*.cc)
+endif
 
-libfetchers_CXXFLAGS += -I src/libutil -I src/libstore
+# Not just for this library itself, but also for downstream libraries using this library
+
+INCLUDE_libfetchers := -I $(d)
+ifdef HOST_UNIX
+  INCLUDE_libfetchers += -I $(d)/unix
+endif
+
+libfetchers_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers)
 
 libfetchers_LDFLAGS += $(THREAD_LDFLAGS) $(LIBGIT2_LIBS) -larchive
 

src/libfetchers/unix/git.cc

@@ -147,9 +147,12 @@ std::vector<PublicKey> getPublicKeys(const Attrs & attrs)
 {
     std::vector<PublicKey> publicKeys;
     if (attrs.contains("publicKeys")) {
-        nlohmann::json publicKeysJson = nlohmann::json::parse(getStrAttr(attrs, "publicKeys"));
-        ensureType(publicKeysJson, nlohmann::json::value_t::array);
-        publicKeys = publicKeysJson.get<std::vector<PublicKey>>();
+        auto pubKeysJson = nlohmann::json::parse(getStrAttr(attrs, "publicKeys"));
+        auto & pubKeys = getArray(pubKeysJson);
+
+        for (auto & key : pubKeys) {
+            publicKeys.push_back(key);
+        }
     }
     if (attrs.contains("publicKey"))
         publicKeys.push_back(PublicKey{maybeGetStrAttr(attrs, "keytype").value_or("ssh-ed25519"),getStrAttr(attrs, "publicKey")});
@@ -585,7 +588,7 @@ struct GitInputScheme : InputScheme
                         repoInfo.url
                         );
             } else
-                input.attrs.insert_or_assign("rev", Hash::parseAny(chomp(readFile(localRefFile)), HashAlgorithm::SHA1).gitRev());
+                input.attrs.insert_or_assign("rev", repo->resolveRef(ref).gitRev());
 
             // cache dir lock is removed at scope end; we will only use read-only operations on specific revisions in the remainder
         }

src/libmain/local.mk

@@ -5,8 +5,13 @@ libmain_NAME = libnixmain
 libmain_DIR := $(d)
 
 libmain_SOURCES := $(wildcard $(d)/*.cc)
+ifdef HOST_UNIX
+  libmain_SOURCES += $(wildcard $(d)/unix/*.cc)
+endif
 
-libmain_CXXFLAGS += -I src/libutil -I src/libstore
+INCLUDE_libmain := -I $(d)
+
+libmain_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libmain)
 
 libmain_LDFLAGS += $(OPENSSL_LIBS)
 

src/libmain/progress-bar.cc

@@ -123,14 +123,18 @@ public:
     }
 
     void pause() override {
-        state_.lock()->paused = true;
+        auto state (state_.lock());
+        state->paused = true;
+        if (state->active)
             writeToStderr("\r\e[K");
     }
 
     void resume() override {
-        state_.lock()->paused = false;
+        auto state (state_.lock());
+        state->paused = false;
+        if (state->active)
             writeToStderr("\r\e[K");
-        state_.lock()->haveUpdate = true;
+        state->haveUpdate = true;
         updateCV.notify_one();
     }
 
@@ -162,9 +166,7 @@ public:
             writeToStderr("\r\e[K" + filterANSIEscapes(s, !isTTY) + ANSI_NORMAL "\n");
             draw(state);
         } else {
-            auto s2 = s + ANSI_NORMAL "\n";
-            if (!isTTY) s2 = filterANSIEscapes(s2, true);
-            writeToStderr(s2);
+            writeToStderr(filterANSIEscapes(s, !isTTY) + "\n");
         }
     }
 
@@ -519,7 +521,7 @@ public:
     std::optional<char> ask(std::string_view msg) override
     {
         auto state(state_.lock());
-        if (!state->active || !isatty(STDIN_FILENO)) return {};
+        if (!state->active) return {};
         std::cerr << fmt("\r\e[K%s ", msg);
         auto s = trim(readLine(STDIN_FILENO));
         if (s.size() != 1) return {};
@@ -535,7 +537,7 @@ public:
 
 Logger * makeProgressBar()
 {
-    return new ProgressBar(shouldANSI());
+    return new ProgressBar(isTTY());
 }
 
 void startProgressBar()

src/libmain/shared.cc

@@ -121,7 +121,7 @@ void initNix()
 
     initLibStore();
 
-    startSignalHandlerThread();
+    unix::startSignalHandlerThread();
 
     /* Reset SIGCHLD to its default. */
     struct sigaction act;
@@ -308,7 +308,7 @@ void printVersion(const std::string & programName)
 void showManPage(const std::string & name)
 {
     restoreProcessContext();
-    setenv("MANPATH", settings.nixManDir.c_str(), 1);
+    setEnv("MANPATH", settings.nixManDir.c_str());
     execlp("man", "man", name.c_str(), nullptr);
     throw SysError("command 'man %1%' failed", name.c_str());
 }
@@ -369,7 +369,7 @@ RunPager::RunPager()
         if (dup2(toPager.readSide.get(), STDIN_FILENO) == -1)
             throw SysError("dupping stdin");
         if (!getenv("LESS"))
-            setenv("LESS", "FRSXMK", 1);
+            setEnv("LESS", "FRSXMK");
         restoreProcessContext();
         if (pager)
             execl("/bin/sh", "sh", "-c", pager, nullptr);

src/libstore-c/local.mk

@@ -0,0 +1,21 @@
+libraries += libstorec
+
+libstorec_NAME = libnixstorec
+
+libstorec_DIR := $(d)
+
+libstorec_SOURCES := $(wildcard $(d)/*.cc)
+
+libstorec_LIBS = libutil libstore libutilc
+
+libstorec_LDFLAGS += $(THREAD_LDFLAGS)
+
+# Not just for this library itself, but also for downstream libraries using this library
+
+INCLUDE_libstorec := -I $(d)
+libstorec_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libutilc) \
+		    $(INCLUDE_libstore) $(INCLUDE_libstorec)
+
+$(eval $(call install-file-in, $(d)/nix-store-c.pc, $(libdir)/pkgconfig, 0644))
+
+libstorec_FORCE_INSTALL := 1

src/libstore-c/nix-store-c.pc.in

@@ -0,0 +1,9 @@
+prefix=@prefix@
+libdir=@libdir@
+includedir=@includedir@
+
+Name: Nix
+Description: Nix Store - C API
+Version: @PACKAGE_VERSION@
+Libs: -L${libdir} -lnixstorec -lnixutilc
+Cflags: -I${includedir}/nix

src/libstore-c/nix_api_store.cc

@@ -0,0 +1,134 @@
+#include "nix_api_store.h"
+#include "nix_api_store_internal.h"
+#include "nix_api_util.h"
+#include "nix_api_util_internal.h"
+
+#include "path.hh"
+#include "store-api.hh"
+#include "build-result.hh"
+
+#include "globals.hh"
+
+nix_err nix_libstore_init(nix_c_context * context)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        nix::initLibStore();
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_init_plugins(nix_c_context * context)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        nix::initPlugins();
+    }
+    NIXC_CATCH_ERRS
+}
+
+Store * nix_store_open(nix_c_context * context, const char * uri, const char *** params)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        std::string uri_str = uri ? uri : "";
+
+        if (uri_str.empty())
+            return new Store{nix::openStore()};
+
+        if (!params)
+            return new Store{nix::openStore(uri_str)};
+
+        nix::Store::Params params_map;
+        for (size_t i = 0; params[i] != nullptr; i++) {
+            params_map[params[i][0]] = params[i][1];
+        }
+        return new Store{nix::openStore(uri_str, params_map)};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+void nix_store_free(Store * store)
+{
+    delete store;
+}
+
+nix_err nix_store_get_uri(nix_c_context * context, Store * store, void * callback, void * user_data)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto res = store->ptr->getUri();
+        return call_nix_get_string_callback(res, callback, user_data);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_store_get_version(nix_c_context * context, Store * store, void * callback, void * user_data)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto res = store->ptr->getVersion();
+        return call_nix_get_string_callback(res.value_or(""), callback, user_data);
+    }
+    NIXC_CATCH_ERRS
+}
+
+bool nix_store_is_valid_path(nix_c_context * context, Store * store, StorePath * path)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        return store->ptr->isValidPath(path->path);
+    }
+    NIXC_CATCH_ERRS_RES(false);
+}
+
+StorePath * nix_store_parse_path(nix_c_context * context, Store * store, const char * path)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        nix::StorePath s = store->ptr->parseStorePath(path);
+        return new StorePath{std::move(s)};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+nix_err nix_store_realise(
+    nix_c_context * context,
+    Store * store,
+    StorePath * path,
+    void * userdata,
+    void (*callback)(void * userdata, const char *, const char *))
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+
+        const std::vector<nix::DerivedPath> paths{nix::DerivedPath::Built{
+            .drvPath = nix::makeConstantStorePathRef(path->path), .outputs = nix::OutputsSpec::All{}}};
+
+        const auto nixStore = store->ptr;
+        auto results = nixStore->buildPathsWithResults(paths, nix::bmNormal, nixStore);
+
+        if (callback) {
+            for (const auto & result : results) {
+                for (const auto & [outputName, realisation] : result.builtOutputs) {
+                    auto op = store->ptr->printStorePath(realisation.outPath);
+                    callback(userdata, outputName.c_str(), op.c_str());
+                }
+            }
+        }
+    }
+    NIXC_CATCH_ERRS
+}
+
+void nix_store_path_free(StorePath * sp)
+{
+    delete sp;
+}

src/libstore-c/nix_api_store.h

@@ -0,0 +1,148 @@
+#ifndef NIX_API_STORE_H
+#define NIX_API_STORE_H
+/**
+ * @defgroup libstore libstore
+ * @brief C bindings for nix libstore
+ *
+ * libstore is used for talking to a Nix store
+ * @{
+ */
+/** @file
+ * @brief Main entry for the libstore C bindings
+ */
+
+#include "nix_api_util.h"
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+/** @brief Reference to a Nix store */
+typedef struct Store Store;
+/** @brief Nix store path */
+typedef struct StorePath StorePath;
+
+/**
+ * @brief Initializes the Nix store library
+ *
+ * This function should be called before creating a Store
+ * This function can be called multiple times.
+ *
+ * @param[out] context Optional, stores error information
+ * @return NIX_OK if the initialization was successful, an error code otherwise.
+ */
+nix_err nix_libstore_init(nix_c_context * context);
+
+/**
+ * @brief Loads the plugins specified in Nix's plugin-files setting.
+ *
+ * Call this once, after calling your desired init functions and setting
+ * relevant settings.
+ *
+ * @param[out] context Optional, stores error information
+ * @return NIX_OK if the initialization was successful, an error code otherwise.
+ */
+nix_err nix_init_plugins(nix_c_context * context);
+
+/**
+ * @brief Open a nix store
+ * Store instances may share state and resources behind the scenes.
+ * @param[out] context Optional, stores error information
+ * @param[in] uri URI of the nix store, copied
+ * @param[in] params optional, array of key-value pairs, {{"endpoint",
+ * "https://s3.local"}}
+ * @return a Store pointer, NULL in case of errors
+ * @see nix_store_free
+ */
+Store * nix_store_open(nix_c_context *, const char * uri, const char *** params);
+
+/**
+ * @brief Deallocate a nix store and free any resources if not also held by other Store instances.
+ *
+ * Does not fail.
+ *
+ * @param[in] store the store to free
+ */
+void nix_store_free(Store * store);
+
+/**
+ * @brief get the URI of a nix store
+ * @param[out] context Optional, stores error information
+ * @param[in] store nix store reference
+ * @param[in] callback Called with the URI.
+ * @param[in] user_data optional, arbitrary data, passed to the callback when it's called.
+ * @see nix_get_string_callback
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_store_get_uri(nix_c_context * context, Store * store, void * callback, void * user_data);
+
+// returns: owned StorePath*
+/**
+ * @brief Parse a Nix store path into a StorePath
+ *
+ * @note Don't forget to free this path using nix_store_path_free()!
+ * @param[out] context Optional, stores error information
+ * @param[in] store nix store reference
+ * @param[in] path Path string to parse, copied
+ * @return owned store path, NULL on error
+ */
+StorePath * nix_store_parse_path(nix_c_context * context, Store * store, const char * path);
+
+/** @brief Deallocate a StorePath
+ *
+ * Does not fail.
+ * @param[in] p the path to free
+ */
+void nix_store_path_free(StorePath * p);
+
+/**
+ * @brief Check if a StorePath is valid (i.e. that corresponding store object and its closure of references exists in
+ * the store)
+ * @param[out] context Optional, stores error information
+ * @param[in] store Nix Store reference
+ * @param[in] path Path to check
+ * @return true or false, error info in context
+ */
+bool nix_store_is_valid_path(nix_c_context * context, Store * store, StorePath * path);
+// nix_err nix_store_ensure(Store*, const char*);
+// nix_err nix_store_build_paths(Store*);
+/**
+ * @brief Realise a Nix store path
+ *
+ * Blocking, calls callback once for each realised output
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] store Nix Store reference
+ * @param[in] path Path to build
+ * @param[in] userdata data to pass to every callback invocation
+ * @param[in] callback called for every realised output
+ */
+nix_err nix_store_realise(
+    nix_c_context * context,
+    Store * store,
+    StorePath * path,
+    void * userdata,
+    void (*callback)(void * userdata, const char * outname, const char * out));
+
+/**
+ * @brief get the version of a nix store.
+ * If the store doesn't have a version (like the dummy store), returns an empty string.
+ * @param[out] context Optional, stores error information
+ * @param[in] store nix store reference
+ * @param[in] callback Called with the version.
+ * @param[in] user_data optional, arbitrary data, passed to the callback when it's called.
+ * @see nix_get_string_callback
+ * @return error code, NIX_OK on success.
+ */
+nix_err nix_store_get_version(nix_c_context * context, Store * store, void * callback, void * user_data);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+/**
+ * @}
+ */
+#endif // NIX_API_STORE_H

src/libstore-c/nix_api_store_internal.h

@@ -0,0 +1,15 @@
+#ifndef NIX_API_STORE_INTERNAL_H
+#define NIX_API_STORE_INTERNAL_H
+#include "store-api.hh"
+
+struct Store
+{
+    nix::ref<nix::Store> ptr;
+};
+
+struct StorePath
+{
+    nix::StorePath path;
+};
+
+#endif

src/libstore/binary-cache-store.cc

@@ -124,14 +124,6 @@ void BinaryCacheStore::writeNarInfo(ref<NarInfo> narInfo)
         diskCache->upsertNarInfo(getUri(), std::string(narInfo->path.hashPart()), std::shared_ptr<NarInfo>(narInfo));
 }
 
-AutoCloseFD openFile(const Path & path)
-{
-    auto fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
-    if (!fd)
-        throw SysError("opening file '%1%'", path);
-    return fd;
-}
-
 ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
     Source & narSource, RepairFlag repair, CheckSigsFlag checkSigs,
     std::function<ValidPathInfo(HashResult)> mkInfo)

src/libstore/build/local-derivation-goal.cc

@@ -17,7 +17,6 @@
 #include "cgroup.hh"
 #include "personality.hh"
 #include "current-process.hh"
-#include "namespaces.hh"
 #include "child.hh"
 #include "unix-domain-socket.hh"
 #include "posix-fs-canonicalise.hh"
@@ -48,6 +47,7 @@
 # include <sys/param.h>
 # include <sys/mount.h>
 # include <sys/syscall.h>
+# include "namespaces.hh"
 # if HAVE_SECCOMP
 #   include <seccomp.h>
 # endif
@@ -488,7 +488,7 @@ void LocalDerivationGoal::startBuilder()
 
     /* Create a temporary directory where the build will take
        place. */
-    tmpDir = createTempDir("", "nix-build-" + std::string(drvPath.name()), false, false, 0700);
+    tmpDir = createTempDir(settings.buildDir.get().value_or(""), "nix-build-" + std::string(drvPath.name()), false, false, 0700);
 
     chownToBuilder(tmpDir);
 
@@ -2053,13 +2053,13 @@ void LocalDerivationGoal::runChild()
                             i.first, i.second.source);
 
                     std::string path = i.first;
-                    struct stat st;
-                    if (lstat(path.c_str(), &st)) {
-                        if (i.second.optional && errno == ENOENT)
+                    auto optSt = maybeLstat(path.c_str());
+                    if (!optSt) {
+                        if (i.second.optional)
                             continue;
-                        throw SysError("getting attributes of path '%s", path);
+                        throw SysError("getting attributes of required path '%s", path);
                     }
-                    if (S_ISDIR(st.st_mode))
+                    if (S_ISDIR(optSt->st_mode))
                         sandboxProfile += fmt("\t(subpath \"%s\")\n", path);
                     else
                         sandboxProfile += fmt("\t(literal \"%s\")\n", path);
@@ -2089,11 +2089,12 @@ void LocalDerivationGoal::runChild()
             bool allowLocalNetworking = parsedDrv->getBoolAttr("__darwinAllowLocalNetworking");
 
             /* The tmpDir in scope points at the temporary build directory for our derivation. Some packages try different mechanisms
-               to find temporary directories, so we want to open up a broader place for them to dump their files, if needed. */
-            Path globalTmpDir = canonPath(getEnvNonEmpty("TMPDIR").value_or("/tmp"), true);
+               to find temporary directories, so we want to open up a broader place for them to put their files, if needed. */
+            Path globalTmpDir = canonPath(defaultTempDir(), true);
 
             /* They don't like trailing slashes on subpath directives */
-            if (globalTmpDir.back() == '/') globalTmpDir.pop_back();
+            while (!globalTmpDir.empty() && globalTmpDir.back() == '/')
+                globalTmpDir.pop_back();
 
             if (getEnv("_NIX_TEST_NO_SANDBOX") != "1") {
                 builder = "/usr/bin/sandbox-exec";
@@ -2270,14 +2271,12 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
             continue;
         }
 
-        struct stat st;
-        if (lstat(actualPath.c_str(), &st) == -1) {
-            if (errno == ENOENT)
+        auto optSt = maybeLstat(actualPath.c_str());
+        if (!optSt)
             throw BuildError(
                 "builder for '%s' failed to produce output path for output '%s' at '%s'",
                 worker.store.printStorePath(drvPath), outputName, actualPath);
-            throw SysError("getting attributes of path '%s'", actualPath);
-        }
+        struct stat & st = *optSt;
 
 #ifndef __CYGWIN__
         /* Check that the output is not group or world writable, as

src/libstore/builtins/buildenv.cc

@@ -64,9 +64,9 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,
             continue;
 
         else if (S_ISDIR(srcSt.st_mode)) {
-            struct stat dstSt;
-            auto res = lstat(dstFile.c_str(), &dstSt);
-            if (res == 0) {
+            auto dstStOpt = maybeLstat(dstFile.c_str());
+            if (dstStOpt) {
+                auto & dstSt = *dstStOpt;
                 if (S_ISDIR(dstSt.st_mode)) {
                     createLinks(state, srcFile, dstFile, priority);
                     continue;
@@ -82,14 +82,13 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,
                     createLinks(state, srcFile, dstFile, priority);
                     continue;
                 }
-            } else if (errno != ENOENT)
-                throw SysError("getting status of '%1%'", dstFile);
+            }
         }
 
         else {
-            struct stat dstSt;
-            auto res = lstat(dstFile.c_str(), &dstSt);
-            if (res == 0) {
+            auto dstStOpt = maybeLstat(dstFile.c_str());
+            if (dstStOpt) {
+                auto & dstSt = *dstStOpt;
                 if (S_ISLNK(dstSt.st_mode)) {
                     auto prevPriority = state.priorities[dstFile];
                     if (prevPriority == priority)
@@ -104,8 +103,7 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,
                         throw SysError("unlinking '%1%'", dstFile);
                 } else if (S_ISDIR(dstSt.st_mode))
                     throw Error("collision between non-directory '%1%' and directory '%2%'", srcFile, dstFile);
-            } else if (errno != ENOENT)
-                throw SysError("getting status of '%1%'", dstFile);
+            }
         }
 
         createSymlink(srcFile, dstFile);

src/libstore/daemon.cc

@@ -1,5 +1,6 @@
 #include "daemon.hh"
 #include "monitor-fd.hh"
+#include "signals.hh"
 #include "worker-protocol.hh"
 #include "worker-protocol-impl.hh"
 #include "build-result.hh"
@@ -254,7 +255,7 @@ struct ClientSettings
                 else if (setSubstituters(settings.substituters))
                     ;
                 else
-                    debug("ignoring the client-specified setting '%s', because it is a restricted setting and you are not a trusted user", name);
+                    warn("ignoring the client-specified setting '%s', because it is a restricted setting and you are not a trusted user", name);
             } catch (UsageError & e) {
                 warn(e.what());
             }
@@ -1038,7 +1039,7 @@ void processConnection(
     unsigned int opCount = 0;
 
     Finally finally([&]() {
-        _isInterrupted = false;
+        setInterrupted(false);
         printMsgUsing(prevLogger, lvlDebug, "%d operations", opCount);
     });
 

src/libstore/derivations.cc

@@ -1239,16 +1239,14 @@ DerivationOutput DerivationOutput::fromJSON(
     const ExperimentalFeatureSettings & xpSettings)
 {
     std::set<std::string_view> keys;
-    ensureType(_json, nlohmann::detail::value_t::object);
-    auto json = (std::map<std::string, nlohmann::json>) _json;
+    auto & json = getObject(_json);
 
     for (const auto & [key, _] : json)
         keys.insert(key);
 
     auto methodAlgo = [&]() -> std::pair<ContentAddressMethod, HashAlgorithm> {
-        std::string hashAlgoStr = json["hashAlgo"];
-        // remaining to parse, will be mutated by parsers
-        std::string_view s = hashAlgoStr;
+        auto & str = getString(valueAt(json, "hashAlgo"));
+        std::string_view s = str;
         ContentAddressMethod method = ContentAddressMethod::parsePrefix(s);
         if (method == TextIngestionMethod {})
             xpSettings.require(Xp::DynamicDerivations);
@@ -1258,7 +1256,7 @@ DerivationOutput DerivationOutput::fromJSON(
 
     if (keys == (std::set<std::string_view> { "path" })) {
         return DerivationOutput::InputAddressed {
-            .path = store.parseStorePath((std::string) json["path"]),
+            .path = store.parseStorePath(getString(valueAt(json, "path"))),
         };
     }
 
@@ -1267,10 +1265,10 @@ DerivationOutput DerivationOutput::fromJSON(
         auto dof = DerivationOutput::CAFixed {
             .ca = ContentAddress {
                 .method = std::move(method),
-                .hash = Hash::parseNonSRIUnprefixed((std::string) json["hash"], hashAlgo),
+                .hash = Hash::parseNonSRIUnprefixed(getString(valueAt(json, "hash")), hashAlgo),
             },
         };
-        if (dof.path(store, drvName, outputName) != store.parseStorePath((std::string) json["path"]))
+        if (dof.path(store, drvName, outputName) != store.parseStorePath(getString(valueAt(json, "path"))))
             throw Error("Path doesn't match derivation output");
         return dof;
     }
@@ -1357,20 +1355,19 @@ nlohmann::json Derivation::toJSON(const StoreDirConfig & store) const
 
 Derivation Derivation::fromJSON(
     const StoreDirConfig & store,
-    const nlohmann::json & json,
+    const nlohmann::json & _json,
     const ExperimentalFeatureSettings & xpSettings)
 {
     using nlohmann::detail::value_t;
 
     Derivation res;
 
-    ensureType(json, value_t::object);
+    auto & json = getObject(_json);
 
-    res.name = ensureType(valueAt(json, "name"), value_t::string);
+    res.name = getString(valueAt(json, "name"));
 
     try {
-        auto & outputsObj = ensureType(valueAt(json, "outputs"), value_t::object);
-        for (auto & [outputName, output] : outputsObj.items()) {
+        for (auto & [outputName, output] : getObject(valueAt(json, "outputs"))) {
             res.outputs.insert_or_assign(
                 outputName,
                 DerivationOutput::fromJSON(store, res.name, outputName, output));
@@ -1381,8 +1378,7 @@ Derivation Derivation::fromJSON(
     }
 
     try {
-        auto & inputsList = ensureType(valueAt(json, "inputSrcs"), value_t::array);
-        for (auto & input : inputsList)
+        for (auto & input : getArray(valueAt(json, "inputSrcs")))
             res.inputSrcs.insert(store.parseStorePath(static_cast<const std::string &>(input)));
     } catch (Error & e) {
         e.addTrace({}, "while reading key 'inputSrcs'");
@@ -1391,18 +1387,17 @@ Derivation Derivation::fromJSON(
 
     try {
         std::function<DerivedPathMap<StringSet>::ChildNode(const nlohmann::json &)> doInput;
-        doInput = [&](const auto & json) {
+        doInput = [&](const auto & _json) {
+            auto & json = getObject(_json);
             DerivedPathMap<StringSet>::ChildNode node;
-            node.value = static_cast<const StringSet &>(
-                ensureType(valueAt(json, "outputs"), value_t::array));
-            for (auto & [outputId, childNode] : ensureType(valueAt(json, "dynamicOutputs"), value_t::object).items()) {
+            node.value = getStringSet(valueAt(json, "outputs"));
+            for (auto & [outputId, childNode] : getObject(valueAt(json, "dynamicOutputs"))) {
                 xpSettings.require(Xp::DynamicDerivations);
                 node.childMap[outputId] = doInput(childNode);
             }
             return node;
         };
-        auto & inputDrvsObj = ensureType(valueAt(json, "inputDrvs"), value_t::object);
-        for (auto & [inputDrvPath, inputOutputs] : inputDrvsObj.items())
+        for (auto & [inputDrvPath, inputOutputs] : getObject(valueAt(json, "inputDrvs")))
             res.inputDrvs.map[store.parseStorePath(inputDrvPath)] =
                 doInput(inputOutputs);
     } catch (Error & e) {
@@ -1410,10 +1405,10 @@ Derivation Derivation::fromJSON(
         throw;
     }
 
-    res.platform = ensureType(valueAt(json, "system"), value_t::string);
-    res.builder = ensureType(valueAt(json, "builder"), value_t::string);
-    res.args = ensureType(valueAt(json, "args"), value_t::array);
-    res.env = ensureType(valueAt(json, "env"), value_t::object);
+    res.platform = getString(valueAt(json, "system"));
+    res.builder = getString(valueAt(json, "builder"));
+    res.args = getStringList(valueAt(json, "args"));
+    res.env = getStringMap(valueAt(json, "env"));
 
     return res;
 }

src/libstore/filetransfer.cc

@@ -1,5 +1,4 @@
 #include "filetransfer.hh"
-#include "namespaces.hh"
 #include "globals.hh"
 #include "store-api.hh"
 #include "s3.hh"
@@ -12,6 +11,10 @@
 #include <aws/core/client/ClientConfiguration.h>
 #endif
 
+#if __linux__
+# include "namespaces.hh"
+#endif
+
 #include <unistd.h>
 #include <fcntl.h>
 
@@ -257,9 +260,9 @@ struct curlFileTransfer : public FileTransfer
             try {
                 act.progress(dlnow, dltotal);
             } catch (nix::Interrupted &) {
-              assert(_isInterrupted);
+                assert(getInterrupted());
             }
-            return _isInterrupted;
+            return getInterrupted();
         }
 
         static int progressCallbackWrapper(void * userp, double dltotal, double dlnow, double ultotal, double ulnow)
@@ -463,7 +466,7 @@ struct curlFileTransfer : public FileTransfer
                 if (errorSink)
                     response = std::move(errorSink->s);
                 auto exc =
-                    code == CURLE_ABORTED_BY_CALLBACK && _isInterrupted
+                    code == CURLE_ABORTED_BY_CALLBACK && getInterrupted()
                     ? FileTransferError(Interrupted, std::move(response), "%s of '%s' was interrupted", request.verb(), request.uri)
                     : httpStatus != 0
                     ? FileTransferError(err,
@@ -568,7 +571,9 @@ struct curlFileTransfer : public FileTransfer
             stopWorkerThread();
         });
 
+        #if __linux__
         unshareFilesystem();
+        #endif
 
         std::map<CURL *, std::shared_ptr<TransferItem>> items;
 

src/libstore/globals.cc

@@ -2,7 +2,6 @@
 #include "current-process.hh"
 #include "archive.hh"
 #include "args.hh"
-#include "users.hh"
 #include "abstract-setting-to-json.hh"
 #include "compute-levels.hh"
 
@@ -57,7 +56,7 @@ Settings::Settings()
     , nixManDir(canonPath(NIX_MAN_DIR))
     , nixDaemonSocketFile(canonPath(getEnvNonEmpty("NIX_DAEMON_SOCKET_PATH").value_or(nixStateDir + DEFAULT_SOCKET_PATH)))
 {
-    buildUsersGroup = getuid() == 0 ? "nixbld" : "";
+    buildUsersGroup = isRootUser() ? "nixbld" : "";
     allowSymlinkedStore = getEnv("NIX_IGNORE_SYMLINK_STORE") == "1";
 
     auto sslOverride = getEnv("NIX_SSL_CERT_FILE").value_or(getEnv("SSL_CERT_FILE").value_or(""));
@@ -346,6 +345,12 @@ void initPlugins()
                 dlopen(file.c_str(), RTLD_LAZY | RTLD_LOCAL);
             if (!handle)
                 throw Error("could not dynamically open plugin file '%s': %s", file, dlerror());
+
+            /* Older plugins use a statically initialized object to run their code.
+               Newer plugins can also export nix_plugin_entry() */
+            void (*nix_plugin_entry)() = (void (*)())dlsym(handle, "nix_plugin_entry");
+            if (nix_plugin_entry)
+                nix_plugin_entry();
         }
     }
 
@@ -404,6 +409,7 @@ void assertLibStoreInitialized() {
 }
 
 void initLibStore() {
+    if (initLibStoreDone) return;
 
     initLibUtil();
 
@@ -415,7 +421,7 @@ void initLibStore() {
        sshd). This breaks build users because they don't have access
        to the TMPDIR, in particular in ‘nix-store --serve’. */
 #if __APPLE__
-    if (hasPrefix(getEnv("TMPDIR").value_or("/tmp"), "/var/folders/"))
+    if (hasPrefix(defaultTempDir(), "/var/folders/"))
         unsetenv("TMPDIR");
 #endif
 

src/libstore/globals.hh

@@ -5,6 +5,7 @@
 #include "config.hh"
 #include "environment-variables.hh"
 #include "experimental-features.hh"
+#include "users.hh"
 
 #include <map>
 #include <limits>
@@ -665,7 +666,7 @@ public:
     Setting<bool> sandboxFallback{this, true, "sandbox-fallback",
         "Whether to disable sandboxing when the kernel doesn't allow it."};
 
-    Setting<bool> requireDropSupplementaryGroups{this, getuid() == 0, "require-drop-supplementary-groups",
+    Setting<bool> requireDropSupplementaryGroups{this, isRootUser(), "require-drop-supplementary-groups",
         R"(
           Following the principle of least privilege,
           Nix will attempt to drop supplementary groups when building with sandboxing.
@@ -687,6 +688,8 @@ public:
     Setting<std::string> sandboxShmSize{
         this, "50%", "sandbox-dev-shm-size",
         R"(
+            *Linux only*
+
             This option determines the maximum size of the `tmpfs` filesystem
             mounted on `/dev/shm` in Linux sandboxes. For the format, see the
             description of the `size` option of `tmpfs` in mount(8). The default
@@ -694,9 +697,27 @@ public:
         )"};
 
     Setting<Path> sandboxBuildDir{this, "/build", "sandbox-build-dir",
-        "The build directory inside the sandbox."};
+        R"(
+            *Linux only*
+
+            The build directory inside the sandbox.
+
+            This directory is backed by [`build-dir`](#conf-build-dir) on the host.
+        )"};
 #endif
 
+    Setting<std::optional<Path>> buildDir{this, std::nullopt, "build-dir",
+        R"(
+            The directory on the host, in which derivations' temporary build directories are created.
+
+            If not set, Nix will use the system temporary directory indicated by the `TMPDIR` environment variable.
+            Note that builds are often performed by the Nix daemon, so its `TMPDIR` is used, and not that of the Nix command line interface.
+
+            This is also the location where [`--keep-failed`](@docroot@/command-ref/opt-common.md#opt-keep-failed) leaves its files.
+
+            If Nix runs without sandbox, or if the platform does not support sandboxing with bind mounts (e.g. macOS), then the [`builder`](@docroot@/language/derivations.md#attr-builder)'s environment will contain this directory, instead of the virtual location [`sandbox-build-dir`](#conf-sandbox-build-dir).
+        )"};
+
     Setting<PathSet> allowedImpureHostPrefixes{this, {}, "allowed-impure-host-deps",
         "Which prefixes to allow derivations to ask for access to (primarily for Darwin)."};
 
@@ -1136,9 +1157,10 @@ public:
         this, {}, "plugin-files",
         R"(
           A list of plugin files to be loaded by Nix. Each of these files will
-          be dlopened by Nix, allowing them to affect execution through static
-          initialization. In particular, these plugins may construct static
-          instances of RegisterPrimOp to add new primops or constants to the
+          be dlopened by Nix. If they contain the symbol `nix_plugin_entry()`,
+          this symbol will be called. Alternatively, they can affect execution
+          through static initialization. In particular, these plugins may construct
+          static instances of RegisterPrimOp to add new primops or constants to the
           expression language, RegisterStoreImplementation to add new store
           implementations, RegisterCommand to add new subcommands to the `nix`
           command, and RegisterSetting to add new nix config settings. See the

src/libstore/http-binary-cache-store.cc

@@ -49,7 +49,7 @@ public:
         , BinaryCacheStore(params)
         , cacheUri(scheme + "://" + _cacheUri)
     {
-        if (cacheUri.back() == '/')
+        while (!cacheUri.empty() && cacheUri.back() == '/')
             cacheUri.pop_back();
 
         diskCache = getNarInfoDiskCache();

src/libstore/local-store.cc

@@ -16,6 +16,7 @@
 #include "posix-fs-canonicalise.hh"
 #include "posix-source-accessor.hh"
 #include "keys.hh"
+#include "users.hh"
 
 #include <iostream>
 #include <algorithm>
@@ -223,7 +224,7 @@ LocalStore::LocalStore(const Params & params)
 
     /* Optionally, create directories and set permissions for a
        multi-user install. */
-    if (getuid() == 0 && settings.buildUsersGroup != "") {
+    if (isRootUser() && settings.buildUsersGroup != "") {
         mode_t perm = 01775;
 
         struct group * gr = getgrnam(settings.buildUsersGroup.get().c_str());
@@ -558,6 +559,19 @@ void LocalStore::openDB(State & state, bool create)
         sqlite3_exec(db, ("pragma main.journal_mode = " + mode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
         SQLiteError::throw_(db, "setting journal mode");
 
+    if (mode == "wal") {
+        /* persist the WAL files when the db connection is closed. This allows
+           for read-only connections without write permissions on the
+           containing directory to succeed on a closed db. Setting the
+           journal_size_limit to 2^40 bytes results in the WAL files getting
+           truncated to 0 on exit and limits the on disk size of the WAL files
+           to 2^40 bytes following a checkpoint */
+        if (sqlite3_exec(db, "pragma main.journal_size_limit = 1099511627776;", 0, 0, 0) == SQLITE_OK) {
+            int enable = 1;
+            sqlite3_file_control(db, NULL, SQLITE_FCNTL_PERSIST_WAL, &enable);
+        }
+    }
+
     /* Increase the auto-checkpoint interval to 40000 pages.  This
        seems enough to ensure that instantiating the NixOS system
        derivation is done in a single fsync(). */
@@ -579,7 +593,7 @@ void LocalStore::openDB(State & state, bool create)
 void LocalStore::makeStoreWritable()
 {
 #if __linux__
-    if (getuid() != 0) return;
+    if (!isRootUser()) return;
     /* Check if /nix/store is on a read-only mount. */
     struct statvfs stat;
     if (statvfs(realStoreDir.get().c_str(), &stat) != 0)
@@ -1588,7 +1602,7 @@ static void makeMutable(const Path & path)
 /* Upgrade from schema 6 (Nix 0.15) to schema 7 (Nix >= 1.3). */
 void LocalStore::upgradeStore7()
 {
-    if (getuid() != 0) return;
+    if (!isRootUser()) return;
     printInfo("removing immutable bits from the Nix store (this may take a while)...");
     makeMutable(realStoreDir);
 }

src/libstore/local.mk

@@ -5,6 +5,9 @@ libstore_NAME = libnixstore
 libstore_DIR := $(d)
 
 libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc $(d)/build/*.cc)
+ifdef HOST_UNIX
+  libstore_SOURCES += $(wildcard $(d)/unix/*.cc)
+endif
 
 libstore_LIBS = libutil
 
@@ -27,8 +30,15 @@ ifeq ($(HAVE_SECCOMP), 1)
   libstore_LDFLAGS += $(LIBSECCOMP_LIBS)
 endif
 
+# Not just for this library itself, but also for downstream libraries using this library
+
+INCLUDE_libstore := -I $(d) -I $(d)/build
+ifdef HOST_UNIX
+  INCLUDE_libstore += -I $(d)/unix
+endif
+
 libstore_CXXFLAGS += \
- -I src/libutil -I src/libstore -I src/libstore/build \
+ $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libstore) \
  -DNIX_PREFIX=\"$(prefix)\" \
  -DNIX_STORE_DIR=\"$(storedir)\" \
  -DNIX_DATA_DIR=\"$(datadir)\" \

src/libstore/lock.cc

@@ -2,6 +2,7 @@
 #include "file-system.hh"
 #include "globals.hh"
 #include "pathlocks.hh"
+#include "users.hh"
 
 #include <pwd.h>
 #include <grp.h>
@@ -192,10 +193,10 @@ std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds, bool useUserNamespace)
 bool useBuildUsers()
 {
     #if __linux__
-    static bool b = (settings.buildUsersGroup != "" || settings.autoAllocateUids) && getuid() == 0;
+    static bool b = (settings.buildUsersGroup != "" || settings.autoAllocateUids) && isRootUser();
     return b;
     #elif __APPLE__
-    static bool b = settings.buildUsersGroup != "" && getuid() == 0;
+    static bool b = settings.buildUsersGroup != "" && isRootUser();
     return b;
     #else
     return false;

src/libstore/nar-info.cc

@@ -172,19 +172,18 @@ NarInfo NarInfo::fromJSON(
     };
 
     if (json.contains("url"))
-        res.url = ensureType(valueAt(json, "url"), value_t::string);
+        res.url = getString(valueAt(json, "url"));
 
     if (json.contains("compression"))
-        res.compression = ensureType(valueAt(json, "compression"), value_t::string);
+        res.compression = getString(valueAt(json, "compression"));
 
     if (json.contains("downloadHash"))
         res.fileHash = Hash::parseAny(
-            static_cast<const std::string &>(
-                ensureType(valueAt(json, "downloadHash"), value_t::string)),
+            getString(valueAt(json, "downloadHash")),
             std::nullopt);
 
     if (json.contains("downloadSize"))
-        res.fileSize = ensureType(valueAt(json, "downloadSize"), value_t::number_integer);
+        res.fileSize = getInteger(valueAt(json, "downloadSize"));
 
     return res;
 }

src/libstore/path-info.cc

@@ -190,23 +190,18 @@ nlohmann::json UnkeyedValidPathInfo::toJSON(
 
 UnkeyedValidPathInfo UnkeyedValidPathInfo::fromJSON(
     const Store & store,
-    const nlohmann::json & json)
+    const nlohmann::json & _json)
 {
-    using nlohmann::detail::value_t;
-
     UnkeyedValidPathInfo res {
         Hash(Hash::dummy),
     };
 
-    ensureType(json, value_t::object);
-    res.narHash = Hash::parseAny(
-        static_cast<const std::string &>(
-            ensureType(valueAt(json, "narHash"), value_t::string)),
-        std::nullopt);
-    res.narSize = ensureType(valueAt(json, "narSize"), value_t::number_integer);
+    auto & json = getObject(_json);
+    res.narHash = Hash::parseAny(getString(valueAt(json, "narHash")), std::nullopt);
+    res.narSize = getInteger(valueAt(json, "narSize"));
 
     try {
-        auto & references = ensureType(valueAt(json, "references"), value_t::array);
+        auto references = getStringList(valueAt(json, "references"));
         for (auto & input : references)
             res.references.insert(store.parseStorePath(static_cast<const std::string &>
 (input)));
@@ -216,20 +211,16 @@ UnkeyedValidPathInfo UnkeyedValidPathInfo::fromJSON(
     }
 
     if (json.contains("ca"))
-        res.ca = ContentAddress::parse(
-            static_cast<const std::string &>(
-                ensureType(valueAt(json, "ca"), value_t::string)));
+        res.ca = ContentAddress::parse(getString(valueAt(json, "ca")));
 
     if (json.contains("deriver"))
-        res.deriver = store.parseStorePath(
-            static_cast<const std::string &>(
-                ensureType(valueAt(json, "deriver"), value_t::string)));
+        res.deriver = store.parseStorePath(getString(valueAt(json, "deriver")));
 
     if (json.contains("registrationTime"))
-        res.registrationTime = ensureType(valueAt(json, "registrationTime"), value_t::number_integer);
+        res.registrationTime = getInteger(valueAt(json, "registrationTime"));
 
     if (json.contains("ultimate"))
-        res.ultimate = ensureType(valueAt(json, "ultimate"), value_t::boolean);
+        res.ultimate = getBoolean(valueAt(json, "ultimate"));
 
     if (json.contains("signatures"))
         res.sigs = valueAt(json, "signatures");

src/libstore/profiles.cc

@@ -308,7 +308,7 @@ std::string optimisticLockProfile(const Path & profile)
 Path profilesDir()
 {
     auto profileRoot =
-        (getuid() == 0)
+        isRootUser()
         ? rootProfilesDir()
         : createNixStateDir() + "/profiles";
     createDirs(profileRoot);
@@ -332,7 +332,7 @@ Path getDefaultProfile()
         // Backwards compatibiliy measure: Make root's profile available as
         // `.../default` as it's what NixOS and most of the init scripts expect
         Path globalProfileLink = settings.nixStateDir + "/profiles/default";
-        if (getuid() == 0 && !pathExists(globalProfileLink)) {
+        if (isRootUser() && !pathExists(globalProfileLink)) {
             replaceSymlink(profile, globalProfileLink);
         }
         return absPath(readLink(profileLink), dirOf(profileLink));

src/libstore/sqlite.cc

@@ -7,6 +7,7 @@
 #include <sqlite3.h>
 
 #include <atomic>
+#include <thread>
 
 namespace nix {
 
@@ -256,10 +257,8 @@ void handleSQLiteBusy(const SQLiteBusy & e, time_t & nextWarning)
     /* Sleep for a while since retrying the transaction right away
        is likely to fail again. */
     checkInterrupt();
-    struct timespec t;
-    t.tv_sec = 0;
-    t.tv_nsec = (random() % 100) * 1000 * 1000; /* <= 0.1s */
-    nanosleep(&t, 0);
+    /* <= 0.1s */
+    std::this_thread::sleep_for(std::chrono::milliseconds { rand() % 100 });
 }
 
 }

src/libstore/store-api.cc

@@ -1307,7 +1307,7 @@ std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Para
         #if __linux__
         else if (!pathExists(stateDir)
             && params.empty()
-            && getuid() != 0
+            && !isRootUser()
             && !getEnv("NIX_STORE_DIR").has_value()
             && !getEnv("NIX_STATE_DIR").has_value())
         {

src/libutil-c/local.mk

@@ -0,0 +1,18 @@
+libraries += libutilc
+
+libutilc_NAME = libnixutilc
+
+libutilc_DIR := $(d)
+
+libutilc_SOURCES := $(wildcard $(d)/*.cc)
+
+# Not just for this library itself, but also for downstream libraries using this library
+
+INCLUDE_libutilc := -I $(d)
+libutilc_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libutilc)
+
+libutilc_LIBS = libutil
+
+libutilc_LDFLAGS += $(THREAD_LDFLAGS)
+
+libutilc_FORCE_INSTALL := 1

src/libutil-c/nix_api_util.cc

@@ -0,0 +1,148 @@
+#include "nix_api_util.h"
+#include "config.hh"
+#include "error.hh"
+#include "nix_api_util_internal.h"
+#include "util.hh"
+
+#include <cxxabi.h>
+#include <typeinfo>
+
+nix_c_context * nix_c_context_create()
+{
+    return new nix_c_context();
+}
+
+void nix_c_context_free(nix_c_context * context)
+{
+    delete context;
+}
+
+nix_err nix_context_error(nix_c_context * context)
+{
+    if (context == nullptr) {
+        throw;
+    }
+    try {
+        throw;
+    } catch (nix::Error & e) {
+        /* Storing this exception is annoying, take what we need here */
+        context->last_err = e.what();
+        context->info = e.info();
+        int status;
+        const char * demangled = abi::__cxa_demangle(typeid(e).name(), 0, 0, &status);
+        if (demangled) {
+            context->name = demangled;
+            // todo: free(demangled);
+        } else {
+            context->name = typeid(e).name();
+        }
+        context->last_err_code = NIX_ERR_NIX_ERROR;
+        return context->last_err_code;
+    } catch (const std::exception & e) {
+        context->last_err = e.what();
+        context->last_err_code = NIX_ERR_UNKNOWN;
+        return context->last_err_code;
+    }
+    // unreachable
+}
+
+nix_err nix_set_err_msg(nix_c_context * context, nix_err err, const char * msg)
+{
+    if (context == nullptr) {
+        // todo last_err_code
+        throw nix::Error("Nix C api error: %s", msg);
+    }
+    context->last_err_code = err;
+    context->last_err = msg;
+    return err;
+}
+
+const char * nix_version_get()
+{
+    return PACKAGE_VERSION;
+}
+
+// Implementations
+
+nix_err nix_setting_get(nix_c_context * context, const char * key, void * callback, void * user_data)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        std::map<std::string, nix::AbstractConfig::SettingInfo> settings;
+        nix::globalConfig.getSettings(settings);
+        if (settings.contains(key)) {
+            return call_nix_get_string_callback(settings[key].value, callback, user_data);
+        } else {
+            return nix_set_err_msg(context, NIX_ERR_KEY, "Setting not found");
+        }
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_setting_set(nix_c_context * context, const char * key, const char * value)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    if (nix::globalConfig.set(key, value))
+        return NIX_OK;
+    else {
+        return nix_set_err_msg(context, NIX_ERR_KEY, "Setting not found");
+    }
+}
+
+nix_err nix_libutil_init(nix_c_context * context)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        nix::initLibUtil();
+        return NIX_OK;
+    }
+    NIXC_CATCH_ERRS
+}
+
+const char * nix_err_msg(nix_c_context * context, const nix_c_context * read_context, unsigned int * n)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    if (read_context->last_err) {
+        if (n)
+            *n = read_context->last_err->size();
+        return read_context->last_err->c_str();
+    }
+    nix_set_err_msg(context, NIX_ERR_UNKNOWN, "No error message");
+    return nullptr;
+}
+
+nix_err nix_err_name(nix_c_context * context, const nix_c_context * read_context, void * callback, void * user_data)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    if (read_context->last_err_code != NIX_ERR_NIX_ERROR) {
+        return nix_set_err_msg(context, NIX_ERR_UNKNOWN, "Last error was not a nix error");
+    }
+    return call_nix_get_string_callback(read_context->name, callback, user_data);
+}
+
+nix_err nix_err_info_msg(nix_c_context * context, const nix_c_context * read_context, void * callback, void * user_data)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    if (read_context->last_err_code != NIX_ERR_NIX_ERROR) {
+        return nix_set_err_msg(context, NIX_ERR_UNKNOWN, "Last error was not a nix error");
+    }
+    return call_nix_get_string_callback(read_context->info->msg.str(), callback, user_data);
+}
+
+nix_err nix_err_code(const nix_c_context * read_context)
+{
+    return read_context->last_err_code;
+}
+
+// internal
+nix_err call_nix_get_string_callback(const std::string str, void * callback, void * user_data)
+{
+    ((nix_get_string_callback) callback)(str.c_str(), str.size(), user_data);
+    return NIX_OK;
+}

src/libutil-c/nix_api_util.h

@@ -0,0 +1,301 @@
+#ifndef NIX_API_UTIL_H
+#define NIX_API_UTIL_H
+/**
+ * @defgroup libutil libutil
+ * @brief C bindings for nix libutil
+ *
+ * libutil is used for functionality shared between
+ * different Nix modules.
+ * @{
+ */
+/** @file
+ * @brief Main entry for the libutil C bindings
+ *
+ * Also contains error handling utilities
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+/** @defgroup errors Handling errors
+ * @brief Dealing with errors from the Nix side
+ *
+ * To handle errors that can be returned from the Nix API,
+ * a nix_c_context can be passed to any function that potentially returns an
+ * error.
+ *
+ * Error information will be stored in this context, and can be retrieved
+ * using nix_err_code and nix_err_msg.
+ *
+ * Passing NULL instead will cause the API to throw C++ errors.
+ *
+ * Example:
+ * @code{.c}
+ * int main() {
+ *     nix_c_context* ctx = nix_c_context_create();
+ *     nix_libutil_init(ctx);
+ *     if (nix_err_code(ctx) != NIX_OK) {
+ *         printf("error: %s\n", nix_err_msg(NULL, ctx, NULL));
+ *         return 1;
+ *     }
+ *     return 0;
+ * }
+ * @endcode
+ *  @{
+ */
+// Error codes
+/**
+ * @brief Type for error codes in the NIX system
+ *
+ * This type can have one of several predefined constants:
+ * - NIX_OK: No error occurred (0)
+ * - NIX_ERR_UNKNOWN: An unknown error occurred (-1)
+ * - NIX_ERR_OVERFLOW: An overflow error occurred (-2)
+ * - NIX_ERR_KEY: A key error occurred (-3)
+ * - NIX_ERR_NIX_ERROR: A generic Nix error occurred (-4)
+ */
+typedef int nix_err;
+
+/**
+ * @brief No error occurred.
+ *
+ * This error code is returned when no error has occurred during the function
+ * execution.
+ */
+#define NIX_OK 0
+
+/**
+ * @brief An unknown error occurred.
+ *
+ * This error code is returned when an unknown error occurred during the
+ * function execution.
+ */
+#define NIX_ERR_UNKNOWN -1
+
+/**
+ * @brief An overflow error occurred.
+ *
+ * This error code is returned when an overflow error occurred during the
+ * function execution.
+ */
+#define NIX_ERR_OVERFLOW -2
+
+/**
+ * @brief A key error occurred.
+ *
+ * This error code is returned when a key error occurred during the function
+ * execution.
+ */
+#define NIX_ERR_KEY -3
+
+/**
+ * @brief A generic Nix error occurred.
+ *
+ * This error code is returned when a generic Nix error occurred during the
+ * function execution.
+ */
+#define NIX_ERR_NIX_ERROR -4
+
+/**
+ * @brief This object stores error state.
+ * @struct nix_c_context
+ *
+ * Passed as a first parameter to functions that can fail, to store error
+ * information.
+ *
+ * Optional wherever it can be used, passing NULL instead will throw a C++
+ * exception.
+ *
+ * The struct is laid out so that it can also be cast to nix_err* to inspect
+ * directly:
+ * @code{.c}
+ * assert(*(nix_err*)ctx == NIX_OK);
+ * @endcode
+ * @note These can be reused between different function calls,
+ *  but make sure not to use them for multiple calls simultaneously (which can
+ * happen in callbacks).
+ */
+typedef struct nix_c_context nix_c_context;
+
+/**
+ * @brief Called to get the value of a string owned by Nix.
+ *
+ * @param[in] start the string to copy.
+ * @param[in] n the string length.
+ * @param[in] user_data optional, arbitrary data, passed to the nix_get_string_callback when it's called.
+ */
+typedef void (*nix_get_string_callback)(const char * start, unsigned int n, void * user_data);
+
+// Function prototypes
+
+/**
+ * @brief Allocate a new nix_c_context.
+ * @throws std::bad_alloc
+ * @return allocated nix_c_context, owned by the caller. Free using
+ * `nix_c_context_free`.
+ */
+nix_c_context * nix_c_context_create();
+/**
+ * @brief Free a nix_c_context. Does not fail.
+ * @param[out] context The context to free, mandatory.
+ */
+void nix_c_context_free(nix_c_context * context);
+/**
+ *  @}
+ */
+
+/**
+ * @brief Initializes nix_libutil and its dependencies.
+ *
+ * This function can be called multiple times, but should be called at least
+ * once prior to any other nix function.
+ *
+ * @param[out] context Optional, stores error information
+ * @return NIX_OK if the initialization is successful, or an error code
+ * otherwise.
+ */
+nix_err nix_libutil_init(nix_c_context * context);
+
+/** @defgroup settings
+ *  @{
+ */
+/**
+ * @brief Retrieves a setting from the nix global configuration.
+ *
+ * This function requires nix_libutil_init() to be called at least once prior to
+ * its use.
+ *
+ * @param[out] context optional, Stores error information
+ * @param[in] key The key of the setting to retrieve.
+ * @param[in] callback Called with the setting value.
+ * @param[in] user_data optional, arbitrary data, passed to the callback when it's called.
+ * @see nix_get_string_callback
+ * @return NIX_ERR_KEY if the setting is unknown, or NIX_OK if the setting was retrieved
+ * successfully.
+ */
+nix_err nix_setting_get(nix_c_context * context, const char * key, void * callback, void * user_data);
+
+/**
+ * @brief Sets a setting in the nix global configuration.
+ *
+ * Use "extra-<setting name>" to append to the setting's value.
+ *
+ * Settings only apply for new State%s. Call nix_plugins_init() when you are
+ * done with the settings to load any plugins.
+ *
+ * @param[out] context optional, Stores error information
+ * @param[in] key The key of the setting to set.
+ * @param[in] value The value to set for the setting.
+ * @return NIX_ERR_KEY if the setting is unknown, or NIX_OK if the setting was
+ * set successfully.
+ */
+nix_err nix_setting_set(nix_c_context * context, const char * key, const char * value);
+
+/**
+ *  @}
+ */
+// todo: nix_plugins_init()
+
+/**
+ * @brief Retrieves the nix library version.
+ *
+ * Does not fail.
+ * @return A static string representing the version of the nix library.
+ */
+const char * nix_version_get();
+
+/** @addtogroup errors
+ *  @{
+ */
+/**
+ * @brief Retrieves the most recent error message from a context.
+ *
+ * @pre This function should only be called after a previous nix function has
+ * returned an error.
+ *
+ * @param[out] context optional, the context to store errors in if this function
+ * fails
+ * @param[in] ctx the context to retrieve the error message from
+ * @param[out] n optional: a pointer to an unsigned int that is set to the
+ * length of the error.
+ * @return nullptr if no error message was ever set,
+ *         a borrowed pointer to the error message otherwise.
+ */
+const char * nix_err_msg(nix_c_context * context, const nix_c_context * ctx, unsigned int * n);
+
+/**
+ * @brief Retrieves the error message from errorInfo in a context.
+ *
+ * Used to inspect nix Error messages.
+ *
+ * @pre This function should only be called after a previous nix function has
+ * returned a NIX_ERR_NIX_ERROR
+ *
+ * @param[out] context optional, the context to store errors in if this function
+ * fails
+ * @param[in] read_context the context to retrieve the error message from.
+ * @param[in] callback Called with the error message.
+ * @param[in] user_data optional, arbitrary data, passed to the callback when it's called.
+ * @see nix_get_string_callback
+ * @return NIX_OK if there were no errors, an error code otherwise.
+ */
+nix_err
+nix_err_info_msg(nix_c_context * context, const nix_c_context * read_context, void * callback, void * user_data);
+
+/**
+ * @brief Retrieves the error name from a context.
+ *
+ * Used to inspect nix Error messages.
+ *
+ * @pre This function should only be called after a previous nix function has
+ * returned a NIX_ERR_NIX_ERROR
+ *
+ * @param context optional, the context to store errors in if this function
+ * fails
+ * @param[in] read_context the context to retrieve the error message from
+ * @param[in] callback Called with the error name.
+ * @param[in] user_data optional, arbitrary data, passed to the callback when it's called.
+ * @see nix_get_string_callback
+ * @return NIX_OK if there were no errors, an error code otherwise.
+ */
+nix_err nix_err_name(nix_c_context * context, const nix_c_context * read_context, void * callback, void * user_data);
+
+/**
+ * @brief Retrieves the most recent error code from a nix_c_context
+ *
+ * Equivalent to reading the first field of the context.
+ *
+ * Does not fail
+ *
+ * @param[in] read_context the context to retrieve the error message from
+ * @return most recent error code stored in the context.
+ */
+nix_err nix_err_code(const nix_c_context * read_context);
+
+/**
+ * @brief Set an error message on a nix context.
+ *
+ * This should be used when you want to throw an error from a PrimOp callback.
+ *
+ * All other use is internal to the API.
+ *
+ * @param context context to write the error message to, or NULL
+ * @param err The error code to set and return
+ * @param msg The error message to set.
+ * @returns the error code set
+ */
+nix_err nix_set_err_msg(nix_c_context * context, nix_err err, const char * msg);
+
+/**
+ *  @}
+ */
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+
+/** @} */
+#endif // NIX_API_UTIL_H

src/libutil-c/nix_api_util_internal.h

@@ -0,0 +1,49 @@
+#ifndef NIX_API_UTIL_INTERNAL_H
+#define NIX_API_UTIL_INTERNAL_H
+
+#include <string>
+#include <optional>
+
+#include "error.hh"
+#include "nix_api_util.h"
+
+struct nix_c_context
+{
+    nix_err last_err_code = NIX_OK;
+    std::optional<std::string> last_err = {};
+    std::optional<nix::ErrorInfo> info = {};
+    std::string name = "";
+};
+
+nix_err nix_context_error(nix_c_context * context);
+
+/**
+ * Internal use only.
+ *
+ * Helper to invoke nix_get_string_callback
+ * @param context optional, the context to store errors in if this function
+ * fails
+ * @param str The string to observe
+ * @param callback Called with the observed string.
+ * @param user_data optional, arbitrary data, passed to the callback when it's called.
+ * @return NIX_OK if there were no errors.
+ * @see nix_get_string_callback
+ */
+nix_err call_nix_get_string_callback(const std::string str, void * callback, void * user_data);
+
+#define NIXC_CATCH_ERRS \
+    catch (...) \
+    { \
+        return nix_context_error(context); \
+    } \
+    return NIX_OK;
+
+#define NIXC_CATCH_ERRS_RES(def) \
+    catch (...) \
+    { \
+        nix_context_error(context); \
+        return def; \
+    }
+#define NIXC_CATCH_ERRS_NULL NIXC_CATCH_ERRS_RES(nullptr)
+
+#endif // NIX_API_UTIL_INTERNAL_H

src/libutil/args.cc

@@ -285,7 +285,7 @@ void RootArgs::parseCmdline(const Strings & _cmdline, bool allowShebang)
 
                 std::string line;
                 std::getline(stream,line);
-                static const std::string commentChars("#/\\%@*-");
+                static const std::string commentChars("#/\\%@*-(");
                 std::string shebangContent;
                 while (std::getline(stream,line) && !line.empty() && commentChars.find(line[0]) != std::string::npos){
                     line = chomp(line);

src/libutil/compression.cc

@@ -12,8 +12,6 @@
 #include <brotli/decode.h>
 #include <brotli/encode.h>
 
-#include <iostream>
-
 namespace nix {
 
 static const int COMPRESSION_LEVEL_DEFAULT = -1;
@@ -40,20 +38,26 @@ struct ArchiveDecompressionSource : Source
 {
     std::unique_ptr<TarArchive> archive = 0;
     Source & src;
-    ArchiveDecompressionSource(Source & src) : src(src) {}
+    std::optional<std::string> compressionMethod;
+    ArchiveDecompressionSource(Source & src, std::optional<std::string> compressionMethod = std::nullopt)
+        : src(src)
+        , compressionMethod(std::move(compressionMethod))
+    {
+    }
     ~ArchiveDecompressionSource() override {}
-    size_t read(char * data, size_t len) override {
+    size_t read(char * data, size_t len) override
+    {
         struct archive_entry * ae;
         if (!archive) {
-            archive = std::make_unique<TarArchive>(src, true);
-            this->archive->check(archive_read_next_header(this->archive->archive, &ae),
-                "failed to read header (%s)");
+            archive = std::make_unique<TarArchive>(src, /*raw*/ true, compressionMethod);
+            this->archive->check(archive_read_next_header(this->archive->archive, &ae), "failed to read header (%s)");
             if (archive_filter_count(this->archive->archive) < 2) {
                 throw CompressionError("input compression not recognized");
             }
         }
         ssize_t result = archive_read_data(this->archive->archive, data, len);
-        if (result > 0) return result;
+        if (result > 0)
+            return result;
         if (result == 0) {
             throw EndOfFile("reached end of compressed file");
         }
@@ -67,16 +71,19 @@ struct ArchiveCompressionSink : CompressionSink
     Sink & nextSink;
     struct archive * archive;
 
-    ArchiveCompressionSink(Sink & nextSink, std::string format, bool parallel, int level = COMPRESSION_LEVEL_DEFAULT) : nextSink(nextSink)
+    ArchiveCompressionSink(Sink & nextSink, std::string format, bool parallel, int level = COMPRESSION_LEVEL_DEFAULT)
+        : nextSink(nextSink)
     {
         archive = archive_write_new();
-        if (!archive) throw Error("failed to initialize libarchive");
+        if (!archive)
+            throw Error("failed to initialize libarchive");
         check(archive_write_add_filter_by_name(archive, format.c_str()), "couldn't initialize compression (%s)");
         check(archive_write_set_format_raw(archive));
         if (parallel)
             check(archive_write_set_filter_option(archive, format.c_str(), "threads", "0"));
         if (level != COMPRESSION_LEVEL_DEFAULT)
-            check(archive_write_set_filter_option(archive, format.c_str(), "compression-level", std::to_string(level).c_str()));
+            check(archive_write_set_filter_option(
+                archive, format.c_str(), "compression-level", std::to_string(level).c_str()));
         // disable internal buffering
         check(archive_write_set_bytes_per_block(archive, 0));
         // disable output padding
@@ -86,7 +93,8 @@ struct ArchiveCompressionSink : CompressionSink
 
     ~ArchiveCompressionSink() override
     {
-        if (archive) archive_write_free(archive);
+        if (archive)
+            archive_write_free(archive);
     }
 
     void finish() override
@@ -106,7 +114,8 @@ struct ArchiveCompressionSink : CompressionSink
     void writeUnbuffered(std::string_view data) override
     {
         ssize_t result = archive_write_data(archive, data.data(), data.length());
-        if (result <= 0) check(result);
+        if (result <= 0)
+            check(result);
     }
 
 private:
@@ -130,13 +139,20 @@ private:
 struct NoneSink : CompressionSink
 {
     Sink & nextSink;
-    NoneSink(Sink & nextSink, int level = COMPRESSION_LEVEL_DEFAULT) : nextSink(nextSink)
+    NoneSink(Sink & nextSink, int level = COMPRESSION_LEVEL_DEFAULT)
+        : nextSink(nextSink)
     {
         if (level != COMPRESSION_LEVEL_DEFAULT)
             warn("requested compression level '%d' not supported by compression method 'none'", level);
     }
-    void finish() override { flush(); }
-    void writeUnbuffered(std::string_view data) override { nextSink(data); }
+    void finish() override
+    {
+        flush();
+    }
+    void writeUnbuffered(std::string_view data) override
+    {
+        nextSink(data);
+    }
 };
 
 struct BrotliDecompressionSink : ChunkedCompressionSink
@@ -145,7 +161,8 @@ struct BrotliDecompressionSink : ChunkedCompressionSink
     BrotliDecoderState * state;
     bool finished = false;
 
-    BrotliDecompressionSink(Sink & nextSink) : nextSink(nextSink)
+    BrotliDecompressionSink(Sink & nextSink)
+        : nextSink(nextSink)
     {
         state = BrotliDecoderCreateInstance(nullptr, nullptr, nullptr);
         if (!state)
@@ -173,10 +190,7 @@ struct BrotliDecompressionSink : ChunkedCompressionSink
         while (!finished && (!data.data() || avail_in)) {
             checkInterrupt();
 
-            if (!BrotliDecoderDecompressStream(state,
-                    &avail_in, &next_in,
-                    &avail_out, &next_out,
-                    nullptr))
+            if (!BrotliDecoderDecompressStream(state, &avail_in, &next_in, &avail_out, &next_out, nullptr))
                 throw CompressionError("error while decompressing brotli file");
 
             if (avail_out < sizeof(outbuf) || avail_in == 0) {
@@ -206,8 +220,8 @@ std::unique_ptr<FinishSink> makeDecompressionSink(const std::string & method, Si
     else if (method == "br")
         return std::make_unique<BrotliDecompressionSink>(nextSink);
     else
-        return sourceToSink([&](Source & source) {
-            auto decompressionSource = std::make_unique<ArchiveDecompressionSource>(source);
+        return sourceToSink([method, &nextSink](Source & source) {
+            auto decompressionSource = std::make_unique<ArchiveDecompressionSource>(source, method);
             decompressionSource->drainInto(nextSink);
         });
 }
@@ -219,7 +233,8 @@ struct BrotliCompressionSink : ChunkedCompressionSink
     BrotliEncoderState * state;
     bool finished = false;
 
-    BrotliCompressionSink(Sink & nextSink) : nextSink(nextSink)
+    BrotliCompressionSink(Sink & nextSink)
+        : nextSink(nextSink)
     {
         state = BrotliEncoderCreateInstance(nullptr, nullptr, nullptr);
         if (!state)
@@ -247,11 +262,9 @@ struct BrotliCompressionSink : ChunkedCompressionSink
         while (!finished && (!data.data() || avail_in)) {
             checkInterrupt();
 
-            if (!BrotliEncoderCompressStream(state,
-                    data.data() ? BROTLI_OPERATION_PROCESS : BROTLI_OPERATION_FINISH,
-                    &avail_in, &next_in,
-                    &avail_out, &next_out,
-                    nullptr))
+            if (!BrotliEncoderCompressStream(
+                    state, data.data() ? BROTLI_OPERATION_PROCESS : BROTLI_OPERATION_FINISH, &avail_in, &next_in,
+                    &avail_out, &next_out, nullptr))
                 throw CompressionError("error while compressing brotli compression");
 
             if (avail_out < sizeof(outbuf) || avail_in == 0) {
@@ -267,9 +280,8 @@ struct BrotliCompressionSink : ChunkedCompressionSink
 
 ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel, int level)
 {
-    std::vector<std::string> la_supports = {
-        "bzip2", "compress", "grzip", "gzip", "lrzip", "lz4", "lzip", "lzma", "lzop", "xz", "zstd"
-    };
+    std::vector<std::string> la_supports = {"bzip2", "compress", "grzip", "gzip", "lrzip", "lz4",
+                                            "lzip",  "lzma",     "lzop",  "xz",   "zstd"};
     if (std::find(la_supports.begin(), la_supports.end(), method) != la_supports.end()) {
         return make_ref<ArchiveCompressionSink>(nextSink, method, parallel, level);
     }

src/libutil/compression.hh

@@ -22,7 +22,8 @@ std::unique_ptr<FinishSink> makeDecompressionSink(const std::string & method, Si
 
 std::string compress(const std::string & method, std::string_view in, const bool parallel = false, int level = -1);
 
-ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel = false, int level = -1);
+ref<CompressionSink>
+makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel = false, int level = -1);
 
 MakeError(UnknownCompressionMethod, Error);
 

src/libutil/config.cc

@@ -124,7 +124,7 @@ static void applyConfigInner(const std::string & contents, const std::string & p
             auto p = absPath(tokens[1], dirOf(path));
             if (pathExists(p)) {
                 try {
-                    std::string includedContents = readFile(path);
+                    std::string includedContents = readFile(p);
                     applyConfigInner(includedContents, p, parsedContents);
                 } catch (SystemError &) {
                     // TODO: Do we actually want to ignore this? Or is it better to fail?

src/libutil/current-process.cc

@@ -2,7 +2,6 @@
 #include <cstring>
 
 #include "current-process.hh"
-#include "namespaces.hh"
 #include "util.hh"
 #include "finally.hh"
 #include "file-system.hh"
@@ -17,6 +16,7 @@
 # include <mutex>
 # include <sys/resource.h>
 # include "cgroup.hh"
+# include "namespaces.hh"
 #endif
 
 #include <sys/mount.h>
@@ -82,9 +82,11 @@ void setStackSize(rlim_t stackSize)
 
 void restoreProcessContext(bool restoreMounts)
 {
-    restoreSignals();
+    unix::restoreSignals();
     if (restoreMounts) {
+        #if __linux__
         restoreMountNamespace();
+        #endif
     }
 
     if (savedStackSize) {

src/libutil/environment-variables.cc

@@ -32,7 +32,6 @@ std::map<std::string, std::string> getEnv()
     return env;
 }
 
-
 void clearEnv()
 {
     for (auto & name : getEnv())
@@ -43,7 +42,7 @@ void replaceEnv(const std::map<std::string, std::string> & newEnv)
 {
     clearEnv();
     for (auto & newEnvVar : newEnv)
-        setenv(newEnvVar.first.c_str(), newEnvVar.second.c_str(), 1);
+        setEnv(newEnvVar.first.c_str(), newEnvVar.second.c_str());
 }
 
 }

src/libutil/environment-variables.hh

@@ -28,6 +28,14 @@ std::optional<std::string> getEnvNonEmpty(const std::string & key);
  */
 std::map<std::string, std::string> getEnv();
 
+/**
+ * Like POSIX `setenv`, but always overrides.
+ *
+ * We don't need the non-overriding version, and this is easier to
+ * reimplement on Windows.
+ */
+int setEnv(const char * name, const char * value);
+
 /**
  * Clear the environment.
  */