From 2799fe4cdbe77e017544f2fe61ae9baef650dbe6 Mon Sep 17 00:00:00 2001
From: pennae <github@quasiparticle.net>
Date: Tue, 21 Dec 2021 19:34:40 +0100
Subject: [PATCH 01/12] enable LTO in optimized builds
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

gives 2-5% performance improvement across a board of tests.
LTO is broken when using clang; some libs link fine while others crash
the linker with a segfault in the llvm linker plugin. 🙁
---
 Makefile                                |  3 ++-
 Makefile.config.in                      |  1 +
 configure.ac                            | 14 ++++++++++++++
 doc/manual/src/release-notes/rl-next.md |  3 +++
 mk/libraries.mk                         |  6 +++---
 mk/programs.mk                          |  4 ++--
 6 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index 5040d2884..903787e1a 100644
--- a/Makefile
+++ b/Makefile
@@ -27,7 +27,8 @@ makefiles = \
 OPTIMIZE = 1
 
 ifeq ($(OPTIMIZE), 1)
-  GLOBAL_CXXFLAGS += -O3
+  GLOBAL_CXXFLAGS += -O3 $(CXXLTO)
+  GLOBAL_LDFLAGS += $(CXXLTO)
 else
   GLOBAL_CXXFLAGS += -O0 -U_FORTIFY_SOURCE
 endif
diff --git a/Makefile.config.in b/Makefile.config.in
index 3505f337e..d724853fa 100644
--- a/Makefile.config.in
+++ b/Makefile.config.in
@@ -7,6 +7,7 @@ CC = @CC@
 CFLAGS = @CFLAGS@
 CXX = @CXX@
 CXXFLAGS = @CXXFLAGS@
+CXXLTO = @CXXLTO@
 EDITLINE_LIBS = @EDITLINE_LIBS@
 ENABLE_S3 = @ENABLE_S3@
 GTEST_LIBS = @GTEST_LIBS@
diff --git a/configure.ac b/configure.ac
index 8a01c33ec..a86d88fad 100644
--- a/configure.ac
+++ b/configure.ac
@@ -147,6 +147,20 @@ if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
     LDFLAGS="-latomic $LDFLAGS"
 fi
 
+# LTO is currently broken with clang for unknown reasons; ld segfaults in the llvm plugin
+AC_ARG_ENABLE(lto, AS_HELP_STRING([--enable-lto],[Enable LTO (only supported with GCC) [default=no]]),
+  lto=$enableval, lto=no)
+if test "$lto" = yes; then
+    if $CXX --version | grep -q GCC; then
+        AC_SUBST(CXXLTO, [-flto=jobserver])
+    else
+        echo "error: LTO is only supported with GCC at the moment" >&2
+        exit 1
+    fi
+else
+    AC_SUBST(CXXLTO, [""])
+fi
+
 PKG_PROG_PKG_CONFIG
 
 AC_ARG_ENABLE(shared, AS_HELP_STRING([--enable-shared],[Build shared libraries for Nix [default=yes]]),
diff --git a/doc/manual/src/release-notes/rl-next.md b/doc/manual/src/release-notes/rl-next.md
index 7dd8387d8..d81e54e49 100644
--- a/doc/manual/src/release-notes/rl-next.md
+++ b/doc/manual/src/release-notes/rl-next.md
@@ -26,3 +26,6 @@
 
 * Templates can now define a `welcomeText` attribute, which is printed out by
   `nix flake {init,new} --template <template>`.
+
+* Nix can now be built with LTO by passing `--enable-lto` to `configure`.
+  LTO is currently only supported when building with GCC.
diff --git a/mk/libraries.mk b/mk/libraries.mk
index ffd7b5610..876148a55 100644
--- a/mk/libraries.mk
+++ b/mk/libraries.mk
@@ -91,7 +91,7 @@ define build-library
     $(1)_PATH := $$(_d)/$$($(1)_NAME).$(SO_EXT)
 
     $$($(1)_PATH): $$($(1)_OBJS) $$(_libs) | $$(_d)/
-	$$(trace-ld) $(CXX) -o $$(abspath $$@) -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE)) $$($(1)_LDFLAGS_UNINSTALLED)
+	+$$(trace-ld) $(CXX) -o $$(abspath $$@) -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE)) $$($(1)_LDFLAGS_UNINSTALLED)
 
     ifndef HOST_DARWIN
       $(1)_LDFLAGS_USE += -Wl,-rpath,$$(abspath $$(_d))
@@ -105,7 +105,7 @@ define build-library
     $$(eval $$(call create-dir, $$($(1)_INSTALL_DIR)))
 
     $$($(1)_INSTALL_PATH): $$($(1)_OBJS) $$(_libs_final) | $(DESTDIR)$$($(1)_INSTALL_DIR)/
-	$$(trace-ld) $(CXX) -o $$@ -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
+	+$$(trace-ld) $(CXX) -o $$@ -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
 
     $(1)_LDFLAGS_USE_INSTALLED += -L$$(DESTDIR)$$($(1)_INSTALL_DIR) -l$$(patsubst lib%,%,$$(strip $$($(1)_NAME)))
     ifndef HOST_DARWIN
@@ -125,7 +125,7 @@ define build-library
     $(1)_PATH := $$(_d)/$$($(1)_NAME).a
 
     $$($(1)_PATH): $$($(1)_OBJS) | $$(_d)/
-	$$(trace-ld) $(LD) -Ur -o $$(_d)/$$($(1)_NAME).o $$?
+	+$$(trace-ld) $(LD) -Ur -o $$(_d)/$$($(1)_NAME).o $$?
 	$$(trace-ar) $(AR) crs $$@ $$(_d)/$$($(1)_NAME).o
 
     $(1)_LDFLAGS_USE += $$($(1)_PATH) $$($(1)_LDFLAGS)
diff --git a/mk/programs.mk b/mk/programs.mk
index d0cf5baf0..0fc1990f7 100644
--- a/mk/programs.mk
+++ b/mk/programs.mk
@@ -32,7 +32,7 @@ define build-program
   $$(eval $$(call create-dir, $$(_d)))
 
   $$($(1)_PATH): $$($(1)_OBJS) $$(_libs) | $$(_d)/
-	$$(trace-ld) $(CXX) -o $$@ $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE))
+	+$$(trace-ld) $(CXX) -o $$@ $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE))
 
   $(1)_INSTALL_DIR ?= $$(bindir)
 
@@ -49,7 +49,7 @@ define build-program
       _libs_final := $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_INSTALL_PATH))
 
       $(DESTDIR)$$($(1)_INSTALL_PATH): $$($(1)_OBJS) $$(_libs_final) | $(DESTDIR)$$($(1)_INSTALL_DIR)/
-	$$(trace-ld) $(CXX) -o $$@ $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
+	+$$(trace-ld) $(CXX) -o $$@ $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
 
     else
 

From 417aaf4ff7ac1ca501c5a460775fa25d8e078c8a Mon Sep 17 00:00:00 2001
From: regnat <rg@regnat.ovh>
Date: Wed, 22 Dec 2021 11:31:14 +0100
Subject: [PATCH 02/12] Correctly hijack the `file://` uri scheme with
 `_NIX_FORCE_HTTP`

Setting the `_NIX_FORCE_HTTP` environment variable is supposed to force `file://` store urls to use the `HttpBinaryCacheStore` implementation rather than the `LocalBinaryCacheStore` one (very useful for testing).
However because of a name mismatch, the `LocalBinaryCacheStore` was still registering the `file` scheme when this variable was set, meaning that the actual store implementation picked up on `file://` uris was dependent on the registration order of the stores (itself dependent on the link order of the object files).

Fix this by making the `LocalBinaryCacheStore` gracefully not register the `file` uri scheme when the variable is set.
---
 src/libstore/local-binary-cache-store.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libstore/local-binary-cache-store.cc b/src/libstore/local-binary-cache-store.cc
index f754770f9..a3c3e4806 100644
--- a/src/libstore/local-binary-cache-store.cc
+++ b/src/libstore/local-binary-cache-store.cc
@@ -107,7 +107,7 @@ bool LocalBinaryCacheStore::fileExists(const std::string & path)
 
 std::set<std::string> LocalBinaryCacheStore::uriSchemes()
 {
-    if (getEnv("_NIX_FORCE_HTTP_BINARY_CACHE_STORE") == "1")
+    if (getEnv("_NIX_FORCE_HTTP") == "1")
         return {};
     else
         return {"file"};

From 685107c6c8ed9ffaa74101ebc78489903eaf88c0 Mon Sep 17 00:00:00 2001
From: Cole Helbling <cole.e.helbling@outlook.com>
Date: Mon, 16 May 2022 11:46:44 -0700
Subject: [PATCH 03/12] flake: use github: reference to nixpkgs

This allows flakes that don't override the Nixpkgs input and also have a
different flake registry.
---
 flake.lock | 10 ++++++----
 flake.nix  |  4 ++--
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/flake.lock b/flake.lock
index cd79fa85e..31c1910df 100644
--- a/flake.lock
+++ b/flake.lock
@@ -26,9 +26,10 @@
         "type": "github"
       },
       "original": {
-        "id": "nixpkgs",
+        "owner": "NixOS",
         "ref": "nixos-21.05-small",
-        "type": "indirect"
+        "repo": "nixpkgs",
+        "type": "github"
       }
     },
     "nixpkgs-regression": {
@@ -41,9 +42,10 @@
         "type": "github"
       },
       "original": {
-        "id": "nixpkgs",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
         "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
-        "type": "indirect"
+        "type": "github"
       }
     },
     "root": {
diff --git a/flake.nix b/flake.nix
index dd3a25e9e..b33d7d1b3 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,8 +1,8 @@
 {
   description = "The purely functional package manager";
 
-  inputs.nixpkgs.url = "nixpkgs/nixos-21.05-small";
-  inputs.nixpkgs-regression.url = "nixpkgs/215d4d0fd80ca5163643b03a33fde804a29cc1e2";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-21.05-small";
+  inputs.nixpkgs-regression.url = "github:NixOS/nixpkgs/215d4d0fd80ca5163643b03a33fde804a29cc1e2";
   inputs.lowdown-src = { url = "github:kristapsdz/lowdown"; flake = false; };
 
   outputs = { self, nixpkgs, nixpkgs-regression, lowdown-src }:

From 027fd45230b74c67e65d06e7073c04b62c60eb4e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Th=C3=A9ophane=20Hufschmitt?=
 <theophane.hufschmitt@tweag.io>
Date: Fri, 27 May 2022 16:15:28 +0200
Subject: [PATCH 04/12] Fix a segfault in the git fetcher

The git fetcher code used to dereference the (potentially empty) `ref`
input attribute. This was magically working, probably because the
compiler somehow outsmarted us, but is now blowing up with newer nixpkgs
versions.

Fix that by not trying to access this field while we don't know for sure
that it has been defined.

Fix #6554
---
 src/libfetchers/git.cc | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index a71bff76f..9cbd39247 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -449,11 +449,10 @@ struct GitInputScheme : InputScheme
             }
         }
 
-        const Attrs unlockedAttrs({
+        Attrs unlockedAttrs({
             {"type", cacheType},
             {"name", name},
             {"url", actualUrl},
-            {"ref", *input.getRef()},
         });
 
         Path repoDir;
@@ -466,6 +465,7 @@ struct GitInputScheme : InputScheme
                     head = "master";
                 }
                 input.attrs.insert_or_assign("ref", *head);
+                unlockedAttrs.insert_or_assign("ref", *head);
             }
 
             if (!input.getRev())
@@ -482,6 +482,7 @@ struct GitInputScheme : InputScheme
                     head = "master";
                 }
                 input.attrs.insert_or_assign("ref", *head);
+                unlockedAttrs.insert_or_assign("ref", *head);
             }
 
             if (auto res = getCache()->lookup(store, unlockedAttrs)) {

From 8e8e9d8705a68e1be63d6d8059c6c07127826525 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 30 May 2022 11:32:37 +0200
Subject: [PATCH 05/12] Respect the outputSpecified attribute

E.g. 'nix build nixpkgs#libxml2.dev' will build the 'dev' output.
---
 doc/manual/src/release-notes/rl-next.md |  3 --
 src/libcmd/installables.cc              |  9 +++++-
 src/libexpr/eval.cc                     |  1 +
 src/libexpr/eval.hh                     |  3 +-
 src/libexpr/get-drvs.cc                 | 37 +++++++++++++++++--------
 5 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/doc/manual/src/release-notes/rl-next.md b/doc/manual/src/release-notes/rl-next.md
index 878916dc9..7151751dd 100644
--- a/doc/manual/src/release-notes/rl-next.md
+++ b/doc/manual/src/release-notes/rl-next.md
@@ -22,9 +22,6 @@
   `meta.outputsToInstall` attribute if it exists, or all outputs
   otherwise.
 
-  Selecting derivation outputs using the attribute selection syntax
-  (e.g. `nixpkgs#glibc.dev`) no longer works.
-
 * Running nix with the new `--debugger` flag will cause it to start a repl session if
   there is an exception thrown during eval, or if `builtins.break` is called.  From
   there one can inspect symbol values and evaluate nix expressions.  In debug mode
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 635ce19b6..21db2b08b 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -623,7 +623,14 @@ std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableF
     std::set<std::string> outputsToInstall;
     std::optional<NixInt> priority;
 
-    if (auto aMeta = attr->maybeGetAttr(state->sMeta)) {
+    if (auto aOutputSpecified = attr->maybeGetAttr(state->sOutputSpecified)) {
+        if (aOutputSpecified->getBool()) {
+            if (auto aOutputName = attr->maybeGetAttr("outputName"))
+                outputsToInstall = { aOutputName->getString() };
+        }
+    }
+
+    else if (auto aMeta = attr->maybeGetAttr(state->sMeta)) {
         if (auto aOutputsToInstall = aMeta->maybeGetAttr("outputsToInstall"))
             for (auto & s : aOutputsToInstall->getListOfStrings())
                 outputsToInstall.insert(s);
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 18baf1cb7..40462afdf 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -459,6 +459,7 @@ EvalState::EvalState(
     , sKey(symbols.create("key"))
     , sPath(symbols.create("path"))
     , sPrefix(symbols.create("prefix"))
+    , sOutputSpecified(symbols.create("outputSpecified"))
     , repair(NoRepair)
     , emptyBindings(0)
     , store(store)
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 0a32d5885..7b8732169 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -103,7 +103,8 @@ public:
         sOutputHash, sOutputHashAlgo, sOutputHashMode,
         sRecurseForDerivations,
         sDescription, sSelf, sEpsilon, sStartSet, sOperator, sKey, sPath,
-        sPrefix;
+        sPrefix,
+        sOutputSpecified;
     Symbol sDerivationNix;
 
     /* If set, force copying files to the Nix store even if they
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index d616b3921..346741dd5 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -132,23 +132,36 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
         } else
             outputs.emplace("out", withPaths ? std::optional{queryOutPath()} : std::nullopt);
     }
+
     if (!onlyOutputsToInstall || !attrs)
         return outputs;
 
-    /* Check for `meta.outputsToInstall` and return `outputs` reduced to that. */
-    const Value * outTI = queryMeta("outputsToInstall");
-    if (!outTI) return outputs;
-    const auto errMsg = Error("this derivation has bad 'meta.outputsToInstall'");
-        /* ^ this shows during `nix-env -i` right under the bad derivation */
-    if (!outTI->isList()) throw errMsg;
-    Outputs result;
-    for (auto elem : outTI->listItems()) {
-        if (elem->type() != nString) throw errMsg;
-        auto out = outputs.find(elem->string.s);
-        if (out == outputs.end()) throw errMsg;
+    Bindings::iterator i;
+    if (attrs && (i = attrs->find(state->sOutputSpecified)) != attrs->end() && state->forceBool(*i->value, i->pos)) {
+        Outputs result;
+        auto out = outputs.find(queryOutputName());
+        if (out == outputs.end())
+            throw Error("derivation does not have output '%s'", queryOutputName());
         result.insert(*out);
+        return result;
+    }
+
+    else {
+        /* Check for `meta.outputsToInstall` and return `outputs` reduced to that. */
+        const Value * outTI = queryMeta("outputsToInstall");
+        if (!outTI) return outputs;
+        const auto errMsg = Error("this derivation has bad 'meta.outputsToInstall'");
+            /* ^ this shows during `nix-env -i` right under the bad derivation */
+        if (!outTI->isList()) throw errMsg;
+        Outputs result;
+        for (auto elem : outTI->listItems()) {
+            if (elem->type() != nString) throw errMsg;
+            auto out = outputs.find(elem->string.s);
+            if (out == outputs.end()) throw errMsg;
+            result.insert(*out);
+        }
+        return result;
     }
-    return result;
 }
 
 

From b8faa837429cbcb4f950248571c761c98895e7cd Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 30 May 2022 13:24:04 +0200
Subject: [PATCH 06/12] HttpBinaryCacheStore::getFile(): Don't throw an
 exception

This violates the noexcept specification.

Fixes #6445.
---
 src/libstore/http-binary-cache-store.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index 3cb5efdbf..73bcd6e81 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -161,7 +161,12 @@ protected:
     void getFile(const std::string & path,
         Callback<std::optional<std::string>> callback) noexcept override
     {
-        checkEnabled();
+        try {
+            checkEnabled();
+        } catch (...) {
+            callback.rethrow();
+            return;
+        }
 
         auto request(makeRequest(path));
 

From 6378f0bb328437de759f7ed8405fcafbb3bcac54 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 30 May 2022 13:27:13 +0200
Subject: [PATCH 07/12] RemoteStore::queryRealisationUncached(): Fix potential
 noexcept violation

---
 src/libstore/remote-store.cc | 56 +++++++++++++++++-------------------
 1 file changed, 27 insertions(+), 29 deletions(-)

diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 14aeba75c..bc36aef5d 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -718,36 +718,34 @@ void RemoteStore::registerDrvOutput(const Realisation & info)
 void RemoteStore::queryRealisationUncached(const DrvOutput & id,
     Callback<std::shared_ptr<const Realisation>> callback) noexcept
 {
-    auto conn(getConnection());
-
-    if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 27) {
-        warn("the daemon is too old to support content-addressed derivations, please upgrade it to 2.4");
-        try {
-            callback(nullptr);
-        } catch (...) { return callback.rethrow(); }
-    }
-
-    conn->to << wopQueryRealisation;
-    conn->to << id.to_string();
-    conn.processStderr();
-
-    auto real = [&]() -> std::shared_ptr<const Realisation> {
-        if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 31) {
-            auto outPaths = worker_proto::read(
-                *this, conn->from, Phantom<std::set<StorePath>> {});
-            if (outPaths.empty())
-                return nullptr;
-            return std::make_shared<const Realisation>(Realisation { .id = id, .outPath = *outPaths.begin() });
-        } else {
-            auto realisations = worker_proto::read(
-                *this, conn->from, Phantom<std::set<Realisation>> {});
-            if (realisations.empty())
-                return nullptr;
-            return std::make_shared<const Realisation>(*realisations.begin());
-        }
-    }();
-
     try {
+        auto conn(getConnection());
+
+        if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 27) {
+            warn("the daemon is too old to support content-addressed derivations, please upgrade it to 2.4");
+            return callback(nullptr);
+        }
+
+        conn->to << wopQueryRealisation;
+        conn->to << id.to_string();
+        conn.processStderr();
+
+        auto real = [&]() -> std::shared_ptr<const Realisation> {
+            if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 31) {
+                auto outPaths = worker_proto::read(
+                    *this, conn->from, Phantom<std::set<StorePath>> {});
+                if (outPaths.empty())
+                    return nullptr;
+                return std::make_shared<const Realisation>(Realisation { .id = id, .outPath = *outPaths.begin() });
+            } else {
+                auto realisations = worker_proto::read(
+                    *this, conn->from, Phantom<std::set<Realisation>> {});
+                if (realisations.empty())
+                    return nullptr;
+                return std::make_shared<const Realisation>(*realisations.begin());
+            }
+        }();
+
         callback(std::shared_ptr<const Realisation>(real));
     } catch (...) { return callback.rethrow(); }
 }

From 948515efb775c22df5a2585443a0c7f86d2dc64d Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 30 May 2022 13:35:28 +0200
Subject: [PATCH 08/12] Set meta.platforms

'nix-serve' in nixpkgs expects the nix package to set this.
---
 flake.nix | 1 +
 1 file changed, 1 insertion(+)

diff --git a/flake.nix b/flake.nix
index 77b016ff0..6e0e4d423 100644
--- a/flake.nix
+++ b/flake.nix
@@ -380,6 +380,7 @@
               postUnpack = "sourceRoot=$sourceRoot/perl";
             };
 
+            meta.platforms = systems;
           };
 
           lowdown-nix = with final; currentStdenv.mkDerivation rec {

From 452dba510de2f500eae35bbb9dfb5ff825ca0351 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 30 May 2022 14:01:35 +0200
Subject: [PATCH 09/12] Mark nix-perl as a Perl module

The call to perl.withPackages in nix-serve expects this.
---
 flake.nix | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/flake.nix b/flake.nix
index 6e0e4d423..1aa4c4479 100644
--- a/flake.nix
+++ b/flake.nix
@@ -348,7 +348,7 @@
 
             strictDeps = true;
 
-            passthru.perl-bindings = with final; currentStdenv.mkDerivation {
+            passthru.perl-bindings = with final; perl.pkgs.toPerlModule (currentStdenv.mkDerivation {
               name = "nix-perl-${version}";
 
               src = self;
@@ -378,7 +378,7 @@
               enableParallelBuilding = true;
 
               postUnpack = "sourceRoot=$sourceRoot/perl";
-            };
+            });
 
             meta.platforms = systems;
           };

From de13b445730e94a24690fed6480f86a5f9c102c8 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 30 May 2022 20:39:38 +0200
Subject: [PATCH 10/12] Branch 2.9 release notes

---
 doc/manual/src/SUMMARY.md.in            |  1 +
 doc/manual/src/release-notes/rl-2.9.md  | 47 +++++++++++++++++++++++++
 doc/manual/src/release-notes/rl-next.md | 38 --------------------
 3 files changed, 48 insertions(+), 38 deletions(-)
 create mode 100644 doc/manual/src/release-notes/rl-2.9.md

diff --git a/doc/manual/src/SUMMARY.md.in b/doc/manual/src/SUMMARY.md.in
index 860222337..825a8b4c0 100644
--- a/doc/manual/src/SUMMARY.md.in
+++ b/doc/manual/src/SUMMARY.md.in
@@ -72,6 +72,7 @@
   - [CLI guideline](contributing/cli-guideline.md)
 - [Release Notes](release-notes/release-notes.md)
   - [Release X.Y (202?-??-??)](release-notes/rl-next.md)
+  - [Release 2.9 (2022-05-30)](release-notes/rl-2.9.md)
   - [Release 2.8 (2022-04-19)](release-notes/rl-2.8.md)
   - [Release 2.7 (2022-03-07)](release-notes/rl-2.7.md)
   - [Release 2.6 (2022-01-24)](release-notes/rl-2.6.md)
diff --git a/doc/manual/src/release-notes/rl-2.9.md b/doc/manual/src/release-notes/rl-2.9.md
new file mode 100644
index 000000000..ab4b9e42f
--- /dev/null
+++ b/doc/manual/src/release-notes/rl-2.9.md
@@ -0,0 +1,47 @@
+# Release 2.9 (2022-05-30)
+
+* Running Nix with the new `--debugger` flag will cause it to start a
+  repl session if if an exception is thrown during evaluation, or if
+  `builtins.break` is called.  From there you can inspect the values
+  of variables and evaluate Nix expressions.  In debug mode, the
+  following new repl commands are available:
+
+  ```
+  :env          Show env stack
+  :bt           Show trace stack
+  :st           Show current trace
+  :st <idx>     Change to another trace in the stack
+  :c            Go until end of program, exception, or builtins.break().
+  :s            Go one step
+  ```
+
+  Read more about the debugger
+  [here](https://www.zknotes.com/note/5970).
+
+* Nix now provides better integration with zsh's `run-help`
+  feature. It is now included in the Nix installation in the form of
+  an autoloadable shell function, `run-help-nix`. It picks up Nix
+  subcommands from the currently typed in command and directs the user
+  to the associated man pages.
+
+* `nix repl` has a new build-and-link (`:bl`) command that builds a
+  derivation while creating GC root symlinks.
+
+* The path produced by `builtins.toFile` is now allowed to be imported
+  or read even with restricted evaluation. Note that this will not
+  work with a read-only store.
+
+* `nix build` has a new `--print-out-paths` flag to print the
+  resulting output paths.  This matches the default behaviour of
+  `nix-build`.
+
+* You can now specify which outputs of a derivation `nix` should
+  operate on using the syntax `installable^outputs`,
+  e.g. `nixpkgs#glibc^dev,static` or `nixpkgs#glibc^*`. By default,
+  `nix` will use the outputs specified by the derivation's
+  `meta.outputsToInstall` attribute if it exists, or all outputs
+  otherwise.
+
+* `builtins.fetchTree` (and flake inputs) can now be used to fetch
+  plain files over the `http(s)` and `file` protocols in addition to
+  directory tarballs.
diff --git a/doc/manual/src/release-notes/rl-next.md b/doc/manual/src/release-notes/rl-next.md
index 7151751dd..c869b5e2f 100644
--- a/doc/manual/src/release-notes/rl-next.md
+++ b/doc/manual/src/release-notes/rl-next.md
@@ -1,39 +1 @@
 # Release X.Y (202?-??-??)
-
-* Nix now provides better integration with zsh's run-help feature. It is now
-  included in the Nix installation in the form of an autoloadable shell
-  function, run-help-nix. It picks up Nix subcommands from the currently typed
-  in command and directs the user to the associated man pages.
-
-* `nix repl` has a new build-'n-link (`:bl`) command that builds a derivation
-  while creating GC root symlinks.
-
-* The path produced by `builtins.toFile` is now allowed to be imported or read
-  even with restricted evaluation. Note that this will not work with a
-  read-only store.
-
-* `nix build` has a new `--print-out-paths` flag to print the resulting output paths.
-  This matches the default behaviour of `nix-build`.
-
-* You can now specify which outputs of a derivation `nix` should
-  operate on using the syntax `installable^outputs`,
-  e.g. `nixpkgs#glibc^dev,static` or `nixpkgs#glibc^*`. By default,
-  `nix` will use the outputs specified by the derivation's
-  `meta.outputsToInstall` attribute if it exists, or all outputs
-  otherwise.
-
-* Running nix with the new `--debugger` flag will cause it to start a repl session if
-  there is an exception thrown during eval, or if `builtins.break` is called.  From
-  there one can inspect symbol values and evaluate nix expressions.  In debug mode
-  the following new repl commands are available:
-  ```
-  :env          Show env stack
-  :bt           Show trace stack
-  :st           Show current trace
-  :st <idx>     Change to another trace in the stack
-  :c            Go until end of program, exception, or builtins.break().
-  :s            Go one step
-  ```
-
-* `builtins.fetchTree` (and flake inputs) can now be used to fetch plain files
-  over the `http(s)` and `file` protocols in addition to directory tarballs.

From 929ab5b195cb063f7f38e7d6aceb262aaabbeee0 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 30 May 2022 21:11:20 +0200
Subject: [PATCH 11/12] Bump version

---
 .version | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.version b/.version
index f3ac133c5..f161b5d80 100644
--- a/.version
+++ b/.version
@@ -1 +1 @@
-2.9.0
\ No newline at end of file
+2.10.0
\ No newline at end of file

From 04a699b8a9cebd83ece0011ec3a99e38a2adc3a8 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 31 May 2022 10:37:51 +0200
Subject: [PATCH 12/12] Typo

---
 doc/manual/src/release-notes/rl-2.9.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/manual/src/release-notes/rl-2.9.md b/doc/manual/src/release-notes/rl-2.9.md
index ab4b9e42f..98cc4235d 100644
--- a/doc/manual/src/release-notes/rl-2.9.md
+++ b/doc/manual/src/release-notes/rl-2.9.md
@@ -1,7 +1,7 @@
 # Release 2.9 (2022-05-30)
 
 * Running Nix with the new `--debugger` flag will cause it to start a
-  repl session if if an exception is thrown during evaluation, or if
+  repl session if an exception is thrown during evaluation, or if
   `builtins.break` is called.  From there you can inspect the values
   of variables and evaluate Nix expressions.  In debug mode, the
   following new repl commands are available: