Merge remote-tracking branch 'upstream/master' into support-hardlinks-in-tarballs

src/external-api-docs/.gitignore

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

src/external-api-docs/.version

@@ -0,0 +1 @@
+../../.version

src/external-api-docs/README.md

@@ -0,0 +1,121 @@
+# 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{#nix_evaluator_example}
+
+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>
+#include <stdlib.h>
+#include <string.h>
+
+// NOTE: This example lacks all error handling. Production code must check for
+// errors, as some return values will be undefined.
+
+void my_get_string_cb(const char * start, unsigned int n, void * user_data)
+{
+    *((char **) user_data) = strdup(start);
+}
+
+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);
+
+    char * version;
+    nix_get_string(NULL, value, my_get_string_cb, &version);
+    printf("Nix version: %s\n", version);
+
+    free(version);
+    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
+```

src/external-api-docs/doxygen.cfg.in

@@ -0,0 +1,58 @@
+# 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         = @PROJECT_NUMBER@
+
+OUTPUT_DIRECTORY       = @OUTPUT_DIRECTORY@
+
+# 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@/src/libutil-c \
+  @src@/src/libexpr-c \
+  @src@/src/libstore-c \
+  @src@/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.
+
+EXCLUDE_PATTERNS = *_internal.h
+GENERATE_TREEVIEW = YES
+OPTIMIZE_OUTPUT_FOR_C  = YES
+
+USE_MDFILE_AS_MAINPAGE = doc/external-api/README.md

src/external-api-docs/meson.build

@@ -0,0 +1,31 @@
+project('nix-external-api-docs',
+  version : files('.version'),
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+fs = import('fs')
+
+doxygen_cfg = configure_file(
+  input : 'doxygen.cfg.in',
+  output : 'doxygen.cfg',
+  configuration : {
+    'PROJECT_NUMBER': meson.project_version(),
+    'OUTPUT_DIRECTORY' : meson.current_build_dir(),
+    'src' : fs.parent(fs.parent(meson.project_source_root())),
+  },
+)
+
+doxygen = find_program('doxygen', native : true, required : true)
+
+custom_target(
+  'external-api-docs',
+  command : [ doxygen , doxygen_cfg ],
+  input : [
+    doxygen_cfg,
+  ],
+  output : 'html',
+  install : true,
+  install_dir : get_option('datadir') / 'doc/nix/external-api',
+  build_always_stale : true,
+)

src/external-api-docs/package.nix

@@ -0,0 +1,63 @@
+{ lib
+, mkMesonDerivation
+
+, meson
+, ninja
+, doxygen
+
+# Configuration Options
+
+, version
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-external-api-docs";
+  inherit version;
+
+  workDir = ./.;
+  fileset =
+    let
+      cpp = fileset.fileFilter (file: file.hasExt "cc" || file.hasExt "h");
+    in
+    fileset.unions [
+      ./.version
+      ../../.version
+      ./meson.build
+      ./doxygen.cfg.in
+      ./README.md
+      # Source is not compiled, but still must be available for Doxygen
+      # to gather comments.
+      (cpp ../libexpr-c)
+      (cpp ../libstore-c)
+      (cpp ../libutil-c)
+    ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    doxygen
+  ];
+
+  preConfigure =
+    ''
+      chmod u+w ./.version
+      echo ${finalAttrs.version} > ./.version
+    '';
+
+  postInstall = ''
+    mkdir -p ''${!outputDoc}/nix-support
+    echo "doc external-api-docs $out/share/doc/nix/external-api/html" >> ''${!outputDoc}/nix-support/hydra-build-products
+  '';
+
+  enableParallelBuilding = true;
+
+  strictDeps = true;
+
+  meta = {
+    platforms = lib.platforms.all;
+  };
+})

src/internal-api-docs/.gitignore

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

src/internal-api-docs/.version

@@ -0,0 +1 @@
+../../.version

src/internal-api-docs/doxygen.cfg.in

@@ -0,0 +1,99 @@
+# 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         = @PROJECT_NUMBER@
+
+OUTPUT_DIRECTORY       = @OUTPUT_DIRECTORY@
+
+# 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; unstable internal interfaces"
+
+# 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@/libcmd \
+  @src@/libexpr \
+  @src@/libexpr/flake \
+  @src@/nix-expr-tests \
+  @src@/nix-expr-tests/value \
+  @src@/nix-expr-test-support/test \
+  @src@/nix-expr-test-support/test/value \
+  @src@/libexpr/value \
+  @src@/libfetchers \
+  @src@/libmain \
+  @src@/libstore \
+  @src@/libstore/build \
+  @src@/libstore/builtins \
+  @src@/nix-store-tests \
+  @src@/nix-store-test-support/test \
+  @src@/libutil \
+  @src@/nix-util-tests \
+  @src@/nix-util-test-support/test \
+  @src@/nix \
+  @src@/nix-env \
+  @src@/nix-store
+
+# If the MACRO_EXPANSION tag is set to YES, doxygen will expand all macro names
+# in the source code. If set to NO, only conditional compilation will be
+# performed. Macro expansion can be done in a controlled way by setting
+# EXPAND_ONLY_PREDEF to YES.
+# The default value is: NO.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+MACRO_EXPANSION        = YES
+
+# If the EXPAND_ONLY_PREDEF and MACRO_EXPANSION tags are both set to YES then
+# the macro expansion is limited to the macros specified with the PREDEFINED and
+# EXPAND_AS_DEFINED tags.
+# The default value is: NO.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+EXPAND_ONLY_PREDEF     = YES
+
+# The INCLUDE_PATH tag can be used to specify one or more directories that
+# contain include files that are not input files but should be processed by the
+# preprocessor. Note that the INCLUDE_PATH is not recursive, so the setting of
+# RECURSIVE has no effect here.
+# This tag requires that the tag SEARCH_INCLUDES is set to YES.
+
+INCLUDE_PATH           =
+
+# If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
+# tag can be used to specify a list of macro names that should be expanded. The
+# macro definition that is found in the sources will be used. Use the PREDEFINED
+# tag if you want to use a different macro definition that overrules the
+# definition found in the source code.
+# This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
+
+EXPAND_AS_DEFINED      = \
+  DECLARE_COMMON_SERIALISER \
+  DECLARE_WORKER_SERIALISER \
+  DECLARE_SERVE_SERIALISER \
+  LENGTH_PREFIXED_PROTO_HELPER

src/internal-api-docs/meson.build

@@ -0,0 +1,31 @@
+project('nix-internal-api-docs',
+  version : files('.version'),
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+fs = import('fs')
+
+doxygen_cfg = configure_file(
+  input : 'doxygen.cfg.in',
+  output : 'doxygen.cfg',
+  configuration : {
+    'PROJECT_NUMBER': meson.project_version(),
+    'OUTPUT_DIRECTORY' : meson.current_build_dir(),
+    'src' : fs.parent(fs.parent(meson.project_source_root())) / 'src',
+  },
+)
+
+doxygen = find_program('doxygen', native : true, required : true)
+
+custom_target(
+  'internal-api-docs',
+  command : [ doxygen , doxygen_cfg ],
+  input : [
+    doxygen_cfg,
+  ],
+  output : 'html',
+  install : true,
+  install_dir : get_option('datadir') / 'doc/nix/internal-api',
+  build_always_stale : true,
+)

src/internal-api-docs/package.nix

@@ -0,0 +1,58 @@
+{ lib
+, mkMesonDerivation
+
+, meson
+, ninja
+, doxygen
+
+# Configuration Options
+
+, version
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-internal-api-docs";
+  inherit version;
+
+  workDir = ./.;
+  fileset = let
+    cpp = fileset.fileFilter (file: file.hasExt "cc" || file.hasExt "hh");
+  in fileset.unions [
+    ./.version
+    ../../.version
+    ./meson.build
+    ./doxygen.cfg.in
+    # Source is not compiled, but still must be available for Doxygen
+    # to gather comments.
+    (cpp ../.)
+  ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    doxygen
+  ];
+
+  preConfigure =
+    ''
+      chmod u+w ./.version
+      echo ${finalAttrs.version} > ./.version
+    '';
+
+  postInstall = ''
+    mkdir -p ''${!outputDoc}/nix-support
+    echo "doc internal-api-docs $out/share/doc/nix/internal-api/html" >> ''${!outputDoc}/nix-support/hydra-build-products
+  '';
+
+  enableParallelBuilding = true;
+
+  strictDeps = true;
+
+  meta = {
+    platforms = lib.platforms.all;
+  };
+})

src/libcmd/.version

@@ -0,0 +1 @@
+../../.version

src/libcmd/build-utils-meson

@@ -0,0 +1 @@
+../../build-utils-meson

src/libcmd/command.cc

@@ -127,12 +127,12 @@ ref<EvalState> EvalCommand::getEvalState()
     if (!evalState) {
         evalState =
             #if HAVE_BOEHMGC
-            std::allocate_shared<EvalState>(traceable_allocator<EvalState>(),
-                lookupPath, getEvalStore(), getStore())
+            std::allocate_shared<EvalState>(
+                traceable_allocator<EvalState>(),
             #else
             std::make_shared<EvalState>(
-                lookupPath, getEvalStore(), getStore())
             #endif
+                lookupPath, getEvalStore(), evalSettings, getStore())
             ;
 
         evalState->repair = repair;

src/libcmd/common-eval-args.cc

@@ -1,6 +1,7 @@
 #include "eval-settings.hh"
 #include "common-eval-args.hh"
 #include "shared.hh"
+#include "config-global.hh"
 #include "filetransfer.hh"
 #include "eval.hh"
 #include "fetchers.hh"
@@ -10,9 +11,35 @@
 #include "command.hh"
 #include "tarball.hh"
 #include "fetch-to-store.hh"
+#include "compatibility-settings.hh"
+#include "eval-settings.hh"
 
 namespace nix {
 
+EvalSettings evalSettings {
+    settings.readOnlyMode,
+    {
+        {
+            "flake",
+            [](ref<Store> store, std::string_view rest) {
+                experimentalFeatureSettings.require(Xp::Flakes);
+                // FIXME `parseFlakeRef` should take a `std::string_view`.
+                auto flakeRef = parseFlakeRef(std::string { rest }, {}, true, false);
+                debug("fetching flake search path element '%s''", rest);
+                auto storePath = flakeRef.resolve(store).fetchTree(store).first;
+                return store->toRealPath(storePath);
+            },
+        },
+    },
+};
+
+static GlobalConfig::Register rEvalSettings(&evalSettings);
+
+CompatibilitySettings compatibilitySettings {};
+
+static GlobalConfig::Register rCompatibilitySettings(&compatibilitySettings);
+
+
 MixEvalArgs::MixEvalArgs()
 {
     addFlag({
@@ -54,7 +81,7 @@ MixEvalArgs::MixEvalArgs()
         .description = R"(
   Add *path* to the Nix search path. The Nix search path is
   initialized from the colon-separated [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH) environment
-  variable, and is used to look up the location of Nix expressions using [paths](@docroot@/language/values.md#type-path) enclosed in angle
+  variable, and is used to look up the location of Nix expressions using [paths](@docroot@/language/types.md#type-path) enclosed in angle
   brackets (i.e., `<nixpkgs>`).
 
   For instance, passing

src/libcmd/common-eval-args.hh

@@ -12,9 +12,21 @@ namespace nix {
 
 class Store;
 class EvalState;
+struct EvalSettings;
+struct CompatibilitySettings;
 class Bindings;
 struct SourcePath;
 
+/**
+ * @todo Get rid of global setttings variables
+ */
+extern EvalSettings evalSettings;
+
+/**
+ * Settings that control behaviors that have changed since Nix 2.3.
+ */
+extern CompatibilitySettings compatibilitySettings;
+
 struct MixEvalArgs : virtual Args, virtual MixRepair
 {
     static constexpr auto category = "Common evaluation options";

src/libcmd/compatibility-settings.hh

@@ -0,0 +1,19 @@
+#pragma once
+#include "config.hh"
+
+namespace nix {
+struct CompatibilitySettings : public Config
+{
+
+    CompatibilitySettings() = default;
+
+    Setting<bool> nixShellAlwaysLooksForShellNix{this, true, "nix-shell-always-looks-for-shell-nix", R"(
+        Before Nix 2.24, [`nix-shell`](@docroot@/command-ref/nix-shell.md) would only look at `shell.nix` if it was in the working directory - when no file was specified.
+
+        Since Nix 2.24, `nix-shell` always looks for a `shell.nix`, whether that's in the working directory, or in a directory that was passed as an argument.
+
+        You may set this to `false` to revert to the Nix 2.3 behavior.
+    )"};
+};
+
+};

src/libcmd/local.mk

@@ -6,10 +6,10 @@ libcmd_DIR := $(d)
 
 libcmd_SOURCES := $(wildcard $(d)/*.cc)
 
-libcmd_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libexpr) $(INCLUDE_libmain)
+libcmd_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libexpr) $(INCLUDE_libflake) $(INCLUDE_libmain)
 
 libcmd_LDFLAGS = $(EDITLINE_LIBS) $(LOWDOWN_LIBS) $(THREAD_LDFLAGS)
 
-libcmd_LIBS = libstore libutil libexpr libmain libfetchers
+libcmd_LIBS = libutil libstore libfetchers libflake libexpr libmain
 
 $(eval $(call install-file-in, $(buildprefix)$(d)/nix-cmd.pc, $(libdir)/pkgconfig, 0644))

src/libcmd/meson.build

@@ -0,0 +1,128 @@
+project('nix-cmd', 'cpp',
+  version : files('.version'),
+  default_options : [
+    'cpp_std=c++2a',
+    # TODO(Qyriad): increase the warning level
+    'warning_level=1',
+    'debug=true',
+    'optimization=2',
+    'errorlogs=true', # Please print logs for tests that fail
+  ],
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+cxx = meson.get_compiler('cpp')
+
+subdir('build-utils-meson/deps-lists')
+
+configdata = configuration_data()
+
+deps_private_maybe_subproject = [
+]
+deps_public_maybe_subproject = [
+  dependency('nix-util'),
+  dependency('nix-store'),
+  dependency('nix-fetchers'),
+  dependency('nix-expr'),
+  dependency('nix-flake'),
+  dependency('nix-main'),
+]
+subdir('build-utils-meson/subprojects')
+
+nlohmann_json = dependency('nlohmann_json', version : '>= 3.9')
+deps_public += nlohmann_json
+
+lowdown = dependency('lowdown', version : '>= 0.9.0', required : get_option('markdown'))
+deps_private += lowdown
+configdata.set('HAVE_LOWDOWN', lowdown.found().to_int())
+
+readline_flavor = get_option('readline-flavor')
+if readline_flavor == 'editline'
+  editline = dependency('libeditline', 'editline', version : '>=1.14')
+  deps_private += editline
+elif readline_flavor == 'readline'
+  readline = dependency('readline')
+  deps_private += readline
+  configdata.set(
+    'USE_READLINE',
+    1,
+    description: 'Use readline instead of editline',
+  )
+else
+  error('illegal editline flavor', readline_flavor)
+endif
+
+config_h = configure_file(
+  configuration : configdata,
+  output : 'config-cmd.hh',
+)
+
+add_project_arguments(
+  # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
+  # It would be nice for our headers to be idempotent instead.
+  '-include', 'config-util.hh',
+  '-include', 'config-store.hh',
+  # '-include', 'config-fetchers.h',
+  '-include', 'config-expr.hh',
+  '-include', 'config-main.hh',
+  '-include', 'config-cmd.hh',
+  language : 'cpp',
+)
+
+subdir('build-utils-meson/diagnostics')
+
+sources = files(
+  'built-path.cc',
+  'command-installable-value.cc',
+  'command.cc',
+  'common-eval-args.cc',
+  'editor-for.cc',
+  'installable-attr-path.cc',
+  'installable-derived-path.cc',
+  'installable-flake.cc',
+  'installable-value.cc',
+  'installables.cc',
+  'legacy.cc',
+  'markdown.cc',
+  'misc-store-flags.cc',
+  'network-proxy.cc',
+  'repl-interacter.cc',
+  'repl.cc',
+)
+
+include_dirs = [include_directories('.')]
+
+headers = [config_h] + files(
+  'built-path.hh',
+  'command-installable-value.hh',
+  'command.hh',
+  'common-eval-args.hh',
+  'compatibility-settings.hh',
+  'editor-for.hh',
+  'installable-attr-path.hh',
+  'installable-derived-path.hh',
+  'installable-flake.hh',
+  'installable-value.hh',
+  'installables.hh',
+  'legacy.hh',
+  'markdown.hh',
+  'misc-store-flags.hh',
+  'network-proxy.hh',
+  'repl-interacter.hh',
+  'repl.hh',
+)
+
+this_library = library(
+  'nixcmd',
+  sources,
+  dependencies : deps_public + deps_private + deps_other,
+  prelink : true, # For C++ static initializers
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix', preserve_path : true)
+
+libraries_private = []
+
+subdir('build-utils-meson/export')

src/libcmd/meson.options

@@ -0,0 +1,15 @@
+# vim: filetype=meson
+
+option(
+  'markdown',
+  type: 'feature',
+  description: 'Enable Markdown rendering in the Nix binary (requires lowdown)',
+)
+
+option(
+  'readline-flavor',
+  type : 'combo',
+  choices : ['editline', 'readline'],
+  value : 'editline',
+  description : 'Which library to use for nice line editing with the Nix language REPL',
+)

src/libcmd/network-proxy.cc

@@ -1,7 +1,6 @@
 #include "network-proxy.hh"
 
 #include <algorithm>
-#include <boost/algorithm/string.hpp>
 
 #include "environment-variables.hh"
 
@@ -13,7 +12,10 @@ static StringSet getAllVariables()
 {
     StringSet variables = lowercaseVariables;
     for (const auto & variable : lowercaseVariables) {
-        variables.insert(boost::to_upper_copy(variable));
+        std::string upperVariable;
+        std::transform(
+            variable.begin(), variable.end(), upperVariable.begin(), [](unsigned char c) { return std::toupper(c); });
+        variables.insert(std::move(upperVariable));
     }
     return variables;
 }

src/libcmd/package.nix

@@ -0,0 +1,110 @@
+{ lib
+, stdenv
+, mkMesonDerivation
+, releaseTools
+
+, meson
+, ninja
+, pkg-config
+
+, nix-util
+, nix-store
+, nix-fetchers
+, nix-expr
+, nix-flake
+, nix-main
+, editline
+, readline
+, lowdown
+, nlohmann_json
+
+# Configuration Options
+
+, version
+
+# Whether to enable Markdown rendering in the Nix binary.
+, enableMarkdown ? !stdenv.hostPlatform.isWindows
+
+# Which interactive line editor library to use for Nix's repl.
+#
+# Currently supported choices are:
+#
+# - editline (default)
+# - readline
+, readlineFlavor ? if stdenv.hostPlatform.isWindows then "readline" else "editline"
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-cmd";
+  inherit version;
+
+  workDir = ./.;
+  fileset = fileset.unions [
+    ../../build-utils-meson
+    ./build-utils-meson
+    ../../.version
+    ./.version
+    ./meson.build
+    ./meson.options
+    (fileset.fileFilter (file: file.hasExt "cc") ./.)
+    (fileset.fileFilter (file: file.hasExt "hh") ./.)
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    pkg-config
+  ];
+
+  buildInputs = [
+    ({ inherit editline readline; }.${readlineFlavor})
+  ] ++ lib.optional enableMarkdown lowdown;
+
+  propagatedBuildInputs = [
+    nix-util
+    nix-store
+    nix-fetchers
+    nix-expr
+    nix-flake
+    nix-main
+    nlohmann_json
+  ];
+
+  preConfigure =
+    # "Inline" .version so it's not a symlink, and includes the suffix.
+    # Do the meson utils, without modification.
+    ''
+      chmod u+w ./.version
+      echo ${version} > ../../.version
+    '';
+
+  mesonFlags = [
+    (lib.mesonEnable "markdown" enableMarkdown)
+    (lib.mesonOption "readline-flavor" readlineFlavor)
+  ];
+
+  env = lib.optionalAttrs (stdenv.isLinux && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")) {
+    LDFLAGS = "-fuse-ld=gold";
+  };
+
+  enableParallelBuilding = true;
+
+  separateDebugInfo = !stdenv.hostPlatform.isStatic;
+
+  # TODO `releaseTools.coverageAnalysis` in Nixpkgs needs to be updated
+  # to work with `strictDeps`.
+  strictDeps = true;
+
+  hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+})

src/libcmd/repl-interacter.cc

@@ -18,7 +18,7 @@ extern "C" {
 #include "finally.hh"
 #include "repl-interacter.hh"
 #include "file-system.hh"
-#include "libcmd/repl.hh"
+#include "repl.hh"
 
 namespace nix {
 

src/libcmd/repl.cc

@@ -3,11 +3,12 @@
 #include <cstring>
 #include <climits>
 
-#include "libcmd/repl-interacter.hh"
+#include "repl-interacter.hh"
 #include "repl.hh"
 
 #include "ansicolor.hh"
 #include "shared.hh"
+#include "config-global.hh"
 #include "eval.hh"
 #include "eval-cache.hh"
 #include "eval-inline.hh"

src/libexpr-c/.version

@@ -0,0 +1 @@
+../../.version

src/libexpr-c/build-utils-meson

@@ -0,0 +1 @@
+../../build-utils-meson

src/libexpr-c/meson.build

@@ -0,0 +1,91 @@
+project('nix-expr-c', 'cpp',
+  version : files('.version'),
+  default_options : [
+    'cpp_std=c++2a',
+    # TODO(Qyriad): increase the warning level
+    'warning_level=1',
+    'debug=true',
+    'optimization=2',
+    'errorlogs=true', # Please print logs for tests that fail
+  ],
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+cxx = meson.get_compiler('cpp')
+
+subdir('build-utils-meson/deps-lists')
+
+configdata = configuration_data()
+
+deps_private_maybe_subproject = [
+  dependency('nix-util'),
+  dependency('nix-store'),
+  dependency('nix-expr'),
+]
+deps_public_maybe_subproject = [
+  dependency('nix-util-c'),
+  dependency('nix-store-c'),
+]
+subdir('build-utils-meson/subprojects')
+
+# TODO rename, because it will conflict with downstream projects
+configdata.set_quoted('PACKAGE_VERSION', meson.project_version())
+
+config_h = configure_file(
+  configuration : configdata,
+  output : 'config-expr.h',
+)
+
+add_project_arguments(
+  # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
+  # It would be nice for our headers to be idempotent instead.
+
+  # From C++ libraries, only for internals
+  '-include', 'config-util.hh',
+  '-include', 'config-store.hh',
+  '-include', 'config-expr.hh',
+
+  # From C libraries, for our public, installed headers too
+  '-include', 'config-util.h',
+  '-include', 'config-store.h',
+  '-include', 'config-expr.h',
+  language : 'cpp',
+)
+
+subdir('build-utils-meson/diagnostics')
+
+sources = files(
+  'nix_api_expr.cc',
+  'nix_api_external.cc',
+  'nix_api_value.cc',
+)
+
+include_dirs = [include_directories('.')]
+
+headers = [config_h] + files(
+  'nix_api_expr.h',
+  'nix_api_external.h',
+  'nix_api_value.h',
+)
+
+# TODO move this header to libexpr, maybe don't use it in tests?
+headers += files('nix_api_expr_internal.h')
+
+subdir('build-utils-meson/export-all-symbols')
+
+this_library = library(
+  'nixexprc',
+  sources,
+  dependencies : deps_public + deps_private + deps_other,
+  include_directories : include_dirs,
+  link_args: linker_export_flags,
+  prelink : true, # For C++ static initializers
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix', preserve_path : true)
+
+libraries_private = []
+
+subdir('build-utils-meson/export')

src/libexpr-c/nix_api_expr.cc

@@ -7,6 +7,7 @@
 #include "eval.hh"
 #include "globals.hh"
 #include "util.hh"
+#include "eval-settings.hh"
 
 #include "nix_api_expr.h"
 #include "nix_api_expr_internal.h"
@@ -42,56 +43,56 @@ nix_err nix_libexpr_init(nix_c_context * context)
 }
 
 nix_err nix_expr_eval_from_string(
-    nix_c_context * context, EvalState * state, const char * expr, const char * path, Value * value)
+    nix_c_context * context, EvalState * state, const char * expr, const char * path, nix_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);
+        state->state.eval(parsedExpr, value->value);
+        state->state.forceValue(value->value, nix::noPos);
     }
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_value_call(nix_c_context * context, EvalState * state, Value * fn, Value * arg, Value * value)
+nix_err nix_value_call(nix_c_context * context, EvalState * state, Value * fn, nix_value * arg, nix_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);
+        state->state.callFunction(fn->value, arg->value, value->value, nix::noPos);
+        state->state.forceValue(value->value, nix::noPos);
     }
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_value_call_multi(nix_c_context * context, EvalState * state, Value * fn, size_t nargs, Value ** args, Value * value)
+nix_err nix_value_call_multi(nix_c_context * context, EvalState * state, nix_value * fn, size_t nargs, nix_value ** args, nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
     try {
-        state->state.callFunction(*(nix::Value *) fn, nargs, (nix::Value * *)args, *(nix::Value *) value, nix::noPos);
-        state->state.forceValue(*(nix::Value *) value, nix::noPos);
+        state->state.callFunction(fn->value, nargs, (nix::Value * *)args, value->value, nix::noPos);
+        state->state.forceValue(value->value, nix::noPos);
     }
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_value_force(nix_c_context * context, EvalState * state, Value * value)
+nix_err nix_value_force(nix_c_context * context, EvalState * state, nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
     try {
-        state->state.forceValue(*(nix::Value *) value, nix::noPos);
+        state->state.forceValue(value->value, nix::noPos);
     }
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, Value * value)
+nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
     try {
-        state->state.forceValueDeep(*(nix::Value *) value);
+        state->state.forceValueDeep(value->value);
     }
     NIXC_CATCH_ERRS
 }
@@ -106,7 +107,21 @@ EvalState * nix_state_create(nix_c_context * context, const char ** lookupPath_c
             for (size_t i = 0; lookupPath_c[i] != nullptr; i++)
                 lookupPath.push_back(lookupPath_c[i]);
 
-        return new EvalState{nix::EvalState(nix::LookupPath::parse(lookupPath), store->ptr)};
+        void * p = ::operator new(
+            sizeof(EvalState),
+            static_cast<std::align_val_t>(alignof(EvalState)));
+        auto * p2 = static_cast<EvalState *>(p);
+        new (p) EvalState {
+            .settings = nix::EvalSettings{
+                nix::settings.readOnlyMode,
+            },
+            .state = nix::EvalState(
+                nix::LookupPath::parse(lookupPath),
+                store->ptr,
+                p2->settings),
+        };
+        loadConfFile(p2->settings);
+        return p2;
     }
     NIXC_CATCH_ERRS_NULL
 }
@@ -181,6 +196,15 @@ nix_err nix_gc_decref(nix_c_context * context, const void *)
 void nix_gc_now() {}
 #endif
 
+nix_err nix_value_incref(nix_c_context * context, nix_value *x)
+{
+    return nix_gc_incref(context, (const void *) x);
+}
+nix_err nix_value_decref(nix_c_context * context, nix_value *x)
+{
+    return nix_gc_decref(context, (const void *) x);
+}
+
 void nix_gc_register_finalizer(void * obj, void * cd, void (*finalizer)(void * obj, void * cd))
 {
 #ifdef HAVE_BOEHMGC

src/libexpr-c/nix_api_expr.h

@@ -29,14 +29,23 @@ extern "C" {
  * @see nix_state_create
  */
 typedef struct EvalState EvalState; // nix::EvalState
-/**
- * @brief Represents a value in the Nix language.
+
+/** @brief A Nix language value, or thunk that may evaluate to a value.
+ *
+ * Values are the primary objects manipulated in the Nix language.
+ * They are considered to be immutable from a user's perspective, but the process of evaluating a value changes its
+ * ValueType if it was a thunk. After a value has been evaluated, its ValueType does not change.
+ *
+ * Evaluation in this context refers to the process of evaluating a single value object, also called "forcing" the
+ * value; see `nix_value_force`.
+ *
+ * The evaluator manages its own memory, but your use of the C API must follow the reference counting rules.
  *
- * Owned by the garbage collector.
- * @struct Value
  * @see value_manip
+ * @see nix_value_incref, nix_value_decref
  */
-typedef void Value; // nix::Value
+typedef struct nix_value nix_value;
+[[deprecated("use nix_value instead")]] typedef nix_value Value;
 
 // Function prototypes
 /**
@@ -65,7 +74,7 @@ nix_err nix_libexpr_init(nix_c_context * context);
  * @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);
+    nix_c_context * context, EvalState * state, const char * expr, const char * path, nix_value * value);
 
 /**
  * @brief Calls a Nix function with an argument.
@@ -79,7 +88,7 @@ nix_err nix_expr_eval_from_string(
  * @see nix_init_apply() for a similar function that does not performs the call immediately, but stores it as a thunk.
  *      Note the different argument order.
  */
-nix_err nix_value_call(nix_c_context * context, EvalState * state, Value * fn, Value * arg, Value * value);
+nix_err nix_value_call(nix_c_context * context, EvalState * state, nix_value * fn, nix_value * arg, nix_value * value);
 
 /**
  * @brief Calls a Nix function with multiple arguments.
@@ -98,7 +107,7 @@ nix_err nix_value_call(nix_c_context * context, EvalState * state, Value * fn, V
  * @see NIX_VALUE_CALL           For a macro that wraps this function for convenience.
  */
 nix_err nix_value_call_multi(
-    nix_c_context * context, EvalState * state, Value * fn, size_t nargs, Value ** args, Value * value);
+    nix_c_context * context, EvalState * state, nix_value * fn, size_t nargs, nix_value ** args, nix_value * value);
 
 /**
  * @brief Calls a Nix function with multiple arguments.
@@ -116,7 +125,7 @@ nix_err nix_value_call_multi(
  */
 #define NIX_VALUE_CALL(context, state, value, fn, ...)                      \
     do {                                                                    \
-        Value * args_array[] = {__VA_ARGS__};                               \
+        nix_value * args_array[] = {__VA_ARGS__};                           \
         size_t nargs = sizeof(args_array) / sizeof(args_array[0]);          \
         nix_value_call_multi(context, state, fn, nargs, args_array, value); \
     } while (0)
@@ -124,12 +133,10 @@ nix_err nix_value_call_multi(
 /**
  * @brief Forces the evaluation of a Nix value.
  *
- * The Nix interpreter is lazy, and not-yet-evaluated Values can be
+ * 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 This function is mainly needed before calling @ref getters, but not for API calls that return a `Value`.
+ * This function mutates such a `nix_value`, so that, if successful, it has its final type.
  *
  * @param[out] context Optional, stores error information
  * @param[in] state The state of the evaluation.
@@ -138,7 +145,7 @@ nix_err nix_value_call_multi(
  * @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);
+nix_err nix_value_force(nix_c_context * context, EvalState * state, nix_value * value);
 
 /**
  * @brief Forces the deep evaluation of a Nix value.
@@ -154,7 +161,7 @@ nix_err nix_value_force(nix_c_context * context, EvalState * state, Value * valu
  * @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);
+nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, nix_value * value);
 
 /**
  * @brief Create a new Nix language evaluator state.
@@ -188,6 +195,11 @@ void nix_state_free(EvalState * state);
  * you're done with a value returned by the evaluator.
  * @{
  */
+
+// TODO: Deprecate nix_gc_incref in favor of the type-specific reference counting functions?
+//       e.g. nix_value_incref.
+//       It gives implementors more flexibility, and adds safety, so that generated
+//       bindings can be used without fighting the host type system (where applicable).
 /**
  * @brief Increment the garbage collector reference counter for the given object.
  *

src/libexpr-c/nix_api_expr_internal.h

@@ -2,11 +2,13 @@
 #define NIX_API_EXPR_INTERNAL_H
 
 #include "eval.hh"
+#include "eval-settings.hh"
 #include "attr-set.hh"
 #include "nix_api_value.h"
 
 struct EvalState
 {
+    nix::EvalSettings settings;
     nix::EvalState state;
 };
 
@@ -20,6 +22,11 @@ struct ListBuilder
     nix::ListBuilder builder;
 };
 
+struct nix_value
+{
+    nix::Value value;
+};
+
 struct nix_string_return
 {
     std::string str;

src/libexpr-c/nix_api_value.cc

@@ -21,49 +21,54 @@
 #endif
 
 // Internal helper functions to check [in] and [out] `Value *` parameters
-static const nix::Value & check_value_not_null(const Value * value)
+static const nix::Value & check_value_not_null(const nix_value * value)
 {
     if (!value) {
-        throw std::runtime_error("Value is null");
+        throw std::runtime_error("nix_value is null");
     }
     return *((const nix::Value *) value);
 }
 
-static nix::Value & check_value_not_null(Value * value)
+static nix::Value & check_value_not_null(nix_value * value)
 {
     if (!value) {
-        throw std::runtime_error("Value is null");
+        throw std::runtime_error("nix_value is null");
     }
-    return *((nix::Value *) value);
+    return value->value;
 }
 
-static const nix::Value & check_value_in(const Value * value)
+static const nix::Value & check_value_in(const nix_value * value)
 {
     auto & v = check_value_not_null(value);
     if (!v.isValid()) {
-        throw std::runtime_error("Uninitialized Value");
+        throw std::runtime_error("Uninitialized nix_value");
     }
     return v;
 }
 
-static nix::Value & check_value_in(Value * value)
+static nix::Value & check_value_in(nix_value * value)
 {
     auto & v = check_value_not_null(value);
     if (!v.isValid()) {
-        throw std::runtime_error("Uninitialized Value");
+        throw std::runtime_error("Uninitialized nix_value");
     }
     return v;
 }
 
-static nix::Value & check_value_out(Value * value)
+static nix::Value & check_value_out(nix_value * value)
 {
     auto & v = check_value_not_null(value);
     if (v.isValid()) {
-        throw std::runtime_error("Value already initialized. Variables are immutable");
+        throw std::runtime_error("nix_value already initialized. Variables are immutable");
     }
     return v;
 }
 
+static inline nix_value * as_nix_value_ptr(nix::Value * v)
+{
+    return reinterpret_cast<nix_value *>(v);
+}
+
 /**
  * Helper function to convert calls from nix into C API.
  *
@@ -87,7 +92,7 @@ static void nix_c_primop_wrapper(
     // or maybe something to make blackholes work better; we don't know).
     nix::Value vTmp;
 
-    f(userdata, &ctx, (EvalState *) &state, (Value **) args, (Value *) &vTmp);
+    f(userdata, &ctx, (EvalState *) &state, (nix_value **) args, (nix_value *) &vTmp);
 
     if (ctx.last_err_code != NIX_OK) {
         /* TODO: Throw different errors depending on the error code */
@@ -154,19 +159,19 @@ nix_err nix_register_primop(nix_c_context * context, PrimOp * primOp)
     NIXC_CATCH_ERRS
 }
 
-Value * nix_alloc_value(nix_c_context * context, EvalState * state)
+nix_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_value * res = as_nix_value_ptr(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)
+ValueType nix_get_type(nix_c_context * context, const nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -202,7 +207,7 @@ ValueType nix_get_type(nix_c_context * context, const Value * value)
     NIXC_CATCH_ERRS_RES(NIX_TYPE_NULL);
 }
 
-const char * nix_get_typename(nix_c_context * context, const Value * value)
+const char * nix_get_typename(nix_c_context * context, const nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -214,7 +219,7 @@ const char * nix_get_typename(nix_c_context * context, const Value * value)
     NIXC_CATCH_ERRS_NULL
 }
 
-bool nix_get_bool(nix_c_context * context, const Value * value)
+bool nix_get_bool(nix_c_context * context, const nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -226,7 +231,8 @@ bool nix_get_bool(nix_c_context * context, const Value * value)
     NIXC_CATCH_ERRS_RES(false);
 }
 
-nix_err nix_get_string(nix_c_context * context, const Value * value, nix_get_string_callback callback, void * user_data)
+nix_err
+nix_get_string(nix_c_context * context, const nix_value * value, nix_get_string_callback callback, void * user_data)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -238,7 +244,7 @@ nix_err nix_get_string(nix_c_context * context, const Value * value, nix_get_str
     NIXC_CATCH_ERRS
 }
 
-const char * nix_get_path_string(nix_c_context * context, const Value * value)
+const char * nix_get_path_string(nix_c_context * context, const nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -257,7 +263,7 @@ const char * nix_get_path_string(nix_c_context * context, const Value * value)
     NIXC_CATCH_ERRS_NULL
 }
 
-unsigned int nix_get_list_size(nix_c_context * context, const Value * value)
+unsigned int nix_get_list_size(nix_c_context * context, const nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -269,7 +275,7 @@ unsigned int nix_get_list_size(nix_c_context * context, const Value * value)
     NIXC_CATCH_ERRS_RES(0);
 }
 
-unsigned int nix_get_attrs_size(nix_c_context * context, const Value * value)
+unsigned int nix_get_attrs_size(nix_c_context * context, const nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -281,7 +287,7 @@ unsigned int nix_get_attrs_size(nix_c_context * context, const Value * value)
     NIXC_CATCH_ERRS_RES(0);
 }
 
-double nix_get_float(nix_c_context * context, const Value * value)
+double nix_get_float(nix_c_context * context, const nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -293,7 +299,7 @@ double nix_get_float(nix_c_context * context, const Value * value)
     NIXC_CATCH_ERRS_RES(0.0);
 }
 
-int64_t nix_get_int(nix_c_context * context, const Value * value)
+int64_t nix_get_int(nix_c_context * context, const nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -305,7 +311,7 @@ int64_t nix_get_int(nix_c_context * context, const Value * value)
     NIXC_CATCH_ERRS_RES(0);
 }
 
-ExternalValue * nix_get_external(nix_c_context * context, Value * value)
+ExternalValue * nix_get_external(nix_c_context * context, nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -317,7 +323,7 @@ ExternalValue * nix_get_external(nix_c_context * context, Value * value)
     NIXC_CATCH_ERRS_NULL;
 }
 
-Value * nix_get_list_byidx(nix_c_context * context, const Value * value, EvalState * state, unsigned int ix)
+nix_value * nix_get_list_byidx(nix_c_context * context, const nix_value * value, EvalState * state, unsigned int ix)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -328,12 +334,12 @@ Value * nix_get_list_byidx(nix_c_context * context, const Value * value, EvalSta
         nix_gc_incref(nullptr, p);
         if (p != nullptr)
             state->state.forceValue(*p, nix::noPos);
-        return (Value *) p;
+        return as_nix_value_ptr(p);
     }
     NIXC_CATCH_ERRS_NULL
 }
 
-Value * nix_get_attr_byname(nix_c_context * context, const Value * value, EvalState * state, const char * name)
+nix_value * nix_get_attr_byname(nix_c_context * context, const nix_value * value, EvalState * state, const char * name)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -345,7 +351,7 @@ Value * nix_get_attr_byname(nix_c_context * context, const Value * value, EvalSt
         if (attr) {
             nix_gc_incref(nullptr, attr->value);
             state->state.forceValue(*attr->value, nix::noPos);
-            return attr->value;
+            return as_nix_value_ptr(attr->value);
         }
         nix_set_err_msg(context, NIX_ERR_KEY, "missing attribute");
         return nullptr;
@@ -353,7 +359,7 @@ Value * nix_get_attr_byname(nix_c_context * context, const Value * value, EvalSt
     NIXC_CATCH_ERRS_NULL
 }
 
-bool nix_has_attr_byname(nix_c_context * context, const Value * value, EvalState * state, const char * name)
+bool nix_has_attr_byname(nix_c_context * context, const nix_value * value, EvalState * state, const char * name)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -369,8 +375,8 @@ bool nix_has_attr_byname(nix_c_context * context, const Value * value, EvalState
     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)
+nix_value * nix_get_attr_byidx(
+    nix_c_context * context, const nix_value * value, EvalState * state, unsigned int i, const char ** name)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -380,12 +386,13 @@ nix_get_attr_byidx(nix_c_context * context, const Value * value, EvalState * sta
         *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;
+        return as_nix_value_ptr(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)
+const char *
+nix_get_attr_name_byidx(nix_c_context * context, const nix_value * value, EvalState * state, unsigned int i)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -397,7 +404,7 @@ const char * nix_get_attr_name_byidx(nix_c_context * context, const Value * valu
     NIXC_CATCH_ERRS_NULL
 }
 
-nix_err nix_init_bool(nix_c_context * context, Value * value, bool b)
+nix_err nix_init_bool(nix_c_context * context, nix_value * value, bool b)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -409,7 +416,7 @@ nix_err nix_init_bool(nix_c_context * context, Value * value, bool b)
 }
 
 // todo string context
-nix_err nix_init_string(nix_c_context * context, Value * value, const char * str)
+nix_err nix_init_string(nix_c_context * context, nix_value * value, const char * str)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -420,7 +427,7 @@ nix_err nix_init_string(nix_c_context * context, Value * value, const char * str
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_init_path_string(nix_c_context * context, EvalState * s, Value * value, const char * str)
+nix_err nix_init_path_string(nix_c_context * context, EvalState * s, nix_value * value, const char * str)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -431,7 +438,7 @@ nix_err nix_init_path_string(nix_c_context * context, EvalState * s, Value * val
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_init_float(nix_c_context * context, Value * value, double d)
+nix_err nix_init_float(nix_c_context * context, nix_value * value, double d)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -442,7 +449,7 @@ nix_err nix_init_float(nix_c_context * context, Value * value, double d)
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_init_int(nix_c_context * context, Value * value, int64_t i)
+nix_err nix_init_int(nix_c_context * context, nix_value * value, int64_t i)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -453,7 +460,7 @@ nix_err nix_init_int(nix_c_context * context, Value * value, int64_t i)
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_init_null(nix_c_context * context, Value * value)
+nix_err nix_init_null(nix_c_context * context, nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -464,7 +471,7 @@ nix_err nix_init_null(nix_c_context * context, Value * value)
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_init_apply(nix_c_context * context, Value * value, Value * fn, Value * arg)
+nix_err nix_init_apply(nix_c_context * context, nix_value * value, nix_value * fn, nix_value * arg)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -477,7 +484,7 @@ nix_err nix_init_apply(nix_c_context * context, Value * value, Value * fn, Value
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_init_external(nix_c_context * context, Value * value, ExternalValue * val)
+nix_err nix_init_external(nix_c_context * context, nix_value * value, ExternalValue * val)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -504,7 +511,8 @@ ListBuilder * nix_make_list_builder(nix_c_context * context, EvalState * state,
     NIXC_CATCH_ERRS_NULL
 }
 
-nix_err nix_list_builder_insert(nix_c_context * context, ListBuilder * list_builder, unsigned int index, Value * value)
+nix_err
+nix_list_builder_insert(nix_c_context * context, ListBuilder * list_builder, unsigned int index, nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -524,7 +532,7 @@ void nix_list_builder_free(ListBuilder * list_builder)
 #endif
 }
 
-nix_err nix_make_list(nix_c_context * context, ListBuilder * list_builder, Value * value)
+nix_err nix_make_list(nix_c_context * context, ListBuilder * list_builder, nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -535,7 +543,7 @@ nix_err nix_make_list(nix_c_context * context, ListBuilder * list_builder, Value
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_init_primop(nix_c_context * context, Value * value, PrimOp * p)
+nix_err nix_init_primop(nix_c_context * context, nix_value * value, PrimOp * p)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -546,7 +554,7 @@ nix_err nix_init_primop(nix_c_context * context, Value * value, PrimOp * p)
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_copy_value(nix_c_context * context, Value * value, const Value * source)
+nix_err nix_copy_value(nix_c_context * context, nix_value * value, const nix_value * source)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -558,7 +566,7 @@ nix_err nix_copy_value(nix_c_context * context, Value * value, const Value * sou
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_make_attrs(nix_c_context * context, Value * value, BindingsBuilder * b)
+nix_err nix_make_attrs(nix_c_context * context, nix_value * value, BindingsBuilder * b)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -584,7 +592,7 @@ BindingsBuilder * nix_make_bindings_builder(nix_c_context * context, EvalState *
     NIXC_CATCH_ERRS_NULL
 }
 
-nix_err nix_bindings_builder_insert(nix_c_context * context, BindingsBuilder * bb, const char * name, Value * value)
+nix_err nix_bindings_builder_insert(nix_c_context * context, BindingsBuilder * bb, const char * name, nix_value * value)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -605,7 +613,7 @@ void nix_bindings_builder_free(BindingsBuilder * bb)
 #endif
 }
 
-nix_realised_string * nix_string_realise(nix_c_context * context, EvalState * state, Value * value, bool isIFD)
+nix_realised_string * nix_string_realise(nix_c_context * context, EvalState * state, nix_value * value, bool isIFD)
 {
     if (context)
         context->last_err_code = NIX_OK;

src/libexpr-c/nix_api_value.h

@@ -35,8 +35,11 @@ typedef enum {
 } ValueType;
 
 // forward declarations
-typedef void Value;
+typedef struct nix_value nix_value;
 typedef struct EvalState EvalState;
+
+[[deprecated("use nix_value instead")]] typedef nix_value Value;
+
 // type defs
 /** @brief Stores an under-construction set of bindings
  * @ingroup value_manip
@@ -90,7 +93,8 @@ typedef struct nix_realised_string nix_realised_string;
  * @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);
+typedef void (*PrimOpFun)(
+    void * user_data, nix_c_context * context, EvalState * state, nix_value ** args, nix_value * ret);
 
 /** @brief Allocate a PrimOp
  *
@@ -142,10 +146,29 @@ nix_err nix_register_primop(nix_c_context * context, PrimOp * primOp);
  * @return value, or null in case of errors
  *
  */
-Value * nix_alloc_value(nix_c_context * context, EvalState * state);
+nix_value * nix_alloc_value(nix_c_context * context, EvalState * state);
+
+/**
+ * @brief Increment the garbage collector reference counter for the given `nix_value`.
+ *
+ * The Nix language evaluator C API keeps track of alive objects by reference counting.
+ * When you're done with a refcounted pointer, call nix_value_decref().
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] value The object to keep alive
+ */
+nix_err nix_value_incref(nix_c_context * context, nix_value * value);
+
+/**
+ * @brief Decrement the garbage collector reference counter for the given object
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] value The object to stop referencing
+ */
+nix_err nix_value_decref(nix_c_context * context, nix_value * value);
 
 /** @addtogroup value_manip Manipulating values
- * @brief Functions to inspect and change Nix language values, represented by Value.
+ * @brief Functions to inspect and change Nix language values, represented by nix_value.
  * @{
  */
 /** @anchor getters
@@ -157,7 +180,7 @@ Value * nix_alloc_value(nix_c_context * context, EvalState * state);
  * @param[in] value Nix value to inspect
  * @return type of nix value
  */
-ValueType nix_get_type(nix_c_context * context, const Value * value);
+ValueType nix_get_type(nix_c_context * context, const nix_value * value);
 
 /** @brief Get type name of value as defined in the evaluator
  * @param[out] context Optional, stores error information
@@ -165,14 +188,14 @@ ValueType nix_get_type(nix_c_context * context, const Value * value);
  * @return type name, owned string
  * @todo way to free the result
  */
-const char * nix_get_typename(nix_c_context * context, const Value * value);
+const char * nix_get_typename(nix_c_context * context, const nix_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);
+bool nix_get_bool(nix_c_context * context, const nix_value * value);
 
 /** @brief Get the raw string
  *
@@ -186,7 +209,7 @@ bool nix_get_bool(nix_c_context * context, const Value * value);
  * @return error code, NIX_OK on success.
  */
 nix_err
-nix_get_string(nix_c_context * context, const Value * value, nix_get_string_callback callback, void * user_data);
+nix_get_string(nix_c_context * context, const nix_value * value, nix_get_string_callback callback, void * user_data);
 
 /** @brief Get path as string
  * @param[out] context Optional, stores error information
@@ -194,42 +217,42 @@ nix_get_string(nix_c_context * context, const Value * value, nix_get_string_call
  * @return string
  * @return NULL in case of error.
  */
-const char * nix_get_path_string(nix_c_context * context, const Value * value);
+const char * nix_get_path_string(nix_c_context * context, const nix_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);
+unsigned int nix_get_list_size(nix_c_context * context, const nix_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);
+unsigned int nix_get_attrs_size(nix_c_context * context, const nix_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);
+double nix_get_float(nix_c_context * context, const nix_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);
+int64_t nix_get_int(nix_c_context * context, const nix_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 *);
+ExternalValue * nix_get_external(nix_c_context * context, nix_value *);
 
 /** @brief Get the ix'th element of a list
  *
@@ -240,7 +263,7 @@ ExternalValue * nix_get_external(nix_c_context * context, Value *);
  * @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);
+nix_value * nix_get_list_byidx(nix_c_context * context, const nix_value * value, EvalState * state, unsigned int ix);
 
 /** @brief Get an attr by name
  *
@@ -251,7 +274,7 @@ Value * nix_get_list_byidx(nix_c_context * context, const Value * value, EvalSta
  * @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);
+nix_value * nix_get_attr_byname(nix_c_context * context, const nix_value * value, EvalState * state, const char * name);
 
 /** @brief Check if an attribute name exists on a value
  * @param[out] context Optional, stores error information
@@ -260,7 +283,7 @@ Value * nix_get_attr_byname(nix_c_context * context, const Value * value, EvalSt
  * @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);
+bool nix_has_attr_byname(nix_c_context * context, const nix_value * value, EvalState * state, const char * name);
 
 /** @brief Get an attribute by index in the sorted bindings
  *
@@ -274,8 +297,8 @@ bool nix_has_attr_byname(nix_c_context * context, const Value * value, EvalState
  * @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);
+nix_value * nix_get_attr_byidx(
+    nix_c_context * context, const nix_value * value, EvalState * state, unsigned int i, const char ** name);
 
 /** @brief Get an attribute name by index in the sorted bindings
  *
@@ -288,7 +311,8 @@ nix_get_attr_byidx(nix_c_context * context, const Value * value, EvalState * sta
  * @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);
+const char *
+nix_get_attr_name_byidx(nix_c_context * context, const nix_value * value, EvalState * state, unsigned int i);
 
 /**@}*/
 /** @name Initializers
@@ -305,7 +329,7 @@ const char * nix_get_attr_name_byidx(nix_c_context * context, const Value * valu
  * @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);
+nix_err nix_init_bool(nix_c_context * context, nix_value * value, bool b);
 
 /** @brief Set a string
  * @param[out] context Optional, stores error information
@@ -313,7 +337,7 @@ nix_err nix_init_bool(nix_c_context * context, Value * value, bool b);
  * @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);
+nix_err nix_init_string(nix_c_context * context, nix_value * value, const char * str);
 
 /** @brief Set a path
  * @param[out] context Optional, stores error information
@@ -321,7 +345,7 @@ nix_err nix_init_string(nix_c_context * context, Value * value, const char * str
  * @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);
+nix_err nix_init_path_string(nix_c_context * context, EvalState * s, nix_value * value, const char * str);
 
 /** @brief Set a float
  * @param[out] context Optional, stores error information
@@ -329,7 +353,7 @@ nix_err nix_init_path_string(nix_c_context * context, EvalState * s, Value * val
  * @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);
+nix_err nix_init_float(nix_c_context * context, nix_value * value, double d);
 
 /** @brief Set an int
  * @param[out] context Optional, stores error information
@@ -338,13 +362,13 @@ nix_err nix_init_float(nix_c_context * context, Value * value, double d);
  * @return error code, NIX_OK on success.
  */
 
-nix_err nix_init_int(nix_c_context * context, Value * value, int64_t i);
+nix_err nix_init_int(nix_c_context * context, nix_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);
+nix_err nix_init_null(nix_c_context * context, nix_value * value);
 
 /** @brief Set the value to a thunk that will perform a function application when needed.
  *
@@ -360,7 +384,7 @@ nix_err nix_init_null(nix_c_context * context, Value * value);
  * @see nix_value_call() for a similar function that performs the call immediately and only stores the return value.
  *      Note the different argument order.
  */
-nix_err nix_init_apply(nix_c_context * context, Value * value, Value * fn, Value * arg);
+nix_err nix_init_apply(nix_c_context * context, nix_value * value, nix_value * fn, nix_value * arg);
 
 /** @brief Set an external value
  * @param[out] context Optional, stores error information
@@ -368,7 +392,7 @@ nix_err nix_init_apply(nix_c_context * context, Value * value, Value * fn, Value
  * @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);
+nix_err nix_init_external(nix_c_context * context, nix_value * value, ExternalValue * val);
 
 /** @brief Create a list from a list builder
  * @param[out] context Optional, stores error information
@@ -376,7 +400,7 @@ nix_err nix_init_external(nix_c_context * context, Value * value, ExternalValue
  * @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);
+nix_err nix_make_list(nix_c_context * context, ListBuilder * list_builder, nix_value * value);
 
 /** @brief Create a list builder
  * @param[out] context Optional, stores error information
@@ -393,7 +417,8 @@ ListBuilder * nix_make_list_builder(nix_c_context * context, EvalState * state,
  * @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);
+nix_err
+nix_list_builder_insert(nix_c_context * context, ListBuilder * list_builder, unsigned int index, nix_value * value);
 
 /** @brief Free a list builder
  *
@@ -408,7 +433,7 @@ void nix_list_builder_free(ListBuilder * list_builder);
  * @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);
+nix_err nix_make_attrs(nix_c_context * context, nix_value * value, BindingsBuilder * b);
 
 /** @brief Set primop
  * @param[out] context Optional, stores error information
@@ -417,14 +442,14 @@ nix_err nix_make_attrs(nix_c_context * context, Value * value, BindingsBuilder *
  * @see nix_alloc_primop
  * @return error code, NIX_OK on success.
  */
-nix_err nix_init_primop(nix_c_context * context, Value * value, PrimOp * op);
+nix_err nix_init_primop(nix_c_context * context, nix_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, const Value * source);
+nix_err nix_copy_value(nix_c_context * context, nix_value * value, const nix_value * source);
 /**@}*/
 
 /** @brief Create a bindings builder
@@ -444,7 +469,7 @@ BindingsBuilder * nix_make_bindings_builder(nix_c_context * context, EvalState *
  * @return error code, NIX_OK on success.
  */
 nix_err
-nix_bindings_builder_insert(nix_c_context * context, BindingsBuilder * builder, const char * name, Value * value);
+nix_bindings_builder_insert(nix_c_context * context, BindingsBuilder * builder, const char * name, nix_value * value);
 
 /** @brief Free a bindings builder
  *
@@ -471,7 +496,7 @@ void nix_bindings_builder_free(BindingsBuilder * builder);
                     You should set this to false when building for your application's purpose.
  * @return NULL if failed, are a new nix_realised_string, which must be freed with nix_realised_string_free
  */
-nix_realised_string * nix_string_realise(nix_c_context * context, EvalState * state, Value * value, bool isIFD);
+nix_realised_string * nix_string_realise(nix_c_context * context, EvalState * state, nix_value * value, bool isIFD);
 
 /** @brief Start of the string
  * @param[in] realised_string

src/libexpr-c/package.nix

@@ -0,0 +1,78 @@
+{ lib
+, stdenv
+, mkMesonDerivation
+
+, meson
+, ninja
+, pkg-config
+
+, nix-store-c
+, nix-expr
+
+# Configuration Options
+
+, version
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-expr-c";
+  inherit version;
+
+  workDir = ./.;
+  fileset = fileset.unions [
+    ../../build-utils-meson
+    ./build-utils-meson
+    ../../.version
+    ./.version
+    ./meson.build
+    # ./meson.options
+    (fileset.fileFilter (file: file.hasExt "cc") ./.)
+    (fileset.fileFilter (file: file.hasExt "hh") ./.)
+    (fileset.fileFilter (file: file.hasExt "h") ./.)
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    pkg-config
+  ];
+
+  propagatedBuildInputs = [
+    nix-store-c
+    nix-expr
+  ];
+
+  preConfigure =
+    # "Inline" .version so it's not a symlink, and includes the suffix.
+    # Do the meson utils, without modification.
+    ''
+      chmod u+w ./.version
+      echo ${version} > ../../.version
+    '';
+
+  mesonFlags = [
+  ];
+
+  env = lib.optionalAttrs (stdenv.isLinux && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")) {
+    LDFLAGS = "-fuse-ld=gold";
+  };
+
+  enableParallelBuilding = true;
+
+  separateDebugInfo = !stdenv.hostPlatform.isStatic;
+
+  strictDeps = true;
+
+  hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+})

src/libexpr/.version

@@ -0,0 +1 @@
+../../.version

src/libexpr/build-utils-meson

@@ -0,0 +1 @@
+../../build-utils-meson

src/libexpr/eval-gc.cc

@@ -0,0 +1,226 @@
+#include "error.hh"
+#include "environment-variables.hh"
+#include "serialise.hh"
+#include "eval-gc.hh"
+
+#if HAVE_BOEHMGC
+
+#  include <pthread.h>
+#  if __FreeBSD__
+#    include <pthread_np.h>
+#  endif
+
+#  include <gc/gc.h>
+#  include <gc/gc_cpp.h>
+#  include <gc/gc_allocator.h>
+
+#  include <boost/coroutine2/coroutine.hpp>
+#  include <boost/coroutine2/protected_fixedsize_stack.hpp>
+#  include <boost/context/stack_context.hpp>
+
+#endif
+
+namespace nix {
+
+#if HAVE_BOEHMGC
+/* Called when the Boehm GC runs out of memory. */
+static void * oomHandler(size_t requested)
+{
+    /* Convert this to a proper C++ exception. */
+    throw std::bad_alloc();
+}
+
+class BoehmGCStackAllocator : public StackAllocator
+{
+    boost::coroutines2::protected_fixedsize_stack stack{
+        // We allocate 8 MB, the default max stack size on NixOS.
+        // A smaller stack might be quicker to allocate but reduces the stack
+        // depth available for source filter expressions etc.
+        std::max(boost::context::stack_traits::default_size(), static_cast<std::size_t>(8 * 1024 * 1024))};
+
+    // This is specific to boost::coroutines2::protected_fixedsize_stack.
+    // The stack protection page is included in sctx.size, so we have to
+    // subtract one page size from the stack size.
+    std::size_t pfss_usable_stack_size(boost::context::stack_context & sctx)
+    {
+        return sctx.size - boost::context::stack_traits::page_size();
+    }
+
+public:
+    boost::context::stack_context allocate() override
+    {
+        auto sctx = stack.allocate();
+
+        // Stacks generally start at a high address and grow to lower addresses.
+        // Architectures that do the opposite are rare; in fact so rare that
+        // boost_routine does not implement it.
+        // So we subtract the stack size.
+        GC_add_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
+        return sctx;
+    }
+
+    void deallocate(boost::context::stack_context sctx) override
+    {
+        GC_remove_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
+        stack.deallocate(sctx);
+    }
+};
+
+static BoehmGCStackAllocator boehmGCStackAllocator;
+
+/**
+ * When a thread goes into a coroutine, we lose its original sp until
+ * control flow returns to the thread.
+ * While in the coroutine, the sp points outside the thread stack,
+ * so we can detect this and push the entire thread stack instead,
+ * as an approximation.
+ * The coroutine's stack is covered by `BoehmGCStackAllocator`.
+ * This is not an optimal solution, because the garbage is scanned when a
+ * coroutine is active, for both the coroutine and the original thread stack.
+ * However, the implementation is quite lean, and usually we don't have active
+ * coroutines during evaluation, so this is acceptable.
+ */
+void fixupBoehmStackPointer(void ** sp_ptr, void * _pthread_id)
+{
+    void *& sp = *sp_ptr;
+    auto pthread_id = reinterpret_cast<pthread_t>(_pthread_id);
+    pthread_attr_t pattr;
+    size_t osStackSize;
+    void * osStackLow;
+    void * osStackBase;
+
+#  ifdef __APPLE__
+    osStackSize = pthread_get_stacksize_np(pthread_id);
+    osStackLow = pthread_get_stackaddr_np(pthread_id);
+#  else
+    if (pthread_attr_init(&pattr)) {
+        throw Error("fixupBoehmStackPointer: pthread_attr_init failed");
+    }
+#    ifdef HAVE_PTHREAD_GETATTR_NP
+    if (pthread_getattr_np(pthread_id, &pattr)) {
+        throw Error("fixupBoehmStackPointer: pthread_getattr_np failed");
+    }
+#    elif HAVE_PTHREAD_ATTR_GET_NP
+    if (!pthread_attr_init(&pattr)) {
+        throw Error("fixupBoehmStackPointer: pthread_attr_init failed");
+    }
+    if (!pthread_attr_get_np(pthread_id, &pattr)) {
+        throw Error("fixupBoehmStackPointer: pthread_attr_get_np failed");
+    }
+#    else
+#      error "Need one of `pthread_attr_get_np` or `pthread_getattr_np`"
+#    endif
+    if (pthread_attr_getstack(&pattr, &osStackLow, &osStackSize)) {
+        throw Error("fixupBoehmStackPointer: pthread_attr_getstack failed");
+    }
+    if (pthread_attr_destroy(&pattr)) {
+        throw Error("fixupBoehmStackPointer: pthread_attr_destroy failed");
+    }
+#  endif
+    osStackBase = (char *) osStackLow + osStackSize;
+    // NOTE: We assume the stack grows down, as it does on all architectures we support.
+    //       Architectures that grow the stack up are rare.
+    if (sp >= osStackBase || sp < osStackLow) { // lo is outside the os stack
+        sp = osStackBase;
+    }
+}
+
+/* Disable GC while this object lives. Used by CoroutineContext.
+ *
+ * Boehm keeps a count of GC_disable() and GC_enable() calls,
+ * and only enables GC when the count matches.
+ */
+class BoehmDisableGC
+{
+public:
+    BoehmDisableGC()
+    {
+        GC_disable();
+    };
+    ~BoehmDisableGC()
+    {
+        GC_enable();
+    };
+};
+
+static inline void initGCReal()
+{
+    /* Initialise the Boehm garbage collector. */
+
+    /* Don't look for interior pointers. This reduces the odds of
+       misdetection a bit. */
+    GC_set_all_interior_pointers(0);
+
+    /* We don't have any roots in data segments, so don't scan from
+       there. */
+    GC_set_no_dls(1);
+
+    GC_INIT();
+
+    GC_set_oom_fn(oomHandler);
+
+    StackAllocator::defaultAllocator = &boehmGCStackAllocator;
+
+// TODO: Remove __APPLE__ condition.
+//       Comment suggests an implementation that works on darwin and windows
+//       https://github.com/ivmai/bdwgc/issues/362#issuecomment-1936672196
+#  if GC_VERSION_MAJOR >= 8 && GC_VERSION_MINOR >= 2 && GC_VERSION_MICRO >= 4 && !defined(__APPLE__)
+    GC_set_sp_corrector(&fixupBoehmStackPointer);
+
+    if (!GC_get_sp_corrector()) {
+        printTalkative("BoehmGC on this platform does not support sp_corrector; will disable GC inside coroutines");
+        /* Used to disable GC when entering coroutines on macOS */
+        create_coro_gc_hook = []() -> std::shared_ptr<void> { return std::make_shared<BoehmDisableGC>(); };
+    }
+#  else
+#    warning \
+        "BoehmGC version does not support GC while coroutine exists. GC will be disabled inside coroutines. Consider updating bdw-gc to 8.2.4 or later."
+#  endif
+
+    /* Set the initial heap size to something fairly big (25% of
+       physical RAM, up to a maximum of 384 MiB) so that in most cases
+       we don't need to garbage collect at all.  (Collection has a
+       fairly significant overhead.)  The heap size can be overridden
+       through libgc's GC_INITIAL_HEAP_SIZE environment variable.  We
+       should probably also provide a nix.conf setting for this.  Note
+       that GC_expand_hp() causes a lot of virtual, but not physical
+       (resident) memory to be allocated.  This might be a problem on
+       systems that don't overcommit. */
+    if (!getEnv("GC_INITIAL_HEAP_SIZE")) {
+        size_t size = 32 * 1024 * 1024;
+#  if HAVE_SYSCONF && defined(_SC_PAGESIZE) && defined(_SC_PHYS_PAGES)
+        size_t maxSize = 384 * 1024 * 1024;
+        long pageSize = sysconf(_SC_PAGESIZE);
+        long pages = sysconf(_SC_PHYS_PAGES);
+        if (pageSize != -1)
+            size = (pageSize * pages) / 4; // 25% of RAM
+        if (size > maxSize)
+            size = maxSize;
+#  endif
+        debug("setting initial heap size to %1% bytes", size);
+        GC_expand_hp(size);
+    }
+}
+
+#endif
+
+static bool gcInitialised = false;
+
+void initGC()
+{
+    if (gcInitialised)
+        return;
+
+#if HAVE_BOEHMGC
+    initGCReal();
+#endif
+
+    gcInitialised = true;
+}
+
+void assertGCInitialized()
+{
+    assert(gcInitialised);
+}
+
+}

src/libexpr/eval-gc.hh

@@ -0,0 +1,16 @@
+#pragma once
+///@file
+
+namespace nix {
+
+/**
+ * Initialise the Boehm GC, if applicable.
+ */
+void initGC();
+
+/**
+ * Make sure `initGC` has already been called.
+ */
+void assertGCInitialized();
+
+}

src/libexpr/eval-settings.cc

@@ -1,4 +1,5 @@
 #include "users.hh"
+#include "config-global.hh"
 #include "globals.hh"
 #include "profiles.hh"
 #include "eval.hh"
@@ -44,7 +45,9 @@ static Strings parseNixPath(const std::string & s)
     return res;
 }
 
-EvalSettings::EvalSettings()
+EvalSettings::EvalSettings(bool & readOnlyMode, EvalSettings::LookupPathHooks lookupPathHooks)
+    : readOnlyMode{readOnlyMode}
+    , lookupPathHooks{lookupPathHooks}
 {
     auto var = getEnv("NIX_PATH");
     if (var) nixPath = parseNixPath(*var);
@@ -54,7 +57,7 @@ EvalSettings::EvalSettings()
         builtinsAbortOnWarn = true;
 }
 
-Strings EvalSettings::getDefaultNixPath()
+Strings EvalSettings::getDefaultNixPath() const
 {
     Strings res;
     auto add = [&](const Path & p, const std::string & s = std::string()) {
@@ -67,7 +70,7 @@ Strings EvalSettings::getDefaultNixPath()
         }
     };
 
-    if (!evalSettings.restrictEval && !evalSettings.pureEval) {
+    if (!restrictEval && !pureEval) {
         add(getNixDefExpr() + "/channels");
         add(rootChannelsDir() + "/nixpkgs", "nixpkgs");
         add(rootChannelsDir());
@@ -93,16 +96,12 @@ std::string EvalSettings::resolvePseudoUrl(std::string_view url)
         return std::string(url);
 }
 
-const std::string & EvalSettings::getCurrentSystem()
+const std::string & EvalSettings::getCurrentSystem() const
 {
     const auto & evalSystem = currentSystem.get();
     return evalSystem != "" ? evalSystem : settings.thisSystem.get();
 }
 
-EvalSettings evalSettings;
-
-static GlobalConfig::Register rEvalSettings(&evalSettings);
-
 Path getNixDefExpr()
 {
     return settings.useXDGBaseDirectories

src/libexpr/eval-settings.hh

@@ -5,16 +5,51 @@
 
 namespace nix {
 
+class Store;
+
 struct EvalSettings : Config
 {
-    EvalSettings();
+    /**
+     * Function used to interpet look path entries of a given scheme.
+     *
+     * The argument is the non-scheme part of the lookup path entry (see
+     * `LookupPathHooks` below).
+     *
+     * The return value is (a) whether the entry was valid, and, if so,
+     * what does it map to.
+     *
+     * @todo Return (`std::optional` of) `SourceAccssor` or something
+     * more structured instead of mere `std::string`?
+     */
+    using LookupPathHook = std::optional<std::string>(ref<Store> store, std::string_view);
 
-    static Strings getDefaultNixPath();
+    /**
+     * Map from "scheme" to a `LookupPathHook`.
+     *
+     * Given a lookup path value (i.e. either the whole thing, or after
+     * the `<key>=`) in the form of:
+     *
+     * ```
+     * <scheme>:<arbitrary string>
+     * ```
+     *
+     * if `<scheme>` is a key in this map, then `<arbitrary string>` is
+     * passed to the hook that is the value in this map.
+     */
+    using LookupPathHooks = std::map<std::string, std::function<LookupPathHook>>;
+
+    EvalSettings(bool & readOnlyMode, LookupPathHooks lookupPathHooks = {});
+
+    bool & readOnlyMode;
+
+    Strings getDefaultNixPath() const;
 
     static bool isPseudoUrl(std::string_view s);
 
     static std::string resolvePseudoUrl(std::string_view url);
 
+    LookupPathHooks lookupPathHooks;
+
     Setting<bool> enableNativeCode{this, false, "allow-unsafe-native-code-during-evaluation", R"(
         Enable built-in functions that allow executing native code.
 
@@ -39,7 +74,7 @@ struct EvalSettings : Config
         R"(
           List of search paths to use for [lookup path](@docroot@/language/constructs/lookup-path.md) resolution.
           This setting determines the value of
-          [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath) and can be used with [`builtins.findFile`](@docroot@/language/builtin-constants.md#builtins-findFile).
+          [`builtins.nixPath`](@docroot@/language/builtins.md#builtins-nixPath) and can be used with [`builtins.findFile`](@docroot@/language/builtins.md#builtins-findFile).
 
           The default value is
 
@@ -60,7 +95,7 @@ struct EvalSettings : Config
         this, "", "eval-system",
         R"(
           This option defines
-          [`builtins.currentSystem`](@docroot@/language/builtin-constants.md#builtins-currentSystem)
+          [`builtins.currentSystem`](@docroot@/language/builtins.md#builtins-currentSystem)
           in the Nix language if it is set as a non-empty string.
           Otherwise, if it is defined as the empty string (the default), the value of the
           [`system` ](#conf-system)
@@ -74,14 +109,14 @@ struct EvalSettings : Config
      * Implements the `eval-system` vs `system` defaulting logic
      * described for `eval-system`.
      */
-    const std::string & getCurrentSystem();
+    const std::string & getCurrentSystem() const;
 
     Setting<bool> restrictEval{
         this, false, "restrict-eval",
         R"(
           If set to `true`, the Nix evaluator will not allow access to any
           files outside of
-          [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath),
+          [`builtins.nixPath`](@docroot@/language/builtins.md#builtins-nixPath),
           or to URIs outside of
           [`allowed-uris`](@docroot@/command-ref/conf-file.md#conf-allowed-uris).
         )"};
@@ -92,10 +127,10 @@ struct EvalSettings : Config
 
           - Restrict file system and network access to files specified by cryptographic hash
           - Disable impure constants:
-            - [`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)
+            - [`builtins.currentSystem`](@docroot@/language/builtins.md#builtins-currentSystem)
+            - [`builtins.currentTime`](@docroot@/language/builtins.md#builtins-currentTime)
+            - [`builtins.nixPath`](@docroot@/language/builtins.md#builtins-nixPath)
+            - [`builtins.storePath`](@docroot@/language/builtins.md#builtins-storePath)
         )"
         };
 
@@ -193,8 +228,6 @@ struct EvalSettings : Config
         )"};
 };
 
-extern EvalSettings evalSettings;
-
 /**
  * Conventionally part of the default nix path in impure mode.
  */

src/libexpr/eval.cc

@@ -3,13 +3,12 @@
 #include "hash.hh"
 #include "primops.hh"
 #include "print-options.hh"
-#include "shared.hh"
+#include "exit.hh"
 #include "types.hh"
 #include "util.hh"
 #include "store-api.hh"
 #include "derivations.hh"
 #include "downstream-placeholder.hh"
-#include "globals.hh"
 #include "eval-inline.hh"
 #include "filetransfer.hh"
 #include "function-trace.hh"
@@ -22,7 +21,6 @@
 #include "url.hh"
 #include "fetch-to-store.hh"
 #include "tarball.hh"
-#include "flake/flakeref.hh"
 #include "parser-tab.hh"
 
 #include <algorithm>
@@ -40,22 +38,16 @@
 #include <boost/container/small_vector.hpp>
 
 #ifndef _WIN32 // TODO use portable implementation
-# include <sys/resource.h>
+#  include <sys/resource.h>
 #endif
 
 #if HAVE_BOEHMGC
 
-#define GC_INCLUDE_NEW
+#  define GC_INCLUDE_NEW
 
-#include <pthread.h>
-
-#include <gc/gc.h>
-#include <gc/gc_cpp.h>
-#include <gc/gc_allocator.h>
-
-#include <boost/coroutine2/coroutine.hpp>
-#include <boost/coroutine2/protected_fixedsize_stack.hpp>
-#include <boost/context/stack_context.hpp>
+#  include <gc/gc.h>
+#  include <gc/gc_cpp.h>
+#  include <gc/gc_allocator.h>
 
 #endif
 
@@ -208,97 +200,6 @@ bool Value::isTrivial() const
 }
 
 
-#if HAVE_BOEHMGC
-/* Called when the Boehm GC runs out of memory. */
-static void * oomHandler(size_t requested)
-{
-    /* Convert this to a proper C++ exception. */
-    throw std::bad_alloc();
-}
-
-class BoehmGCStackAllocator : public StackAllocator {
-    boost::coroutines2::protected_fixedsize_stack stack {
-        // We allocate 8 MB, the default max stack size on NixOS.
-        // A smaller stack might be quicker to allocate but reduces the stack
-        // depth available for source filter expressions etc.
-        std::max(boost::context::stack_traits::default_size(), static_cast<std::size_t>(8 * 1024 * 1024))
-    };
-
-    // This is specific to boost::coroutines2::protected_fixedsize_stack.
-    // The stack protection page is included in sctx.size, so we have to
-    // subtract one page size from the stack size.
-    std::size_t pfss_usable_stack_size(boost::context::stack_context &sctx) {
-        return sctx.size - boost::context::stack_traits::page_size();
-    }
-
-  public:
-    boost::context::stack_context allocate() override {
-        auto sctx = stack.allocate();
-
-        // Stacks generally start at a high address and grow to lower addresses.
-        // Architectures that do the opposite are rare; in fact so rare that
-        // boost_routine does not implement it.
-        // So we subtract the stack size.
-        GC_add_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
-        return sctx;
-    }
-
-    void deallocate(boost::context::stack_context sctx) override {
-        GC_remove_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
-        stack.deallocate(sctx);
-    }
-
-};
-
-static BoehmGCStackAllocator boehmGCStackAllocator;
-
-/**
- * When a thread goes into a coroutine, we lose its original sp until
- * control flow returns to the thread.
- * While in the coroutine, the sp points outside the thread stack,
- * so we can detect this and push the entire thread stack instead,
- * as an approximation.
- * The coroutine's stack is covered by `BoehmGCStackAllocator`.
- * This is not an optimal solution, because the garbage is scanned when a
- * coroutine is active, for both the coroutine and the original thread stack.
- * However, the implementation is quite lean, and usually we don't have active
- * coroutines during evaluation, so this is acceptable.
- */
-void fixupBoehmStackPointer(void ** sp_ptr, void * pthread_id) {
-    void *& sp = *sp_ptr;
-    pthread_attr_t pattr;
-    size_t osStackSize;
-    void * osStackLow;
-    void * osStackBase;
-
-    #ifdef __APPLE__
-    osStackSize = pthread_get_stacksize_np((pthread_t)pthread_id);
-    osStackLow = pthread_get_stackaddr_np((pthread_t)pthread_id);
-    #else
-    if (pthread_attr_init(&pattr)) {
-        throw Error("fixupBoehmStackPointer: pthread_attr_init failed");
-    }
-    if (pthread_getattr_np((pthread_t)pthread_id, &pattr)) {
-        throw Error("fixupBoehmStackPointer: pthread_getattr_np failed");
-    }
-    if (pthread_attr_getstack(&pattr, &osStackLow, &osStackSize)) {
-        throw Error("fixupBoehmStackPointer: pthread_attr_getstack failed");
-    }
-    if (pthread_attr_destroy(&pattr)) {
-        throw Error("fixupBoehmStackPointer: pthread_attr_destroy failed");
-    }
-    #endif
-    osStackBase = (char *)osStackLow + osStackSize;
-    // NOTE: We assume the stack grows down, as it does on all architectures we support.
-    //       Architectures that grow the stack up are rare.
-    if (sp >= osStackBase || sp < osStackLow) { // lo is outside the os stack
-        sp = osStackBase;
-    }
-}
-
-#endif
-
-
 static Symbol getName(const AttrName & name, EvalState & state, Env & env)
 {
     if (name.symbol) {
@@ -311,99 +212,15 @@ static Symbol getName(const AttrName & name, EvalState & state, Env & env)
     }
 }
 
-#if HAVE_BOEHMGC
-/* Disable GC while this object lives. Used by CoroutineContext.
- *
- * Boehm keeps a count of GC_disable() and GC_enable() calls,
- * and only enables GC when the count matches.
- */
-class BoehmDisableGC {
-public:
-    BoehmDisableGC() {
-        GC_disable();
-    };
-    ~BoehmDisableGC() {
-        GC_enable();
-    };
-};
-#endif
-
-static bool gcInitialised = false;
-
-void initGC()
-{
-    if (gcInitialised) return;
-
-#if HAVE_BOEHMGC
-    /* Initialise the Boehm garbage collector. */
-
-    /* Don't look for interior pointers. This reduces the odds of
-       misdetection a bit. */
-    GC_set_all_interior_pointers(0);
-
-    /* We don't have any roots in data segments, so don't scan from
-       there. */
-    GC_set_no_dls(1);
-
-    GC_INIT();
-
-    GC_set_oom_fn(oomHandler);
-
-    StackAllocator::defaultAllocator = &boehmGCStackAllocator;
-
-    // TODO: Remove __APPLE__ condition.
-    //       Comment suggests an implementation that works on darwin and windows
-    //       https://github.com/ivmai/bdwgc/issues/362#issuecomment-1936672196
-    #if GC_VERSION_MAJOR >= 8 && GC_VERSION_MINOR >= 2 && GC_VERSION_MICRO >= 4 && !defined(__APPLE__)
-    GC_set_sp_corrector(&fixupBoehmStackPointer);
-
-    if (!GC_get_sp_corrector()) {
-        printTalkative("BoehmGC on this platform does not support sp_corrector; will disable GC inside coroutines");
-        /* Used to disable GC when entering coroutines on macOS */
-        create_coro_gc_hook = []() -> std::shared_ptr<void> {
-            return std::make_shared<BoehmDisableGC>();
-        };
-    }
-    #else
-    #warning "BoehmGC version does not support GC while coroutine exists. GC will be disabled inside coroutines. Consider updating bdw-gc to 8.2.4 or later."
-    #endif
-
-
-    /* Set the initial heap size to something fairly big (25% of
-       physical RAM, up to a maximum of 384 MiB) so that in most cases
-       we don't need to garbage collect at all.  (Collection has a
-       fairly significant overhead.)  The heap size can be overridden
-       through libgc's GC_INITIAL_HEAP_SIZE environment variable.  We
-       should probably also provide a nix.conf setting for this.  Note
-       that GC_expand_hp() causes a lot of virtual, but not physical
-       (resident) memory to be allocated.  This might be a problem on
-       systems that don't overcommit. */
-    if (!getEnv("GC_INITIAL_HEAP_SIZE")) {
-        size_t size = 32 * 1024 * 1024;
-#if HAVE_SYSCONF && defined(_SC_PAGESIZE) && defined(_SC_PHYS_PAGES)
-        size_t maxSize = 384 * 1024 * 1024;
-        long pageSize = sysconf(_SC_PAGESIZE);
-        long pages = sysconf(_SC_PHYS_PAGES);
-        if (pageSize != -1)
-            size = (pageSize * pages) / 4; // 25% of RAM
-        if (size > maxSize) size = maxSize;
-#endif
-        debug("setting initial heap size to %1% bytes", size);
-        GC_expand_hp(size);
-    }
-
-#endif
-
-    gcInitialised = true;
-}
-
 static constexpr size_t BASE_ENV_SIZE = 128;
 
 EvalState::EvalState(
     const LookupPath & _lookupPath,
     ref<Store> store,
+    const EvalSettings & settings,
     std::shared_ptr<Store> buildStore)
-    : sWith(symbols.create("<with>"))
+    : settings{settings}
+    , sWith(symbols.create("<with>"))
     , sOutPath(symbols.create("outPath"))
     , sDrvPath(symbols.create("drvPath"))
     , sType(symbols.create("type"))
@@ -423,6 +240,12 @@ EvalState::EvalState(
     , sRight(symbols.create("right"))
     , sWrong(symbols.create("wrong"))
     , sStructuredAttrs(symbols.create("__structuredAttrs"))
+    , sAllowedReferences(symbols.create("allowedReferences"))
+    , sAllowedRequisites(symbols.create("allowedRequisites"))
+    , sDisallowedReferences(symbols.create("disallowedReferences"))
+    , sDisallowedRequisites(symbols.create("disallowedRequisites"))
+    , sMaxSize(symbols.create("maxSize"))
+    , sMaxClosureSize(symbols.create("maxClosureSize"))
     , sBuilder(symbols.create("builder"))
     , sArgs(symbols.create("args"))
     , sContentAddressed(symbols.create("__contentAddressed"))
@@ -453,10 +276,10 @@ EvalState::EvalState(
     , repair(NoRepair)
     , emptyBindings(0)
     , rootFS(
-        evalSettings.restrictEval || evalSettings.pureEval
+        settings.restrictEval || settings.pureEval
         ? ref<SourceAccessor>(AllowListSourceAccessor::create(getFSSourceAccessor(), {},
-            [](const CanonPath & path) -> RestrictedPathError {
-                auto modeInformation = evalSettings.pureEval
+            [&settings](const CanonPath & path) -> RestrictedPathError {
+                auto modeInformation = settings.pureEval
                     ? "in pure evaluation mode (use '--impure' to override)"
                     : "in restricted mode";
                 throw RestrictedPathError("access to absolute path '%1%' is forbidden %2%", path, modeInformation);
@@ -470,7 +293,7 @@ EvalState::EvalState(
     )}
     , callFlakeInternal{internalFS->addFile(
         CanonPath("call-flake.nix"),
-        #include "flake/call-flake.nix.gen.hh"
+        #include "call-flake.nix.gen.hh"
     )}
     , store(store)
     , buildStore(buildStore ? buildStore : store)
@@ -493,7 +316,7 @@ EvalState::EvalState(
 
     countCalls = getEnv("NIX_COUNT_CALLS").value_or("0") != "0";
 
-    assert(gcInitialised);
+    assertGCInitialized();
 
     static_assert(sizeof(Env) <= 16, "environment must be <= 16 bytes");
 
@@ -507,10 +330,10 @@ EvalState::EvalState(
     vStringUnknown.mkString("unknown");
 
     /* Initialise the Nix expression search path. */
-    if (!evalSettings.pureEval) {
+    if (!settings.pureEval) {
         for (auto & i : _lookupPath.elements)
             lookupPath.elements.emplace_back(LookupPath::Elem {i});
-        for (auto & i : evalSettings.nixPath.get())
+        for (auto & i : settings.nixPath.get())
             lookupPath.elements.emplace_back(LookupPath::Elem::parse(i));
     }
 
@@ -588,9 +411,9 @@ bool isAllowedURI(std::string_view uri, const Strings & allowedUris)
 
 void EvalState::checkURI(const std::string & uri)
 {
-    if (!evalSettings.restrictEval) return;
+    if (!settings.restrictEval) return;
 
-    if (isAllowedURI(uri, evalSettings.allowedUris.get())) return;
+    if (isAllowedURI(uri, settings.allowedUris.get())) return;
 
     /* If the URI is a path, then check it against allowedPaths as
        well. */
@@ -635,7 +458,7 @@ void EvalState::addConstant(const std::string & name, Value * v, Constant info)
 
     constantInfos.push_back({name2, info});
 
-    if (!(evalSettings.pureEval && info.impureOnly)) {
+    if (!(settings.pureEval && info.impureOnly)) {
         /* Check the type, if possible.
 
            We might know the type of a thunk in advance, so be allowed
@@ -1590,11 +1413,11 @@ public:
 
 void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const PosIdx pos)
 {
-    if (callDepth > evalSettings.maxCallDepth)
+    if (callDepth > settings.maxCallDepth)
         error<EvalError>("stack overflow; max-call-depth exceeded").atPos(pos).debugThrow();
     CallDepth _level(callDepth);
 
-    auto trace = evalSettings.traceFunctionCalls
+    auto trace = settings.traceFunctionCalls
         ? std::make_unique<FunctionCallTrace>(positions[pos])
         : nullptr;
 
@@ -2480,7 +2303,7 @@ StorePath EvalState::copyPathToStore(NixStringContext & context, const SourcePat
                 path.resolveSymlinks(),
                 settings.readOnlyMode ? FetchMode::DryRun : FetchMode::Copy,
                 path.baseName(),
-                FileIngestionMethod::Recursive,
+                ContentAddressMethod::Raw::NixArchive,
                 nullptr,
                 repair);
             allowPath(dstPath);
@@ -2827,7 +2650,7 @@ void EvalState::printStatistics()
 }
 
 
-SourcePath resolveExprPath(SourcePath path)
+SourcePath resolveExprPath(SourcePath path, bool addDefaultNix)
 {
     unsigned int followCount = 0, maxFollow = 1024;
 
@@ -2843,7 +2666,7 @@ SourcePath resolveExprPath(SourcePath path)
     }
 
     /* If `path' refers to a directory, append `/default.nix'. */
-    if (path.resolveSymlinks().lstat().type == SourceAccessor::tDirectory)
+    if (addDefaultNix && path.resolveSymlinks().lstat().type == SourceAccessor::tDirectory)
         return path / "default.nix";
 
     return path;
@@ -2922,7 +2745,7 @@ SourcePath EvalState::findFile(const LookupPath & lookupPath, const std::string_
         return {corepkgsFS, CanonPath(path.substr(3))};
 
     error<ThrownError>(
-        evalSettings.pureEval
+        settings.pureEval
             ? "cannot look up '<%s>' in pure evaluation mode (use '--impure' to override)"
             : "file '%s' was not found in the Nix search path (add it using $NIX_PATH or -I)",
         path
@@ -2936,14 +2759,18 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
     auto i = lookupPathResolved.find(value);
     if (i != lookupPathResolved.end()) return i->second;
 
-    std::optional<std::string> res;
+    auto finish = [&](std::string res) {
+        debug("resolved search path element '%s' to '%s'", value, res);
+        lookupPathResolved.emplace(value, res);
+        return res;
+    };
 
     if (EvalSettings::isPseudoUrl(value)) {
         try {
             auto accessor = fetchers::downloadTarball(
                 EvalSettings::resolvePseudoUrl(value)).accessor;
             auto storePath = fetchToStore(*store, SourcePath(accessor), FetchMode::Copy);
-            res = { store->toRealPath(storePath) };
+            return finish(store->toRealPath(storePath));
         } catch (Error & e) {
             logWarning({
                 .msg = HintFmt("Nix search path entry '%1%' cannot be downloaded, ignoring", value)
@@ -2951,15 +2778,17 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
         }
     }
 
-    else if (hasPrefix(value, "flake:")) {
-        experimentalFeatureSettings.require(Xp::Flakes);
-        auto flakeRef = parseFlakeRef(value.substr(6), {}, true, false);
-        debug("fetching flake search path element '%s''", value);
-        auto storePath = flakeRef.resolve(store).fetchTree(store).first;
-        res = { store->toRealPath(storePath) };
+    if (auto colPos = value.find(':'); colPos != value.npos) {
+        auto scheme = value.substr(0, colPos);
+        auto rest = value.substr(colPos + 1);
+        if (auto * hook = get(settings.lookupPathHooks, scheme)) {
+            auto res = (*hook)(store, rest);
+            if (res)
+                return finish(std::move(*res));
+        }
     }
 
-    else {
+    {
         auto path = absPath(value);
 
         /* Allow access to paths in the search path. */
@@ -2976,22 +2805,17 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
         }
 
         if (pathExists(path))
-            res = { path };
+            return finish(std::move(path));
         else {
             logWarning({
                 .msg = HintFmt("Nix search path entry '%1%' does not exist, ignoring", value)
             });
-            res = std::nullopt;
         }
     }
 
-    if (res)
-        debug("resolved search path element '%s' to '%s'", value, *res);
-    else
-        debug("failed to resolve search path element '%s'", value);
+    debug("failed to resolve search path element '%s'", value);
+    return std::nullopt;
 
-    lookupPathResolved.emplace(value, res);
-    return res;
 }
 
 
@@ -3002,7 +2826,7 @@ Expr * EvalState::parse(
     const SourcePath & basePath,
     std::shared_ptr<StaticEnv> & staticEnv)
 {
-    auto result = parseExprFromBuf(text, length, origin, basePath, symbols, positions, rootFS, exprSymbols);
+    auto result = parseExprFromBuf(text, length, origin, basePath, symbols, settings, positions, rootFS, exprSymbols);
 
     result->bindVars(*this, staticEnv);
 

src/libexpr/eval.hh

@@ -3,6 +3,7 @@
 
 #include "attr-set.hh"
 #include "eval-error.hh"
+#include "eval-gc.hh"
 #include "types.hh"
 #include "value.hh"
 #include "nixexpr.hh"
@@ -29,6 +30,7 @@ namespace nix {
 constexpr size_t maxPrimOpArity = 8;
 
 class Store;
+struct EvalSettings;
 class EvalState;
 class StorePath;
 struct SingleDerivedPath;
@@ -38,7 +40,6 @@ namespace eval_cache {
     class EvalCache;
 }
 
-
 /**
  * Function that implements a primop.
  */
@@ -146,12 +147,6 @@ std::string printValue(EvalState & state, Value & v);
 std::ostream & operator << (std::ostream & os, const ValueType t);
 
 
-/**
- * Initialise the Boehm GC, if applicable.
- */
-void initGC();
-
-
 struct RegexCache;
 
 std::shared_ptr<RegexCache> makeRegexCache();
@@ -167,13 +162,17 @@ struct DebugTrace {
 class EvalState : public std::enable_shared_from_this<EvalState>
 {
 public:
+    const EvalSettings & settings;
     SymbolTable symbols;
     PosTable positions;
 
     const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sValue,
         sSystem, sOverrides, sOutputs, sOutputName, sIgnoreNulls,
         sFile, sLine, sColumn, sFunctor, sToString,
-        sRight, sWrong, sStructuredAttrs, sBuilder, sArgs,
+        sRight, sWrong, sStructuredAttrs,
+        sAllowedReferences, sAllowedRequisites, sDisallowedReferences, sDisallowedRequisites,
+        sMaxSize, sMaxClosureSize,
+        sBuilder, sArgs,
         sContentAddressed, sImpure,
         sOutputHash, sOutputHashAlgo, sOutputHashMode,
         sRecurseForDerivations,
@@ -354,6 +353,7 @@ public:
     EvalState(
         const LookupPath & _lookupPath,
         ref<Store> store,
+        const EvalSettings & settings,
         std::shared_ptr<Store> buildStore = nullptr);
     ~EvalState();
 
@@ -850,8 +850,10 @@ std::string showType(const Value & v);
 
 /**
  * If `path` refers to a directory, then append "/default.nix".
+ *
+ * @param addDefaultNix Whether to append "/default.nix" after resolving symlinks.
  */
-SourcePath resolveExprPath(SourcePath path);
+SourcePath resolveExprPath(SourcePath path, bool addDefaultNix = true);
 
 /**
  * Whether a URI is allowed, assuming restrictEval is enabled

src/libexpr/get-drvs.cc

@@ -374,21 +374,26 @@ static void getDerivations(EvalState & state, Value & vIn,
            bound to the attribute with the "lower" name should take
            precedence). */
         for (auto & i : v.attrs()->lexicographicOrder(state.symbols)) {
-            debug("evaluating attribute '%1%'", state.symbols[i->name]);
-            if (!std::regex_match(std::string(state.symbols[i->name]), attrRegex))
-                continue;
-            std::string pathPrefix2 = addToPath(pathPrefix, state.symbols[i->name]);
-            if (combineChannels)
-                getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
-            else if (getDerivation(state, *i->value, pathPrefix2, drvs, done, ignoreAssertionFailures)) {
-                /* If the value of this attribute is itself a set,
-                   should we recurse into it?  => Only if it has a
-                   `recurseForDerivations = true' attribute. */
-                if (i->value->type() == nAttrs) {
-                    auto j = i->value->attrs()->get(state.sRecurseForDerivations);
-                    if (j && state.forceBool(*j->value, j->pos, "while evaluating the attribute `recurseForDerivations`"))
-                        getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
+            try {
+                debug("evaluating attribute '%1%'", state.symbols[i->name]);
+                if (!std::regex_match(std::string(state.symbols[i->name]), attrRegex))
+                    continue;
+                std::string pathPrefix2 = addToPath(pathPrefix, state.symbols[i->name]);
+                if (combineChannels)
+                    getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
+                else if (getDerivation(state, *i->value, pathPrefix2, drvs, done, ignoreAssertionFailures)) {
+                    /* If the value of this attribute is itself a set,
+                    should we recurse into it?  => Only if it has a
+                    `recurseForDerivations = true' attribute. */
+                    if (i->value->type() == nAttrs) {
+                        auto j = i->value->attrs()->get(state.sRecurseForDerivations);
+                        if (j && state.forceBool(*j->value, j->pos, "while evaluating the attribute `recurseForDerivations`"))
+                            getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
+                    }
                 }
+            } catch (Error & e) {
+                e.addTrace(state.positions[i->pos], "while evaluating the attribute '%s'", state.symbols[i->name]);
+                throw;
             }
         }
     }

src/libexpr/local.mk

@@ -8,7 +8,6 @@ libexpr_SOURCES := \
   $(wildcard $(d)/*.cc) \
   $(wildcard $(d)/value/*.cc) \
   $(wildcard $(d)/primops/*.cc) \
-  $(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
@@ -16,7 +15,7 @@ libexpr_SOURCES := \
 INCLUDE_libexpr := -I $(d)
 
 libexpr_CXXFLAGS += \
-	$(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libmain) $(INCLUDE_libexpr) \
+	$(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libexpr) \
 	-DGC_THREADS
 
 libexpr_LIBS = libutil libstore libfetchers
@@ -45,11 +44,7 @@ $(eval $(call install-file-in, $(buildprefix)$(d)/nix-expr.pc, $(libdir)/pkgconf
 
 $(foreach i, $(wildcard src/libexpr/value/*.hh), \
   $(eval $(call install-file-in, $(i), $(includedir)/nix/value, 0644)))
-$(foreach i, $(wildcard src/libexpr/flake/*.hh), \
-  $(eval $(call install-file-in, $(i), $(includedir)/nix/flake, 0644)))
 
 $(d)/primops.cc: $(d)/imported-drv-to-derivation.nix.gen.hh
 
-$(d)/eval.cc: $(d)/primops/derivation.nix.gen.hh $(d)/fetchurl.nix.gen.hh $(d)/flake/call-flake.nix.gen.hh
-
-$(buildprefix)src/libexpr/primops/fromTOML.o:	ERROR_SWITCH_ENUM =
+$(d)/eval.cc: $(d)/primops/derivation.nix.gen.hh $(d)/fetchurl.nix.gen.hh $(d)/call-flake.nix.gen.hh

src/libexpr/meson.build

@@ -0,0 +1,202 @@
+project('nix-expr', 'cpp',
+  version : files('.version'),
+  default_options : [
+    'cpp_std=c++2a',
+    # TODO(Qyriad): increase the warning level
+    'warning_level=1',
+    'debug=true',
+    'optimization=2',
+    'errorlogs=true', # Please print logs for tests that fail
+  ],
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+cxx = meson.get_compiler('cpp')
+
+subdir('build-utils-meson/deps-lists')
+
+configdata = configuration_data()
+
+deps_private_maybe_subproject = [
+]
+deps_public_maybe_subproject = [
+  dependency('nix-util'),
+  dependency('nix-store'),
+  dependency('nix-fetchers'),
+]
+subdir('build-utils-meson/subprojects')
+
+subdir('build-utils-meson/threads')
+
+boost = dependency(
+  'boost',
+  modules : ['container', 'context'],
+)
+# boost is a public dependency, but not a pkg-config dependency unfortunately, so we
+# put in `deps_other`.
+deps_other += boost
+
+nlohmann_json = dependency('nlohmann_json', version : '>= 3.9')
+deps_public += nlohmann_json
+
+bdw_gc = dependency('bdw-gc', required : get_option('gc'))
+if bdw_gc.found()
+  deps_public += bdw_gc
+  foreach funcspec : [
+    'pthread_attr_get_np',
+    'pthread_getattr_np',
+  ]
+    define_name = 'HAVE_' + funcspec.underscorify().to_upper()
+    define_value = cxx.has_function(funcspec).to_int()
+    configdata.set(define_name, define_value)
+  endforeach
+  configdata.set('GC_THREADS', 1)
+endif
+configdata.set('HAVE_BOEHMGC', bdw_gc.found().to_int())
+
+toml11 = dependency('toml11', version : '>=3.7.0', method : 'cmake')
+deps_other += toml11
+
+config_h = configure_file(
+  configuration : configdata,
+  output : 'config-expr.hh',
+)
+
+add_project_arguments(
+  # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
+  # It would be nice for our headers to be idempotent instead.
+  '-include', 'config-util.hh',
+  '-include', 'config-store.hh',
+  # '-include', 'config-fetchers.h',
+  '-include', 'config-expr.hh',
+  language : 'cpp',
+)
+
+subdir('build-utils-meson/diagnostics')
+
+parser_tab = custom_target(
+  input : 'parser.y',
+  output : [
+    'parser-tab.cc',
+    'parser-tab.hh',
+  ],
+  command : [
+    'bison',
+    '-v',
+    '-o',
+    '@OUTPUT0@',
+    '@INPUT@',
+    '-d',
+  ],
+  # NOTE(Qyriad): Meson doesn't support installing only part of a custom target, so we add
+  # an install script below which removes parser-tab.cc.
+  install : true,
+  install_dir : get_option('includedir') / 'nix',
+)
+
+lexer_tab = custom_target(
+  input : [
+    'lexer.l',
+    parser_tab,
+  ],
+  output : [
+    'lexer-tab.cc',
+    'lexer-tab.hh',
+  ],
+  command : [
+    'flex',
+    '--outfile',
+    '@OUTPUT0@',
+    '--header-file=' + '@OUTPUT1@',
+    '@INPUT0@',
+  ],
+  # NOTE(Qyriad): Meson doesn't support installing only part of a custom target, so we add
+  # an install script below which removes lexer-tab.cc.
+  install : true,
+  install_dir : get_option('includedir') / 'nix',
+)
+
+subdir('build-utils-meson/generate-header')
+
+generated_headers = []
+foreach header : [
+  'imported-drv-to-derivation.nix',
+  'fetchurl.nix',
+  'call-flake.nix',
+]
+  generated_headers += gen_header.process(header)
+endforeach
+
+sources = files(
+  'attr-path.cc',
+  'attr-set.cc',
+  'eval-cache.cc',
+  'eval-error.cc',
+  'eval-gc.cc',
+  'eval-settings.cc',
+  'eval.cc',
+  'function-trace.cc',
+  'get-drvs.cc',
+  'json-to-value.cc',
+  'nixexpr.cc',
+  'paths.cc',
+  'primops.cc',
+  'print-ambiguous.cc',
+  'print.cc',
+  'search-path.cc',
+  'value-to-json.cc',
+  'value-to-xml.cc',
+  'value/context.cc',
+)
+
+include_dirs = [include_directories('.')]
+
+headers = [config_h] + files(
+  'attr-path.hh',
+  'attr-set.hh',
+  'eval-cache.hh',
+  'eval-error.hh',
+  'eval-gc.hh',
+  'eval-inline.hh',
+  'eval-settings.hh',
+  'eval.hh',
+  'function-trace.hh',
+  'gc-small-vector.hh',
+  'get-drvs.hh',
+  'json-to-value.hh',
+  'nixexpr.hh',
+  'parser-state.hh',
+  'pos-idx.hh',
+  'pos-table.hh',
+  'primops.hh',
+  'print-ambiguous.hh',
+  'print-options.hh',
+  'print.hh',
+  'repl-exit-status.hh',
+  'search-path.hh',
+  'symbol-table.hh',
+  'value-to-json.hh',
+  'value-to-xml.hh',
+  'value.hh',
+  'value/context.hh',
+)
+
+subdir('primops')
+
+this_library = library(
+  'nixexpr',
+  sources,
+  parser_tab,
+  lexer_tab,
+  generated_headers,
+  dependencies : deps_public + deps_private + deps_other,
+  prelink : true, # For C++ static initializers
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix', preserve_path : true)
+
+libraries_private = []
+
+subdir('build-utils-meson/export')

src/libexpr/meson.options

@@ -0,0 +1,3 @@
+option('gc', type : 'feature',
+  description : 'enable garbage collection in the Nix expression evaluator (requires Boehm GC)',
+)

src/libexpr/package.nix

@@ -0,0 +1,117 @@
+{ lib
+, stdenv
+, mkMesonDerivation
+, releaseTools
+
+, meson
+, ninja
+, pkg-config
+, bison
+, flex
+, cmake # for resolving toml11 dep
+
+, nix-util
+, nix-store
+, nix-fetchers
+, boost
+, boehmgc
+, nlohmann_json
+, toml11
+
+# Configuration Options
+
+, version
+
+# Whether to use garbage collection for the Nix language evaluator.
+#
+# If it is disabled, we just leak memory, but this is not as bad as it
+# 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.)
+#
+# Temporarily disabled on Windows because the `GC_throw_bad_alloc`
+# symbol is missing during linking.
+, enableGC ? !stdenv.hostPlatform.isWindows
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-expr";
+  inherit version;
+
+  workDir = ./.;
+  fileset = fileset.unions [
+    ../../build-utils-meson
+    ./build-utils-meson
+    ../../.version
+    ./.version
+    ./meson.build
+    ./meson.options
+    ./primops/meson.build
+    (fileset.fileFilter (file: file.hasExt "cc") ./.)
+    (fileset.fileFilter (file: file.hasExt "hh") ./.)
+    ./lexer.l
+    ./parser.y
+    (fileset.fileFilter (file: file.hasExt "nix") ./.)
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    pkg-config
+    bison
+    flex
+    cmake
+  ];
+
+  buildInputs = [
+    toml11
+  ];
+
+  propagatedBuildInputs = [
+    nix-util
+    nix-store
+    nix-fetchers
+    boost
+    nlohmann_json
+  ] ++ lib.optional enableGC boehmgc;
+
+  preConfigure =
+    # "Inline" .version so it's not a symlink, and includes the suffix.
+    # Do the meson utils, without modification.
+    ''
+      chmod u+w ./.version
+      echo ${version} > ../../.version
+    '';
+
+  mesonFlags = [
+    (lib.mesonEnable "gc" enableGC)
+  ];
+
+  env = {
+    # Needed for Meson to find Boost.
+    # https://github.com/NixOS/nixpkgs/issues/86131.
+    BOOST_INCLUDEDIR = "${lib.getDev boost}/include";
+    BOOST_LIBRARYDIR = "${lib.getLib boost}/lib";
+  } // lib.optionalAttrs (stdenv.isLinux && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")) {
+    LDFLAGS = "-fuse-ld=gold";
+  };
+
+  enableParallelBuilding = true;
+
+  separateDebugInfo = !stdenv.hostPlatform.isStatic;
+
+  strictDeps = true;
+
+  hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+})

src/libexpr/parser-state.hh

@@ -46,6 +46,7 @@ struct ParserState
     PosTable::Origin origin;
     const ref<SourceAccessor> rootFS;
     const Expr::AstSymbols & s;
+    const EvalSettings & settings;
 
     void dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos);
     void dupAttr(Symbol attr, const PosIdx pos, const PosIdx prevPos);

src/libexpr/parser.y

@@ -25,7 +25,6 @@
 #include "nixexpr.hh"
 #include "eval.hh"
 #include "eval-settings.hh"
-#include "globals.hh"
 #include "parser-state.hh"
 
 #define YYLTYPE ::nix::ParserLocation
@@ -40,6 +39,7 @@ Expr * parseExprFromBuf(
     Pos::Origin origin,
     const SourcePath & basePath,
     SymbolTable & symbols,
+    const EvalSettings & settings,
     PosTable & positions,
     const ref<SourceAccessor> rootFS,
     const Expr::AstSymbols & astSymbols);
@@ -294,7 +294,7 @@ path_start
     $$ = new ExprPath(ref<SourceAccessor>(state->rootFS), std::move(path));
   }
   | HPATH {
-    if (evalSettings.pureEval) {
+    if (state->settings.pureEval) {
         throw Error(
             "the path '%s' can not be resolved in pure mode",
             std::string_view($1.p, $1.l)
@@ -429,6 +429,7 @@ Expr * parseExprFromBuf(
     Pos::Origin origin,
     const SourcePath & basePath,
     SymbolTable & symbols,
+    const EvalSettings & settings,
     PosTable & positions,
     const ref<SourceAccessor> rootFS,
     const Expr::AstSymbols & astSymbols)
@@ -441,6 +442,7 @@ Expr * parseExprFromBuf(
         .origin = positions.addOrigin(origin, length),
         .rootFS = rootFS,
         .s = astSymbols,
+        .settings = settings,
     };
 
     yylex_init(&scanner);

src/libexpr/primops.cc

@@ -5,7 +5,6 @@
 #include "eval.hh"
 #include "eval-settings.hh"
 #include "gc-small-vector.hh"
-#include "globals.hh"
 #include "json-to-value.hh"
 #include "names.hh"
 #include "path-references.hh"
@@ -78,8 +77,8 @@ StringMap EvalState::realiseContext(const NixStringContext & context, StorePathS
 
     if (drvs.empty()) return {};
 
-    if (isIFD && !evalSettings.enableImportFromDerivation)
-        error<EvalError>(
+    if (isIFD && !settings.enableImportFromDerivation)
+        error<EvalBaseError>(
             "cannot build '%1%' during evaluation because the option 'allow-import-from-derivation' is disabled",
             drvs.begin()->to_string(*store)
         ).debugThrow();
@@ -733,11 +732,12 @@ static RegisterPrimOp primop_genericClosure(PrimOp {
       Each attribute set in the list `startSet` and the list returned by `operator` must have an attribute `key`, which must support equality comparison.
       The value of `key` can be one of the following types:
 
-      - [Number](@docroot@/language/values.md#type-number)
-      - [Boolean](@docroot@/language/values.md#type-boolean)
-      - [String](@docroot@/language/values.md#type-string)
-      - [Path](@docroot@/language/values.md#type-path)
-      - [List](@docroot@/language/values.md#list)
+      - [Int](@docroot@/language/types.md#type-int)
+      - [Float](@docroot@/language/types.md#type-float)
+      - [Boolean](@docroot@/language/types.md#type-boolean)
+      - [String](@docroot@/language/types.md#type-string)
+      - [Path](@docroot@/language/types.md#type-path)
+      - [List](@docroot@/language/types.md#list)
 
       The result is produced by calling the `operator` on each `item` that has not been called yet, including newly added items, until no new items are added.
       Items are compared by their `key` attribute.
@@ -901,7 +901,7 @@ static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Va
     MaintainCount trylevel(state.trylevel);
 
     ReplExitStatus (* savedDebugRepl)(ref<EvalState> es, const ValMap & extraEnv) = nullptr;
-    if (state.debugRepl && evalSettings.ignoreExceptionsDuringTry)
+    if (state.debugRepl && state.settings.ignoreExceptionsDuringTry)
     {
         /* to prevent starting the repl from exceptions withing a tryEval, null it. */
         savedDebugRepl = state.debugRepl;
@@ -950,7 +950,7 @@ static RegisterPrimOp primop_tryEval({
 static void prim_getEnv(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     std::string name(state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.getEnv"));
-    v.mkString(evalSettings.restrictEval || evalSettings.pureEval ? "" : getEnv(name).value_or(""));
+    v.mkString(state.settings.restrictEval || state.settings.pureEval ? "" : getEnv(name).value_or(""));
 }
 
 static RegisterPrimOp primop_getEnv({
@@ -1017,7 +1017,7 @@ static void prim_trace(EvalState & state, const PosIdx pos, Value * * args, Valu
         printError("trace: %1%", args[0]->string_view());
     else
         printError("trace: %1%", ValuePrinter(state, *args[0]));
-    if (evalSettings.builtinsTraceDebugger) {
+    if (state.settings.builtinsTraceDebugger) {
         state.runDebugRepl(nullptr);
     }
     state.forceValue(*args[1], pos);
@@ -1056,11 +1056,11 @@ static void prim_warn(EvalState & state, const PosIdx pos, Value * * args, Value
         logWarning(info);
     }
 
-    if (evalSettings.builtinsAbortOnWarn) {
+    if (state.settings.builtinsAbortOnWarn) {
         // Not an EvalError or subclass, which would cause the error to be stored in the eval cache.
         state.error<EvalBaseError>("aborting to reveal stack trace of warning, as abort-on-warn is set").setIsFromExpr().debugThrow();
     }
-    if (evalSettings.builtinsTraceDebugger || evalSettings.builtinsDebuggerOnWarn) {
+    if (state.settings.builtinsTraceDebugger || state.settings.builtinsDebuggerOnWarn) {
         state.runDebugRepl(nullptr);
     }
     state.forceValue(*args[1], pos);
@@ -1163,12 +1163,34 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
     }
 }
 
+/**
+ * Early validation for the derivation name, for better error message.
+ * It is checked again when constructing store paths.
+ *
+ * @todo Check that the `.drv` suffix also fits.
+ */
+static void checkDerivationName(EvalState & state, std::string_view drvName)
+{
+    try {
+        checkName(drvName);
+    } catch (BadStorePathName & e) {
+        // "Please pass a different name": Users may not be aware that they can
+        //     pass a different one, in functions like `fetchurl` where the name
+        //     is optional.
+        // Note that Nixpkgs generally won't trigger this, because `mkDerivation`
+        // sanitizes the name.
+        state.error<EvalError>("invalid derivation name: %s. Please pass a different '%s'.", Uncolored(e.message()), "name").debugThrow();
+    }
+}
+
 static void derivationStrictInternal(
     EvalState & state,
     const std::string & drvName,
     const Bindings * attrs,
     Value & v)
 {
+    checkDerivationName(state, drvName);
+
     /* Check whether attributes should be passed as a JSON file. */
     using nlohmann::json;
     std::optional<json> jsonObject;
@@ -1209,7 +1231,7 @@ static void derivationStrictInternal(
         auto handleHashMode = [&](const std::string_view s) {
             if (s == "recursive") {
                 // back compat, new name is "nar"
-                ingestionMethod = FileIngestionMethod::Recursive;
+                ingestionMethod = ContentAddressMethod::Raw::NixArchive;
             } else try {
                 ingestionMethod = ContentAddressMethod::parse(s);
             } catch (UsageError &) {
@@ -1217,9 +1239,9 @@ static void derivationStrictInternal(
                     "invalid value '%s' for 'outputHashMode' attribute", s
                 ).atPos(v).debugThrow();
             }
-            if (ingestionMethod == TextIngestionMethod {})
+            if (ingestionMethod == ContentAddressMethod::Raw::Text)
                 experimentalFeatureSettings.require(Xp::DynamicDerivations);
-            if (ingestionMethod == FileIngestionMethod::Git)
+            if (ingestionMethod == ContentAddressMethod::Raw::Git)
                 experimentalFeatureSettings.require(Xp::GitHashing);
         };
 
@@ -1308,6 +1330,20 @@ static void derivationStrictInternal(
                         handleOutputs(ss);
                     }
 
+                    if (i->name == state.sAllowedReferences)
+                        warn("In a derivation named '%s', 'structuredAttrs' disables the effect of the derivation attribute 'allowedReferences'; use 'outputChecks.<output>.allowedReferences' instead", drvName);
+                    if (i->name == state.sAllowedRequisites)
+                        warn("In a derivation named '%s', 'structuredAttrs' disables the effect of the derivation attribute 'allowedRequisites'; use 'outputChecks.<output>.allowedRequisites' instead", drvName);
+                    if (i->name == state.sDisallowedReferences)
+                        warn("In a derivation named '%s', 'structuredAttrs' disables the effect of the derivation attribute 'disallowedReferences'; use 'outputChecks.<output>.disallowedReferences' instead", drvName);
+                    if (i->name == state.sDisallowedRequisites)
+                        warn("In a derivation named '%s', 'structuredAttrs' disables the effect of the derivation attribute 'disallowedRequisites'; use 'outputChecks.<output>.disallowedRequisites' instead", drvName);
+                    if (i->name == state.sMaxSize)
+                        warn("In a derivation named '%s', 'structuredAttrs' disables the effect of the derivation attribute 'maxSize'; use 'outputChecks.<output>.maxSize' instead", drvName);
+                    if (i->name == state.sMaxClosureSize)
+                        warn("In a derivation named '%s', 'structuredAttrs' disables the effect of the derivation attribute 'maxClosureSize'; use 'outputChecks.<output>.maxClosureSize' instead", drvName);
+
+
                 } else {
                     auto s = state.coerceToString(pos, *i->value, context, context_below, true).toOwned();
                     drv.env.emplace(key, s);
@@ -1377,7 +1413,7 @@ static void derivationStrictInternal(
 
     /* Check whether the derivation name is valid. */
     if (isDerivation(drvName) &&
-        !(ingestionMethod == ContentAddressMethod { TextIngestionMethod { } } &&
+        !(ingestionMethod == ContentAddressMethod::Raw::Text &&
           outputs.size() == 1 &&
           *(outputs.begin()) == "out"))
     {
@@ -1399,7 +1435,7 @@ static void derivationStrictInternal(
 
         auto h = newHashAllowEmpty(*outputHash, outputHashAlgo);
 
-        auto method = ingestionMethod.value_or(FileIngestionMethod::Flat);
+        auto method = ingestionMethod.value_or(ContentAddressMethod::Raw::Flat);
 
         DerivationOutput::CAFixed dof {
             .ca = ContentAddress {
@@ -1418,7 +1454,7 @@ static void derivationStrictInternal(
                 .atPos(v).debugThrow();
 
         auto ha = outputHashAlgo.value_or(HashAlgorithm::SHA256);
-        auto method = ingestionMethod.value_or(FileIngestionMethod::Recursive);
+        auto method = ingestionMethod.value_or(ContentAddressMethod::Raw::NixArchive);
 
         for (auto & i : outputs) {
             drv.env[i] = hashPlaceholder(i);
@@ -1564,7 +1600,7 @@ static RegisterPrimOp primop_toPath({
    corner cases. */
 static void prim_storePath(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    if (evalSettings.pureEval)
+    if (state.settings.pureEval)
         state.error<EvalError>(
             "'%s' is not allowed in pure evaluation mode",
             "builtins.storePath"
@@ -1674,7 +1710,7 @@ static RegisterPrimOp primop_baseNameOf({
     .name = "baseNameOf",
     .args = {"x"},
     .doc = R"(
-      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.
+      Return the *base name* of either a [path value](@docroot@/language/types.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.
@@ -1808,7 +1844,7 @@ static RegisterPrimOp primop_findFile(PrimOp {
     .doc = R"(
       Find *lookup-path* in *search-path*.
 
-      A search path is represented list of [attribute sets](./values.md#attribute-set) with two attributes:
+      A search path is represented list of [attribute sets](./types.md#attribute-set) with two attributes:
       - `prefix` is a relative path.
       - `path` denotes a file system location
       The exact syntax depends on the command line interface.
@@ -1829,14 +1865,14 @@ static RegisterPrimOp primop_findFile(PrimOp {
         }
         ```
 
-      The lookup algorithm checks each entry until a match is found, returning a [path value](@docroot@/language/values.html#type-path) of the match:
+      The lookup algorithm checks each entry until a match is found, returning a [path value](@docroot@/language/types.md#type-path) of the match:
 
       - If *lookup-path* matches `prefix`, then the remainder of *lookup-path* (the "suffix") is searched for within the directory denoted by `path`.
         Note that the `path` may need to be downloaded at this point to look inside.
       - If the suffix is found inside that directory, then the entry is a match.
         The combined absolute path of the directory (now downloaded if need be) and the suffix is returned.
 
-      [Lookup path](@docroot@/language/constructs/lookup-path.md) expressions are [desugared](https://en.wikipedia.org/wiki/Syntactic_sugar) using this and [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath):
+      [Lookup path](@docroot@/language/constructs/lookup-path.md) expressions are [desugared](https://en.wikipedia.org/wiki/Syntactic_sugar) using this and [`builtins.nixPath`](#builtins-nixPath):
 
       ```nix
       <nixpkgs>
@@ -2194,7 +2230,7 @@ static void prim_toFile(EvalState & state, const PosIdx pos, Value * * args, Val
         })
         : ({
             StringSource s { contents };
-            state.store->addToStoreFromDump(s, name, FileSerialisationMethod::Flat, TextIngestionMethod {}, HashAlgorithm::SHA256, refs, state.repair);
+            state.store->addToStoreFromDump(s, name, FileSerialisationMethod::Flat, ContentAddressMethod::Raw::Text, HashAlgorithm::SHA256, refs, state.repair);
         });
 
     /* Note: we don't need to add `context' to the context of the
@@ -2257,7 +2293,7 @@ static RegisterPrimOp primop_toFile({
       ```
 
       Note that `${configFile}` is a
-      [string interpolation](@docroot@/language/values.md#type-string), so the result of the
+      [string interpolation](@docroot@/language/types.md#type-string), so the result of the
       expression `configFile`
       (i.e., a path like `/nix/store/m7p7jfny445k...-foo.conf`) will be
       spliced into the resulting string.
@@ -2377,7 +2413,7 @@ static void prim_filterSource(EvalState & state, const PosIdx pos, Value * * arg
         "while evaluating the second argument (the path to filter) passed to 'builtins.filterSource'");
     state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.filterSource");
 
-    addPath(state, pos, path.baseName(), path, args[0], FileIngestionMethod::Recursive, std::nullopt, v, context);
+    addPath(state, pos, path.baseName(), path, args[0], ContentAddressMethod::Raw::NixArchive, std::nullopt, v, context);
 }
 
 static RegisterPrimOp primop_filterSource({
@@ -2440,7 +2476,7 @@ static void prim_path(EvalState & state, const PosIdx pos, Value * * args, Value
     std::optional<SourcePath> path;
     std::string name;
     Value * filterFun = nullptr;
-    ContentAddressMethod method = FileIngestionMethod::Recursive;
+    auto method = ContentAddressMethod::Raw::NixArchive;
     std::optional<Hash> expectedHash;
     NixStringContext context;
 
@@ -2456,8 +2492,8 @@ static void prim_path(EvalState & state, const PosIdx pos, Value * * args, Value
             state.forceFunction(*(filterFun = attr.value), attr.pos, "while evaluating the `filter` parameter passed to builtins.path");
         else if (n == "recursive")
             method = state.forceBool(*attr.value, attr.pos, "while evaluating the `recursive` attribute passed to builtins.path")
-                ? FileIngestionMethod::Recursive
-                : FileIngestionMethod::Flat;
+                ? ContentAddressMethod::Raw::NixArchive
+                : ContentAddressMethod::Raw::Flat;
         else if (n == "sha256")
             expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the `sha256` attribute passed to builtins.path"), HashAlgorithm::SHA256);
         else
@@ -4483,7 +4519,7 @@ void EvalState::createBaseEnv()
     addConstant("builtins", v, {
         .type = nAttrs,
         .doc = R"(
-          Contains all the [built-in functions](@docroot@/language/builtins.md) and values.
+          Contains all the built-in functions and values.
 
           Since built-in functions were added over time, [testing for attributes](./operators.md#has-attribute) in `builtins` can be used for graceful fallback on older Nix installations:
 
@@ -4503,7 +4539,7 @@ void EvalState::createBaseEnv()
           It can be returned by
           [comparison operators](@docroot@/language/operators.md#Comparison)
           and used in
-          [conditional expressions](@docroot@/language/constructs.md#Conditionals).
+          [conditional expressions](@docroot@/language/syntax.md#Conditionals).
 
           The name `true` is not special, and can be shadowed:
 
@@ -4523,7 +4559,7 @@ void EvalState::createBaseEnv()
           It can be returned by
           [comparison operators](@docroot@/language/operators.md#Comparison)
           and used in
-          [conditional expressions](@docroot@/language/constructs.md#Conditionals).
+          [conditional expressions](@docroot@/language/syntax.md#Conditionals).
 
           The name `false` is not special, and can be shadowed:
 
@@ -4548,7 +4584,7 @@ void EvalState::createBaseEnv()
         )",
     });
 
-    if (!evalSettings.pureEval) {
+    if (!settings.pureEval) {
         v.mkInt(time(0));
     }
     addConstant("__currentTime", v, {
@@ -4575,8 +4611,8 @@ void EvalState::createBaseEnv()
         .impureOnly = true,
     });
 
-    if (!evalSettings.pureEval)
-        v.mkString(evalSettings.getCurrentSystem());
+    if (!settings.pureEval)
+        v.mkString(settings.getCurrentSystem());
     addConstant("__currentSystem", v, {
         .type = nString,
         .doc = R"(
@@ -4656,7 +4692,7 @@ void EvalState::createBaseEnv()
 
 #ifndef _WIN32 // TODO implement on Windows
     // Miscellaneous
-    if (evalSettings.enableNativeCode) {
+    if (settings.enableNativeCode) {
         addPrimOp({
             .name = "__importNative",
             .arity = 2,
@@ -4679,7 +4715,7 @@ void EvalState::createBaseEnv()
           error if `--trace-verbose` is enabled. Then return *e2*. This function
           is useful for debugging.
         )",
-        .fun = evalSettings.traceVerbose ? prim_trace : prim_second,
+        .fun = settings.traceVerbose ? prim_trace : prim_second,
     });
 
     /* Add a value containing the current Nix expression search path. */

src/libexpr/primops/fetchMercurial.cc

@@ -53,7 +53,7 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
     // whitelist. Ah well.
     state.checkURI(url);
 
-    if (evalSettings.pureEval && !rev)
+    if (state.settings.pureEval && !rev)
         throw Error("in pure evaluation mode, 'fetchMercurial' requires a Mercurial revision");
 
     fetchers::Attrs attrs;

src/libexpr/primops/fetchTree.cc

@@ -1,4 +1,4 @@
-#include "libfetchers/attrs.hh"
+#include "attrs.hh"
 #include "primops.hh"
 #include "eval-inline.hh"
 #include "eval-settings.hh"
@@ -171,10 +171,10 @@ static void fetchTree(
         }
     }
 
-    if (!evalSettings.pureEval && !input.isDirect() && experimentalFeatureSettings.isEnabled(Xp::Flakes))
+    if (!state.settings.pureEval && !input.isDirect() && experimentalFeatureSettings.isEnabled(Xp::Flakes))
         input = lookupInRegistries(state.store, input).first;
 
-    if (evalSettings.pureEval && !input.isLocked()) {
+    if (state.settings.pureEval && !input.isLocked()) {
         auto fetcher = "fetchTree";
         if (params.isFetchGit)
             fetcher = "fetchGit";
@@ -431,7 +431,10 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
 
     state.forceValue(*args[0], pos);
 
-    if (args[0]->type() == nAttrs) {
+    bool isArgAttrs = args[0]->type() == nAttrs;
+    bool nameAttrPassed = false;
+
+    if (isArgAttrs) {
 
         for (auto & attr : *args[0]->attrs()) {
             std::string_view n(state.symbols[attr.name]);
@@ -439,8 +442,10 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
                 url = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the url we should fetch");
             else if (n == "sha256")
                 expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the sha256 of the content we should fetch"), HashAlgorithm::SHA256);
-            else if (n == "name")
+            else if (n == "name") {
+                nameAttrPassed = true;
                 name = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the name of the content we should fetch");
+            }
             else
                 state.error<EvalError>("unsupported argument '%s' to '%s'", n, who)
                 .atPos(pos).debugThrow();
@@ -453,14 +458,27 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
         url = state.forceStringNoCtx(*args[0], pos, "while evaluating the url we should fetch");
 
     if (who == "fetchTarball")
-        url = evalSettings.resolvePseudoUrl(*url);
+        url = state.settings.resolvePseudoUrl(*url);
 
     state.checkURI(*url);
 
     if (name == "")
         name = baseNameOf(*url);
 
-    if (evalSettings.pureEval && !expectedHash)
+    try {
+        checkName(name);
+    } catch (BadStorePathName & e) {
+        auto resolution =
+            nameAttrPassed ? HintFmt("Please change the value for the 'name' attribute passed to '%s', so that it can create a valid store path.", who) :
+            isArgAttrs ? HintFmt("Please add a valid 'name' attribute to the argument for '%s', so that it can create a valid store path.", who) :
+            HintFmt("Please pass an attribute set with 'url' and 'name' attributes to '%s',  so that it can create a valid store path.", who);
+
+        state.error<EvalError>(
+            std::string("invalid store path name when fetching URL '%s': %s. %s"), *url, Uncolored(e.message()), Uncolored(resolution.str()))
+        .atPos(pos).debugThrow();
+    }
+
+    if (state.settings.pureEval && !expectedHash)
         state.error<EvalError>("in pure evaluation mode, '%s' requires a 'sha256' argument", who).atPos(pos).debugThrow();
 
     // early exit if pinned and already in the store
@@ -468,7 +486,7 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
         auto expectedPath = state.store->makeFixedOutputPath(
             name,
             FixedOutputInfo {
-                .method = unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat,
+                .method = unpack ? FileIngestionMethod::NixArchive : FileIngestionMethod::Flat,
                 .hash = *expectedHash,
                 .references = {}
             });

src/libexpr/primops/fromTOML.cc

@@ -1,9 +1,8 @@
 #include "primops.hh"
 #include "eval-inline.hh"
 
-#include "../../toml11/toml.hpp"
-
 #include <sstream>
+#include <toml.hpp>
 
 namespace nix {
 

src/libexpr/primops/meson.build

@@ -0,0 +1,12 @@
+generated_headers += gen_header.process(
+  'derivation.nix',
+  preserve_path_from: meson.project_source_root(),
+)
+
+sources += files(
+  'context.cc',
+  'fetchClosure.cc',
+  'fetchMercurial.cc',
+  'fetchTree.cc',
+  'fromTOML.cc',
+)

src/libexpr/print.cc

@@ -163,8 +163,8 @@ private:
     EvalState & state;
     PrintOptions options;
     std::optional<ValuesSeen> seen;
-    size_t attrsPrinted = 0;
-    size_t listItemsPrinted = 0;
+    size_t totalAttrsPrinted = 0;
+    size_t totalListItemsPrinted = 0;
     std::string indent;
 
     void increaseIndent()
@@ -345,11 +345,13 @@ private:
 
             auto prettyPrint = shouldPrettyPrintAttrs(sorted);
 
+            size_t currentAttrsPrinted = 0;
+
             for (auto & i : sorted) {
                 printSpace(prettyPrint);
 
-                if (attrsPrinted >= options.maxAttrs) {
-                    printElided(sorted.size() - attrsPrinted, "attribute", "attributes");
+                if (totalAttrsPrinted >= options.maxAttrs) {
+                    printElided(sorted.size() - currentAttrsPrinted, "attribute", "attributes");
                     break;
                 }
 
@@ -357,7 +359,8 @@ private:
                 output << " = ";
                 print(*i.second, depth + 1);
                 output << ";";
-                attrsPrinted++;
+                totalAttrsPrinted++;
+                currentAttrsPrinted++;
             }
 
             decreaseIndent();
@@ -402,11 +405,14 @@ private:
             output << "[";
             auto listItems = v.listItems();
             auto prettyPrint = shouldPrettyPrintList(listItems);
+
+            size_t currentListItemsPrinted = 0;
+
             for (auto elem : listItems) {
                 printSpace(prettyPrint);
 
-                if (listItemsPrinted >= options.maxListItems) {
-                    printElided(listItems.size() - listItemsPrinted, "item", "items");
+                if (totalListItemsPrinted >= options.maxListItems) {
+                    printElided(listItems.size() - currentListItemsPrinted, "item", "items");
                     break;
                 }
 
@@ -415,7 +421,8 @@ private:
                 } else {
                     printNullptr();
                 }
-                listItemsPrinted++;
+                totalListItemsPrinted++;
+                currentListItemsPrinted++;
             }
 
             decreaseIndent();
@@ -588,8 +595,8 @@ public:
 
     void print(Value & v)
     {
-        attrsPrinted = 0;
-        listItemsPrinted = 0;
+        totalAttrsPrinted = 0;
+        totalListItemsPrinted = 0;
         indent.clear();
 
         if (options.trackRepeated) {

src/libfetchers/.version

@@ -0,0 +1 @@
+../../.version

src/libfetchers/build-utils-meson

@@ -0,0 +1 @@
+../../build-utils-meson

src/libfetchers/fetch-settings.cc

@@ -1,4 +1,5 @@
 #include "fetch-settings.hh"
+#include "config-global.hh"
 
 namespace nix {
 

src/libfetchers/fetch-settings.hh

@@ -70,30 +70,6 @@ struct FetchSettings : public Config
     Setting<bool> warnDirty{this, true, "warn-dirty",
         "Whether to warn about dirty Git/Mercurial trees."};
 
-    Setting<std::string> flakeRegistry{this, "https://channels.nixos.org/flake-registry.json", "flake-registry",
-        R"(
-          Path or URI of the global flake registry.
-
-          When empty, disables the global flake registry.
-        )",
-        {}, true, Xp::Flakes};
-
-    Setting<bool> useRegistries{this, true, "use-registries",
-        "Whether to use flake registries to resolve flake references.",
-        {}, true, Xp::Flakes};
-
-    Setting<bool> acceptFlakeConfig{this, false, "accept-flake-config",
-        "Whether to accept nix configuration from a flake without prompting.",
-        {}, true, Xp::Flakes};
-
-    Setting<std::string> commitLockFileSummary{
-        this, "", "commit-lock-file-summary",
-        R"(
-          The commit summary to use when committing changed flake lock files. If
-          empty, the summary is generated based on the action performed.
-        )",
-        {"commit-lockfile-summary"}, true, Xp::Flakes};
-
     Setting<bool> trustTarballsFromGitForges{
         this, true, "trust-tarballs-from-git-forges",
         R"(
@@ -108,7 +84,6 @@ struct FetchSettings : public Config
           `narHash` attribute is specified,
           e.g. `github:NixOS/patchelf/7c2f768bf9601268a4e71c2ebe91e2011918a70f?narHash=sha256-PPXqKY2hJng4DBVE0I4xshv/vGLUskL7jl53roB8UdU%3D`.
         )"};
-
 };
 
 // FIXME: don't use a global variable.

src/libfetchers/fetch-to-store.hh

@@ -18,7 +18,7 @@ StorePath fetchToStore(
     const SourcePath & path,
     FetchMode mode,
     std::string_view name = "source",
-    ContentAddressMethod method = FileIngestionMethod::Recursive,
+    ContentAddressMethod method = ContentAddressMethod::Raw::NixArchive,
     PathFilter * filter = nullptr,
     RepairFlag repair = NoRepair);
 

src/libfetchers/fetchers.cc

@@ -260,6 +260,7 @@ std::pair<ref<SourceAccessor>, Input> Input::getAccessorUnchecked(ref<Store> sto
 
     auto [accessor, final] = scheme->getAccessor(store, *this);
 
+    assert(!accessor->fingerprint);
     accessor->fingerprint = scheme->getFingerprint(store, final);
 
     return {accessor, std::move(final)};
@@ -305,7 +306,7 @@ StorePath Input::computeStorePath(Store & store) const
     if (!narHash)
         throw Error("cannot compute store path for unlocked input '%s'", to_string());
     return store.makeFixedOutputPath(getName(), FixedOutputInfo {
-        .method = FileIngestionMethod::Recursive,
+        .method = FileIngestionMethod::NixArchive,
         .hash = *narHash,
         .references = {},
     });
@@ -418,7 +419,7 @@ namespace nlohmann {
 using namespace nix;
 
 fetchers::PublicKey adl_serializer<fetchers::PublicKey>::from_json(const json & json) {
-    fetchers::PublicKey res = {  };
+    fetchers::PublicKey res = { };
     if (auto type = optionalValueAt(json, "type"))
         res.type = getString(*type);
 

src/libfetchers/git-utils.cc

@@ -851,10 +851,10 @@ struct GitFileSystemObjectSinkImpl : GitFileSystemObjectSink
     }
 
     void createRegularFile(
-        const Path & path,
+        const CanonPath & path,
         std::function<void(CreateRegularFileSink &)> func) override
     {
-        auto pathComponents = tokenizeString<std::vector<std::string>>(path, "/");
+        auto pathComponents = tokenizeString<std::vector<std::string>>(path.rel(), "/");
         if (!prepareDirs(pathComponents, false)) return;
 
         git_writestream * stream = nullptr;
@@ -862,11 +862,11 @@ struct GitFileSystemObjectSinkImpl : GitFileSystemObjectSink
             throw Error("creating a blob stream object: %s", git_error_last()->message);
 
         struct CRF : CreateRegularFileSink {
-            const Path & path;
+            const CanonPath & path;
             GitFileSystemObjectSinkImpl & back;
             git_writestream * stream;
             bool executable = false;
-            CRF(const Path & path, GitFileSystemObjectSinkImpl & back, git_writestream * stream)
+            CRF(const CanonPath & path, GitFileSystemObjectSinkImpl & back, git_writestream * stream)
                 : path(path), back(back), stream(stream)
             {}
             void operator () (std::string_view data) override
@@ -891,15 +891,15 @@ struct GitFileSystemObjectSinkImpl : GitFileSystemObjectSink
             : GIT_FILEMODE_BLOB);
     }
 
-    void createDirectory(const Path & path) override
+    void createDirectory(const CanonPath & path) override
     {
-        auto pathComponents = tokenizeString<std::vector<std::string>>(path, "/");
+        auto pathComponents = tokenizeString<std::vector<std::string>>(path.rel(), "/");
         (void) prepareDirs(pathComponents, true);
     }
 
-    void createSymlink(const Path & path, const std::string & target) override
+    void createSymlink(const CanonPath & path, const std::string & target) override
     {
-        auto pathComponents = tokenizeString<std::vector<std::string>>(path, "/");
+        auto pathComponents = tokenizeString<std::vector<std::string>>(path.rel(), "/");
         if (!prepareDirs(pathComponents, false)) return;
 
         git_oid oid;

src/libfetchers/git.cc

@@ -41,21 +41,6 @@ bool isCacheFileWithinTtl(time_t now, const struct stat & st)
     return st.st_mtime + settings.tarballTtl > now;
 }
 
-bool touchCacheFile(const Path & path, time_t touch_time)
-{
-#ifndef _WIN32 // TODO implement
-    struct timeval times[2];
-    times[0].tv_sec = touch_time;
-    times[0].tv_usec = 0;
-    times[1].tv_sec = touch_time;
-    times[1].tv_usec = 0;
-
-    return lutimes(path.c_str(), times) == 0;
-#else
-    return false;
-#endif
-}
-
 Path getCachePath(std::string_view key, bool shallow)
 {
     return getCacheDir()
@@ -594,8 +579,11 @@ struct GitInputScheme : InputScheme
                     warn("could not update local clone of Git repository '%s'; continuing with the most recent version", repoInfo.url);
                 }
 
-                if (!touchCacheFile(localRefFile, now))
-                    warn("could not update mtime for file '%s': %s", localRefFile, strerror(errno));
+                try {
+                    setWriteTime(localRefFile, now, now);
+                } catch (Error & e) {
+                    warn("could not update mtime for file '%s': %s", localRefFile, e.msg());
+                }
                 if (!originalRef && !storeCachedHead(repoInfo.url, ref))
                     warn("could not update cached head '%s' for '%s'", ref, repoInfo.url);
             }

src/libfetchers/github.cc

@@ -433,7 +433,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
                 store->toRealPath(
                     downloadFile(store, url, "source", headers).storePath)));
 
-        if (json.is_array() && json.size() == 1 && json[0]["id"] != nullptr) {
+        if (json.is_array() && json.size() >= 1 && json[0]["id"] != nullptr) {
           return RefInfo {
               .rev = Hash::parseAny(std::string(json[0]["id"]), HashAlgorithm::SHA1)
           };

src/libfetchers/mercurial.cc

@@ -213,7 +213,7 @@ struct MercurialInputScheme : InputScheme
                 auto storePath = store->addToStore(
                     input.getName(),
                     {getFSSourceAccessor(), CanonPath(actualPath)},
-                    FileIngestionMethod::Recursive, HashAlgorithm::SHA256, {},
+                    ContentAddressMethod::Raw::NixArchive, HashAlgorithm::SHA256, {},
                     filter);
 
                 return storePath;

src/libfetchers/meson.build

@@ -0,0 +1,93 @@
+project('nix-fetchers', 'cpp',
+  version : files('.version'),
+  default_options : [
+    'cpp_std=c++2a',
+    # TODO(Qyriad): increase the warning level
+    'warning_level=1',
+    'debug=true',
+    'optimization=2',
+    'errorlogs=true', # Please print logs for tests that fail
+  ],
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+cxx = meson.get_compiler('cpp')
+
+subdir('build-utils-meson/deps-lists')
+
+configdata = configuration_data()
+
+deps_private_maybe_subproject = [
+]
+deps_public_maybe_subproject = [
+  dependency('nix-util'),
+  dependency('nix-store'),
+]
+subdir('build-utils-meson/subprojects')
+
+nlohmann_json = dependency('nlohmann_json', version : '>= 3.9')
+deps_public += nlohmann_json
+
+libgit2 = dependency('libgit2')
+deps_private += libgit2
+
+add_project_arguments(
+  # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
+  # It would be nice for our headers to be idempotent instead.
+  '-include', 'config-util.hh',
+  '-include', 'config-store.hh',
+  # '-include', 'config-fetchers.h',
+  language : 'cpp',
+)
+
+subdir('build-utils-meson/diagnostics')
+
+sources = files(
+  'attrs.cc',
+  'cache.cc',
+  'fetch-settings.cc',
+  'fetch-to-store.cc',
+  'fetchers.cc',
+  'filtering-source-accessor.cc',
+  'git.cc',
+  'git-utils.cc',
+  'github.cc',
+  'indirect.cc',
+  'mercurial.cc',
+  'mounted-source-accessor.cc',
+  'path.cc',
+  'store-path-accessor.cc',
+  'registry.cc',
+  'tarball.cc',
+)
+
+include_dirs = [include_directories('.')]
+
+headers = files(
+  'attrs.hh',
+  'cache.hh',
+  'fetch-settings.hh',
+  'fetch-to-store.hh',
+  'filtering-source-accessor.hh',
+  'git-utils.hh',
+  'mounted-source-accessor.hh',
+  'fetchers.hh',
+  'registry.hh',
+  'store-path-accessor.hh',
+  'tarball.hh',
+)
+
+this_library = library(
+  'nixfetchers',
+  sources,
+  dependencies : deps_public + deps_private + deps_other,
+  prelink : true, # For C++ static initializers
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix', preserve_path : true)
+
+libraries_private = []
+
+subdir('build-utils-meson/export')

src/libfetchers/package.nix

@@ -0,0 +1,84 @@
+{ lib
+, stdenv
+, mkMesonDerivation
+, releaseTools
+
+, meson
+, ninja
+, pkg-config
+
+, nix-util
+, nix-store
+, nlohmann_json
+, libgit2
+, man
+
+# Configuration Options
+
+, version
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-fetchers";
+  inherit version;
+
+  workDir = ./.;
+  fileset = fileset.unions [
+    ../../build-utils-meson
+    ./build-utils-meson
+    ../../.version
+    ./.version
+    ./meson.build
+    (fileset.fileFilter (file: file.hasExt "cc") ./.)
+    (fileset.fileFilter (file: file.hasExt "hh") ./.)
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    pkg-config
+  ];
+
+  buildInputs = [
+    libgit2
+  ];
+
+  propagatedBuildInputs = [
+    nix-store
+    nix-util
+    nlohmann_json
+  ];
+
+  preConfigure =
+    # "Inline" .version so it's not a symlink, and includes the suffix.
+    # Do the meson utils, without modification.
+    ''
+      chmod u+w ./.version
+      echo ${version} > ../../.version
+    '';
+
+  env = lib.optionalAttrs (stdenv.isLinux && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")) {
+    LDFLAGS = "-fuse-ld=gold";
+  };
+
+  enableParallelBuilding = true;
+
+  separateDebugInfo = !stdenv.hostPlatform.isStatic;
+
+  # TODO `releaseTools.coverageAnalysis` in Nixpkgs needs to be updated
+  # to work with `strictDeps`.
+  strictDeps = true;
+
+  hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+})

src/libfetchers/registry.cc

@@ -1,12 +1,11 @@
 #include "registry.hh"
 #include "tarball.hh"
 #include "users.hh"
+#include "config-global.hh"
 #include "globals.hh"
 #include "store-api.hh"
 #include "local-fs-store.hh"
 
-#include "fetch-settings.hh"
-
 #include <nlohmann/json.hpp>
 
 namespace nix::fetchers {
@@ -149,10 +148,25 @@ void overrideRegistry(
     flagRegistry->add(from, to, extraAttrs);
 }
 
+struct RegistrySettings : Config
+{
+    Setting<std::string> flakeRegistry{this, "https://channels.nixos.org/flake-registry.json", "flake-registry",
+        R"(
+          Path or URI of the global flake registry.
+
+          When empty, disables the global flake registry.
+        )",
+        {}, true, Xp::Flakes};
+};
+
+RegistrySettings registrySettings;
+
+static GlobalConfig::Register rRegistrySettings(&registrySettings);
+
 static std::shared_ptr<Registry> getGlobalRegistry(ref<Store> store)
 {
     static auto reg = [&]() {
-        auto path = fetchSettings.flakeRegistry.get();
+        auto path = registrySettings.flakeRegistry.get();
         if (path == "") {
             return std::make_shared<Registry>(Registry::Global); // empty registry
         }

src/libfetchers/tarball.cc

@@ -365,6 +365,16 @@ struct TarballInputScheme : CurlInputScheme
 
         return {result.accessor, input};
     }
+
+    std::optional<std::string> getFingerprint(ref<Store> store, const Input & input) const override
+    {
+        if (auto narHash = input.getNarHash())
+            return narHash->to_string(HashFormat::SRI, true);
+        else if (auto rev = input.getRev())
+            return rev->gitRev();
+        else
+            return std::nullopt;
+    }
 };
 
 static auto rTarballInputScheme = OnStartup([] { registerInputScheme(std::make_unique<TarballInputScheme>()); });

src/libflake/.version

@@ -0,0 +1 @@
+../../.version

src/libflake/build-utils-meson

@@ -0,0 +1 @@
+../../build-utils-meson

src/libflake/flake-settings.cc

@@ -0,0 +1,12 @@
+#include "flake-settings.hh"
+#include "config-global.hh"
+
+namespace nix {
+
+FlakeSettings::FlakeSettings() {}
+
+FlakeSettings flakeSettings;
+
+static GlobalConfig::Register rFlakeSettings(&flakeSettings);
+
+}

src/libflake/flake-settings.hh

@@ -0,0 +1,53 @@
+#pragma once
+///@file
+
+#include "types.hh"
+#include "config.hh"
+#include "util.hh"
+
+#include <map>
+#include <limits>
+
+#include <sys/types.h>
+
+namespace nix {
+
+struct FlakeSettings : public Config
+{
+    FlakeSettings();
+
+    Setting<bool> useRegistries{
+        this,
+        true,
+        "use-registries",
+        "Whether to use flake registries to resolve flake references.",
+        {},
+        true,
+        Xp::Flakes};
+
+    Setting<bool> acceptFlakeConfig{
+        this,
+        false,
+        "accept-flake-config",
+        "Whether to accept nix configuration from a flake without prompting.",
+        {},
+        true,
+        Xp::Flakes};
+
+    Setting<std::string> commitLockFileSummary{
+        this,
+        "",
+        "commit-lock-file-summary",
+        R"(
+          The commit summary to use when committing changed flake lock files. If
+          empty, the summary is generated based on the action performed.
+        )",
+        {"commit-lockfile-summary"},
+        true,
+        Xp::Flakes};
+};
+
+// TODO: don't use a global variable.
+extern FlakeSettings flakeSettings;
+
+}

src/libflake/flake/config.cc

@@ -1,6 +1,6 @@
 #include "users.hh"
-#include "globals.hh"
-#include "fetch-settings.hh"
+#include "config-global.hh"
+#include "flake-settings.hh"
 #include "flake.hh"
 
 #include <nlohmann/json.hpp>
@@ -51,7 +51,7 @@ void ConfigFile::apply()
         else
             assert(false);
 
-        if (!whitelist.count(baseName) && !nix::fetchSettings.acceptFlakeConfig) {
+        if (!whitelist.count(baseName) && !nix::flakeSettings.acceptFlakeConfig) {
             bool trusted = false;
             auto trustedList = readTrustedList();
             auto tlname = get(trustedList, name);

src/libflake/flake/flake.cc

@@ -9,6 +9,7 @@
 #include "fetchers.hh"
 #include "finally.hh"
 #include "fetch-settings.hh"
+#include "flake-settings.hh"
 #include "value-to-json.hh"
 #include "local-fs-store.hh"
 
@@ -346,7 +347,7 @@ LockedFlake lockFlake(
 
     FlakeCache flakeCache;
 
-    auto useRegistries = lockFlags.useRegistries.value_or(fetchSettings.useRegistries);
+    auto useRegistries = lockFlags.useRegistries.value_or(flakeSettings.useRegistries);
 
     auto flake = getFlake(state, topRef, useRegistries, flakeCache);
 
@@ -691,7 +692,7 @@ LockedFlake lockFlake(
                             if (lockFlags.commitLockFile) {
                                 std::string cm;
 
-                                cm = fetchSettings.commitLockFileSummary.get();
+                                cm = flakeSettings.commitLockFileSummary.get();
 
                                 if (cm == "") {
                                     cm = fmt("%s: %s", relPath, lockFileExists ? "Update" : "Add");
@@ -803,7 +804,7 @@ static void prim_getFlake(EvalState & state, const PosIdx pos, Value * * args, V
 {
     std::string flakeRefS(state.forceStringNoCtx(*args[0], pos, "while evaluating the argument passed to builtins.getFlake"));
     auto flakeRef = parseFlakeRef(flakeRefS, {}, true);
-    if (evalSettings.pureEval && !flakeRef.input.isLocked())
+    if (state.settings.pureEval && !flakeRef.input.isLocked())
         throw Error("cannot call 'getFlake' on unlocked flake reference '%s', at %s (use --impure to override)", flakeRefS, state.positions[pos]);
 
     callFlake(state,
@@ -811,8 +812,8 @@ static void prim_getFlake(EvalState & state, const PosIdx pos, Value * * args, V
             LockFlags {
                 .updateLockFile = false,
                 .writeLockFile = false,
-                .useRegistries = !evalSettings.pureEval && fetchSettings.useRegistries,
-                .allowUnlocked = !evalSettings.pureEval,
+                .useRegistries = !state.settings.pureEval && flakeSettings.useRegistries,
+                .allowUnlocked = !state.settings.pureEval,
             }),
         v);
 }
@@ -949,10 +950,20 @@ std::optional<Fingerprint> LockedFlake::getFingerprint(ref<Store> store) const
     auto fingerprint = flake.lockedRef.input.getFingerprint(store);
     if (!fingerprint) return std::nullopt;
 
+    *fingerprint += fmt(";%s;%s", flake.lockedRef.subdir, lockFile);
+
+    /* Include revCount and lastModified because they're not
+       necessarily implied by the content fingerprint (e.g. for
+       tarball flakes) but can influence the evaluation result. */
+    if (auto revCount = flake.lockedRef.input.getRevCount())
+        *fingerprint += fmt(";revCount=%d", *revCount);
+    if (auto lastModified = flake.lockedRef.input.getLastModified())
+        *fingerprint += fmt(";lastModified=%d", *lastModified);
+
     // FIXME: as an optimization, if the flake contains a lock file
     // and we haven't changed it, then it's sufficient to use
     // flake.sourceInfo.storePath for the fingerprint.
-    return hashString(HashAlgorithm::SHA256, fmt("%s;%s;%s", *fingerprint, flake.lockedRef.subdir, lockFile));
+    return hashString(HashAlgorithm::SHA256, *fingerprint);
 }
 
 Flake::~Flake() { }

src/libflake/local.mk

@@ -0,0 +1,17 @@
+libraries += libflake
+
+libflake_NAME = libnixflake
+
+libflake_DIR := $(d)
+
+libflake_SOURCES := $(wildcard $(d)/*.cc $(d)/flake/*.cc)
+
+# Not just for this library itself, but also for downstream libraries using this library
+
+INCLUDE_libflake := -I $(d)
+
+libflake_CXXFLAGS += $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libfetchers) $(INCLUDE_libexpr) $(INCLUDE_libflake)
+
+libflake_LDFLAGS += $(THREAD_LDFLAGS)
+
+libflake_LIBS = libutil libstore libfetchers libexpr

src/libflake/meson.build

@@ -0,0 +1,75 @@
+project('nix-flake', 'cpp',
+  version : files('.version'),
+  default_options : [
+    'cpp_std=c++2a',
+    # TODO(Qyriad): increase the warning level
+    'warning_level=1',
+    'debug=true',
+    'optimization=2',
+    'errorlogs=true', # Please print logs for tests that fail
+  ],
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+cxx = meson.get_compiler('cpp')
+
+subdir('build-utils-meson/deps-lists')
+
+deps_private_maybe_subproject = [
+]
+deps_public_maybe_subproject = [
+  dependency('nix-util'),
+  dependency('nix-store'),
+  dependency('nix-fetchers'),
+  dependency('nix-expr'),
+]
+subdir('build-utils-meson/subprojects')
+
+nlohmann_json = dependency('nlohmann_json', version : '>= 3.9')
+deps_public += nlohmann_json
+
+add_project_arguments(
+  # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
+  # It would be nice for our headers to be idempotent instead.
+  '-include', 'config-util.hh',
+  '-include', 'config-store.hh',
+  # '-include', 'config-fetchers.h',
+  '-include', 'config-expr.hh',
+  language : 'cpp',
+)
+
+subdir('build-utils-meson/diagnostics')
+
+sources = files(
+  'flake-settings.cc',
+  'flake/config.cc',
+  'flake/flake.cc',
+  'flake/flakeref.cc',
+  'flake/url-name.cc',
+  'flake/lockfile.cc',
+)
+
+include_dirs = [include_directories('.')]
+
+headers = files(
+  'flake-settings.hh',
+  'flake/flake.hh',
+  'flake/flakeref.hh',
+  'flake/lockfile.hh',
+  'flake/url-name.hh',
+)
+
+this_library = library(
+  'nixflake',
+  sources,
+  dependencies : deps_public + deps_private + deps_other,
+  prelink : true, # For C++ static initializers
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix', preserve_path : true)
+
+libraries_private = []
+
+subdir('build-utils-meson/export')

src/libflake/package.nix

@@ -0,0 +1,84 @@
+{ lib
+, stdenv
+, mkMesonDerivation
+, releaseTools
+
+, meson
+, ninja
+, pkg-config
+
+, nix-util
+, nix-store
+, nix-fetchers
+, nix-expr
+, nlohmann_json
+, libgit2
+, man
+
+# Configuration Options
+
+, version
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-flake";
+  inherit version;
+
+  workDir = ./.;
+  fileset = fileset.unions [
+    ../../build-utils-meson
+    ./build-utils-meson
+    ../../.version
+    ./.version
+    ./meson.build
+    (fileset.fileFilter (file: file.hasExt "cc") ./.)
+    (fileset.fileFilter (file: file.hasExt "hh") ./.)
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    pkg-config
+  ];
+
+  propagatedBuildInputs = [
+    nix-store
+    nix-util
+    nix-fetchers
+    nix-expr
+    nlohmann_json
+  ];
+
+  preConfigure =
+    # "Inline" .version so it's not a symlink, and includes the suffix.
+    # Do the meson utils, without modification.
+    ''
+      chmod u+w ./.version
+      echo ${version} > ../../.version
+    '';
+
+  env = lib.optionalAttrs (stdenv.isLinux && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")) {
+    LDFLAGS = "-fuse-ld=gold";
+  };
+
+  enableParallelBuilding = true;
+
+  separateDebugInfo = !stdenv.hostPlatform.isStatic;
+
+  # TODO `releaseTools.coverageAnalysis` in Nixpkgs needs to be updated
+  # to work with `strictDeps`.
+  strictDeps = true;
+
+  hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+})

src/libmain/.version

@@ -0,0 +1 @@
+../../.version

src/libmain/build-utils-meson

@@ -0,0 +1 @@
+../../build-utils-meson

src/libmain/common-args.cc

@@ -1,5 +1,6 @@
 #include "common-args.hh"
 #include "args/root.hh"
+#include "config-global.hh"
 #include "globals.hh"
 #include "logging.hh"
 #include "loggers.hh"

src/libmain/meson.build

@@ -0,0 +1,98 @@
+project('nix-main', 'cpp',
+  version : files('.version'),
+  default_options : [
+    'cpp_std=c++2a',
+    # TODO(Qyriad): increase the warning level
+    'warning_level=1',
+    'debug=true',
+    'optimization=2',
+    'errorlogs=true', # Please print logs for tests that fail
+  ],
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+cxx = meson.get_compiler('cpp')
+
+subdir('build-utils-meson/deps-lists')
+
+configdata = configuration_data()
+
+deps_private_maybe_subproject = [
+]
+deps_public_maybe_subproject = [
+  dependency('nix-util'),
+  dependency('nix-store'),
+]
+subdir('build-utils-meson/subprojects')
+
+
+pubsetbuf_test = '''
+#include <iostream>
+
+using namespace std;
+
+char buf[1024];
+
+int main() {
+  cerr.rdbuf()->pubsetbuf(buf, sizeof(buf));
+}
+'''
+
+configdata.set(
+  'HAVE_PUBSETBUF',
+  cxx.compiles(pubsetbuf_test).to_int(),
+  description: 'Optionally used for buffering on standard error'
+)
+
+config_h = configure_file(
+  configuration : configdata,
+  output : 'config-main.hh',
+)
+
+add_project_arguments(
+  # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
+  # It would be nice for our headers to be idempotent instead.
+  '-include', 'config-util.hh',
+  '-include', 'config-store.hh',
+  '-include', 'config-main.hh',
+  language : 'cpp',
+)
+
+subdir('build-utils-meson/diagnostics')
+
+sources = files(
+  'common-args.cc',
+  'loggers.cc',
+  'progress-bar.cc',
+  'shared.cc',
+)
+
+if host_machine.system() != 'windows'
+  sources += files(
+    'unix/stack.cc',
+  )
+endif
+
+include_dirs = [include_directories('.')]
+
+headers = [config_h] + files(
+  'common-args.hh',
+  'loggers.hh',
+  'progress-bar.hh',
+  'shared.hh',
+)
+
+this_library = library(
+  'nixmain',
+  sources,
+  dependencies : deps_public + deps_private + deps_other,
+  prelink : true, # For C++ static initializers
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix', preserve_path : true)
+
+libraries_private = []
+
+subdir('build-utils-meson/export')

src/libmain/package.nix

@@ -0,0 +1,79 @@
+{ lib
+, stdenv
+, mkMesonDerivation
+, releaseTools
+
+, meson
+, ninja
+, pkg-config
+
+, openssl
+
+, nix-util
+, nix-store
+
+# Configuration Options
+
+, version
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-main";
+  inherit version;
+
+  workDir = ./.;
+  fileset = fileset.unions [
+    ../../build-utils-meson
+    ./build-utils-meson
+    ../../.version
+    ./.version
+    ./meson.build
+    (fileset.fileFilter (file: file.hasExt "cc") ./.)
+    (fileset.fileFilter (file: file.hasExt "hh") ./.)
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    pkg-config
+  ];
+
+  propagatedBuildInputs = [
+    nix-util
+    nix-store
+    openssl
+  ];
+
+  preConfigure =
+    # "Inline" .version so it's not a symlink, and includes the suffix.
+    # Do the meson utils, without modification.
+    ''
+      chmod u+w ./.version
+      echo ${version} > ../../.version
+    '';
+
+  env = lib.optionalAttrs (stdenv.isLinux && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")) {
+    LDFLAGS = "-fuse-ld=gold";
+  };
+
+  enableParallelBuilding = true;
+
+  separateDebugInfo = !stdenv.hostPlatform.isStatic;
+
+  # TODO `releaseTools.coverageAnalysis` in Nixpkgs needs to be updated
+  # to work with `strictDeps`.
+  strictDeps = true;
+
+  hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+})

src/libmain/shared.cc

@@ -320,6 +320,10 @@ void showManPage(const std::string & name)
     restoreProcessContext();
     setEnv("MANPATH", settings.nixManDir.c_str());
     execlp("man", "man", name.c_str(), nullptr);
+    if (errno == ENOENT) {
+        // Not SysError because we don't want to suffix the errno, aka No such file or directory.
+        throw Error("The '%1%' command was not found, but it is needed for '%2%' and some other '%3%' commands' help text. Perhaps you could install the '%1%' command?", "man", name.c_str(), "nix-*");
+    }
     throw SysError("command 'man %1%' failed", name.c_str());
 }
 

src/libstore-c/.version

@@ -0,0 +1 @@
+../../.version

src/libstore-c/build-utils-meson

@@ -0,0 +1 @@
+../../build-utils-meson

src/libstore-c/meson.build

@@ -0,0 +1,83 @@
+project('nix-store-c', 'cpp',
+  version : files('.version'),
+  default_options : [
+    'cpp_std=c++2a',
+    # TODO(Qyriad): increase the warning level
+    'warning_level=1',
+    'debug=true',
+    'optimization=2',
+    'errorlogs=true', # Please print logs for tests that fail
+  ],
+  meson_version : '>= 1.1',
+  license : 'LGPL-2.1-or-later',
+)
+
+cxx = meson.get_compiler('cpp')
+
+subdir('build-utils-meson/deps-lists')
+
+configdata = configuration_data()
+
+deps_private_maybe_subproject = [
+  dependency('nix-util'),
+  dependency('nix-store'),
+]
+deps_public_maybe_subproject = [
+  dependency('nix-util-c'),
+]
+subdir('build-utils-meson/subprojects')
+
+# TODO rename, because it will conflict with downstream projects
+configdata.set_quoted('PACKAGE_VERSION', meson.project_version())
+
+config_h = configure_file(
+  configuration : configdata,
+  output : 'config-store.h',
+)
+
+add_project_arguments(
+  # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
+  # It would be nice for our headers to be idempotent instead.
+
+  # From C++ libraries, only for internals
+  '-include', 'config-util.hh',
+  '-include', 'config-store.hh',
+
+  # From C libraries, for our public, installed headers too
+  '-include', 'config-util.h',
+  '-include', 'config-store.h',
+  language : 'cpp',
+)
+
+subdir('build-utils-meson/diagnostics')
+
+sources = files(
+  'nix_api_store.cc',
+)
+
+include_dirs = [include_directories('.')]
+
+headers = [config_h] + files(
+  'nix_api_store.h',
+)
+
+# TODO don't install this once tests don't use it and/or move the header into `libstore`, non-`c`
+headers += files('nix_api_store_internal.h')
+
+subdir('build-utils-meson/export-all-symbols')
+
+this_library = library(
+  'nixstorec',
+  sources,
+  dependencies : deps_public + deps_private + deps_other,
+  include_directories : include_dirs,
+  link_args: linker_export_flags,
+  prelink : true, # For C++ static initializers
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix', preserve_path : true)
+
+libraries_private = []
+
+subdir('build-utils-meson/export')

src/libstore-c/package.nix

@@ -0,0 +1,79 @@
+{ lib
+, stdenv
+, mkMesonDerivation
+, releaseTools
+
+, meson
+, ninja
+, pkg-config
+
+, nix-util-c
+, nix-store
+
+# Configuration Options
+
+, version
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonDerivation (finalAttrs: {
+  pname = "nix-store-c";
+  inherit version;
+
+  workDir = ./.;
+  fileset = fileset.unions [
+    ../../build-utils-meson
+    ./build-utils-meson
+    ../../.version
+    ./.version
+    ./meson.build
+    # ./meson.options
+    (fileset.fileFilter (file: file.hasExt "cc") ./.)
+    (fileset.fileFilter (file: file.hasExt "hh") ./.)
+    (fileset.fileFilter (file: file.hasExt "h") ./.)
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  nativeBuildInputs = [
+    meson
+    ninja
+    pkg-config
+  ];
+
+  propagatedBuildInputs = [
+    nix-util-c
+    nix-store
+  ];
+
+  preConfigure =
+    # "Inline" .version so it's not a symlink, and includes the suffix.
+    # Do the meson utils, without modification.
+    ''
+      chmod u+w ./.version
+      echo ${version} > ../../.version
+    '';
+
+  mesonFlags = [
+  ];
+
+  env = lib.optionalAttrs (stdenv.isLinux && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")) {
+    LDFLAGS = "-fuse-ld=gold";
+  };
+
+  enableParallelBuilding = true;
+
+  separateDebugInfo = !stdenv.hostPlatform.isStatic;
+
+  strictDeps = true;
+
+  hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+})

src/libstore/.version

@@ -0,0 +1 @@
+../../.version

src/libstore/binary-cache-store.cc

@@ -322,7 +322,7 @@ StorePath BinaryCacheStore::addToStoreFromDump(
         if (static_cast<FileIngestionMethod>(dumpMethod) == hashMethod.getFileIngestionMethod())
             caHash = hashString(HashAlgorithm::SHA256, dump2.s);
         switch (dumpMethod) {
-        case FileSerialisationMethod::Recursive:
+        case FileSerialisationMethod::NixArchive:
             // The dump is already NAR in this case, just use it.
             nar = dump2.s;
             break;
@@ -339,7 +339,7 @@ StorePath BinaryCacheStore::addToStoreFromDump(
     } else {
         // Otherwise, we have to do th same hashing as NAR so our single
         // hash will suffice for both purposes.
-        if (dumpMethod != FileSerialisationMethod::Recursive || hashAlgo != HashAlgorithm::SHA256)
+        if (dumpMethod != FileSerialisationMethod::NixArchive || hashAlgo != HashAlgorithm::SHA256)
             unsupported("addToStoreFromDump");
     }
     StringSource narDump { nar };

src/libstore/build-utils-meson

@@ -0,0 +1 @@
+../../build-utils-meson

src/libstore/build/derivation-goal.cc

@@ -3,6 +3,7 @@
 #  include "hook-instance.hh"
 #endif
 #include "processes.hh"
+#include "config-global.hh"
 #include "worker.hh"
 #include "builtins.hh"
 #include "builtins/buildenv.hh"
@@ -25,6 +26,10 @@
 #include <fcntl.h>
 #include <unistd.h>
 
+#ifndef _WIN32 // TODO abstract over proc exit status
+#  include <sys/wait.h>
+#endif
+
 #include <nlohmann/json.hpp>
 
 namespace nix {
@@ -1033,7 +1038,7 @@ void DerivationGoal::buildDone()
 
         BuildResult::Status st = BuildResult::MiscFailure;
 
-#ifndef _WIN32
+#ifndef _WIN32 // TODO abstract over proc exit status
         if (hook && WIFEXITED(status) && WEXITSTATUS(status) == 101)
             st = BuildResult::TimedOut;
 

src/libstore/build/worker.cc

@@ -19,7 +19,6 @@ Worker::Worker(Store & store, Store & evalStore)
     , store(store)
     , evalStore(evalStore)
 {
-    /* Debugging: prevent recursive workers. */
     nrLocalBuilds = 0;
     nrSubstitutions = 0;
     lastWokenUp = steady_time_point::min();
@@ -530,7 +529,7 @@ bool Worker::pathContentsGood(const StorePath & path)
     else {
         auto current = hashPath(
             {store.getFSAccessor(), CanonPath(store.printStorePath(path))},
-            FileIngestionMethod::Recursive, info->narHash.algo).first;
+            FileIngestionMethod::NixArchive, info->narHash.algo).first;
         Hash nullHash(HashAlgorithm::SHA256);
         res = info->narHash == nullHash || info->narHash == current;
     }