Meson build for libexpr and libflake

src/libflake/.version

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+../../.version

src/libflake/meson.build

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+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')
+
+# See note in ../nix-util/meson.build
+deps_private = [ ]
+
+# See note in ../nix-util/meson.build
+deps_public = [ ]
+
+# See note in ../nix-util/meson.build
+deps_public_subproject = [ ]
+
+# See note in ../nix-util/meson.build
+deps_other = [ ]
+
+foreach nix_dep : [
+  dependency('nix-util'),
+  dependency('nix-store'),
+  dependency('nix-fetchers'),
+  dependency('nix-expr'),
+]
+  if nix_dep.type_name() == 'internal'
+    deps_public_subproject += nix_dep
+    # subproject sadly no good for pkg-config module
+    deps_other += nix_dep
+  else
+    deps_public += nix_dep
+  endif
+endforeach
+
+nlohmann_json = dependency('nlohmann_json', version : '>= 3.9')
+deps_public += nlohmann_json
+
+libgit2 = dependency('libgit2')
+deps_public += 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.h',
+  '-include', 'config-store.h',
+  # '-include', 'config-fetchers.h',
+  '-include', 'config-expr.h',
+  '-Wno-deprecated-declarations',
+  '-Wimplicit-fallthrough',
+  '-Werror=switch',
+  '-Werror=switch-enum',
+  '-Wdeprecated-copy',
+  '-Wignored-qualifiers',
+  # Enable assertions in libstdc++ by default. Harmless on libc++. Benchmarked
+  # at ~1% overhead in `nix search`.
+  #
+  # FIXME: remove when we get meson 1.4.0 which will default this to on for us:
+  # https://mesonbuild.com/Release-notes-for-1-4-0.html#ndebug-setting-now-controls-c-stdlib-assertions
+  '-D_GLIBCXX_ASSERTIONS=1',
+  language : 'cpp',
+)
+
+sources = files(
+  'flake-settings.cc',
+  'flake/config.cc',
+  'flake/flake.cc',
+  'flake/flakeref.cc',
+  'flake/url-name.cc',
+  'flake/lockfile.cc',
+)
+
+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,
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix', preserve_path : true)
+
+requires = []
+foreach dep : deps_public_subproject
+  requires += dep.name()
+endforeach
+requires += deps_public
+
+import('pkgconfig').generate(
+  this_library,
+  filebase : meson.project_name(),
+  name : 'Nix',
+  description : 'Nix Package Manager',
+  subdirs : ['nix'],
+  extra_cflags : ['-std=c++2a'],
+  requires : requires,
+  requires_private : deps_private,
+)
+
+meson.override_dependency(meson.project_name(), declare_dependency(
+  include_directories : include_directories('.'),
+  link_with : this_library,
+  compile_args : ['-std=c++2a'],
+  dependencies : deps_public_subproject + deps_public,
+))

src/libflake/package.nix

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+{ lib
+, stdenv
+, releaseTools
+
+, meson
+, ninja
+, pkg-config
+
+, nix-util
+, nix-store
+, nix-fetchers
+, nix-expr
+, nlohmann_json
+, libgit2
+, man
+
+# Configuration Options
+
+, versionSuffix ? ""
+
+# Check test coverage of Nix. Probably want to use with with at least
+# one of `doCheck` or `doInstallCheck` enabled.
+, withCoverageChecks ? false
+
+}:
+
+let
+  inherit (lib) fileset;
+
+  version = lib.fileContents ./.version + versionSuffix;
+
+  mkDerivation =
+    if withCoverageChecks
+    then
+      # TODO support `finalAttrs` args function in
+      # `releaseTools.coverageAnalysis`.
+      argsFun:
+         releaseTools.coverageAnalysis (let args = argsFun args; in args)
+    else stdenv.mkDerivation;
+in
+
+mkDerivation (finalAttrs: {
+  pname = "nix-flake";
+  inherit version;
+
+  src = fileset.toSource {
+    root = ./.;
+    fileset = fileset.unions [
+      ./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 its not a symlink, and includes the suffix
+    ''
+      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 = !withCoverageChecks;
+
+  hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+} // lib.optionalAttrs withCoverageChecks {
+  lcovFilter = [ "*-tab.*" ];
+
+  hardeningDisable = ["fortify"];
+})