Allow gc-ing with a rootless daemon

meson.build

@@ -14,6 +14,7 @@ project(
 
 # Internal Libraries
 subproject('libutil')
+subproject('libroots')
 subproject('libstore')
 subproject('libfetchers')
 subproject('libexpr')

packaging/components.nix

@@ -411,6 +411,8 @@ in
   nix-flake-c = callPackage ../src/libflake-c/package.nix { };
   nix-flake-tests = callPackage ../src/libflake-tests/package.nix { };
 
+  nix-roots = callPackage ../src/libroots/package.nix { };
+
   nix-main = callPackage ../src/libmain/package.nix { };
   nix-main-c = callPackage ../src/libmain-c/package.nix { };
 

packaging/hydra.nix

@@ -59,6 +59,7 @@ let
         "nix-flake-tests"
         "nix-main"
         "nix-main-c"
+        "nix-roots"
         "nix-cmd"
         "nix-cli"
         "nix-functional-tests"

src/libroots/.version

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

src/libroots/include/nix/roots/meson.build

@@ -0,0 +1,5 @@
+# Public headers directory
+
+include_dirs = [ include_directories('../..') ]
+
+headers = files('roots.hh')

src/libroots/include/nix/roots/roots.hh

@@ -0,0 +1,31 @@
+#pragma once
+
+#include "nix/util/strings.hh"
+#include <boost/unordered/unordered_flat_map.hpp>
+#include <boost/unordered/unordered_flat_set.hpp>
+#include <filesystem>
+
+namespace nix::roots_tracer {
+
+struct TracerConfig
+{
+    const std::filesystem::path storeDir = "/nix/store";
+    const std::filesystem::path stateDir = "/nix/var/nix";
+    const std::filesystem::path socketPath = "/nix/var/nix/gc-socket/socket";
+};
+
+/**
+ * A value of type `Roots` is a mapping from a store path to the set of roots that keep it alive
+ */
+typedef boost::unordered_flat_map<
+    std::string,
+    boost::unordered_flat_set<std::string, StringViewHash, std::equal_to<>>,
+    StringViewHash,
+    std::equal_to<>>
+    UncheckedRoots;
+
+void findRuntimeRoots(const TracerConfig & opts, UncheckedRoots & unchecked, bool censor);
+
+void findRoots(const TracerConfig & opts, const Path & path, std::filesystem::file_type type, UncheckedRoots & roots);
+
+} // namespace nix::roots_tracer

src/libroots/meson.build

@@ -0,0 +1,73 @@
+project(
+  'nix-roots',
+  'cpp',
+  version : files('.version'),
+  default_options : [
+    'cpp_std=c++23',
+    # TODO(Qyriad): increase the warning level
+    'warning_level=1',
+    '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('nix-meson-build-support/deps-lists')
+
+deps_private_maybe_subproject = []
+deps_public_maybe_subproject = [ dependency('nix-util') ]
+subdir('nix-meson-build-support/subprojects')
+
+subdir('nix-meson-build-support/common')
+
+boost = dependency(
+  'boost',
+  modules : [
+    'container',
+  ],
+  include_type : 'system',
+)
+deps_other += boost
+
+configdata_priv = configuration_data()
+
+lsof = find_program('lsof', required : false)
+configdata_priv.set_quoted(
+  'LSOF',
+  lsof.found() ? lsof.full_path()
+  # Just look up on the PATH
+: 'lsof',
+)
+
+config_priv_h = configure_file(
+  configuration : configdata_priv,
+  output : 'roots-config-private.hh',
+)
+
+sources = files(
+  'roots.cc',
+)
+
+subdir('include/nix/roots')
+
+subdir('nix-meson-build-support/export-all-symbols')
+subdir('nix-meson-build-support/windows-version')
+
+this_library = library(
+  'nixroots',
+  sources,
+  config_priv_h,
+  soversion : nix_soversion,
+  dependencies : deps_public + deps_private + deps_other,
+  include_directories : include_dirs,
+  link_args : linker_export_flags,
+  install : true,
+)
+
+install_headers(headers, subdir : 'nix/roots', preserve_path : true)
+
+libraries_private = []
+
+subdir('nix-meson-build-support/export')

src/libroots/nix-meson-build-support

@@ -0,0 +1 @@
+../../nix-meson-build-support

src/libroots/package.nix

@@ -0,0 +1,40 @@
+{
+  lib,
+  mkMesonLibrary,
+
+  nix-util,
+
+  # Configuration Options
+
+  version,
+}:
+
+let
+  inherit (lib) fileset;
+in
+
+mkMesonLibrary (finalAttrs: {
+  pname = "nix-roots";
+  inherit version;
+
+  workDir = ./.;
+  fileset = fileset.unions [
+    ../../nix-meson-build-support
+    ./nix-meson-build-support
+    ../../.version
+    ./.version
+    ./meson.build
+    ./include/nix/roots/meson.build
+    (fileset.fileFilter (file: file.hasExt "cc") ./.)
+    (fileset.fileFilter (file: file.hasExt "hh") ./.)
+  ];
+
+  propagatedBuildInputs = [
+    nix-util
+  ];
+
+  meta = {
+    platforms = lib.platforms.unix ++ lib.platforms.windows;
+  };
+
+})