nixpkgs / pkgs / build-support / trivial-builders / default.nix

{
  lib,
  config,
  stdenv,
  stdenvNoCC,
  jq,
  lndir,
  runtimeShell,
  shellcheck-minimal,
}:

let
  inherit (lib)
    optionalAttrs
    optionalString
    hasPrefix
    warn
    map
    isList
    ;
in

rec {

  # Docs in doc/build-helpers/trivial-build-helpers.chapter.md
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-runCommand
  runCommand =
    name: env:
    runCommandWith {
      stdenv = stdenvNoCC;
      runLocal = false;
      inherit name;
      derivationArgs = env;
    };
  # Docs in doc/build-helpers/trivial-build-helpers.chapter.md
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-runCommandLocal
  runCommandLocal =
    name: env:
    runCommandWith {
      stdenv = stdenvNoCC;
      runLocal = true;
      inherit name;
      derivationArgs = env;
    };
  # Docs in doc/build-helpers/trivial-build-helpers.chapter.md
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-runCommandCC
  runCommandCC =
    name: env:
    runCommandWith {
      stdenv = stdenv;
      runLocal = false;
      inherit name;
      derivationArgs = env;
    };
  # `runCommandCCLocal` left out on purpose.
  # We shouldn’t force the user to have a cc in scope.

  # Docs in doc/build-helpers/trivial-build-helpers.chapter.md
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-runCommandWith
  runCommandWith =
    let
      # prevent infinite recursion for the default stdenv value
      defaultStdenv = stdenv;
    in
    {
      # which stdenv to use, defaults to a stdenv with a C compiler, pkgs.stdenv
      stdenv ? defaultStdenv,
      # whether to build this derivation locally instead of substituting
      runLocal ? false,
      # extra arguments to pass to stdenv.mkDerivation
      derivationArgs ? { },
      # name of the resulting derivation
      name,
    # TODO(@Artturin): enable strictDeps always
    }:
    buildCommand:
    stdenv.mkDerivation (
      {
        enableParallelBuilding = true;
        inherit buildCommand name;
        passAsFile = [ "buildCommand" ] ++ (derivationArgs.passAsFile or [ ]);
      }
      // lib.optionalAttrs (!derivationArgs ? meta) {
        pos =
          let
            args = builtins.attrNames derivationArgs;
          in
          if builtins.length args > 0 then
            builtins.unsafeGetAttrPos (builtins.head args) derivationArgs
          else
            null;
      }
      // (lib.optionalAttrs runLocal {
        preferLocalBuild = true;
        allowSubstitutes = false;
      })
      // builtins.removeAttrs derivationArgs [ "passAsFile" ]
    );

  # Docs in doc/build-helpers/trivial-build-helpers.chapter.md
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-writeTextFile
  writeTextFile =
    {
      name,
      text,
      executable ? false,
      destination ? "",
      checkPhase ? "",
      meta ? { },
      passthru ? { },
      allowSubstitutes ? false,
      preferLocalBuild ? true,
      derivationArgs ? { },
    }:
    assert lib.assertMsg (destination != "" -> (lib.hasPrefix "/" destination && destination != "/")) ''
      destination must be an absolute path, relative to the derivation's out path,
      got '${destination}' instead.

      Ensure that the path starts with a / and specifies at least the filename.
    '';

    let
      matches = builtins.match "/bin/([^/]+)" destination;
    in
    runCommand name
      (
        {
          inherit
            text
            executable
            checkPhase
            allowSubstitutes
            preferLocalBuild
            ;
          passAsFile = [ "text" ] ++ derivationArgs.passAsFile or [ ];
          meta =
            lib.optionalAttrs (executable && matches != null) {
              mainProgram = lib.head matches;
            }
            // meta
            // derivationArgs.meta or { };
          passthru = passthru // derivationArgs.passthru or { };
        }
        // removeAttrs derivationArgs [
          "passAsFile"
          "meta"
          "passthru"
        ]
      )
      ''
        target=$out${lib.escapeShellArg destination}
        mkdir -p "$(dirname "$target")"

        if [ -e "$textPath" ]; then
          mv "$textPath" "$target"
        else
          echo -n "$text" > "$target"
        fi

        if [ -n "$executable" ]; then
          chmod +x "$target"
        fi

        eval "$checkPhase"
      '';

  # See doc/build-helpers/trivial-build-helpers.chapter.md
  # or https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-text-writing
  writeText =
    name: text:
    # TODO: To fully deprecate, replace the assertion with `lib.isString` and remove the warning
    assert lib.assertMsg (lib.strings.isConvertibleWithToString text)
      ''pkgs.writeText ${lib.strings.escapeNixString name}: The second argument should be a string, but it's a ${builtins.typeOf text} instead.'';
    lib.warnIf (!lib.isString text)
      ''pkgs.writeText ${lib.strings.escapeNixString name}: The second argument should be a string, but it's a ${builtins.typeOf text} instead, which is deprecated. Use `toString` to convert the value to a string first.''
      writeTextFile
      { inherit name text; };

  # See doc/build-helpers/trivial-build-helpers.chapter.md
  # or https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-text-writing
  writeTextDir =
    path: text:
    writeTextFile {
      inherit text;
      name = builtins.baseNameOf path;
      destination = "/${path}";
    };

  # See doc/build-helpers/trivial-build-helpers.chapter.md
  # or https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-text-writing
  writeScript =
    name: text:
    writeTextFile {
      inherit name text;
      executable = true;
    };

  # See doc/build-helpers/trivial-build-helpers.chapter.md
  # or https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-text-writing
  writeScriptBin =
    name: text:
    writeTextFile {
      inherit name text;
      executable = true;
      destination = "/bin/${name}";
    };

  # See doc/build-helpers/trivial-build-helpers.chapter.md
  # or https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-text-writing
  writeShellScript =
    name: text:
    writeTextFile {
      inherit name;
      executable = true;
      text = ''
        #!${runtimeShell}
        ${text}
      '';
      checkPhase = ''
        ${stdenv.shellDryRun} "$target"
      '';
    };

  # See doc/build-helpers/trivial-build-helpers.chapter.md
  # or https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-text-writing
  writeShellScriptBin =
    name: text:
    writeTextFile {
      inherit name;
      executable = true;
      destination = "/bin/${name}";
      text = ''
        #!${runtimeShell}
        ${text}
      '';
      checkPhase = ''
        ${stdenv.shellDryRun} "$target"
      '';
      meta.mainProgram = name;
    };

  # TODO: move parameter documentation to the Nixpkgs manual
  # See doc/build-helpers/trivial-build-helpers.chapter.md
  # or https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-writeShellApplication
  writeShellApplication =
    {
      /*
         The name of the script to write.

         Type: String
      */
      name,
      /*
         The shell script's text, not including a shebang.

         Type: String
      */
      text,
      /*
         Inputs to add to the shell script's `$PATH` at runtime.

         Type: [String|Derivation]
      */
      runtimeInputs ? [ ],
      /*
         Extra environment variables to set at runtime.

         Type: AttrSet
      */
      runtimeEnv ? null,
      /*
         `stdenv.mkDerivation`'s `meta` argument.

         Type: AttrSet
      */
      meta ? { },
      /*
         `stdenv.mkDerivation`'s `passthru` argument.

         Type: AttrSet
      */
      passthru ? { },
      /*
         The `checkPhase` to run. Defaults to `shellcheck` on supported
         platforms and `bash -n`.

         The script path will be given as `$target` in the `checkPhase`.

         Type: String
      */
      checkPhase ? null,
      /*
         Checks to exclude when running `shellcheck`, e.g. `[ "SC2016" ]`.

         See <https://www.shellcheck.net/wiki/> for a list of checks.

         Type: [String]
      */
      excludeShellChecks ? [ ],
      /*
         Extra command-line flags to pass to ShellCheck.

         Type: [String]
      */
      extraShellCheckFlags ? [ ],
      /*
         Bash options to activate with `set -o` at the start of the script.

         Defaults to `[ "errexit" "nounset" "pipefail" ]`.

         Type: [String]
      */
      bashOptions ? [
        "errexit"
        "nounset"
        "pipefail"
      ],
      /*
        Extra arguments to pass to `stdenv.mkDerivation`.

        :::{.caution}
        Certain derivation attributes are used internally,
        overriding those could cause problems.
        :::

        Type: AttrSet
      */
      derivationArgs ? { },
      /*
         Whether to inherit the current `$PATH` in the script.

         Type: Bool
      */
      inheritPath ? true,
    }:
    writeTextFile {
      inherit
        name
        meta
        passthru
        derivationArgs
        ;
      executable = true;
      destination = "/bin/${name}";
      allowSubstitutes = true;
      preferLocalBuild = false;
      text = ''
        #!${runtimeShell}
        ${lib.concatMapStringsSep "\n" (option: "set -o ${option}") bashOptions}
      ''
      + lib.optionalString (runtimeEnv != null) (
        lib.concatStrings (
          lib.mapAttrsToList (name: value: ''
            ${lib.toShellVar name value}
            export ${name}
          '') runtimeEnv
        )
      )
      + lib.optionalString (runtimeInputs != [ ]) ''

        export PATH="${lib.makeBinPath runtimeInputs}${lib.optionalString inheritPath ":$PATH"}"
      ''
      + ''

        ${text}
      '';

      checkPhase =
        let
          excludeFlags = lib.optionals (excludeShellChecks != [ ]) [
            "--exclude"
            (lib.concatStringsSep "," excludeShellChecks)
          ];
          # GHC (=> shellcheck) isn't supported on some platforms (such as risc-v)
          # but we still want to use writeShellApplication on those platforms
          shellcheckCommand = lib.optionalString shellcheck-minimal.compiler.bootstrapAvailable ''
            # use shellcheck which does not include docs
            # pandoc takes long to build and documentation isn't needed for just running the cli
            ${lib.getExe shellcheck-minimal} ${
              lib.escapeShellArgs (excludeFlags ++ extraShellCheckFlags)
            } "$target"
          '';
        in
        if checkPhase == null then
          ''
            runHook preCheck
            ${stdenv.shellDryRun} "$target"
            ${shellcheckCommand}
            runHook postCheck
          ''
        else
          checkPhase;
    };

  # Create a C binary
  # TODO: add to writers? pkgs/build-support/writers
  writeCBin =
    pname: code:
    runCommandCC pname
      {
        inherit pname code;
        executable = true;
        passAsFile = [ "code" ];
        # Pointless to do this on a remote machine.
        preferLocalBuild = true;
        allowSubstitutes = false;
        meta = {
          mainProgram = pname;
        };
      }
      ''
        n=$out/bin/${pname}
        mkdir -p "$(dirname "$n")"
        mv "$codePath" code.c
        $CC -x c code.c -o "$n"
      '';

  # TODO: deduplicate with documentation in doc/build-helpers/trivial-build-helpers.chapter.md
  #       see also https://github.com/NixOS/nixpkgs/pull/249721
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-concatText
  /*
    concat a list of files to the nix store.
    The contents of files are added to the file in the store.

    Example:

    # Writes my-file to /nix/store/<store path>
    concatTextFile {
      name = "my-file";
      files = [ drv1 "${drv2}/path/to/file" ];
    }

    See also the `concatText` helper function below.

    # Writes executable my-file to /nix/store/<store path>/bin/my-file
    concatTextFile {
      name = "my-file";
      files = [ drv1 "${drv2}/path/to/file" ];
      executable = true;
      destination = "/bin/my-file";
    }
  */
  concatTextFile =
    {
      name, # the name of the derivation
      files,
      executable ? false, # run chmod +x ?
      destination ? "", # relative path appended to $out eg "/bin/foo"
      checkPhase ? "", # syntax checks, e.g. for scripts
      meta ? { },
      passthru ? { },
    }:
    runCommandLocal name
      {
        inherit
          files
          executable
          checkPhase
          meta
          passthru
          destination
          ;
      }
      ''
        file=$out$destination
        mkdir -p "$(dirname "$file")"
        cat $files > "$file"

        if [ -n "$executable" ]; then
          chmod +x "$file"
        fi

        eval "$checkPhase"
      '';

  # TODO: deduplicate with documentation in doc/build-helpers/trivial-build-helpers.chapter.md
  #       see also https://github.com/NixOS/nixpkgs/pull/249721
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-concatText
  /*
    Writes a text file to nix store with no optional parameters available.

    Example:

    # Writes contents of files to /nix/store/<store path>
    concatText "my-file" [ file1 file2 ]
  */
  concatText = name: files: concatTextFile { inherit name files; };

  # TODO: deduplicate with documentation in doc/build-helpers/trivial-build-helpers.chapter.md
  #       see also https://github.com/NixOS/nixpkgs/pull/249721
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-concatText
  /*
    Writes a text file to nix store with and mark it as executable.

    Example:
    # Writes contents of files to /nix/store/<store path>
    concatScript "my-file" [ file1 file2 ]
  */
  concatScript =
    name: files:
    concatTextFile {
      inherit name files;
      executable = true;
    };

  /*
    TODO: Deduplicate this documentation.
    More docs in doc/build-helpers/trivial-build-helpers.chapter.md
    See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-symlinkJoin

    Create a forest of symlinks to the files in `paths`.

    This creates a single derivation that replicates the directory structure
    of all the input paths.

    BEWARE: it may not "work right" when the passed paths contain symlinks to directories.

    Example:

    # adds symlinks of hello to current build.
    symlinkJoin { name = "myhello"; paths = [ pkgs.hello ]; }

    # adds symlinks of hello and stack to current build and prints "links added"
    symlinkJoin { name = "myexample"; paths = [ pkgs.hello pkgs.stack ]; postBuild = "echo links added"; }

    This creates a derivation with a directory structure like the following:

    /nix/store/sglsr5g079a5235hy29da3mq3hv8sjmm-myexample
    |-- bin
    |   |-- hello -> /nix/store/qy93dp4a3rqyn2mz63fbxjg228hffwyw-hello-2.10/bin/hello
    |   `-- stack -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/bin/stack
    `-- share
        |-- bash-completion
        |   `-- completions
        |       `-- stack -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/share/bash-completion/completions/stack
        |-- fish
        |   `-- vendor_completions.d
        |       `-- stack.fish -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/share/fish/vendor_completions.d/stack.fish
    ...

    To create a directory structure from a specific subdirectory of input `paths` instead of their full trees,
    you can either append the subdirectory path to each input path, or use the `stripPrefix` argument to
    remove the common prefix during linking.

    Example:

    # create symlinks of tmpfiles.d rules from multiple packages
    symlinkJoin { name = "tmpfiles.d"; paths = [ pkgs.lvm2 pkgs.nix ]; stripPrefix = "/lib/tmpfiles.d"; }

    This creates a derivation with a directory structure like the following:

    /nix/store/m5s775yicb763hfa133jwml5hwmwzv14-tmpfiles.d
    |-- lvm2.conf -> /nix/store/k6js0l5f0zpvrhay49579fj939j77p2w-lvm2-2.03.29/lib/tmpfiles.d/lvm2.conf
    `-- nix-daemon.conf -> /nix/store/z4v2s3s3y79fmabhps5hakb3c5dwaj5a-nix-1.33.7/lib/tmpfiles.d/nix-daemon.conf

    By default, packages that don't contain the specified subdirectory are silently skipped.
    Set `failOnMissing = true` to make the build fail if any input package is missing the subdirectory
    (this is the default behavior when not using stripPrefix).

    symlinkJoin and linkFarm are similar functions, but they output
    derivations with different structure.

    symlinkJoin is used to create a derivation with a familiar directory
    structure (top-level bin/, share/, etc), but with all actual files being symlinks to
    the files in the input derivations.

    symlinkJoin is used many places in nixpkgs to create a single derivation
    that appears to contain binaries, libraries, documentation, etc from
    multiple input derivations.

    linkFarm is instead used to create a simple derivation with symlinks to
    other derivations.  A derivation created with linkFarm is often used in CI
    as a easy way to build multiple derivations at once.
  */
  symlinkJoin =
    args_@{
      name ?
        assert lib.assertMsg (
          args_ ? pname && args_ ? version
        ) "symlinkJoin requires either a `name` OR `pname` and `version`";
        "${args_.pname}-${args_.version}",
      paths,
      stripPrefix ? "",
      preferLocalBuild ? true,
      allowSubstitutes ? false,
      postBuild ? "",
      failOnMissing ? stripPrefix == "",
      ...
    }:
    assert lib.assertMsg (stripPrefix != "" -> (hasPrefix "/" stripPrefix && stripPrefix != "/")) ''
      stripPrefix must be either an empty string (disable stripping behavior), or relative path prefixed with /.

      Ensure that the path starts with / and specifies path to the subdirectory.
    '';

    let
      mapPaths =
        f: paths:
        map (
          path:
          if path == null then
            null
          else if isList path then
            mapPaths f path
          else
            f path
        ) paths;
      args =
        removeAttrs args_ [
          "name"
          "postBuild"
          "stripPrefix"
          "paths"
          "failOnMissing"
        ]
        // {
          inherit preferLocalBuild allowSubstitutes;
          paths = mapPaths (path: "${path}${stripPrefix}") paths;
          passAsFile = [ "paths" ];
        }; # pass the defaults
    in
    runCommand name args ''
      mkdir -p $out
      for i in $(cat $pathsPath); do
        ${optionalString (!failOnMissing) "if test -d $i; then "}${lndir}/bin/lndir -silent $i $out${
          optionalString (!failOnMissing) "; fi"
        }
      done
      ${postBuild}
    '';

  # TODO: move linkFarm docs to the Nixpkgs manual
  /*
    Quickly create a set of symlinks to derivations.

    This creates a simple derivation with symlinks to all inputs.

    entries can be a list of attribute sets like

    [ { name = "name" ; path = "/nix/store/..."; } ]

    or an attribute set name -> path like:

    { name = "/nix/store/..."; other = "/nix/store/..."; }

    Example:

    # Symlinks hello and stack paths in store to current $out/hello-test and
    # $out/foobar.
    linkFarm "myexample" [ { name = "hello-test"; path = pkgs.hello; } { name = "foobar"; path = pkgs.stack; } ]

    This creates a derivation with a directory structure like the following:

    /nix/store/qc5728m4sa344mbks99r3q05mymwm4rw-myexample
    |-- foobar -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1
    `-- hello-test -> /nix/store/qy93dp4a3rqyn2mz63fbxjg228hffwyw-hello-2.10

    See the note on symlinkJoin for the difference between linkFarm and symlinkJoin.
  */
  linkFarm =
    name: entries:
    let
      entries' =
        if (lib.isAttrs entries) then
          entries
        # We do this foldl to have last-wins semantics in case of repeated entries
        else if (lib.isList entries) then
          lib.foldl (a: b: a // { "${b.name}" = b.path; }) { } entries
        else
          throw "linkFarm entries must be either attrs or a list!";

      linkCommands = lib.mapAttrsToList (name: path: ''
        mkdir -p -- "$(dirname -- ${lib.escapeShellArg "${name}"})"
        ln -s -- ${lib.escapeShellArg "${path}"} ${lib.escapeShellArg "${name}"}
      '') entries';
    in
    runCommand name
      {
        preferLocalBuild = true;
        allowSubstitutes = false;
        passthru.entries = entries';
      }
      ''
        mkdir -p $out
        cd $out
        ${lib.concatStrings linkCommands}
      '';

  # TODO: move linkFarmFromDrvs docs to the Nixpkgs manual
  /*
    Easily create a linkFarm from a set of derivations.

    This calls linkFarm with a list of entries created from the list of input
    derivations.  It turns each input derivation into an attribute set
    like { name = drv.name ; path = drv }, and passes this to linkFarm.

    Example:

    # Symlinks the hello, gcc, and ghc derivations in $out
    linkFarmFromDrvs "myexample" [ pkgs.hello pkgs.gcc pkgs.ghc ]

    This creates a derivation with a directory structure like the following:

    /nix/store/m3s6wkjy9c3wy830201bqsb91nk2yj8c-myexample
    |-- gcc-wrapper-9.2.0 -> /nix/store/fqhjxf9ii4w4gqcsx59fyw2vvj91486a-gcc-wrapper-9.2.0
    |-- ghc-8.6.5 -> /nix/store/gnf3s07bglhbbk4y6m76sbh42siym0s6-ghc-8.6.5
    `-- hello-2.10 -> /nix/store/k0ll91c4npk4lg8lqhx00glg2m735g74-hello-2.10
  */
  linkFarmFromDrvs =
    name: drvs:
    let
      mkEntryFromDrv = drv: {
        name = drv.name;
        path = drv;
      };
    in
    linkFarm name (map mkEntryFromDrv drvs);

  # TODO: move onlyBin docs to the Nixpkgs manual
  /*
    Produce a derivation that links to the target derivation's `/bin`,
    and *only* `/bin`.

    This is useful when your favourite package doesn't have a separate
    bin output and other contents of the package's output (e.g. setup
    hooks) cause trouble when used in your environment.
  */
  onlyBin =
    drv:
    runCommand "${drv.name}-only-bin" { } ''
      mkdir -p $out
      ln -s ${lib.getBin drv}/bin $out/bin
    '';

  # Docs in doc/build-helpers/special/makesetuphook.section.md
  # See https://nixos.org/manual/nixpkgs/unstable/#sec-pkgs.makeSetupHook
  makeSetupHook =
    {
      name ? lib.warn "calling makeSetupHook without passing a name is deprecated." "hook",
      # hooks go in nativeBuildInputs so these will be nativeBuildInputs
      propagatedBuildInputs ? [ ],
      propagatedNativeBuildInputs ? [ ],
      # these will be buildInputs
      depsTargetTargetPropagated ? [ ],
      meta ? { },
      passthru ? { },
      substitutions ? { },
    }:
    script:
    runCommand name
      (
        substitutions
        // {
          # TODO(@Artturin:) substitutions should be inside the env attrset
          # but users are likely passing non-substitution arguments through substitutions
          # turn off __structuredAttrs to unbreak substituteAll
          __structuredAttrs = false;
          inherit meta;
          inherit depsTargetTargetPropagated;
          inherit propagatedBuildInputs;
          inherit propagatedNativeBuildInputs;
          strictDeps = true;
          # TODO 2023-01, no backport: simplify to inherit passthru;
          passthru =
            passthru
            // optionalAttrs (substitutions ? passthru) (
              warn "makeSetupHook (name = ${lib.strings.escapeNixString name}): `substitutions.passthru` is deprecated. Please set `passthru` directly." substitutions.passthru
            );
        }
      )
      (
        ''
          mkdir -p $out/nix-support
          cp ${script} $out/nix-support/setup-hook
          recordPropagatedDependencies
        ''
        + lib.optionalString (substitutions != { }) ''
          substituteAll ${script} $out/nix-support/setup-hook
        ''
      );

  # Docs in doc/build-helpers/trivial-build-helpers.chapter.md
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-writeClosure
  writeClosure =
    paths:
    runCommand "runtime-deps"
      {
        # Get the cleaner exportReferencesGraph interface
        __structuredAttrs = true;
        exportReferencesGraph.graph = paths;
        nativeBuildInputs = [ jq ];
      }
      ''
        jq -r ".graph | map(.path) | sort | .[]" "$NIX_ATTRS_JSON_FILE" > "$out"
      '';

  # Docs in doc/build-helpers/trivial-build-helpers.chapter.md
  # See https://nixos.org/manual/nixpkgs/unstable/#trivial-builder-writeDirectReferencesToFile
  writeDirectReferencesToFile =
    path:
    runCommand "runtime-references"
      {
        exportReferencesGraph = [
          "graph"
          path
        ];
        inherit path;
      }
      ''
        touch ./references
        while read p; do
          read dummy
          read nrRefs
          if [[ $p == $path ]]; then
            for ((i = 0; i < nrRefs; i++)); do
              read ref;
              echo $ref >>./references
            done
          else
            for ((i = 0; i < nrRefs; i++)); do
              read ref;
            done
          fi
        done < graph
        sort ./references >$out
      '';

  # TODO: move writeStringReferencesToFile docs to the Nixpkgs manual
  /*
    Extract a string's references to derivations and paths (its
    context) and write them to a text file, removing the input string
    itself from the dependency graph. This is useful when you want to
    make a derivation depend on the string's references, but not its
    contents (to avoid unnecessary rebuilds, for example).

    Note that this only works as intended on Nix >= 2.3.
  */
  writeStringReferencesToFile =
    string:
    /*
       The basic operation this performs is to copy the string context
       from `string` to a second string and wrap that string in a
       derivation. However, that alone is not enough, since nothing in the
       string refers to the output paths of the derivations/paths in its
       context, meaning they'll be considered build-time dependencies and
       removed from the wrapper derivation's closure. Putting the
       necessary output paths in the new string is however not very
       straightforward - the attrset returned by `getContext` contains
       only references to derivations' .drv-paths, not their output
       paths. In order to "convert" them, we try to extract the
       corresponding paths from the original string using regex.
    */
    let
      # Taken from https://github.com/NixOS/nix/blob/130284b8508dad3c70e8160b15f3d62042fc730a/src/libutil/hash.cc#L84
      nixHashChars = "0123456789abcdfghijklmnpqrsvwxyz";
      context = builtins.getContext string;
      derivations = lib.filterAttrs (n: v: v ? outputs) context;
      # Objects copied from outside of the store, such as paths and
      # `builtins.fetch*`ed ones
      sources = lib.attrNames (lib.filterAttrs (n: v: v ? path) context);
      packages = lib.mapAttrs' (name: value: {
        inherit value;
        name = lib.head (builtins.match "${builtins.storeDir}/[${nixHashChars}]+-(.*)\\.drv" name);
      }) derivations;
      # The syntax of output paths differs between outputs named `out`
      # and other, explicitly named ones. For explicitly named ones,
      # the output name is suffixed as `-name`, but `out` outputs
      # aren't suffixed at all, and thus aren't easily distinguished
      # from named output paths. Therefore, we find all the named ones
      # first so we can use them to remove false matches when looking
      # for `out` outputs (see the definition of `outputPaths`).
      namedOutputPaths = lib.flatten (
        lib.mapAttrsToList (
          name: value:
          (map (
            output:
            lib.filter lib.isList (
              builtins.split "(${builtins.storeDir}/[${nixHashChars}]+-${name}-${output})" string
            )
          ) (lib.remove "out" value.outputs))
        ) packages
      );
      # Only `out` outputs
      outputPaths = lib.flatten (
        lib.mapAttrsToList (
          name: value:
          if lib.elem "out" value.outputs then
            lib.filter (
              x:
              lib.isList x
              &&
                # If the matched path is in `namedOutputPaths`,
                # it's a partial match of an output path where
                # the output name isn't `out`
                lib.all (o: !lib.hasPrefix (lib.head x) o) namedOutputPaths
            ) (builtins.split "(${builtins.storeDir}/[${nixHashChars}]+-${name})" string)
          else
            [ ]
        ) packages
      );
      allPaths = lib.concatStringsSep "\n" (lib.unique (sources ++ namedOutputPaths ++ outputPaths));
      allPathsWithContext = builtins.appendContext allPaths context;
    in
    if builtins ? getContext then
      writeText "string-references" allPathsWithContext
    else
      writeDirectReferencesToFile (writeText "string-file" string);

  # Docs in doc/build-helpers/fetchers.chapter.md
  # See https://nixos.org/manual/nixpkgs/unstable/#requirefile
  requireFile =
    {
      name ? null,
      sha256 ? null,
      sha1 ? null,
      hash ? null,
      url ? null,
      message ? null,
      hashMode ? "flat",
    }:
    assert (message != null) || (url != null);
    assert (sha256 != null) || (sha1 != null) || (hash != null);
    assert (name != null) || (url != null);
    let
      msg =
        if message != null then
          message
        else
          ''
            Unfortunately, we cannot download file ${name_} automatically.
            Please go to ${url} to download it yourself, and add it to the Nix store
            using either
              nix-store --add-fixed ${hashAlgo} ${name_}
            or
              nix-prefetch-url --type ${hashAlgo} file:///path/to/${name_}
          '';
      hashAlgo =
        if hash != null then
          (builtins.head (lib.strings.splitString "-" hash))
        else if sha256 != null then
          "sha256"
        else
          "sha1";
      hashAlgo_ = if hash != null then "" else hashAlgo;
      hash_ =
        if hash != null then
          hash
        else if sha256 != null then
          sha256
        else
          sha1;
      name_ = if name == null then baseNameOf (toString url) else name;
    in
    stdenvNoCC.mkDerivation {
      name = name_;
      outputHashMode = hashMode;
      outputHashAlgo = hashAlgo_;
      outputHash = hash_;
      preferLocalBuild = true;
      allowSubstitutes = false;
      builder = writeScript "restrict-message" ''
        source ${stdenvNoCC}/setup
        cat <<_EOF_

        ***
        ${msg}
        ***

        _EOF_
        exit 1
      '';
    };

  # TODO: move copyPathToStore docs to the Nixpkgs manual
  /*
    Copy a path to the Nix store.
    Nix automatically copies files to the store before stringifying paths.
    If you need the store path of a file, ${copyPathToStore <path>} can be
    shortened to ${<path>}.
  */
  copyPathToStore = builtins.filterSource (p: t: true);

  # TODO: move copyPathsToStore docs to the Nixpkgs manual
  # Copy a list of paths to the Nix store.
  copyPathsToStore = builtins.map copyPathToStore;

  # TODO: move applyPatches docs to the Nixpkgs manual
  /*
    Applies a list of patches to a source directory.

    Example:

    # Patching nixpkgs:

    applyPatches {
      src = pkgs.path;
      patches = [
        (pkgs.fetchpatch {
          url = "https://github.com/NixOS/nixpkgs/commit/1f770d20550a413e508e081ddc08464e9d08ba3d.patch";
          sha256 = "1nlzx171y3r3jbk0qhvnl711kmdk57jlq4na8f8bs8wz2pbffymr";
        })
      ];
    }
  */
  applyPatches =
    {
      src,
      name ?
        (
          if builtins.typeOf src == "path" then
            builtins.baseNameOf src
          else if builtins.isAttrs src && builtins.hasAttr "name" src then
            src.name
          else
            throw "applyPatches: please supply a `name` argument because a default name can only be computed when the `src` is a path or is an attribute set with a `name` attribute."
        )
        + "-patched",
      patches ? [ ],
      prePatch ? "",
      postPatch ? "",
      ...
    }@args:
    assert lib.assertMsg (
      !args ? meta
    ) "applyPatches will not merge 'meta', change it in 'src' instead";
    assert lib.assertMsg (
      !args ? passthru
    ) "applyPatches will not merge 'passthru', change it in 'src' instead";
    if patches == [ ] && prePatch == "" && postPatch == "" then
      src # nothing to do, so use original src to avoid additional drv
    else
      let
        keepAttrs = names: lib.filterAttrs (name: val: lib.elem name names);
        # enables tools like nix-update to determine what src attributes to replace
        extraPassthru = lib.optionalAttrs (lib.isAttrs src) (
          keepAttrs [
            "rev"
            "tag"
            "url"
            "outputHash"
            "outputHashAlgo"
          ] src
        );
      in
      stdenvNoCC.mkDerivation (
        {
          inherit
            name
            src
            patches
            prePatch
            postPatch
            ;
          preferLocalBuild = true;
          allowSubstitutes = false;
          phases = "unpackPhase patchPhase installPhase";
          installPhase = "cp -R ./ $out";
        }
        # Carry (and merge) information from the underlying `src` if present.
        // (optionalAttrs (src ? meta) {
          inherit (src) meta;
        })
        // (optionalAttrs (extraPassthru != { } || src ? passthru) {
          passthru = extraPassthru // src.passthru or { };
        })
        # Forward any additional arguments to the derivation
        // (removeAttrs args [
          "src"
          "name"
          "patches"
          "prePatch"
          "postPatch"
        ])
      );

  # TODO: move docs to Nixpkgs manual
  # An immutable file in the store with a length of 0 bytes.
  emptyFile = runCommand "empty-file" {
    outputHash = "sha256-d6xi4mKdjkX2JFicDIv5niSzpyI0m/Hnm8GGAIU04kY=";
    outputHashMode = "recursive";
    preferLocalBuild = true;
  } "touch $out";

  # TODO: move docs to Nixpkgs manual
  # An immutable empty directory in the store.
  emptyDirectory = runCommand "empty-directory" {
    outputHashAlgo = "sha256";
    outputHashMode = "recursive";
    outputHash = "0sjjj9z1dhilhpc8pq4154czrb79z9cm044jvn75kxcjv6v5l2m5";
    preferLocalBuild = true;
  } "mkdir $out";
}