nixpkgs/pkgs/build-support/buildenv/default.nix

# buildEnv creates a tree of symlinks to the specified paths.  This is
# a fork of the hardcoded buildEnv in the Nix distribution.

{ buildPackages, runCommand, lib, substituteAll, writeClosure }:

let
  builder = substituteAll {
    src = ./builder.pl;
    inherit (builtins) storeDir;
  };
in

lib.makeOverridable
({ name

, # The manifest file (if any).  A symlink $out/manifest will be
  # created to it.
  manifest ? ""

, # The paths to symlink.
  paths

, # Whether to ignore collisions or abort.
  ignoreCollisions ? false

, # Whether to include closures of all input paths.
  includeClosures ? false

, # If there is a collision, check whether the contents and permissions match
  # and only if not, throw a collision error.
  checkCollisionContents ? true

, # The paths (relative to each element of `paths') that we want to
  # symlink (e.g., ["/bin"]).  Any file not inside any of the
  # directories in the list is not symlinked.
  pathsToLink ? ["/"]

, # The package outputs to include. By default, only the default
  # output is included.
  extraOutputsToInstall ? []

, # Root the result in directory "$out${extraPrefix}", e.g. "/share".
  extraPrefix ? ""

, # Shell commands to run after building the symlink tree.
  postBuild ? ""

# Additional inputs
, nativeBuildInputs ? [] # Handy e.g. if using makeWrapper in `postBuild`.
, buildInputs ? []

, passthru ? {}
, meta ? {}
}:
let
  chosenOutputs = map (drv: {
    paths =
      # First add the usual output(s): respect if user has chosen explicitly,
      # and otherwise use `meta.outputsToInstall`. The attribute is guaranteed
      # to exist in mkDerivation-created cases. The other cases (e.g. runCommand)
      # aren't expected to have multiple outputs.
      (if (! drv ? outputSpecified || ! drv.outputSpecified)
          && drv.meta.outputsToInstall or null != null
        then map (outName: drv.${outName}) drv.meta.outputsToInstall
        else [ drv ])
      # Add any extra outputs specified by the caller of `buildEnv`.
      ++ lib.filter (p: p!=null)
        (builtins.map (outName: drv.${outName} or null) extraOutputsToInstall);
    priority = drv.meta.priority or lib.meta.defaultPriority;
  }) paths;

  pathsForClosure = lib.pipe chosenOutputs [
    (map (p: p.paths))
    lib.flatten
    (lib.remove null)
  ];
in runCommand name
  rec {
    inherit manifest ignoreCollisions checkCollisionContents passthru
            meta pathsToLink extraPrefix postBuild
            nativeBuildInputs buildInputs;
    pkgs = builtins.toJSON chosenOutputs;
    extraPathsFrom = lib.optional includeClosures (writeClosure pathsForClosure);
    preferLocalBuild = true;
    allowSubstitutes = false;
    # XXX: The size is somewhat arbitrary
    passAsFile = if builtins.stringLength pkgs >= 128*1024 then [ "pkgs" ] else [ ];
  }
  ''
    ${buildPackages.perl}/bin/perl -w ${builder}
    eval "$postBuild"
  '')