{ stdenv }@orig:
# srcOnly is a utility builder that only fetches and unpacks the given `src`,
# maybe pathings it in the process with the optional `patches` and
# `buildInputs` attributes.
#
# It can be invoked directly, or be used to wrap an existing derivation. Eg:
#
# > srcOnly pkgs.hello
#
attrs:
let
  args = if builtins.hasAttr "drvAttrs" attrs then attrs.drvAttrs else attrs;
  name = if builtins.hasAttr "name" args then args.name else "${args.pname}-${args.version}";
in
stdenv.mkDerivation (args // {
  name = "${name}-source";
  installPhase = "cp -r . $out";
  phases = ["unpackPhase" "patchPhase" "installPhase"];
})