core/pkgs/build-support/fetchhg/default.nix

{
  lib,
  stdenvNoCC,
  mercurial,
}:
{
  name ? null,
  url,
  rev ? null,
  sha256 ? null,
  hash ? null,
  fetchSubrepos ? false,
  preferLocalBuild ? true,
}:

if hash != null && sha256 != null then
  throw "Only one of sha256 or hash can be set"
else
  # TODO: statically check if mercurial as the https support if the url starts woth https.
  stdenvNoCC.mkDerivation {
    name = "hg-archive" + (lib.optionalString (name != null) "-${name}");
    builder = ./builder.sh;
    nativeBuildInputs = [ mercurial ];

    impureEnvVars = lib.fetchers.proxyImpureEnvVars;

    subrepoClause = lib.optionalString fetchSubrepos "S";

    outputHashAlgo = if hash != null then null else "sha256";
    outputHashMode = "recursive";
    outputHash =
      if hash != null then
        hash
      else if sha256 != null then
        sha256
      else
        lib.fakeSha256;

    inherit url rev;
    inherit preferLocalBuild;
  }