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

{
  stdenv,
  lib,
  fossil,
  cacert,
}:

{
  name ? null,
  url,
  rev,
  sha256 ? "",
  hash ? "",
}:

if hash != "" && sha256 != "" then
  throw "Only one of sha256 or hash can be set"
else
  stdenv.mkDerivation {
    name = "fossil-archive" + (lib.optionalString (name != null) "-${name}");
    builder = ./builder.sh;
    nativeBuildInputs = [
      fossil
      cacert
    ];

    # Envvar docs are hard to find. A link for the future:
    # https://www.fossil-scm.org/index.html/doc/trunk/www/env-opts.md
    impureEnvVars = [ "http_proxy" ];

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

    inherit url rev;
    preferLocalBuild = true;
  }