{
  lib,
  stdenv,
  fetchurl,
  fetchpatch,
  python3Packages,
  makeWrapper,
  gettext,
  installShellFiles,
  re2Support ? true,
  # depends on rust-cpython which won't support python312
  # https://github.com/dgrunwald/rust-cpython/commit/e815555629e557be084813045ca1ddebc2f76ef9
  rustSupport ? (stdenv.hostPlatform.isLinux && python3Packages.pythonOlder "3.12"),
  cargo,
  rustPlatform,
  rustc,
  fullBuild ? false,
  gitSupport ? fullBuild,
  guiSupport ? fullBuild,
  tk,
  highlightSupport ? fullBuild,
  ApplicationServices,
# for passthru.tests
# , runCommand
# , unzip
# , which
# , sqlite
# , git
# , cacert
# , gnupg
}:

let
  inherit (python3Packages)
    docutils
    python
    fb-re2
    pygit2
    pygments
    ;

  self = python3Packages.buildPythonApplication rec {
    pname = "mercurial${lib.optionalString fullBuild "-full"}";
    version = "6.6.3";

    src = fetchurl {
      url = "https://mercurial-scm.org/release/mercurial-${version}.tar.gz";
      hash = "sha256-911qSnWCOht9cTpJZ+yi9Zb0ZuWPxrwG1yZCky/X4wc=";
    };

    format = "other";

    passthru = {
      inherit python;
    }; # pass it so that the same version can be used in hg2git

    cargoDeps =
      if rustSupport then
        rustPlatform.fetchCargoTarball {
          inherit src;
          name = "mercurial-${version}";
          sha256 = "sha256-G5tzwoIGOgpVI35rYXDeelnBgTbAiq7BDcXCHQzqSrs=";
          sourceRoot = "mercurial-${version}/rust";
        }
      else
        null;
    cargoRoot = if rustSupport then "rust" else null;

    propagatedBuildInputs =
      lib.optional re2Support fb-re2
      ++ lib.optional gitSupport pygit2
      ++ lib.optional highlightSupport pygments;
    nativeBuildInputs =
      [
        makeWrapper
        gettext
        installShellFiles
        python3Packages.setuptools
      ]
      ++ lib.optionals rustSupport [
        rustPlatform.cargoSetupHook
        cargo
        rustc
      ];
    buildInputs = [ docutils ] ++ lib.optionals stdenv.isDarwin [ ApplicationServices ];

    makeFlags = [ "PREFIX=$(out)" ] ++ lib.optional rustSupport "PURE=--rust";

    postInstall =
      (lib.optionalString guiSupport ''
        mkdir -p $out/etc/mercurial
        cp contrib/hgk $out/bin
        cat >> $out/etc/mercurial/hgrc << EOF
        [extensions]
        hgk=$out/${python.sitePackages}/hgext/hgk.py
        EOF
        # setting HG so that hgk can be run itself as well (not only hg view)
        WRAP_TK=" --set TK_LIBRARY ${tk}/lib/${tk.libPrefix}
                  --set HG $out/bin/hg
                  --prefix PATH : ${tk}/bin "
      '')
      + ''
        for i in $(cd $out/bin && ls); do
          wrapProgram $out/bin/$i \
            $WRAP_TK
        done

        # copy hgweb.cgi to allow use in apache
        mkdir -p $out/share/cgi-bin
        cp -v hgweb.cgi contrib/hgweb.wsgi $out/share/cgi-bin
        chmod u+x $out/share/cgi-bin/hgweb.cgi

        installShellCompletion --cmd hg \
          --bash contrib/bash_completion \
          --zsh contrib/zsh_completion
      '';

    # passthru.tests = {
    #   mercurial-tests = makeTests { flags = "--with-hg=$MERCURIAL_BASE/bin/hg"; };
    # };

    meta = with lib; {
      description = "A fast, lightweight SCM system for very large distributed projects";
      homepage = "https://www.mercurial-scm.org";
      downloadPage = "https://www.mercurial-scm.org/release/";
      changelog = "https://wiki.mercurial-scm.org/Release${versions.majorMinor version}";
      license = licenses.gpl2Plus;
      maintainers = with maintainers; [
        eelco
        lukegb
        pacien
        techknowlogick
      ];
      platforms = platforms.unix;
      mainProgram = "hg";
    };
  };

  # makeTests = { mercurial ? self, nameSuffix ? "", flags ? "" }: runCommand "${mercurial.pname}${nameSuffix}-tests" {
  #   inherit (mercurial) src;

  #   SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";  # needed for git
  #   MERCURIAL_BASE = mercurial;
  #   nativeBuildInputs = [
  #     python
  #     unzip
  #     which
  #     sqlite
  #     git
  #     gnupg
  #   ];

  #   postPatch = ''
  #     patchShebangs .

  #     for f in **/*.{py,c,t}; do
  #       # not only used in shebangs
  #       substituteAllInPlace "$f" '/bin/sh' '${stdenv.shell}'
  #     done

  #     for f in **/*.t; do
  #       substituteInPlace 2>/dev/null "$f" \
  #         --replace '*/hg:' '*/*hg*:' \${/* paths emitted by our wrapped hg look like ..hg-wrapped-wrapped */""}
  #         --replace '"$PYTHON" "$BINDIR"/hg' '"$BINDIR"/hg' ${/* 'hg' is a wrapper; don't run using python directly */""}
  #     done
  #   '';

  #   # This runs Mercurial _a lot_ of times.
  #   requiredSystemFeatures = [ "big-parallel" ];

  #   # Don't run tests if not-Linux or if cross-compiling.
  #   meta.broken = !stdenv.hostPlatform.isLinux || stdenv.buildPlatform != stdenv.hostPlatform;
  # } ''
  #   addToSearchPathWithCustomDelimiter : PYTHONPATH "${mercurial}/${python.sitePackages}"

  #   unpackPhase
  #   cd "$sourceRoot"
  #   patchPhase

  #   cat << EOF > tests/blacklists/nix
  #   # tests enforcing "/usr/bin/env" shebangs, which are patched for nix
  #   test-run-tests.t
  #   test-check-shbang.t

  #   # unstable experimental/unsupported features
  #   # https://bz.mercurial-scm.org/show_bug.cgi?id=6633#c1
  #   test-git-interop.t

  #   # doesn't like the extra setlocale warnings emitted by our bash wrappers
  #   test-locale.t

  #   # Python 3.10-3.12 deprecation warning: asyncore
  #   # https://bz.mercurial-scm.org/show_bug.cgi?id=6727
  #   test-patchbomb-tls.t
  #   EOF

in
#   export HGTEST_REAL_HG="${mercurial}/bin/hg"
#   # include tests for native components
#   export HGMODULEPOLICY="rust+c"
#   # extended timeout necessary for tests to pass on the busy CI workers
#   export HGTESTFLAGS="--blacklist blacklists/nix --timeout 1800 -j$NIX_BUILD_CORES ${flags}"
#   make check
#   touch $out
# '';
self.overridePythonAttrs (origAttrs: {
  passthru = origAttrs.passthru // rec {
    # withExtensions takes a function which takes the python packages set and
    # returns a list of extensions to install.
    #
    # for instance: mercurial.withExtension (pm: [ pm.hg-evolve ])
    withExtensions =
      f:
      let
        python = self.python;
        mercurialHighPrio =
          ps:
          (ps.toPythonModule self).overrideAttrs (oldAttrs: {
            meta = oldAttrs.meta // {
              priority = 50;
            };
          });
        plugins = (f python.pkgs) ++ [ (mercurialHighPrio python.pkgs) ];
        env = python.withPackages (ps: plugins);
      in
      stdenv.mkDerivation {
        pname = "${self.pname}-with-extensions";

        inherit (self) src version meta;

        buildInputs = self.buildInputs ++ self.propagatedBuildInputs;
        nativeBuildInputs = self.nativeBuildInputs;

        dontUnpack = true;
        dontPatch = true;
        dontConfigure = true;
        dontBuild = true;
        doCheck = false;

        installPhase = ''
          runHook preInstall

          mkdir -p $out/bin

          for bindir in ${lib.concatStringsSep " " (map (d: "${lib.getBin d}/bin") plugins)}; do
            for bin in $bindir/*; do
              ln -s ${env}/bin/$(basename $bin) $out/bin/
            done
          done

          ln -s ${self}/share $out/share

          runHook postInstall
        '';

        installCheckPhase = ''
          runHook preInstallCheck

          $out/bin/hg help >/dev/null || exit 1

          runHook postInstallCheck
        '';
      };

    # tests = origAttrs.passthru.tests // {
    #   withExtensions = withExtensions (pm: [ pm.hg-evolve ]);
    # };
  };
})