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

{
  lib,
  stdenvNoCC,
  git,
  git-lfs,
  cacert,
}:
let
  urlToName =
    url: rev:
    let
      inherit (lib) removeSuffix splitString last;
      base = last (splitString ":" (baseNameOf (removeSuffix "/" url)));

      matched = builtins.match "(.*)\\.git" base;

      short = builtins.substring 0 7 rev;

      appendShort = lib.optionalString ((builtins.match "[a-f0-9]*" rev) != null) "-${short}";
    in
    "${if matched == null then base else builtins.head matched}${appendShort}";
in
lib.makeOverridable (
  {
    url,
    rev ? "HEAD",
    sha256 ? "",
    hash ? "",
    leaveDotGit ? deepClone,
    fetchSubmodules ? true,
    deepClone ? false,
    branchName ? null,
    sparseCheckout ? [ ],
    nonConeMode ? false,
    name ? urlToName url rev,
    # Shell code executed after the file has been fetched
    # successfully. This can do things like check or transform the file.
    postFetch ? "",
    preferLocalBuild ? true,
    fetchLFS ? false,
    # Shell code to build a netrc file for BASIC auth
    netrcPhase ? null,
    # Impure env vars (https://nixos.org/nix/manual/#sec-advanced-attributes)
    # needed for netrcPhase
    netrcImpureEnvVars ? [ ],
    passthru ? { },
    meta ? { },
    allowedRequisites ? null,
  }:

  /*
    NOTE:
    fetchgit has one problem: git fetch only works for refs.
    This is because fetching arbitrary (maybe dangling) commits creates garbage collection risks
    and checking whether a commit belongs to a ref is expensive. This may
    change in the future when some caching is added to git (?)
    Usually refs are either tags (refs/tags/*) or branches (refs/heads/*)
    Cloning branches will make the hash check fail when there is an update.
    But not all patches we want can be accessed by tags.

    The workaround is getting the last n commits so that it's likely that they
    still contain the hash we want.

    for now : increase depth iteratively (TODO)

    real fix: ask git folks to add a
    git fetch $HASH contained in $BRANCH
    facility because checking that $HASH is contained in $BRANCH is less
    expensive than fetching --depth $N.
    Even if git folks implemented this feature soon it may take years until
    server admins start using the new version?
  */

  assert deepClone -> leaveDotGit;
  assert nonConeMode -> (sparseCheckout != [ ]);

  if hash != "" && sha256 != "" then
    throw "Only one of sha256 or hash can be set"
  else if builtins.isString sparseCheckout then
    # Changed to throw on 2023-06-04
    throw
      "Please provide directories/patterns for sparse checkout as a list of strings. Passing a (multi-line) string is not supported any more."
  else
    stdenvNoCC.mkDerivation {
      inherit name;
      builder = ./builder.sh;
      fetcher = ./nix-prefetch-git;

      nativeBuildInputs = [ git ] ++ lib.optionals fetchLFS [ git-lfs ];

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

      # git-sparse-checkout(1) says:
      # > When the --stdin option is provided, the directories or patterns are read
      # > from standard in as a newline-delimited list instead of from the arguments.
      sparseCheckout = builtins.concatStringsSep "\n" sparseCheckout;

      inherit
        url
        rev
        leaveDotGit
        fetchLFS
        fetchSubmodules
        deepClone
        branchName
        nonConeMode
        postFetch
        ;

      postHook =
        if netrcPhase == null then
          null
        else
          ''
            ${netrcPhase}
            # required that git uses the netrc file
            mv {,.}netrc
            export NETRC=$PWD/.netrc
            export HOME=$PWD
          '';

      GIT_SSL_CAINFO = "${cacert}/etc/ssl/certs/ca-bundle.crt";

      impureEnvVars =
        lib.fetchers.proxyImpureEnvVars
        ++ netrcImpureEnvVars
        ++ [
          "GIT_PROXY_COMMAND"
          "NIX_GIT_SSL_CAINFO"
          "SOCKS_SERVER"
        ];

      inherit preferLocalBuild meta allowedRequisites;

      passthru = passthru // {
        gitRepoUrl = url;
      };
    }
)