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 ? []
, 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 = {
    gitRepoUrl = url;
  };
}
)