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

{
  lib,
  fetchgit,
  fetchzip,
}:

lib.makeOverridable (
  {
    owner,
    repo,
    rev,
    name ? null, # Override with null to use the default value
    pname ? "source-${githubBase}-${owner}-${repo}",
    fetchSubmodules ? false,
    leaveDotGit ? null,
    deepClone ? false,
    private ? false,
    forceFetchGit ? false,
    sparseCheckout ? [ ],
    githubBase ? "github.com",
    varPrefix ? null,
    passthru ? { },
    meta ? { },
    ... # For hash agility
  }@args:

  let
    name = if args.name or null != null then args.name else "${pname}-${rev}";

    position = (
      if args.meta.description or null != null then
        builtins.unsafeGetAttrPos "description" args.meta
      else
        builtins.unsafeGetAttrPos "rev" args
    );
    baseUrl = "https://${githubBase}/${owner}/${repo}";
    newPassthru = passthru // {
      inherit rev owner repo;
    };
    newMeta =
      meta
      // {
        homepage = meta.homepage or baseUrl;
      }
      // lib.optionalAttrs (position != null) {
        # to indicate where derivation originates, similar to make-derivation.nix's mkDerivation
        position = "${position.file}:${toString position.line}";
      };
    passthruAttrs = removeAttrs args [
      "owner"
      "repo"
      "rev"
      "fetchSubmodules"
      "forceFetchGit"
      "private"
      "githubBase"
      "varPrefix"
    ];
    varBase = "NIX${lib.optionalString (varPrefix != null) "_${varPrefix}"}_GITHUB_PRIVATE_";
    useFetchGit =
      fetchSubmodules || (leaveDotGit == true) || deepClone || forceFetchGit || (sparseCheckout != [ ]);
    # We prefer fetchzip in cases we don't need submodules as the hash
    # is more stable in that case.
    fetcher =
      if useFetchGit then
        fetchgit
      # fetchzip may not be overridable when using external tools, for example nix-prefetch
      else if fetchzip ? override then
        fetchzip.override { withUnzip = false; }
      else
        fetchzip;
    privateAttrs = lib.optionalAttrs private {
      netrcPhase = ''
        if [ -z "''$${varBase}USERNAME" -o -z "''$${varBase}PASSWORD" ]; then
          echo "Error: Private fetchFromGitHub requires the nix building process (nix-daemon in multi user mode) to have the ${varBase}USERNAME and ${varBase}PASSWORD env vars set." >&2
          exit 1
        fi
        cat > netrc <<EOF
        machine ${githubBase}
                login ''$${varBase}USERNAME
                password ''$${varBase}PASSWORD
        EOF
      '';
      netrcImpureEnvVars = [
        "${varBase}USERNAME"
        "${varBase}PASSWORD"
      ];
    };

    gitRepoUrl = "${baseUrl}.git";

    fetcherArgs =
      (
        if useFetchGit then
          {
            inherit
              rev
              deepClone
              fetchSubmodules
              sparseCheckout
              ;
            url = gitRepoUrl;
            passthru = newPassthru;
          }
          // lib.optionalAttrs (leaveDotGit != null) { inherit leaveDotGit; }
        else
          {
            url = "${baseUrl}/archive/${rev}.tar.gz";

            passthru = newPassthru // {
              inherit gitRepoUrl;
            };
          }
      )
      // privateAttrs
      // passthruAttrs
      // {
        inherit name;
      };
  in

  (fetcher fetcherArgs).overrideAttrs (finalAttrs: previousAttrs: { meta = newMeta; })
)