fetchgit.nix

{pkgs}:
{
  # Fetches a tag from a github repo.
  fetchRepo = {owner, repo, tag, sha256, requireToken ? false}:
    let
      url = "https://api.github.com/repos/${owner}/${repo}/tarball/${tag}";
    in
    pkgs.stdenv.mkDerivation {
      inherit requireToken;
      name = "${repo}-${tag}-snapshot.tar.gz";
      buildInputs = [pkgs.curl pkgs.cacert];
      # Environment variable read by curl
      CURL_CA_BUNDLE = "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt";
      outputHash = sha256;
      outputHashAlgo = "sha256";
      outputHashMode = "flat";
      github_token = getEnv "GITHUB_TOKEN";
      buildCommand = ''
        if [ -z $github_token ] && [ ! -z $requireToken ]; then
          echo "Please set the GITHUB_TOKEN environment variable."
          exit 1
        elif ! [ -z $github_token ]; then
          curl --fail -fL -H "Authorization: token $github_token" ${url} > $out
        else
          curl --fail -fL ${url} > $out
        fi
      '';
    };

  # Uses the repo fetched from `fetchRepo` to pull the package source out.
  fetchPathInRepo = {owner, repo, tag, pathInRepo, requireToken ? false, sha256}:
    let
      fetchedRepo = fetchRepo {inherit owner repo tag sha256 requireToken;};
    in
    pkgs.stdenv.mkDerivation {
      name = "${tag}-folder";
      buildCommand = ''
        tar -xf ${fetchedRepo}
        cp -r ${owner}-${repo}-*/${pathInRepo} $out
      '';
    };
}