console

[spacekitteh@spaceserv:~/nix-patches/nixpkgs/pkgs/build-support/fetchgitrepo]$ nix-build test.nix
these derivations will be built:
  /nix/store/dl2ajlh08n7fpbn0rkc78hdylkpsmrn9-foo.drv
building path(s) ‘/nix/store/mrsbrb4abqgw0lidbc2bqkw33bab7wd8-foo’
warning: gpg (GnuPG) is not available.
warning: Installing it is strongly encouraged.

fatal: Cannot get https://gerrit.googlesource.com/git-repo/clone.bundle
fatal: error [Errno -2] Name or service not known
builder for ‘/nix/store/dl2ajlh08n7fpbn0rkc78hdylkpsmrn9-foo.drv’ failed with exit code 1
error: build of ‘/nix/store/dl2ajlh08n7fpbn0rkc78hdylkpsmrn9-foo.drv’ failed

default.nix

{stdenv, git, gitRepo, gnupg ? null}:
{name, manifest, rev ? "HEAD", sha256 ? "", repoRepoURL ? "", repoRepoRev ? "", referenceDir ? "", 
localManifests ? {} }:

assert repoRepoRev != "" -> repoRepoURL != "";

stdenv.mkDerivation {
  inherit name;
  buildCommand = with stdenv.lib; ''
  mkdir -p $out
  cd $out
  mkdir $out/.repo
  export HOME=$out/.repo
  repo init -u ${manifest} -b ${rev} \
    ${optionalString (repoRepoURL != "") "--repo-url=${repoRepoURL}"} \
    ${optionalString (repoRepoRev != "") "--repo-branch=${repoRepoRev}"} \
    ${optionalString (referenceDir != "") "--reference=${referenceDir}"} \
    --depth=1

  repo sync --jobs=$NIX_BUILD_CORES --current-branch
  rm -rf $out/.repo
'';
  buildInputs = [git gitRepo ] ++ 
stdenv.lib.optional (gnupg != null) [gnupg] ;

  outputHashAlgo = "sha256";
  outputHashMode = "recursive";
  outputHash = sha256;

  impureEnvVars = stdenv.lib.fetchers.proxyImpureEnvVars;
  preferLocalBuild = true;

  inherit manifest rev repoRepoURL repoRepoRev referenceDir;
}

test.nix

with import <nixpkgs> {};
let fetcher = import ./default.nix {inherit stdenv 
git gitRepo gnupg;};
in
  fetcher {
  name = "foo";
  manifest = "https://github.com/CopperheadOS/platform_manifest.git";  
}