nix buildPhase fails, "fatal: not a git repository", the .git dir isn't being copied into the build dir?

Question

I'm trying to create a flake for the peer to peer web browser, agregore ( https://github.com/AgregoreWeb/agregore-browser ). It's my first flake and I'm having major difficulties.

Here's the full flake, which I have placed in a clone of the above agregore git repo. I think the relevant section is all just this:

packages.default = stdenv.mkDerivation {
  pname = "agregore";
  version = (builtins.fromJSON (builtins.readFile ./package.json)).version;
  buildInputs = [
    pkgs.git
    pkgs.nodejs
    pkgs.nodePackages.node-gyp
    pkgs.nodePackages.npm
    pkgs.yarn
  ];
  buildPhase = ''
    git submodule update --init --recursive
    yarn
  '';
  installPhase = ''
    mkdir -p $out/bin
    #TODO find the build output
    ln -s build/agregore $out/bin/agregore
  '';
  src = ./.;
};

Logs produced:

@nix { "action": "setPhase", "phase": "unpackPhase" }
unpacking sources
unpacking source archive /nix/store/va0hnynmqf8h29f580sb6h7d3z9kxcpm-1q603n538l>
source root is 1q603n538laqf3nvkgb5mdr6am8apbda-source
@nix { "action": "setPhase", "phase": "patchPhase" }
patching sources
@nix { "action": "setPhase", "phase": "configurePhase" }
configuring
no configure script, doing nothing
@nix { "action": "setPhase", "phase": "buildPhase" }
building
fatal: not a git repository (or any of the parent directories): .git

I've tried inserting commands like ls .git/ > out.txt into the buildPhase, and this produces ls: cannot access '.git/': No such file or directory, so they are indeed not being copied over to nix's temporary build directory for this flake (and running the same command with build/ instead of .git/ doesn't produce this error.). I can't understand why this would be.

The same command, git submodule update --init --recursive, works fine in the original project dir (and I'm running nixos btw), also within a nix develop session, so the .git directory really should to be there?

Answer 1

I believe mkDerivation by default cleans .git from the source, because it's not appropriate to include it in a reproducible build (.git contains things like dangling references to old branches and the like which are completely client-specific). That said, in my opinion git submodule update --init --recursive doesn't really belong in the Nix code, because the Nix code assumes that it's operating on a "sane" source structure.