Nix issues

"Fatal: not a tree object" when using fetchGit

You use fetchGit:

  repo = builtins.fetchGit {
      url = "git@bitbucket.org:org/repo.git";
      rev = "6364b4e00771a531c7df389a0b849d7cc40d2b68";
  };

It fails with:

fatal: not a tree object: 6364b4e00771a531c7df389a0b849d7cc40d2b68
error: program 'git' failed with exit code 128
(use '--show-trace' to show detailed location information)

The problem is that there's also an invisible ref parameter, defaulting to "master", and the commit must be reachable from that ref. So if you choose a commit that isn't in master, you have to specify the branch as well:

  repo = builtins.fetchGit {
      url = "git@bitbucket.org:org/repo.git";
      ref = "some-branch";
      rev = "6364b4e00771a531c7df389a0b849d7cc40d2b68";
  };