Git dependency in extra-deps doesn't work if specified commit isn't reachable from remote HEAD

[isomorpheme]

For example, having something like:

- git: https://github.com/circuithub/ghc-source-gen.git
  commit: 7a6aac047b706508e85ba2054b5bedbecfd7eb7a

in extra-deps fails with an error like:

error: Cannot find Git revision '7a6aac047b706508e85ba2054b5bedbecfd7eb7a' in ref 'refs/heads/master' of repository 'https://github.com/circuithub/ghc-source-gen.git'! Please make sure that the rev exists on the ref you've specified or add allRefs = true; to fetchGit.

I think this is because of this fetchGit call:

stacklock2nix/nix/build-support/stacklock2nix/default.nix

Lines 379 to 383 in 10d5316

	rawSrc = builtins.fetchGit {
	url = haskPkgLock.git;
	name = srcName;
	rev = haskPkgLock.commit;
	};

Adding allRefs = true as the error suggests would solve this, but there's probably repos where it's much slower to do that, so maybe there's a cleverer solution, or it can just be made configurable?

[cdepillabout]

Thanks for submitting this!

I released https://github.com/cdepillabout/stacklock2nix/releases/tag/v4.0.0, which uses your suggested fix from runtimeverification/hs-backend-booster@62139cd.