ghcWithIndexer nix packaging

[mpickering]

Nix provides a very convenient wrapper, ghcWithHoogle which generates hoogle indexes for all dependencies of your project. It would be similarly convenient if there was a ghcWithIndexer wrapper which instead built kythe indexes using haskell-indexer.

I indent to implement this but this ticket is for the contingency that I don't.

[mpickering]

Here is how far I got trying to package kythe on nix..

NixOS/nixpkgs#27590

It was much harder than I expected.

[mpickering]

I now have a nearly working implementation of this but it is not really in a usable state by anyone else. I need to work to upstream a lot of related pieces.

[mpickering]

This is the commit which implements ghcWithIndexer. It is blocked on a hackage release of all the packages but after that it should be easy to upstream.

mpickering/nixpkgs@9d18805