@Ericson2314 Thanks for upstreaming this type of stuff!

I tried testing this locally and it appears to work:

$ nix-build -E 'with (import ./. {}); haskellPackages.hackage2nix "lens" "4.17.1"'
...
/nix/store/0kvij1wikr9lklz7ac3rh6wqh6sb6s5b-cabal2nix-lens-4.17.1
$ cat /nix/store/0kvij1wikr9lklz7ac3rh6wqh6sb6s5b-cabal2nix-lens-4.17.1/default.nix
...

The generated default.nix file looks good to me.

However, I'm not very familiar with the cross compilation support in nixpkgs (which I think is the difference between buildPackages and pkgs in this file??). I didn't actually try this with any sort of cross compilation target, so I guess I haven't really tested it. Although it makes sense that it should work, since the cabal2nix we get from buildPackages should work the same as the cabal2nix we get from pkgs?

cc @peti

@Ericson2314 Oh, also, is this the type of thing that should go into the haskell-updates branch (instead of the master branch)?

I think it's fine to merge directly to master. This code is not used inside of Nixpkgs itself, so the test builds that happen on haskell-updates are not going to generate any useful insights anyway.

For those wondering, source does doesn't really have a host platform per-se, it is agnostic so it doesn't much matter which runCommand we use. Ideally the hashes would also be the same, since there's no C compiler or anything, but that's unsolved tech debt.