Haskell: Added haskellPackages.shellFor #36393
Motivation for this change
Building multi-package projects is pretty common, and nixpkgs currently doesn't provide a standard way to work on them simultaneously with an incremental tool like cabal new-build. This function achieves that by extracting your packages' build inputs and making a shell with those available.
@Ericson2314 I think it would suffice to simply leave a warning about that case. But a more comprehensive solution would be nice :) I just wouldn't want certain packages to be not built without the user having any idea why, so I think I'd rather see that case become an error than have it handled implicitly.