haskell-nix.extraPkgconfigMappings

[ramirez7]

Fixes #1664

You can try the sdl-gpu-minimal example here https://gitlab.com/macaroni.dev/macaroni.nix/-/merge_requests/12

It maps multiple new libraries and works on Linux and Windows (see #1666 for a change I had to make) currently.

[ramirez7]

I thought making this an attribute of haskell-nix and leveraging overlays would be the most composable route to propagating this to where it needed to go (similar to defaultModules).

[L-as]

This should probably be part of the project-common module.

[hamishmack]

I'm wondering if a better fix might be to just add these packages (SDL_gpu and SDL_FontCache) to the mapping in haskell.nix.

It used to be that there was an implicit mapping for all packages where the names matched (as is the case here).

We had to loose that mapping with the new dummy pkg-config because some packages in nixpkgs blow up eval if you even look for a .version (there is no way to know which packages these will be for all nixpkgs so we can't have a black list).

I'll merge this feature though because there is a use case where multiple nixpkgs packages all provide the same pkg-config package. This will let us override the default without having to resort to replacing it in pkgs.

It might also be useful to have a way to exclude things from the mapping for example if:

• The version of nixpkgs in use does not have a .pc file yet.
• We don't want cabal to use a certain pkg-config package in its plan.

[hamishmack]

bors try

[iohk-bors]

try

Build succeeded:

• ci/hydra:Cardano:haskell-nix:required
• buildkite/haskell-dot-nix

[ramirez7]

I'm wondering if a better fix might be to just add these packages (SDL_gpu and SDL_FontCache) to the mapping in haskell.nix.

Neither library emits a .pc file upstream, so they only work for me because I have Nix packaging to explicitly emit a .pc file. So if/when I upstream that logic to nixpkgs or to the libraries themselves, I will be sure to send a PR to haskell.nix with the official mapping.

But for now, I'll continue to use this. In general, users will likely run into unpackaged C libraries they wish to package themselves with pkgconfig to take advantage of the infrastructure around it in cabal + haskell.nix. So this feature is definitely useful regardless!

[yvan-sraka]

Should we document that directly on the https://input-output-hk.github.io/haskell.nix/ manual?