Build GHC without GMP integer library

[k0ral]

I didn't find a way to build/install GHC without GMP with current nixpkgs. It boils down to adding INTEGER_LIBRARY = integer-simple in the build.mk file.

I'm willing to contribute, if this is indeed missing, but given that the haskell-related derivations are organized in a specific and well-thought manner, I figured I should ask for pointers before naively stepping in the wrong direction.

At first glance, I would do the following:

• patch development/compilers/ghc/X.Y.Z.nix derivations to accept a new useIntegerSimple flag as input;
• use the extraArgs of packagesFun (from haskell-defaults.nix) to forward this flag if needed.

What do you think ?

[peti]

Note that the Haskell package set structure is going to become much simpler in the future: https://github.com/peti/nixpkgs/blob/haskell-ng/pkgs/top-level/all-packages.nix#L3350.

I guess, it would be nice to have a generic buildmk argument to GHC that people can use to pass arbitrary settings to the build. I'll try to figure something out.

[k0ral]

This is really nice, I'm looking forward to it, thank you.

[puffnfresh]

@peti the buildInputs need to change to use integer-simple instead of integer-gmp for the derivations. There's usually also flags such as -finteger-simple or -fuse-integer-simple which need to be used to toggle the dependencies. Not sure if hackage2nix can handle that, but would be good if we could make the derivations be parameterised with what the .cabal files has in conditionals.

[peti]

We probably don't have to worry about the Cabal flags as those are auto-detected at compile time based on the available build environment. Dependencies on integer-gmp are no problem, I suppose, because that name is defined as null anyway since it's a core library. I believe the changes mostly comes down to extending the GHC options to support that particular build variant.

Personally, I'd love a generic mechanism for our GHC builds that can be used to pass an arbitrary build.mk file so that people can build GHC with any option they please.

[Profpatsch]

(triage) can we close this @peti?

[peti]

#22121 will remedy this issue once it's merged.