Support 'extra-libraries: m'

[ramirez7]

I've been using this overlay in my project (compiling natively on NixOS + x-compiling to Windows) for over a year now.

hgeometry is the most notable Haskell library I know of that does this.

Fixes #1128

[angerman]

Shouldn't this be a system package mapped to null?

[ramirez7]

I wasn't aware of that functionality - so I can just have m = null; at the top level in nixpkgs and that'll fix it? Also, is there a better place in haskell.nix to do this than where I've done it?

[hamishmack]

is there a better place in haskell.nix to do this than where I've done it?

Oh, yes. Try putting it in here https://github.com/input-output-hk/haskell.nix/blob/master/lib/system-nixpkgs-map.nix

[ramirez7]

@hamishmack @angerman I've updated it to map m to null.

I also made this minimal reproduction for good measure: https://gitlab.com/ramirez7/bug-repros/-/tree/864172f0637cc58b82217525f62037c73d302a9d/haskell.nix/2022/05/libm-1128

[hamishmack]

bors try

[iohk-bors]

try

Timed out.