Generated packages should include packages for *all* platforms

[michaelpj]

fsnotify depends on shelly only on linux. The generated Nix code to build fsnotify correctly reifies this cabal conditional to require shelly only if we're building on linux. But if you generate the Nix for a project that includes fsnotify, the packages will contain shelly iff you generated the plan on linux.

This means that, although the build expression for fsnotify itself is platform-independent, the Nix for the whole project is not. This means:

• You can't pin the plan-sha256 unconditionally, you need a different sha for linux and non-linux.
• If you do pin it with, say, the linux sha and then try to build on darwin, you will pull down the linux plan-nix, and this will fail because it will try to depend on shelly which isn't there. (Note: I haven't tried this, but I'm extrapolating)

You can observe this with IntersectMBO/plutus#2581, compare:

nix-build default.nix -A plutus.haskell.extraPackages.haskell-language-server.project.plan-nix --argstr system x86_64-linux

and

nix-build default.nix -A plutus.haskell.extraPackages.haskell-language-server.project.plan-nix --argstr system x86_64-darwin

[michaelpj]

Oh, to be clear, I think we should put all the packages we might need with any conditionals into packages.

[quetz]

Having this issue with haskell-language-server (different build plans on darwin and linux).
So proposed solution is either unpinning plan-sha256 or using conditional like in https://github.com/input-output-hk/plutus/blob/c4685b8ad54cdb8ca33d67a7be252ecccbccd31f/nix/pkgs/haskell/extra.nix#L91 ?

[michaelpj]

Yes. It's quite painful :(

[hamishmack]

I think this will require #1696