Add exceptions and stm to nonReinstallablePkgs

[locallycompact]

Fixes #1177

[hamishmack]

It might be better to set nonReinstallablePkgs in a module in the project in question (by passing modules = [{nonReinstallablePkgs = [...];};). Changing the default might result in an old version of exceptions or stm being used on projects using older GHC version.

[locallycompact]

I don't understand what you have in mind. I've changed it so it only acts on 9.0.1 now.

[hamishmack]

I can't seem to access https://github.com/locallycompact/haskell-nix-ghc-bug (I just get a 404), but if I understand the issue correctly it does not build unless we add exceptions and stm to nonReinstallablePkgs. We should normally be able to do that in the project rather than changing it globally in haskell.nix. Something like:

project = haskell-nix.cabalProject {
  src = ...;
  modules = [{
    nonReinstallablePkgs = [...];
  }];
};

[locallycompact]

Thanks, its public now.

This would need to be on for every ghc 9 project IIUC so why would we not want it globally?

[hamishmack]

why would we not want it globally?

For anything in nonReinstallablePkgs haskell.nix will ignore the version selected by the cabal solver or stack resolver. Even setting it for ghc 9.0.1 would be a problem. If a new versions of exceptions or stm was uploaded to hackage it would make it hard to use them.

[ocharles]

Is there anything I can do to help this? I believe it's what's blocking ocharles/weeder#68 (https://github.com/ocharles/weeder/runs/3220946774)

[hamishmack]

For now I think ocharles/weeder#81 is the best work around.

Adding dependencies of GHC to the default nonReinstallablePkgs is not ideal.

A better fix would be to modify the way nonReinstallablePkgs works. It might be possible to make it automatic. It could include only packages where the version matches the version of the package that comes with ghc (as well as the versions of all the dependencies of that package).

Fixing modules = [{ reinstallableLibGhc = true; }]; for GHC 9.0.1 would also provide a nicer work around. When it works reinstallableLibGhc clears out nonReinstallablePkgs and makes ghc just a regular package. Currently it is failing with:

...
Building library for transformers-compat-0.6.6..
Preprocessing library for ghc-9.0.1..
Building library for cryptonite-0.29..
Setup: can't find source for GHC/Settings/Config in ., dist/build/autogen,
dist/build/global-autogen

[ocharles]

Another ping here, I really do think we should do something that means Haskell.nix can be used with GHC 9 out-of-the-box. Especially now that Stackage LTS is on 9.0.