@utdemir Do you know of some library that I can try compiling that uses exceptions and compiles correctly with ghcHEAD?

I want to test that setting exceptions to null actually works for compiling libraries (well, at least one library) that depend on it.

I don't think ghcHEAD is widely used, so breaking it is not the worst thing in the world, but I guess it is better to be safe than sorry.

Also, I've confirmed that exceptions is actually a boot library. The following is on the current haskell-updates branch (commit 0e2ed7a):

$ nix-shell -I nixpkgs=./. -p haskell.compiler.ghcHEAD --run 'ghc-pkg list | grep exception'
    exceptions-0.10.4

Hmm, https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/libraries/version-history seems to indicate that it is a boot library even with GHC-8.10.

Do we need to add this to the configuration-ghc8.10.nix file as well?

$ nix-shell -I nixpkgs=./. -p haskell.compiler.ghc8101 --run 'ghc-pkg list | grep exception'
    exceptions-0.10.4

Do we need to add this to the configuration-ghc8.10.nix file as well?

It looks like it is already the case, it was added by: 2514bdd . Probably we simply forgot updating ghcHEAD, as you said it's not as widely used.

@utdemir Do you know of some library that I can try compiling that uses exceptions and compiles correctly with ghcHEAD?

Not easily. I had the issue when compiling doctest's tests, where I hit this case:

Unfortunately, it requires hundreds of lines of overrides to get doctest dependencies compile, even after that tests fail for a different reason after applying this patch. As an alternative, I tried safe-exceptions which is pretty dependency-light, however it did compile successfully both with and without this patch. That confuses me, I don't know why is it complaining on doctest but not on safe-exceptions. I'll try to get a small reproducing example tomorrow.

I tried safe-exceptions which is pretty dependency-light, however it did compile successfully both with and without this patch.

That is somewhat confusing.

Although like you say, it seems like this is necessary, so maybe we should go ahead and merge it even if you can't get some sort of reproducible example.