Unable to use ghcid

[srid]

Full build (nix-build) succeeds, but I can't use ghcid for some reason.

[snowleopard]

I'm not using Nix, and can't reproduce with my setup.

Note that DeriveFunctor is in the default-extensions in the common stanza. Perhaps, you are using an old Cabal that doesn't support common stanzas?

[andrewthad]

The problem is almost certainly the use of default-extensions. If ghcid is just invoking ghci (rather than cabal repl), then the expecting extensions will not be enabled, and compilation will fail. The solution is simple: put {-# language DeriveFunctor #-} at the top of every module instead of using default-extensions.

[snowleopard]

@andrewthad Default extensions can also be enabled in the .ghci script, as I'm doing here:

alga/.ghci

Lines 7 to 12 in f338259

	:set -XFlexibleContexts
	:set -XFlexibleInstances
	:set -XGeneralizedNewtypeDeriving
	:set -XScopedTypeVariables
	:set -XTupleSections
	:set -XTypeFamilies

Perhaps, it's just a matter of adding DeriveFunctor there? I'd be happy to accept a PR that does that if it fixes this issue for you.

[andrewthad]

I suspect that would fix it too. I don't use nix though, so I cannot replicate the OP's issue.

[wbadart]

@srid can you share the derivation you're using?

[srid]

I don't remember right now, but I believe I was using alga as an obelisk thunk in a GHC 8.6 project.

I'll close this as I'm not looking for a solution to this anymore, but feel free to open if anybody thinks this is worth supporting.