hlint fixity issues

[ivan-m]

Your environment

Which OS do you use: Red Hat 7 VM
Which lsp-client do you use: Emacs
Describe your project (alternative: link to the project): Shake + Stack; internal project so can't be shared

Steps to reproduce

# .hlint.yaml
- fixity: "infixl 3 <!>"

Haskell source file:

-- https://hackage.haskell.org/package/semigroupoids-5.3.6/docs/Data-Functor-Alt.html
import Data.Functor.Alt ((<!>))

-- Simplified function matching behaviour of actual functions
foo :: Char -> Maybe Int -> Maybe String
foo c mInt =
      show <$> mInt
  <!> pure <$> Just c

-- Note the relative fixities here: this is equivalent to: (...) <!> (...)

Load this in $EDITOR, list all suggestions from hls.

Expected behaviour

No warnings related to foo.

Actual behaviour

Functor law
 Found:
   show <$> mInt <!> pure <$> Just c
 Why not:
   show . (mInt <!> pure) <$> Just c

Include debug information

Running hlint explicitly does not have any problems.

The .hlint.yaml file is indeed being picked up by the hls hlint plugin as other suggestions are appearing based upon the configuration (custom linting rules, etc.). As such, this might be due to ndmitchell/hlint#1232

haskell-language-server-wrapper --debug . output only partially shown as it's quite large:

haskell-language-server version: 1.5.1.0 (GHC: 8.10.7) (PATH: /home/<elided>/haskell-language-server) (GIT hash: 1d82c8ec31628fc84f0ffe55ff572602212e07a2)
 ghcide setup tester in /home/<elided>
Report bugs at https://github.com/haskell/haskell-language-server/issues

Step 1/4: Finding files to test in /home/<elided>
Found 16145 files

Logs from LSP client:

Command "~/<elided>/haskell-language-server --lsp" is present on the path.
Command "~/<elided>/haskell-language-server --lsp" is present on the path.
Found the following clients for /path/to/Module.hs: (server-id lsp-haskell, priority 0)
The following clients were selected based on priority: (server-id lsp-haskell, priority 0)

[jneira]

Thanks for the bug report, i wonder what happens if you set the rule via file pragma f.e.

[ivan-m]

AFAICT, the fixity information can only be specified in .hlint.yaml.

I did try adding {-# ANN module ("HLint: fixity: infixl 3 <!>" :: String) #-} but it had no effect.

[eddiemundo]

I looked into this and it seems to be that the hlint plugin in the end gets the HLINT_ON_GHC_LIB flag not set, and because of some cpp, flags (specifically fixities) from the .hlint.yaml are ignored:

haskell-language-server/plugins/hls-hlint-plugin/src/Ide/Plugin/Hlint.hs

Lines 238 to 246 in 4cd1082

	where moduleEx :: ParseFlags -> Action (Maybe (Either ParseError ModuleEx))
	#ifndef HLINT_ON_GHC_LIB
	moduleEx _flags = do
	mbpm <- getParsedModuleWithComments nfp
	return $ createModule <$> mbpm
	where createModule pm = Right (createModuleEx anns modu)
	where anns = pm_annotations pm
	modu = pm_parsed_source pm
	#else

I think applying fixities in the flags to modu before passing it to createModuleEx would do the trick.