Unused import warnings

[georgefst]

$ ./haskell-language-server-0.5.1-linux-8.10.2 --probe-tools
haskell-language-server version: 0.5.1.0 (GHC: 8.10.2) (PATH: /home/gthomas/.config/Code/User/globalStorage/haskell.haskell/haskell-language-server-0.5.1-linux-8.10.2) (GIT hash: e3fe0e7546aa91e44cc56cfe8ec078a026cf533a)
Tool versions found on the $PATH
cabal:		3.2.0.0
stack:		Not found
ghc:		8.10.2

import Data.Functor -- doesn't matter what module this is

main = putStrLn "hi"

Standalone file, no warnings enabled. I still get a blue, info-level, message about the unused import. There's seemingly no way to turn this off, and some would regard it as unwanted noise (particularly this person).

[ndmitchell]

I think we generate the info message so we can colour it in gray. Would be best to hide it though...

[serras]

As I mentioned in haskell/ghcide#902, the current LSP spec requires each "unused element" to be tied to a diagnostic. That was the original reason for enabling extra warnings, but demoting them if they were not in the set of original ones.

@ndmitchell @jneira I am happy to send a PR to remove the behavior of enabling the "unused X" warnings when the user hadn't requested them. But I only want to do that if you think that should be the correct behavior.

Another choice is to have a middle ground. Maybe we want to always enable "unused variables", but not "unused imports", right now we just do all of them. I think most people would be happy with WarnUnusedLocalBinds, WarnUnusedMatches, WarnUnusedForalls, WarnInaccessibleCode and WarnWarningsDeprecations by default. Here's the entire list for reference:

unnecessaryDeprecationWarningFlags
  = [ Opt_WarnUnusedTopBinds
    , Opt_WarnUnusedLocalBinds
    , Opt_WarnUnusedPatternBinds
    , Opt_WarnUnusedImports
    , Opt_WarnUnusedMatches
    , Opt_WarnUnusedTypePatterns
    , Opt_WarnUnusedForalls
#if MIN_GHC_API_VERSION(8,10,0)
    , Opt_WarnUnusedRecordWildcards
#endif
    , Opt_WarnInaccessibleCode
    , Opt_WarnWarningsDeprecations
    ]

[jneira]

@serras thanks for take vare, i like your last proposal as default

Another choice is to have a middle ground. Maybe we want to always enable "unused variables", but not "unused imports",

but sure there will be users that might want to remove all of them so

to remove the behavior of enabling the "unused X" warnings when the user hadn't requested them

seems to be the more generic one

[serras]

@jneira unfortunately, since we don't have a way to configure the plug-in, we need to make one choice.

[jneira]

mmm in fact I think we could configure it, like we are doing in the hlint plugin but if I had to choose one I would pick the based in user request (we will reuse the ghc config)

EDIT: sorry, it is included in ghcide and it has config disabled, so we should extract it as a plugin before

[jneira]

It seems this was closed by haskell/ghcide#907
Feel free to reopen if that is not the case