To cite rwbarton from #9757:

...

I think the purpose of compiler warnings should be to warn about code

#3085: warn about language extensions that are not used -------------------------------------+------------------------------------- Reporter: | Owner: PVerswyvelen | Status: new Type: feature | Milestone: 7.10.1 request | Version: 6.10.1 Priority: normal | Keywords: warnings Component: Compiler | extensions language Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: #9757 None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by Lemming): Replying to [comment:33 thomie]: that is probably bad, not code that is probably fine that could be written in a (potentially) better way. (After all, we don't warn about excess parentheses in code either.) That is the domain of hlint, as Richard notes.

Anyone disagree with a `wontfix` here as well?

GHC already warns about unused variables and unused imports. Is the warning about unused instances much different? If you think, that the warning is not essential it may not be enabled by -Wall. And there are already non-Wall warnings that pointed me to bad code, like the warning about incomplete case analysis of pattern matches in lambda expressions. (I think it's `-fwarn-incomplete-uni-patterns`.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/3085#comment:34 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler