
#10635: -fwarn-redundant-constraints should not be part of -Wall -------------------------------------+------------------------------------- Reporter: Lemming | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.11 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #9939, #9973, | Differential Rev(s): #10100, #10183 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari):
GHC-8.0 does not warn about any of these two. Should it?
Indeed GHC 8.0 warns that the `a ~ b` constraint is redundant. This is arguably wrong and I've opened #11582 for this case. This is almost certainly not the last example of this sort that we will find. However, I suspect that `-Wredundant-constraints` will help more users in the situation that mboes describes than it would hurt users with the cases you describe if enabled in `-Wall`. It doesn't seem unreasonable to me to require users writing code like `asTypeOf1` to explicitly disable this warning. At the moment this can only be done on with module-level granularity but hopefully in the future we will have [[Design/LocalWarningPragmas|mechanisms]] for silencing warnings with greater precision. Regardless, your points have demonstrated that there are some tricky issues here. It would be helpful if you could collect these thoughts on [[Design/Warnings/RedundantConstraints]]. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10635#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler