#12142: -Wredundant-constraints warns about constraints introduced via type synonyms. -------------------------------------+------------------------------------- Reporter: scshunt | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Linux | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): In the interest of not getting drowned in complaints by the users of `lens` on GHC 8, we'll likely just add the constraint to `to` and rely on `{-# INLINE #-}` dropping it out in practice. This is a common enough scenario to warrant us eating the noise on our side. Of course, you'll get the same sort of thing if you go to declare a non- law abiding traversal as a fold, etc. There i'm afraid the only answer will be to squelch the warning. GHC can't see 'laws'. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12142#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler