#14237: -Wredundant-constraints incorrectly treats all type equality constraints as redundant -------------------------------------+------------------------------------- Reporter: lexi.lambda | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple error/warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #12700 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by lexi.lambda): I disagree that this is “very similar” to #12700. This is a **regression** from GHC 8.0, which did not have this problem. The type equality in the example given in #12700 is arguably redundant, since the program would compile without it, but the examples I’ve given in this ticket will fail to compile if the equalities are removed. When compiling these with `-Wredundant-constraints` in GHC 8.0.2, no warning is produced. In GHC 8.2.1, a warning ''is'' produced. I’m not sure why this happens, but it seems like a real step backwards, and it’s much more severe than #12700. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14237#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler