Re: [GHC] #14880: GHC panic: updateRole

#14880: GHC panic: updateRole -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: 8.6.2 Component: Compiler (Type | Version: 8.2.2 checker) | Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: 15592 Related Tickets: #15076 | Differential Rev(s): Phab:D4769, | Phab:D5141, Phab:D5147, Phab:D5150, Wiki Page: | Phab:D5208 -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"503514b94f8dc7bd9eab5392206649aee45f140b/ghc" 503514b/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="503514b94f8dc7bd9eab5392206649aee45f140b" Fix nasty bug in the type free-var finder, at last Consider the type forall k. b -> k where b :: k -> Type Here the 'k' in b's kind must be a different 'k' to the forall k, because 'b' is free in the expression. So we must return 'k' among the free vars returned from tyCoVarsOfType applied that type. But we weren't. This is an outright bug, although we don't have a program that fails because of it. It's easy to fix, too: see TyCoRep Note [Closing over free variable kinds] This fix has been in the pipeline for ages because it fell into the Trac #14880 swamp. But this patch nails it. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14880#comment:153 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler