#13813: DeriveFunctor spuriously rejects existential context with type synonym mentioning the last type variable -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3635 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ryan Scott <ryan.gl.scott@…>): In [changeset:"85731000d8b13476ed3c5bde22af610a27fb00f8/ghc" 8573100/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="85731000d8b13476ed3c5bde22af610a27fb00f8" Look through type synonyms in existential contexts when deriving Functor Summary: This amounts to using `exactTyCoVarsOfType` instead of `tyCoVarsOfType` in the right place. I also fixed a similar issue for `-XDatatypeContexts` while I was in town (but couldn't be bothered to add a test for it). Test Plan: make test TEST=T13813 Reviewers: austin, bgamari, simonpj Reviewed By: simonpj Subscribers: simonpj, rwbarton, thomie GHC Trac Issues: #13813 Differential Revision: https://phabricator.haskell.org/D3635 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13813#comment:2> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler