#15231: UndecidableInstances validity checking is wrong in the presence of QuantifiedConstraints -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: 8.6.1 Component: Compiler (Type | Version: 8.5 checker) | Keywords: Resolution: | QuantifiedConstraints 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:D4819 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari <ben@…>): In [changeset:"91822e4eee295a42f69489c7e9e878b296e897bc/ghc" 91822e4e/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="91822e4eee295a42f69489c7e9e878b296e897bc" Add "quantified constraint" context in error message, fix #15231. This patch adds "quantified constraint" context in error message when UndecidableInstances checking fails for quantified constraints. See Trac #15231:comment#1. This patch also pretty-prints the instance head for better error messages. Test Plan: make test TEST="T15231" Reviewers: bgamari, simonpj Reviewed By: simonpj Subscribers: simonpj, rwbarton, thomie, carter GHC Trac Issues: #15231 Differential Revision: https://phabricator.haskell.org/D4819 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15231#comment:4> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler