Re: [GHC] #13777: Poor error message around CUSKs

#13777: Poor error message around CUSKs -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: TypeInType, | CUSKs Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4771 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"ac91d07399207f4e22467bea3577cafd27a937d7/ghc" ac91d073/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="ac91d07399207f4e22467bea3577cafd27a937d7" Fix #13777 by improving the underdetermined CUSK error message The error message that GHC emits from underdetermined CUSKs is rather poor, since: 1. It may print an empty list of user-written variables if there are none in the declaration. 2. It may not mention any `forall`-bound, underdetermined variables in the result kind. To resolve these issues, this patch: 1. Doesn't bother printing a herald about user-written variables if there are none. 2. Prints the result kind to advertise any underdetermination it may exhibit. Test Plan: make test TEST=T13777 Reviewers: goldfire, bgamari Reviewed By: goldfire Subscribers: rwbarton, thomie, carter GHC Trac Issues: #13777 Differential Revision: https://phabricator.haskell.org/D4771 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13777#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler