Re: [GHC] #13183: Template Haskell needlessly pretty-prints empty instance contexts

#13183: Template Haskell needlessly pretty-prints empty instance contexts -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: patch Priority: normal | Milestone: 8.2.1 Component: Template Haskell | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3018 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ryan Scott ): In [changeset:"ad3d2dfa19a1ed788c682e8b0c7c6e66e63d3f79/ghc" ad3d2dfa/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="ad3d2dfa19a1ed788c682e8b0c7c6e66e63d3f79" Don't unnecessarily qualify TH-converted instances with empty contexts Summary: The addition of rigorous pretty-printer tests (499e43824bda967546ebf95ee33ec1f84a114a7c) had the unfortunate side-effect of revealing a bug in `hsSyn/Convert.hs` wherein instances are _always_ qualified with an instance context, even if the context is empty. This led to instances like this: ``` instance Foo Int ``` being pretty-printed like this! ``` instance () => Foo Int ``` We can prevent this by checking if the context is empty before adding an HsQualTy to the type. Also does some refactoring around HsForAllTys in `Convert` while I was in town. Fixes #13183. Test Plan: ./validate Reviewers: goldfire, bgamari, austin, alanz Reviewed By: alanz Subscribers: mpickering, thomie Differential Revision: https://phabricator.haskell.org/D3018 GHC Trac Issues: #13183 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13183#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler