1. 19 Apr, 2018 1 commit
    • Ryan Scott's avatar
      Fix #15012 with a well-placed use of Any · b08a6d75
      Ryan Scott authored
      Previously, derived `Generic1` instances could have associated `Rep1`
      type family instances with unbound variables, such as in the following
      example:
      
      ```lang=haskell
      data T a = MkT (FakeOut a) deriving Generic1
      type FakeOut a = Int
      
      ==>
      
      instance Generic1 T where
        type Rep1 T = ... (Rec0 (FakeOut a))
      ```
      
      Yikes! To avoid this, we simply map the last type variable in a
      derived `Generic1` instance to `Any`.
      
      Test Plan: make test TEST=T15012
      
      Reviewers: bgamari
      
      Reviewed By: bgamari
      
      Subscribers: simonpj, thomie, carter
      
      GHC Trac Issues: #15012
      
      Differential Revision: https://phabricator.haskell.org/D4602
      b08a6d75