[GHC] #15704: Different saturations of the same polymorphic-kinded type constructor aren't seen as apart types

[GHC]

#15704: Different saturations of the same polymorphic-kinded type constructor
aren't seen as apart types
-------------------------------------+-------------------------------------
        Reporter:  mniip             |                Owner:  mniip
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.6.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9371             |  Differential Rev(s):  Phab:D5206
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"f877d9cc99dd1ba0c038e70527031e9ba0934cd3/ghc" f877d9c/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="f877d9cc99dd1ba0c038e70527031e9ba0934cd3"
 Move eta-reduced coaxiom compatibility handling quirks into FamInstEnv.

 The quirk caused an issue where GHC concluded that 'D' is possibly
 unifiable with 'D a' (the two types could have the same kind if D is a
 data family).

 Test Plan:
 Ensure T9371 stays fixed.
 Introduce T15704

 Reviewers: goldfire, bgamari

 Reviewed By: goldfire

 Subscribers: RyanGlScott, rwbarton, carter

 GHC Trac Issues: #15704

 Differential Revision: https://phabricator.haskell.org/D5206
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15704#comment:7>
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