[GHC] #16059: checkValidType is defeated by a type synonym

[GHC]

#16059: checkValidType is defeated by a type synonym
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  upstream
        Priority:  normal            |            Milestone:  8.10.1
       Component:  Compiler (Type    |              Version:  8.7
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:  16140
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |  https://gitlab.haskell.org/ghc/ghc/merge_requests/112
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Comment (by simonpj):

 As noted in my comment on the MR, I don't think this is Cabal's fault.

 I took a quick look but I can't see immediately why that is happening.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16059#comment:15>
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