[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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Changes (by RyanGlScott):

 * status:  patch => upstream


Comment:

 As noted in
 https://gitlab.haskell.org/ghc/ghc/merge_requests/112#note_2409, the MR I
 linked to above is failing to validate due to a sneaky use of
 impredicativity in `Cabal` that went unnoticed until this patch revealed
 it. I've opened a `Cabal` issue upstream
 [https://github.com/haskell/cabal/issues/5833 here].

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16059#comment:14>
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