[GHC] #15954: LiberalTypeSynonyms unsaturation check doesn't kick in

[GHC]

#15954: LiberalTypeSynonyms unsaturation check doesn't kick in
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.3
       Component:  Compiler (Type    |              Version:  8.6.2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 > I suppose the prudent thing to do here would be to conjure up variations
 of tcSplitForAllVarBndrs and tcSplitPhiTy that don't expand type synonyms?

 Actually I think it would suffice simply to put this `check_type` equation
 (the one you cite in comment:2) last, after the one for `TyConApp`.  The
 latter does the right thing for synonyms, and expands them.

 Oh, the `FunTy` case should still follow the moved equation; consider `t1
 => t2`.

 Would you like to try that?  Thanks!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15954#comment:3>
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