[GHC] #15918: GHC panic from QuantifiedConstraints(?)

[GHC]

#15918: GHC panic from QuantifiedConstraints(?)
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.10.1
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
                                     |  QuantifiedConstraints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  quantified-
                                     |  constraints/T15918
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |  https://gitlab.haskell.org/ghc/ghc/merge_requests/489
-------------------------------------+-------------------------------------
Changes (by simonpj):

 * status:  closed => new
 * resolution:  fixed =>


Comment:

 Actually on second thoughts I cannot recall our Plan for `mkCastTy`, so
 I'm not sure this problem is truly fixed. Maybe it's just harder to
 trigger now!  Let's see what Richard remembers.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15918#comment:16>
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