[GHC] #15370: Typed hole panic on GHC 8.6 (tcTyVarDetails)

[GHC]

#15370: Typed hole panic on GHC 8.6 (tcTyVarDetails)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.4.3
  checker)                           |             Keywords:  TypeInType,
      Resolution:                    |  TypedHoles
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Simpler example:

 {{{#!hs
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE TypeOperators #-}
 module Bug where

 import Data.Type.Equality

 data S (a :: Either x y)

 mkRefl :: n :~: j
 mkRefl = Refl

 right :: forall (r :: Either x y).
          S r -> ()
 right no =
   case mkRefl @x @y of
     Refl -> no + _
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15370#comment:1>
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