[GHC] #14270: GHC HEAD's ghc-stage1 panics on Data.Typeable.Internal

[GHC]

#14270: GHC HEAD's ghc-stage1 panics on Data.Typeable.Internal
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        Reporter:  hvr               |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14236            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Ahh, I see what is going on here: When `Unify.unify_ty` needs to match a
 type `CastTy ty co` with something else, it doesn't even attempt to match
 `co` (on account of `Note [Matching in the presence of casts]`). Instead,
 it simply matches `ty` (adjusting the kind coercion accordingly).
 Consequently, template variables that occur only in `co` will never be
 matched.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14270#comment:5>
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