[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:  Tritlo
            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 Tritlo):

 I'm on a branch based on 973ff4a142e77e247caebf828aa51f9810394938, with
 the changes from b202e7a48401bd8e805a92dcfe5ea059cbd8e41c on top. In
 b202e7a4, I remove the call to  `tcTyVarLevel`, which was calling
 `tcTyVarDetails` and causing the original panic. I suspect
 af624071fa063158d6e963e171280676f9c0a0b0, which I believe changes the
 `hole{co_a1wi} {0}:: y_a1vM[sk:1] GHC.Prim.~# x_a1vL[sk:1]` constraint
 that was causing the crash. I'll check to confirm.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15370#comment:6>
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