[GHC] #15778: GHC HEAD-only panic (zonkTcTyVarToTyVar)

[GHC]

#15778: GHC HEAD-only panic (zonkTcTyVarToTyVar)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.8.1
       Component:  Compiler (Type    |              Version:  8.7
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
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 Simon Peyton Jones <simonpj@…>):

 In [changeset:"29978ef1f834d77dc31bf7054590d526d068df7e/ghc" 29978ef/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="29978ef1f834d77dc31bf7054590d526d068df7e"
 Remove a zonkTcTyVarToTyVar

 This patch fixes Trac #15778 by removing a zonkTcTyVarToTyVar
 from tcHsSigType.

 Nww that a pattern-bound type variable can refer to a type, it's
 obvoiusly wrong to expect it to be a TyVar!  Moreover, that zonk
 is entirely unnecessary.

 I added a new Note [Type variables in the type environment]
 in TcRnTypes
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15778#comment:6>
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