[GHC] #12785: GHC panic, `tcTyVarDetails` is missing a case

[GHC]

#12785: GHC panic, `tcTyVarDetails` is missing a case
-------------------------------------+-------------------------------------
        Reporter:  heisenbug         |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Compile-time      |            Test Case:
  crash or panic                     |  typecheck/should_compile/T12785a,
                                     |  typecheck/should_fail/T12785b
      Blocked By:                    |             Blocking:
 Related Tickets:  #12590            |  Differential Rev(s):  Phab:D2931
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by RyanGlScott):

 * status:  new => closed
 * testcase:  yes => typecheck/should_compile/T12785a,
     typecheck/should_fail/T12785b
 * resolution:   => fixed
 * milestone:   => 8.2.1


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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12785#comment:14>
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