[GHC] #12957: In a record-update construct:ghc-stage2: panic! (the 'impossible' happened)

[GHC]

#12957: In a record-update construct:ghc-stage2: panic! (the 'impossible' happened)
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        Reporter:  niteria           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 It is unfortunate the compiler doesn't throw a type error earlier. The
 warning comes from the desugaring of the record update so it would still
 be difficult for users to act upon.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12957#comment:2>
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