[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)
-------------------------------------+-------------------------------------
        Reporter:  niteria           |                Owner:  mpickering
            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:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3065,
       Wiki Page:                    |  Phab:D3064
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"3cfef763ab6ccd23f72604e5ee2f027a4b6ce043/ghc"
 3cfef763/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="3cfef763ab6ccd23f72604e5ee2f027a4b6ce043"
 Kill inaccessible-branch complaints in record update

 Trac #12957 (the original case in the Description) showed a record
 update that yielded an "inaccessible code" warning. This should not
 happen; it's just some redundant code generated by the desugarer (later
 pruned away) and it's not the user's fault.

 This patch suppresses the warning.  See Check.hs
 Note [Inaccessible warnings for record updates]
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12957#comment:12>
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