[GHC] #12130: ghc: panic! (the 'impossible' happened): find_tycon Block []

[GHC]

#12130: ghc: panic! (the 'impossible' happened): find_tycon Block []
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        Reporter:  jeiea             |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.0.2
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  DisambiguateRecordFields
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:  th/T12130
      Blocked By:                    |             Blocking:
 Related Tickets:  #11228            |  Differential Rev(s):  Phab:D2321
       Wiki Page:                    |
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Changes (by adamgundry):

 * status:  new => patch
 * testcase:   => th/T12130
 * differential:   => Phab:D2321


Comment:

 Thanks for the great test case!

 It turns out this bug was lingering already in 7.10, but laziness meant we
 didn't hit the panic by sheer luck. Simple fix: replace the panic with
 `Nothing`, which is reasonable in this context: if the datacon isn't in
 scope, don't use it for disambiguating record fields.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12130#comment:3>
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