[GHC] #8129: Constraint solver panic due to derived type function equality

[GHC]

#8129: Constraint solver panic due to derived type function equality
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        Reporter:  adamgundry               |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  high                     |        Milestone:
       Component:  Compiler (Type checker)  |          Version:  7.7
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  Compile-time crash       |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:8cfbdccb7f8716c2b6b13b3c7884f52b1087d782/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="8cfbdccb7f8716c2b6b13b3c7884f52b1087d782"
 Accommodate Derived constraints in two places (fix Trac #8129, #8134)

 If we have
    class (F a ~ b) => C a b
 then we can produce *derived* CFunEqCans.  These were not being
 treated properly in two places:

 a) in TcMType.zonkFlats (Trac #8134)
 b) in TcSMonad.prepareInertsForImplications (Trac #8129)

 This patch fixes both.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8129#comment:2>
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