[GHC] #15290: QuantifiedConstraints: panic "addTcEvBind NoEvBindsVar"

[GHC]

#15290: QuantifiedConstraints: panic "addTcEvBind NoEvBindsVar"
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
                                     |  QuantifiedConstraints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:  9123, 14883
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Wait, you're saying that deriving classes with methods that use higher-
 rank types will no longer work? If so, that is going to break enormous
 swaths of code both in the wild and in the test suite (see
 [http://git.haskell.org/ghc.git/blob/3048a87a3f2ef97d9f6559064d7a32ec7566542b:/testsuite/tests/deriving/should_compile/T8631.hs#l14
 here] for one example).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15290#comment:8>
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