[GHC] #9071: Panic with -XDeriveFunctor when deriving from a non-Functor in a separate module

[GHC]

#9071: Panic with -XDeriveFunctor when deriving from a non-Functor in a separate
module
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        Reporter:  bens                |            Owner:  simonpj
            Type:  bug                 |           Status:  new
        Priority:  normal              |        Milestone:
       Component:  Compiler            |          Version:  7.8.2
      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:"13a330e87cf459311a7f164e1e57baf877741da6/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="13a330e87cf459311a7f164e1e57baf877741da6"
 Fix Trac #9071, an egregious bug in TcDeriv.inferConstraints

 The constraints for Functor don't line up 1-1 with the arguments
 (they are fetched out from sub-terms of the type), but the surrounding
 code was mistakenly assuming they were in 1-1 association.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9071#comment:4>
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