[GHC] #8651: 'Untouchable' error when using type function in class constraint in rank-2 type

[GHC]

#8651: 'Untouchable' error when using type function in class constraint in rank-2
type
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        Reporter:  sbarclay                 |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler (Type checker)  |          Version:  7.7
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  None/Unknown             |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:  #8644
                                            |  #7594
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"5d2fb2ee94fea4cf62ba767eb1555e42f4f21f46/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="5d2fb2ee94fea4cf62ba767eb1555e42f4f21f46"
 Further refine the test for 'given' equalities

 Trac #8651 revealed that my previous fix (itself in response to #8644)
 wasn't quite right.  The plan, using the CtOrigin to identify
 constraints arising from flattening, is described in TcSimplify,
 Note [When does an implication have given equalities?]
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8651#comment:1>
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