[GHC] #5392: Warnings about impossible MPTCs would be nice

[GHC]

#5392: Warnings about impossible MPTCs would be nice
-------------------------------------+-------------------------------------
              Reporter:  pumpkin     |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:  7.10.1
              Priority:  normal      |          Version:  7.0.4
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  Incorrect   |  Related Tickets:
  warning at compile-time            |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
Changes (by thomie):

 * difficulty:   => Unknown
 * failure:  None/Unknown => Incorrect warning at compile-time


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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5392#comment:4>
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