[GHC] #8958: Allow role inference on datatype contexts

[GHC]

#8958: Allow role inference on datatype contexts
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        Reporter:  goldfire          |            Owner:  goldfire
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.1-rc2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by Richard Eisenberg <eir@…>):

 In [changeset:"d468cd376ffc02cf9f4755275a316be914c482be/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="d468cd376ffc02cf9f4755275a316be914c482be"
 Fix #8958.

 We now do role inference on stupid datatype contexts, allowing a
 lightweight role annotation syntax.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8958#comment:1>
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