[GHC] #8883: FlexibleContexts checking should happen also on inferred signature

[GHC]

#8883: FlexibleContexts checking should happen also on inferred signature
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        Reporter:  Blaisorblade      |            Owner:  jstolarek
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      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 jstolarek):

 I finally had some time to look into this one. I traced what happens when
 the type signature is present and when it has to be inferred. I see what
 is the flow of control in both cases, but I don't understand details of
 type inference itself. From what I've observed in the latter case type
 signature for `fold` is inferred in `tcPolyKind` by calling
 `simplifyInfer` (in `TcBinds.lhs`). The question is whether the missing
 language extension should be detected *during* type inference or *after*
 type inference?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8883#comment:7>
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