[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):

 Inserting a call to `checkValidTheta` after the theta has been zonked (in
 `tcPolyInfer`) indeed does the job but I can't solve one problem.
 `checkValidTheta` requires `UserTypeCtxt` parameter. I assume that in this
 case the value should be `InfSigCtxt`, since we are dealing with inferred
 signature. The problem is that `InfSigCtxt` requires name of function for
 which the type has been inferred. This information doesn't seem to be
 easily available inside `tcPolyInfer`. I noticed that the name is stored
 inside `name_taus` so I did a hack that calls `checkValidTheta (InfSigCtxt
 (fst . head $ name_taus)) theta`. In this particular case it works because
 `fold` name is stored as first in the list. But I don't know what is a
 general solution for finding name of function for which we are inferring
 the signature.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8883#comment:10>
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