[GHC] #16146: Trivial partial type signature kills type inference in the presence of GADTs

[GHC]

#16146: Trivial partial type signature kills type inference in the presence of
GADTs
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Well I suppose we could have a different typing rule for the case where
 there is no quantification.  I'm not very keen on this, because it changes
 behaviour in a subtle way, and just adding an unrelated quantifier to the
 partial signature would completely change its typing rule.

 It's user-facing, so perhaps GHC-proposal-worthy?

 The relevant function is `tcExprSig`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16146#comment:4>
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