[GHC] #15438: Misleading error message for higher rank type

[GHC]

#15438: Misleading error message for higher rank type
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      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 Simon Peyton Jones <simonpj@…>):

 In [changeset:"12c0f03a66bcd978bda6472384ddc0348c5a1d7a/ghc"
 12c0f03a/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="12c0f03a66bcd978bda6472384ddc0348c5a1d7a"
 Set GenSigCtxt for the argument part of tcSubType

 The reason for this change is described in TcUnify
 Note [Settting the argument context], and Trac #15438.

 The only effect is on error messages, where it stops GHC
 reporting an outright falsity (about the type signature for
 a function) when it finds an errors in a higher-rank situation.

 The testsuite changes in this patch illustrate the problem.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15438#comment:1>
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