[GHC] #12151: GHC 8 allows ambiguous type without AllowAmbiguousTypes

[GHC]

#12151: GHC 8 allows ambiguous type without AllowAmbiguousTypes
-------------------------------------+-------------------------------------
        Reporter:  thomie            |                Owner:
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.0.2
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Incorrect         |            Test Case:
  warning at compile-time            |  typecheck/should_fail/T12151
      Blocked By:                    |             Blocking:
 Related Tickets:  #7437             |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * testcase:   => typecheck/should_fail/T12151
 * status:  new => merge
 * milestone:   => 8.0.2


Comment:

 Could merge, but only if it goes easily

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12151#comment:2>
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