[GHC] #10118: No ambiguity check when `ConstrainedClassMethods` is on

[GHC]

#10118: No ambiguity check when `ConstrainedClassMethods` is on
-------------------------------------+-------------------------------------
              Reporter:  thomie      |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:  7.12.1
             Component:  Compiler    |           Version:  7.10.1-rc2
  (Type checker)                     |  Operating System:  Unknown/Multiple
              Keywords:              |   Type of failure:  None/Unknown
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:  #7854
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 The following program is wrongfully accepted when
 `ConstrainedClassMethods` is on:

 {{{#!hs
 module ShouldFail where
 class Foo a where
   op :: Eq b => a -> Int
 }}}

 I have a fix.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10118>
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