[GHC] #7854: Constrained method type accepted in Haskell 98 mode

[GHC]

#7854: Constrained method type accepted in Haskell 98 mode
-------------------------------------+-------------------------------------
        Reporter:  refold            |                   Owner:  thomie
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler (Type    |                 Version:  7.6.3
  checker)                           |                Keywords:  newcomer
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |  typechecker/should_fail/T7854
 Related Tickets:  #10118, #10119    |                Blocking:
                                     |  Differential Revisions:  Phab:D688
-------------------------------------+-------------------------------------
Changes (by thomie):

 * status:  new => patch
 * testcase:   => typechecker/should_fail/T7854
 * differential:   => Phab:D688
 * related:   => #10118, #10119


Comment:

 Patches are ready for review in Phab:D686, Phab:D687 and Phab:D688.

 Instead of deprecating `ConstrainedClassMethods`, I have tried fixing it
 instead. Phab:D688 turns on `ConstrainedClassMethods` for all modes
 (Haskell98, Haskell2010 and default), to not break any programs. I added a
 section to "Known bugs and infelicities".

 Existing tests `tcfail149` and `tcfail150` have been reenabled, and I
 added `T7854` for the `MultiParamTypeClasses` case.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7854#comment:10>
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