[GHC] #11525: Using a dummy typechecker plugin causes an ambiguity check error

[GHC]

#11525: Using a dummy typechecker plugin causes an ambiguity check error
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        Reporter:  jme               |                Owner:  darchon
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.0.3
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |             Keywords:
      Resolution:                    |  UndecidableSuperClasses, plugin
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:  T11525
      Blocked By:                    |             Blocking:
 Related Tickets:  #12780            |  Differential Rev(s):  Phab:D3105
       Wiki Page:                    |
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Changes (by bgamari):

 * status:  new => merge
 * milestone:  8.2.1 => 8.0.3


Comment:

 If we do a 8.0.3 it would likely be worthwhile trying to backport this
 since it's a regression.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11525#comment:13>
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