[GHC] #14266: AllowAmbiguousTypes doesn't play well with default class methods

[GHC]

#14266: AllowAmbiguousTypes doesn't play well with default class methods
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        Reporter:  chris-martin      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      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 RyanGlScott):

 I'm incredibly confused. We seem to be talking about two different issues
 here:

 * The fact that `InstanceSigs`' "more-general-than" check gets confused
 when `AllowAmbiguousTypes` comes into play. That is indeed a perplexing
 issue, and I can't offer a suggestion on how to fix it. But it's a
 distraction, since I was only using `InstanceSigs` to motivate the
 original issue, which is...
 * `DefaultSignatures` gets confused when interacting with
 `AllowAmbiguousTypes`. We needn't bother with any sort of "more-general-
 than" check here, because `DefaultSignatures` emits code that doesn't use
 any instance signatures, right?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14266#comment:13>
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