[GHC] #12907: ExtendedDefaultRules-related regression in GHC 8.0.2

[GHC]

#12907: ExtendedDefaultRules-related regression in GHC 8.0.2
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.0.2
       Component:  Compiler (Type    |              Version:  8.0.2-rc1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2774
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * status:  new => patch
 * differential:   => Phab:D2774


Comment:

 Thanks, hvr, that section of the Haskell Report is helpful. And it's also
 nice to know that the author (goldfire) intended for this to happen. Now
 that I better understand all the actors in this production, I also agree
 that this behavior is reasonable.

 The only thing missing from
 https://git.haskell.org/ghc.git/commit/9a34bf1985035858ece043bf38b47b6ff4b88efb
 was a note in the users' guide. I've opened Phab:D2774 for this.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12907#comment:4>
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