[GHC] #10642: Coercible regression from 7.10 to HEAD

[GHC]

#10642: Coercible regression from 7.10 to HEAD
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        Reporter:  darchon           |                   Owner:  goldfire
            Type:  bug               |                  Status:  closed
        Priority:  highest           |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.11
      Resolution:  fixed             |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |               Test Case:
      Blocked By:                    |  typecheck/should_compile/T10642
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by goldfire):

 For reasons I'm not quite sure of (performance, probably), the following
 classes are always derived using GND when derived for newtypes: `Eq`,
 `Ord`, `Ix`, `Bounded`. This is true in a file with no extensions enabled.
 I don't know precisely why `Eq` didn't trigger this bug, but it wasn't
 worth exploring.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10642#comment:6>
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