[GHC] #12784: Typechecker regression in GHC 8.0.2 involving DefaultSignatures

[GHC]

#12784: Typechecker regression in GHC 8.0.2 involving DefaultSignatures
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #12918            |  Differential Rev(s):  Phab:D2682
       Wiki Page:                    |
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Comment (by rwbarton):

 By the way it seems I was pretty far off in my estimation of how frequent
 this pattern is in user code (it even showed up on StackOverflow);
 RyanGlScott if you want to add some minimal example of this issue to the
 release notes I'd be in favor of that after all.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12784#comment:24>
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