[GHC] #15122: GHC HEAD typechecker regression involving overlapping instances

[GHC]

#15122: GHC HEAD typechecker regression involving overlapping instances
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        Reporter:  fmixing           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * cc: goldfire (added)


Comment:

 This regression was introduced in commit
 e3dbb44f53b2f9403d20d84e27f187062755a089 (Fix #12919 by making the
 flattener homegeneous.).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15122#comment:5>
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