[GHC] #15412: "Instance head is not headed by a class" when `Constraint` replaced with `type C = Constraint`

[GHC]

#15412: "Instance head is not headed by a class" when `Constraint` replaced with
`type C = Constraint`
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  testsuite/tests/typecheck/should_compile/T15412
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by simonpj):

 * status:  new => merge
 * testcase:   => testsuite/tests/typecheck/should_compile/T15412


Comment:

 Wow, that was bad!  Thank you for reporting; now fixed.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15412#comment:5>
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