[GHC] #15772: Strange constraint error that disappears when adding another top-level declaration

[GHC]

#15772: Strange constraint error that disappears when adding another top-level
declaration
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        Reporter:  kosmikus          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.6.1
  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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Comment (by RyanGlScott):

 I think your hunch about `Note [FunEq occurs-check principle]` is right on
 the mark, since commit 1eec1f21268af907f59b5d5c071a9a25de7369c7 (`Another
 major constraint-solver refactoring`), which introduced that Note, is the
 first commit to demonstrate this bug.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15772#comment:5>
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