[GHC] #14880: GHC panic: updateRole

[GHC]

#14880: GHC panic: updateRole
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        Reporter:  RyanGlScott       |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15076            |  Differential Rev(s):  Phab:D4769
       Wiki Page:                    |
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Comment (by RyanGlScott):

 `poly_merge1` is likely coming from the `mergeWithKey'` function from
 `Data.IntMap` (which `unionVarSet` is implemented in terms of), as it has
 a helper function named `merge1`. The question, I suppose, is //which//
 use(s) of `unionVarSet` are problematic. There are at least a couple new
 uses of `unionVarSet` in Phab:D4769:

 * In `mapUnionVarSetSet`, which is used in the pivotal `closeOverKinds`
 function
 * Directly in `closeOverKinds` itself
 * In `nonDetCmpTypes`

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:45>
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