[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:  8.8.1
       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:                    |  Phab:D5141
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Comment (by simonpj):

 > Hence, we should not move the closing-over-kinds part at all, and
 instead just modify the TyVar branch of ty_co_vars_of_type so that it
 handles each variable it encounters exactly once (comment:123)

 Correct, that's what I'm suggesting.

 > I had been implementing Simon's suggestion from comment:122, and at
 least while still using mapUnionVarSet, I'm still getting regressions on 4
 tests,

 I'd be surprised if you still got regressions if you adopted the more
 efficient `closeOverKinds` from comment:122.  But (a) I've been surprised
 many times by this zombie and (b) I think comment:123 is better anyway.

 TL;DR: do comment:123.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:128>
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