[GHC] #13524: GHC does not preserve order of forall'd vars with TypeApplications

[GHC]

#13524: GHC does not preserve order of forall'd vars with TypeApplications
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        Reporter:  crockeea          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
                                     |  TypeApplications
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: niteria (added)


Comment:

 This regression first popped up in
 c9bcaf3165586ac214fa694e61c55eb45eb131ab (Kill varSetElemsWellScoped in
 quantifyTyVars). You can also reproduce the same error in GHC 8.0.1 by
 compiling with `-dunique-increment=-1` (after uncommenting the partial
 type signature, of course).

 cc'ing niteria, in case he has an idea of what might be happening here.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13524#comment:2>
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