[GHC] #11224: Program doesn't preserve semantics after pattern synonym inlining.

[GHC]

#11224: Program doesn't preserve semantics after pattern synonym inlining.
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        Reporter:  anton.dubovik     |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Windows           |         Architecture:  x86_64
 Type of failure:  Incorrect result  |  (amd64)
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 I think the problem is in this part of `tcTySig`

 {{{
        ; let (_, pat_ty) = tcSplitFunTys ty'
              univ_set = tyCoVarsOfType pat_ty
              (univ_tvs, ex_tvs) = partition (`elemVarSet` univ_set) qtvs'
 }}}

 Maybe the correct solution is to avoid splitting tyvars into ex/univ at
 this stage as it's impossible to tell which they are without looking at
 the pattern.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11224#comment:5>
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