[GHC] #10233: Reexporting GHC.Exts does not export Constraint

[GHC]

#10233: Reexporting GHC.Exts does not export Constraint
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              Reporter:  int-e       |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 I expected the following code

 {{{
 module T (module GHC.Exts) where

 import GHC.Exts (Constraint)
 }}}

 to reexport `Constraint`, but in fact `T` exports nothing at all.
 Explicitely exporting `Constraint` from `T` works as expected.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10233>
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