[GHC] #12494: Implementation of setenv in base incorrectly claims empty environment variable not supported on Windows

[GHC]

#12494: Implementation of setenv in base incorrectly claims empty environment
variable not supported on Windows
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        Reporter:  ezyang            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by adamgundry):

 I'm inclined to agree that we could just change this, and mention in the
 new docs that the function had different behaviour in older versions of
 `base`. While we're at it, perhaps it is worth explicitly documenting the
 fact that `setEnv` is not thread safe? This may be obvious to others, but
 it wasn't to me, and has been causing segfaults in a production Haskell
 application.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12494#comment:7>
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