https://issues.dlang.org/show_bug.cgi?id=13477

          Issue ID: 13477
           Summary: std.process should ignore unnamed service variables on
                    Windows
           Product: D
           Version: D2
          Hardware: All
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Phobos
          Assignee: nobody@puremagic.com
          Reporter: thecybershadow@gmail.com

Windows uses the environment block to keep track of the individual drives' current directories (to allow the command "X:" to return to drive X's current directory). These service variables can be seen in the output of the "set" command:

C:\> set
=C:=C:\
=D:=D:\Downloads
...

std.process.environment.toAA() should, however, ignore them, since:

1) Only one such variable will be stored (with an empty name), as since they
have the same name, previous values will be overwritten in the AA.
2) Setting them results an error, which unnecessarily complicates saving and
restoring the entire environment.

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