SERVER-42911 Pass %APPDATA% into ENV for python subprocesses on Windows

Author: Mathew Robinson

SConstruct

@@ -1922,6 +1922,15 @@ if env.TargetOSIs('posix'):
         except KeyError:
             pass
 
+    # Python uses APPDATA to determine the location of user installed
+    # site-packages. If we do not pass this variable down to Python
+    # subprocesses then anything installed with `pip install --user`
+    # will be inaccessible leading to import errors.
+    if env.TargetOSIs('windows'):
+        appdata = os.getenv('APPDATA', None)
+        if appdata is not None:
+            env['ENV']['APPDATA'] = appdata
+
     if env.TargetOSIs('linux') and has_option( "gcov" ):
         env.Append( CCFLAGS=["-fprofile-arcs", "-ftest-coverage", "-fprofile-update=single"] )
         env.Append( LINKFLAGS=["-fprofile-arcs", "-ftest-coverage", "-fprofile-update=single"] )