Fix Windows subprocess calls with cwd are broken

Signed-off-by: Bernát Gábor <bgabor8@bloomberg.net>

docs/changelog/1982.bugfix.rst

@@ -1 +1 @@
-Bump embeded setuptools from ``50.3.0`` to ``50.3.1`` - by :user:`gaborbernat`.
+Bump embedded setuptools from ``50.3.0`` to ``50.3.1`` - by :user:`gaborbernat`.

docs/changelog/1983.bugfix.rst

@@ -0,0 +1 @@
+After importing virtualenv passing cwd to a subprocess calls breaks with ``invalid directory`` - by :user:`gaborbernat`.

src/virtualenv/util/subprocess/_win_subprocess.py

@@ -107,13 +107,19 @@ def CreateProcess(
         wenv = (c_wchar * len(env))()
         wenv.value = env
 
+    wcwd = None
+    if cwd is not None:
+        cwd = unicode(cwd) + unicode("\0")
+        wcwd = (c_wchar * len(cwd))()
+        wcwd.value = cwd
+
     pi = PROCESS_INFORMATION()
     creation_flags |= CREATE_UNICODE_ENVIRONMENT
 
     if CreateProcessW(
         executable, args, None, None,
         inherit_handles, creation_flags,
-        wenv, cwd, byref(si), byref(pi),
+        wenv, wcwd, byref(si), byref(pi),
     ):
         return (
             DUMMY_HANDLE(pi.hProcess), DUMMY_HANDLE(pi.hThread),

tests/unit/test_util.py

@@ -1,5 +1,11 @@
 from __future__ import absolute_import, unicode_literals
 
+import subprocess
+import sys
+
+import pytest
+
+from virtualenv.info import IS_WIN, PY2
 from virtualenv.util.subprocess import run_cmd
 
 
@@ -8,3 +14,8 @@ def test_run_fail(tmp_path):
     assert err
     assert not out
     assert code
+
+
+@pytest.mark.skipif(not (PY2 and IS_WIN), reason="subprocess patch only applied on Windows python2")
+def test_windows_py2_cwd_works(tmp_path):
+    subprocess.check_call([sys.executable, "-c", "print(1)"], cwd=str(tmp_path))