bpo-36814: ensure os.posix_spawn() handles None (GH-13144)

Fix an issue where os.posix_spawn() would incorrectly raise a TypeError
when file_actions is None.

Author: tonybaloney

Lib/test/test_posix.py

@@ -1550,6 +1550,15 @@ def test_specify_environment(self):
         with open(envfile) as f:
             self.assertEqual(f.read(), 'bar')
 
+    def test_none_file_actions(self):
+        pid = self.spawn_func(
+            self.NOOP_PROGRAM[0],
+            self.NOOP_PROGRAM,
+            os.environ,
+            file_actions=None
+        )
+        self.assertEqual(os.waitpid(pid, 0), (pid, 0))
+
     def test_empty_file_actions(self):
         pid = self.spawn_func(
             self.NOOP_PROGRAM[0],

Misc/NEWS.d/next/Library/2019-05-06-23-13-26.bpo-36814.dSeMz_.rst

@@ -0,0 +1 @@
+Fix an issue where os.posix_spawnp() would incorrectly raise a TypeError when file_actions is None.

Modules/posixmodule.c

@@ -5465,7 +5465,7 @@ py_posix_spawn(int use_posix_spawnp, PyObject *module, path_t *path, PyObject *a
         goto exit;
     }
 
-    if (file_actions != NULL) {
+    if (file_actions != NULL && file_actions != Py_None) {
         /* There is a bug in old versions of glibc that makes some of the
          * helper functions for manipulating file actions not copy the provided
          * buffers. The problem is that posix_spawn_file_actions_addopen does not