gh-90872: Fix subprocess.Popen.wait() for negative timeout

Lib/subprocess.py

@@ -1586,6 +1586,8 @@ def _wait(self, timeout):
             """Internal implementation of wait() on Windows."""
             if timeout is None:
                 timeout_millis = _winapi.INFINITE
+            elif timeout <= 0:
+                timeout_millis = 0
             else:
                 timeout_millis = int(timeout * 1000)
             if self.returncode is None:

Lib/test/test_subprocess.py

@@ -1607,6 +1607,22 @@ def test_class_getitems(self):
         self.assertIsInstance(subprocess.Popen[bytes], types.GenericAlias)
         self.assertIsInstance(subprocess.CompletedProcess[str], types.GenericAlias)
 
+    @unittest.skipUnless(hasattr(subprocess, '_winapi'),
+                         'need subprocess._winapi')
+    def test_wait_negative_timeout(self):
+        proc = subprocess.Popen(ZERO_RETURN_CMD)
+        with proc:
+            patch = mock.patch.object(
+                subprocess._winapi,
+                'WaitForSingleObject',
+                return_value=subprocess._winapi.WAIT_OBJECT_0)
+            with patch as mock_wait:
+                proc.wait(-1)  # negative timeout
+                mock_wait.assert_called_once_with(proc._handle, 0)
+                proc.returncode = None
+
+            self.assertEqual(proc.wait(), 0)
+
 
 class RunFuncTestCase(BaseTestCase):
     def run_python(self, code, **kwargs):

Misc/NEWS.d/next/Library/2024-03-19-11-08-26.gh-issue-90872.ghys95.rst

@@ -0,0 +1,3 @@
+On Windows, :meth:`subprocess.Popen.wait` no longer calls
+``WaitForSingleObject()`` with a negative timeout: pass ``0`` ms if the
+timeout is negative. Patch by Victor Stinner.