gh-148402: add missing stacklevel to warnings.warn() in subprocess.Popen

Add stacklevel to two warnings.warn() calls in subprocess.Popen so that
warnings point to the caller's code instead of subprocess.py internals:

- POSIX path (__init__): stacklevel=2
- Windows path (_execute_child): stacklevel=3 (extra frame depth)

Add regression tests that assert warning.filename == __file__.

Author: stef41

Lib/subprocess.py

@@ -912,7 +912,7 @@ def __init__(self, args, bufsize=-1, executable=None,
         else:
             # POSIX
             if pass_fds and not close_fds:
-                warnings.warn("pass_fds overriding close_fds.", RuntimeWarning)
+                warnings.warn("pass_fds overriding close_fds.", RuntimeWarning, stacklevel=2)
                 close_fds = True
             if startupinfo is not None:
                 raise ValueError("startupinfo is only supported on Windows "
@@ -1567,7 +1567,8 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
                 if handle_list:
                     if not close_fds:
                         warnings.warn("startupinfo.lpAttributeList['handle_list'] "
-                                      "overriding close_fds", RuntimeWarning)
+                                      "overriding close_fds", RuntimeWarning,
+                                      stacklevel=3)
 
                     # When using the handle_list we always request to inherit
                     # handles but the only handles that will be inherited are

Lib/test/test_subprocess.py

@@ -3177,6 +3177,18 @@ def test_pass_fds(self):
                         close_fds=False, pass_fds=(fd, )))
             self.assertIn('overriding close_fds', str(context.warning))
 
+    def test_pass_fds_overriding_close_fds_warning_location(self):
+        # gh-148402: the warning should point to the caller, not subprocess.py
+        fd = os.dup(1)
+        self.addCleanup(os.close, fd)
+        os.set_inheritable(fd, True)
+        with self.assertWarns(RuntimeWarning) as context:
+            p = subprocess.Popen(ZERO_RETURN_CMD,
+                                 close_fds=False, pass_fds=(fd,))
+            p.wait()
+        self.assertIn('overriding close_fds', str(context.warning))
+        self.assertEqual(context.filename, __file__)
+
     def test_pass_fds_inheritable(self):
         script = support.findfile("fd_status.py", subdir="subprocessdata")
 
@@ -3762,8 +3774,7 @@ def test_close_fds_with_stdio(self):
         self.assertIn(b"OSError", stderr)
 
         # Check for a warning due to using handle_list and close_fds=False
-        with warnings_helper.check_warnings((".*overriding close_fds",
-                                             RuntimeWarning)):
+        with self.assertWarns(RuntimeWarning) as context:
             startupinfo = subprocess.STARTUPINFO()
             startupinfo.lpAttributeList = {"handle_list": handles[:]}
             p = subprocess.Popen([sys.executable, "-c",
@@ -3772,6 +3783,9 @@ def test_close_fds_with_stdio(self):
                                  startupinfo=startupinfo, close_fds=False)
             stdout, stderr = p.communicate()
             self.assertEqual(p.returncode, 0)
+        self.assertIn('overriding close_fds', str(context.warning))
+        # gh-148402: warning should point to the caller, not subprocess.py
+        self.assertEqual(context.filename, __file__)
 
     def test_empty_attribute_list(self):
         startupinfo = subprocess.STARTUPINFO()

Misc/NEWS.d/next/Library/2026-04-11-14-28-56.gh-issue-148402.zey6m1.rst

@@ -0,0 +1,3 @@
+Add missing ``stacklevel`` to two :func:`warnings.warn` calls in
+:class:`subprocess.Popen` so that warnings correctly point to the caller's
+code instead of ``subprocess.py`` internals.