gh-117941: Reject option names starting with "--no-" in argparse.BooleanOptionalAction (GH-125894)

They never worked correctly.

Author: serhiy-storchaka

Lib/argparse.py

@@ -863,6 +863,9 @@ def __init__(self,
             _option_strings.append(option_string)
 
             if option_string.startswith('--'):
+                if option_string.startswith('--no-'):
+                    raise ValueError(f'invalid option name {option_string!r} '
+                                     f'for BooleanOptionalAction')
                 option_string = '--no-' + option_string[2:]
                 _option_strings.append(option_string)
 

Lib/test/test_argparse.py

@@ -789,6 +789,13 @@ def test_const(self):
 
         self.assertIn("got an unexpected keyword argument 'const'", str(cm.exception))
 
+    def test_invalid_name(self):
+        parser = argparse.ArgumentParser()
+        with self.assertRaises(ValueError) as cm:
+            parser.add_argument('--no-foo', action=argparse.BooleanOptionalAction)
+        self.assertEqual(str(cm.exception),
+                         "invalid option name '--no-foo' for BooleanOptionalAction")
+
 class TestBooleanOptionalActionRequired(ParserTestCase):
     """Tests BooleanOptionalAction required"""
 

Misc/NEWS.d/next/Library/2024-10-23-20-44-30.gh-issue-117941.Y9jdlW.rst

@@ -0,0 +1,2 @@
+:class:`!argparse.BooleanOptionalAction` now rejects option names starting
+with ``--no-``.