gh-125254: Fix error report about ambiguous option in argparse (GH-125273)

This was a regression introduced in gh-58573. It was only tested for the
case when the ambiguous option is the last argument in the command line.

Author: serhiy-storchaka

Lib/argparse.py

@@ -2019,7 +2019,7 @@ def consume_optional(start_index):
             if len(option_tuples) > 1:
                 options = ', '.join([option_string
                     for action, option_string, sep, explicit_arg in option_tuples])
-                args = {'option': arg_string, 'matches': options}
+                args = {'option': arg_strings[start_index], 'matches': options}
                 msg = _('ambiguous option: %(option)s could match %(matches)s')
                 raise ArgumentError(None, msg % args)
 

Lib/test/test_argparse.py

@@ -6730,9 +6730,19 @@ def test_conflicting_mutually_exclusive_args_zero_or_more_with_metavar2(self):
     def test_ambiguous_option(self):
         self.parser.add_argument('--foobaz')
         self.parser.add_argument('--fooble', action='store_true')
+        self.parser.add_argument('--foogle')
         self.assertRaisesRegex(argparse.ArgumentError,
-                               "ambiguous option: --foob could match --foobaz, --fooble",
-                               self.parser.parse_args, ['--foob'])
+                "ambiguous option: --foob could match --foobaz, --fooble",
+            self.parser.parse_args, ['--foob'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                "ambiguous option: --foob=1 could match --foobaz, --fooble$",
+            self.parser.parse_args, ['--foob=1'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                "ambiguous option: --foob could match --foobaz, --fooble$",
+            self.parser.parse_args, ['--foob', '1', '--foogle', '2'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                "ambiguous option: --foob=1 could match --foobaz, --fooble$",
+            self.parser.parse_args, ['--foob=1', '--foogle', '2'])
 
     def test_os_error(self):
         self.parser.add_argument('file')

Misc/NEWS.d/next/Library/2024-10-10-19-57-35.gh-issue-125254.RtZxXS.rst

@@ -0,0 +1 @@
+Fix a bug where ArgumentError includes the incorrect ambiguous option in :mod:`argparse`.