[3.11] gh-109475: Fix support of explicit option value "--" in argparse (GH-114814) (GH-115037)

For example "--option=--".
(cherry picked from commit 4aa4f0906d)

Lib/argparse.py

@@ -2464,7 +2464,7 @@ def parse_known_intermixed_args(self, args=None, namespace=None):
     # ========================
     def _get_values(self, action, arg_strings):
         # for everything but PARSER, REMAINDER args, strip out first '--'
-        if action.nargs not in [PARSER, REMAINDER]:
+        if not action.option_strings and action.nargs not in [PARSER, REMAINDER]:
             try:
                 arg_strings.remove('--')
             except ValueError:

Lib/test/test_argparse.py

@@ -5272,6 +5272,23 @@ def test_mixed(self):
         self.assertEqual(NS(v=3, spam=True, badger="B"), args)
         self.assertEqual(["C", "--foo", "4"], extras)
 
+    def test_double_dash(self):
+        parser = argparse.ArgumentParser()
+        parser.add_argument('-f', '--foo', nargs='*')
+        parser.add_argument('bar', nargs='*')
+
+        args = parser.parse_args(['--foo=--'])
+        self.assertEqual(NS(foo=['--'], bar=[]), args)
+        args = parser.parse_args(['--foo', '--'])
+        self.assertEqual(NS(foo=[], bar=[]), args)
+        args = parser.parse_args(['-f--'])
+        self.assertEqual(NS(foo=['--'], bar=[]), args)
+        args = parser.parse_args(['-f', '--'])
+        self.assertEqual(NS(foo=[], bar=[]), args)
+        args = parser.parse_args(['--foo', 'a', 'b', '--', 'c', 'd'])
+        self.assertEqual(NS(foo=['a', 'b'], bar=['c', 'd']), args)
+
+
 # ===========================
 # parse_intermixed_args tests
 # ===========================

Misc/NEWS.d/next/Library/2024-01-31-20-07-11.gh-issue-109475.lmTb9S.rst

@@ -0,0 +1,2 @@
+Fix support of explicit option value "--" in :mod:`argparse` (e.g.
+``--option=--``).