gh-58572: Fix behavior when '--' as argument to option in argparse

Lib/argparse.py

@@ -1959,6 +1959,9 @@ def consume_positionals(start_index):
             for action, arg_count in zip(positionals, arg_counts):
                 args = arg_strings[start_index: start_index + arg_count]
                 start_index += arg_count
+                if action.nargs not in [PARSER, REMAINDER]:
+                    if '--' in args:
+                        args.remove('--')
                 take_action(action, args)
 
             # slice off the Positionals that we just parsed and return the
@@ -2352,13 +2355,6 @@ def parse_known_intermixed_args(self, args=None, namespace=None):
     # Value conversion methods
     # ========================
     def _get_values(self, action, arg_strings):
-        # for everything but PARSER, REMAINDER args, strip out first '--'
-        if action.nargs not in [PARSER, REMAINDER]:
-            try:
-                arg_strings.remove('--')
-            except ValueError:
-                pass
-
         # optional argument produces a default when not present
         if not arg_strings and action.nargs == OPTIONAL:
             if action.option_strings:

Lib/test/test_argparse.py

@@ -5262,6 +5262,47 @@ def test_help_with_metavar(self):
             '''))
 
 
+class TestDoubleDashRemoval(ParserTestCase):
+    """Test actions with multiple -- values"""
+
+    """argparse removed all '--'
+    a 3-2012 patch removed just the 1st -- of each positional group
+    this new patch removes just the 1st --
+    this change is most valuable when passing arg strings to another process"""
+
+    argument_signatures = [
+        Sig('-f', '--foo', help='an optional'),
+        Sig('cmd', help='a command'),
+        Sig('rest', nargs='*', help='zero or more args'),
+    ]
+    failures = ['cmd --foo bar 1 2 3', 'cmd -f1 2 3']
+    successes = [
+        ('-f1 1 -- 2 3', NS(cmd='1', foo='1', rest=['2', '3'])),
+        ('cmd -- --foo bar', NS(cmd='cmd', foo=None, rest=['--foo', 'bar'])),
+        ('cmd -- --foo -- -f2', NS(cmd='cmd', foo=None, rest=['--foo', '-f2'])),
+        ('-- --foo -- --bar 2', NS(cmd='--foo', foo=None, rest=['--bar', '2'])),
+        ('-f1 -- -- 1 -- 2', NS(cmd='--', foo='1', rest=['1', '2'])),
+        ('-- cmd -- -- --foo', NS(cmd='cmd', foo=None, rest=['--', '--foo'])),
+        ('cmd test --foo=--', NS(cmd='cmd', foo='--', rest=['test']))
+    ]
+
+
+class TestDoubleDashRemoval1(ParserTestCase):
+    """Test actions with multiple -- values, with '+' positional"""
+
+    argument_signatures = [
+        Sig('-f', '--foo', help='an optional'),
+        Sig('cmd', help='a command'),
+        Sig('rest', nargs='+', help='1 or more args'),
+    ]
+    failures = ['cmd -f1', '-f1 -- cmd', '-f1 cmd --']
+    successes = [
+        ('cmd -f1 2 3', NS(cmd='cmd', foo='1', rest=['2', '3'])),
+        ('cmd -f1 -- 2 3', NS(cmd='cmd', foo='1', rest=['2', '3'])),
+        ('-f1 -- cmd -- -f2 3', NS(cmd='cmd', foo='1', rest=['-f2', '3']))
+    ]
+
+
 def test_main():
     support.run_unittest(__name__)
     # Remove global references to avoid looking like we have refleaks.

Misc/NEWS.d/next/Library/2019-09-06-06-16-35.bpo-14364.eEtNMR.rst

@@ -0,0 +1,2 @@
+'--' should be treated as other characters when '--' is
+a part of argument.