gh-101979: argparse: fix a bug where parentheses in metavar argument of add_argument() were dropped (GH-102318)

(cherry picked from commit 9a478be1a4)

Co-authored-by: Yeojin Kim <yeojin.dev@gmail.com>

Lib/argparse.py

@@ -400,10 +400,18 @@ class HelpFormatter(object):
             except ValueError:
                 continue
             else:
-                end = start + len(group._group_actions)
+                group_action_count = len(group._group_actions)
+                end = start + group_action_count
                 if actions[start:end] == group._group_actions:
+
+                    suppressed_actions_count = 0
                     for action in group._group_actions:
                         group_actions.add(action)
+                        if action.help is SUPPRESS:
+                            suppressed_actions_count += 1
+
+                    exposed_actions_count = group_action_count - suppressed_actions_count
+
                     if not group.required:
                         if start in inserts:
                             inserts[start] += ' ['
@@ -413,7 +421,7 @@ class HelpFormatter(object):
                             inserts[end] += ']'
                         else:
                             inserts[end] = ']'
-                    else:
+                    elif exposed_actions_count > 1:
                         if start in inserts:
                             inserts[start] += ' ('
                         else:
@@ -487,7 +495,6 @@ class HelpFormatter(object):
         text = _re.sub(r'(%s) ' % open, r'\1', text)
         text = _re.sub(r' (%s)' % close, r'\1', text)
         text = _re.sub(r'%s *%s' % (open, close), r'', text)
-        text = _re.sub(r'\(([^|]*)\)', r'\1', text)
         text = text.strip()
 
         # return the text

Lib/test/test_argparse.py

@@ -3729,6 +3729,28 @@ class TestHelpUsage(HelpTestCase):
     version = ''
 
 
+class TestHelpUsageWithParentheses(HelpTestCase):
+    parser_signature = Sig(prog='PROG')
+    argument_signatures = [
+        Sig('positional', metavar='(example) positional'),
+        Sig('-p', '--optional', metavar='{1 (option A), 2 (option B)}'),
+    ]
+
+    usage = '''\
+        usage: PROG [-h] [-p {1 (option A), 2 (option B)}] (example) positional
+        '''
+    help = usage + '''\
+
+        positional arguments:
+          (example) positional
+
+        options:
+          -h, --help            show this help message and exit
+          -p {1 (option A), 2 (option B)}, --optional {1 (option A), 2 (option B)}
+        '''
+    version = ''
+
+
 class TestHelpOnlyUserGroups(HelpTestCase):
     """Test basic usage messages"""
 

Misc/NEWS.d/next/Library/2023-02-28-09-52-25.gh-issue-101979.or3hXV.rst

@@ -0,0 +1,2 @@
+Fix a bug where parentheses in the ``metavar`` argument to :meth:`argparse.ArgumentParser.add_argument` were
+dropped. Patch by Yeojin Kim.