From 7c42ba232ab03a7bb2378f452dab34e6956b3206 Mon Sep 17 00:00:00 2001
From: Daniel Mach <daniel.mach@suse.com>
Date: Wed, 21 Feb 2024 14:58:04 +0100
Subject: [PATCH] gh-96310: Fix a traceback in argparse when all options in a
 mutually exclusive group are suppressed (GH-96311)

Reproducer depends on terminal size - the traceback occurs when there's
an option long enough so the usage line doesn't fit the terminal width.
Option order is also important for reproducibility.

Excluding empty groups (with all options suppressed) from inserts
fixes the problem.
---
 Lib/argparse.py                               |  2 ++
 Lib/test/test_argparse.py                     | 21 +++++++++++++++++++
 ...2-08-26-15-50-53.gh-issue-96310.0NssDh.rst |  2 ++
 3 files changed, 25 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2022-08-26-15-50-53.gh-issue-96310.0NssDh.rst

diff --git a/Lib/argparse.py b/Lib/argparse.py
index ea39d26687b9314..f86658baf7f2bac 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -413,6 +413,8 @@ def _format_actions_usage(self, actions, groups):
                             suppressed_actions_count += 1
 
                     exposed_actions_count = group_action_count - suppressed_actions_count
+                    if not exposed_actions_count:
+                        continue
 
                     if not group.required:
                         if start in inserts:
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 65fd9cf1a4a567a..617b1721f3dbb1c 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -2864,6 +2864,27 @@ def test_help(self):
               '''
         self.assertEqual(parser.format_help(), textwrap.dedent(expected))
 
+    def test_help_subparser_all_mutually_exclusive_group_members_suppressed(self):
+        self.maxDiff = None
+        parser = ErrorRaisingArgumentParser(prog='PROG')
+        commands = parser.add_subparsers(title="commands", dest="command")
+        cmd_foo = commands.add_parser("foo")
+        group = cmd_foo.add_mutually_exclusive_group()
+        group.add_argument('--verbose', action='store_true', help=argparse.SUPPRESS)
+        group.add_argument('--quiet', action='store_true', help=argparse.SUPPRESS)
+        longopt = '--' + 'long'*32
+        longmeta = 'LONG'*32
+        cmd_foo.add_argument(longopt)
+        expected = f'''\
+            usage: PROG foo [-h]
+                            [{longopt} {longmeta}]
+
+            options:
+              -h, --help            show this help message and exit
+              {longopt} {longmeta}
+              '''
+        self.assertEqual(cmd_foo.format_help(), textwrap.dedent(expected))
+
     def test_empty_group(self):
         # See issue 26952
         parser = argparse.ArgumentParser()
diff --git a/Misc/NEWS.d/next/Library/2022-08-26-15-50-53.gh-issue-96310.0NssDh.rst b/Misc/NEWS.d/next/Library/2022-08-26-15-50-53.gh-issue-96310.0NssDh.rst
new file mode 100644
index 000000000000000..f8efb0002e104a4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-08-26-15-50-53.gh-issue-96310.0NssDh.rst
@@ -0,0 +1,2 @@
+Fix a traceback in :mod:`argparse` when all options in a mutually exclusive
+group are suppressed.