bpo-29298: Fix crash with required subparsers without dest (GH-3680) (GH-27303)

(cherry picked from commit 17575f73ce2cb9f3a4eb4cc416c690f9a4e7205c)

Co-authored-by: Anthony Sottile <asottile@umich.edu>

2 files changed, 26 insertions, 0 deletions

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 8a12dea..e3a49e7 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -727,6 +727,8 @@ def _get_action_name(argument):
         return argument.metavar
     elif argument.dest not in (None, SUPPRESS):
         return argument.dest
+    elif argument.choices:
+        return '{' + ','.join(argument.choices) + '}'
     else:
         return None
 
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 4d0316f..0994e70 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -2060,6 +2060,30 @@ class TestAddSubparsers(TestCase):
         ret = parser.parse_args(())
         self.assertIsNone(ret.command)
 
+    def test_required_subparsers_no_destination_error(self):
+        parser = ErrorRaisingArgumentParser()
+        subparsers = parser.add_subparsers(required=True)
+        subparsers.add_parser('foo')
+        subparsers.add_parser('bar')
+        with self.assertRaises(ArgumentParserError) as excinfo:
+            parser.parse_args(())
+        self.assertRegex(
+            excinfo.exception.stderr,
+            'error: the following arguments are required: {foo,bar}\n$'
+        )
+
+    def test_wrong_argument_subparsers_no_destination_error(self):
+        parser = ErrorRaisingArgumentParser()
+        subparsers = parser.add_subparsers(required=True)
+        subparsers.add_parser('foo')
+        subparsers.add_parser('bar')
+        with self.assertRaises(ArgumentParserError) as excinfo:
+            parser.parse_args(('baz',))
+        self.assertRegex(
+            excinfo.exception.stderr,
+            r"error: argument {foo,bar}: invalid choice: 'baz' \(choose from 'foo', 'bar'\)\n$"
+        )
+
     def test_optional_subparsers(self):
         parser = ErrorRaisingArgumentParser()
         subparsers = parser.add_subparsers(dest='command', required=False)