Breaking change: Python nested message class __qualname__ now contains the outer message name. (Previous __qualname__ has the same result with __name__ for nested message that outer message name was not included)

example:

message Foo {
  message Bar {
    bool bool_field = 1;
  }
}
nested = test_pb2.Foo.Bar()
self.assertEqual('Bar', nested.__class__.__name__)
self.assertEqual('Foo.Bar', nested.__class__.__qualname__) # It was 'Bar' before
PiperOrigin-RevId: 695817876

csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs

@@ -1,17 +0,0 @@
-#region Copyright notice and license
-// Protocol Buffers - Google's data interchange format
-// Copyright 2008 Google Inc.  All rights reserved.
-//
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file or at
-// https://developers.google.com/open-source/licenses/bsd
-#endregion
-
-namespace Google.Protobuf.Reflection;
-
-internal sealed partial class FeatureSetDescriptor
-{
-    // Canonical serialized form of the edition defaults, generated by embed_edition_defaults.
-    private const string DefaultsBase64 =
-        "ChMYhAciACoMCAEQAhgCIAMoATACChMY5wciACoMCAIQARgBIAIoATABChMY6AciDAgBEAEYASACKAEwASoAIOYHKOgH";
-}

python/google/protobuf/internal/builder.py

@@ -54,12 +54,13 @@ def BuildTopDescriptorsAndMessages(file_des, module_name, module):
     module: Generated _pb2 module
   """
 
-  def BuildMessage(msg_des):
+  def BuildMessage(msg_des, prefix):
     create_dict = {}
     for (name, nested_msg) in msg_des.nested_types_by_name.items():
-      create_dict[name] = BuildMessage(nested_msg)
+      create_dict[name] = BuildMessage(nested_msg, prefix + msg_des.name + '.')
     create_dict['DESCRIPTOR'] = msg_des
     create_dict['__module__'] = module_name
+    create_dict['__qualname__'] = prefix + msg_des.name
     message_class = _reflection.GeneratedProtocolMessageType(
         msg_des.name, (_message.Message,), create_dict)
     _sym_db.RegisterMessage(message_class)
@@ -83,7 +84,7 @@ def BuildTopDescriptorsAndMessages(file_des, module_name, module):
 
   # Build messages.
   for (name, msg_des) in file_des.message_types_by_name.items():
-    module[name] = BuildMessage(msg_des)
+    module[name] = BuildMessage(msg_des, '')
 
 
 def AddHelpersToExtensions(file_des):

python/google/protobuf/internal/message_test.py

@@ -1337,6 +1337,18 @@ class MessageTest(unittest.TestCase):
     self.assertIn('oneof_bytes', m)
     self.assertNotIn('oneof_string', m)
 
+  def testMessageClassName(self, message_module):
+    m = message_module.TestAllTypes()
+    self.assertEqual('TestAllTypes', type(m).__name__)
+    self.assertEqual('TestAllTypes', m.__class__.__qualname__)
+
+    nested = message_module.TestAllTypes.NestedMessage()
+    self.assertEqual('NestedMessage', type(nested).__name__)
+    self.assertEqual('NestedMessage', nested.__class__.__name__)
+    self.assertEqual(
+        'TestAllTypes.NestedMessage', nested.__class__.__qualname__
+    )
+
 
 # Class to test proto2-only features (required, extensions, etc.)
 @testing_refleaks.TestCase