Ensure protobuf Message.__dir__ returns proto fields

Update Message.__dir__ method to ensure all proto fields of a message
are included in the list of attributes. This solves the inconsistency
between the Fast C++ and UPB proto implementation. The Fast C++
implementation was always returning fields while UPB never. Improve
a unit test to detect that.

PiperOrigin-RevId: 708262631

python/google/protobuf/internal/message_test.py

@@ -1278,11 +1278,15 @@ def testReturningType(self, message_module):
   def testDir(self, message_module):
     m = message_module.TestAllTypes()
     attributes = dir(m)
-    self.assertGreaterEqual(len(attributes), 55)
+    self.assertGreaterEqual(len(attributes), 124)
+
+    attribute_set = set(attributes)
     self.assertIn('DESCRIPTOR', attributes)
+    self.assertIn('oneof_string', attribute_set)
+    self.assertIn('optional_double', attribute_set)
+    self.assertIn('repeated_float', attribute_set)
 
     class_attributes = dir(type(m))
-    attribute_set = set(attributes)
     for attr in class_attributes:
       if attr != 'Extensions':
         self.assertIn(attr, attribute_set)

python/google/protobuf/message.py

@@ -60,18 +60,27 @@ def __deepcopy__(self, memo=None):
     return clone
 
   def __dir__(self):
-    """Filters out attributes that would raise AttributeError if accessed."""
-    missing_attributes = set()
+    """Provides the list of all accessible Message attributes."""
+    message_attributes = set(super().__dir__())
+
+    # TODO: Remove this once the UPB implementation is improved.
+    # The UPB proto implementation currently doesn't provide proto fields as
+    # attributes and they have to added.
+    if self.DESCRIPTOR is not None:
+      for field in self.DESCRIPTOR.fields:
+        message_attributes.add(field.name)
+
+    # The Fast C++ proto implementation provides inaccessible attributes that
+    # have to be removed.
     for attribute in _INCONSISTENT_MESSAGE_ATTRIBUTES:
+      if attribute not in message_attributes:
+        continue
       try:
         getattr(self, attribute)
       except AttributeError:
-        missing_attributes.add(attribute)
-    return [
-        attribute
-        for attribute in super().__dir__()
-        if attribute not in missing_attributes
-    ]
+        message_attributes.remove(attribute)
+
+    return sorted(message_attributes)
 
   def __eq__(self, other_msg):
     """Recursively compares two messages by value and structure."""