Override protobuf Message.__dir__ method

Add a new implementation of Message.__dir__ method that filters out
attributes which are not accessible. Such an attribute is currently
only `Extensions`, which is only accessible if any extension exists.
Add a unit test that verifies all remaining attributes can be accessed.

PiperOrigin-RevId: 700778715

python/google/protobuf/internal/message_test.py

@@ -1268,6 +1268,27 @@ def testReturningType(self, message_module):
     self.assertEqual(bool, type(m.repeated_bool[0]))
     self.assertEqual(True, m.repeated_bool[0])
 
+  def testDir(self, message_module):
+      m = message_module.TestAllTypes()
+      attributes = dir(m)
+      self.assertGreaterEqual(len(attributes), 55)
+      self.assertIn('DESCRIPTOR', attributes)
+
+      class_attributes = dir(type(m))
+      attribute_set = set(attributes)
+      for attr in class_attributes:
+        if attr != 'Extensions':
+          self.assertIn(attr, attribute_set)
+
+  def testAllAttributeFromDirAccessible(self, message_module):
+    m = message_module.TestAllTypes()
+    attributes = dir(m)
+    for attribute in attributes:
+      try:
+        getattr(m, attribute)
+      except AttributeError:
+        self.fail(f'Attribute {attribute} is not accessible.')
+
   def testEquality(self, message_module):
     m = message_module.TestAllTypes()
     m2 = message_module.TestAllTypes()

python/google/protobuf/message.py

@@ -13,6 +13,9 @@
 
 __author__ = 'robinson@google.com (Will Robinson)'
 
+_INCONSISTENT_MESSAGE_ATTRIBUTES = ('Extensions',)
+
+
 class Error(Exception):
   """Base error type for this module."""
   pass
@@ -56,6 +59,20 @@ def __deepcopy__(self, memo=None):
     clone.MergeFrom(self)
     return clone
 
+  def __dir__(self):
+    """Filters out attributes that would raise AttributeError if accessed."""
+    missing_attributes = set()
+    for attribute in _INCONSISTENT_MESSAGE_ATTRIBUTES:
+      try:
+        getattr(self, attribute)
+      except AttributeError:
+        missing_attributes.add(attribute)
+    return [
+        attribute
+        for attribute in super().__dir__()
+        if attribute not in missing_attributes
+    ]
+
   def __eq__(self, other_msg):
     """Recursively compares two messages by value and structure."""
     raise NotImplementedError