Deprecate Descriptor Label. As an alternative, add helper methods for checking whether a field is required or repeated.

java/core/src/main/java/com/google/protobuf/Descriptors.java

@@ -1351,7 +1351,12 @@ public boolean isRequired() {
           == DescriptorProtos.FeatureSet.FieldPresence.LEGACY_REQUIRED;
     }
 
-    /** Is this field declared optional? */
+    /**
+     * Is this field declared optional? *
+     *
+     * <p>This method is deprecated. Use !isRequired() && !isRepeated() instead.
+     */
+    @Deprecated
     public boolean isOptional() {
       return proto.getLabel() == FieldDescriptorProto.Label.LABEL_OPTIONAL
           && getFeatures().getFieldPresence()
@@ -1450,7 +1455,8 @@ public OneofDescriptor getRealContainingOneof() {
     boolean hasOptionalKeyword() {
       return isProto3Optional
           || (file.getEdition() == Edition.EDITION_PROTO2
-              && isOptional()
+              && !isRequired()
+              && !isRepeated()
               && getContainingOneof() == null);
     }
 
@@ -1937,9 +1943,9 @@ void validateFeatures() throws DescriptorValidationException {
       if (containingType != null
           && containingType.toProto().getOptions().getMessageSetWireFormat()) {
         if (isExtension()) {
-          if (!isOptional() || getType() != Type.MESSAGE) {
+          if (isRequired() || isRepeated() || getType() != Type.MESSAGE) {
             throw new DescriptorValidationException(
-                this, "Extensions of MessageSets must be optional messages.");
+                this, "Extensions of MessageSets may not be required or repeated messages.");
           }
         }
       }

python/BUILD.bazel

@@ -160,5 +160,6 @@ py_extension(
         "//upb/hash",
         "//upb/util:def_to_proto",
         "//upb/util:required_fields",
+        "@abseil-cpp//absl/base:core_headers",
     ],
 )

python/descriptor.c

@@ -1056,9 +1056,23 @@ static PyObject* PyUpb_FieldDescriptor_GetCppType(PyUpb_DescriptorBase* self,
 
 static PyObject* PyUpb_FieldDescriptor_GetLabel(PyUpb_DescriptorBase* self,
                                                 void* closure) {
+  PyErr_WarnEx(
+      PyExc_DeprecationWarning,
+      "label() is deprecated. Use is_required() or is_repeated() instead.", 2);
+
   return PyLong_FromLong(upb_FieldDef_Label(self->def));
 }
 
+static PyObject* PyUpb_FieldDescriptor_IsRequired(PyUpb_DescriptorBase* self,
+                                                  void* closure) {
+  return PyBool_FromLong(upb_FieldDef_IsRequired(self->def));
+}
+
+static PyObject* PyUpb_FieldDescriptor_IsRepeated(PyUpb_DescriptorBase* self,
+                                                  void* closure) {
+  return PyBool_FromLong(upb_FieldDef_IsRepeated(self->def));
+}
+
 static PyObject* PyUpb_FieldDescriptor_GetIsExtension(
     PyUpb_DescriptorBase* self, void* closure) {
   return PyBool_FromLong(upb_FieldDef_IsExtension(self->def));
@@ -1165,6 +1179,10 @@ static PyGetSetDef PyUpb_FieldDescriptor_Getters[] = {
     {"type", (getter)PyUpb_FieldDescriptor_GetType, NULL, "Type"},
     {"cpp_type", (getter)PyUpb_FieldDescriptor_GetCppType, NULL, "C++ Type"},
     {"label", (getter)PyUpb_FieldDescriptor_GetLabel, NULL, "Label"},
+    {"is_required", (getter)PyUpb_FieldDescriptor_IsRequired, NULL,
+     "Is Required"},
+    {"is_repeated", (getter)PyUpb_FieldDescriptor_IsRepeated, NULL,
+     "Is Repeated"},
     {"number", (getter)PyUpb_FieldDescriptor_GetNumber, NULL, "Number"},
     {"index", (getter)PyUpb_FieldDescriptor_GetIndex, NULL, "Index"},
     {"default_value", (getter)PyUpb_FieldDescriptor_GetDefaultValue, NULL,

python/google/protobuf/descriptor.py

@@ -721,13 +721,33 @@ def type(self, val):
 
   @property
   def label(self):
+    warnings.warn(
+        'Call to deprecated label property. Use is_required() or is_repeated()'
+        ' methods instead.',
+        category=DeprecationWarning,
+        stacklevel=2,
+    )
+
     if (
         self._GetFeatures().field_presence
         == _FEATURESET_FIELD_PRESENCE_LEGACY_REQUIRED
     ):
       return FieldDescriptor.LABEL_REQUIRED
     return self._label
 
+  @property
+  def is_required(self):
+    """Returns if the field is required."""
+    return (
+        self._GetFeatures().field_presence
+        == _FEATURESET_FIELD_PRESENCE_LEGACY_REQUIRED
+    )
+
+  @property
+  def is_repeated(self):
+    """Returns if the field is repeated."""
+    return self._label == FieldDescriptor.LABEL_REPEATED
+
   @property
   def camelcase_name(self):
     """Camelcase name of this field.
@@ -746,7 +766,7 @@ def has_presence(self):
     Raises:
       RuntimeError: singular field that is not linked with message nor file.
     """
-    if self.label == FieldDescriptor.LABEL_REPEATED:
+    if self.is_repeated:
       return False
     if (
         self.cpp_type == FieldDescriptor.CPPTYPE_MESSAGE
@@ -763,7 +783,7 @@ def has_presence(self):
   @property
   def is_packed(self):
     """Returns if the field is packed."""
-    if self.label != FieldDescriptor.LABEL_REPEATED:
+    if not self.is_repeated:
       return False
     field_type = self.type
     if (field_type == FieldDescriptor.TYPE_STRING or

python/google/protobuf/internal/descriptor_test.py

@@ -588,12 +588,16 @@ def testDefault(self):
     message_descriptor = unittest_pb2.TestAllTypes.DESCRIPTOR
     field = message_descriptor.fields_by_name['repeated_int32']
     self.assertEqual(field.default_value, [])
+    self.assertTrue(field.is_repeated)
     field = message_descriptor.fields_by_name['repeated_nested_message']
     self.assertEqual(field.default_value, [])
+    self.assertTrue(field.is_repeated)
     field = message_descriptor.fields_by_name['optionalgroup']
     self.assertEqual(field.default_value, None)
+    self.assertFalse(field.is_required)
     field = message_descriptor.fields_by_name['optional_nested_message']
     self.assertEqual(field.default_value, None)
+    self.assertFalse(field.is_required)
 
 
 class NewDescriptorTest(DescriptorTest):
@@ -650,6 +654,7 @@ def CheckFieldDescriptor(self, field_descriptor):
     self.assertIn(field_descriptor, {field_descriptor: None})
     self.assertEqual(None, field_descriptor.extension_scope)
     self.assertEqual(None, field_descriptor.enum_type)
+    self.assertFalse(field_descriptor.is_required)
     self.assertTrue(field_descriptor.has_presence)
     if api_implementation.Type() == 'cpp':
       # For test coverage only
@@ -1288,10 +1293,7 @@ def testFeaturesStripped(self):
 
   def testLegacyRequiredTransform(self):
     desc = unittest_legacy_features_pb2.TestEditionsMessage.DESCRIPTOR
-    self.assertEqual(
-        desc.fields_by_name['required_field'].label,
-        descriptor.FieldDescriptor.LABEL_REQUIRED,
-    )
+    self.assertTrue(desc.fields_by_name['required_field'].is_required)
 
   def testLegacyGroupTransform(self):
     desc = unittest_legacy_features_pb2.TestEditionsMessage.DESCRIPTOR

python/google/protobuf/internal/python_message.py

@@ -269,7 +269,6 @@ def _IsMessageMapField(field):
   return value_type.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE
 
 def _AttachFieldHelpers(cls, field_descriptor):
-  is_repeated = field_descriptor.label == _FieldDescriptor.LABEL_REPEATED
   field_descriptor._default_constructor = _DefaultValueConstructorForField(
       field_descriptor
   )
@@ -282,7 +281,9 @@ def AddFieldByTag(wiretype, is_packed):
       type_checkers.FIELD_TYPE_TO_WIRE_TYPE[field_descriptor.type], False
   )
 
-  if is_repeated and wire_format.IsTypePackable(field_descriptor.type):
+  if field_descriptor.is_repeated and wire_format.IsTypePackable(
+      field_descriptor.type
+  ):
     # To support wire compatibility of adding packed = true, add a decoder for
     # packed values regardless of the field's options.
     AddFieldByTag(wire_format.WIRETYPE_LENGTH_DELIMITED, True)
@@ -291,7 +292,7 @@ def AddFieldByTag(wiretype, is_packed):
 def _MaybeAddEncoder(cls, field_descriptor):
   if hasattr(field_descriptor, '_encoder'):
     return
-  is_repeated = (field_descriptor.label == _FieldDescriptor.LABEL_REPEATED)
+  is_repeated = field_descriptor.is_repeated
   is_map_entry = _IsMapField(field_descriptor)
   is_packed = field_descriptor.is_packed
 
@@ -316,7 +317,7 @@ def _MaybeAddDecoder(cls, field_descriptor):
   if hasattr(field_descriptor, '_decoders'):
     return
 
-  is_repeated = field_descriptor.label == _FieldDescriptor.LABEL_REPEATED
+  is_repeated = field_descriptor.is_repeated
   is_map_entry = _IsMapField(field_descriptor)
   helper_decoders = {}
 
@@ -387,7 +388,7 @@ def _AddEnumValues(descriptor, cls):
 
 
 def _GetInitializeDefaultForMap(field):
-  if field.label != _FieldDescriptor.LABEL_REPEATED:
+  if not field.is_repeated:
     raise ValueError('map_entry set on non-repeated field %s' % (
         field.name))
   fields_by_name = field.message_type.fields_by_name
@@ -425,7 +426,7 @@ def _DefaultValueConstructorForField(field):
   if _IsMapField(field):
     return _GetInitializeDefaultForMap(field)
 
-  if field.label == _FieldDescriptor.LABEL_REPEATED:
+  if field.is_repeated:
     if field.has_default_value and field.default_value != []:
       raise ValueError('Repeated field default value not empty list: %s' % (
           field.default_value))
@@ -517,7 +518,7 @@ def init(self, **kwargs):
       if field_value is None:
         # field=None is the same as no field at all.
         continue
-      if field.label == _FieldDescriptor.LABEL_REPEATED:
+      if field.is_repeated:
         field_copy = field._default_constructor(self)
         if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:  # Composite
           if _IsMapField(field):
@@ -636,7 +637,7 @@ def _AddPropertiesForField(field, cls):
   constant_name = field.name.upper() + '_FIELD_NUMBER'
   setattr(cls, constant_name, field.number)
 
-  if field.label == _FieldDescriptor.LABEL_REPEATED:
+  if field.is_repeated:
     _AddPropertiesForRepeatedField(field, cls)
   elif field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
     _AddPropertiesForNonRepeatedCompositeField(field, cls)
@@ -838,7 +839,7 @@ def _IsPresent(item):
   """Given a (FieldDescriptor, value) tuple from _fields, return true if the
   value should be included in the list returned by ListFields()."""
 
-  if item[0].label == _FieldDescriptor.LABEL_REPEATED:
+  if item[0].is_repeated:
     return bool(item[1])
   elif item[0].cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
     return item[1]._is_present_in_parent
@@ -862,7 +863,7 @@ def _AddHasFieldMethod(message_descriptor, cls):
 
   hassable_fields = {}
   for field in message_descriptor.fields:
-    if field.label == _FieldDescriptor.LABEL_REPEATED:
+    if field.is_repeated:
       continue
     # For proto3, only submessages and fields inside a oneof have presence.
     if not field.has_presence:
@@ -950,7 +951,7 @@ def _AddHasExtensionMethod(cls):
   """Helper for _AddMessageMethods()."""
   def HasExtension(self, field_descriptor):
     extension_dict._VerifyExtensionHandle(self, field_descriptor)
-    if field_descriptor.label == _FieldDescriptor.LABEL_REPEATED:
+    if field_descriptor.is_repeated:
       raise KeyError('"%s" is repeated.' % field_descriptor.full_name)
 
     if field_descriptor.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
@@ -1284,7 +1285,7 @@ def IsInitialized(self, errors=None):
 
     for field, value in list(self._fields.items()):  # dict can change size!
       if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
-        if field.label == _FieldDescriptor.LABEL_REPEATED:
+        if field.is_repeated:
           if (field.message_type._is_map_entry):
             continue
           for element in value:
@@ -1332,7 +1333,7 @@ def FindInitializationErrors(self):
           else:
             # ScalarMaps can't have any initialization errors.
             pass
-        elif field.label == _FieldDescriptor.LABEL_REPEATED:
+        elif field.is_repeated:
           for i in range(len(value)):
             element = value[i]
             prefix = '%s[%d].' % (name, i)
@@ -1357,7 +1358,6 @@ def _FullyQualifiedClassName(klass):
 
 
 def _AddMergeFromMethod(cls):
-  LABEL_REPEATED = _FieldDescriptor.LABEL_REPEATED
   CPPTYPE_MESSAGE = _FieldDescriptor.CPPTYPE_MESSAGE
 
   def MergeFrom(self, msg):
@@ -1373,7 +1373,7 @@ def MergeFrom(self, msg):
     fields = self._fields
 
     for field, value in msg._fields.items():
-      if field.label == LABEL_REPEATED:
+      if field.is_repeated:
         field_value = fields.get(field)
         if field_value is None:
           # Construct a new object to represent this field.
@@ -1442,7 +1442,7 @@ def _DiscardUnknownFields(self):
         if _IsMessageMapField(field):
           for key in value:
             value[key].DiscardUnknownFields()
-      elif field.label == _FieldDescriptor.LABEL_REPEATED:
+      elif field.is_repeated:
         for sub_message in value:
           sub_message.DiscardUnknownFields()
       else: