Use has_presence instead of syntax check in text_format.

Remove syntax check in descriptor_test.py

PiperOrigin-RevId: 487362335

python/google/protobuf/internal/descriptor_test.py

@@ -472,7 +472,6 @@ def testFileDescriptor(self):
     self.assertEqual(self.my_file.package, 'protobuf_unittest')
     self.assertEqual(self.my_file.pool, self.pool)
     self.assertFalse(self.my_file.has_options)
-    self.assertEqual('proto2', self.my_file.syntax)
     file_proto = descriptor_pb2.FileDescriptorProto()
     self.my_file.CopyToProto(file_proto)
     self.assertEqual(self.my_file.serialized_pb,

python/google/protobuf/text_format.py

@@ -1091,12 +1091,6 @@ def _MergeMessageField(self, tokenizer, message, field):
       else:
         getattr(message, field.name)[sub_message.key] = sub_message.value
 
-  @staticmethod
-  def _IsProto3Syntax(message):
-    message_descriptor = message.DESCRIPTOR
-    return (hasattr(message_descriptor, 'syntax') and
-            message_descriptor.syntax == 'proto3')
-
   def _MergeScalarField(self, tokenizer, message, field):
     """Merges a single scalar field into a message.
 
@@ -1148,7 +1142,7 @@ def _MergeScalarField(self, tokenizer, message, field):
     else:
       if field.is_extension:
         if (not self._allow_multiple_scalars and
-            not self._IsProto3Syntax(message) and
+            field.has_presence and
             message.HasExtension(field)):
           raise tokenizer.ParseErrorPreviousToken(
               'Message type "%s" should not have multiple "%s" extensions.' %
@@ -1158,12 +1152,12 @@ def _MergeScalarField(self, tokenizer, message, field):
       else:
         duplicate_error = False
         if not self._allow_multiple_scalars:
-          if self._IsProto3Syntax(message):
-            # Proto3 doesn't represent presence so we try best effort to check
-            # multiple scalars by compare to default values.
-            duplicate_error = bool(getattr(message, field.name))
-          else:
+          if field.has_presence:
             duplicate_error = message.HasField(field.name)
+          else:
+            # For field that doesn't represent presence, try best effort to
+            # check multiple scalars by compare to default values.
+            duplicate_error = bool(getattr(message, field.name))
 
         if duplicate_error:
           raise tokenizer.ParseErrorPreviousToken(