1 files changed, 26 insertions, 5 deletions
diff --git a/generator/google/protobuf/descriptor_database.py b/generator/google/protobuf/descriptor_database.py
index 8665d3c..1333f99 100644
--- a/generator/google/protobuf/descriptor_database.py
+++ b/generator/google/protobuf/descriptor_database.py
@@ -1,6 +1,6 @@
 # Protocol Buffers - Google's data interchange format
 # Copyright 2008 Google Inc.  All rights reserved.
-# http://code.google.com/p/protobuf/
+# https://developers.google.com/protocol-buffers/
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
@@ -33,6 +33,14 @@
 __author__ = 'matthewtoia@google.com (Matt Toia)'
 
 
+class Error(Exception):
+  pass
+
+
+class DescriptorDatabaseConflictingDefinitionError(Error):
+  """Raised when a proto is added with the same name & different descriptor."""
+
+
 class DescriptorDatabase(object):
   """A container accepting FileDescriptorProtos and maps DescriptorProtos."""
 
@@ -45,9 +53,19 @@ class DescriptorDatabase(object):
 
     Args:
       file_desc_proto: The FileDescriptorProto to add.
+    Raises:
+      DescriptorDatabaseException: if an attempt is made to add a proto
+        with the same name but different definition than an exisiting
+        proto in the database.
     """
-
-    self._file_desc_protos_by_file[file_desc_proto.name] = file_desc_proto
+    proto_name = file_desc_proto.name
+    if proto_name not in self._file_desc_protos_by_file:
+      self._file_desc_protos_by_file[proto_name] = file_desc_proto
+    elif self._file_desc_protos_by_file[proto_name] != file_desc_proto:
+      raise DescriptorDatabaseConflictingDefinitionError(
+          '%s already added, but with different descriptor.' % proto_name)
+
+    # Add the top-level Message, Enum and Extension descriptors to the index.
     package = file_desc_proto.package
     for message in file_desc_proto.message_type:
       self._file_desc_protos_by_symbol.update(
@@ -55,6 +73,9 @@ class DescriptorDatabase(object):
     for enum in file_desc_proto.enum_type:
       self._file_desc_protos_by_symbol[
           '.'.join((package, enum.name))] = file_desc_proto
+    for extension in file_desc_proto.extension:
+      self._file_desc_protos_by_symbol[
+          '.'.join((package, extension.name))] = file_desc_proto
 
   def FindFileByName(self, name):
     """Finds the file descriptor proto by file name.
@@ -116,5 +137,5 @@ def _ExtractSymbols(desc_proto, package):
   for nested_type in desc_proto.nested_type:
     for symbol in _ExtractSymbols(nested_type, message_name):
       yield symbol
-    for enum_type in desc_proto.enum_type:
-      yield '.'.join((message_name, enum_type.name))
+  for enum_type in desc_proto.enum_type:
+    yield '.'.join((message_name, enum_type.name))