Support nullable types in mojom.

mojo/public/tools/bindings/pylib/mojom/parse/translate.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Translates parse tree to Mojom IR."""
 
 
 import ast
 import re
 
@@ skipping 17 matching lines @@
                  'uint32': 'u32',
                  'uint64': 'u64',
                  'float': 'f',
                  'double': 'd',
                  'string': 's',
                  'handle': 'h',
                  'handle<data_pipe_consumer>': 'h:d:c',
                  'handle<data_pipe_producer>': 'h:d:p',
                  'handle<message_pipe>': 'h:m',
                  'handle<shared_buffer>': 'h:s'}
+  if kind.endswith('?'):
+    base_kind = _MapKind(kind[0:-1])
+    # NOTE: This doesn't rule out enum types. Those will be detected later, when
+    # cross-reference is established.
+    reference_kinds = ('s', 'h', 'a', 'r', 'x')
+    if base_kind[0] not in reference_kinds:
+      raise Exception(
+          'A type (spec "%s") cannot be made nullable' % base_kind)
+    return '?' + base_kind
   if kind.endswith('[]'):
     typename = kind[0:-2]
     if _FIXED_ARRAY_REGEXP.search(typename):
-      raise Exception("Arrays of fixed sized arrays not supported")
+      raise Exception('Arrays of fixed sized arrays not supported')
     return 'a:' + _MapKind(typename)
   if kind.endswith(']'):
     lbracket = kind.rfind('[')
     typename = kind[0:lbracket]
     if typename.find('[') != -1:
-      raise Exception("Fixed sized arrays of arrays not supported")
+      raise Exception('Fixed sized arrays of arrays not supported')
     return 'a' + kind[lbracket+1:-1] + ':' + _MapKind(typename)
   if kind.endswith('&'):
     return 'r:' + _MapKind(kind[0:-1])
   if kind in map_to_kind:
     return map_to_kind[kind]
   return 'x:' + kind
 
 def _AttributeListToDict(attribute_list):
   if attribute_list is None:
     return {}
@@ skipping 83 matching lines @@
         _MapTreeForType(InterfaceToDict, tree.definition_list, ast.Interface)
     self.mojom['enums'] = \
         _MapTreeForType(_EnumToDict, tree.definition_list, ast.Enum)
     self.mojom['constants'] = \
         _MapTreeForType(_ConstToDict, tree.definition_list, ast.Const)
     return self.mojom
 
 
 def Translate(tree, name):
   return _MojomBuilder().Build(tree, name)