mojo: Allow circular dependencies between structs

mojo/public/python/mojo/bindings/descriptor.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.
 
 """
 The descriptors used to define generated elements of the mojo python bindings.
 """
 
 import array
 import itertools
@@ skipping 354 matching lines @@
     result = array.array(self.array_typecode)
     result.fromstring(buffer(data,
                              serialization.HEADER_STRUCT.size,
                              size - serialization.HEADER_STRUCT.size))
     return result
 
 
 class StructType(PointerType):
   """Type object for structs."""
 
-  def __init__(self, struct_type, nullable=False):
+  def __init__(self, struct_type_getter, nullable=False):
     PointerType.__init__(self)
-    self.struct_type = struct_type
+    self._struct_type_getter = struct_type_getter
+    self._struct_type = None
     self.nullable = nullable
 
+  @property
+  def struct_type(self):
+    if not self._struct_type:
+      self._struct_type = self._struct_type_getter()
+    return self._struct_type
+
   def Convert(self, value):
     if value is None or isinstance(value, self.struct_type):
       return value
     raise TypeError('%r is not an instance of %r' % (value, self.struct_type))
 
   def GetDefaultValue(self, value):
     if value:
       return self.struct_type()
     return None
 
@@ skipping 156 matching lines @@
 
 
 def _ConvertByteToBooleans(value, min_size=0):
   "Unpack an integer into a list of booleans."""
   res = []
   while value:
     res.append(bool(value&1))
     value = value / 2
   res.extend([False] * (min_size - len(res)))
   return res