API functions returning Promises should not throw exceptions.

Source/bindings/scripts/v8_types.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 505 matching lines @@
         expression_format = '(to{ref_ptr_type}NativeArray<{native_array_element_type}, V8{native_array_element_type}>({v8_value}, {index}, {isolate}))'
         add_includes_for_type(native_array_element_type)
     else:
         ref_ptr_type = None
         this_cpp_type = native_array_element_type.cpp_type
         expression_format = 'toNativeArray<{cpp_type}>({v8_value}, {index}, {isolate})'
     expression = expression_format.format(native_array_element_type=native_array_element_type.name, cpp_type=this_cpp_type, index=index, ref_ptr_type=ref_ptr_type, v8_value=v8_value, isolate=isolate)
     return expression
 
 
-def v8_value_to_local_cpp_value(idl_type, extended_attributes, v8_value, variable_name, index=None, declare_variable=True, isolate='info.GetIsolate()', used_in_private_script=False):
+def v8_value_to_local_cpp_value(idl_type, extended_attributes, v8_value, variable_name, index=None, declare_variable=True, isolate='info.GetIsolate()', used_in_private_script=False, async=False):
     """Returns an expression that converts a V8 value to a C++ value and stores it as a local value."""
 
     # FIXME: Support union type.
     if idl_type.is_union_type:
         return ''
 
     this_cpp_type = idl_type.cpp_type_args(extended_attributes=extended_attributes, raw_type=True)
 
     idl_type = idl_type.preprocessed_type
     cpp_value = v8_value_to_cpp_value(idl_type, extended_attributes, v8_value, index, isolate)
     args = [variable_name, cpp_value]
     if idl_type.base_type == 'DOMString' and not idl_type.native_array_element_type:
         macro = 'TOSTRING_DEFAULT' if used_in_private_script else 'TOSTRING_VOID'
     elif idl_type.may_raise_exception_on_conversion:
         macro = 'TONATIVE_DEFAULT_EXCEPTIONSTATE' if used_in_private_script else 'TONATIVE_VOID_EXCEPTIONSTATE'
         args.append('exceptionState')
     else:
         macro = 'TONATIVE_DEFAULT' if used_in_private_script else 'TONATIVE_VOID'
 
     if used_in_private_script:
         args.append('false')
 
     # Macros come in several variants, to minimize expensive creation of
     # v8::TryCatch.
     suffix = ''
 
+    if async:
+        suffix += '_ASYNC'
+        args.append('info')
+        if macro == 'TONATIVE_VOID_EXCEPTIONSTATE':

[haraken, 2014/07/31 07:54:47]

A slightly better condition would be:

  if idl_type.may_raise_exception_on_conversion:

[yhirano, 2014/08/01 02:27:57]

That condition can be true when macro is 'TOSTRING_DEFAULT', right?
I don't want to provide the ScriptState in such a case.

+            args.insert(0, 'ScriptState::current(%s)' % isolate)

[haraken, 2014/07/31 07:54:47]

Can we move the ScriptState argument to the last argument and just use
args.append() ? (Basically we put the ScriptState at the first argument, but it
would be more important to keep the IDL compiler logic simpler.)

[yhirano, 2014/08/01 02:27:57]

Done.

+
     if declare_variable:
         args.insert(0, this_cpp_type)
     else:
         suffix += '_INTERNAL'
 
     return '%s(%s)' % (macro + suffix, ', '.join(args))
 
 
 IdlType.v8_value_to_local_cpp_value = v8_value_to_local_cpp_value
 IdlUnionType.v8_value_to_local_cpp_value = v8_value_to_local_cpp_value
@@ skipping 235 matching lines @@
 
 def is_explicit_nullable(idl_type):
     # Nullable type that isn't implicit nullable (see above.) For such types,
     # we use Nullable<T> or similar explicit ways to represent a null value.
     return idl_type.is_nullable and not idl_type.is_implicit_nullable
 
 IdlType.is_implicit_nullable = property(is_implicit_nullable)
 IdlType.is_explicit_nullable = property(is_explicit_nullable)
 IdlUnionType.is_implicit_nullable = False
 IdlUnionType.is_explicit_nullable = property(is_explicit_nullable)