Use dictionaries for context creation attributes. Eliminate custom bindings.

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 697 matching lines @@
 
 def v8_conversion_type(idl_type, extended_attributes):
     """Returns V8 conversion type, adding any additional includes.
 
     The V8 conversion type is used to select the C++ -> V8 conversion function
     or v8SetReturnValue* function; it can be an idl_type, a cpp_type, or a
     separate name for the type of conversion (e.g., 'DOMWrapper').
     """
     extended_attributes = extended_attributes or {}
 
+    # Nullable dictionaries need to be handled differently than either
+    # non-nullable dictionaries or unions.

[bashi, 2014/12/12 00:35:24]

Or we can make IDL dictionaries be 'implicit_nullable'.
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

That said, using Nullable<D> looks better because nullable dictionaries are not
commonly used.

[Ken Russell (switch to Gerrit), 2014/12/12 06:59:31]

I'd rather not make IDL dictionaries implicit_nullable. As mentioned below,
passing a nullable dictionary as an argument needs a lot more work, and no place
on the web platform requires that pattern. However, returning a nullable
dictionary from getContextAttributes does need to be supported (and is tested by
the WebGL conformance tests).

[bashi, 2014/12/12 08:31:33]

Acknowledged.

+    if idl_type.is_dictionary and idl_type.is_nullable:
+        return 'NullableDictionary'
+
     if idl_type.is_dictionary or idl_type.is_union_type:
         return 'DictionaryOrUnion'
 
     # Array or sequence types
     native_array_element_type = idl_type.native_array_element_type
     if native_array_element_type:
         if native_array_element_type.is_interface_type:
             add_includes_for_type(native_array_element_type)
         return 'array'
 
@@ skipping 54 matching lines @@
     'Date': 'v8SetReturnValue(info, {cpp_value})',
     'EventHandler': 'v8SetReturnValue(info, {cpp_value})',
     'ScriptValue': 'v8SetReturnValue(info, {cpp_value})',
     'SerializedScriptValue': 'v8SetReturnValue(info, {cpp_value})',
     # DOMWrapper
     'DOMWrapperForMainWorld': 'v8SetReturnValueForMainWorld(info, WTF::getPtr({cpp_value}))',
     'DOMWrapperFast': 'v8SetReturnValueFast(info, WTF::getPtr({cpp_value}), {script_wrappable})',
     'DOMWrapperDefault': 'v8SetReturnValue(info, {cpp_value})',
     # Generic dictionary type
     'Dictionary': 'v8SetReturnValue(info, {cpp_value})',
+    # Nullable dictionaries
+    'NullableDictionary': 'v8SetReturnValue(info, result.get())',
     # Union types or dictionaries
     'DictionaryOrUnion': 'v8SetReturnValue(info, result)',
 }
 
 
 def v8_set_return_value(idl_type, cpp_value, extended_attributes=None, script_wrappable='', release=False, for_main_world=False):
     """Returns a statement that converts a C++ value to a V8 value and sets it as a return value.
 
     """
     def dom_wrapper_conversion_type():
@@ skipping 44 matching lines @@
     'StringOrNull': '{cpp_value}.isNull() ? v8::Handle<v8::Value>(v8::Null({isolate})) : v8String({isolate}, {cpp_value})',
     'StringOrUndefined': '{cpp_value}.isNull() ? v8Undefined() : v8String({isolate}, {cpp_value})',
     # Special cases
     'Dictionary': '{cpp_value}.v8Value()',
     'EventHandler': '{cpp_value} ? v8::Handle<v8::Value>(V8AbstractEventListener::cast({cpp_value})->getListenerObject(impl->executionContext())) : v8::Handle<v8::Value>(v8::Null({isolate}))',
     'ScriptValue': '{cpp_value}.v8Value()',
     'SerializedScriptValue': '{cpp_value} ? {cpp_value}->deserialize() : v8::Handle<v8::Value>(v8::Null({isolate}))',
     # General
     'array': 'toV8({cpp_value}, {creation_context}, {isolate})',
     'DOMWrapper': 'toV8({cpp_value}, {creation_context}, {isolate})',
+    # Passing nullable dictionaries isn't a pattern currently used
+    # anywhere in the web platform, and more work would be needed in
+    # the code generator to distinguish between passing null, and
+    # passing an object which happened to not contain any of the
+    # dictionary's defined attributes. For now, don't define
+    # NullableDictionary here, which will cause an exception to be
+    # thrown during code generation if an argument to a method is a
+    # nullable dictionary type.
+    #
     # Union types or dictionaries
     'DictionaryOrUnion': 'toV8({cpp_value}, {creation_context}, {isolate})',
 }
 
 
 def cpp_value_to_v8_value(idl_type, cpp_value, isolate='info.GetIsolate()', creation_context='info.Holder()', extended_attributes=None):
     """Returns an expression that converts a C++ value to a V8 value."""
     # the isolate parameter is needed for callback interfaces
     idl_type, cpp_value = preprocess_idl_type_and_value(idl_type, cpp_value, extended_attributes)
     this_v8_conversion_type = idl_type.v8_conversion_type(extended_attributes)
@@ skipping 65 matching lines @@
     number_of_nullable_member_types_union)
 
 
 def includes_nullable_type_union(idl_type):
     # http://heycam.github.io/webidl/#dfn-includes-a-nullable-type
     return idl_type.number_of_nullable_member_types == 1
 
 IdlTypeBase.includes_nullable_type = False
 IdlNullableType.includes_nullable_type = True
 IdlUnionType.includes_nullable_type = property(includes_nullable_type_union)