IDL: Support using nullable on any method return type

Source/bindings/scripts/v8_methods.py

Index: Source/bindings/scripts/v8_methods.py
diff --git a/Source/bindings/scripts/v8_methods.py b/Source/bindings/scripts/v8_methods.py
index d70230aa4b9f888013b218f83d16b23241fcfcf9..92e4fbc6eacefa672eb0d93773fef20730f0681b 100644
--- a/Source/bindings/scripts/v8_methods.py
+++ b/Source/bindings/scripts/v8_methods.py
@@ -67,6 +67,16 @@ def argument_needs_try_catch(argument):
         (base_type == 'DOMString' and not argument.is_variadic))
 
 
+def use_local_result(method):
+    extended_attributes = method.extended_attributes
+    idl_type = method.idl_type
+    return (has_extended_attribute_value(method, 'CallWith', 'ScriptState') or
+            'ImplementedInPrivateScript' in extended_attributes or
+            'RaisesException' in extended_attributes or
+            idl_type.is_union_type or
+            (idl_type.is_nullable and not idl_type.is_nullable_simple))
+
+
 def method_context(interface, method):
     arguments = method.arguments
     extended_attributes = method.extended_attributes
@@ -110,6 +120,8 @@ def method_context(interface, method):
     arguments_need_try_catch = any(argument_needs_try_catch(argument)
                                    for argument in arguments)
 
+    is_nullable = idl_type.is_nullable and not idl_type.is_nullable_simple
+
     return {
         'activity_logging_world_list': v8_utilities.activity_logging_world_list(method),  # [ActivityLogging]
         'arguments': [argument_context(interface, method, argument, index)
@@ -118,7 +130,8 @@ def method_context(interface, method):
             argument_declarations_for_private_script(interface, method),
         'arguments_need_try_catch': arguments_need_try_catch,
         'conditional_string': v8_utilities.conditional_string(method),
-        'cpp_type': idl_type.cpp_type,
+        'cpp_type': (v8_types.cpp_template_type('Nullable', idl_type.cpp_type)
+                     if is_nullable else idl_type.cpp_type),
         'cpp_value': this_cpp_value,
         'custom_registration_extended_attributes':
             CUSTOM_REGISTRATION_EXTENDED_ATTRIBUTES.intersection(
@@ -146,12 +159,14 @@ def method_context(interface, method):
         'is_do_not_check_security': 'DoNotCheckSecurity' in extended_attributes,
         'is_do_not_check_signature': 'DoNotCheckSignature' in extended_attributes,
         'is_implemented_in_private_script': is_implemented_in_private_script,
+        'is_nullable': is_nullable,
         'is_partial_interface_member':
             'PartialInterfaceImplementedAs' in extended_attributes,
         'is_per_world_bindings': 'PerWorldBindings' in extended_attributes,
         'is_raises_exception': is_raises_exception,
         'is_read_only': 'Unforgeable' in extended_attributes,
         'is_static': is_static,
+        'use_local_result': use_local_result(method),
         'is_variadic': arguments and arguments[-1].is_variadic,
         'measure_as': v8_utilities.measure_as(method),  # [MeasureAs]
         'name': name,
@@ -317,11 +332,12 @@ def v8_set_return_value(interface_name, method, cpp_value, for_main_world=False)
 
     release = False
     # [CallWith=ScriptState], [RaisesException]
-    if (has_extended_attribute_value(method, 'CallWith', 'ScriptState') or
-        'ImplementedInPrivateScript' in extended_attributes or
-        'RaisesException' in extended_attributes or
-        idl_type.is_union_type):
-        cpp_value = 'result'  # use local variable for value
+    if use_local_result(method):
+        if idl_type.is_nullable and not idl_type.is_nullable_simple:
+            # result is of type Nullable<T>
+            cpp_value = 'result.get()'
+        else:
+            cpp_value = 'result'
         release = idl_type.release
 
     script_wrappable = 'impl' if inherits_interface(interface_name, 'Node') else ''