IDL: Simplify [TypeChecking=Interface] code generation

Source/bindings/templates/methods.cpp

 {##############################################################################}
 {% macro generate_method(method, world_suffix) %}
 {% filter conditional(method.conditional_string) %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     {# Local variables #}
     {% if method.has_exception_state %}
     ExceptionState exceptionState(ExceptionState::ExecutionContext, "{{method.name}}", "{{interface_name}}", info.Holder(), info.GetIsolate());
     {% endif %}
     {# Overloaded methods have length checked during overload resolution #}
@@ skipping 91 matching lines @@
     {{cpp_method_call(method, argument.v8_set_return_value_for_main_world, argument.cpp_value) | indent}}
     {% else %}
     {{cpp_method_call(method, argument.v8_set_return_value, argument.cpp_value) | indent}}
     {% endif %}
     {% if argument.has_event_listener_argument %}
     {{hidden_dependency_action(method.name) | indent}}
     {% endif %}
     return;
 }
 {% endif %}
-{% if argument.has_type_checking_interface and not argument.is_variadic_wrapper_type %}
-{# Type checking for wrapper interface types (if interface not implemented,
-   throw a TypeError), per http://www.w3.org/TR/WebIDL/#es-interface
-   Note: for variadic arguments, the type checking is done for each matched
-   argument instead; see argument.is_variadic_wrapper_type code-path below. #}
-if (info.Length() > {{argument.index}} && {% if argument.is_nullable %}!isUndefinedOrNull(info[{{argument.index}}]) && {% endif %}!V8{{argument.idl_type}}::hasInstance(info[{{argument.index}}], info.GetIsolate())) {
-    {{throw_type_error(method, '"parameter %s is not of type \'%s\'."' %
-                               (argument.index + 1, argument.idl_type)) | indent}}
-    return;
-}
-{% endif %}{# argument.has_type_checking_interface #}
 {% if argument.is_callback_interface %}
 {# FIXME: remove EventListener special case #}
 {% if argument.idl_type == 'EventListener' %}
 {% if method.name == 'removeEventListener' or method.name == 'removeListener' %}
 {{argument.name}} = V8EventListenerList::getEventListener(ScriptState::current(info.GetIsolate()), info[{{argument.index}}], false, ListenerFindOnly);
 {% else %}{# method.name == 'addEventListener' #}
 {{argument.name}} = V8EventListenerList::getEventListener(ScriptState::current(info.GetIsolate()), info[{{argument.index}}], false, ListenerFindOrCreate);
 {% endif %}{# method.name #}
 {% else %}{# argument.idl_type == 'EventListener' #}
 {# Callback functions must be functions:
@@ skipping 47 matching lines @@
    http://www.w3.org/TR/WebIDL/#es-type-mapping #}
 {% if argument.has_type_checking_unrestricted %}
 {# Non-finite floating point values (NaN, +Infinity or −Infinity), per:
    http://heycam.github.io/webidl/#es-float
    http://heycam.github.io/webidl/#es-double #}
 if (!std::isfinite({{argument.name}})) {
     {{throw_type_error(method, '"%s parameter %s is non-finite."' %
                                (argument.idl_type, argument.index + 1)) | indent}}
     return;
 }
+{% elif argument.has_type_checking_interface and not argument.is_variadic_wrapper_type %}
+{# Type checking for wrapper interface types (if interface not implemented,
+   throw a TypeError), per http://www.w3.org/TR/WebIDL/#es-interface
+   Note: for variadic arguments, the type checking is done for each matched
+   argument instead; see argument.is_variadic_wrapper_type code-path above. #}
+if (!{{argument.name}}{% if argument.is_nullable %} && !isUndefinedOrNull(info[{{argument.index}}]){% endif %}) {
+    {{throw_type_error(method, '"parameter %s is not of type \'%s\'."' %
+                               (argument.index + 1, argument.idl_type)) | indent}}
+    return;
+}
 {% elif argument.enum_validation_expression %}
 {# Invalid enum values: http://www.w3.org/TR/WebIDL/#idl-enums #}
 String string = {{argument.name}};
 if (!({{argument.enum_validation_expression}})) {
     {{throw_type_error(method,
           '"parameter %s (\'" + string + "\') is not a valid enum value."' %
               (argument.index + 1)) | indent}}
     return;
 }
 {% elif argument.idl_type == 'Promise' %}
@@ skipping 453 matching lines @@
                               if method.overloads else
                               method.runtime_enabled_function) %}
     prototypeObject->Set(v8AtomicString(isolate, "{{method.name}}"), v8::FunctionTemplate::New(isolate, {{cpp_class_or_partial}}V8Internal::{{method.name}}MethodCallback, v8Undefined(), defaultSignature, {{method.number_of_required_arguments}})->GetFunction());
     {% endfilter %}{# runtime_enabled() #}
     {% endfilter %}{# exposed() #}
     {% endfilter %}{# per_context_enabled() #}
     {% endfor %}
     {% endif %}
 }
 {%- endmacro %}