Version: 52
OS: All

What steps will reproduce the problem?
(1) Add a new API to "navigator". Call it something that comes alphabetically before "Battery". Say, "NavigatorActions".
(2) Create a partial interface, NavigatorActions.idl.
(3) Give the new partial interface a RuntimeEnabled condition with status=experimental:

[
  RuntimeEnabled=Ballista,
] partial interface Navigator {
  readonly attribute Actions actions;
};

(see: https://codereview.chromium.org/1806253002/#ps240001)

What is the expected output?
New attribute navigator.actions is present only when --enable-experimental-web-platform-features is on. When that flag is off, navigator.actions is undefined.

What do you see instead?
When --enable-experimental-web-platform-features is off, MOST OF THE ATTRIBUTES IN navigator ARE UNDEFINED!!!
For example:

> navigator.getBattery()
Uncaught TypeError: navigator.getBattery is not a function(…)

This is the generated code in V8NavigatorPartial.cpp; V8NavigatorPartial::installV8NavigatorTemplate:


    // Register DOM constants, attributes and operations.
    if (RuntimeEnabledFeatures::ballistaEnabled()) {
        V8DOMConfiguration::installAccessors(isolate, instanceTemplate, prototypeTemplate, interfaceTemplate, signature, V8NavigatorAccessors, WTF_ARRAY_LENGTH(V8NavigatorAccessors));
        V8DOMConfiguration::installMethods(isolate, instanceTemplate, prototypeTemplate, interfaceTemplate, signature, V8NavigatorMethods, WTF_ARRAY_LENGTH(V8NavigatorMethods));
    } // if (RuntimeEnabledFeatures::ballistaEnabled())

    if (RuntimeEnabledFeatures::ballistaEnabled()) {
        const V8DOMConfiguration::AccessorConfiguration accessoractionsConfiguration = \
        {"actions", NavigatorPartialV8Internal::actionsAttributeGetterCallback, 0, 0, 0, 0, v8::DEFAULT, static_cast<v8::PropertyAttribute>(v8::ReadOnly), V8DOMConfiguration::ExposedToAllScripts, V8DOMConfiguration::OnPrototype, V8DOMConfiguration::CheckHolder};
        V8DOMConfiguration::installAccessor(isolate, instanceTemplate, prototypeTemplate, interfaceTemplate, signature, accessoractionsConfiguration);
    }

    ....

All of the accessors and methods in the default set (V8NavigatorAccessors and V8NavigatorMethods) are conditional on ballistaEnabled() for some reason. The RuntimeEnabled=Ballista flag is now controlling ALL the features in navigator.

So it turns out that whichever partial interface comes first alphabetically will have its extended attributes (such as the RuntimeEnabled attribute) applied to the entire interface. Currently, the Navigator interface is getting its extended attributes from the NavigatorBattery partial interface, which fortunately has no extended attributes so everything is "fine". If you try to add a new partial interface that alphabetically precedes "Battery", you're gonna have a bad time.

Some debug logging of interfaces ("x of y" refers to the interface name and idl_name) and extended attributes to show the problem:

1) DEBUG:root:generate_code(['NavigatorActions'], 'Navigator')
2) DEBUG:root:interface_context(<IdlInterface: Navigator of NavigatorActions>)
3) DEBUG:root:runtime_feature_name(<IdlInterface: Navigator of NavigatorActions> => extended_attributes = {'RuntimeEnabled': 'Ballista', 'GarbageCollected': None})
4) DEBUG:root:runtime_enabled_function_name(<IdlInterface: Navigator of NavigatorActions> => 'RuntimeEnabledFeatures::ballistaEnabled')
5) DEBUG:root:runtime_enabled_function_name(<IdlAttribute: actions of NavigatorActions> => 'RuntimeEnabledFeatures::ballistaEnabled')
6) DEBUG:root:runtime_enabled_function_name(<IdlAttribute: bluetooth of NavigatorBluetooth> => None)
....

Note: Lines 5 onwards are correctly getting the extended attributes of the specific IDL attributes ("actions of NavigatorActions" is correct). But Lines 1--4 show that the main IdlInterface keyed by "Navigator" is in fact the NavigatorActions partial interface, and so it incorrectly inherits NavigatorActions' extended attributes.