[css-typed-om-1] Interfaces with value iterators need additional attributes and operations

[rakuco]

The WebIDL spec says: "a value iterator must only be declared on an interface that supports indexed properties".

Another section defines that an interface "supports indexed properties" when it has an indexed property getter and defines an integer-typed attribute named “length”. This then gives an interface with an iterable<V> declaration several operations for free (they come from %ArrayPrototype%) such as forEach() and keys().

With that said:

• CSSUnparsedValue has an iterable<(DOMString or CSSVariableReferenceValue)> declaration with no length attribute or indexed getter.
• CSSTransformValue has an iterable<CSSTransformComponent> declaration with no length attribute or indexed getter.

This means a WebIDL-ECMAScript bindings generator should reject those interfaces (which is something I'm trying to implement in Blink).

The css-typed-om-1 spec should be updated to include those missing attributes and operations, as well as some prose describing what sort of value the getter needs to return.

[rakuco]

@shans @tabatkins (apologies if you already received a notification)

[shans]

CSSUnparsedValue is fixed. Tab - does the same fix apply to CSSTranformValue?

[shans]

There's also this: whatwg/webidl#291.

Specifically, it might be that we want these things to be "array-like" instead of iterators.

[tabatkins]

Yes, it does apply to both. And yeah, I got deep into the array-like discussion; short version is that there's no good answer right now. I'll see about reviving the discussions again.

[rakuco]

For future reference: whatwg/webidl#338