[font-metrics-api] FontMetrics IDL is invalid

[Ms2ger]

https://drafts.css-houdini.org/font-metrics-api/#fontmetrics-definition has sequence-valued attributes; such attributes are not allowed in IDL.

[kojiishi]

@Ms2ger I'm not very familiar with IDL, a novice question. Is what you meant that advances, baselines, and fonts attributes that return sequence<...> are not allowed, and they need to be functions, or not to return sequence<...>?

[Ms2ger]

Indeed. An attribute with a sequence<…> return type would by definition return a new Array every time you access it, and that's considered a bad API. You can use FrozenArray, or make them functions.

[kojiishi]

Understood, thank you. I was missing the difference between sequence and FrozenArray.

We're trying to sync this with Canvas API, and its Canvas API has FrozenArray. We should fix this one too to match to the Canvas API.