CanvasDrawImage uses CanvasImageSource union that contains types not exposed to workers

[jdm]

OffscreenCanvasRenderingContext implements the CanvasImageSource interface, so they're both marked Exposed=(Window,Worker). However, CanvasImageSource contains HTMLVideoElement, HTMLCanvasElement, and HTMLOrSVGImageElement which are only exposed in Window.

[domenic]

OffscreenCanvasRenderingContext implements the CanvasImageSource interface

Assuming you mean OffscreenCanvasRenderingContext2D, this doesn't appear to be true; I can't find implements CanvasImageSource anywhere in its definition.

[jdm]

Sorry, I meant it implements the CanvasDrawImage interface, which uses the CanvasImageSource union.

[domenic]

I see. Is this a problem? I assume that just means you'd never be able to pass a HTMLVideoElement etc. to the drawImage method, which seems working as intended.

[jdm]

Having read through relevant sections of the WebIDL spec about exposing things, it seems Gecko/Servo's parser has more restrictive rules than the specification about exposing interfaces through operations to globals in which those interfaces are otherwise not exposed. I guess that's a problem we need to sort out, rather than this specification.