Take sizes from <img> if a <source> doesn't have a sizes attribute

[jakearchibald]

Fixes #6633 by allowing sizes data to come from the <img> if a particular sibling <source> doesn't have a sizes attribute.

• At least two implementers are interested (and none opposed):
  • Mozilla
  • …
• Tests are written and can be reviewed and commented upon at:
  • Sources without sizes should take their sizes from the img web-platform-tests/wpt#54360
• Implementation bugs are filed:
  • Chrome: …
  • Firefox: …
  • Safari: …

(See WHATWG Working Mode: Changes for more details.)

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/images.html ( diff )
/infrastructure.html ( diff )

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/embedded-content.html ( diff )
/images.html ( diff )

[jakearchibald]

I'll create the implementation bugs if folks are happy with this.

[jakearchibald]

Open question, should the return of source.sizes reflect this change?

[zcorpan]

Open question, should the return of source.sizes reflect this change?

I think no. It's less surprising if it more closely reflects getAttribute(). We also don't do anything special for width and height IDL attributes.

[zcorpan]

The document conformance requirements should be changed to allow specifying sizes on img (maybe unconditionally for simplicity). And require sizes on img if one of the sources uses w and omits sizes.

[jakearchibald]

TODO: Simplify sizes just to cases where it must be there. It 'may' be there in other cases. Update tests too.