[css-values-4] [css-cascade-4] [css-color-5] [css-fonts-4] [css-images-4] [css-shapes-2] Clean up fetching

[noamr]

This fixes a few cases around fetching external URLs for style resources:

• The base URL is the sheet's base URL if exists, otherwise the sheet's location, otherwise the document base URL.
• The algorithm can take either a rule or declaration block, and derive the correct stylesheet and base URL from that. Updated the calling sites to take that onto account.
• Removed redundant URL parsing in "@import".

Closes #12065
Closes #12068
Closes #12086
Closes #12147

[noamr]

/cc @AtkinsSJ @weinig, please check that this change is sane :)

[svgeesus]

LGTM but others should review in detail

[AtkinsSJ]

Thanks, this looks pretty solid to me.

One thing that I've been alerted to this morning, (see LadybirdBrowser/ladybird#4972) that's related to this, is that the fetch algorithms operate on relative URLs (and expect them to not be resolved yet) but the values spec requires that the computed value of an URL is absolute:

When a appears in the computed value of a property, it is resolved to an absolute URL, as described in the preceding paragraph. The computed value of a URL that the UA cannot resolve to an absolute URL is the specified value.
https://drafts.csswg.org/css-values-4/#relative-urls

That suggests that either we're absolutizing URLs in two different places with potentially different rules, or that the absolutization in fetch is redundant as the URL will already be absolute. (Or I'm missing something.) Sorry for not catching this earlier!

[noamr]

Thanks, this looks pretty solid to me.

One thing that I've been alerted to this morning, (see LadybirdBrowser/ladybird#4972) that's related to this, is that the fetch algorithms operate on relative URLs (and expect them to not be resolved yet) but the values spec requires that the computed value of an URL is absolute:

When a appears in the computed value of a property, it is resolved to an absolute URL, as described in the preceding paragraph. The computed value of a URL that the UA cannot resolve to an absolute URL is the specified value.
https://drafts.csswg.org/css-values-4/#relative-urls

That suggests that either we're absolutizing URLs in two different places with potentially different rules, or that the absolutization in fetch is redundant as the URL will already be absolute. (Or I'm missing something.) Sorry for not catching this earlier!

Good spotting, thanks to both you and to the Ladybird project for keeping the specs honest!

I've extracted out the "resolve to absolute URL" bit, and referred to it from https://drafts.csswg.org/css-values-4/#relative-urls. IO think it should make a lot more sense now.

[AtkinsSJ]

One typo nit, otherwise I think this is good! Thank you. :^)

[AtkinsSJ]

Arg, I missed a thing until I now tried to implement this! 😅

I think this:

given an CSS rule or a css declaration cssRuleOrDeclaration

...is referring to the wrong definition of "CSS declaration". style resource base URL checks for CSSStyleDeclaration and that seems to be the one we want. The naming of these is unhelpful.

[noamr]

Arg, I missed a thing until I now tried to implement this! 😅

I think this:

given an CSS rule or a css declaration cssRuleOrDeclaration

...is referring to the wrong definition of "CSS declaration". style resource base URL checks for CSSStyleDeclaration and that seems to be the one we want. The naming of these is unhelpful.

Ah yes it needs to be a CSS declaration block.

[AtkinsSJ]

"a a"

[noamr]

Thanks, fixed