1427715 - Implement supports() syntax for @import rules

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, enhancement, P3)

Description

[Sebastian Zartner [:sebo]]

CSS Cascading 4 defines a supports() syntax for @import rules allowing support-dependent importing of other style sheets.

This feature should be implemented accordingly.

Sebastian

Comment 1

[Oliver Medhurst [:canadahonk]]

Attachment: Bug 1427715 - Implement supports() syntax for @import rules

Implemented supports conditions using supports() in @import rules as per
CSS Cascading and Inheritance Level 4.

Spec: https://drafts.csswg.org/css-cascade-4/#conditional-import
WPT tests: https://wpt.fyi/results/css/css-cascade/import-conditions.html

WIP. Todo:

• Format
• Test functionality
• Update WPT expectations
• Potentially add more WPT tests for supports()?

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1427715 - Add (unused for now) parsing for support conditions in @import. r=CanadaHonk

You can use this as:

input.try_parse(SupportsCondition::parse_for_import).ok()

Or so.

Comment 3

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1427715 - Fix @import supports() test. r=CanadaHonk

The #target in the data URI is the url hash, not a selector.

Depends on D172668

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5ff4991cd681
Add (unused for now) parsing for support conditions in @import. r=CanadaHonk
https://hg.mozilla.org/integration/autoland/rev/5abfd5ad2e35
Fix @import supports() test. r=CanadaHonk

Comment 5

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/39013 for changes under testing/web-platform/tests

Comment 6

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/5ff4991cd681
https://hg.mozilla.org/mozilla-central/rev/5abfd5ad2e35

Comment 7

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot

Comment 8

[Oliver Medhurst [:canadahonk]]

Attachment: crash.html

@emilio could you have a poke at this crash case, still can't trace locally on my machine. Happens specifically when using a not in an @import supports() and then accessing the CSS rule in JS. Checked some areas, it is not related to serialization/to_css at least.

Comment 9

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1427715 - Allow CSSImportRule.styleSheet to be null. r=#style,#layout,canadahonk

Comment 10

[Emilio Cobos Álvarez [:emilio]]

You need something like comment 9. This unwrap is failing.

This is technically a spec issue or mismatch (https://github.com/w3c/csswg-drafts/issues/8608), but I think it's an oversight, and we should assert that CSSImportRule.styleSheet is null when the supports() condition doesn't match and probably remove some of the comments referencing bug 1326509 from dom/webidl/CSSImportRule.webidl.

Comment 11

[Emilio Cobos Álvarez [:emilio]]

We should tweak this code to probably pass around the condition, so that we don't load these speculatively.

https://searchfox.org/mozilla-central/source/layout/style/test/gtest/ImportScannerTest.cpp has some tests where we want to add some. Follow-up is probably ok tho.

Comment 12

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/d6f0f149da07
Allow CSSImportRule.styleSheet to be null. r=CanadaHonk,webidl,smaug

Comment 13

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/d6f0f149da07

Comment 14

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/22cb06c53db5
Implement supports() syntax for @import rules r=emilio

Comment 15

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/39521 for changes under testing/web-platform/tests

Comment 16

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot

Comment 17

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/22cb06c53db5