1855110 - [css-properties-values-api] Registered property dependency cycles with font/line-height relative units

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, enhancement)

Description

[Zach Hoffman [:zrhoffman]]

Registered custom properties follow the same rules for dependency cycle resolution as unregistered custom properties, with the following additional constraints:

For any registered custom property with a <length> or <length-percentage> syntax component:

• If the property contains any of the following units: em, ex, cap, ch, ic, lh; then add an edge between the property and the font-size of the current element.

• If the property contains the lh unit, add an edge between the property and the line-height of the current element.

• If the property contains any of the following units: rem, rlh; then add an edge between the property and the font-size' of the root element.

• If the property contains the rlh unit, add an edge between the property and the line-height' of the root element.

For example, given this registration:

CSS.registerProperty({
  name: "--my-font-size",
  syntax: "<length>",
  initialValue: "0px",
  inherits: false
});

the following will produce a dependency cycle:

div {
  --my-font-size: 10em;
  font-size: var(--my-font-size);
}

and font-size will behave as if the value unset was specified.

Comment 1

[Zach Hoffman [:zrhoffman]]

As noted in https://github.com/w3c/css-houdini-drafts/issues/1080:

• Dependency cycles need to be checked for properties with every syntax except *, not just <length> and <length-percentage>
• We will need to add an edge to every font-* property, not just font-size.

Comment 2

[David Shin[:dshin]]

Attachment: Bug 1855110: Part 1 - Don't use CSS Typed OM in `unit-cycles.html` WPT test. r=#style

Comment 3

[David Shin[:dshin]]

Attachment: Bug 1855110: Part 2 - Track and mark dependency cycles between custom properties and font-related properties. r=#style

Registered custom properties may utilize font-relative units such as em,
ex, etc. Font-related properties (More with calc() unit algebra), in
turn, may refer to such registered custom properties, leading to a cycle
(Note, unregistered properties are effectively copy-pastes, so it does not
suffer from this issue).

This patch:

1. Defers computation of registstered custom properties using font-relative
   units
2. Keeps track of custom properties utilizing font-relative units
3. Keeps track of non-custom, font-related properties making variable
   references
4. Expands the cycle detection to non-custom properties

Because of 1, this patch causes registered custom property using
font-relative units to resolve as if they're unregistered - this will be
addressed in the next patch.

Depends on D196193

Comment 4

[David Shin[:dshin]]

Attachment: Bug 1855110: Part 3 - Properly resolve registered custom properties using font-relative units. r=#style

Resolution of such custom properties (And other properties depending on them)
must take place after font-related properties (Which are prioritary) are
resolved. Resolution of custom properties is therefore split into two phases,
before and after prioritary properties are resolved.

Depends on D196194

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/a965e291d156
Part 1 - Don't use CSS Typed OM in `unit-cycles.html` WPT test. r=firefox-style-system-reviewers,emilio
https://hg.mozilla.org/integration/autoland/rev/9514e79f3209
Part 2 - Track and mark dependency cycles between custom properties and font-related properties. r=firefox-style-system-reviewers,emilio
https://hg.mozilla.org/integration/autoland/rev/be11cd2890f6
Part 3 - Properly resolve registered custom properties using font-relative units. r=firefox-style-system-reviewers,emilio

Comment 6

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

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/44023 for changes under testing/web-platform/tests

Comment 7

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/a965e291d156
https://hg.mozilla.org/mozilla-central/rev/9514e79f3209
https://hg.mozilla.org/mozilla-central/rev/be11cd2890f6

Comment 8

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

Upstream PR merged by moz-wptsync-bot

Comment 9

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

Upstream PR merged by moz-wptsync-bot