[css-anchor-position-1] Accommodate pseudo-elements when sorting anchor elements by tree order

[tuankiet65]

24688fe

[css-anchor-position-1] Accommodate pseudo-elements when sorting anchor elements by tree order
rdar://173032203
https://bugs.webkit.org/show_bug.cgi?id=310398

Reviewed by NOBODY (OOPS!).

When determining which element is the anchor, the last element in tree order that satistifes
the anchor query wins [1]:

> If an ancestor of query el satisfies the following conditions, return the nearest such element
> to query el. Otherwise, return the last element el in tree order that satisfies the conditions.

WebKit implemented this by sorting anchors with the same anchor name in reverse tree order,
using treeOrder<ComposedTree> to determine the order. But treeOrder doesn't work with
pseudo-elements (e.g ::before, ::after). Fix this by re-writing the sort comparison logic
to handle pseudo-elements:

* If two elements aren't pseudo-elements, use treeOrder as usual
* If one is, and the other isn't, the order is the order between the pseudo-element's host and the non-pseudo element
* If both are pseudo-elements of different hosts: the order is their host elements' order
* Otherwise, both are pseudo-elements of the same host, and ::before is before ::after

[1]: https://drafts.csswg.org/css-anchor-position-1/#target

Tests: imported/w3c/web-platform-tests/css/css-anchor-position/anchor-function-chain-pseudo-elements.html
       imported/w3c/web-platform-tests/css/css-anchor-position/anchor-size-function-chain-pseudo-elements.html
       imported/w3c/web-platform-tests/css/css-anchor-position/position-area-chain-pseudo-elements.html
       imported/w3c/web-platform-tests/css/css-anchor-position/pseudo-element-anchor-tree-order.html

* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/anchor-function-chain-pseudo-elements-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/anchor-function-chain-pseudo-elements.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/anchor-size-function-chain-pseudo-elements-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/anchor-size-function-chain-pseudo-elements-ref.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/anchor-size-function-chain-pseudo-elements.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/position-area-chain-pseudo-elements-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/position-area-chain-pseudo-elements.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/pseudo-element-anchor-tree-order-expected.txt: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/pseudo-element-anchor-tree-order.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-anchor-position/reference/pseudo-element-chain-ref.html: Added.
* Source/WebCore/style/AnchorPositionEvaluator.cpp:
(WebCore::Style::orderInComposedTreeAccountingForPseudoElements):
(WebCore::Style::collectAnchorsForAnchorName):

24688fe

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	⏳ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests	⏳ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		⏳ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash 24688fe)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	⏳ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests	⏳ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		⏳ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

[nt1m]

We should try to consolidate this with: https://searchfox.org/wubkat/source/Source/WebCore/animation/WebAnimationUtilities.cpp#68

[tuankiet65]

The sorting logic in WebAnimationUtilities.cpp follows the defined ordering in the CSS animation spec, while the anchor spec just says "in tree order" without specifying the order of pseudo-elements. I can certainly try to consolidate them, but that would imply that CSS animations and anchor element use the same ordering (are they?) Maybe this is worth raising an issue to CSSWG?