Carryover evaluation: Scrolling

[nairnandu]

To evaluate continuation of the Scrolling focus area in Interop 2024

Original proposal:

• Scroll-behavior & overscroll-behavior #21
• Carried over from 2022

Labeled tests (2023):

• All tests
• Failing tests

Also consider the possibility of adding new tests in 2024

[foolip]

We should consider the overlap between this and #492 filed by @johannesodland.

There are a lot of unlabeled tests for scroll snap to consider.

[brunostasse]

I strongly recommend that scrolling be carried over.

There are still plenty of interoperability issues in this area. To point to a few in WebKit:

Body scrolling which cannot be reliably prevented (mentioned before interop 2023):

• Extend Scrolling to cover Body Scroll Issues  #84
• https://bugs.webkit.org/show_bug.cgi?id=240860
• https://bugs.webkit.org/show_bug.cgi?id=240859

Issues with CSS pointer-events:
Working in Firefox, fixed recently in Chromium (although not fully) and broken in WebKit.

• https://wpt.fyi/results/pointerevents/pointerevent_hit_test_scroll_visible_descendant.html?label=master&label=experimental&product=chrome&product=firefox&product=safari&aligned&view=interop&q=label%3Ainterop-2023-events
• https://bugs.webkit.org/show_bug.cgi?id=258255
• https://bugs.webkit.org/show_bug.cgi?id=183870

Other issues related to touch/pointer events, overscroll and scroll-snap:

• https://bugs.webkit.org/show_bug.cgi?id=251513
• https://bugs.webkit.org/show_bug.cgi?id=240183
• https://bugs.webkit.org/show_bug.cgi?id=240235
• https://bugs.webkit.org/show_bug.cgi?id=236536
• https://bugs.webkit.org/show_bug.cgi?id=253080
• https://bugs.webkit.org/show_bug.cgi?id=240241

[skobes-chromium]

We reviewed the full list of failing tests in css-scroll-snap and identified a high-impact subset to focus on for Scrolling Interop 2024. That subset falls broadly into two groups.

Honoring scroll-snap-align for non-input scrolls

css/css-scroll-snap/scroll-target-align-001.html
css/css-scroll-snap/scroll-target-align-002.html
css/css-scroll-snap/scroll-target-snap-001.html
css/css-scroll-snap/scroll-target-snap-002.html

Nested and scrollport-covering snap areas

css/css-scroll-snap/input/snap-area-overflow-boundary.html
css/css-scroll-snap/overflowing-snap-areas.html
css/css-scroll-snap/overscroll-snap.html
css/css-scroll-snap/scroll-on-large-element-not-covering-snapport.tentative.html
css/css-scroll-snap/scroll-snap-nested-snap-area-layout-changed.html
css/css-scroll-snap/scroll-snap-stop-002.html
css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-align.html
css/css-scroll-snap/snap-into-covering-area.html

In the first group, scroll-target-snap-* is also in scope for Interop 2023 and the Chrome fix is tracked by crbug.com/1325845. The scroll-target-align-* tests expect scroll-snap-align to be honored even inside scroll-snap-type:none, which is called out as optional behavior in the spec. However we should adopt this behavior if we plan to introduce scroll-align as an equivalent.

The second group consists mainly of changes that Chrome has recently made to its handling of covering and nested snap areas, described in the blink-dev PSA and links therein. There is an open issue to provide greater spec clarity here.

[johannesodland]

Issue #492 was closed in favor of this issue, so I'm pasting over a list of scroll-snap bugs from that issue. I doubt that these bugs are covered by WPT as most occur on mobile devices – related to the dynamic mobile viewport, gestures such as scroll-to-top, search, screen readers and so on.

I hope these bugs can be included in Interop 2024, or that an effort can be made to investigate how one can improve test coverage for these kinds of issues.

This is not a complete list of bugs, but a list of issues I'm aware of or found through a quick search.

https://bugs.webkit.org/show_bug.cgi?id=251003
https://bugs.webkit.org/show_bug.cgi?id=218709
https://bugs.webkit.org/show_bug.cgi?id=245722
https://bugs.webkit.org/show_bug.cgi?id=253056
https://bugs.webkit.org/show_bug.cgi?id=255592
https://bugs.webkit.org/show_bug.cgi?id=255592
https://bugs.chromium.org/p/chromium/issues/detail?id=953285
https://bugs.chromium.org/p/chromium/issues/detail?id=1404006
https://bugs.chromium.org/p/chromium/issues/detail?id=1245459
https://bugs.chromium.org/p/chromium/issues/detail?id=1154509
https://bugs.chromium.org/p/chromium/issues/detail?id=1423359
https://bugzilla.mozilla.org/show_bug.cgi?id=1848917

[denvercoder21]

This came to our attention recently and probably belongs here as well.

https://bugzilla.mozilla.org/show_bug.cgi?id=1857898

[foolip]

Here's a wpt.fyi view of the proposed test expansion in #471 (comment):

https://wpt.fyi/results/css/css-scroll-snap?label=master&label=experimental&product=chrome&product=firefox&product=safari&aligned&view=interop&q=path%3A%2Fcss%2Fcss-scroll-snap%2Fscroll-target-align-001.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Fscroll-target-align-002.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Fscroll-target-snap-001.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Fscroll-target-snap-002.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Finput%2Fsnap-area-overflow-boundary.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Foverflowing-snap-areas.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Foverscroll-snap.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Fscroll-on-large-element-not-covering-snapport.tentative.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Fscroll-snap-nested-snap-area-layout-changed.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Fscroll-snap-stop-002.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Fsnap-after-relayout%2Fchanging-scroll-snap-align.html%20or%20path%3A%2Fcss%2Fcss-scroll-snap%2Fsnap-into-covering-area.html