[Webkit-unassigned] [Bug 239605] New: Focusing scroll container before scrolling breaks smooth scrolling

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=239605

            Bug ID: 239605
           Summary: Focusing scroll container before scrolling breaks
                    smooth scrolling
           Product: WebKit
           Version: Safari 15
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Scrolling
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ldebeasi at gmail.com
                CC: simon.fraser at apple.com

Created attachment 458061

  --> https://bugs.webkit.org/attachment.cgi?id=458061&action=review

Code reproduction

Focusing a scroll container before performing a smooth scroll operation causes smooth scrolling to not work. Non-smooth scrolling works as expected.

Steps to reproduce:

1. Open attached code reproduction on an iOS device that supports smooth scrolling.
2. Tap the "Smooth scroll to end" button. Observe that the container does not scroll to the end.
3. Tap the "Non Smooth scroll to end" button. Observe that the container scrolls to the end.

Expected Behavior:

I would expect that the container scrolls regardless of smooth scroll status.

Actual Behavior:

The scroll container does not scroll if smooth scrolling is enabled.

Other Information:

- This works as expected on Chrome and Firefox.
- Disabling CSSOM View Smooth Scrolling in Settings > Safari > Experimental Features resolves the issue.
- Wrapping the scroll operation in a requestAnimationFrame fixes the issue.

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