[Webkit-unassigned] [Bug 240744] New: WebKit doesn't create scrollable overflow (doesn't show scrollbar) for legitimately overflowing content that's off the left side of a zero-size position:sticky parent

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=240744

            Bug ID: 240744
           Summary: WebKit doesn't create scrollable overflow (doesn't
                    show scrollbar) for legitimately overflowing content
                    that's off the left side of a zero-size
                    position:sticky parent
           Product: WebKit
           Version: Safari 15
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: dholbert at mozilla.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 459630

  --> https://bugs.webkit.org/attachment.cgi?id=459630&action=review

testcase

STR:
1. Load attached testcase.

EXPECTED RESULTS:
There should be a functional scrollbar inside the black-bordered area, and it should let you scroll to the purple bottom-border.

ACTUAL RESULTS:
The scrollbar tracks are disabled, as if there were no scrollable overflow (but in fact there is!)


Firefox 100 gives EXPECTED RESULTS.
Safari 15.4 and Chrome 103 give ACTUAL RESULTS (Chrome bug report: https://bugs.chromium.org/p/chromium/issues/detail?id=1327794 )

(Note, this was initially reported as a Firefox bug at https://bugzilla.mozilla.org/show_bug.cgi?id=1769060 ; the reporter there has a custom-scrollbar implementation which happens to depend on this bug. It worked in Firefox as well for a while because of another related Firefox bug, but it "broke" in Firefox when we fixed that bug. Really, the new rendering in Firefox is correct, and the component is inadvertently depending on this WebKit/Blink bug.)

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