initial horizontal scrollbar positions for RTL elements is wrong

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Cameron McCormack (:heycam)]

Scrollable elements that place their vertical scrollbar on the left (e.g. when they're `direction: rtl` or when the OS language is RTL and the relevant setting to always follow OS scrollbar side is used) have an incorrect scroll origin, which leads to creating a horizontal scrollbar with an incorrect initial offset.  This is because RenderLayerScrollableArea::computeScrollDimensions runs prior to the scrollbars being created.

[Cameron McCormack (:heycam)]

Created attachment 425693 [details]
Patch

[Darin Adler]

Comment on attachment 425693 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=425693&action=review

> Source/WebCore/rendering/RenderLayerScrollableArea.cpp:1032
> +        m_hBar->offsetDidChange();

This is unconditionally called, even if the code above sets the origin to the same value it’s already set to. Should there be a check?

[Cameron McCormack (:heycam)]

(In reply to Darin Adler from comment #2)
> This is unconditionally called, even if the code above sets the origin to
> the same value it’s already set to. Should there be a check?

offsetDidChange() will do an almost equivalent check, when it recomputes its m_position based on the scroll offset, and avoid actually updating the thumb position.  So I figured it's not necessary.

[EWS]

Committed r275811 (236382@main): <https://commits.webkit.org/236382@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 425693 [details].

[Radar WebKit Bug Importer]

<rdar://problem/76516885>