1704122 - Firefox always places the root element's scrollbar on the right side (vs. "end" side for other scrollable elements)

Status: NEW

(Core :: Layout: Scrolling and Overflow, defect)

Description

[Daniel Holbert [:dholbert]]

Attachment: testcase 1 (writing-mode:vertical-rl)

STR:

1. Load attached testcase, in a browser with non-overlay scrollbars (not mac/Android, or on Mac with "Show Scrollbars: Always")
2. Compare the vertical-scrollbar placement on the full viewport, vs. the scrollbar on the black-bordered element. Are these scrollbar tracks on the left side or the right side?

ACTUAL RESULTS: For the viewport, the scrollbar is on the right side, but on the black-bordered element, it's on the left side.

EXPECTED RESULTS: It should probably be consistent (i.e. consistently be placed on the "end side" per the element's writing-mode/direction.)

heycam ran into a similar thing in WebKit when fixing https://bugs.webkit.org/show_bug.cgi?id=224224 , and had to adjust some web-platform tests to allow placement on either side in https://github.com/web-platform-tests/wpt/pull/28425

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: testcase 2 (direction: rtl)

Comment 2

[Daniel Holbert [:dholbert]]

The "see also" webkit/chromium bugs aren't exactly the same issue; they're about a related inconsistency in scrollbar-placement between direction:rtl vs writing-mode:vertical-rl handling in those engines (for any scrollable area, not specifically the root one).

Comment 3

[Timothy Nikkel (:tnikkel)]

Looks like ScrollFrameHelper::IsScrollbarOnRight is probably the relevant code here.

Note that if the scrollbar has never been allowed on the left for the root then I would expect letting it be on the left for the first time might uncover bugs. The root is pretty special (it can be zoomed for example).