1517287 - Scrollable overflow rect is computed incorrectly for negative relative positioning

Status: NEW

(Core :: Layout: Scrolling and Overflow, defect, P3)

Description

[Ryan Hunt [:rhunt]]

Attachment: scrollable-overflow-negative-position.html

Ran into this test case in the scroll-anchoring WPT [1].

I'll attach a visual test case. In this test you shouldn't be able to scroll the frame vertically. You're able to scroll it in Gecko, but not Chrome.

The problem seems to be the computation of the scrollable overflow rect. In this case it's `scr-overflow=0,-54000,36000,114000` which is y=-900px, h=1900px. I'm not sure how it's calculating this rect yet.

[1] https://searchfox.org/mozilla-central/rev/0ee0b63732d35d16ba22d5a1120622e2e8d58c29/testing/web-platform/tests/css/css-scroll-anchoring/negative-layout-overflow.html

Comment 1

[Ryan Hunt [:rhunt]]

Attachment: frame-dump.txt

Comment 2

[Emilio Cobos Álvarez [:emilio]]

This looks like a similar cause to bug 1498772, which jwatt was looking at recently.

Comment 3

[Jonathan Watt [:jwatt]]

Does P3 sound about right, Ryan? Otherwise maybe set it higher.

Comment 4

[Ryan Hunt [:rhunt]]

Yeah that sounds good to me. It's not blocking anything for scroll anchoring.

Comment 5

[Hiroyuki Ikezoe (:hiro)]

(In reply to Ryan Hunt [:rhunt] from comment #0)

The problem seems to be the computation of the scrollable overflow rect. In
this case it's scr-overflow=0,-54000,36000,114000 which is y=-900px,
h=1900px. I'm not sure how it's calculating this rect yet.

Probably we should use YMost() in the calculation. I am not sure where it is. (I was just looking for existing bugs in GetScrollableOverflowRect on RTL scrollable frame)