1768921 - [css-overflow-3] Incorporate "padding-inflated bounds of in-flow children" into scrollable elements' scrollable-overflow area

Status: ASSIGNED

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

Description

[Mozilla Apprentice]

A resolution was made for csswg-drafts/#129.

[css-overflow-3] Clarify padding in overflow content

• RESOLVED: Always require inline-end padding to be added against the inline-end alignment edge for block/flow layout when it’s a scroll container, thus matching the tests.

Discussion.

Comment 1

[Daniel Holbert [:dholbert]]

A test for this behavior (in which we fail some subtests) is here:
https://wpt.fyi/results/css/css-overflow/scrollable-overflow-padding.html

This test will eventually live in our tree as well as a WPT test, though it doesn't look like we've merged it over yet. But when we do, it will be at
https://searchfox.org/mozilla-central/source/testing/web-platform/tests/css/css-overflow/scrollable-overflow-padding.html

Comment 2

[Daniel Holbert [:dholbert]]

I think this will basically fix bug 1700858, which we can maybe consider to be a metabug at this point.

Comment 3

[Daniel Holbert [:dholbert]]

[clarifying bug-summary to be less vague & to sum up what I think the Chromium behavior basically is, which the CSSWG resolved to adopt]

Comment 4

[David Shin[:dshin]]

Attachment: Bug 1768921 - Ensure that padding inflated bounds of in-flow children are included in the scrollable element's overflow area. r=dholbert,#layout-reviewers

A scrollable element's overflow area:

• Includes direct childrens' margin rect
  • Zero area rects are included
  • In-flow positioned rects are included and padding inflated
  • Out-of-flow positioned rects are included but not padding inflated
• Includes overflow (border rect) of direct children, but not padding inflated

Comment 6

[Daniel Holbert [:dholbert]]

Attachment: breaktest 1

As discussed on slack: here's a testcase that I think is currently broken by the attached patch (we fail to scroll far enough to show a find-in-page match), but it works properly if we revert the PresShell.cpp changes.

(It's using the overflow-clip-box property, which isn't user-exposed by default, so likely nobody would notice -- but ideally we should avoid needlessly/accidentally breaking it.)