1712496 - Empty flexbox with `flex-direction: *-reverse`, `overflow: auto`, and non-zero padding is overflown

Status: RESOLVED FIXED

(Core :: Layout: Flexbox, defect)

Description

[xofe]

Attachment: flex overflow testcase

An flexbox element is overflown where all the following are true:

• it is empty
• flex-direction is row-reverse or column-reverse
• overflow is auto
• padding is not zero

If flex-direction is row or column (i.e. not a *-reverse value), there is no overflow. If there is any children (for example, a text node containing single letter A), there is no overflow.

I've included a testcase with four empty divs, each with a different flex-direction value, that shows the issue.

I would expect no overflow if the element is empty, even if the flex-direction is a *-reverse value.

Reproducible in v89 beta 14, v90 build 20210522213852.

mozregression bisect says bug 1697349 is responsible.

Thanks to anyone who takes a look!

Comment 1

[Ting-Yu Lin [:TYLin] (PST, UTC-8)]

Thanks for the report and the testcase. I'll take a look.

Comment 2

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1697349

Comment 3

[Ting-Yu Lin [:TYLin] (PST, UTC-8)]

Attachment: Bug 1712496 - Adjust flex container's overflow area only if there are flex items. r?dholbert

The rect flexItemMarginBoxBounds is initialized at position (0, 0),
not the flex container's content-box origin. Inflating its initial value
with flex container's padding is just wrong.

Comment 4

[Ting-Yu Lin [:TYLin] (PST, UTC-8)]

The patch is simple, and I'd like to uplift it to beta to fix the regression.

Comment 5

[Pascal Chevrel:pascalc]

We are past betas and have already built our RC, I am not wontfixing ot for 89 as I may take a patch in a potential dot release or as a ride along to an RC2 if we have one.

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/17d9dd4ab631
Adjust flex container's overflow area only if there are flex items. r=dholbert

Comment 7

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/29114 for changes under testing/web-platform/tests

Comment 8

[Alexandru Michis [:malexandru]]

https://hg.mozilla.org/mozilla-central/rev/17d9dd4ab631

Comment 9

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot