1270891 - [css-flex][css-break] Flexbox container honors forced breaks also when not inside a fragmentainer

Status: RESOLVED FIXED

(Core :: Layout, defect)

Description

[Mats Palmgren (inactive)]

Attachment: testcase

I don't see anything inside the Flexbox spec that says we should honor
these properties unless the flexbox container is inside a fragmentainer.
We're essentially treating the flexbox container itself as a fragmentainer
which seems wrong to me.

Specifically, 9.3.5 says "(or until a forced break is encountered, see §10 Fragmenting Flex Layout)":
https://drafts.csswg.org/css-flexbox/#main-sizing

But all of §10 only applies on the condition there is a fragmentainer.
https://drafts.csswg.org/css-flexbox/#pagination
so the "until a forced break is encountered" only applies on condition
there is a fragmentainer.

Neither css-flexbox nor css-break mentions that a flexbox container can
act as a fragmentainer, AFAICT.
https://drafts.csswg.org/css-break

Comment 1

[Mats Palmgren (inactive)]

I can sympathize with the use case though - forcing the item to start
a new row.  I think we should ask the CSSWG for a separate feature to
support this use case, and possibly make it work for Grid item
placement and block line breaking too.

Comment 2

[Daniel Holbert [:dholbert]]

Yeah, looks like this spec-text has changed.

When I implemented this behavior, the spec said:
> Otherwise, starting from the first uncollected item,
> collect consecutive items one by one until [...],
> or until a forced break is encountered. [...]
> A break is forced wherever the CSS2.1
> page-break-before/page-break-after [CSS21] or the
> CSS3 break-before/break-after [CSS3-BREAK] properties
> specify a fragmentation break. 

Here's a snapshot of the spec from back then
https://www.w3.org/TR/2014/WD-css-flexbox-1-20140325/#algo-line-break

Comment 3

[Daniel Holbert [:dholbert]]

(I'm mostly out today, but I'll take a closer look at this over the weekend or next week, and perhaps email the editors to clarify whether they think forced line-breaking should be possible.)

Comment 4

[Mats Palmgren (inactive)]

I wonder if our current behavior is what wrap-before/wrap-after:flex is supposed to do:
https://www.w3.org/TR/css-text-4/#wrap-before

Comment 5

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

(In reply to Mats Palmgren (inactive) from comment #4)

I wonder if our current behavior is what wrap-before/wrap-after:flex is supposed to do:
https://www.w3.org/TR/css-text-4/#wrap-before

Filed bug 1822586 to implement wrap-before/wrap-after.

Comment 6

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

Attachment: Bug 1270891 - Don't honor forced break properties when generating flex lines.

This behavior was based on the old spec. See the spec changes in
https://drafts.csswg.org/css-flexbox-1/#change-201409-algo-breaks

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c8cc6f915008
Don't honor forced break properties when generating flex lines. r=dholbert

Comment 8

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/c8cc6f915008