1471758 - [css-grid-2][css-contain] contain:paint and contain:layout on a subgrid need to *prevent* it from being a subgrid

Status: RESOLVED FIXED

(Core :: Layout, defect, P3)

Description

[Daniel Holbert [:dholbert]]

contain:layout and contain:paint are specced as making an element "[establish] an independent formatting context"
https://drafts.csswg.org/css-contain/#containment-layout
https://drafts.csswg.org/css-contain/#containment-paint

(For blocks, this prevents margin-collapsing and float interactions across the containment boundary.)

For grid: if this is set on an element which is a subgrid, it needs to make that element *not* be a subgrid. (It can't participate in its parent's grid formatting context.)

(There might be other things that make an element "establish an independent formatting context" that we need to consider for subgrid-disabling, too...? not sure)

Comment 1

[Mats Palmgren (inactive)]

(In reply to Daniel Holbert [:dholbert] from comment #0)
> For grid: if this is set on an element which is a subgrid, it needs to make
> that element *not* be a subgrid. (It can't participate in its parent's grid
> formatting context.)

This seems simple enough.  In nsGridContainerFrame::Init where we require
that the parent is a grid container we could also check 'contain' on
the frame itself and simply not set the subgrid frame bits if so.

> (There might be other things that make an element "establish an independent
> formatting context" that we need to consider for subgrid-disabling, too...?
> not sure)

Not participating the item baseline alignment group perhaps?

Comment 2

[Mats Palmgren (inactive)]

> Not participating the item baseline alignment group perhaps?

Or behave as overflow:hidden when calculating its baseline?

Comment 3

[Morgan Reschenberg [:morgan]]

(In reply to Daniel Holbert [:dholbert] from comment #0)
> contain:layout and contain:size are specced as making an element
> "[establish] an independent formatting context"
> https://drafts.csswg.org/css-contain/#containment-layout
> https://drafts.csswg.org/css-contain/#containment-paint

To clarify: this applies to contain:layout and contain:paint, right? (not contain:size)

[EDIT from dholbert: to avoid confusion, I just fixed this via an inline edit in comment 0 (now that we can edit comments), and I'm marking this comment as obsolete to autocollapse it.]

Comment 4

[Daniel Holbert [:dholbert]]

(In reply to Mats Palmgren (:mats) from comment #1)
> > (There might be other things that make an element "establish an independent
> > formatting context" that we need to consider for subgrid-disabling, too...?
> > not sure)
> 
> Not participating the item baseline alignment group perhaps?
[...]
> Or behave as overflow:hidden when calculating its baseline?

I suspect this behavior would be triggered by "contain:size", *not* by "contain:layout". [EDIT: The spec has now changed on this so that `contain:layout` is now the thing that suppresses baselines from leaking out, as Florian notes below]

Comment 5

[Mats Palmgren (inactive)]

(In reply to Daniel Holbert [:dholbert] from comment #4)
> I suspect this behavior would be triggered by "contain:size", *not* by
> "contain:layout".

OK, I haven't read the 'contain' spec in detail so you're probably
right.  Still, baselines are a bit of an edge case in the sense that
they are normally derived from the box' contents and the goal of
'contain:layout' seems to be about not "leaking" out any layout
details outside it.  Anyway, seems off-topic for this bug, sorry
for the digression.

Comment 6

[Florian Rivoal]

Suppression of baselines is triggered by layout containment, not by size containment. The spec (now) has normative text and a note clarifying that.

Size containment sizes the element as if it had no content. Other effects, such as laying out out its descendants within that size, or placing the element within its parent are done with its actual content, and baselines are generated normally.

Layout containment does suppress baseline alignment, otherwise changes in the internal layout of the element would have effects on the rest of document.

Comment 7

[Florian Rivoal]

The baseline alignment part of this bug is also tracked (in the more general case, not limited to subgrids) in https://bugzilla.mozilla.org/show_bug.cgi?id=1508441

Comment 8

[Florian Rivoal]

oops, followed the wrong link above. That one was specific to buttons, the generic one is https://bugzilla.mozilla.org/show_bug.cgi?id=1491235, which has been fixed already. Sorry for the noise.

Comment 9

[Daniel Holbert [:dholbert]]

(In reply to Florian Rivoal from comment #6)

Suppression of baselines is triggered by layout containment, not by size containment. The spec (now) has normative text and a note clarifying that.

Yup -- I've edited comment 4 to reflect that. (At the time I wrote comment 4, contain:size was the thing that triggered baseline suppression, but that has indeed changed now.)

Comment 10

[Mats Palmgren (inactive)]

(I filed bug 1548709 on implementing contain:size on a subgrid)

Comment 11

[Mats Palmgren (inactive)]

Attachment: Bug 1471758 - [css-grid-2][css-contain] 'contain:paint' and 'contain:layout' inhibits a grid container from being a subgrid. r=dholbert

Comment 12

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/8a0c6e30d738
[css-grid-2][css-contain] Make 'contain:paint' and 'contain:layout' inhibit a grid container from being a subgrid.  r=dholbert

Comment 13

[Stefan Hindli [:stefan_hindli]]

https://hg.mozilla.org/mozilla-central/rev/8a0c6e30d738

Comment 14

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

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/16953 for changes under testing/web-platform/tests

Comment 15

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

Upstream web-platform-tests status checks passed, PR will merge once commit reaches central.

Comment 16

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

Upstream PR merged