1871719 - Grid baseline-alignment doesn't take subgrid offsets (margin/border/padding/gap) into account

Status: ASSIGNED

(Core :: Layout: Grid, defect)

Description

[Daniel Holbert [:dholbert]]

Right now, we consider items-within-subgrids when doing baseline alignment in grids (as part of doing track sizing); but we end up dropping the baseline-aligned offsets of those items on the floor, per https://searchfox.org/mozilla-central/rev/05178ae3d8ed27d47b340094de52bd3f572a5e1d/layout/generic/nsGridContainerFrame.cpp#3744-3746 . So we effectively just start-align or end-align those ostensibly baseline-aligned grid items.

Bug 1833482 is fixing that by preserving those baseline-aligned offsets. However, it also reveals that we're not accounting for certain forms of padding when baseline-aligning those items (in particular: margin/border/padding/gap on the subgrid).

This bug here is about honoring these forms of padding when baseline-aligning grid items in a subgrid.

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: testcase 1: border on subgrid

Comment 2

[Daniel Holbert [:dholbert]]

Attachment: testcase 2: padding on subgrid

Comment 3

[Daniel Holbert [:dholbert]]

Attachment: testcase 3: margin on subgrid

Comment 4

[Daniel Holbert [:dholbert]]

Attachment: testcase 4: row-gap in subgrid

Comment 5

[Daniel Holbert [:dholbert]]

All 4 testcases here are expected to have ABCD be baseline-aligned, but they aren't (due to this bug) in Firefox Nightly right now.

(They are baseline-aligned in Chrome, though.)

Comment 6

[Daniel Holbert [:dholbert]]

I think this bug covers the same issue that's causing WPTs subgrid-baseline-005.html through subgrid-baseline-009.html to fail. --> Adding those bugs to dependency list.

Comment 7

[Daniel Holbert [:dholbert]]

This issue ("we're not accounting for..." in comment 0) is almost certainly responsible for our failure in https://wpt.fyi/results/css/css-grid/subgrid/align-self-baseline-with-subgrid-mbp.html as well.

That's tracked in bug 1883951 --> adding dependency.