1990901 - Anchor-positioned elements are placed at wrong location in a grid, if their anchor element is anywhere besides the grid top-left corner

Status: RESOLVED DUPLICATE of bug 1924786

(Core :: Layout, defect)

Description

[Daniel Holbert [:dholbert]]

Spinning this off for some reduced versions of this WPT:
https://wpt.live/css/css-anchor-position/anchor-position-grid-001.html

That full WPT -- which we currently fail -- uses anchor-and-grid-in-a-multicol, but we also get the wrong result if you remove the multicol wrapper.)

I think we've got an issue with placing the anchor-positioned elements whenever the anchor element is anywhere other than the top-left corner of the grid. It looks like we apply the anchor element's offset-from-its-parent twice when establishing the positions for its anchor-positioned friends, for some reason.

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: testcase 1 (with anchor element at x=50 y=20 within its grid by virtue of being in second row and column)

Comment 2

[Daniel Holbert [:dholbert]]

Attachment: testcase 2 (with anchor element at x=50 y=20 within its grid by virtue of nonzero `padding` on the grid)

Comment 3

[Daniel Holbert [:dholbert]]

Attachment: testcase 3 (with anchor element at x=50 y=20 within its grid by virtue of grid container being larger than its grid tracks, and end-aligning them with {justify/align}-content)

Comment 4

[Daniel Holbert [:dholbert]]

Attachment: testcase 4 [works correctly!] (with anchor element at x=50 y=20 within its grid by virtue of being end-aligned in its grid cell)

Here's a testcase that I was expecting might be broken, but this one works correctly.

As with the rest, the anchor element is at x=50 y=20 within the grid container, in this case because its grid cell is large (150px-by-120px) and the anchor element is smaller (100px-by-100px) and end-aligned within that cell (align-self: end;justify-self: end;).

For whatever reason, we get things correct in this case; we draw the lime anchor-positioned "borders" at the proper location around the anchor element, covering up the red borders.

The expectation here is that all four testcases should render identically (like we currently render this one), with the anchor positioning pref enabled.

Comment 5

[Daniel Holbert [:dholbert]]

(looks like bug 1924786 is already tracking some pieces that are known-to-not-work-yet in CSS grid, so this is probably a version of that bug. Maybe/hopefully the testcases here will all work properly when that bug is fixed. --> adding dependency.)

Comment 6

[David Shin[:dshin]]

Queued for triage, ni? to investigate to see if it should just be a dupe.

Comment 7

[David Shin[:dshin]]

Right, this is bug 1924786 comment 1 - we don't handle cases where absolute containing block size shrinks to the grid via grid-column and grid-row (EDIT: To confirm - removing these properties off of anchor positioned elements renders as expected).