1951887 - Multi-column layout in css/css-multicol/getclientrects-004.html is unstable/broken in vertical-rl writing mode

Status: NEW

(Core :: Layout: Columns, defect)

Description

[Jonathan Kew [:jfkthame]]

A testcase involving writing-mode:vertical-rl and CSS columns exhibits unstable, incorrect layout.

STR:

• load https://wpt.live/css/css-multicol/getclientrects-004.html
• on initial load, the test reports "Found 13 tests / 6 Pass / 7 Fail"
• press Cmd-+ (or Ctrl-+) to zoom the display
• observe that as the page is zoomed, the test elements (yellow and cyan blocks) change their layout, sometimes breaking into different pieces; and various fragments of another black-bordered block sometimes appear
• clicking the Re-run button may give different test results, e.g. "Found 13 tests / 3 Pass / 10 Fail"

The unpredictable/unstable layout is clearly a bug; and none of the renderings appear to match the (stable) layout seen in Chrome, where all 13 tests pass.

This seems similar to the layout instability seen in bug 1951486.

(I note that quite a few multicol tests are annotated as failing due to not giving the expected layout, including tests that do not involve writing-mode at all; however, the layout instability seen here seems to be specific to writing-mode:vertical-rl.)