Filed by: nbeleuzu [at] mozilla.com
Parsed log: https://treeherder.mozilla.org/logviewer?job_id=336539158&repo=autoland
Full log: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/cjxHn-cGT0OEPLIqOisvKg/runs/0/artifacts/public/logs/live_backing.log
Reftest URL: https://hg.mozilla.org/mozilla-central/raw-file/tip/layout/tools/reftest/reftest-analyzer.xhtml#logurl=https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/cjxHn-cGT0OEPLIqOisvKg/runs/0/artifacts/public/logs/live_backing.log&only_show_unexpected=1

[task 2021-04-14T19:50:28.015Z] 19:50:28     INFO - PID 1614 | [Child 1626, Main Thread] WARNING: Shouldn't call SchedulePaint in a detached pres context: file /builds/worker/checkouts/gecko/layout/generic/nsIFrame.cpp:7138
[task 2021-04-14T19:50:28.027Z] 19:50:28     INFO - PID 1614 | 1618429828025	Marionette	INFO	Testing http://web-platform.test:8000/css/css-ui/text-overflow-022.html == http://web-platform.test:8000/css/css-ui/reference/text-overflow-022-ref.html
[task 2021-04-14T19:50:28.050Z] 19:50:28     INFO - PID 1643 | [Child 1649, Main Thread] WARNING: nsAppShell::Exit() called redundantly: file /builds/worker/checkouts/gecko/widget/cocoa/nsAppShell.mm:751
[task 2021-04-14T19:50:28.053Z] 19:50:28     INFO - PID 1643 | ###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
[task 2021-04-14T19:50:28.059Z] 19:50:28     INFO - PID 1643 | ###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
[task 2021-04-14T19:50:28.061Z] 19:50:28     INFO - PID 1643 | [Child 1650, Main Thread] WARNING: nsAppShell::Exit() called redundantly: file /builds/worker/checkouts/gecko/widget/cocoa/nsAppShell.mm:751
[task 2021-04-14T19:50:28.062Z] 19:50:28     INFO - PID 1643 | ###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
[task 2021-04-14T19:50:28.103Z] 19:50:28     INFO - PID 1643 | [2021-04-14T19:50:28Z WARN  xulstore::persist] tried to remove key that isn't in the store
[task 2021-04-14T19:50:28.104Z] 19:50:28     INFO - PID 1643 | [2021-04-14T19:50:28Z WARN  xulstore::persist] tried to remove key that isn't in the store
[task 2021-04-14T19:50:28.116Z] 19:50:28     INFO - PID 1643 | [Child 1650, Main Thread] WARNING: Extra shutdown CC: 'i < NORMAL_SHUTDOWN_COLLECTIONS', file /builds/worker/checkouts/gecko/xpcom/base/nsCycleCollector.cpp:3361
[task 2021-04-14T19:50:28.118Z] 19:50:28     INFO - PID 1643 | [Child 1650, Main Thread] WARNING: '!obs', file /builds/worker/checkouts/gecko/toolkit/components/sessionstore/RestoreTabContentObserver.cpp:58
[task 2021-04-14T19:50:28.127Z] 19:50:28     INFO - PID 1643 | [Child 1650, Main Thread] WARNING: NS_ENSURE_TRUE(Preferences::InitStaticMembers()) failed: file /builds/worker/checkouts/gecko/modules/libpref/Preferences.cpp:4442
[task 2021-04-14T19:50:28.175Z] 19:50:28     INFO - PID 1614 | 1618429828173	Marionette	INFO	Allowed 0-12 pixels different, maximum difference per channel 172-172
[task 2021-04-14T19:50:28.213Z] 19:50:28     INFO - PID 1643 | [Child 1649, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80040111 (NS_ERROR_NOT_AVAILABLE): file /builds/worker/checkouts/gecko/caps/BasePrincipal.cpp:111
[task 2021-04-14T19:50:28.242Z] 19:50:28     INFO - TEST-UNEXPECTED-FAIL | /css/css-ui/text-overflow-022.html | Testing http://web-platform.test:8000/css/css-ui/text-overflow-022.html == http://web-platform.test:8000/css/css-ui/reference/text-overflow-022-ref.html
[task 2021-04-14T19:50:28.242Z] 19:50:28     INFO - Found 12 pixels different, maximum difference per channel 192
[task 2021-04-14T19:50:28.242Z] 19:50:28     INFO - REFTEST   IMAGE 1 (TEST): data:image/png;base64,
[task 2021-04-14T19:50:28.242Z] 19:50:28     INFO - REFTEST   IMAGE 2 (REFERENCE): data:image/png;base64,
[task 2021-04-14T19:50:28.242Z] 19:50:28     INFO - TEST-INFO took 263ms```

https://hg.mozilla.org/mozilla-central/rev/7f8d1b667187

Backed out changeset 7f8d1b667187 (bug 1705193) for causing wpt failures in text-overflow-022.html.
https://hg.mozilla.org/integration/autoland/rev/7597fc53ef49e9ae69cebbcc60163109685ed67e

Push with failures:
https://treeherder.mozilla.org/jobs?repo=autoland&revision=7f8d1b667187916539f125e511dea2aca7745d4b&selectedTaskRun=U_aIhZYjQoWryifdS9_RBA.0

Failure log:
https://treeherder.mozilla.org/logviewer?job_id=336937909&repo=autoland&lineNumber=19171

Backout of initial landing (comment 4) merged: https://hg.mozilla.org/mozilla-central/rev/7597fc53ef49

https://hg.mozilla.org/mozilla-central/rev/7b7232360d51

https://hg.mozilla.org/releases/mozilla-beta/rev/b5c205ccd6fd

https://hg.mozilla.org/mozilla-central/rev/3c4ddda8d3e8

I couldn't make any sense of this, since the error is in the reference file, and appears to be a truncated ellipsis glyph. So I ran mozregression myself and found Bug 1704255 as the regressor, which matches what I'm seeing. I'm setting that as the regressing bug and taking myself off this bug.

I see what's happening here: the reference file includes the <span>l&#x20DE;</span> after the ellipsis, presumably to ensure it gets the same baseline as the testcase, and sets its color to white so that it won't show up. But ⃞ is an enclosing mark that surrounds the previous character, and depending on the fonts that get used, it can end up slightly overlapping and therefore erasing part of the ellipsis.

A simple fix should be to make this span transparent rather than white, to ensure it is truly invisible and doesn't affect the visible text regardless of exactly where the combining-square glyph ends up.

Pushed a try run at https://treeherder.mozilla.org/#/jobs?repo=try&revision=103fd13ac074f7fb2ea657c8ffd10400e6c5677a to confirm this works as expected.

https://hg.mozilla.org/mozilla-central/rev/b38986a96a39

https://hg.mozilla.org/releases/mozilla-beta/rev/98158038e9d5