1383985 - stylo: Mutation observer is not invoked when anonymous child is added via changing display value

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect, P2)

Description

[Xidorn Quan [:xidorn] UTC+11]

See test dom/base/test/test_mutateobserver_anonymous.html. This test fails on the subtest "testAddedDueToDisplay", in which it waits for the mutation notification for creation of the pseudo elements after switching their parent from display: none to block.

Comment 1

[Xidorn Quan [:xidorn] UTC+11]

This test needs MutationObserverInit.nativeAnonymousChildList, which is a ChromeOnly feature, so I suppose this doesn't affect web content. But I can see usage of this inside devtools, so I'm less sure whether this is something would block shipping, since it could regress devtools functionality.

ni? jryans for how important it is.

Comment 2

[J. Ryan Stinnett [:jryans] (Use needinfo, replies may be slow)]

(In reply to Xidorn Quan [:xidorn] UTC+10 from comment #1)
> This test needs MutationObserverInit.nativeAnonymousChildList, which is a
> ChromeOnly feature, so I suppose this doesn't affect web content. But I can
> see usage of this inside devtools, so I'm less sure whether this is
> something would block shipping, since it could regress devtools
> functionality.

(To clarify, the DOM test is actually named "dom/base/test/test_mutationobserver_anonymous.html".)

Hmm, this DOM test appears to pass for me locally with Stylo enabled on macOS (based on rev https://hg.mozilla.org/integration/autoland/rev/c4d89120f88d33aea7d41b217da5b79dfd376cb0).

Does it pass for you as well now?

DevTools does use `nativeAnonymousChildList` starting with bug 1208544 (~2 years ago) to watch pseudo mutations.  There is a DevTools test "devtools/client/markupview/test/browser_markupview_mutation_01.js" that was updated in that bug (since renamed to "devtools/client/inspector/markup/test/browser_markup_mutation_01.js"), and the test passes in Stylo.

It looks like most use cases are also covered by other mutation notifications to DevTools, such as "attribute" mutations.  DevTools also watches for reflows and manually scans for display changes, so it will send "display-changed" mutations of its own.  If there's still something wrong with `nativeAnonymousChildList`, let's investigate more deeply which cases in DevTools aren't covered by other mutation notifications.  (I tried to test locally, but I can't test accurately since I appear to have `nativeAnonymousChildList` working with Stylo.)

Comment 3

[Xidorn Quan [:xidorn] UTC+11]

Yeah, it passes now. I think I could reproduce that failure locally, but today it passes. Probably it has been fixed somehow.

Comment 4

[Xidorn Quan [:xidorn] UTC+11]

Well, it passes locally, but still doesn't on CI.

See https://treeherder.mozilla.org/#/jobs?repo=try&revision=b1f9504fbc383472969fd12d06f3017d635c0bfe&selectedJob=121303751

And it happens on both Linux and Mac.

Comment 5

[Hiroyuki Ikezoe (:hiro)]

As of today the test can pass.

For Linux64
https://treeherder.mozilla.org/#/jobs?repo=try&revision=4c0a4ad73733690c969e30204aad95edf91f8d70

For all platforms
https://treeherder.mozilla.org/#/jobs?repo=try&revision=a633272cf43982e54f833ca9b97d3a954dd0ce60

Comment 6

[Hiroyuki Ikezoe (:hiro)]

Attachment: Bug 1383985 - Enable test_mutationobserver_anonymous.html on stylo.

Review commit: https://reviewboard.mozilla.org/r/173146/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/173146/

Comment 7

[Xidorn Quan [:xidorn] UTC+11]

Comment on attachment 8901713 [details]
Bug 1383985 - Enable test_mutationobserver_anonymous.html on stylo.

https://reviewboard.mozilla.org/r/173146/#review178794

r=me as far as it passes.

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/e64539ca6dbd
Enable test_mutationobserver_anonymous.html on stylo. r=xidorn

Comment 9

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/e64539ca6dbd