1657173 - [rel=preload] stylesheets that are only preloaded with <link rel=preload> must not block document's onload

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[Honza Bambas (:mayhemer)]

Loader::PostLoadEvent calls IncrementOngoingLoadCount and Loader::NotifyObservers calls DecrementOngoingLoadCount regardless if the css load is a link-preload only or not.

This will probably not be that simple to solve. In case we find the stylesheet actually used we need to increase the blocker count and then decrease when this coalesced and used load is done.

Comment 1

[Nhi Nguyen (:nhi)]

Please triage

Comment 2

[Emilio Cobos Álvarez (:emilio)]

(In reply to Honza Bambas (:mayhemer) from comment #0)

This will probably not be that simple to solve.

Actually I think it'd be as simple as that. We call that before looking at the cache, so if we use the sheet we enter that (and NotifyObservers) twice, once for the preload and once for the link.

Comment 3

[Honza Bambas (:mayhemer)]

Emilio, would you be willing to work on this for this release? (81)

Comment 4

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1657173 - Make <link rel=preload as=style> not block onload incorrectly. r=mayhemer

And fix the only WPT for this while at it which was using the wrong URL
(and thus would always pass).

This actually makes me a bit uncomfortable given the amount of times
I've seen the pattern:

<link href="important.css" rel="preload" as="style" onload="this.rel = 'stylesheet'">

As that means that important.css won't block the load event. But let's
try.

Comment 5

[Emilio Cobos Álvarez (:emilio)]

Sure, why not.

Comment 6

[Emilio Cobos Álvarez (:emilio)]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=4e4faf137f59ff9f3686822f27a63404d1f4d0ab

Comment 7

[Daniel Holbert [:dholbert]]

[Triage: I'm guessing this is S3, and emilio can adjust if that seems off.]

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/d1e2ee395d42
Make <link rel=preload as=style> not block onload incorrectly. r=mayhemer

Comment 9

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/24950 for changes under testing/web-platform/tests

Comment 10

[Alexandru Michis [:malexandru]]

https://hg.mozilla.org/mozilla-central/rev/d1e2ee395d42

Comment 11

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by jgraham