1639368 - Additional mouseenter are fired while holding left button then switch tabs using keyboard

Status: VERIFIED FIXED

(Core :: DOM: UI Events & Focus Handling, defect, P2)

Description

[Edgar Chen [:edgar]]

STR

1. Open multiple tabs.
2. Load https://codepen.io/edgarchen-the-decoder/pen/ExVONrm in one of the tabs.
3. Move the mouse to the green area.
4. Click and hold mouse left button.
5. Switch to another tab via keyboard shortcut (control+tab in MAC for example)
6. Release the mouse button.
7. Switch back to the condepen tab via clicking in tab bar.

Expected result:

Only mouseenter and mouseleave are logged in the green area.
The mouseenter is from step 3.
The mouseleave is fired because of switching to another tab in step 5.

Actual results:

Additional mouseenter is fired. And another mouseleave is fired while mousing over the web content.

Comment 1

[Edgar Chen [:edgar]]

It doesn't look like a recent regression, given that I could reproduce this bug in 76 for example.

Comment 2

[Edgar Chen [:edgar]]

While the mouse moves from the old tab to the new tab, we should dispatch a eMouseExitFromWidget to the old tab and a eMouseEnterIntoWidget to the new tab, but the eMouseEnterIntoWidget is somehow dispatched to old tab instead.

I suspect it is because we track the mouse down for dragging gesture in https://searchfox.org/mozilla-central/rev/9193635dca8cfdcb68f114306194ffc860456044/dom/events/EventStateManager.cpp#1674, and use it as mCurrentTarget in https://searchfox.org/mozilla-central/rev/9193635dca8cfdcb68f114306194ffc860456044/dom/events/EventStateManager.cpp#1827.

Comment 3

[Edgar Chen [:edgar]]

We probably need to overwrite mCurrentTarget for eMouseEnterIntoWidget like what we do for eMouseExitFromWidget in https://searchfox.org/mozilla-central/rev/9193635dca8cfdcb68f114306194ffc860456044/dom/events/EventStateManager.cpp#4218-4222.

Comment 4

[Edgar Chen [:edgar]]

Attachment: Bug 1639368 - Restore `mCurrentTarget` after handling drag gesture;

Comment 5

[Edgar Chen [:edgar]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=0b12f3bbbce3766d313a58f322cc9b451bb479cf

Comment 6

[Edgar Chen [:edgar]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=58b4fa2f859ff193d3f6b217075dd435b0d85970

Comment 7

[Edgar Chen [:edgar]]

(In reply to Edgar Chen [:edgar] from comment #6)

https://treeherder.mozilla.org/#/jobs?repo=try&revision=58b4fa2f859ff193d3f6b217075dd435b0d85970

There is an intermittent failure on test verification on opt build.

Comment 8

[Edgar Chen [:edgar]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=fc7d1e8e3469dbc664900264330b7100ee24a161

Comment 9

[Edgar Chen [:edgar]]

https://treeherder.mozilla.org/#/jobs?repo=try&group_state=expanded&searchStr=tv&revision=58fd3f79baab265cde19547aff580d5367fc1249

I think the test is stable enough now.

Comment 10

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5a00363d2a4a
Restore `mCurrentTarget` after handling drag gesture; r=smaug

Comment 11

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/5a00363d2a4a

Comment 12

[Oana Botisan, Desktop QA]

I managed to reproduce the issue using an older version of Nightly (2020-05-19). I retested everything on macOS 10.13, Windows 10 x64 and Ubuntu 18.04x64 using the latest Nightly 80.a1 and Firefox 79.0b3. The issue is not reproducing anymore.