731659 - ASSERTION: Placeholder relationship should have been torn down already; this might mean we have a stray placeholder in the tree.: '!placeholder || nsLayoutUtils::IsProperAncestorFrame(aDestructRoot, placeholder)', layout/generic/nsFrame.cpp, line 615

Status: NEW

(Core :: Layout: Positioned, defect)

Description

[Mats Palmgren (inactive)]

Attachment: Testcase

STR: load testcase, wait one second

ASSERTION: Placeholder relationship should have been torn down already; this might mean we have a stray placeholder in the tree.: '!placeholder || nsLayoutUtils::IsProperAncestorFrame(aDestructRoot, placeholder)', layout/generic/nsFrame.cpp, line 615

Comment 1

[Boris Zbarsky [:bzbarsky]]

So in this case aDestructRoot is the first continuation of the <span>'s frames, while the placeholder is a kid of the fourth continuation.

The issue, of course, is that the abs pos kids are on the first continuation, so getting torn down with it, which is before the placeholder has been destroyed in this case...

Comment 2

[Boris Zbarsky [:bzbarsky]]

Just ran into this again, but with nested columnsets this time, with an abs pos container in the second continuation of the inner columnset.

Fundamentally, this assert is just wrong; it should be claiming that aDestructRoot has a some continuation that is an ancestor of placeholder or something, no?

Comment 3

[Neerja Pancholi[:neerja]]

Attachment: 621424-1-Modified.html

Comment 4

[Neerja Pancholi[:neerja]]

I just encountered this same assertion. Attached test case 621424-1-Modified.html to reproduce this.

This happens because the -moz-column-content block inside the multicol has a second continuation inside the overflow container list and this second continuation contains the OOF for a placeholder in the first continuation.

When trying to delete the multicol, we jump to deleting the overflow container list first and so we try to delete the OOF before its placeholder and that's when we get this assertion. 

We might see this assertion more often now because with the fix for Bug 616436, we recreate everything under the multicol parent in case of an append/insert/remove operation.

Comment 5

[Intermittent Failures Robot]

1 failures in 4289 pushes (0.0 failures/push) were associated with this bug in the last 7 days.

Repository breakdown:

• mozilla-esr68: 1

Platform breakdown:

• macosx1014-64: 1

For more details, see:
https://treeherder.mozilla.org/intermittent-failures.html#/bugdetails?bug=731659&startday=2020-07-27&endday=2020-08-02&tree=all