152799 - Mixing :hover, display: none, and :first-letter yields jumping characters

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[Tim]

From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.1a) Gecko/20020617
BuildID:    2002061708

If you have a P containing some text followed by two+ inline text elements (I
only tested with SPAN), add style such that those inline elts get display: none
on :hover, and mention P:first-letter (even if devoid of rules), rapidly
triggering the SPANs' :hover causes one or both to jump before the P's first letter.

Reproducible: Always
Steps to Reproduce:
1. Load the test case I'm about to attach
2. Switch to the Problematic style (view, use style)
3. Rapidly move the mouse around the purple letters ('AB')

Actual Results:  One or both of the letters eventually appear(s) in front of the
first letter of that P (before 'This').

Expected Results:  The letters reappear in the region from which they
disappeared (after 'test.').

The test case includes a working version of Problematic that behaves as expected
(the sole difference is the lack of reference to P:first-letter).  Also included
is a version mentioning P:first-letter, but using visibility: none instead of
display: none (this case also works fine).

Note that this is far from CSS one would expect in the wild (at least from
non-sadistic web designers), but it exposes a potential problem.

Also note that the sample operates in Standards-compliance mode (it exhibits the
same problems in Quirks mode).

Comment 1

[Tim]

Attachment: Multi-purpose test case

Note that the first activated selectable style is a working case, not the
broken one.

Comment 2

[Esben Mose Hansen]

Seeing this on  on windows 2000, Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US;
rv:1.1a) Gecko/20020611. 

Bug is not a frequent bug, is reproducible and meets QA standard->Confirmed. OS
changed to all. Adding some keywords.

Comment 3

[Greg K.]

WorksForMe using FizzillaCFM/2002071208.

Comment 4

[Tim]

Still occurs in CVS debug build from Sat Jul 13 01:18:43 EDT 2002 (Athlon,
Debian/Sid).
Make sure you select the "problematic" stylesheet (view->Use Style) since the
default stylesheet does not display the error.

Comment 5

[Tim]

Found this on the console in a debug build:
###!!! ASSERTION: prev sibling not in line list: 'Not Reached', file
nsBlockFrame.cpp, line 4905
Break: at file nsBlockFrame.cpp, line 4905

It occurs when in the problematic style, the moment any of the characters jumps
to the beginning of the line.

Convenience link:
http://lxr.mozilla.org/seamonkey/source/layout/html/base/src/nsBlockFrame.cpp#4905

I'll wait to get in contact with someone who knows this code before I spin my
wheels collecting useless information.

Comment 6

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

The assertion mentioned in comment 5 seems likely to be related to the bug.  The
assertion is complaining about a condition that shouldn't be happening -- that
we can't find a frame for the previous sibling.  The question is why we're
hitting that assertion -- is it an incorrect assumption that the code is making
(for example, about something not being 'display: none' (and we didn't check the
undisplayed content map)), or is it something wrong with the calling code.

Comment 7

[Boris Zbarsky [:bzbarsky]]

The patch in bug 277686 fixes this.

Comment 8

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

What patch?

Comment 9

[Boris Zbarsky [:bzbarsky]]

Fixed by checkin for bug 277686