369610 - Ghost/empty vertical scrollbar in XUL box just going into overflow

Status: RESOLVED WORKSFORME

(Core :: Layout, defect)

Description

[Wayne Woods]

Attachment: Test case for the bug

Another bug, related to bug 330673, regressing from bug 192767. Trunk only.

1. Load the XUL testcase, attached.
2. Move the splitter very slowly downward until it *just* reaches the point where the lower boxes begins to overflow.
3. For just the first px into overflow, an empty or ghost vertical scrollbar will appear. Move it 1px further and the proper scrollbar appears. If this doesn't work the first time, try again.

Note that this isn't the same as the bug where the scrollbar is empty when too small. Quite the reverse... in this case it's empty at its very largest size.

This bug first appeared in the 20060316 build (bug 192767), however it manifested in a slightly different way until recently. In builds from 20060316 until 20070103, a ghost *horizontal* scrollbar appears instead (along with a normal vertical one), but if you then move the splitter upwards again by 1px, then the horizontal one vanishes and the vertical ghost one appears. From 20070104, after the ghost horizontal scrollbar was fixed in bug 330673, the situation is as described before.

I'll attach screenshot to illustrate, next.

Comment 1

[Wayne Woods]

Attachment: Screenshot of the bug. Note the empty scrollbar in the lower box

Comment 2

[Wayne Woods]

Attachment: Screenshot of the bug in older (pre-20070104) builds

Comment 3

[Wayne Woods]

(David if you have a sec, could you please comment on the last paragraph of this post?)

I can't seem to reproduce this on Windows. I guess it's Mac-only, despite the timing of the regression.

I've discovered a Mac-only homolog with the browser window: go to a page that is short enough not to be in overflow when first loaded, but can be put into overflow by shrinking, e.g.:
http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-trunk/mac-xpi/
Using the resize widget, shrink the window until it just reaches the overflow point. For the first px of overflow, the scrollbar will appear in its ghost form, just like with the box/splitter testcase here.

The regression time of the window bug is between 20050627 and 20050628 (probably as a result of the check-in for bug 274036), even though the box/splitter version of the bug didn't regress till ~9 months later.

So I wonder if David's check-in for bug 192767 wasn't the true cause of this bug, but rather exposed it, i.e. he changed overflow for XUL boxes in a way that made it more like overflow for windows?

Comment 4

[Wayne Woods]

WORKSFORME now - seems to have been fixed by the checkin for bug 177805, which happened on the very day I reported this.

This is the second time in a fortnight that a long-standing unreported bug was coincidentally fixed just as I reported it. Not that I'm complaining :)