Re: Strange font-lock/invisible/intangible bug

["Stefan Monnier" <monnier+gnu/emacs@rum.cs.yale.edu>]

> I've been trying to debug some weird behavior with emacs-wiki.el on
> the nearly-latest CVS (as of about a week ago). emacs-wiki.el uses font-lock
> mode to convert a string of the form "*foo*" to bold, in the process
> propertizing the "*"s as invisible and intangible.
> 
> Now, there is a difficult to reproduce bug in the latest CVS which wasn't
> around in previous emacs releases. Sometimes (maybe 1 in 20 times?), when
> typing "*foo* ", point is suddenly moved to the line below. Infact, not just
> space, but any command - Even C-x =, which you'd expect to show no character
> (as I'm at the end of the buffer), instead says "C-j" in the minibuffer and
> point is suddenly moved to the start of the next line. Repeating C-x = now
> indicates that there's no character on point.
> 
> The other strange thing is that pressing backspace a few times and repeating
> the same key combination results in it working. But if you undo the previous
> line instead, and type it again, the strange behavior results.
> 
> Does anyone have a 'hunch' on where this bug might be, or any tips on how I
> might debug where this is going on? My C knowledge is somewhat rusty.

It's in adjust_point_for_properties.  Same problem as reported
earlier for some wnn input method system.

Since both cases show up in conjunction with `intangible' (which
is made unnecessary by the new problematic code), maybe we can simply
disable that code in case there is an `intangible' property around.

I don't have time to try it out right now, but I'll look at it later.


	Stefan