Re: Display problems with 'before-string in overlay

[Lennart Borgman (gmail)]

Chong Yidong wrote:
> Richard Stallman <address@hidden> writes:
>
> >     > You could add code inside a conditional which tests for that case.
> >     > Then you know it won't affect any other cases.
> >
> >     I don't have a clue to how to write the "conditional which tests for that 
> > case".
> >
> > Have you tried to figure out how?
> >
> > To figure out what this conditional is, one must first get to the bottom
> > of the failure.  If you explain the failure mode to me, I will try to figure
> > out a safe fix.
>
> I already explained twice what the problem is, and why it's better to
> postphone the fix.


I took the sketchial patch Chong sent, inserted a lot of dump messages 
and played with it to try to understand what is happening. The patch 
looks bigger than it actually is. I mean much of it just adds another 
parameter to string_buffer_pos and that is rather harmless from a 
stability point of view.

I think I see several small bugs, most related to the 'display property, 
but not all:

A) It looks like set_cursor_from_row gets called over and over again in 
some circumstances. I might have done something stupid that triggers 
this, I am not sure at the moment, but if I move to the end of the file 
with right error this happens. If stops when I press down arrow.

B) Moving with right arrow across the 'display part on the screen moves 
point across the part of the buffer that has the 'display property. In 
contrast moving with left arrow make point stop at the first of the 
characters that has the overlay with the 'display property (which is the 
correct behavior I believe). This seems to be a bug in another part than 
the ones Chong tried to cover with his patch sketch.

C) Even when moving with left arrow the cursor stops at the wrong 
position. It stops after the 'display part. (This behavior is correct 
for 'before-string and 'after-string, but not for 'display strings.)

D) When the cursor is at the second 'display area of Kim's example 
set_cursor_from_row gets called over and over again. It does not matter 
how that row was entered AFAICS.

Can others reproduce the bug in B? If so I believe this is the most 
serious one.