Re: Display problems with `before-string' in overlay

[Lennart Borgman (gmail)]

Eli Zaretskii wrote:

> > > Then what arguments are actually convincing to you?
> > At this point in time, just days short of the intented release? Either
> > the bug crashes Emacs, or it does cause trouble for some really major
> > package, or it is very common and/or confusing for many users.
>
> And such bugs are almost unthinkable at this stage, given the long
> pretest -- unless, that is, they were caused by unsafe changes we did
> very recently, on one of the occasions we failed to exercise will
> power and resist the temptation of fixing ``one more bug''.
>
> But let me turn the table around, Lennart, and ask you: what arguments
> will actually convince _you_ to change your mind on this?  Following
> Karl Popper, if your answer is ``nothing will change my mind'', then
> this is a religious type of argument that we should just stop, because
> it has no hope of any agreement whatsoever.

That is a good question. I am of course also worried about stability. We 
can unfortunately not only use logical thinking, the problem is too 
complex for that. So we are arguing about how to look upon the different 
arguments.

I agree that a managerial/economical view is good to use as a tool for 
deciding. And there must be a decision at the end. Just "fixing" the bug 
is not enough for this kind of bug.

My guess is that so far we do not differ very much, or?

A note: What makes me a bit upset is more that I get the feeling that 
you think the bug is unimportant though I have said that I do have a 
real use case where it will show up. Note that I do not say that you 
actually think so, it is perhaps more my feelings.

Anyway those feelings are noticeable in my replies. This is part of the 
difficulties with arguing now. Probably I disturb you in a similar 
manner. I think that from both sides this is unintentional, but it is 
worth noting when we try to solve this.

I have tried to explain in similar situations before that I always try 
to look at the problem at different levels. When you ask for what 
arguments will convince me this is key. If you want to convince me the 
best you can do is try to argument on all the different levels of the 
problem.

Maybe you think that you have done so by referring to the experts on 
this code for their opinion? The difficulty I have with this is that the 
actual arguments on the details gets hidden. I can not argue at all then 
since I am trying to estimate the stability by looking at the details.

That said I must point out that I can not say anything for sure about 
the stability. I give my arguments, hope for feedback from the experts. 
The may very well kill my arguments, no problems, but I do have some 
arguments that I think may be worth listening too. I feel very much 
better if the arguments are killed than if they are never looked upon. 
(This is kind of human I think.) Killed by some sound logic of course.

I have tried to list my argumenting below (except the one above). If you 
want to you can comment on it.


I do not know if it matters now, but to frame the situation I think we 
can state something like this:

- We all want a release. I think we may feel a little bit weary.
- There is/was a bug in cursor positionining that affects multiline 
'before-string, 'after-string or 'display properties in characters or 
overlays.
- This bug is perhaps not seen very often.
- I have however a use case were it will be seen.
- A bug in cursor positioning is confusing and can lead a user to 
suspect that something is terribly wrong (and indeed that is often a 
plausible thinking when the cursor is in the wrong position). I have got 
a milder reaction of this kind - the user thought something was wrong in 
my code, not in Emacs.
- The display code is complex, very complex.
- There is/was a bug now, which may indicate that it is "fragile" too 
(in the sense that one should be very careful and thoughtful when 
changing it).
- We see some consequences of this bug, but there may be more, even 
instability.
- We have not seen any instability for 2 years however with the bug.
- As far as I remember we did not see any instability either with the 
old bug (for how many years? 1-2?) that unfortunately was cured in such 
a way that it created this new bug.
- The fix (that Chong installed a version of) is in a sense a middle way 
between the two bugs above. This does not prove it does not cause 
instability, but it may be seen as an indication (which I prefer to see 
it as).
- The fix is rather local and as far as I can see it only affects 
multi-line 'before-string, 'after-string and 'display. That makes my 
worries for stability less.