bug#29279: Sharing the margins

[Dmitry Gutov]

On 11/19/17 5:34 PM, Eli Zaretskii wrote:

> > Hmm, I'm not sure it would be as pointless as you say: normally, it's
> > most important to be notified of some change _eventually_, and not
> > necessarily during some process such as redisplay. It would at least
> > save the user the problem of puzzling out how to do this, and what to
> > compare.
>
> What is the difference between being notified when the width changed,
> and figuring out when it was changed by comparing two numbers?

The latter approach requires more user code.

I'd say it's a bit like the difference between having a 
post-self-insert-hook and not having it, asking users to rely on 
post-command-hook.

> > On the other hand, it could be the argument for margin changes not to
> > run the usual hooks, because any sane called could compare margin widths
> > before and after.
>
> It's the other way around: we are talking about hooks that would like
> to change the margins.

I don't know these uses, so can't really comment, I guess.

> Anyway, could we please stop mixing these two issues?

Sure. I think we've collected the requirements by now, though. Time for 
an implementation?

> This discussion
> is about margin sharing, not about a (missing) hook for changes in
> line-number width.

IMHO the question of removing the irregularity introduced by the native 
line numbers using the new shared margins support is a fairly important 
one. But it's not urgent, of course.