Re: Window splitting issues with margins

[Joost Kremers <joostkremers@fastmail.fm>]

On Do, Nov 19 2015, Joost Kremers <joostkremers@fastmail.fm> wrote:
> On Di, Nov 17 2015, martin rudalics <rudalics@gmx.at> wrote:
>> The only thing we can do is to say in the documentation that when two
>> packages contend for the same margin, the one that tries to do that
>> later in the redisplay cycle will succeed.
>
> Perhaps it could also be added that in order to reduce (though not
> eliminate) the risk of interoperability problems, packages (1) should
> examine the width of the margins before changing them (e.g., in
> `window-configuration-change-hook'); (2) should not set the margins to a
> width lower than the existing width; and (3) should restore the original
> width when they are disabled (or rather, restore the width that existed
> before the last time they changed the margins).

[These comments are mainly for future reference, in case anyone
revisits this discussion.]

Well, I tried implementing this policy in `visual-fill-column-mode', but
it didn't work, because it's not clear at all where margins come from.
E.g., suppose `nlinum-mode' and `visual-fill-column-mode' are both
active in a buffer. Now, `nlinum-mode' only sets the left margin, so
when `visual-fill-column-mode' needs to reset the margins, the existing
width of the right margin has been set by `visual-fill-column-mode'
during the previous margin update. The problem is that
`visual-fill-column-mode' has no way of knowing this and therefore
assumes it cannot reduce the right margin, even though it can.

So, summarising, the situation as it is doesn't really provide a way to
allow multiple packages to use the margins safely. Making that possible
would require some big changes to the way margins are handled.


-- 
Joost Kremers
Life has its moments