bug#29279: Sharing the margins

[Eli Zaretskii]

> Cc: 29279@debbugs.gnu.org, joostkremers@fastmail.fm
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Sun, 19 Nov 2017 01:46:29 +0200
> 
> On 11/16/17 5:39 PM, Eli Zaretskii wrote:
> 
> >>> Regardless of the reasons for this change, it doesn't affect the issue
> >>> at hand: calling window-size-change-functions from inside redisplay
> >>> has the same issues as calling window-configuration-change-hook.
> 
> Could you clarify what is the exact issue, BTW?

The same ones described up-thread: the adverse effects of calling
these due to change in line-number width.

> >> But margin size changes won't have to call window-size-change-functions,
> >> right? Then it might be possible to move all the heavy consumers to this
> >> hook, leaving window-configuration-change-hook relatively lightweight
> >> (right)?
> > 
> > For some value of "lightweight".  The ones that I think about would
> > want to change window dimensions, e.g. by enlarging or shrinking the
> > margins, and that is not "lightweight", as I explained up-thread.
> 
> Are window-size-change-functions really supposed to be called when only 
> the margin size has changed, but not the window's outer dimensions?

It's the other way around: in the cases discussed here the hooks will
most probably _want_ to change the margins or some other window
dimensions.