bug#19576: write-file writes the wrong buffer

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 19 Nov 2015 09:12:50 +0100
> From: martin rudalics <rudalics@gmx.at>
> CC: andlind@gmail.com, 19576@debbugs.gnu.org
> 
>  > Thanks for working on this, Martin.  However, I don't think we should
>  > install this change.  We call Lisp hooks from many places, including
>  > maybe a dozen in the display engine.  It makes little sense to make
>  > only one of them resistant to this kind of problems.  OTOH, if we do
>  > this everywhere, I feel that we will unduly punish 99.999% percent of
>  > legitimate users of these hooks just because one of them had a bug.
> 
> 100% agreed.  But run_window_configuration_change_hook goes a long way
> saving and restoring current buffer and selected window around each call
> to a function on ‘window-configuration-change-hook’.

That function isn't called by the display engine, but only by a
handful of functions that react to changes in windows.  So I really
don't consider that to be an analogous case, sorry.

> People who put their functions on ‘window-size-change-functions’ and
> ‘window-configuration-change-hook’ usually don't care about the precise
> reason why these function get called.  They simply want to cover all
> cases where a new window appears or a specific window changes size.  Do
> we really expect them to add a ‘save-window-excursion’ in one case and
> avoid it in the other because it would mean unnecessary extra work?

Yes, we do.  Hooks called by the display engine should be coded very
carefully, because they are a large part of that proverbial rope that
Emacs gives us to hang ourselves.  If they don't write those hooks
with great care, they get what they deserve.