Re: Should text-scale trigger hooks?

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 6 Nov 2024 20:17:50 -0500
> From: James Cherti <contact@jamescherti.com>
> 
> I've identified an issue that affects Emacs packages like eat (terminal) 
> and visual-fill-column.
> 
> The core problem is that functions such as text-scale-increase, 
> text-scale-decrease, and text-scale-set do not trigger hooks such as 
> window-configuration-change-hook. Because of that, eat does not 
> instantly update the window when the text scale is changed and 
> visual-fill-column does not update the margin until we resize the window.

There's a huge gape between invocation of text-scale-increase and our
need that window-configuration-change-hook should be run.  I cannot
cross that gap, so please explain the relation between these two, and
in particular why you need that hook to run and not some other
mechanism.

The functions which manipulate face-remapping-alist force redisplay of
the buffer in which the alist was changed, and from Emacs display POV
this is the only thing that should happen to make sure the affected
buffer's display is redrawn.  Please explain why buffer's redisplay is
not enough for the packages you mention to do their job.

OTOH, window-configuration-change-hook is for specific events,
documented thusly:

 -- Variable: window-configuration-change-hook
     This variable specifies functions called during redisplay when
     either the buffer or the size of a window has changed.

text-scale-increase/decrease don't fit this description, so expecting
that hook to be called in those cases is wrong, and asking Emacs to
run that hook is against the documented behavior of the hook.  So if
redisplaying a buffer somehow cannot allow these packages to do their
job (but please explain in detail why), we will have to think about
some different mechanism of doing that;
window-configuration-change-hook doesn't sound like the right tool for
this.

> While these workarounds work, I believe a more robust solution would be 
> to have text-scale functions automatically trigger hooks such as 
> window-configuration-change-hook, or perhaps introduce a dedicated hook 
> for text scale that other plugins could utilize.

As you have discovered, there's already such a hook.  Does it mean
that your problems are solved?