Re: Why does signaling an error not call set-message-function?

[Eli Zaretskii]

> From: Mario Lang <mlang@blind.guru>
> Date: Tue, 05 Apr 2022 14:05:00 +0200
> 
> > Are you sure it is a good idea to allow running arbitrary Lisp when
> > Emacs wants to signal an error?
> 
> My motivation is that I am trying to redirect echo area messages to an
> external display.  Why?  Think of it like Emacspeak for braille users.
> When I press M-< "Mark set" is displayed,
> but if I press cursor up, "Beginning of buffer" is not.
> This seems arbitrary.  I realize that signals which pop up the
> debugger / backtrace might be problematic to interfere with, but...
> The messages from `user-error' and those error symbols which only
> display an echo area message should be easier to programmatically see IMO.

AFAIR, the set-message-function feature is explicitly for controlling
the output that goes via calls to 'message'.  Maybe we should
emphasize this in the doc string.