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

[Mario Lang]

Eli Zaretskii <eliz@gnu.org> writes:

>> 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.

OK, I get it, `set-message-function' is for `message' only.

@Raman: How do you solve this in Emacspeak?
IOW, if (user-error "foo") or (signal 'beginning-of-buffer nil) are
called, how does Emacspeak collect the resulting echo area output?

The only hack I can think of is to advice `user-error'
and `signal', and DTRT if `signal' is called with a symbol that has an
error-message slot.

-- 
CYa,
  ⡍⠁⠗⠊⠕