bug#13752: Suggestions regarding the minibuffer

[Juri Linkov <juri@linkov.net>]

>> > But does `signal' use one of too low-level messaging functions?
>> > I can't find what function displays the error message in the echo area.
>>
>> I hoped that was only me.  :-)  I tried following the logic from Ferror
>> to Fsignal to signal_or_quit, but it wasn't at all obvious to me where
>> that's actually displaying the message.
>>
>> I instrumented set_message, and that's called by Fsignal at some point,
>> but even with Vset_message_function set properly, the error message
>> still ends up in the echo area...
>
> 'set_message' isn't called to display errors signaled by 'signal',
> because those messages don't go the 'message' route.  Those messages
> go through cmd_error, which eventually calls command-error-function.
> The latter is by default bound to command-error-default-function,
> which displays the error message via print_error_message.
>
> I think Lisp programs that want to control this should bind
> command-error-function to the function of their liking.

Unbelievable that I forgot that recently I already implemented

  (setq-local command-error-function 'minibuffer-error-function)

for the minibuffer :-)

So like we already have 'set-message-function' that can be set to
'set-minibuffer-message', the corresponding pair of existing error-related
functions are 'command-error-function' and 'minibuffer-error-function'.

This there is nothing to do more here?