bug#52314: Set message functions

[Lars Ingebrigtsen]

Juri Linkov <juri@linkov.net> writes:

> To address several requests, there is a patch for Emacs 29 that supports:
>
> 1. inhibiting messages selectively like discussed in bug#42865, bug#44629;
>
> 2. multi-line accumulated messages like discussed on emacs-devel
>    under subject "Intelligent stacking of messages in the echo area";
>
> 3. combining all them plus minibuffer messages into a pipeline:
>    first inhibit-message can filter out some messages, then the second
>    function can accumulate 10 old messages into a multi-line message,
>    then the third function will display them in the active minibuffer.
>
> By default, 'set-message-functions' will be '(set-minibuffer-message)'
> with the current behavior, but can be customized to
> '(inhibit-message set-multi-message set-minibuffer-message)'
> to implement the hook-like list of functions described above:

Hm...  the patch only had the defcustom and some helper functions, so
was this just to get feedback on the interface?

If so, I think it looks good -- but I'm a bit vague about what
set-multi-message would look like.