bug#48669: Inconsistent overlay placement between minibuffer-message and set-minibuffer-message

[Juri Linkov]

> `minibuffer-message' and `set-minibuffer-message' place the overlay
> containing the message slightly differently, resulting in a different
> behaviour when there are other overlays present at the end of the
> minibuffer.
>
> The overlay created by `minibuffer-message' always gets added to the
> end of the minibuffer.
> The overlay created by `set-minibuffer-message' also gets added to the
> end of the minibuffer, but its properties make it so that it is shown
> before other overlays at the position.
> This is particularly important when the user uses packages that add
> overlays to the minibuffer, such as vertical completion packages like
> selectrum, vertico, and others.
> The way `set-minibuffer-message' configures the overlays makes it so
> that the overlay is displayed before the other overlays, which I
> believe is more compatible with external packages (see attached image
> for a visual example).

To support completion packages such as icomplete, the overlay in
`set-minibuffer-message' was fixed, but not `minibuffer-message'.

> Would it make sense to change this behaviour (i.e. overlay
> configuration) so that it is consistent in both functions?

Right, `minibuffer-message' should be consistent with `set-minibuffer-message'
by copying this part:

        ;; Make sure the overlay with the message is displayed before
        ;; any other overlays in that position, in case they have
        ;; resize-mini-windows set to nil and the other overlay strings
        ;; are too long for the mini-window width.  This makes sure the
        ;; temporary message will always be visible.
        (overlay-put minibuffer-message-overlay 'priority 1100)