bug#68698: 30.0.50; Making xt-mouse emit `wheel-up/down`

[Eli Zaretskii]

> Date: Wed, 24 Jan 2024 15:31:32 -0500
> From:  Stefan Monnier via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Package: Emacs
> Version: 30.0.50
> 
> 
> Currently, wheel-up/down events are generated in most setups instead
> of the old mouse-4/5.  There are still two exceptions:
> - X11 builds not using XInput2.
> - text terminals.
> The attached patch intends to fix the second bullet.
> Text terminals themselves only give us info equivalent to `mouse-4/5`
> and don't actually tell us that it's a wheel movement, but we can still
> turn those things into `wheel-up/down`.
> 
> This is related to bug#49803.

Jared, any comments on the patch, or related issues?

Thanks.

> The second step would be to do something similar for the non-XInput2 X11
> build: make it generate `wheel-up/down` events according to
> `mouse-wheel-down/up-event` settings.  Then packages like
> `completion-preview` and `mwheel` won't need to pay attention to the
> (confusingly named) `mouse-wheel-down/up-event` vars any more.
> 
> 
>         Stefan
> 
> diff --git a/lisp/mwheel.el b/lisp/mwheel.el
> index 53042085bf6..66a1fa1a706 100644
> --- a/lisp/mwheel.el
> +++ b/lisp/mwheel.el
> @@ -59,7 +59,7 @@ mouse-wheel-change-button
>  (defvar mouse-wheel-obey-old-style-wheel-buttons t
>    "If non-nil, treat mouse-4/5/6/7 events as mouse wheel events.
>  These are the event names used historically in X11 before XInput2.
> -They are sometimes generated by things like `xterm-mouse-mode' as well.")
> +They are sometimes generated by things like text-terminals as well.")
>  
>  (defcustom mouse-wheel-down-event
>    (if mouse-wheel-obey-old-style-wheel-buttons 'mouse-4)
> diff --git a/lisp/xt-mouse.el b/lisp/xt-mouse.el
> index cd00467f14f..fcc0db1d9eb 100644
> --- a/lisp/xt-mouse.el
> +++ b/lisp/xt-mouse.el
> @@ -40,6 +40,8 @@
>  
>  ;;; Code:
>  
> +(require 'mwheel)
> +
>  (defvar xterm-mouse-debug-buffer nil)
>  
>  (defun xterm-mouse-translate (_event)
> @@ -193,6 +195,12 @@ xterm-mouse--read-number-from-terminal
>            (cons n c))
>        (cons (- (setq c (xterm-mouse--read-coordinate)) 32) c))))
>  
> +(defun xterm-mouse--same-button-p (event btn)
> +  (and (symbolp event)
> +       (string-prefix-p "mouse-" (symbol-name event))
> +       (eq btn (car (read-from-string (symbol-name event)
> +                                      (length "mouse-"))))))
> +
>  ;; XTerm reports mouse events as
>  ;; <EVENT-CODE> <X> <Y> in default mode, and
>  ;; <EVENT-CODE> ";" <X> ";" <Y> <"M" or "m"> in extended mode.
> @@ -231,12 +239,24 @@ xterm-mouse--read-event-sequence
>               ;; event: assume, that the last button was button 1.
>               (t 1)))
>         (sym (if move 'mouse-movement
> -              (intern (concat (if ctrl "C-" "")
> -                              (if meta "M-" "")
> -                              (if shift "S-" "")
> -                              (if down "down-" "")
> -                              "mouse-"
> -                              (number-to-string btn))))))
> +             (intern
> +              (concat
> +               (if ctrl "C-" "")
> +               (if meta "M-" "")
> +               (if shift "S-" "")
> +               (if down "down-" "")
> +               (cond
> +                ;; BEWARE: `mouse-wheel-UP-event' corresponds to
> +                ;; `wheel-DOWN' events and vice versa!!
> +                ((xterm-mouse--same-button-p mouse-wheel-down-event btn)
> +                 "wheel-up")
> +                ((xterm-mouse--same-button-p mouse-wheel-up-event btn)
> +                 "wheel-down")
> +                ((xterm-mouse--same-button-p mouse-wheel-left-event btn)
> +                 "wheel-left")
> +                ((xterm-mouse--same-button-p mouse-wheel-right-event btn)
> +                 "wheel-right")
> +                (t (format "mouse-%d" btn))))))))
>      (list sym (1- x) (1- y))))
>  
>  (defun xterm-mouse--set-click-count (event click-count)