bug#64405: `toggle-side-windows' with 3 or more side windows leads to error; reproducer included

[Eli Zaretskii]

> From: JD Smith <jdtsmith@gmail.com>
> Date: Sat, 1 Jul 2023 15:48:25 -0400
> 
> 
> From a fresh Emacs 28 emacs -Q:
> 
> (progn
>   (display-buffer-in-side-window (get-buffer-create "AA") '((side . right) 
> (slot . -1)))
>   (display-buffer-in-side-window (get-buffer-create "BB") '((side . right) 
> (slot . 0)))
>   (display-buffer-in-side-window (get-buffer-create "CC") '((side . right) 
> (slot . 1)))
>   (window-toggle-side-windows)
>   (window-toggle-side-windows))
> 
> Leads to the error `Specified root is not an ancestor of specified window’.  
> This arises as:
> 
> Debugger entered--Lisp error: (error "Specified root is not an ancestor of 
> specified win...")
>   delete-other-windows-internal(nil #<window 16>)
>   window-state-put((((min-height . 4) (min-width . 10) (min-height-ignore . 
> 2) (min-width-ignore . 7) (min-height-safe . 1) (min-width-safe . 2) 
> (min-pixel-height . 64) (min-pixel-width . 70) (min-pixel-height-ignore . 32) 
> (min-pixel-width-ignore . 49) (min-pixel-height-safe . 16) 
> (min-pixel-width-safe . 14)) leaf (pixel-width . 591) (pixel-height . 560) 
> (total-width . 84) (total-height . 35) (normal-height . 1.0) (normal-width . 
> 1.0) (parameters (clone-of . #<window 3 on *scratch*>)) (buffer #<buffer 
> *scratch*> (selected . t) (hscroll . 0) (fringes 8 8 nil nil) (margins nil) 
> (scroll-bars nil 3 t nil 0 t nil) (vscroll . 0) (dedicated) (point . #<marker 
> at 480 in *scratch*>) (start . #<marker at 1 in *scratch*>))) #<window 16>)
>   window-toggle-side-windows()
>   (progn (display-buffer-in-side-window (get-buffer-create "AA") '((side . 
> right) (slot . -1))) (display-buffer-in-side-window (get-buffer-create "BB") 
> '((side . right) (slot . 0))) (display-buffer-in-side-window 
> (get-buffer-create "CC") '((side . right) (slot . 1))) 
> (window-toggle-side-windows) (window-toggle-side-windows))
>   (progn (progn (display-buffer-in-side-window (get-buffer-create "AA") 
> '((side . right) (slot . -1))) (display-buffer-in-side-window 
> (get-buffer-create "BB") '((side . right) (slot . 0))) 
> (display-buffer-in-side-window (get-buffer-create "CC") '((side . right) 
> (slot . 1))) (window-toggle-side-windows) (window-toggle-side-windows)))
>   elisp--eval-last-sexp(nil)
>   eval-last-sexp(nil)
>   funcall-interactively(eval-last-sexp nil)
>   command-execute(eval-last-sexp)
> 
> Strangely no error is seen with 1 or 2 side windows.

Martin, any ideas or comments?  This still happens in Emacs 29 and
Emacs 30.

Thanks.