bug#8789: 23.3; debug backtrace buffer changes window on step-through

[Stefan Monnier]

> We could also try `window-prev-buffers' and `window-next-buffers' as in
> the rather untested patch below.

Sounds good for the backtrace buffer, but the patch you propose would
affect many more cases, and while I think it might be good to do it
globally like you suggest, I wouldn't want to make such a change so late
in the pretest.
Can you provide another patch that limits the effect to the
backtrace buffer?


        Stefan


> === modified file 'lisp/window.el'
> --- lisp/window.el    2012-02-12 05:10:30 +0000
> +++ lisp/window.el    2012-02-15 16:54:41 +0000
> @@ -4846,6 +4846,39 @@
>        (and pop-up-windows
>          (display-buffer-pop-up-window buffer alist))))

> +(defun window-previously-showing (buffer &optional all-frames dedicated)
> +  "Return a window that previously showed BUFFER.
> +A minibuffer window is never a candidate.  A dedicated window is
> +never a candidate unless DEDICATED is non-nil, so if all windows
> +are dedicated, the value is nil.  Avoid returning the selected
> +window if possible.
> +
> +The following non-nil values of the optional argument ALL-FRAMES
> +have special meanings:
> +
> +- t means consider all windows on all existing frames.
> +
> +- `visible' means consider all windows on all visible frames on
> +  the current terminal.
> +
> +- 0 (the number zero) means consider all windows on all visible
> +  and iconified frames on the current terminal.
> +
> +- A frame means consider all windows on that frame only.
> +
> +Any other value of ALL-FRAMES means consider all windows on the
> +selected frame and no others."
> +  (let (best-window second-best-window)
> +    (dolist (window (window-list-1 nil 'nomini all-frames))
> +      (when (and (or (assq buffer (window-prev-buffers window))
> +                  (assq buffer (window-next-buffers window)))
> +              (or dedicated (not (window-dedicated-p window))))
> +     (if (eq window (selected-window))
> +         (setq second-best-window window)
> +       ;; We probably should throw WINDOW here.
> +       (setq best-window window))))
> +    (or best-window second-best-window)))
> +
>  (defun display-buffer-use-some-window (buffer alist)
>    "Display BUFFER in an existing window.
>  Search for a usable window, set that window to the buffer, and
> @@ -4864,7 +4897,8 @@
>      (unwind-protect
>       (setq window
>             ;; Reuse an existing window.
> -           (or (get-lru-window frame)
> +           (or (window-previously-showing buffer 'visible)
> +               (get-lru-window frame)
>                 (let ((window (get-buffer-window buffer 'visible)))
>                   (unless (and not-this-window
>                                (eq window (selected-window)))