bug#10114: 24.0.91; (not (eq (current-buffer) (window-buffer (selected-window))))

[martin rudalics]

> When you remove the current buffer from the selected window,
> the buffer that gets displayed in the selected window isn't always
> the same as the buffer that gets made the new current buffer.
> The command M-x test (see below) manifests the problem
> for me from runemacs -Q.
>
> Output on Emacs 23.3:
> Current: *Test*<2>; Selected: *Test*<2>; [...]
> Current: *Test*<1>; Selected: *Test*<1>; [...]
>
> Output on Emacs bzr trunk:
> Current: *Test*<2>; Selected: *Test*<2>; [...]
> Current: *Test*<1>; Selected: *scratch*; [...]

The output on Emacs bzr trunk should be

Current: *Test*<2>; Selected: *Test*<2>; [...]
Current: *scratch*; Selected: *scratch*; [...]

because *scratch* was the buffer shown before *Test*<2>*.

> (defun test ()
>   (interactive)
>   (progn
>     ;; This seems to sow enough confusion.
>     (switch-to-buffer-other-window "*Test*<1>")
>     (switch-to-buffer-other-window "*Test*<2>")
>     (delete-other-windows))
>   (while
>       (progn
>         (message
>          "Current: %s; Selected: %s; \
> type k to kill current buffer, \
> any other key to quit"
>          (current-buffer)
>          (window-buffer (selected-window)))
>         (and (eq (read-event) ?k)
>         (kill-buffer))))
>   (clear-this-command-keys t))
>
> In GNU Emacs 24.0.91.1 (i386-mingw-nt6.1.7601)
>  of 2011-11-20 on MACHINE
> Windowing system distributor `Microsoft Corp.', version 6.1.7601
> configured using `configure --with-gcc (4.6)'

The problems happens because `kill-buffer' makes another buffer current
when killing the current buffer and calls `replace-buffer-in-windows'
which ends up calling `switch-to-prev-buffer' for the selected window.
The latter refuses to change the current buffer because the selected
window's buffer is _not_ the current buffer (a behavior needed to make
`switch-to-prev-buffer' work within buffer excursions).

So the solution is to have `kill-buffer' call `replace-buffer-in-windows'
_before_ making another buffer current.

Thanks for the excellent report, martin