Managing Emacs *Man* buffer location?

Question

Emacs behaviour which recently[*] started to irritate me:

• I edit the file, and need some help
• M-x man something
• emacs politely splits frame into two windows and opens manpage there, I see both source and man, great
• while reading man I find that I need to followup further, so I M-x man anothertopic
• emacs opens new manpage in window previously occupied by my source, I see two manpages on the screen and can't edit anymore (until I switch buffer)

Is it possible to make Man prefer reuse existing man window?

Answer 1

Adapting display-buffer-reuse-window to create display-buffer-reuse-major-mode-window, we can then use display-buffer-alist to specify that this be used to display buffers in Man-mode.

Obviously the first form can also be trivially modified to apply to any number of modes besides Man-mode.

(add-to-list 'display-buffer-alist
             (cons (lambda (buffer alist)
                     (with-current-buffer buffer
                       (eq major-mode 'Man-mode)))
                   (cons 'display-buffer-reuse-major-mode-window
                         '((inhibit-same-window . nil)
                           (reusable-frames . visible)
                           (inhibit-switch-frame . nil)))))

(defun display-buffer-reuse-major-mode-window (buffer alist)
  "Return a window displaying a buffer in BUFFER's major mode.
Return nil if no usable window is found.

If ALIST has a non-nil `inhibit-same-window' entry, the selected
window is not eligible for reuse.

If ALIST contains a `reusable-frames' entry, its value determines
which frames to search for a reusable window:
  nil -- the selected frame (actually the last non-minibuffer frame)
  A frame   -- just that frame
  `visible' -- all visible frames
  0   -- all frames on the current terminal
  t   -- all frames.

If ALIST contains no `reusable-frames' entry, search just the
selected frame if `display-buffer-reuse-frames' and
`pop-up-frames' are both nil; search all frames on the current
terminal if either of those variables is non-nil.

If ALIST has a non-nil `inhibit-switch-frame' entry, then in the
event that a window on another frame is chosen, avoid raising
that frame."
  (let* ((alist-entry (assq 'reusable-frames alist))
         (frames (cond (alist-entry (cdr alist-entry))
                       ((if (eq pop-up-frames 'graphic-only)
                            (display-graphic-p)
                          pop-up-frames)
                        0)
                       (display-buffer-reuse-frames 0)
                       (t (last-nonminibuffer-frame))))
         (window (let ((mode (with-current-buffer buffer major-mode)))
                   (if (and (eq mode (with-current-buffer (window-buffer)
                                       major-mode))
                            (not (cdr (assq 'inhibit-same-window alist))))
                       (selected-window)
                     (catch 'window
                       (walk-windows
                        (lambda (w)
                          (and (window-live-p w)
                               (eq mode (with-current-buffer (window-buffer w)
                                          major-mode))
                               (not (eq w (selected-window)))
                               (throw 'window w)))
                        'nomini frames))))))
    (when (window-live-p window)
      (prog1 (window--display-buffer buffer window 'reuse alist)
        (unless (cdr (assq 'inhibit-switch-frame alist))
          (window--maybe-raise-frame (window-frame window)))))))