add command to the “Buffers” menu

Question

Is it possible to ADD commands to the "Buffers" menu? I'd like to add menu entries for:

• Open new window below current buffer
• Split window
• Close current buffer

...and maybe more. I'd want to add them after the existing:

• Next Buffer
• Previous Buffer
• Select Named Buffer...
• List All Buffers

Is that possible? If so, how?

Answer 1

Even if the automatic generation of the buffer menu is a bit complicated the method to add menu items to the buffer menu is quite simple. Just add them with easy-menu-add-item after menu-mode is loaded. The general scheme is:

(eval-after-load "menu-bar"
  (lambda ()
    (easy-menu-add-item nil '("Buffers") ITEM)
    ...))

where ITEM stands for the item you want to add (see the doc for easy-menu-define for the syntax of ITEM).

The interpretation of the menu entries you specified in your question is a bit difficult. I interpret these entries as follows:

• Open new window below current buffer: Split the selected window, select the lower window of the split, and find a file in that window.
• Split window: This is pretty clear: split-window
• Close current buffer: kill-buffer

The following lisp code demonstrates adding menu items to the buffer menu according to your specification (as I interpret it).

You can copy-paste the code into your init file.

(require 'easymenu)

(declare-function find-file-window-below-selected "ext: ")

(eval-after-load "menu-bar"
  (lambda ()
    (easy-menu-add-item nil '("Buffers") ["Find file below selected window" find-file-window-below-selected t])
    (easy-menu-add-item nil '("Buffers") ["Split window" split-window t])
    (easy-menu-add-item nil '("Buffers") ["Kill buffer" kill-buffer t])))

(defun find-file-window-below-selected (filename &optional wildcards)
  "Like `find-file' with args FILENAME and WILDCARDS.
Split window before vertically and display the new file buffer in the
lower window."
  (interactive (find-file-read-args "Find file in new window: "
                    (confirm-nonexistent-file-or-buffer)))
  (select-window (split-window-below))
  (find-file filename wildcards))

Last but not least a short motivation why this method works:

The buffer menu commands are listed in the variable menu-bar-buffers-menu-command-entries. That list is populated by the function menu-bar-update-buffers if it is not set yet. Afterwards menu-bar-buffers-menu-command-entries is appended to global-buffers-menu-map by menu-bar-update-buffers.

Thereby menu-bar-buffers-menu-command-entries is not copied but just appended. Therefore items which you define via easy-menu-add-item at the end of global-buffers-menu-map end up in menu-bar-buffers-menu-command-entries. The value of menu-bar-buffers-menu-command-entries is set when menu-bar-update-buffers is called at loading menu-bar.el[c]?. It is not reset afterwards and always appended to the automatically generated buffer menu.