How to write a helm function to select only from shell buffers

Question

I recently switched from ido to helm. Now I'm using helm-buffers-list to select buffers.

Additionally I want to create a customised helm-buffers-list function which allows me only to select from shell buffers; let's call this new function helm-shell-buffers-list. From earlier times where I used ido I still have a function populating a list with all shell buffers - how can I use this list to create the function helm-shell-buffers-list?

I looked at the source for helm-buffers-list:

(defun helm-buffers-list ()
  (interactive)
  (unless helm-source-buffers-list
    (setq helm-source-buffers-list
          (helm-make-source "Buffers" 'helm-source-buffers)))
  (helm :sources '(helm-source-buffers-list
                   helm-source-ido-virtual-buffers
                   helm-source-buffer-not-found)
        :buffer "*helm buffers*"
        :keymap helm-buffer-map
        :truncate-lines helm-buffers-truncate-lines))

This leads me to believe I have to provide a new class similar to helm-source-buffers:

(defclass helm-source-buffers (helm-source-sync helm-type-buffer)
  ((buffer-list
    :initarg :buffer-list
    :initform #'helm-buffer-list
    :custom function
    :documentation
    "  A function with no arguments to create buffer list.")
   (init :initform 'helm-buffers-list--init)
   (multimatch :initform nil)
   (match :initform 'helm-buffers-match-function)
   (persistent-action :initform 'helm-buffers-list-persistent-action)
   (keymap :initform helm-buffer-map)
   (migemo :initform 'nomultimatch)
   (volatile :initform t)
   (nohighlight :initform t)
   (resume :initform (lambda () (setq helm-buffers-in-project-p nil)))
   (help-message :initform 'helm-buffer-help-message)))

However in that class I have no idea where to provide the list with buffers...

Any help greatly appreciated!

Answer 1

Assuming "shell buffers" means its major-mode is shell-mode, you can supply "shell buffers" via :buffer-list argument while calling helm-make-source:

(defvar helm-source-shell-buffers-list
  (helm-make-source "Shell Buffers" 'helm-source-buffers
    :buffer-list
    (lambda ()
      (mapcar #'buffer-name
              (cl-remove-if-not
               (lambda (buf)
                 (with-current-buffer buf
                   (eq major-mode 'shell-mode)))
               (buffer-list))))))

(defun helm-shell-buffers-list ()
  (interactive)
  (helm :sources helm-source-shell-buffers-list
        :keymap helm-buffer-map
        :truncate-lines helm-buffers-truncate-lines))

BTW, you can filter buffer by their major mode in helm-buffers-list, for example, type "*shell" for all buffers in shell-mode.