Decomposing helm-source-buffers-list in two parts

Question

I'd like to customize helm-mini in such a way that its helm-source-buffers-list would be decomposed in two parts:

1. One source corresponding to buffers visiting a file (i.e. something like (remove-if-not #'buffer-file-name (buffer-list))

2. Another corresponding to the complement of (1) (i.e. (remove-if #'buffer-file-name (buffer-list))

I looked at tutorials like this one which gives me an idea of how I could probably do it:

http://kitchingroup.cheme.cmu.edu/blog/2015/01/24/Anatomy-of-a-helm-source/

but I'm too new to Helm to imagine that whatever solution I will come up with will make complete sense or be minimal enough.. so I'd appreciate any help.

Answer 1

Short answer: Create your own helm buffer sources and modify the helm-mini-default-sources variable to use them.

---

The helm-mini command uses helm-mini-default-sources as its helm sources, so you can choose which sources to use and their order when showing in helm buffer. You cannot customize the helm-source-buffers-list variable itself, except choosing to use it or not. You need to create your own buffer list source to replace helm-source-buffers-list, for example,

(setq helm-mini-default-sources '(my-file-buffers
                                  my-other-buffers
                                  helm-source-recentf
                                  helm-source-buffer-not-found))

here, you need to create two new sources: my-file-buffers and my-other-buffers.

Usually, you should use the helm-source-buffers class to make these two sources, but you cannot use them in one and the same helm command (see closed issue https://github.com/emacs-helm/helm/issues/1034), so you also need to create your own helm buffer source class, it's easy if you use helm-source-buffers as a reference.

PS. helm wiki includes a section on Developping using helm: https://github.com/emacs-helm/helm/wiki#developpingusinghelmframework, it can be considered the official documentation of helm.

Answer 2

With the help of @xuchunyang's excellent answer and after an epic struggle with ELisp, this is the solution I came up with, and which seems to work:

;; This decomposes helm-source-buffers-list in two parts/sources:
;; (1) Files: file-visiting buffers
;; (2) Buffers non-file-visiting buffers

(defclass my-helm-source-file-buffers-class (helm-source-buffers)
  ((candidates :initform
               (lambda ()
                 (mapcar 'buffer-name
                         (cl-remove-if-not #'buffer-file-name (buffer-list)))))))

(defclass my-helm-source-nonfile-buffers-class (helm-source-buffers)
   ((candidates :initform
               (lambda ()
                 (mapcar 'buffer-name
                         (cl-remove-if #'buffer-file-name (buffer-list)))))))

;; Use the decomposition for helm-mini

(setq my-helm-source-file-buffers-list
      (helm-make-source "Files" 'my-helm-source-file-buffers-class)
      my-helm-source-nonfile-buffers-list
      (helm-make-source "Buffers" 'my-helm-source-nonfile-buffers-class))

(setq helm-mini-default-sources '(my-helm-source-file-buffers-list
                                  my-helm-source-nonfile-buffers-list
                                  helm-source-recentf
                                  helm-source-buffer-not-found))