How to create grouped company-backends list and an extra one for specific major mode?

Question

Lately, I'm working on how to configure the best grouped company-backends for different major modes, although having been using company-mode for over one year (already got a configuration long time ago), but recently realized it was not working as I expected, and started looking for the official documentation on how to configure it, but found nothing useful.

For example in emacs-lisp-mode, words in buffers, yasnippet, elisp(company-capf), etc., sorted in this order in the droplist

in c/c++-mode, words in buffers, yasnippet, the name(variable, function, struct etc.), etc,.

in org-mode, words in buffers, yasnippet, etc,

in latex-mode, words in buffers, yasnippet, latex-environment, etc.

If I insert and "/", it should use company-files as the primary backend.

In above examples, there will be a default company-backends for all the major modes when company-mode is enabled, there will be an extra configuration for a specific minor mode to work with the default.

For example:

(setq company-backends
  '(
    (
     company-files
     company-dabbrev
     company-keywords
     company-capf
     company-yasnippet
     )
    (company-abbrev company-dabbrev)
    ))
(add-hook 'emacs-lisp-mode-hook
      (lambda ()
        (set (make-local-variable 'company-backends)
             (append company-backends
                     '((
                        company-elisp
                        ))))))

But I cannot make the company-elisp work, there always are such problems for other major modes, the two backends won't work well for a specific major mode. there always are one or more backends is not working.

No official documentation or examples.

How to create grouped company-backends list to work with an extra one for specific major mode?

Answer 1

I faced with this exact same problem a couple of weeks back. company-mode was not behaving as expected for some major modes and for major modes I got no completion at all.

And it turns out the solution was pretty simple. Here's my config for emacs-lisp-mode :-

(use-package emacs-lisp-mode
  :init
  (defun my-elisp-mode-hook ()
    "Hook for `emacs-lisp-mode'"
    (set (make-local-variable 'company-backends)
         '((company-capf company-dabbrev-code company-yasnippet company-files))))

  (add-hook 'emacs-lisp-mode-hook 'my-elisp-mode-hook)
  (add-hook 'emacs-lisp-mode-hook 'company-mode))

Follow the same recipe for other major modes.

As for creating a grouped backend for company to use for all modes, add something like this to your .emacs :-

  (add-to-list 'company-backends 'company-dabbrev-code)
  (add-to-list 'company-backends 'company-yasnippet)
  (add-to-list 'company-backends 'company-files)