How to stop replacing prefix with item in company backend?

Question

I want to write backend for company-mode. I have this example:

(require 'company)
(require 'cl-lib)

(defun backend-name (command &optional arg &rest ignored)
  (interactive (list 'interactive))
  (cl-case command
    (interactive (company-begin-backend 'backend-name))
    (prefix (when (looking-back "git .*?\\([a-zA-Z-~]+ \\)$") (match-string 1)))
    (candidates (cond
      ((string= arg "reset ) '("--hard" "--soft"))
      (t nil)))))

This does not do what I want. Choosing "--hard" from list replaces word "reset ". It should append "--hard" to the end of word "reset ".

Answer 1

The literal answer would be "you can't" because the prefix is the thing that's supposed to be replaced.

What you can (should) do instead, is return a smaller string as prefix (e.g. ""), but then inside the candidates handler search back e.g. using the same regexp, see whether the previous word is "reset", and act accordingly.