Thoughts on "Native shell completion in Emacs"

Native shell completion in Emacs by Troy Hinckley is must read for completion in shell-mode.

One problem is my ~/.bashrc executes /etc/bash_completion,

if [ -f /etc/bash_completion ]; then
    . /etc/bash_completion
fi

Unfortunately /etc/bash_completion makes complete -p output some lines the Emacs function bash-completion-tokenize can't analyze.

Here is output of complete -p at my PC,

...
complete -F _known_hosts mtr
complete -o default -o nospace -W 'homepc
192.168.1.104
github.com
gitlab.com' scp
complete -o default -f -X '!*.dvi' dvipdf
...

The line gitlab.com' scp will crash bash-completion-tokenize. Obviously, one line complete -o default -o nospace -W 'homepc 192.168.1.104 github.com gitlab.com' scp is wrongly split into multiple lines by complete -p.

In shell-mode, completion functions might call bash-completion-tokenize. If bash-completion-tokenize crashes, the completion in shell-mode won't work.

Besides, if company-mode provides auto-completion UI, it's better to place the backend company-files before company-native-complete. It's because the backend company-files displays the full file path in candidates. So users can complete the whole path in one shot.

My setup code for the packages Troy Hinckley suggested,

;; Enable auto-completion in `shell'.
(with-eval-after-load 'shell
  (native-complete-setup-bash))

;; `bash-completion-tokenize' can handle garbage output of "complete -p"
(defadvice bash-completion-tokenize (around bash-completion-tokenize-hack activate)
  (let* ((args (ad-get-args 0))
         (beg (nth 0 args))
         (end (nth 1 args)))
    ;; original code extracts tokens from output of "complete -p" line by line
    (cond
     ((not (string-match-p "^complete " (buffer-substring beg end)))
      ;; filter out some wierd lines
      (setq ad-return-value nil))
     (t
      ad-do-it))))

(defun shell-mode-hook-setup ()
  "Set up `shell-mode'."
  ;; hook `completion-at-point', optional
  (add-hook 'completion-at-point-functions #'native-complete-at-point nil t)
  (setq-local company-backends '((company-files company-native-complete)))
  ;; `company-native-complete' is better than `completion-at-point'
  (local-set-key (kbd "TAB") 'company-complete))
(add-hook 'shell-mode-hook 'shell-mode-hook-setup)

Screenshot,