Don't show uninteresting files in Emacs completion window

Question

How do I prevent Emacs from showing me all the files I'm not interested in (such as ~ backup files, .pyc files, or .orig files) when I: C-x C-f TAB ?

It is working in one respect: if I know the file I want to open begins with foo and I type foo TAB then the mini-buffer correctly autocompletes all the way to foo.py. It correctly ignored foo~ and foo.pyc, because both ~ and .pyc are in completion-ignored-extensions. It also correctly lets me open either ignored file if I really want to by typing in all the letters my self.

However, if I just hit TAB to to bring up the completion list buffer then that list includes files with extensions in completion-ignored-extensions, which makes it very difficult to find what I'm looking for.

Clearly the code to ignore uninteresting files is there and working. How do I get the completion list buffer to respect completion-ignored-extensions?

(by-the-by, can I make dired behave similarly?)

Answer 1

I don't know of an answer for completion, I'm afraid. I think this is by design - when you know the name you're looking for, you probably don't want e.g. the backup file. But when you don't know, it's probably better to have a list of all of the files.

However, for dired, you can load the 'dired-x' package on startup (in your .emacs), and this provides dired-omit-mode:

(load "dired-x")

You can use 'M-x customize-variable<RET>dired-omit-files' to set the actual patterns to ignore. Then when you are in dired mode you can use M-O (the letter, not the number) to toggle 'omission' on and off.

Answer 2

This piece of advice filters out files with extensions listed in 'completion-ignored-extensions:

(defadvice completion--file-name-table (after 
                                        ignoring-backups-f-n-completion 
                                        activate)
  "filter out results when the have completion-ignored-extensions"
  (let ((res ad-return-value))
(if (and (listp res)
  (stringp (car res))
  (cdr res))                 ; length > 1, don't ignore sole match
    (setq ad-return-value
              (completion-pcm--filename-try-filter res)))))

Note: This doesn't affect dired.

For the dired issue, add this to your .emacs

(eval-after-load "dired"
  '(require 'dired-x))

(add-hook 'dired-mode-hook
          (lambda ()
            (dired-omit-mode 1)))

Read the documentation for dired-x to get an idea of what's available there.