Howto cache completing-read inputs

Question

Is there a simple framework for making previous inputs of completing-read persistent across emacs restarts? For instance if I start with: (completing-read "test:" '("a" "b") nil nil) and enter "c" the next time I start emacs and execute I want the collection to be (completing-read "test:" '("a" "b" "c") nil nil) instead. Is there a simple way to achieve this?

Answer 1

Yes: just put (savehist-mode 1) in your ~/.emacs and that should do the trick.

[ Tho not quite in the way you describe: c will still not be among the completion candidates. But it will be in your history and hence accessible via M-p, M-s, ... ]

Answer 2

1. You can persist any global variable, by adding it to the value of option savehist-additional-variables. This includes any minibuffer history variable.

2. Minibuffer history variables are used (typically) by completing-read. You can use M-p and M-r to retrieve previously used minibuffer inputs when you are prompted by completing-read. See (emacs) Minibuffer History.

3. However, there are many different minibuffer history variables. The most common, catch-all variable is minibuffer-history. You can try persisting all of the minibuffer history variables you can find ;-), but be aware that any code can add a new such variable.

4. None of what I've said puts minibuffer history entries into the default set of completion candidates for any completing-read call. Input history and completion candidates are two different things.

5. If you use Icicles then during minibuffer completion (including completing-read):

   • You can use M-h to match your current input against the minibuffer history directly.

   • Use M-<pause> to restrict the current set of completion candidates to those you've used previously. If you use C-u M-pause, then the previously used candidates are ordered chronologically, most recent first.

6. If you use Icicles then you can use M-o to complete against the history list during any minibuffer inputting, even without completion (i.e., whether the minibuffer is being used by completing-read or some other function).

Answer 3

It seems there is no history for single minibuffer instances so I'm using this approach where magit-gerrit-reviewers is the '("a" "b" "c") list:

Saving history

(defun magit-gerrit-write-review (file)
   (with-temp-file file
       (insert "(setq magit-gerrit-reviewers '")
       (prin1 magit-gerrit-reviewers             (current-buffer))
       (insert ")" )))

Loading history:

(if (file-exists-p "~/.gerrit.reviewers")
             (load "~/.gerrit.reviewers"))

And using it:

(completing-read "Reviewer Name/Email:" magit-gerrit-reviewers nil nil)