bug#591: 23.0.60; lisp-complete-symbol erases extra text

[Drew Adams]

> From: Chong Yidong Sent: Tuesday, July 29, 2008 1:46 PM
> Hi Stefan,
> This bug was introduced by your patch:
>  2008-04-13  Stefan Monnier  <monnier@iro.umontreal.ca>
>  minibuffer.el (display-completion-list):
>  Handle all-completions's new base-size info to set 
>  completion-base-size.
> 
> This sets completion-base-size to 0, which causes the 
> completions buffer to delete everything in the Lisp
> buffer when you make a selection.
> 
> I don't understand why we need the (completely undocumented)
> hack introduced here, where the cdr of the last item on the
> completions list gives completion-base-size.  Does anything
> else in Emacs depend on this? Why not simply add a new
> optional argument to display-completion-list?

I won't pronounce on the hack of putting the base size into the cdr; only Stefan
knows if that is necessary and the right approach. I will say about that change
only that it required me to change my own code in a few places. For example, you
can no longer just apply `length' to the list, because it is no longer a true
list.

My reason for replying to your mail is instead to pass along the code that
Icicles uses for `choose-completion-string', in case it helps. I don't provide
it as a diff for straightforward patching, but rather as something you might
want to think about. The essential differences are these:

1. I use this:
(delete-region
  (+ base-size
     (if mini-p (minibuffer-prompt-end) (point-min)))
  (if mini-p (point-max) (point)))

instead of this:
(delete-region (+ base-size (field-beginning)) (point))

2. After deleting the region I do this:
(when mini-p (goto-char (point-max)))

Here is my definition:

(defun choose-completion-string (choice &optional buffer base-size)
  "Switch to BUFFER and insert the completion choice CHOICE.
BASE-SIZE, if non-nil, says how many characters of BUFFER's text
to keep.  If it is nil, we call `choose-completion-delete-max-match'
to decide what to delete.
If BUFFER is the minibuffer, then exit the minibuffer, unless one of
the following is true:
 - it is reading a file name, CHOICE is a directory, and
   `icicle-dir-candidate-can-exit-p' is nil
 - `completion-no-auto-exit' is non-nil
 - this is just a `lisp-complete-symbol' completion."
  (let* ((buffer (or buffer completion-reference-buffer))
         (mini-p (minibufferp buffer)))
    ;; If BUFFER is a minibuffer, barf unless it's currently active.
    (if (and mini-p
             (or (not (active-minibuffer-window))
                 (not (equal buffer (window-buffer
                                     (active-minibuffer-window))))))
        (error "Minibuffer is not active for completion")
      ;; Set buffer so buffer-local `choose-completion-string-functions' works.
      (set-buffer buffer)
      (unless (run-hook-with-args-until-success
               'choose-completion-string-functions
               choice buffer mini-p base-size)
        ;; Insert completion into buffer where completion was requested.
        (if base-size
            (delete-region
             (+ base-size (if mini-p (minibuffer-prompt-end) (point-min)))
             (if mini-p (point-max) (point)))
          (choose-completion-delete-max-match choice))
        (when mini-p (goto-char (point-max)))
        (insert choice)
        (remove-text-properties
         (- (point) (length choice)) (point) '(mouse-face nil))
        ;; Update point in the window that BUFFER is showing in.
        (let ((window (get-buffer-window buffer 0)))
          (set-window-point window (point)))
        ;; If completing for the minibuffer, exit it with this choice,
        ;; unless this was a `lisp-complete-symbol' completion.
        (and (not completion-no-auto-exit)
             (equal buffer (window-buffer (minibuffer-window)))
             (or minibuffer-completion-table
                 (and icicle-mode
                      (or icicle-extra-candidates icicle-proxy-candidates)))
             (not (eq 'lisp-complete-symbol icicle-cmd-calling-for-completion))
             ;; Exit the minibuffer if `icicle-dir-candidate-can-exit-p',
             ;; or not reading a file name, or chosen file is not a directory.
             (if (or icicle-dir-candidate-can-exit-p
                     (not (eq minibuffer-completion-table
                              'read-file-name-internal))
                     (not (file-directory-p (field-string (point-max)))))
                 (exit-minibuffer)
               (let ((mini (active-minibuffer-window)))
                 (select-window mini)
                 (when minibuffer-auto-raise
                   (raise-frame (window-frame mini))))))))))

HTH - Drew