Feature Request: Auto expand when there is only a single candidate

[davels]

Here is a patch that adds the option of automatically expanding the completion when there is only a single candidate. This is particularly nice of ac-auto-start is nil and completion is started from a key binding.

There is a new defun: ac-start-and-expand-single. It functions exactly like ac-start, but if the initial completion list contains only a single candidate, it is automatically expanded and completion ends.

There is also a var: ac-always-expand-single-p. If non-nil, a candidate is automatically selected whenever the candidate list is reduced down to a single item.

diff -u d\:/emacs/emacs/site-lisp/auto-complete.el.orig d\:/emacs/emacs/site-lisp/auto-complete.el
--- d:/emacs/emacs/site-lisp/auto-complete.el.orig  2009-10-10 07:37:11.943250000 -0700
+++ d:/emacs/emacs/site-lisp/auto-complete.el   2009-10-20 22:33:37.308970300 -0700
@@ -283,6 +283,10 @@
   :group 'auto-complete)
 (defvaralias 'ac-candidate-max 'ac-candidate-limit)

+(defcustom ac-always-expand-single-p nil
+  "Non-nil to automatically complete whenever a single candidate remains."
+  :group 'auto-complete)
+
 (defcustom ac-modes
   '(emacs-lisp-mode lisp-interaction-mode
                     c-mode cc-mode c++-mode java-mode
@@ -732,7 +736,12 @@
                                    'ac-selection-face))
       (setq ac-selection selection))))

-(defun ac-start ()
+(defun ac-start-and-expand-single ()
+  "Start completion, automatically expanding if there is only a single candiate."
+  (interactive)
+  (ac-start t))
+
+(defun ac-start (&optional expand-single)
   "Start completion."
   (interactive)
   (let* ((point (save-excursion (funcall ac-prefix-function)))
@@ -762,17 +771,25 @@
                                (funcall ac-candidate-function))))
         (if ac-candidate-filter-function
             (setq candidates (funcall ac-candidate-filter-function candidates)))
-        (setq width (let ((w '(0)) s)
-                      (dotimes (i ac-candidate-menu-height)
-                        (setq s (nth i candidates))
-                        (if (stringp s) (push (string-width s) w)))
-                      (apply 'max w)))
-        (if (or reposition
-                (null ac-menu)
-                (> width current-width)
-                (< width (- current-width 10)))
-            (ac-setup (* (ceiling (/ width 10.0)) 10)))
-        (ac-update-candidates candidates)))))
+        (if (and (or expand-single ac-always-expand-single-p)
+                 (= 1 (length candidates)))
+            (let* ((candidate (car candidates))
+                   (action (ac-get-candidate-action candidate)))
+              (ac-expand-string candidate)
+              (if action
+                  (funcall action))
+              (ac-abort))
+          (setq width (let ((w '(0)) s)
+                        (dotimes (i ac-candidate-menu-height)
+                          (setq s (nth i candidates))
+                          (if (stringp s) (push (string-width s) w)))
+                        (apply 'max w)))
+          (if (or reposition
+                  (null ac-menu)
+                  (> width current-width)
+                  (< width (- current-width 10)))
+              (ac-setup (* (ceiling (/ width 10.0)) 10)))
+          (ac-update-candidates candidates))))))

 (defun ac-adaptive-candidate-filter (candidates)
   "Filter candidates according to length and history (not yet)."

Diff finished.  Sat Oct 24 19:20:04 2009

[m2ym]

Could you please tell me how do you use this feature?

[davels]

I normally have ac-auto-start set to nil. If I bind TAB to ac-start-and-expand-single then hitting TAB will either show a completion menu if there is >1 candidate or immediately do the expansion if there is only a single candidate.

I like this because it works kind of like normal TAB completion: complete if you can, otherwise show me a list to choose from.

This came up because I've been working on using auto-complete to do tab completion in ipython shell mode.

The ac-always-expand-single-p is something I added just to try out when ac-auto-start is 't. It's a bit jarring at times and I'm pretty neutral on this part of the patch. I'd be willing to re-submit the patch without that part if you'd like.

[m2ym]

It seems very good idea.

I'll implement it in more general way.

[monsanto]

Did this ever get implemented in a more general way?

[m2ym]

The current implementation includes this feature already. So close this issue.