bug#12638: 24.2.50; FR: Some suggestions for icomplete-mode

[Jambunathan K]

Jambunathan K <kjambunathan@gmail.com> writes:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>>> 2. M-x debbugs-gnu
>>>    There is no way I can C-s C-j to the second or third candidates.
>>>    I normally use debbbugs-gnu-search which is the second candidate.
>>
>> Better ask this elsewhere, I'm not up to speed on debbugs-gnu.
>
> I am attaching screenshot of minibuffer. 
>
>     1. M-x debbugs-gnu
>     2. Immediately cycle with C-s
>
> Cycling may happen internally but the UI presents the "most-is-exact"
> always at the head.  This is a definite bug.

The case to be handled is "Complete, but not unique".  

The attached patch fixes the issue by sneaking a Ctrl-M in to the try
try completion field.

Attachments: 
M-x debbugs-gnu RET with icomplete-mode on.

icomplete-1.png:  
        Note the ^M and the empty first entry

icomplete-2.png:  
        After a C-s.  Note the ^M indicator and empty entry pushed to
        the last.

icomplete-3.png:
        This is the second invocation of M-x debbugs-gnu RET.  Note that
        the entry from the recent history is at the head.  Also note ^M
        and the empty entries.

=== modified file 'lisp/ChangeLog'
--- lisp/ChangeLog      2012-12-13 05:29:15 +0000
+++ lisp/ChangeLog      2012-12-13 13:32:58 +0000
@@ -1,3 +1,10 @@
+2012-12-13  Jambunathan K  <kjambunathan@gmail.com>
+
+       * icomplete.el (icomplete-hide-common-prefix): New user variable.
+       (icomplete-first-match): New user face.
+       (icomplete-completions): Honor above settings.  Correctly handle
+       the case when NAME is complete but not unique (Bug#12638).
+
 2012-12-13  Alan Mackenzie  <acm@muc.de>
 
        Make CC Mode not hang when _some_ lines end in CRLF.  Bug #11841.

=== modified file 'lisp/icomplete.el'
--- lisp/icomplete.el   2012-11-30 17:09:55 +0000
+++ lisp/icomplete.el   2012-12-13 13:16:31 +0000
@@ -76,6 +76,18 @@
   :type 'string
   :version "24.4")
 
+(defcustom icomplete-hide-common-prefix t
+  "When non-nil, hide common prefix from completion candidates.
+When nil, show candidates in full."
+  :type 'boolean
+  :version "24.4"
+  :group 'icomplete)
+
+(defface icomplete-first-match  '((t :weight bold))
+  "Face used by icomplete for highlighting first match."
+  :version "24.4"
+  :group 'icomplete)
+
 ;;;_* User Customization variables
 (defcustom icomplete-prospects-height
   ;; 20 is an estimated common size for the prompt + minibuffer content, to
@@ -332,14 +344,12 @@ are exhibited within the square braces.)
             (determ (unless (or (eq t compare) (eq t most-try)
                                 (= (setq compare (1- (abs compare)))
                                    (length most)))
-                      (concat open-bracket
                               (cond
                                ((= compare (length name))
                                  ;; Typical case: name is a prefix.
                                 (substring most compare))
                                ((< compare 5) most)
-                               (t (concat "..." (substring most compare))))
-                              close-bracket)))
+                       (t (concat "..." (substring most compare))))))
             ;;"-prospects" - more than one candidate
             (prospects-len (+ (length determ) 6 ;; take {,...} into account
                                (string-width (buffer-string))))
@@ -350,6 +360,8 @@ are exhibited within the square braces.)
                     ;; one line, increase the allowable space accordingly.
                     (/ prospects-len (window-width)))
                  (window-width)))
+            (prefix (when icomplete-hide-common-prefix
+                      (try-completion "" comps)))
              (prefix-len
               ;; Find the common prefix among `comps'.
              ;; We can't use the optimization below because its assumptions
@@ -359,37 +371,58 @@ are exhibited within the square braces.)
              ;;     ;; Common case.
              ;;     (length most)
              ;; Else, use try-completion.
-             (let ((comps-prefix (try-completion "" comps)))
-               (and (stringp comps-prefix)
-                    (length comps-prefix)))) ;;)
-
+             (and (stringp prefix) (length prefix))) ;;)
             prospects most-is-exact comp limit)
        (if (eq most-try t) ;; (or (null (cdr comps))
            (setq prospects nil)
+         (when (and (cdr comps) (member name comps))
+           ;; NAME is complete but not unique.  This scenario, poses
+           ;; following UI issues:
+           ;;
+           ;; - When common prefix is hidden, NAME is stripped empty.
+           ;;   This would make the entry inconspicuous.
+           ;; - Due to sorting of completions, NAME may not be the
+           ;;   first of the prospects and could be hidden deep in the
+           ;;   displayed string.
+           ;; - Because of truncation, NAME may not even be displayed
+           ;;   to the user.
+           ;;
+           ;; To circumvent all the above problems, provide a visual
+           ;; cue to the user via try completion field.
+           (setq determ "
"))
          (while (and comps (not limit))
            (setq comp
                  (if prefix-len (substring (car comps) prefix-len) (car comps))
                  comps (cdr comps))
-           (cond ((string-equal comp "") (setq most-is-exact t))
-                 ((member comp prospects))
-                 (t (setq prospects-len
+           (setq prospects-len
                            (+ (string-width comp) 1 prospects-len))
                     (if (< prospects-len prospects-max)
                         (push comp prospects)
-                      (setq limit t))))))
+             (setq limit t))))
+       (setq prospects (nreverse prospects))
+       ;; Decorate the first of prospects.
+       (when prospects
+         (let ((first (copy-sequence (pop prospects))))
+           (put-text-property 0 (length first)
+                              'face 'icomplete-first-match first)
+           (push first prospects)))
         ;; Restore the base-size info, since completion-all-sorted-completions
         ;; is cached.
         (if last (setcdr last base-size))
+       (when determ
+         (setq determ (concat open-bracket determ close-bracket)))
        (if prospects
            (concat determ
+                   (if (not (cdr prospects))
+                       ;; NAME is not complete but will complete to
+                       ;; an EXACT match on next try.
+                       ""
+                     (concat
                    "{"
-                   (and most-is-exact
-                         (substring icomplete-separator
-                                    (string-match "[^ ]" icomplete-separator)))
-                   (mapconcat 'identity (nreverse prospects)
-                               icomplete-separator)
+                      (mapconcat 'identity prospects icomplete-separator)
                    (and limit (concat icomplete-separator "…"))
-                   "}")
+                      "}"
+                      )))
          (concat determ " [Matched]"))))))
 
 ;;_* Local emacs vars.

icomplete-3.png
Description: PNG image

icomplete-2.png
Description: PNG image

icomplete-1.png
Description: PNG image