* message.el (message-expand-group): Pass the common

prefix substring of completion to `display-completion-list'.

* mh-comp.el (mh-complete-word): Pass the common
prefix substring of completion to `display-completion-list'.

* dabbrev.el (dabbrev-completion): Pass the common
prefix substring of completion to `display-completion-list'.

* filecache.el (file-cache-minibuffer-complete)
(file-cache-complete): Ditto.

* tempo.el (tempo-display-completions): Ditto.

* wid-edit.el (widget-file-complete, widget-color-complete): Ditto.

* emacs-lisp/lisp.el (lisp-complete-symbol): Ditto.

* eshell/em-hist.el (eshell-list-history): Ditto.

* mail/mailabbrev.el (mail-abbrev-complete-alias): Ditto.

* progmodes/etags.el (complete-tag): Ditto.

* progmodes/make-mode.el (makefile-complete): Ditto.

* progmodes/meta-mode.el (meta-complete-symbol): Ditto.

* progmodes/octave-mod.el (octave-complete-symbol): Ditto.

* progmodes/pascal.el (pascal-complete-word)
(pascal-show-completions): Ditto.

* textmodes/bibtex.el (bibtex-complete-internal): Ditto.

* simple.el (completion-common-substring): New variable.
(completion-setup-function): Use `completion-common-substring'
to put faces.

* minibuf.c (Fdisplay_completion_list): Add new optional
argument COMMON_SUBSTRING. Bind `completion-common-substring'
to the optional argument during running `completion-setup-hook'.

1 files changed, 21 insertions, 5 deletions

diff --git a/lisp/simple.el b/lisp/simple.el
index cab04c135d9..8f98b1cc907 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -4844,10 +4844,13 @@ Called from `temp-buffer-show-hook'."
   "Normal hook run at the end of setting up a completion list buffer.
 When this hook is run, the current buffer is the one in which the
 command to display the completion list buffer was run.
-The completion list buffer is available as the value of `standard-output'.")
+The completion list buffer is available as the value of `standard-output'.
+The common prefix substring for completion may be available as the 
+value of `completion-common-substring'. See also `display-completion-list'.")
+
+
+;; Variables and faces used in `completion-setup-function'.
 
-;; This function goes in completion-setup-hook, so that it is called
-;; after the text of the completion list buffer is written.
 (defface completions-first-difference
   '((t (:inherit bold)))
   "Face put on the first uncommon character in completions in *Completions* buffer."
@@ -4867,6 +4870,17 @@ of the differing parts is, by contrast, slightly highlighted."
 (defvar completion-root-regexp "^/"
   "Regexp to use in `completion-setup-function' to find the root directory.")
 
+(defvar completion-common-substring nil
+  "Common prefix substring to use in `completion-setup-function' to put faces.
+The value is set by `display-completion-list' during running `completion-setup-hook'.
+
+To put faces, `completions-first-difference' and `completions-common-part' 
+into \"*Completions*\* buffer, the common prefix substring in completions is
+needed as a hint. (Minibuffer is a special case. The content of minibuffer itself 
+is the substring.)")
+
+;; This function goes in completion-setup-hook, so that it is called
+;; after the text of the completion list buffer is written.
 (defun completion-setup-function ()
   (let ((mainbuf (current-buffer))
 	(mbuf-contents (minibuffer-contents)))
@@ -4905,9 +4919,11 @@ of the differing parts is, by contrast, slightly highlighted."
 		      (funcall (get minibuffer-completion-table 'completion-base-size-function)))
 	      (setq completion-base-size 0))))
       ;; Put faces on first uncommon characters and common parts.
-      (when completion-base-size
+      (when (or completion-base-size completion-common-substring)
 	(let* ((common-string-length
-		(- (length mbuf-contents) completion-base-size))
+		(if completion-base-size
+		    (- (length mbuf-contents) completion-base-size)
+		  (length completion-common-substring)))
 	       (element-start (next-single-property-change
 			       (point-min)
 			       'mouse-face))