Allow searching interactively over completions in `M-x'

* lisp/simple.el (read-extended-command): Allow doing interactive
searches over the completions (bug#12490).  This restores the
behaviour from Emacs 23 that was lost in Emacs 24.

2 files changed, 15 insertions, 3 deletions

diff --git a/etc/NEWS b/etc/NEWS
index a1255a6f423..34d078b485f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -820,6 +820,12 @@ window after starting).  This variable defaults to nil.
 ** Miscellaneous
 
 ---
+*** 'C-s' in 'M-x' now searches over completions again.
+In Emacs 23, typing 'M-x' ('read-extended-command') and then 'C-s' (to
+do an interactive search) would search over possible completions.
+This was lost in Emacs 24, but is now back again.
+
+---
 *** 'M-x report-emacs-bug' will no longer include "Recent messages" section.
 These were taken from the "*Messages*" buffer, and may inadvertently
 leak information from the reporting user.
diff --git a/lisp/simple.el b/lisp/simple.el
index 755d700cd4b..5f1338abb0c 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -1847,9 +1847,15 @@ to get different commands to edit and resubmit."
 	     (lambda ()
 	       ;; Get a command name at point in the original buffer
 	       ;; to propose it after M-n.
-	       (with-current-buffer (window-buffer (minibuffer-selected-window))
-		 (and (commandp (function-called-at-point))
-		      (format "%S" (function-called-at-point)))))))
+	       (let ((def (with-current-buffer
+			      (window-buffer (minibuffer-selected-window))
+			    (and (commandp (function-called-at-point))
+				 (format "%S" (function-called-at-point)))))
+		     (all (sort (minibuffer-default-add-completions)
+				(lambda (a b) (string< a b)))))
+		 (if def
+		     (cons def (delete def all))
+		   all)))))
     ;; Read a string, completing from and restricting to the set of
     ;; all defined commands.  Don't provide any initial input.
     ;; Save the command read on the extended-command history list.