Optimize lisp/icomplete.el when default completion available

Often, when using icomplete with icomplete-show-matches-on-no-input
and commands like C-h f, icomplete-exhibit will take a long time (like
several seconds) to show all the completions.

However, if there is a non-nil default value, like when the C-h f is
performed exactly on a function name, the minibuffer prompt will
reflect that immediately.  If the user immediately presses RE
(icomplete-force-complete-and-exit) we take that to mean "use the
default" and avoid the long wait.

As an extra performance tweak, this commit also removes an unneeded
call to icomplete-exhibit in icomplete-minibuffer-setup.

* lisp/icomplete.el (icomplete-force-complete-and-exit): Short-circuit
possibility of non-nil minibuffer-default.
(icomplete-minibuffer-setup): No need to explicitly icomplete-exhibit
here since icomplete-post-command-hook will call it unconditionally.

1 files changed, 2 insertions, 4 deletions

diff --git a/lisp/icomplete.el b/lisp/icomplete.el
index 51f2611c6b3..5cd11b125d2 100644
--- a/lisp/icomplete.el
+++ b/lisp/icomplete.el
@@ -156,7 +156,7 @@ icompletion is occurring."
 Use the first of the matches if there are any displayed, and use
 the default otherwise."
   (interactive)
-  (if (or icomplete-show-matches-on-no-input
+  (if (or (and (not minibuffer-default) icomplete-show-matches-on-no-input)
           (> (icomplete--field-end) (icomplete--field-beg)))
       (minibuffer-force-complete-and-exit)
     (minibuffer-complete-and-exit)))
@@ -269,9 +269,7 @@ Usually run by inclusion in `minibuffer-setup-hook'."
     					 (current-local-map)))
     (add-hook 'pre-command-hook  #'icomplete-pre-command-hook  nil t)
     (add-hook 'post-command-hook #'icomplete-post-command-hook nil t)
-    (run-hooks 'icomplete-minibuffer-setup-hook)
-    (when icomplete-show-matches-on-no-input
-      (icomplete-exhibit))))
+    (run-hooks 'icomplete-minibuffer-setup-hook)))
 
 (defvar icomplete--in-region-buffer nil)