Create a buffer-local binding to improve performance

* lisp/ido.el (ido-make-buffer-list-1):
Create a buffer-local binding to improve performance when a lot of
buffers are open (bug#41029).

Copyright-paperwork-exempt: yes

1 files changed, 12 insertions, 7 deletions

diff --git a/lisp/ido.el b/lisp/ido.el
index 4fb01c68dfa..e834916a6da 100644
--- a/lisp/ido.el
+++ b/lisp/ido.el
@@ -3410,13 +3410,18 @@ instead removed from the current item list."
 
 (defun ido-make-buffer-list-1 (&optional frame visible)
   "Return list of non-ignored buffer names."
-  (delq nil
-        (mapcar
-         (lambda (x)
-           (let ((name (buffer-name x)))
-             (if (not (or (ido-ignore-item-p name ido-ignore-buffers) (member name visible)))
-                 name)))
-         (buffer-list frame))))
+  (with-temp-buffer
+    ;; Each call to ido-ignore-item-p LET-binds case-fold-search.
+    ;; That is slow if there's no buffer-local binding available,
+    ;; roughly O(number of buffers).  This hack avoids it.
+    (setq-local case-fold-search nil)
+    (delq nil
+          (mapcar
+           (lambda (x)
+             (let ((name (buffer-name x)))
+               (if (not (or (ido-ignore-item-p name ido-ignore-buffers) (member name visible)))
+                   name)))
+           (buffer-list frame)))))
 
 (defun ido-make-buffer-list (default)
   "Return the current list of buffers.