Speed up vc-dir-update

* lisp/vc/vc-dir.el (vc-dir-update): Speed up.
(https://lists.gnu.org/archive/html/emacs-devel/2019-12/msg00568.html)

1 files changed, 15 insertions, 12 deletions

diff --git a/lisp/vc/vc-dir.el b/lisp/vc/vc-dir.el
index e2259785923..ad25e8aa537 100644
--- a/lisp/vc/vc-dir.el
+++ b/lisp/vc/vc-dir.el
@@ -390,19 +390,22 @@ If NOINSERT, ignore elements on ENTRIES which are not in the ewoc."
     ;; We assume the ewoc is sorted too, which should be the
     ;; case if we always add entries with vc-dir-update.
     (setq entries
+          (let ((entry-dirs
+                 (mapcar (lambda (entry)
+                           (cons (file-name-directory
+                                  (directory-file-name (expand-file-name (car entry))))
+                                 entry))
+                         entries)))
           ;; Sort: first files and then subdirectories.
-          ;; XXX: this is VERY inefficient, it computes the directory
-          ;; names too many times
-          (sort entries
-                (lambda (entry1 entry2)
-                  (let ((dir1 (file-name-directory
-                                (directory-file-name (expand-file-name (car entry1)))))
-                        (dir2 (file-name-directory
-                               (directory-file-name (expand-file-name (car entry2))))))
-                    (cond
-                     ((string< dir1 dir2) t)
-                     ((not (string= dir1 dir2)) nil)
-                     ((string< (car entry1) (car entry2))))))))
+            (mapcar #'cdr
+                    (sort entry-dirs
+                          (lambda (pair1 pair2)
+                            (let ((dir1 (car pair1))
+                                  (dir2 (car pair2)))
+                              (cond
+                               ((string< dir1 dir2) t)
+                               ((not (string= dir1 dir2)) nil)
+                               ((string< (cadr pair1) (cadr pair2))))))))))
     ;; Insert directory entries in the right places.
     (let ((entry (car entries))
           (node (ewoc-nth vc-ewoc 0))