(vc-cvs-diff): If backup files exist, diff them

instead of doing "cvs diff" in order to avoid accessing the
repository.

2 files changed, 42 insertions, 5 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 28533a7a177..083934494fc 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,9 @@
+2007-11-12  Dan Nicolaescu  <dann@ics.uci.edu>
+
+        * vc-cvs.el (vc-cvs-diff): If backup files exist, diff them
+        instead of doing "cvs diff" in order to avoid accessing the
+        repository.
+
 2007-11-12  Kevin Ryde  <user42@zip.com.au>
 
         * progmodes/compilation-perl.el:
diff --git a/lisp/vc-cvs.el b/lisp/vc-cvs.el
index d6573db9df2..c9c50fceba2 100644
--- a/lisp/vc-cvs.el
+++ b/lisp/vc-cvs.el
@@ -513,15 +513,46 @@ The changes are between FIRST-REVISION and SECOND-REVISION."
 
 (defun vc-cvs-diff (files &optional oldvers newvers buffer)
   "Get a difference report using CVS between two revisions of FILE."
-    (let* ((async (and (not vc-disable-async-diff) 
-                       (vc-stay-local-p files)))
-           (status (apply 'vc-cvs-command (or buffer "*vc-diff*")
+  (let* ((async (and (not vc-disable-async-diff)
+                     (vc-stay-local-p files)))
+         (invoke-cvs-diff-list nil)
+         status)
+    ;; Look through the file list and see if any files have backups
+    ;; that can be used to do a plain "diff" instead of "cvs diff".
+    (dolist (file files)
+      (let ((ov oldvers)
+            (nv newvers))
+        (when (or (not ov) (string-equal ov ""))
+          (setq ov (vc-working-revision file)))
+        (when (string-equal nv "")
+          (setq nv nil))
+        (let ((file-oldvers (vc-version-backup-file file ov))
+              (file-newvers (if (not nv)
+                                file
+                              (vc-version-backup-file file nv)))
+              (coding-system-for-read (vc-coding-system-for-diff file)))
+          (if (and file-oldvers file-newvers)
+              (progn
+                (apply 'vc-do-command (or buffer "*vc-diff*") 1 "diff" nil
+                       (append (if (listp diff-switches)
+                                   diff-switches
+                                 (list diff-switches))
+                               (if (listp vc-diff-switches)
+                                   vc-diff-switches
+                                 (list vc-diff-switches))
+                               (list (file-relative-name file-oldvers)
+                                     (file-relative-name file-newvers))))
+                (setq status 0))
+            (push file invoke-cvs-diff-list)))))
+    (when invoke-cvs-diff-list
+      (setq status (apply 'vc-cvs-command (or buffer "*vc-diff*")
                           (if async 'async 1)
-                          files "diff"
+                          invoke-cvs-diff-list "diff"
                           (and oldvers (concat "-r" oldvers))
                           (and newvers (concat "-r" newvers))
                           (vc-switches 'CVS 'diff))))
-      (if async 1 status)))             ; async diff, pessimistic assumption
+    (if async 1 status))) ; async diff, pessimistic assumption
+
 
 (defun vc-cvs-diff-tree (dir &optional rev1 rev2)
   "Diff all files at and below DIR."