1 files changed, 24 insertions, 8 deletions

diff --git a/lisp/diff.el b/lisp/diff.el
index 221d7b2e363..534a84d4317 100644
--- a/lisp/diff.el
+++ b/lisp/diff.el
@@ -67,9 +67,10 @@ CODE is the exit code of the process.  It should be 0 iff no diffs were found."
   (if diff-new-temp-file (delete-file diff-new-temp-file))
   (save-excursion
     (goto-char (point-max))
-    (insert (format "\nDiff finished%s.  %s\n"
-                    (if (equal 0 code) " (no differences)" "")
-                    (current-time-string)))))
+    (let ((inhibit-read-only t))
+      (insert (format "\nDiff finished%s.  %s\n"
+                      (if (equal 0 code) " (no differences)" "")
+                      (current-time-string))))))
 
 ;;;###autoload
 (defun diff (old new &optional switches no-async)
@@ -119,7 +120,8 @@ With prefix arg, prompt for diff switches."
       (set-buffer buf)
       (setq buffer-read-only nil)
       (buffer-disable-undo (current-buffer))
-      (erase-buffer)
+      (let ((inhibit-read-only t))
+        (erase-buffer))
       (buffer-enable-undo (current-buffer))
       (diff-mode)
       (set (make-local-variable 'revert-buffer-function)
@@ -128,21 +130,35 @@ With prefix arg, prompt for diff switches."
       (set (make-local-variable 'diff-old-temp-file) old-alt)
       (set (make-local-variable 'diff-new-temp-file) new-alt)
       (setq default-directory thisdir)
-      (insert command "\n")
+      (let ((inhibit-read-only t))
+        (insert command "\n"))
       (if (and (not no-async) (fboundp 'start-process))
           (progn
             (setq proc (start-process "Diff" buf shell-file-name
                                       shell-command-switch command))
+            (set-process-filter proc 'diff-process-filter)
             (set-process-sentinel
              proc (lambda (proc msg)
                     (with-current-buffer (process-buffer proc)
                       (diff-sentinel (process-exit-status proc))))))
         ;; Async processes aren't available.
-        (diff-sentinel
-         (call-process shell-file-name nil buf nil
-                       shell-command-switch command))))
+        (let ((inhibit-read-only t))
+          (diff-sentinel
+           (call-process shell-file-name nil buf nil
+                         shell-command-switch command)))))
     buf))
 
+(defun diff-process-filter (proc string)
+  (with-current-buffer (process-buffer proc)
+    (let ((moving (= (point) (process-mark proc))))
+      (save-excursion
+        ;; Insert the text, advancing the process marker.
+        (goto-char (process-mark proc))
+        (let ((inhibit-read-only t))
+          (insert string))
+        (set-marker (process-mark proc) (point)))
+      (if moving (goto-char (process-mark proc))))))
+
 ;;;###autoload
 (defun diff-backup (file &optional switches)
   "Diff this file with its backup file or vice versa.