Enable `dont-follow' for inotify file notifications

* doc/lispref/os.texi (File Notifications): Symlinks aren't followed.

* lisp/filenotify.el (file-notify--add-watch-inotify):
Add `dont-follow' flag.

* lisp/net/tramp.el (tramp-handle-file-notify-rm-watch):
Suppress errors when reading process output.

* test/lisp/filenotify-tests.el (file-notify-test11-symlinks)
(file-notify-test11-symlinks-remote): New tests.

4 files changed, 117 insertions, 2 deletions

diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index 35828018417..3e16ac0eb49 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -3175,6 +3175,9 @@ This is not detected by this function, and so a non-@code{nil} return
 value does not guarantee that changes on @var{file} will be actually
 notified.
 
+If @var{file} is a symlink, it doesn't follow that link.  Just
+@var{file} itself will be watched.
+
 @var{flags} is a list of conditions to set what will be watched for.
 It can include the following symbols:
 
diff --git a/lisp/filenotify.el b/lisp/filenotify.el
index 94e07289e32..6b13ed0b725 100644
--- a/lisp/filenotify.el
+++ b/lisp/filenotify.el
@@ -339,6 +339,7 @@ DESC is the back-end descriptor.  ACTIONS is a list of:
   "Add a watch for FILE in DIR with FLAGS, using inotify."
   (inotify-add-watch dir
                      (append
+                      '(dont-follow)
                       (and (memq 'change flags)
                            '(create delete delete-self modify move-self move))
                       (and (memq 'attribute-change flags)
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 90cc03c188e..f18e4c41c3c 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -5173,8 +5173,10 @@ of."
   ;; The descriptor must be a process object.
   (unless (processp proc)
     (tramp-error proc 'file-notify-error "Not a valid descriptor %S" proc))
-  ;; There might be pending output.
-  (while (tramp-accept-process-output proc 0))
+  ;; There might be pending output.  Avoid problems with reentrant
+  ;; call of Tramp.
+  (ignore-errors
+    (while (tramp-accept-process-output proc 0)))
   (tramp-message proc 6 "Kill %S" proc)
   (delete-process proc))
 
diff --git a/test/lisp/filenotify-tests.el b/test/lisp/filenotify-tests.el
index 2d147e900d7..fef3ab80f9a 100644
--- a/test/lisp/filenotify-tests.el
+++ b/test/lisp/filenotify-tests.el
@@ -1571,6 +1571,115 @@ the file watch."
 (file-notify--deftest-remote file-notify-test10-sufficient-resources
   "Check `file-notify-test10-sufficient-resources' for remote files.")
 
+(ert-deftest file-notify-test11-symlinks ()
+  "Check that file notification do not follow symbolic links."
+  :tags '(:expensive-test)
+  (skip-unless (file-notify--test-local-enabled))
+
+  (setq file-notify--test-tmpfile (file-notify--test-make-temp-name)
+        file-notify--test-tmpfile1 (file-notify--test-make-temp-name))
+
+  ;; Symlink a file.
+  (unwind-protect
+      (progn
+	(write-region "any text" nil file-notify--test-tmpfile1 nil 'no-message)
+        (make-symbolic-link file-notify--test-tmpfile1 file-notify--test-tmpfile)
+	(should
+	 (setq file-notify--test-desc
+	       (file-notify--test-add-watch
+                file-notify--test-tmpfile
+                '(attribute-change change) #'file-notify--test-event-handler)))
+        (should (file-notify-valid-p file-notify--test-desc))
+
+        ;; Writing to either the symlink or the target should not
+        ;; raise any event.
+        (file-notify--test-with-actions nil
+          (write-region
+           "another text" nil file-notify--test-tmpfile nil 'no-message)
+          (write-region
+           "another text" nil file-notify--test-tmpfile1 nil 'no-message))
+        ;; Sanity check.
+        (file-notify--test-wait-for-events
+         (file-notify--test-timeout)
+         (not (input-pending-p)))
+        (should-not file-notify--test-events)
+
+        ;; Changing timestamp of the target should not raise any
+        ;; event.  We don't use `nofollow'.
+        (file-notify--test-with-actions nil
+          (set-file-times file-notify--test-tmpfile1 '(0 0))
+          (set-file-times file-notify--test-tmpfile '(0 0)))
+        ;; Sanity check.
+        (file-notify--test-wait-for-events
+         (file-notify--test-timeout)
+         (not (input-pending-p)))
+        (should-not file-notify--test-events)
+
+        ;; Changing timestamp of the symlink shows the event.
+        (file-notify--test-with-actions '(attribute-changed)
+          (set-file-times file-notify--test-tmpfile '(0 0) 'nofollow))
+
+        ;; Deleting the target should not raise any event.
+        (file-notify--test-with-actions nil
+          (delete-file file-notify--test-tmpfile1)
+          (delete-file file-notify--test-tmpfile))
+        ;; Sanity check.
+        (file-notify--test-wait-for-events
+         (file-notify--test-timeout)
+         (not (input-pending-p)))
+        (should-not file-notify--test-events)
+
+        ;; The environment shall be cleaned up.
+	(file-notify-rm-watch file-notify--test-desc)
+        (file-notify--test-cleanup-p))
+
+    ;; Cleanup.
+    (file-notify--test-cleanup))
+
+  (setq file-notify--test-tmpfile1 (file-notify--test-make-temp-name)
+        file-notify--test-tmpfile (file-notify--test-make-temp-name))
+
+  ;; Symlink a directory.
+  (unwind-protect
+      (let ((tmpfile (expand-file-name "foo" file-notify--test-tmpfile))
+            (tmpfile1 (expand-file-name "foo" file-notify--test-tmpfile1)))
+	(make-directory file-notify--test-tmpfile1)
+        (make-symbolic-link file-notify--test-tmpfile1 file-notify--test-tmpfile)
+	(write-region "any text" nil tmpfile1 nil 'no-message)
+	(should
+	 (setq file-notify--test-desc
+	       (file-notify--test-add-watch
+                file-notify--test-tmpfile
+                '(attribute-change change) #'file-notify--test-event-handler)))
+        (should (file-notify-valid-p file-notify--test-desc))
+
+        ;; None of the actions on a file in the symlinked directory will be reported.
+        (file-notify--test-with-actions nil
+          (write-region "another text" nil tmpfile nil 'no-message)
+          (write-region "another text" nil tmpfile1 nil 'no-message)
+          (set-file-times tmpfile '(0 0))
+          (set-file-times tmpfile '(0 0) 'nofollow)
+          (set-file-times tmpfile1 '(0 0))
+          (set-file-times tmpfile1 '(0 0) 'nofollow)
+          (delete-file tmpfile)
+          (delete-file tmpfile1))
+        ;; Sanity check.
+        (file-notify--test-wait-for-events
+         (file-notify--test-timeout)
+         (not (input-pending-p)))
+        (should-not file-notify--test-events)
+
+        ;; The environment shall be cleaned up.
+        (delete-directory file-notify--test-tmpdir 'recursive)
+	(file-notify-rm-watch file-notify--test-desc)
+        (file-notify--test-cleanup-p))
+
+    ;; Cleanup.
+    (file-notify--test-cleanup)))
+
+(file-notify--deftest-remote file-notify-test11-symlinks
+  "Check `file-notify-test11-symlinks' for remote files.")
+
 (defun file-notify-test-all (&optional interactive)
   "Run all tests for \\[file-notify]."
   (interactive "p")