Suppress Tramp session timeout if buffer is modified

* doc/misc/tramp.texi (Predefined connection information): A session
timeout is suppressed if there is a modified buffer, or a buffer
under auto-revert.
(Traces and Profiles): Tramp messages are written to the *Messages*
buffer when level is less than or equal to 3.

* lisp/net/tramp-sh.el (tramp-timeout-session): Do not timeout
when buffer is modified, or in auto-revert mode.

* test/lisp/net/tramp-tests.el (tramp-test48-session-timeout):
Extend test.

doc/misc/tramp.texi

@@ -2376,9 +2376,11 @@ value is @t{"-l"}, but some shells, like @command{ksh}, prefer
 All @file{tramp-sh.el} based methods accept the property
 @t{"session-timeout"}.  This is the time (in seconds) after a
 connection is disabled for security reasons, and must be
-reestablished.  A value of @code{nil} disables this feature.  Most of
-the methods do not set this property except the @option{sudo},
-@option{doas} and @option{run0} methods, which use predefined values.
+reestablished@footnote{If there is a modified buffer, or a buffer
+under @code{auto-revert}, this is suppressed.}.  A value of @code{nil}
+disables this feature.  Most of the methods do not set this property
+except the @option{sudo}, @option{doas} and @option{run0} methods,
+which use predefined values.
 
 @item @t{"~"}@*
 @t{"~user"}
@@ -6834,7 +6836,8 @@ they are kept.  Example:
 
 @value{tramp} messages are raised with verbosity levels ranging from 0
 to 10.  @value{tramp} does not display all messages; only those with a
-verbosity level less than or equal to @code{tramp-verbose}.
+verbosity level less than or equal to 3, when @code{tramp-verbose}
+permits.
 
 @noindent
 The verbosity levels are

lisp/net/tramp-sh.el

@@ -5154,17 +5154,41 @@ Goes through the list `tramp-inline-compress-commands'."
 ;;;###tramp-autoload
 (defun tramp-timeout-session (vec)
   "Close the connection VEC after a session timeout.
-If there is just some editing, retry it after 5 seconds."
-  (if (and (tramp-get-connection-property
+If there is just some editing, retry it after 5 seconds.
+If there is a modified buffer, retry it after 60 seconds."
+  (cond
+   ;; Tramp is locked.  Try it, again.
+   ((and (tramp-get-connection-property
 	  (tramp-get-connection-process vec) "locked")
 	 (tramp-file-name-equal-p vec (car tramp-current-connection)))
-      (progn
     (tramp-message
      vec 5 "Cannot timeout session, trying it again in %s seconds." 5)
     (run-at-time 5 nil #'tramp-timeout-session vec))
+   ;; There's a modified buffer.  Try it, again.
+   ((seq-some
+     (lambda (buf)
+       (and-let* (((or (buffer-modified-p buf)
+		       (with-current-buffer buf
+			 ;; We don't know whether autorevert.el has
+			 ;; been loaded alreaddy.
+			 (tramp-compat-funcall 'auto-revert-active-p))))
+		  (bfn (buffer-file-name buf))
+		  (v (tramp-ensure-dissected-file-name bfn))
+		  ((tramp-file-name-equal-p vec v)))))
+     (tramp-list-remote-buffers))
     (tramp-message
+     vec 5
+     (concat
+      "Cannot timeout session (modified buffer), "
+      "trying it again in %s seconds.")
+     (tramp-get-method-parameter vec 'tramp-session-timeout))
+    (run-at-time
+     (tramp-get-method-parameter vec 'tramp-session-timeout) nil
+     #'tramp-timeout-session vec))
+   ;; Do it.
+   (t (tramp-message
        vec 3 "Timeout session %s" (tramp-make-tramp-file-name vec 'noloc))
-    (tramp-cleanup-connection vec 'keep-debug nil 'keep-processes)))
+      (tramp-cleanup-connection vec 'keep-debug nil 'keep-processes))))
 
 (defun tramp-maybe-open-connection (vec)
   "Maybe open a connection VEC.

test/lisp/net/tramp-tests.el

@@ -8471,7 +8471,37 @@ process sentinels.  They shall not disturb each other."
 		    (cl-letf (((symbol-function #'ask-user-about-lock) #'always))
 		      (save-buffer)))
 		  (should-not
-		   (string-match-p "File is missing:" captured-messages))))))
+		   (string-match-p "File is missing:" captured-messages)))))
+
+	    ;; A modified buffer suppresses session timeout.
+	    (with-temp-buffer
+	      (set-visited-file-name tmp-name)
+	      (insert "foo")
+	      (should (buffer-modified-p))
+	      (tramp-timeout-session tramp-test-vec)
+	      (should
+	       (process-live-p (tramp-get-connection-process tramp-test-vec)))
+	      ;; Steal the file lock.
+	      (cl-letf (((symbol-function #'ask-user-about-lock) #'always))
+		(save-buffer))
+	      (tramp-timeout-session tramp-test-vec)
+	      (should-not
+	       (process-live-p (tramp-get-connection-process tramp-test-vec))))
+
+	    ;; An auto-reverted buffer suppresses session timeout.
+	    (with-temp-buffer
+	      (set-visited-file-name tmp-name)
+	      (auto-revert-mode 1)
+	      ;; Steal the file lock.
+	      (cl-letf (((symbol-function #'ask-user-about-lock) #'always))
+		(save-buffer))
+	      (tramp-timeout-session tramp-test-vec)
+	      (should
+	       (process-live-p (tramp-get-connection-process tramp-test-vec)))
+	      (auto-revert-mode -1)
+	      (tramp-timeout-session tramp-test-vec)
+	      (should-not
+	       (process-live-p (tramp-get-connection-process tramp-test-vec)))))
 
 	;; Cleanup.
 	(ignore-errors (delete-file tmp-name))))))