Do not load Tramp unless `tramp-mode' is non-nil

* lisp/net/tramp.el (tramp-autoload-file-name-handler): Load Tramp only if
`tramp-mode' is non-nil.
(tramp-unload-file-name-handlers): Unload also
`tramp-autoload-file-name-handler'.

* test/lisp/net/tramp-tests.el (tramp-test42-delay-load): Extend test.

lisp/net/tramp.el

@@ -2305,8 +2305,10 @@ Falls back to normal file name handler if no Tramp file name handler exists."
 ;;;###autoload
 (progn (defun tramp-autoload-file-name-handler (operation &rest args)
   "Load Tramp file name handler, and perform OPERATION."
-  (let ((default-directory temporary-file-directory))
-    (load "tramp" 'noerror 'nomessage))
+  (if tramp-mode
+      (let ((default-directory temporary-file-directory))
+	(load "tramp" 'noerror 'nomessage))
+    (tramp-unload-file-name-handlers))
   (apply operation args)))
 
 ;; `tramp-autoload-file-name-handler' must be registered before
@@ -2422,12 +2424,13 @@ Add operations defined in `HANDLER-alist' to `tramp-file-name-handler'."
       (equal (apply operation args) operation))))
 
 ;;;###autoload
-(defun tramp-unload-file-name-handlers ()
+(progn (defun tramp-unload-file-name-handlers ()
   "Unload Tramp file name handlers from `file-name-handler-alist'."
   (dolist (fnh '(tramp-file-name-handler
-		 tramp-completion-file-name-handler))
+		 tramp-completion-file-name-handler
+		 tramp-autoload-file-name-handler))
     (let ((a1 (rassq fnh file-name-handler-alist)))
-      (setq file-name-handler-alist (delq a1 file-name-handler-alist)))))
+      (setq file-name-handler-alist (delq a1 file-name-handler-alist))))))
 
 (add-hook 'tramp-unload-hook 'tramp-unload-file-name-handlers)
 

test/lisp/net/tramp-tests.el

@@ -4432,23 +4432,27 @@ process sentinels.  They shall not disturb each other."
   "Check that Tramp is loaded lazily, only when needed."
   ;; Tramp is neither loaded at Emacs startup, nor when completing a
   ;; non-Tramp file name like "/foo".  Completing a Tramp-alike file
-  ;; name like "/foo:" autoloads Tramp.
+  ;; name like "/foo:" autoloads Tramp, when `tramp-mode' is t.
   (let ((code
 	 "(progn \
-	   (message \"Tramp loaded: %s\" (featurep 'tramp)) \
+           (setq tramp-mode %s) \
+	   (message \"Tramp loaded: %%s\" (featurep 'tramp)) \
 	   (file-name-all-completions \"/foo\" \"/\") \
-	   (message \"Tramp loaded: %s\" (featurep 'tramp)) \
+	   (message \"Tramp loaded: %%s\" (featurep 'tramp)) \
 	   (file-name-all-completions \"/foo:\" \"/\") \
-	   (message \"Tramp loaded: %s\" (featurep 'tramp)))"))
-    (should
-     (string-match
-      "Tramp loaded: nil[\n\r]+Tramp loaded: nil[\n\r]+Tramp loaded: t[\n\r]+"
-      (shell-command-to-string
-       (format
-	"%s -batch -Q -L %s --eval %s"
-	(expand-file-name invocation-name invocation-directory)
-	(mapconcat 'shell-quote-argument load-path " -L ")
-	(shell-quote-argument code)))))))
+	   (message \"Tramp loaded: %%s\" (featurep 'tramp)))"))
+    (dolist (tm '(t nil))
+      (should
+       (string-match
+	(format
+       "Tramp loaded: nil[\n\r]+Tramp loaded: nil[\n\r]+Tramp loaded: %s[\n\r]+"
+	 tm)
+	(shell-command-to-string
+	 (format
+	  "%s -batch -Q -L %s --eval %s"
+	  (expand-file-name invocation-name invocation-directory)
+	  (mapconcat 'shell-quote-argument load-path " -L ")
+	  (shell-quote-argument (format code tm)))))))))
 
 (ert-deftest tramp-test43-unload ()
   "Check that Tramp and its subpackages unload completely.