Prevent loading tramp-archive when it cannot be used

* lisp/files.el (locate-dominating-file): Check, that FILE is
a directory when traversing the tree.

* lisp/net/tramp-archive.el (tramp-archive-enabled): New defvar.
(tramp-archive-file-name-regexp): Protect against errors.
(tramp-archive-file-name-handler)
(tramp-register-archive-file-name-handler): Use it.
(all) Call `tramp-register-archive-file-name-handler'.

* lisp/net/tramp.el (tramp-register-file-name-handlers):
Use `tramp-archive-enabled'.

* test/lisp/net/tramp-archive-tests.el (all):
Use `tramp-archive-enabled' instead of `tramp-gvfs-enabled'.
(tramp-archive--test-emacs27-p): New defun.
(tramp-archive-test42-auto-load): Skip for older Emacsen.
(tramp-archive-test42-delay-load): Skip for older Emacsen.
Test also behavior when `tramp-archive-enabled' is nil.

3 files changed, 24 insertions, 11 deletions

diff --git a/lisp/files.el b/lisp/files.el
index e884a3acc18..414eb3f93af 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -963,7 +963,8 @@ the function needs to examine, starting with FILE."
                     (null file)
                     (string-match locate-dominating-stop-dir-regexp file)))
       (setq try (if (stringp name)
-                    (file-exists-p (expand-file-name name file))
+                    (and (file-directory-p file)
+                         (file-exists-p (expand-file-name name file)))
                   (funcall name file)))
       (cond (try (setq root file))
             ((equal file (setq file (file-name-directory
diff --git a/lisp/net/tramp-archive.el b/lisp/net/tramp-archive.el
index 23191f11f3e..ac1c4e1448d 100644
--- a/lisp/net/tramp-archive.el
+++ b/lisp/net/tramp-archive.el
@@ -112,6 +112,14 @@
 (defvar url-handler-regexp)
 (defvar url-tramp-protocols)
 
+;; We cannot check `tramp-gvfs-enabled' in loaddefs.el, because this
+;; would load Tramp. So we make a cheaper check.
+;;;###autoload
+(defvar tramp-archive-enabled (featurep 'dbusbind)
+  "Non-nil when GVFS is available.")
+
+(setq tramp-archive-enabled tramp-gvfs-enabled)
+
 ;; <https://github.com/libarchive/libarchive/wiki/LibarchiveFormats>
 ;;;###autoload
 (defconst tramp-archive-suffixes
@@ -169,7 +177,7 @@ It must be supported by libarchive(3).")
 
 ;;;###tramp-autoload
 (defconst tramp-archive-file-name-regexp
-  (tramp-archive-autoload-file-name-regexp)
+  (ignore-errors (tramp-archive-autoload-file-name-regexp))
   "Regular expression matching archive file names.")
 
 ;;;###tramp-autoload
@@ -291,7 +299,7 @@ pass to the OPERATION."
              (tramp-archive-run-real-handler 'file-directory-p (list archive)))
         (tramp-archive-run-real-handler operation args)
       ;; Now run the handler.
-      (unless tramp-gvfs-enabled
+      (unless tramp-archive-enabled
         (tramp-compat-user-error nil "Package `tramp-archive' not supported"))
       (let ((tramp-methods (cons `(,tramp-archive-method) tramp-methods))
             (tramp-gvfs-methods tramp-archive-all-gvfs-methods)
@@ -308,14 +316,17 @@ pass to the OPERATION."
 ;;;###autoload
 (progn (defun tramp-register-archive-file-name-handler ()
   "Add archive file name handler to `file-name-handler-alist'."
-  (add-to-list 'file-name-handler-alist
-               (cons (tramp-archive-autoload-file-name-regexp)
-                     'tramp-autoload-file-name-handler))
-  (put 'tramp-archive-file-name-handler 'safe-magic t)))
+  (when tramp-archive-enabled
+    (add-to-list 'file-name-handler-alist
+                 (cons (tramp-archive-autoload-file-name-regexp)
+                       'tramp-autoload-file-name-handler))
+    (put 'tramp-archive-file-name-handler 'safe-magic t))))
 
 ;;;###autoload
 (add-hook 'after-init-hook 'tramp-register-archive-file-name-handler)
 
+(tramp-register-archive-file-name-handler)
+
 ;; Mark `operations' the handler is responsible for.
 (put 'tramp-archive-file-name-handler 'operations
      (mapcar 'car tramp-archive-file-name-handler-alist))
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 5a2e358daa1..09abd482260 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -2401,10 +2401,11 @@ remote file names."
   (put 'tramp-completion-file-name-handler 'operations
        (mapcar 'car tramp-completion-file-name-handler-alist))
 
-  (add-to-list 'file-name-handler-alist
-               (cons tramp-archive-file-name-regexp
-                     'tramp-archive-file-name-handler))
-  (put 'tramp-archive-file-name-handler 'safe-magic t)
+  (when (bound-and-true-p tramp-archive-enabled)
+    (add-to-list 'file-name-handler-alist
+                 (cons tramp-archive-file-name-regexp
+                       'tramp-archive-file-name-handler))
+    (put 'tramp-archive-file-name-handler 'safe-magic t))
 
   ;; If jka-compr or epa-file are already loaded, move them to the
   ;; front of `file-name-handler-alist'.