Fix Bug#10085

* lisp/net/tramp.el (tramp-find-foreign-file-name-handler):
Add optional arguments OPERATION and COMPETION.  Handle
`file-name-as-directory', `file-name-directory' and
`file-name-nondirectory' also in completion mode.
(tramp-file-name-handler): Use it.  (Bug#10085)

* test/lisp/net/tramp-tests.el (tramp-test06-directory-file-name):
Extend test.

2 files changed, 26 insertions, 5 deletions

diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 4edca5a5998..3da60e93b78 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -1944,7 +1944,8 @@ ARGS are the arguments OPERATION has been called with."
    ;; Unknown file primitive.
    (t (error "unknown file I/O primitive: %s" operation))))
 
-(defun tramp-find-foreign-file-name-handler (filename)
+(defun tramp-find-foreign-file-name-handler
+    (filename &optional operation completion)
   "Return foreign file name handler if exists."
   (when (tramp-tramp-file-p filename)
     (let ((v (tramp-dissect-file-name filename t))
@@ -1952,11 +1953,17 @@ ARGS are the arguments OPERATION has been called with."
           elt res)
       ;; When we are not fully sure that filename completion is safe,
       ;; we should not return a handler.
-      (when (or (tramp-file-name-method v) (tramp-file-name-user v)
+      (when (or (not completion)
+                (tramp-file-name-method v) (tramp-file-name-user v)
                 (and (tramp-file-name-host v)
                      (not (member (tramp-file-name-host v)
                                   (mapcar 'car tramp-methods))))
-                (not (tramp-completion-mode-p)))
+                ;; Some operations are safe by default.
+                (member
+                 operation
+                 '(file-name-as-directory
+                   file-name-directory
+                   file-name-nondirectory)))
         (while handler
           (setq elt (car handler)
                 handler (cdr handler))
@@ -1984,7 +1991,9 @@ Falls back to normal file name handler if no Tramp file name handler exists."
                 (tramp-replace-environment-variables
                  (apply 'tramp-file-name-for-operation operation args)))
                (completion (tramp-completion-mode-p))
-               (foreign (tramp-find-foreign-file-name-handler filename))
+               (foreign
+                (tramp-find-foreign-file-name-handler
+                 filename operation completion))
                result)
           (with-parsed-tramp-file-name filename nil
             ;; Call the backend function.
diff --git a/test/lisp/net/tramp-tests.el b/test/lisp/net/tramp-tests.el
index a12ee387576..5090a5b0e41 100644
--- a/test/lisp/net/tramp-tests.el
+++ b/test/lisp/net/tramp-tests.el
@@ -637,7 +637,19 @@ This checks also `file-name-as-directory', `file-name-directory',
   (should
    (string-equal (file-name-nondirectory "/method:host:/path/to/file/") ""))
   (should-not
-   (unhandled-file-name-directory "/method:host:/path/to/file")))
+   (unhandled-file-name-directory "/method:host:/path/to/file"))
+
+  ;; Bug#10085.
+  (dolist (n-e '(nil t))
+    (let ((non-essential n-e))
+      (dolist (file
+               `(,(file-remote-p tramp-test-temporary-file-directory 'method)
+                 ,(file-remote-p tramp-test-temporary-file-directory 'host)))
+        (setq file (format "/%s:" file))
+        (should (string-equal (directory-file-name file) file))
+        (should (string-equal (file-name-as-directory file) (concat file "./")))
+        (should (string-equal (file-name-directory file) file))
+        (should (string-equal (file-name-nondirectory file) ""))))))
 
 (ert-deftest tramp-test07-file-exists-p ()
   "Check `file-exist-p', `write-region' and `delete-file'."