Fix inconsistency expanding "//" in Tramp

* doc/misc/tramp.texi (File name completion): Adapt example
expanding "//".

* lisp/net/tramp.el (tramp-handle-substitute-in-file-name): "//" shall
expand the localname only, even when on top of the local part.

* test/lisp/net/tramp-tests.el (tramp-test04-substitute-in-file-name):
Adapt test.

3 files changed, 43 insertions, 21 deletions

diff --git a/doc/misc/tramp.texi b/doc/misc/tramp.texi
index 235627cc0f9..ae544b08712 100644
--- a/doc/misc/tramp.texi
+++ b/doc/misc/tramp.texi
@@ -2509,7 +2509,7 @@ Example:
      @print{} @trampfn{ssh,melancholia,/etc}
 
 @kbd{C-x C-f @trampfn{ssh,melancholia,//etc} @key{TAB}}
-     @print{} /etc
+     @print{} @trampfn{ssh,melancholia,/etc}
 
 @kbd{C-x C-f @trampfn{ssh,melancholia,/usr/local/bin///etc} @key{TAB}}
      @print{} /etc
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 09abd482260..b2e20000d3f 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -3554,17 +3554,19 @@ support symbolic links."
     ;; First, we must replace environment variables.
     (setq filename (tramp-replace-environment-variables filename))
     (with-parsed-tramp-file-name filename nil
-      ;; Ignore in LOCALNAME everything before "//" or "/~".
-      (when (and (stringp localname) (string-match ".+?/\\(/\\|~\\)" localname))
-        (setq filename
-              (concat (file-remote-p filename)
-                      (replace-match "\\1" nil nil localname)))
-        ;; "/m:h:~" does not work for completion.  We use "/m:h:~/".
-        (when (string-match "~$" filename)
-          (setq filename (concat filename "/"))))
       ;; We do not want to replace environment variables, again.
       (let (process-environment)
-        (tramp-run-real-handler 'substitute-in-file-name (list filename))))))
+        ;; Ignore in LOCALNAME everything before "//" or "/~".
+        (when (stringp localname)
+          (if (string-match "//\\(/\\|~\\)" localname)
+              (setq filename (substitute-in-file-name localname))
+            (setq filename
+                  (concat (file-remote-p filename)
+                          (substitute-in-file-name localname))))))
+      ;; "/m:h:~" does not work for completion.  We use "/m:h:~/".
+      (if (string-match "~$" filename)
+          (concat filename "/")
+        filename))))
 
 (defun tramp-handle-set-visited-file-modtime (&optional time-list)
   "Like `set-visited-file-modtime' for Tramp files."
diff --git a/test/lisp/net/tramp-tests.el b/test/lisp/net/tramp-tests.el
index 7a12d1468bf..422e71df7c3 100644
--- a/test/lisp/net/tramp-tests.el
+++ b/test/lisp/net/tramp-tests.el
@@ -1712,39 +1712,59 @@ handled properly.  BODY shall not contain a timeout."
 
 (ert-deftest tramp-test04-substitute-in-file-name ()
   "Check `substitute-in-file-name'."
-  (should (string-equal (substitute-in-file-name "/method:host://foo") "/foo"))
+  (should (string-equal (substitute-in-file-name "/method:host:///foo") "/foo"))
   (should
    (string-equal
-    (substitute-in-file-name "/method:host:/path//foo") "/method:host:/foo"))
+    (substitute-in-file-name "/method:host://foo") "/method:host:/foo"))
   (should
    (string-equal (substitute-in-file-name "/method:host:/path///foo") "/foo"))
+  (should
+   (string-equal
+    (substitute-in-file-name "/method:host:/path//foo") "/method:host:/foo"))
   ;; Quoting local part.
   (should
    (string-equal
-    (substitute-in-file-name "/method:host:/://foo") "/method:host:/://foo"))
+    (substitute-in-file-name "/method:host:/:///foo") "/method:host:/:///foo"))
   (should
    (string-equal
-    (substitute-in-file-name "/method:host:/:/path//foo")
-    "/method:host:/:/path//foo"))
+    (substitute-in-file-name "/method:host:/://foo") "/method:host:/://foo"))
   (should
    (string-equal
     (substitute-in-file-name "/method:host:/:/path///foo")
     "/method:host:/:/path///foo"))
+  (should
+   (string-equal
+    (substitute-in-file-name "/method:host:/:/path//foo")
+    "/method:host:/:/path//foo"))
 
   (should
+   (string-equal (substitute-in-file-name "/method:host://~foo") "/~foo"))
+  (should
    (string-equal
-    (substitute-in-file-name "/method:host:/path/~/foo") "/method:host:~/foo"))
+    (substitute-in-file-name "/method:host:/~foo") "/method:host:/~foo"))
   (should
-   (string-equal (substitute-in-file-name "/method:host:/path//~/foo") "~/foo"))
+   (string-equal (substitute-in-file-name "/method:host:/path//~foo") "/~foo"))
+  ;; (substitute-in-file-name "/path/~foo") expands only to "/~foo"",
+  ;; if $LOGNAME or $USER is "foo".  Otherwise, it doesn't expand.
+  (should
+   (string-equal
+    (substitute-in-file-name
+     "/method:host:/path/~foo") "/method:host:/path/~foo"))
   ;; Quoting local part.
   (should
    (string-equal
-    (substitute-in-file-name "/method:host:/:/path/~/foo")
-    "/method:host:/:/path/~/foo"))
+    (substitute-in-file-name "/method:host:/://~foo") "/method:host:/://~foo"))
+  (should
+   (string-equal
+    (substitute-in-file-name "/method:host:/:/~foo") "/method:host:/:/~foo"))
+  (should
+   (string-equal
+    (substitute-in-file-name
+     "/method:host:/:/path//~foo") "/method:host:/:/path//~foo"))
   (should
    (string-equal
-    (substitute-in-file-name "/method:host:/:/path//~/foo")
-    "/method:host:/:/path//~/foo"))
+    (substitute-in-file-name
+     "/method:host:/:/path/~foo") "/method:host:/:/path/~foo"))
 
   (let (process-environment)
     (should