Tramp: Support different proxies for the same destination

* doc/misc/tramp.texi (Ad-hoc multi-hops): New subsection "Using
different proxies for the same destination".

* etc/NEWS: Tramp supports different proxies for the same
destination host name in parallel.
Fix typos.

* lisp/net/tramp-cmds.el (tramp-cleanup-connection): Fix docstring.

* lisp/net/tramp.el (tramp-make-tramp-file-name): Don't call
`tramp-add-hops' during file name completion.
(tramp-handle-file-name-as-directory)
(tramp-handle-file-name-directory): Use `tramp-cache-undefined'
for an empty `tramp-default-proxies-alist'.
(tramp-add-hops): Extend.  Remove existing entries with same
target and different proxy, if needed.  (Bug#74219)

4 files changed, 81 insertions, 27 deletions

diff --git a/doc/misc/tramp.texi b/doc/misc/tramp.texi
index 96ec6d60b9e..a014319c02c 100644
--- a/doc/misc/tramp.texi
+++ b/doc/misc/tramp.texi
@@ -3914,6 +3914,30 @@ shall be taken, add a proper rule to the user option
 @end lisp
 
 
+@subsection Using different proxies for the same destination
+
+@strong{Note}: This feature is experimental, don't use it in
+production systems!
+
+Sometimes, it is needed to specify different proxies for the same
+destination host name.  This can happen for the same destination when
+the local host is located in different networks over the time.  This
+can also happen when the remote destination is specified by the remote
+same file name, although different hosts are meant depending on the
+used proxy.  A typical example are docker containers, which run on
+different hosts under the same docker name.
+
+When the user option @code{tramp-show-ad-hoc-proxies} is
+non-@code{nil}, such ad-hoc multi-hop file names can be used in
+parallel.  In the following, on both remote hosts @samp{host1} and
+@samp{host2} there is a docker container @samp{name}, respectively:
+
+@example
+@trampfn{ssh@value{postfixhop}user1@@host1|docker,name,}
+@trampfn{ssh@value{postfixhop}user2@@host2|docker,name,}
+@end example
+
+
 @node Home directories
 @section Expanding @file{~} to home directory
 
diff --git a/etc/NEWS b/etc/NEWS
index 19b8b7bb70b..689f85270c9 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -183,8 +183,8 @@ Input methods are now implemented for Haudenosaunee languages in the
 Northern Iroquoian language family: 'mohawk-postfix' (Mohawk
 [Kanien’kéha / Onkwehonwehnéha]), 'oneida-postfix' (Oneida [Onʌyota:ká:
 / Ukwehuwehnéha]), 'cayuga-postfix' (Cayuga [Gayogo̱ho:nǫhnéha:ˀ]),
-'onondaga-postfix (Onondaga [[Onųdaʔgegáʔ]), and `seneca-postfix'
-[Onödowá’ga:’]).  Additionally, there is a general-purpose
+'onondaga-postfix' (Onondaga [Onųdaʔgegáʔ]), and 'seneca-postfix'
+(Seneca [Onödowá’ga:’]).  Additionally, there is a general-purpose
 'haudenosaunee-postfix' input method to facilitate writing in the
 orthographies of the five languages simultaneously.
 
@@ -267,7 +267,7 @@ It removes all the buttons in the specified region.
 This command scrolls the screen so that only the current prompt is
 visible, optionally erasing all the previous input/output as well.
 Previously, the Eshell built-in command 'eshell/clear' supported this
-(e.g. to call it via 'M-x'), but this new command behaves more
+(e.g., to call it via 'M-x'), but this new command behaves more
 consistently if you have a partially-typed command at the Eshell prompt.
 
 ---
@@ -486,6 +486,19 @@ The host name for Kubernetes connections can be of kind
 used.  This overrides the setting in 'tramp-kubernetes-namespace', if
 any.
 
++++
+*** Different proxies for the same destination host name can be specified.
+A typical example are docker containers, which run on different hosts
+under the same docker name.  When the user option
+'tramp-show-ad-hoc-proxies' is non-nil, such ad-hoc multi-hop file names
+can be used in parallel.  Example: on both remote hosts "host1" and
+"host2" there is a docker container "name", respectively:
+
+    /ssh:user1@host1|docker:name:
+    /ssh:user2@host2|docker:name:
+
+This feature is experimental.
+
 ** Diff
 
 ---
@@ -562,17 +575,17 @@ be set as a connection-local variable.
 
 ---
 *** New user option 'dired-hide-details-hide-absolute-location'.
-When dired's 'dired-hide-details-mode' is enabled, also hide the
+When Dired's 'dired-hide-details-mode' is enabled, also hide the
 'default-directory' absolute location, typically displayed as the first
-line in a dired buffer.
+line in a Dired buffer.
 
-With dired-hide-details-hide-absolute-location:
+With 'dired-hide-details-hide-absolute-location':
 
-  project: (100 GiB available)
+    project: (100 GiB available)
 
-Without dired-hide-details-hide-absolute-location:
+Without 'dired-hide-details-hide-absolute-location':
 
-  /absolute/path/to/my/important/project: (100 GiB available)
+    /absolute/path/to/my/important/project: (100 GiB available)
 
 ** Grep
 
@@ -622,7 +635,7 @@ The hardcoded '^' shortcut gets you back to the previous menu.
 ---
 *** New user option 'tmm-shortcut-inside-entry'.
 When non-nil, highlight the character shortcut in the menu entry's
-string instead of preprending it and `tmm-mid-prompt' to said entry.
+string instead of preprending it and 'tmm-mid-prompt' to said entry.
 
 ** Foldout
 
@@ -655,8 +668,8 @@ of seconds.  Crossfading can be toggled using the command
 *** New user option 'vc-allow-rewriting-published-history'.
 Some VCS commands can change your copy of published change history
 without warning.  In VC we try to detect before that happens, and stop.
-You can customize this variable to permit rewriting history
-even though Emacs thinks it is dangerous.
+You can customize this option to permit rewriting history even though
+Emacs thinks it is dangerous.
 
 ---
 *** 'vc-clone' is now an interactive command.
@@ -846,7 +859,7 @@ variable 'w32-inhibit-dwrite' to t.  Also see 'w32-dwrite-available' and
 'w32-dwrite-reinit' to check availability and to configure the
 DirectWrite rendering parameters.
 
-To show color Emoji in Emacs, customize the default fontset to use a
+To show color Emojis in Emacs, customize the default fontset to use a
 color Emoji font installed on your system for the 'emoji' script.
 
 +++
diff --git a/lisp/net/tramp-cmds.el b/lisp/net/tramp-cmds.el
index 1b90ba6540b..f2ecf8173be 100644
--- a/lisp/net/tramp-cmds.el
+++ b/lisp/net/tramp-cmds.el
@@ -118,11 +118,11 @@ Each function is called with the current vector as argument.")
 (defun tramp-cleanup-connection
     (vec &optional keep-debug keep-password keep-processes)
   "Flush all connection related objects.
-This includes password cache, file cache, connection cache,
-buffers, processes.  KEEP-DEBUG non-nil preserves the debug
-buffer.  KEEP-PASSWORD non-nil preserves the password cache.
-KEEP-PROCESSES non-nil preserves the asynchronous processes.
-When called interactively, a Tramp connection has to be selected."
+This includes password cache, file cache, connection cache, buffers,
+processes.  KEEP-DEBUG non-nil preserves the debug and trace buffer.
+KEEP-PASSWORD non-nil preserves the password cache.  KEEP-PROCESSES
+non-nil preserves the asynchronous processes.  When called
+interactively, a Tramp connection has to be selected."
   (declare (completion tramp-active-command-completion-p))
   (interactive
    ;; When interactive, select the Tramp remote identification.
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index a137b5aeadc..0a61ca7e40d 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -1886,7 +1886,8 @@ expected to be a string, which will be used."
         ;; Assure that the hops are in `tramp-default-proxies-alist'.
         ;; In tramp-archive.el, the slot `hop' is used for the archive
         ;; file name.
-        (unless (string-equal method tramp-archive-method)
+        (unless (or minibuffer-completing-file-name
+                    (string-equal method tramp-archive-method))
           (tramp-add-hops (car args)))))
 
      (t (setq method (nth 0 args)
@@ -4177,7 +4178,7 @@ Let-bind it when necessary.")
   ;; the empty string.  Suppress adding a hop to
   ;; `tramp-default-proxies-alist' due to non-expanded default values.
   (let ((v (tramp-dissect-file-name file t))
-        tramp-default-proxies-alist)
+        (tramp-default-proxies-alist tramp-cache-undefined))
     ;; Run the command on the localname portion only unless we are in
     ;; completion mode.
     (tramp-make-tramp-file-name
@@ -4271,7 +4272,7 @@ Let-bind it when necessary.")
   ;; the remote file name parts.  Suppress adding a hop to
   ;; `tramp-default-proxies-alist' due to non-expanded default values.
   (let ((v (tramp-dissect-file-name file t))
-        tramp-default-proxies-alist)
+        (tramp-default-proxies-alist tramp-cache-undefined))
     ;; Run the command on the localname portion only.  If this returns
     ;; nil, mark also the localname part of `v' as nil.
     (tramp-make-tramp-file-name
@@ -4912,21 +4913,37 @@ Do not set it manually, it is used buffer-local in `tramp-get-lock-pid'.")
 
 (defun tramp-add-hops (vec)
   "Add ad-hoc proxy definitions to `tramp-default-proxies-alist'."
-  (when-let* ((hops (tramp-file-name-hop vec))
+  ;; `tramp-default-proxies-alist' is bound to `tramp-cache-undefined'
+  ;; in `tramp-handle-file-name-as-directory' and
+  ;; `tramp-handle-file-name-directory' suppressing to add a hop.
+  (when-let* (((not (eq tramp-default-proxies-alist tramp-cache-undefined)))
+              (hops (tramp-file-name-hop vec))
               (item vec))
     (let (signal-hook-function changed)
       (dolist
           (proxy (reverse (split-string hops tramp-postfix-hop-regexp 'omit)))
         (let* ((host-port (tramp-file-name-host-port item))
+               (host-port (and (stringp host-port)
+                               (rx bol (literal host-port) eol)))
                (user-domain (tramp-file-name-user-domain item))
+               (user-domain (and (stringp user-domain)
+                                 (rx bol (literal user-domain) eol)))
                (proxy (concat
                        tramp-prefix-format proxy tramp-postfix-host-format))
                (entry
-                (list (and (stringp host-port)
-                           (rx bol (literal host-port) eol))
-                      (and (stringp user-domain)
-                           (rx bol (literal user-domain) eol))
-                      (propertize proxy 'tramp-ad-hoc t))))
+                (list host-port user-domain (propertize proxy 'tramp-ad-hoc t))))
+          ;; Remove superfluous entries.
+          (when tramp-show-ad-hoc-proxies
+            (dolist (entry1 tramp-default-proxies-alist)
+              (when (and (equal host-port (car entry1))
+                         (equal user-domain (cadr entry1))
+                         (not (equal proxy (caddr entry1))))
+                (tramp-message
+                 vec 5 "Remove %S from `tramp-default-proxies-alist'" entry1)
+                (tramp-cleanup-connection
+                 vec 'keep-debug 'keep-password 'keep-processes)
+                (setq tramp-default-proxies-alist
+                      (delete entry1 tramp-default-proxies-alist)))))
           ;; Add the hop.
           (unless (member entry tramp-default-proxies-alist)
             (tramp-message vec 5 "Add %S to `tramp-default-proxies-alist'" entry)