If current buffer is a TRAMP buffer, use its filename for SSH tunnel

[OknoLombarda]

#3261
#2822

If current buffer is a TRAMP buffer, use its filename for SSH tunnel. This way, username and SSH port will be parsed from existing SSH connection, instead of using current username and default SSH port.

I'll edit changelog and manual (if needed) after review

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[bbatsov]

The proposed change seems reasonable. Probably we should also document this behavior as it might not be obvious to people.

[bbatsov]

Ping :-)

[OknoLombarda]

Yeah, I didn't forget :D. Didn't have much time lately. I added comments, but doesn't this line in docs already imply that CIDER takes care of SSH tunneling if user works with remote files over TRAMP? Or should I describe what exactly it does?

https://docs.cider.mx/cider/basics/up_and_running.html#working-with-remote-hosts

[bbatsov]

I was thinking it might be useful to explain in a bit more details what the TRAMP integration does and what exactly people can do to influence what SSH connection gets established. Maybe cover some edge cases, etc. The current docs are definitely very basic, and I myself never use TRAMP, so I didn't bother to play with this and document it better.

[OknoLombarda]

While checking some cases I found that this change would make cider-connect-* ignore host that was selected by user and still connect to the one of current TRAMP buffer. I guess TRAMP connection should only be taken into account if its host is the same as the one selected by user. Like so (diff with master)

 (defun nrepl--ssh-tunnel-connect (host port)
   "Connect to a remote machine identified by HOST and PORT through SSH tunnel."
   (message "[nREPL] Establishing SSH tunneled connection to %s:%s ..." host port)
-  (let* ((remote-dir (if host (format "/ssh:%s:" host) default-directory))
+  (let* ((current-buf (buffer-file-name))
+         (tramp-file-regexp "/ssh:\\(.+@\\)?\\(.+?\\)\\(:\\|#\\).+")
+         (remote-dir (cond
+                      ;; If current buffer is a TRAMP buffer and its host is
+                      ;; the same as HOST, reuse its connection parameters for
+                      ;; SSH tunnel.
+                      ((and (string-match tramp-file-regexp current-buf)
+                            (string= host (match-string 2 current-buf))) current-buf)
+                      ;; Otherwise, if HOST was provided, use it for connection.
+                      (host (format "/ssh:%s:" host))
+                      ;; Use default directory as fallback.
+                      (t default-directory)))
          (ssh (or (executable-find "ssh")
                   (error "[nREPL] Cannot locate 'ssh' executable")))
          (cmd (nrepl--ssh-tunnel-command ssh remote-dir port))
@@ -598,11 +609,12 @@ If NO-ERROR is non-nil, show messages instead of throwing an error."
     ;; forwarding is set up, which is used to synchronise on, so that
     ;; the port forwarding is up when we try to connect.
     (format-spec
-     "%s -v -N -L %p:localhost:%p %u'%h'"
+     "%s -v -N -L %p:localhost:%p %u'%h' %n"
      `((?s . ,ssh)
        (?p . ,port)
        (?h . ,v-host)
-       (?u . ,(if v-user (format "-l '%s' " v-user) ""))))))
+       (?u . ,(if v-user (format "-l '%s' " v-user) ""))
+       (?n . ,(if v-port (format "-p '%s' " v-port) ""))))))
 
 (autoload 'comint-watch-for-password-prompt "comint"  "(autoload).")

I'd then change the documentation like this:

 You can safely run `cider-jack-in-*` while working with remote files over TRAMP. CIDER
-will handle this use-case transparently for you.
+will reuse existing SSH connection's parameters (like port and username) for establishing SSH tunnel.
+The same will happen if you try to `cider-connect-*` to a host that matches the one you're currently
+connected to.
 
 == Connecting via unix domain file socket

To be honest, I don't know what else can be written about it. I don't use TRAMP that much, too. I just decided to try it out because REPL starts too slow on my laptop :D

[bbatsov]

I guess TRAMP connection should only be taken into account if its host is the same as the one selected by user.

To be honest, I don't know what else can be written about it. I don't use TRAMP that much, too. I just decided to try it out because REPL starts too slow on my laptop :D

Yeah, I get it. I mostly meant to outline what are the assumptions we're making to figure out which SSH host to target. It's fine to keep this short.

[OknoLombarda]

Well, I think that's all

[bbatsov]

Can you just rebase on top of master to address the merge conflict?

[OknoLombarda]

Done