Subject: emacsclient: create a new frame only if one doesn't exist

From: Eddie Hillenbrand <[email-masked]>
Date: Fri, 16 Mar 2012 16:18:33 -0700

I'm using emacsclient with emacs --daemon, but I find myself wanting a
different behavior than the standard options provide.

It would be nice if emacsclient could create a window system frame
only when one doesn't exist and if one does exist simply reuse that
frame.

I know I can get this behavior by initially invoking emacsclient with
-c and then subsequently invoking it without the -c, however I'd
prefer not to think about whether I need to include the -c when
opening files.

server-window was suggested as a possible way to get this
behavior. After inspection of lisp/server.el and trying a few test
cases I found that the server-window variable is not inspected until
after frames are created, thus the best I could do with server-window
is destroy the newly created frame which would be clunky IMHO.

Additionally, lisp/server.el is now lexically scoped (it wasn't in
Emacs 23) so server-window can't access tty-name to check if the
client is requesting a window system frame or a tty frame. The
variable is also not inspected when a file argument is not
provided. But I digress.

As an example:

$ Emacs.app/Contents/MacOS/Emacs -Q --daemon
$ Emacs.app/Contents/MacOS/bin/emacsclient -c -n
Insert and evaluate the following in the scratch buffer:
(setq server-window
      (lambda (next-buffer)
      	(message "SERVER-WINDOW")))
$ Emacs.app/Contents/MacOS/bin/emacsclient -c -n ~/a.txt
Prints the following in *Messages*:
When done with this frame, type C-x 5 0
SERVER-WINDOW

That demonstrates that the frame is created before server-window is
called. So server-window can't be made to provide the desired
behavior.

It is possible to use emacsclient's --eval option to provide this
behavior, but it is extremely ugly. Plus it occurred to me that this
behavior may be general enough to include in emacsclient as a standard
option and would be much cleaner.

I'm proposing adding a -C option to emacsclient that would "create a
new frame if one doesn't exist otherwise use the current Emacs frame."
I'd be happy to make the required changes and submit a patch.

Thanks,

Eddie

In GNU Emacs 24.0.94.1 (x86_64-apple-darwin11.3.0, NS apple-appkit-1138.32)
 of 2012-03-16 on lore.local
Windowing system distributor `Apple', version 10.3.1138
Configured using:
 `configure '--with-ns''