bug#51374: New options for emacsclient

[Gregory Heytings <gregory@heytings.org>]

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>> When emacsclient is used in a terminal, emacsclient FILE opens a 
>> non-graphical Emacs frame, and emacsclient -c FILE always creates a new 
>> graphical Emacs frame. A third option, which creates a graphical frame 
>> if none exist and reuses a graphical frame is one exists, would be 
>> useful (see for example [1] and [2]).
>
> It seems like tons of users are using home-cooked solutions and scripts 
> to do this, so there is a clear need for it.  I think we should add it.
>

Thanks for your comment!

> Your patch LGTM, but it's missing a NEWS entry.
>
> (Perhaps we could also update the man page, but that's no requirement as 
> we don't really make an effort to maintain it.)
>

Updated patch attached.

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From c366e458f567e37b3b844808b56eaa95861be9d8 Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Sat, 30 Oct 2021 22:29:00 +0000
Subject: [PATCH] New emacsclient option to either create or reuse an existing
 frame.

* lib-src/emacsclient.c (reuse_frame): New variable.
(longopts): New option.
(decode_options): Decode the new option.
(print_help_and_exit): Document the new option.
(main): Use the new option.

* doc/emacs/misc.texi (emacsclient Options): Document the new option.

* etc/NEWS: Mention the new option.

* doc/man/emacsclient.1: Mention the new option.
---
 doc/emacs/misc.texi   |  5 +++++
 doc/man/emacsclient.1 |  3 +++
 etc/NEWS              |  8 ++++++++
 lib-src/emacsclient.c | 13 ++++++++++++-
 4 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index 5123a716dc..810d212021 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -1986,6 +1986,11 @@ emacsclient Options
 can customize this behavior with the variable @code{initial-buffer-choice}
 (@pxref{Entering Emacs}).
 
+@item -r
+@itemx --reuse-frame
+Create a new graphical @dfn{client frame} if none exists, otherwise
+use an existing Emacs frame.
+
 @item -F @var{alist}
 @itemx --frame-parameters=@var{alist}
 Set the parameters for a newly-created graphical frame
diff --git a/doc/man/emacsclient.1 b/doc/man/emacsclient.1
index ba64efa282..cc58f106e6 100644
--- a/doc/man/emacsclient.1
+++ b/doc/man/emacsclient.1
@@ -69,6 +69,9 @@ start Emacs in daemon mode, and try to connect to it.
 .B -c, \-\-create-frame
 Create a new frame instead of trying to use the current Emacs frame.
 .TP
+.B -r \-\-reuse-frame
+Reuse an existing frame if one exists, otherwise create a new frame.
+.TP
 .B \-F, \-\-frame-parameters=ALIST
 Set the parameters of a newly-created frame.
 .TP
diff --git a/etc/NEWS b/etc/NEWS
index 6d3256959e..a318d4c262 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -74,6 +74,14 @@ Image specifiers can now use ':type webp'.
 For example, an alist entry as '(window-width . (body-columns . 40))'
 will make the body of the chosen window 40 columns wide.
 \f
+
+** Emacs server and client changes
+
++++
+*** New command-line option '-r' for emacsclient.
+With this command-line option, Emacs reuses an existing graphical client
+frame if one exists; otherwise a new frame is created.
+
 * Editing Changes in Emacs 29.1
 
 ---
diff --git a/lib-src/emacsclient.c b/lib-src/emacsclient.c
index cff3cec2a7..0e800dd7e8 100644
--- a/lib-src/emacsclient.c
+++ b/lib-src/emacsclient.c
@@ -116,6 +116,9 @@ Copyright (C) 1986-1987, 1994, 1999-2021 Free Software Foundation, Inc.
 /* True means open a new frame.  --create-frame etc.  */
 static bool create_frame;
 
+/* True means reuse a frame if it already exists.  */
+static bool reuse_frame;
+
 /* The display on which Emacs should work.  --display.  */
 static char const *display;
 
@@ -165,6 +168,7 @@ Copyright (C) 1986-1987, 1994, 1999-2021 Free Software Foundation, Inc.
   { "tty",	no_argument,       NULL, 't' },
   { "nw",	no_argument,       NULL, 't' },
   { "create-frame", no_argument,   NULL, 'c' },
+  { "reuse-frame", no_argument,   NULL, 'r' },
   { "alternate-editor", required_argument, NULL, 'a' },
   { "frame-parameters", required_argument, NULL, 'F' },
 #ifdef SOCKETS_IN_FILE_SYSTEM
@@ -551,6 +555,11 @@ decode_options (int argc, char **argv)
 	  create_frame = true;
           break;
 
+	case 'r':
+	  create_frame = true;
+	  reuse_frame = true;
+	  break;
+
 	case 'p':
 	  parent_id = optarg;
 	  create_frame = true;
@@ -647,6 +656,8 @@ print_help_and_exit (void)
 -nw, -t, --tty 		Open a new Emacs frame on the current terminal\n\
 -c, --create-frame    	Create a new frame instead of trying to\n\
 			use the current Emacs frame\n\
+-r, --reuse-frame	Create a new frame if none exists, otherwise\n\
+			use the current Emacs frame\n\
 ", "\
 -F ALIST, --frame-parameters=ALIST\n\
 			Set the parameters of a new frame\n\
@@ -1941,7 +1952,7 @@ main (int argc, char **argv)
   if (nowait)
     send_to_emacs (emacs_socket, "-nowait ");
 
-  if (!create_frame)
+  if (!create_frame || reuse_frame)
     send_to_emacs (emacs_socket, "-current-frame ");
 
   if (display)
-- 
2.33.0