Allow panes to be empty (no command), output can be piped to them with

split-window or display-message -I.

cmd-display-message.c

@@ -39,8 +39,8 @@ const struct cmd_entry cmd_display_message_entry = {
 	.name = "display-message",
 	.alias = "display",
 
-	.args = { "ac:pt:F:v", 0, 1 },
+	.args = { "ac:Ipt:F:v", 0, 1 },
-	.usage = "[-apv] [-c target-client] [-F format] "
+	.usage = "[-aIpv] [-c target-client] [-F format] "
 		 CMD_TARGET_PANE_USAGE " [message]",
 
 	.target = { 't', CMD_FIND_PANE, 0 },
@@ -66,10 +66,19 @@ cmd_display_message_exec(struct cmd *self, struct cmdq_item *item)
 	struct winlink		*wl = item->target.wl;
 	struct window_pane	*wp = item->target.wp;
 	const char		*template;
-	char			*msg;
+	char			*msg, *cause;
 	struct format_tree	*ft;
 	int			 flags;
 
+	if (args_has(args, 'I')) {
+		if (window_pane_start_input(wp, item, &cause) != 0) {
+			cmdq_error(item, "%s", cause);
+			free(cause);
+			return (CMD_RETURN_ERROR);
+		}
+		return (CMD_RETURN_WAIT);
+	}
+
 	if (args_has(args, 'F') && args->argc != 0) {
 		cmdq_error(item, "only one of -F or argument must be given");
 		return (CMD_RETURN_ERROR);

cmd-split-window.c

@@ -40,9 +40,10 @@ const struct cmd_entry cmd_split_window_entry = {
 	.name = "split-window",
 	.alias = "splitw",
 
-	.args = { "bc:de:fF:l:hp:Pt:v", 0, -1 },
+	.args = { "bc:de:fF:hIl:p:Pt:v", 0, -1 },
-	.usage = "[-bdefhvP] [-c start-directory] [-e environment] [-F format] "
+	.usage = "[-bdefhIPv] [-c start-directory] [-e environment] "
-		 "[-p percentage|-l size] " CMD_TARGET_PANE_USAGE " [command]",
+		 "[-F format] [-p percentage|-l size] " CMD_TARGET_PANE_USAGE
+		 " [command]",
 
 	.target = { 't', CMD_FIND_PANE, 0 },
 
@@ -63,7 +64,7 @@ cmd_split_window_exec(struct cmd *self, struct cmdq_item *item)
 	enum layout_type	 type;
 	struct layout_cell	*lc;
 	struct cmd_find_state	 fs;
-	int			 size, percentage, flags;
+	int			 size, percentage, flags, input;
 	const char		*template, *add;
 	char			*cause, *cp;
 	struct args_value	*value;
@@ -94,12 +95,15 @@ cmd_split_window_exec(struct cmd *self, struct cmdq_item *item)
 		size = -1;
 
 	server_unzoom_window(wp->window);
+	input = (args_has(args, 'I') && args->argc == 0);
 
 	flags = 0;
 	if (args_has(args, 'b'))
 		flags |= SPAWN_BEFORE;
 	if (args_has(args, 'f'))
 		flags |= SPAWN_FULLSIZE;
+	if (input || (args->argc == 1 && *args->argv[0] == '\0'))
+		flags |= SPAWN_EMPTY;
 
 	lc = layout_split_pane(wp, type, size, flags);
 	if (lc == NULL) {
@@ -134,10 +138,18 @@ cmd_split_window_exec(struct cmd *self, struct cmdq_item *item)
 		sc.flags |= SPAWN_DETACHED;
 
 	if ((new_wp = spawn_pane(&sc, &cause)) == NULL) {
+		layout_close_pane(new_wp);
 		cmdq_error(item, "create pane failed: %s", cause);
 		free(cause);
 		return (CMD_RETURN_ERROR);
 	}
+	if (input && window_pane_start_input(new_wp, item, &cause) != 0) {
+		layout_close_pane(new_wp);
+		window_remove_pane(wp->window, new_wp);
+		cmdq_error(item, "%s", cause);
+		free(cause);
+		return (CMD_RETURN_ERROR);
+	}
 	if (!args_has(args, 'd'))
 		cmd_find_from_winlink_pane(current, wl, new_wp, 0);
 	server_redraw_window(wp->window);
@@ -155,5 +167,7 @@ cmd_split_window_exec(struct cmd *self, struct cmdq_item *item)
 	cmdq_insert_hook(s, item, &fs, "after-split-window");
 
 	environ_free(sc.environ);
+	if (input)
+		return (CMD_RETURN_WAIT);
 	return (CMD_RETURN_NORMAL);
 }

format.c

@@ -2031,7 +2031,10 @@ format_defaults_pane(struct format_tree *ft, struct window_pane *wp)
 
 	if ((wp->flags & PANE_STATUSREADY) && WIFEXITED(status))
 		format_add(ft, "pane_dead_status", "%d", WEXITSTATUS(status));
+	if (~wp->flags & PANE_EMPTY)
 		format_add(ft, "pane_dead", "%d", wp->fd == -1);
+	else
+		format_add(ft, "pane_dead", "0");
 
 	format_add(ft, "pane_left", "%u", wp->xoff);
 	format_add(ft, "pane_top", "%u", wp->yoff);

input.c

@@ -1185,6 +1185,8 @@ input_c0_dispatch(struct input_ctx *ictx)
 	case '\013':	/* VT */
 	case '\014':	/* FF */
 		screen_write_linefeed(sctx, 0, ictx->cell.cell.bg);
+		if (s->mode & MODE_CRLF)
+			screen_write_carriagereturn(sctx);
 		break;
 	case '\015':	/* CR */
 		screen_write_carriagereturn(sctx);

server-client.c

@@ -1671,8 +1671,7 @@ server_client_dispatch(struct imsg *imsg, void *arg)
 			evbuffer_add(c->stdin_data, stdindata.data,
 			    stdindata.size);
 		}
-		c->stdin_callback(c, c->stdin_closed,
+		c->stdin_callback(c, c->stdin_closed, c->stdin_callback_data);
-		    c->stdin_callback_data);
 		break;
 	case MSG_RESIZE:
 		if (datalen != 0)

server-fn.c

@@ -439,7 +439,6 @@ server_check_unattached(void)
 	}
 }
 
-/* Set stdin callback. */
 int
 server_set_stdin_callback(struct client *c, void (*cb)(struct client *, int,
     void *), void *cb_data, char **cause)
@@ -453,7 +452,7 @@ server_set_stdin_callback(struct client *c, void (*cb)(struct client *, int,
 		return (-1);
 	}
 	if (c->stdin_callback != NULL) {
-		*cause = xstrdup("stdin in use");
+		*cause = xstrdup("stdin is in use");
 		return (-1);
 	}
 

spawn.c

@@ -332,6 +332,14 @@ spawn_pane(struct spawn_context *sc, char **cause)
 	cmd_log_argv(new_wp->argc, new_wp->argv, __func__);
 	environ_log(child, "%s: environment ", __func__);
 
+	/* If the command is empty, don't fork a child process. */
+	if (sc->flags & SPAWN_EMPTY) {
+		new_wp->flags |= PANE_EMPTY;
+		new_wp->base.mode &= ~MODE_CURSOR;
+		new_wp->base.mode |= MODE_CRLF;
+		goto complete;
+	}
+
 	/* Initialize the window size. */
 	memset(&ws, 0, sizeof ws);
 	ws.ws_col = screen_size_x(&new_wp->base);
@@ -355,25 +363,8 @@ spawn_pane(struct spawn_context *sc, char **cause)
 	}
 
 	/* In the parent process, everything is done now. */
-	if (new_wp->pid != 0) {
+	if (new_wp->pid != 0)
-		new_wp->pipe_off = 0;
+		goto complete;
-		new_wp->flags &= ~PANE_EXITED;
-
-		sigprocmask(SIG_SETMASK, &oldset, NULL);
-		window_pane_set_event(new_wp);
-
-		if (sc->flags & SPAWN_RESPAWN)
-			return (new_wp);
-		if ((~sc->flags & SPAWN_DETACHED) || w->active == NULL) {
-			if (sc->flags & SPAWN_NONOTIFY)
-				window_set_active_pane(w, new_wp, 0);
-			else
-				window_set_active_pane(w, new_wp, 1);
-		}
-		if (~sc->flags & SPAWN_NONOTIFY)
-			notify_window("window-layout-changed", w);
-		return (new_wp);
-	}
 
 	/*
 	 * Child process. Change to the working directory or home if that
@@ -433,4 +424,23 @@ spawn_pane(struct spawn_context *sc, char **cause)
 		xasprintf(&argv0, "-%s", new_wp->shell);
 	execl(new_wp->shell, argv0, (char *)NULL);
 	_exit(1);
+
+complete:
+	new_wp->pipe_off = 0;
+	new_wp->flags &= ~PANE_EXITED;
+
+	sigprocmask(SIG_SETMASK, &oldset, NULL);
+	window_pane_set_event(new_wp);
+
+	if (sc->flags & SPAWN_RESPAWN)
+		return (new_wp);
+	if ((~sc->flags & SPAWN_DETACHED) || w->active == NULL) {
+		if (sc->flags & SPAWN_NONOTIFY)
+			window_set_active_pane(w, new_wp, 0);
+		else
+			window_set_active_pane(w, new_wp, 1);
+	}
+	if (~sc->flags & SPAWN_NONOTIFY)
+		notify_window("window-layout-changed", w);
+	return (new_wp);
 }

tmux.1

@@ -2204,7 +2204,7 @@ is given and the selected window is already the current window,
 the command behaves like
 .Ic last-window .
 .It Xo Ic split-window
-.Op Fl bdfhvP
+.Op Fl bdfhIvP
 .Op Fl c Ar start-directory
 .Op Fl e Ar environment
 .Oo Fl l
@@ -2240,6 +2240,24 @@ option creates a new pane spanning the full window height (with
 or full window width (with
 .Fl v ) ,
 instead of splitting the active pane.
+.Pp
+An empty
+.Ar shell-command
+('') will create a pane with no command running in it.
+Output can be sent to such a pane with the
+.Ic display-message
+command.
+The
+.Fl I
+flag (if
+.Ar shell-command
+is not specified or empty)
+will create an empty pane and forward any output from stdin to it.
+For example:
+.Bd -literal -offset indent
+$ make 2>&1|tmux splitw -dI &
+.Ed
+.Pp
 All other options have the same meaning as for the
 .Ic new-window
 command.
@@ -2822,7 +2840,7 @@ This option should be configured when
 is used as a login shell.
 .It Ic default-size Ar XxY
 Set the default size of new windows when the
-.Ar window-size
+.Ic window-size
 option is set to manual or when a session is created with
 .Ic new-session
 .Fl d .
@@ -4428,7 +4446,7 @@ option.
 This command works only from inside
 .Nm .
 .It Xo Ic display-message
-.Op Fl apv
+.Op Fl aIpv
 .Op Fl c Ar target-client
 .Op Fl t Ar target-pane
 .Op Ar message
@@ -4455,6 +4473,10 @@ is given, otherwise the active pane for the session attached to
 prints verbose logging as the format is parsed and
 .Fl a
 lists the format variables and their values.
+.Pp
+.Fl I
+forwards any input read from stdin to the empty pane given by
+.Ar target-pane .
 .El
 .Sh BUFFERS
 .Nm

tmux.h

@@ -522,6 +522,7 @@ struct msg_stderr_data {
 #define MODE_FOCUSON 0x800
 #define MODE_MOUSE_ALL 0x1000
 #define MODE_ORIGIN 0x2000
+#define MODE_CRLF 0x4000
 
 #define ALL_MODES 0xffffff
 #define ALL_MOUSE_MODES (MODE_MOUSE_STANDARD|MODE_MOUSE_BUTTON|MODE_MOUSE_ALL)
@@ -802,6 +803,7 @@ struct window_pane {
 #define PANE_EXITED 0x100
 #define PANE_STATUSREADY 0x200
 #define PANE_STATUSDRAWN 0x400
+#define PANE_EMPTY 0x800
 
 	int		 argc;
 	char	       **argv;
@@ -1598,6 +1600,7 @@ struct spawn_context {
 #define SPAWN_BEFORE 0x8
 #define SPAWN_NONOTIFY 0x10
 #define SPAWN_FULLSIZE 0x20
+#define SPAWN_EMPTY 0x40
 };
 
 /* tmux.c */
@@ -2317,6 +2320,8 @@ void		 window_add_ref(struct window *, const char *);
 void		 window_remove_ref(struct window *, const char *);
 void		 winlink_clear_flags(struct winlink *);
 int		 winlink_shuffle_up(struct session *, struct winlink *);
+int		 window_pane_start_input(struct window_pane *,
+		     struct cmdq_item *, char **);
 
 /* layout.c */
 u_int		 layout_count_cells(struct layout_cell *);

window.c

@@ -72,6 +72,11 @@ const struct window_mode *all_window_modes[] = {
 	NULL
 };
 
+struct window_pane_input_data {
+	struct cmdq_item	*item;
+	u_int			 wp;
+};
+
 static struct window_pane *window_pane_create(struct window *, u_int, u_int,
 		    u_int);
 static void	window_pane_destroy(struct window_pane *);
@@ -1466,3 +1471,45 @@ winlink_shuffle_up(struct session *s, struct winlink *wl)
 
 	return (idx);
 }
+
+static void
+window_pane_input_callback(struct client *c, int closed, void *data)
+{
+	struct window_pane_input_data	*cdata = data;
+	struct window_pane		*wp;
+
+	wp = window_pane_find_by_id(cdata->wp);
+	if (wp == NULL || closed || c->flags & CLIENT_DEAD) {
+		c->stdin_callback = NULL;
+		server_client_unref(c);
+
+		cdata->item->flags &= ~CMDQ_WAITING;
+		free(cdata);
+
+		return;
+	}
+
+	if (evbuffer_add_buffer(wp->event->input, c->stdin_data) != 0)
+		evbuffer_drain(c->stdin_data, EVBUFFER_LENGTH(c->stdin_data));
+	input_parse(wp);
+}
+
+int
+window_pane_start_input(struct window_pane *wp, struct cmdq_item *item,
+    char **cause)
+{
+	struct client			*c = item->client;
+	struct window_pane_input_data	*cdata;
+
+	if (~wp->flags & PANE_EMPTY) {
+		*cause = xstrdup("pane is not empty");
+		return (-1);
+	}
+
+	cdata = xmalloc(sizeof *cdata);
+	cdata->item = item;
+	cdata->wp = wp->id;
+
+	return (server_set_stdin_callback(c, window_pane_input_callback, cdata,
+	    cause));
+}