From 67141fb4bb904ea0d539821229d9ce1b85b5273d Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Mon, 9 Mar 2026 15:46:01 +0000
Subject: [PATCH] Add next/previous variables for windows in W: loop, from
 Conor Taylor in GitHub issue 4856.

---
 format.c        | 42 ++++++++++++++++++++++++++++++++++++++++++
 options-table.c |  4 ++--
 tmux.1          | 19 +++++++++++++++++++
 3 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/format.c b/format.c
index 2ed398c2..bdde54a3 100644
--- a/format.c
+++ b/format.c
@@ -4473,6 +4473,37 @@ format_window_name(struct format_expand_state *es, const char *fmt)
 	return (xstrdup("0"));
 }
 
+/* Add neighbor window variables to the format tree. */
+static void
+format_add_window_neighbor(struct format_tree *nft, struct winlink *wl,
+    struct session *s, const char *prefix)
+{
+	struct options_entry	*o;
+	const char		*oname;
+	char			*key, *prefixed, *oval;
+
+	xasprintf(&key, "%s_window_index", prefix);
+	format_add(nft, key, "%u", wl->idx);
+	free(key);
+
+	xasprintf(&key, "%s_window_active", prefix);
+	format_add(nft, key, "%d", wl == s->curw);
+	free(key);
+
+	o = options_first(wl->window->options);
+	while (o != NULL) {
+		oname = options_name(o);
+		if (*oname == '@') {
+			xasprintf(&prefixed, "%s_%s", prefix, oname);
+			oval = options_to_string(o, -1, 1);
+			format_add(nft, prefixed, "%s", oval);
+			free(oval);
+			free(prefixed);
+		}
+		o = options_next(o);
+	}
+}
+
 /* Loop over windows. */
 static char *
 format_loop_windows(struct format_expand_state *es, const char *fmt)
@@ -4516,6 +4547,17 @@ format_loop_windows(struct format_expand_state *es, const char *fmt)
 		nft = format_create(c, item, FORMAT_WINDOW|w->id,
 		    ft->flags|last);
 		format_defaults(nft, ft->c, ft->s, wl, NULL);
+
+		/* Add neighbor window data to the format tree. */
+		format_add(nft, "window_after_active", "%d",
+		    i > 0 && l[i - 1] == ft->s->curw);
+		format_add(nft, "window_before_active", "%d",
+		    i + 1 < n && l[i + 1] == ft->s->curw);
+		if (i + 1 < n)
+			format_add_window_neighbor(nft, l[i + 1], ft->s, "next");
+		if (i > 0)
+			format_add_window_neighbor(nft, l[i - 1], ft->s, "prev");
+
 		format_copy_state(&next, es, 0);
 		next.ft = nft;
 		expanded = format_expand1(&next, use);
diff --git a/options-table.c b/options-table.c
index 78299328..2eb4f6d5 100644
--- a/options-table.c
+++ b/options-table.c
@@ -142,7 +142,7 @@ static const char *options_table_allow_passthrough_list[] = {
 		"#{T:window-status-format}" \
 		"#[pop-default]" \
 		"#[norange default]" \
-		"#{?loop_last_flag,,#{window-status-separator}}" \
+		"#{?loop_last_flag,,#{E:window-status-separator}}" \
 	"," \
 		"#[range=window|#{window_index} list=focus " \
 			"#{?#{!=:#{E:window-status-current-style},default}," \
@@ -169,7 +169,7 @@ static const char *options_table_allow_passthrough_list[] = {
 		"#{T:window-status-current-format}" \
 		"#[pop-default]" \
 		"#[norange list=on default]" \
-		"#{?loop_last_flag,,#{window-status-separator}}" \
+		"#{?loop_last_flag,,#{E:window-status-separator}}" \
 	"}" \
 	"#[nolist align=right range=right #{E:status-right-style}]" \
 	"#[push-default]" \
diff --git a/tmux.1 b/tmux.1
index 32b0c640..c404abab 100644
--- a/tmux.1
+++ b/tmux.1
@@ -6125,6 +6125,21 @@ For example, to get a list of windows formatted like the status line:
 #{W:#{E:window-status-format} ,#{E:window-status-current-format} }
 .Ed
 .Pp
+Within the
+.Ql W:\&
+loop, user options
+.Po
+.Ql @name
+.Pc
+from neighboring windows are available with a
+.Ql next_
+or
+.Ql prev_
+prefix, for example a user option
+.Ql @color
+on the next window is available as
+.Ql next_@color .
+.Pp
 .Ql N:\&
 checks if a window (without any suffix or with the
 .Ql w
@@ -6293,6 +6308,8 @@ The following variables are available, where appropriate:
 .It Li "mouse_x" Ta "" Ta "Mouse X position, if any"
 .It Li "mouse_y" Ta "" Ta "Mouse Y position, if any"
 .It Li "next_session_id" Ta "" Ta "Unique session ID for next new session"
+.It Li "next_window_active" Ta "" Ta "1 if next window in W: loop is active"
+.It Li "next_window_index" Ta "" Ta "Index of next window in W: loop"
 .It Li "origin_flag" Ta "" Ta "Pane origin flag"
 .It Li "pane_active" Ta "" Ta "1 if active pane"
 .It Li "pane_at_bottom" Ta "" Ta "1 if pane is at the bottom of window"
@@ -6336,6 +6353,8 @@ The following variables are available, where appropriate:
 .It Li "pane_unseen_changes" Ta "" Ta "1 if there were changes in pane while in mode"
 .It Li "pane_width" Ta "" Ta "Width of pane"
 .It Li "pid" Ta "" Ta "Server PID"
+.It Li "prev_window_active" Ta "" Ta "1 if previous window in W: loop is active"
+.It Li "prev_window_index" Ta "" Ta "Index of previous window in W: loop"
 .It Li "rectangle_toggle" Ta "" Ta "1 if rectangle selection is activated"
 .It Li "scroll_position" Ta "" Ta "Scroll position in copy mode"
 .It Li "scroll_region_lower" Ta "" Ta "Bottom of scroll region in pane"