From b402687fcd9f99d82b5c47b41e082f8032df1530 Mon Sep 17 00:00:00 2001
From: nicm <nicm@openbsd.org>
Date: Mon, 31 Aug 2026 19:34:09 +0000
Subject: [PATCH] Add a generation counter to pane output, from Michael K
 Darling.

---
 format.c | 18 +++++++++++++++++-
 input.c  |  3 ++-
 tmux.1   |  3 ++-
 tmux.h   |  5 +++--
 4 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/format.c b/format.c
index 477675a57..daca3b30e 100644
--- a/format.c
+++ b/format.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: format.c,v 1.414 2026/08/31 19:27:46 nicm Exp $ */
+/* $OpenBSD: format.c,v 1.415 2026/08/31 19:34:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2011 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -2293,6 +2293,19 @@ format_cb_pane_last_output_time(struct format_tree *ft)
 	return (NULL);
 }
 
+/* Callback for pane_output_generation. */
+static void *
+format_cb_pane_output_generation(struct format_tree *ft)
+{
+	unsigned long long	 value;
+
+	if (ft->wp != NULL) {
+		value = ft->wp->output_generation;
+		return (format_printf("%llu", value));
+	}
+	return (NULL);
+}
+
 /* Callback for pane_last_prompt_time. */
 static void *
 format_cb_pane_last_prompt_time(struct format_tree *ft)
@@ -3871,6 +3884,9 @@ static const struct format_table_entry format_table[] = {
 	{ "pane_mode", FORMAT_TABLE_STRING,
 	  format_cb_pane_mode
 	},
+	{ "pane_output_generation", FORMAT_TABLE_STRING,
+	  format_cb_pane_output_generation
+	},
 	{ "pane_path", FORMAT_TABLE_STRING,
 	  format_cb_pane_path
 	},
diff --git a/input.c b/input.c
index 5f9c5f4ab..9a443b49d 100644
--- a/input.c
+++ b/input.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: input.c,v 1.270 2026/08/17 20:04:00 nicm Exp $ */
+/* $OpenBSD: input.c,v 1.271 2026/08/31 19:34:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1049,6 +1049,7 @@ input_parse_buffer(struct window_pane *wp, const u_char *buf, size_t len)
 	if (len == 0)
 		return;
 
+	wp->output_generation++;
 	window_update_activity(wp->window);
 	if (~wp->flags & PANE_ACTIVITY) {
 		wp->flags |= PANE_ACTIVITY;
diff --git a/tmux.1 b/tmux.1
index 41e0c03e2..2b2b28f17 100644
--- a/tmux.1
+++ b/tmux.1
@@ -1,4 +1,4 @@
-.\" $OpenBSD: tmux.1,v 1.1161 2026/08/31 19:27:46 nicm Exp $
+.\" $OpenBSD: tmux.1,v 1.1162 2026/08/31 19:34:09 nicm Exp $
 .\"
 .\" Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
 .\"
@@ -7418,6 +7418,7 @@ The following variables are available, where appropriate:
 .It Li "pane_marked_set" Ta "" Ta "1 if a marked pane is set"
 .It Li "pane_modal_flag" Ta "" Ta "1 if pane is modal"
 .It Li "pane_mode" Ta "" Ta "Name of pane mode, if any"
+.It Li "pane_output_generation" Ta "" Ta "Generation incremented when pane output is processed"
 .It Li "pane_path" Ta "" Ta "Path of pane (can be set by application)"
 .It Li "pane_pid" Ta "" Ta "PID of first process in pane"
 .It Li "pane_pipe" Ta "" Ta "1 if pane is being piped"
diff --git a/tmux.h b/tmux.h
index 2fa3f3987..02059ccc7 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1431 2026/08/25 08:37:08 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1432 2026/08/31 19:34:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1323,9 +1323,10 @@ struct window_pane {
 	char		 tty[TTY_NAME_MAX];
 	int		 status;
 	struct timeval	 dead_time;
-	struct cmdq_item *wait_item;	/* new-pane -W: waiting for pane exit */
+	struct cmdq_item *wait_item;
 	struct spawn_editor_state *editor;
 
+	uint64_t	 output_generation;
 	time_t		 last_output_time;
 	time_t		 last_prompt_time;
 	time_t		 cmd_start_time;