From e66d0573239ccdff850c34e86777775d6d56651f Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicholas.marriott@gmail.com>
Date: Mon, 28 Sep 2026 12:26:18 +0100
Subject: [PATCH] Test for 5648.

(cherry picked from commit 294bf0bf16187612b589205852a00523b320f492)
---
 regress/sync-output-copy-cursor.sh | 141 +++++++++++++++++++++++++++++
 1 file changed, 141 insertions(+)
 create mode 100755 regress/sync-output-copy-cursor.sh

diff --git a/regress/sync-output-copy-cursor.sh b/regress/sync-output-copy-cursor.sh
new file mode 100755
index 000000000..06a88342a
--- /dev/null
+++ b/regress/sync-output-copy-cursor.sh
@@ -0,0 +1,141 @@
+#!/bin/sh
+
+# A synchronized update on the base screen must not defer cursor movement on
+# the copy-mode screen displayed in its place.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+DIR=$(mktemp -d) || exit 1
+TMUX_TMPDIR=$DIR
+export TMUX_TMPDIR
+
+INNER="$TEST_TMUX -Li$$ -f/dev/null"
+OUTER="$TEST_TMUX -Lo$$ -f/dev/null"
+CLIENT_BYTES=$DIR/client-bytes
+CONTROL=$DIR/control
+EMITTER=$DIR/emitter.pl
+
+fail()
+{
+	echo "$*" >&2
+	exit 1
+}
+
+cleanup()
+{
+	$OUTER kill-server 2>/dev/null
+	$INNER kill-server 2>/dev/null
+	rm -rf "$DIR"
+}
+trap cleanup 0 1 15
+
+wait_for_client()
+{
+	i=0
+	while [ "$i" -lt 50 ]; do
+		$INNER list-clients -F '#{client_termfeatures}' 2>/dev/null |
+		    grep -q 'sync' && return 0
+		sleep 0.1
+		i=$((i + 1))
+	done
+	fail "sync-capable client did not attach"
+}
+
+wait_for_sync()
+{
+	i=0
+	while [ "$i" -lt 50 ]; do
+		[ "$($INNER display-message -p \
+		    '#{synchronized_output_flag}' 2>/dev/null)" = 1 ] &&
+		    return 0
+		sleep 0.1
+		i=$((i + 1))
+	done
+	fail "application did not enter synchronized output"
+}
+
+wait_for_cursor_position()
+{
+	position=$(printf '\033[%d;%dH' "$2" "$1")
+	i=0
+	while [ "$i" -lt 20 ]; do
+		grep -Fq "$position" "$CLIENT_BYTES" 2>/dev/null &&
+		    return 0
+		sleep 0.1
+		i=$((i + 1))
+	done
+	fail "copy-mode cursor position did not reach client"
+}
+
+cat >"$EMITTER" <<'PERL'
+use strict;
+use warnings;
+
+my $control = $ENV{CONTROL};
+(my $dir = $control) =~ s{/[^/]+$}{};
+
+# Leave the application cursor away from the left edge so copy mode can move
+# it left.
+syswrite STDOUT, "copy cursor";
+open my $ready, '>', "$dir/ready" or die "$dir/ready: $!\n";
+close $ready;
+while (!-e $control) {
+	select undef, undef, undef, 0.01;
+}
+
+# Keep a real application synchronized update open while the separately
+# displayed copy-mode screen moves its cursor. Repeating DECSET also keeps the
+# one-second safety timer from ending the update during the assertion.
+for (1 .. 200) {
+	syswrite STDOUT, "\e[?2026h";
+	select undef, undef, undef, 0.05;
+}
+PERL
+
+$INNER new-session -d -s inner -x 80 -y 24 \
+    "CONTROL='$CONTROL' perl '$EMITTER'" || exit 1
+$INNER set-option -g status off || exit 1
+$INNER set-option -g window-size manual || exit 1
+$INNER set-option -as terminal-features '*:sync' || exit 1
+
+$OUTER new-session -d -s outer -x 80 -y 24 \
+    "$TEST_TMUX -Li$$ -f/dev/null attach-session -t inner" || exit 1
+$OUTER set-option -g status off || exit 1
+$OUTER set-option -g window-size manual || exit 1
+wait_for_client
+
+i=0
+while [ "$i" -lt 50 ] && [ ! -e "$DIR/ready" ]; do
+	sleep 0.1
+	i=$((i + 1))
+done
+[ -e "$DIR/ready" ] || fail "application emitter did not become ready"
+
+$INNER copy-mode -t inner:0.0 || exit 1
+before=$($INNER display-message -p -t inner:0.0 '#{copy_cursor_x}') ||
+    exit 1
+[ "$before" -gt 0 ] || fail "copy-mode cursor started at left edge"
+
+: >"$CONTROL"
+wait_for_sync
+sleep 0.5
+
+$OUTER pipe-pane -O -t outer:0.0 "cat >'$CLIENT_BYTES'" || exit 1
+sleep 0.1
+$INNER send-keys -t inner:0.0 -X cursor-left || exit 1
+after=$($INNER display-message -p -t inner:0.0 '#{copy_cursor_x}') ||
+    exit 1
+after_y=$($INNER display-message -p -t inner:0.0 '#{copy_cursor_y}') ||
+    exit 1
+[ "$after" -eq $((before - 1)) ] ||
+    fail "copy-mode cursor did not move logically: $before to $after"
+[ "$($INNER display-message -p '#{synchronized_output_flag}')" = 1 ] ||
+    fail "application synchronized output ended unexpectedly"
+
+wait_for_cursor_position $((after + 1)) $((after_y + 1))
+$OUTER pipe-pane -t outer:0.0 || exit 1