From 5a0440b4f8ce79a88a2710c174d3666fcbe404a0 Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicholas.marriott@gmail.com>
Date: Thu, 24 Sep 2026 19:59:45 +0100
Subject: [PATCH] Test for 5631.

---
 regress/mode-tree-scroll.sh | 168 ++++++++++++++++++++++++++++++++++++
 1 file changed, 168 insertions(+)
 create mode 100644 regress/mode-tree-scroll.sh

diff --git a/regress/mode-tree-scroll.sh b/regress/mode-tree-scroll.sh
new file mode 100644
index 000000000..de3d17db5
--- /dev/null
+++ b/regress/mode-tree-scroll.sh
@@ -0,0 +1,168 @@
+#!/bin/sh
+
+# Tests that the scroll position of a mode tree list (mode-tree.c) is kept
+# when the list is rebuilt, using choose-buffer. Buffer mode rebuilds its list
+# every time the status line is redrawn, which used to move the view so the
+# selected line was on the bottom row (or the list jumped back to the top)
+# even if the selected line was already visible. Also checks that when the
+# list shrinks the view does not leave empty lines at the bottom.
+#
+# The list is drawn on a mode screen which capture-pane does not show, so - as
+# in choose-buffer.sh - a second server provides a client: an inner "tmux
+# attach" runs inside a pane of the second server, and that pane is captured
+# to read what the inner client rendered.
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMP=$(mktemp -d) || exit 1
+TMUX_TMPDIR="$TMP"
+export TMUX_TMPDIR
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX kill-server 2>/dev/null
+	$TMUX2 kill-server 2>/dev/null
+	rm -rf "$TMP"
+}
+trap cleanup EXIT
+
+fail()
+{
+	echo "$1" >&2
+	exit 1
+}
+
+# capture the screen rendered by the inner client
+capture()
+{
+	$TMUX2 capture-pane -p -t out:0 2>/dev/null
+}
+
+# wait_for $marker
+#
+# Wait (up to ~10s) until the rendered screen contains $marker. The matching
+# capture is left in CAPTURED.
+wait_for()
+{
+	i=0
+	while [ "$i" -lt 50 ]; do
+		CAPTURED=$(capture)
+		if printf '%s\n' "$CAPTURED" | grep -F -q "$1"; then
+			return 0
+		fi
+		sleep 0.2
+		i=$((i + 1))
+	done
+	fail "timed out waiting for '$1'"
+}
+
+# wait_gone $marker
+#
+# Wait (up to ~10s) until the rendered screen no longer contains $marker. The
+# matching capture is left in CAPTURED.
+wait_gone()
+{
+	i=0
+	while [ "$i" -lt 50 ]; do
+		CAPTURED=$(capture)
+		if ! printf '%s\n' "$CAPTURED" | grep -F -q "$1"; then
+			return 0
+		fi
+		sleep 0.2
+		i=$((i + 1))
+	done
+	fail "timed out waiting for '$1' to disappear"
+}
+
+# wait_clients $n
+#
+# Wait (up to ~10s) until the test server has exactly $n clients attached.
+wait_clients()
+{
+	i=0
+	while [ "$i" -lt 10 ]; do
+		c=$($TMUX list-clients -F x 2>/dev/null | grep -c x)
+		[ "$c" -eq "$1" ] && return 0
+		sleep 1
+		i=$((i + 1))
+	done
+	return 1
+}
+
+# first_line
+#
+# Print the name of the first buffer shown in CAPTURED.
+first_line()
+{
+	printf '%s\n' "$CAPTURED" | grep -F ': S1' | head -1 | \
+	    sed 's/.*\(buf[0-9a-z]*\): S1.*/\1/'
+}
+
+$TMUX new-session -d -s aaa -x 80 -y 24 'cat' || exit 1
+
+$TMUX2 new-session -d -s out -x 80 -y 24 "$TMUX attach -t aaa" || exit 1
+wait_clients 1 || fail "no client attached to test server"
+
+# Forty buffers, more than fit on the screen.
+n=0
+while [ "$n" -lt 40 ]; do
+	$TMUX set-buffer -b "$(printf 'buf%02d' "$n")" "buffer $n" || exit 1
+	n=$((n + 1))
+done
+
+# Without a preview the list has the whole pane (23 lines with the status
+# line), so buf00 to buf22 are visible.
+$TMUX choose-buffer -t aaa:0 -N -O name -F 'S1' || exit 1
+wait_for 'buf00: S1'
+
+# --- scrolling down moves the view -------------------------------------------
+#
+# Selecting buf30 scrolls so it is on the bottom row: buf08 is at the top.
+$TMUX send-keys -t aaa:0 -N 30 Down || exit 1
+wait_for 'buf30: S1'
+top=$(first_line)
+[ "$top" = "buf08" ] || fail "top line after scrolling is $top, not buf08"
+
+# Moving up to buf20 stays inside the visible lines so the view does not move.
+$TMUX send-keys -t aaa:0 -N 10 Up || exit 1
+
+# --- a rebuild keeps the view where it is ------------------------------------
+#
+# Add a buffer that sorts into the visible part of the list and redraw the
+# status line so the list is rebuilt. Once buf15a appears the rebuild has
+# happened; buf08 must still be the top line. It used to jump back to buf00.
+$TMUX set-buffer -b buf15a "new buffer" || exit 1
+$TMUX refresh-client -S || exit 1
+wait_for 'buf15a: S1'
+top=$(first_line)
+[ "$top" = "buf08" ] || fail "top line after rebuild is $top, not buf08"
+
+# --- a shrinking list does not leave empty lines -----------------------------
+#
+# Go to the end of the list (buf39 is on the bottom row) and delete all but
+# the last ten buffers. They now all fit, so the view goes to the top.
+$TMUX send-keys -t aaa:0 End || exit 1
+wait_for 'buf39: S1'
+for b in $($TMUX list-buffers -F '#{buffer_name}'); do
+	case "$b" in
+	buf3?)
+		;;
+	*)
+		$TMUX delete-buffer -b "$b" || exit 1
+		;;
+	esac
+done
+$TMUX refresh-client -S || exit 1
+wait_gone 'buf29: S1'
+top=$(first_line)
+[ "$top" = "buf30" ] || fail "top line after shrinking is $top, not buf30"
+[ "$(printf '%s\n' "$CAPTURED" | grep -F -c ': S1')" -eq 10 ] || \
+	fail "expected 10 buffers after shrinking"
+
+$TMUX send-keys -t aaa:0 q
+
+exit 0