Add some tests.

regress/cmd-parse-errors.sh

@@ -0,0 +1,51 @@
+#!/bin/sh
+
+# Malformed input rejection and crash/leak canary.
+#
+# Each input below is a syntax error. For every one we require that:
+#   - parsing reports failure (non-zero exit), and
+#   - the server is still alive afterwards (a follow-up command succeeds).
+# The second check is the important one: a parser that crashes or corrupts state
+# on bad input would take the server down here.
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -Ltest -f/dev/null"
+$TMUX kill-server 2>/dev/null
+
+$TMUX -f/dev/null start \; new-session -d 2>/dev/null || exit 1
+
+n=0
+check() {
+	n=$((n + 1))
+	# Expect a parse failure.
+	if $TMUX run-shell -C "$1" >/dev/null 2>&1; then
+		echo "case $n: expected failure but succeeded: $1" >&2
+		exit 1
+	fi
+	# Expect the server to still be responsive.
+	if ! $TMUX list-sessions >/dev/null 2>&1; then
+		echo "case $n: server died after: $1" >&2
+		exit 1
+	fi
+}
+
+check 'if-shell true {'			# unterminated brace body
+check 'display-message a }'		# stray close brace
+check 'if-shell true { display-message a'	# unclosed nested brace
+check 'if-shell true { ; }'		# empty sequence in body
+check '%elif 1'				# %elif with no %if
+check '%endif'				# %endif with no %if
+check '%zzz'				# unknown % directive
+check '; display-message a'		# leading separator
+input='%if 1
+display-message a'
+check "$input"				# unterminated %if
+input='%if 1
+%endif'
+check "$input"				# empty %if body
+
+$TMUX kill-server 2>/dev/null
+exit 0