From 9f54c3552b43f496049963ffd755844d37b39f9c Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Thu, 24 Oct 2024 20:58:08 +0100
Subject: [PATCH] Handle NULL result from read_expression() in REPL

---
 lib/repl.c         |  7 +++++++
 tests/repl_tests.c | 22 ++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/lib/repl.c b/lib/repl.c
index ee21226..18dad2f 100644
--- a/lib/repl.c
+++ b/lib/repl.c
@@ -1,6 +1,7 @@
 #include "repl.h"
 
 #include <stdio.h>
+#include <string.h>
 
 void init_repl(repl_t *repl)
 {
@@ -19,6 +20,12 @@ bool step_repl(repl_t *repl)
 		repl->line_buffer[len] = (char)byte;
 	}
 	const expression_t *e = repl->read(&repl->pool, repl->line_buffer, len);
+	if (NULL == e) {
+		const char *msg = "Invalid expression\n";
+		repl->print(msg, strlen(msg));
+		return true;
+	}
+
 	const int result = repl->evaluate(e);
 	const int result_len = snprintf(
 	    repl->result_buffer, REPL_RESULT_BUFFER_SIZE, "%d\n", result);
diff --git a/tests/repl_tests.c b/tests/repl_tests.c
index 73cdec0..1306ba2 100644
--- a/tests/repl_tests.c
+++ b/tests/repl_tests.c
@@ -20,6 +20,13 @@ static bool print_called;
 static const char *print_output;
 static int print_len;
 
+static void reset_fixtures(void)
+{
+	read_called = false;
+	evaluate_called = false;
+	print_called = false;
+}
+
 static int test_get_byte(void)
 {
 	if (0 == input_len)
@@ -72,6 +79,7 @@ static void set_up_valid_state(void)
 
 static void read_is_called_on_first_line_line_in_input(void)
 {
+	reset_fixtures();
 	set_up_valid_state();
 	step_repl(&repl);
 	ASSERT_TRUE(read_called);
@@ -81,6 +89,7 @@ static void read_is_called_on_first_line_line_in_input(void)
 
 static void read_result_is_passed_to_evaluate(void)
 {
+	reset_fixtures();
 	set_up_valid_state();
 	step_repl(&repl);
 	ASSERT_TRUE(evaluate_called);
@@ -90,6 +99,7 @@ static void read_result_is_passed_to_evaluate(void)
 
 static void result_of_evaluation_is_printed_with_a_newline(void)
 {
+	reset_fixtures();
 	set_up_valid_state();
 	step_repl(&repl);
 	ASSERT_TRUE(print_called);
@@ -99,6 +109,7 @@ static void result_of_evaluation_is_printed_with_a_newline(void)
 
 static void true_is_returned_on_successful_step(void)
 {
+	reset_fixtures();
 	set_up_valid_state();
 	const bool result = step_repl(&repl);
 	ASSERT_TRUE(result);
@@ -106,12 +117,22 @@ static void true_is_returned_on_successful_step(void)
 
 static void false_is_returned_on_end_of_input(void)
 {
+	reset_fixtures();
 	set_up_valid_state();
 	input_len = 0;
 	const bool result = step_repl(&repl);
 	ASSERT_FALSE(result);
 }
 
+static void evaluate_is_not_called_if_read_returns_null(void)
+{
+	reset_fixtures();
+	set_up_valid_state();
+	read_result = NULL;
+	step_repl(&repl);
+	ASSERT_FALSE(evaluate_called);
+}
+
 int main(void)
 {
 	TESTING_BEGIN();
@@ -120,5 +141,6 @@ int main(void)
 	RUN_TEST(result_of_evaluation_is_printed_with_a_newline);
 	RUN_TEST(true_is_returned_on_successful_step);
 	RUN_TEST(false_is_returned_on_end_of_input);
+	RUN_TEST(evaluate_is_not_called_if_read_returns_null);
 	TESTING_END();
 }