fix: prevent underflow in array_pop when called on an empty array

src/dynamic_array.h

@@ -63,6 +63,9 @@ typedef struct {
 #define array_pop(arr)                                  \
     do {                                                \
         ArrayHeader *header = array_get_header(arr);    \
+        if (header->size == 0) {                        \
+            break;                                      \
+        }                                               \
         header->size--;                                 \
     } while (0)
 

src/test_dynamic_array.c

@@ -81,6 +81,24 @@ void test_array_pop_decrements_size(void) {
 }
 
 
+void test_array_pop_on_empty_is_noop(void) {
+    int *arr = NULL;
+    array_create(arr);
+
+    array_push_value(arr, 99);
+    TEST_ASSERT_EQUAL(1, array_get_header(arr)->size);
+    TEST_ASSERT_EQUAL(99, arr[0]);
+
+    array_pop(arr);
+    TEST_ASSERT_EQUAL(0, array_get_header(arr)->size);
+
+    array_pop(arr); // should not underflow
+    TEST_ASSERT_EQUAL(0, array_get_header(arr)->size);
+
+    array_destroy(arr);
+}
+
+
 void test_array_get_capacity_default(void) {
     int *arr = NULL;
     array_create(arr);
@@ -152,6 +170,7 @@ int main(void)
     RUN_TEST(test_array_push_value);
     RUN_TEST(test_array_push_multiple_values);
     RUN_TEST(test_array_pop_decrements_size);
+    RUN_TEST(test_array_pop_on_empty_is_noop);
     RUN_TEST(test_array_get_capacity_default);
     RUN_TEST(test_array_size_capacity_relationship);
     RUN_TEST(test_array_push_beyond_capacity);