lang: fix a bunch of memory leaks

lang/ast/node.c

@@ -252,6 +252,47 @@ void ivy_ast_node_to_string(struct ivy_ast_node *node, struct b_string *out)
 
 void ivy_ast_node_destroy(struct ivy_ast_node *node)
 {
+	struct ivy_ast_node_iterator it = {};
+	b_queue_push_back(&it.it_queue, &node->n_it.it_entry);
+	node->n_it.it_depth = 0;
+
+	b_queue_iterator q_it;
+	b_queue_iterator_begin(&it.it_queue, &q_it);
+
+	while (b_queue_iterator_is_valid(&q_it)) {
+		struct ivy_ast_node_iterator_entry *it_entry = b_unbox(
+			struct ivy_ast_node_iterator_entry, q_it.entry, it_entry);
+		node = b_unbox(struct ivy_ast_node, it_entry, n_it);
+
+		if (!node) {
+			/* this should never happen. */
+			return;
+		}
+
+		const struct ast_node_type *type = get_ast_node_type(node->n_type);
+		if (type->n_collect_children) {
+			it.it_insert_after = q_it.entry;
+			type->n_collect_children(node, &it);
+		}
+
+		b_queue_iterator_next(&q_it);
+	}
+
+	while (!b_queue_empty(&it.it_queue)) {
+		b_queue_entry *entry = b_queue_pop_back(&it.it_queue);
+		if (!entry) {
+			break;
+		}
+
+		node = b_unbox(struct ivy_ast_node, entry, n_it);
+
+		const struct ast_node_type *type = get_ast_node_type(node->n_type);
+		if (type && type->n_destroy) {
+			type->n_destroy(node);
+		}
+
+		free(node);
+	}
 }
 
 #define ENUM_STR(x)                                                            \