Add an API testcase for prototype loop and GC

api-testcases/test-dev-prototype-loop.c

@@ -0,0 +1,44 @@
+/*
+ *  Prototype loop is tricky to handle internally and must not cause e.g.
+ *  GC failures.  Exercise a few common paths.
+ */
+
+/*===
+*** test_1 (duk_safe_call)
+first gc
+make unreachable
+second gc
+==> rc=0, result='undefined'
+===*/
+
+static duk_ret_t test_1(duk_context *ctx) {
+	duk_push_object(ctx);
+	duk_push_object(ctx);
+	duk_dup(ctx, 0);
+	duk_set_prototype(ctx, 1);
+	duk_dup(ctx, 1);
+	duk_set_prototype(ctx, 0);
+
+	/* Both objects are now in a prototype loop.  Force garbage
+	 * collection to ensure nothing breaks.
+	 */
+
+	printf("first gc\n"); fflush(stdout);
+	duk_gc(ctx, 0);
+
+	/* Make the objects unreachable and re-run GC.  This triggers
+	 * e.g. finalizer checks.
+	 */
+
+	printf("make unreachable\n"); fflush(stdout);
+	duk_set_top(ctx, 0);
+
+	printf("second gc\n"); fflush(stdout);
+	duk_gc(ctx, 0);
+
+	return 0;
+}
+
+void test(duk_context *ctx) {
+	TEST_SAFE_CALL(test_1);
+}