Should not call `to_str` in `mrb_vformat`; fix
MODIFY
src/error.c
src/error.c
@@ -269,9 +269,12 @@ mrb_vformat(mrb_state *mrb, const char *format, va_list ap)
if (c == '%') {
if (*p == 'S') {
+ mrb_value val;
+
size = p - b - 1;
mrb_ary_push(mrb, ary, mrb_str_new(mrb, b, size));
- mrb_ary_push(mrb, ary, va_arg(ap, mrb_value));
+ val = va_arg(ap, mrb_value);
+ mrb_ary_push(mrb, ary, mrb_obj_as_string(mrb, val));
b = p + 1;
}
}

Should not call `to_str` in `mrb_vformat`; fix #3773