Error code E0714

A #[marker] trait contained an associated item.

Erroneous code example:

#![feature(marker_trait_attr)] #![feature(associated_type_defaults)] #[marker] trait MarkerConst { const N: usize; // error! } fn main() {}

The items of marker traits cannot be overridden, so there's no need to have them when they cannot be changed per-type anyway. If you wanted them for ergonomic reasons, consider making an extension trait instead.