Error code E0734
A stability attribute has been used outside of the standard library.
Erroneous code example:
#![allow(unused)] fn main() { #[stable(feature = "a", since = "b")] // invalid #[unstable(feature = "b", issue = "none")] // invalid fn foo(){} }
These attributes are meant to only be used by the standard library and are rejected in your own crates.