Static rustc_lint_defs::builtin::DEREF_INTO_DYN_SUPERTRAIT

pub static DEREF_INTO_DYN_SUPERTRAIT: &'static Lint

The deref_into_dyn_supertrait lint is output whenever there is a use of the Deref implementation with a dyn SuperTrait type as Output.

These implementations will become shadowed when the trait_upcasting feature is stabilized. The deref functions will no longer be called implicitly, so there might be behavior change.

Example

#![deny(deref_into_dyn_supertrait)]
#![allow(dead_code)]

use core::ops::Deref;

trait A {}
trait B: A {}
impl<'a> Deref for dyn 'a + B {
    type Target = dyn A;
    fn deref(&self) -> &Self::Target {
        todo!()
    }
}

fn take_a(_: &dyn A) { }

fn take_b(b: &dyn B) {
    take_a(b);
}

{{produces}}

Explanation

The dyn upcasting coercion feature adds new coercion rules, taking priority over certain other coercion rules, which will cause some behavior change.