pub static OPAQUE_HIDDEN_INFERRED_BOUND: &Lint
Expand description
The opaque_hidden_inferred_bound
lint detects cases in which nested
impl Trait
in associated type bounds are not written generally enough
to satisfy the bounds of the associated type.
Explanation
This functionality was removed in #97346, but then rolled back in #99860 because it caused regressions.
We plan on reintroducing this as a hard error, but in the mean time, this lint serves to warn and suggest fixes for any use-cases which rely on this behavior.
Example
#![feature(type_alias_impl_trait)]
trait Duh {}
impl Duh for i32 {}
trait Trait {
type Assoc: Duh;
}
impl<F: Duh> Trait for F {
type Assoc = F;
}
type Tait = impl Sized;
fn test() -> impl Trait<Assoc = Tait> {
42
}
{{produces}}
In this example, test
declares that the associated type Assoc
for
impl Trait
is impl Sized
, which does not satisfy the bound Duh
on the associated type.
Although the hidden type, i32
does satisfy this bound, we do not
consider the return type to be well-formed with this lint. It can be
fixed by changing Tait = impl Sized
into Tait = impl Sized + Duh
.