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#![feature(type_alias_impl_trait)]
use std::fmt::Debug;
type Foo = impl Debug;
fn is_send<T: Send>() {}
fn not_good() {
// Error: this function does not constrain `Foo` to any particular
// hidden type, so it cannot rely on `Send` being true.
is_send::<Foo>();
//~^ ERROR: cannot check whether the hidden type of `reveal_local[9507]::Foo::{opaque#0}` satisfies auto traits
}
fn not_gooder() -> Foo {
// Constrain `Foo = u32`
let x: Foo = 22_u32;
// while we could know this from the hidden type, it would
// need extra roundabout logic to support it.
is_send::<Foo>();
//~^ ERROR: cannot check whether the hidden type of `reveal_local[9507]::Foo::{opaque#0}` satisfies auto traits
x
}
fn main() {}
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