Type alias impl trait types do not check bounds apply to concrete type

[matthewjasper]

The following code runs and prints random values:

#![feature(type_alias_impl_trait)]

type X<'a> = impl Into<&'static str> + From<&'a str>;

fn f<'a: 'static>(t: &'a str) -> X<'a> {
    t
}

fn extend_lt<'a>(o: &'a str) -> &'static str {
    X::<'_>::from(o).into()
}

fn main() {
    let r =
    {
        let s = "abcdef".to_string();
        extend_lt(&s)
    };
    println!("{}", r);
}

ICE using the same issue

#![feature(type_alias_impl_trait)]

type X<T> = impl Clone;

fn f<T: Clone>(t: T) -> X<T> {
    t
}

fn g<T>(o : Option<X<T>>) -> Option<X<T>> {
    o.clone()
}

fn main() {
    g(None::<X<&mut ()>>);
}

Just a curious bystander: the provided example no longer prints random values (rustc 1.46.0-nightly (2f517ce6f 2020-06-28)). Was this fixed?

[matthewjasper]

The first example is UB so it may be target/optimization level dependent. This will be fixed once the ICE is gone.