I tried this code:

fn check<'a, T: Trait<'a> + ?Sized>() {}
trait Trait<'a>: 'static {}

fn check2<'a>() {
    check::<dyn Trait<'a> + 'static>();
}

I expected to see this happen: It compiles

dyn Trait<'a> should have an lifetime independent from 'a. i.e. dyn Trait<'a> + 'b should have lifetime 'b. in this particular case, 'b is 'static.

Instead, this happened:

error: lifetime may not live long enough
 --> src/lib.rs:5:5
  |
4 | fn check2<'a>() {
  |           -- lifetime `'a` defined here
5 |     check::<dyn Trait<'a> + 'static>();
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'a` must outlive `'static`

Related

#88904. Since this is another way of creating dyn Trait: !Trait, except in this case, I think the unsized coercion should be allowed, and dyn Trait does impl Trait.