tests/ui/impl-trait/unsized_coercion.rs

//! This test checks that opaque types get unsized instead of
//! constraining their hidden type to a trait object.

//@ revisions: next old
//@[next] compile-flags: -Znext-solver
//@[old] check-pass

trait Trait {}

impl Trait for u32 {}

fn hello() -> Box<impl Trait> {
    if true {
        let x = hello();
        //[next]~^ ERROR: the size for values of type `dyn Trait` cannot be known at compilation time
        let y: Box<dyn Trait> = x;
    }
    Box::new(1u32)
}

fn main() {}