src/test/ui/feature-gates/feature-gate-type_alias_impl_trait.rs

use std::fmt::Debug;

type Foo = impl Debug; //~ ERROR `impl Trait` in type aliases is unstable

trait Bar {
    type Baa: Debug;
    fn define() -> Self::Baa;
}

impl Bar for () {
    type Baa = impl Debug; //~ ERROR `impl Trait` in type aliases is unstable
    fn define() -> Self::Baa {
        0
    }
}

fn define() -> Foo {
    0
}

trait TraitWithDefault {
    type Assoc = impl Debug;
    //~^ ERROR associated type defaults are unstable
    //~| ERROR `impl Trait` not allowed outside of function
    //~| ERROR `impl Trait` in type aliases is unstable
}

type NestedFree = (Vec<impl Debug>, impl Debug, impl Iterator<Item = impl Debug>);
//~^ ERROR `impl Trait` in type aliases is unstable
//~| ERROR `impl Trait` in type aliases is unstable
//~| ERROR `impl Trait` in type aliases is unstable
//~| ERROR `impl Trait` in type aliases is unstable

fn define_multiple() -> NestedFree {
    (vec![true], 0u8, 0i32..1)
}

impl Bar for u8 {
    type Baa = (Vec<impl Debug>, impl Debug, impl Iterator<Item = impl Debug> + Debug);
    //~^ ERROR `impl Trait` in type aliases is unstable
    //~| ERROR `impl Trait` in type aliases is unstable
    //~| ERROR `impl Trait` in type aliases is unstable
    //~| ERROR `impl Trait` in type aliases is unstable
    fn define() -> Self::Baa {
        (vec![true], 0u8, 0i32..1)
    }
}

fn main() {}