#![feature(generic_associated_types)]
#![allow(invalid_type_param_default)]

trait Trait {
    type Assoc<T = u32>;
}

impl Trait for () {
    type Assoc<T = u32> = u64; 
}

impl Trait for u32 {
    type Assoc<T = u32> = T;
}

trait Other {}
impl Other for u32 {}

fn foo<T>()
where
    T: Trait<Assoc = u32>, 
    T::Assoc: Other {
        
    }
    
fn main() {
    // errors
    foo::<()>();
    // works
    foo::<u32>();
}