rust/tests/ui/const-generics/defaults/doesnt_infer.rs

// test that defaulted const params are not used to help type inference

struct Foo<const N: u32 = 2>;

impl<const N: u32> Foo<N> {
    fn foo() -> Self { loop {} }
}

fn main() {
    let foo = Foo::<1>::foo();
    let foo = Foo::foo();
    //~^ error: type annotations needed for `Foo<N>`
}