empty arg lists get ignored when considering whether to apply default args

[lcnr]

struct Foo<T = u32, U = i32>(T, U);

impl<T, U> Foo<T, U> {
    fn foo() -> Self {
        loop {}
    }
}

fn main() {
    let a = Foo::<u32, i32>::foo();
    let b = Foo::<u32>::foo(); // ok
    let c = Foo::<>::foo(); // ambiguity error
    let d = Foo::foo(); // ambiguity error
}

The same way Foo::<u32> instantiates U with i32, so should Foo::<> for T and U.

My expected behavior is that d is ambiguous while c compiles