1.rs

fn bar(foo: &Foo) {}

fn baz(foo: &Foo) {
    // this call works
    bar(foo);
}

trait Foo {
    fn qux(&self) {
        // this doesn't, and error is
        // error: the trait `core::kinds::Sized` is not implemented for the type `Self`
        bar(self);
    }
}