rust/src/test/ui/infinite/infinite-instantiation.rs

//
// We get an error message at the top of file (dummy span).
// This is not helpful, but also kind of annoying to prevent,
// so for now just live with it.
// This test case was originally for issue #2258.

trait ToOpt: Sized {
    fn to_option(&self) -> Option<Self>;
}

impl ToOpt for usize {
    fn to_option(&self) -> Option<usize> {
        Some(*self)
    }
}

impl<T:Clone> ToOpt for Option<T> {
    fn to_option(&self) -> Option<Option<T>> {
        Some((*self).clone())
    }
}

fn function<T:ToOpt + Clone>(counter: usize, t: T) {
//~^ ERROR reached the recursion limit while instantiating `function::<std::option::Option<
    if counter > 0 {
        function(counter - 1, t.to_option());
        // FIXME(#4287) Error message should be here. It should be
        // a type error to instantiate `test` at a type other than T.
    }
}

fn main() {
    function(22, 22);
}