add cyclic test

Author: BennoLossin

library/std/tests/field-projections-cyclic.rs

@@ -0,0 +1,16 @@
+#![allow(incomplete_features)]
+#![feature(field_projections)]
+
+use std::field::{Field, field_of};
+use std::marker::PhantomData;
+
+struct Work<F: Field> {
+    _phantom: PhantomData<F>,
+}
+
+struct MyMultiWork {
+    a: Work<field_of!(Self, a)>,
+    b: Work<field_of!(Self, b)>,
+}
+
+fn main() {}