1 error[E0720]: cannot resolve opaque type
2 --> $DIR/recursive-generator.rs:5:13
4 LL | fn foo() -> impl Generator<Yield = (), Return = ()> {
5 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ recursive opaque type
9 LL | | let mut gen = Box::pin(foo());
10 | | ------- generator captures itself here
15 | |_____- returning here with type `[generator@$DIR/recursive-generator.rs:9:5: 9:7]`
17 error: aborting due to previous error
19 For more information about this error, try `rustc --explain E0720`.