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