error[E0275]: overflow evaluating the requirement `Option<_>: Sized` --> $DIR/mutual-recursion-issue-75860.rs:11:5 | LL | iso(left, right) | ^^^ | = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`mutual_recursion_issue_75860`) note: required by a bound in `Option` --> $SRC_DIR/core/src/option.rs:LL:COL error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0275`.