error[E0308]: mismatched types --> src/format.rs:51:6 | 51 | ) -> Option<String> { | -------------- expected `std::option::Option<std::string::String>` because of return type 52 | / for ann in annotations { 53 | | match (ann.range.0, ann.range.1) { ... | 71 | | } 72 | | } | |_____^ expected enum `std::option::Option`, found () |