The `rustc_data_structures::sync::OnceCell` is thread-safe when building a parallel compiler. This is unnecessary for the purposes of pattern usefulness checking. Use `!Sync` `std::lazy::OnceCell` instead.
The `rustc_data_structures::sync::OnceCell` is thread-safe when building a parallel compiler. This is unnecessary for the purposes of pattern usefulness checking. Use `!Sync` `std::lazy::OnceCell` instead.