`clippy::arc_with_non_send_sync`

Use Rc for single-threaded sharing, or make the inner value Send and Sync before sharing it across threads.

What it reads

Clippy, with the compiler behind it. The only pass that compiles.

Serious: worth interrupting other work for.

The tier bounds how severe a rule may be; its category bounds the tier.

Turn it off, or make it blocking, without touching the code it flags:

rust-doctor --rule clippy::arc_with_non_send_sync=off .
rust-doctor --rule clippy::arc_with_non_send_sync=error .