[dodobirdlord]

In principle it could perhaps be enforced by the compiler, but it would be very difficult. Whether something is memory-safe to Sync or Send across threads can depend on things like platform-specific atomic operations, thread-local storage, how panics and stack unwinds proceed, etc. Sounds like a nightmare for the compiler to make guarantees about. Maybe when compiling for a specific version of a specific OS, but to do it at the language level would be an incredible feat, and might make the language unusably complex.