[moonchrome]

>Rust has the ability to provide ergonomic fork-join parallelism at the library level

I'm just guessing because I have only vague familiarity with this topic - but implementing that and the rest of OpenMP constructs efficiently does not sound trivial.

pragmas are just a way to consume OpenMP in C++, that part could be done trough library - but leveraging OpenMP implementation, stuff like schedulers, etc. could be useful.