In Rust, you don't need to do this. If you want a blocking version of a non-blocking function, you spin on poll. Several async libraries ship a block_on function that does just that. If you can't do that, but don't want to bring in a proper big-boy executor; you can spin off another thread, have it block, and join it when it's done. (or use something like crossbeam's scoped threads)
Colored functions are a problem in JavaScript because it has to share an event loop with the rest of the browser. For Node.js and Python, that is less of an issue, but those languages are also either practically or actually single-threaded, which also means async behavior is contagious. Rust does not have this problem, at least not until you're writing WASM programs with it (in which case, you're restricted to sharing one thread with the rest of the browser again).
Colored functions are a problem in JavaScript because it has to share an event loop with the rest of the browser. For Node.js and Python, that is less of an issue, but those languages are also either practically or actually single-threaded, which also means async behavior is contagious. Rust does not have this problem, at least not until you're writing WASM programs with it (in which case, you're restricted to sharing one thread with the rest of the browser again).