It's better to have a code action that toggles a function or trait method between async fn method() -> Ret and fn method() -> impl Future<Output = Ret>. Conversion from async fn to impl Future should be lossless, but, of course, the opposite is not.

It's convenient in cases like:

• like to convert an existing -> impl Future function to async fn especially it was generated (e.g. When generating implementation for a trait, emit async fn for functions that return impl Future (+ Send) #16195)
• like to add Send bound to an existing async fn to assert the implementation is Send.