Why does tokio::task::Builder::spawn return a Result?

[hirschenberger]

tokio::spawn does not and it seems the Err variant is not returned anywhere:

https://github.com/tokio-rs/tokio/blob/master/tokio/src/task/builder.rs#L93

[hawkw]

I believe this is partially for consistency with the standard library's std::thread::spawn (which is infallible), and std::thread::Builder::spawn (which similarly returns a result if a thread could not be created). I think at one point in time, this function would return an error if there were no workers in the pool and a worker thread could not be started, but that code path was eventually made infallible.