`tokio-runtime` feature flags.

[realharley91]

To my eyes it seems having "full" features for tokio is unnecessary for the driver. Main reasons being:

• It slows down compile times for dependent applications.
• It slows down compile times for the driver itself.

If the crate does indeed use all the tokio features then I understand. I was willing to dwell on this journey myself but wanted to ask beforehand so as to not throw my efforts into the void.

I do not know the extent of this request. Can someone help to enlighten me?

[isabelatkinson]

Hey @mby, off the top of my head I am not sure whether all feature flags are necessary to compile the driver. It should be fairly simple to determine this by listing them all out manually in our Cargo.toml rather than using full, deleting them one by one, and checking whether the driver will still compile with all of our own feature flags enabled. This is not a priority for the team right now, but I filed RUST-1771 for future prioritization. If you'd like to take this on feel free to make a pull request or post the result of your investigation here or on the Jira ticket!