Suggestion: warn if no await inside async fn or block

[neoeinstein]

In general, if you aren't awaiting anything, then there is no reason to have an async fn or async {…}. Using async where it is not needed can lead to unnecessary overhead. This lint would alert users to cases where they may have started off writing something as async, but then refactored, removing all await points without deleting the async keyword.

[tesuji]

Does rustc lint about this? I think it is better to be linted by rustc.

[neoeinstein]

I was a bit surprised that rustc wasn't complaining about this, but figured I'd post here first. I can make a similar suggestion to the Rust project, and continue this issue only if it is rejected there.

[DevinR528]

Somewhat related, could we also lint if a future is not awaited inside of async context. I kept forgetting to add the .await and since its not an error it silently breaks the program.

[loyd]

#7176

[giraffate]

I'm closing this because the unused_async has been implemented.