I'm not understanding what the supposed problem with these futures getting cancelled is. Since futures are not tasks, as the post itself acknowledges, does it not logically follow that one should not expect futures to complete if the future is not driven to completion, for one reason or another? What else could even be expected to happen?

The examples presented for "cancel unsafe" futures seem to me like the root of the problem is some sort of misalignment of expectations to the reality:

Example 1: one future cancelled on error in the other

let res = tokio::try_join!( do_stuff_async(), more_async_work(), );

Example 2: data not written out on cancellation

let buffer: &[u8] = /* ... */; writer.write_all(buffer)?;

Both of these cases are claimed to not be cancel-safe, because the work gets interrupted and so not driven to completion. But again, what else is supposed to happen? If you want the work to finish regardless of the async context being cancelled, then don't put it in the same async context but spawn a task instead.

I feel like I must be missing something obvious that keeps me from understanding the author's issue here. I thought work getting dropped on cancellation is exactly how futures are supposed to work. What's the nuance that I'm missing?