#[must_use] has a hole in its coverage. Suppose we have some code like this:

let transaction = Transaction::new(&kitchen)
    .catch_frogs(3)
    .set_gas_flow(2.5);
if transaction.is_boiling() {
    println!("How I love a nice bowl of frog soup!");
}

At this point, #[must_use] is satisfied merely because transaction has been inspected (via &self), but the call to transaction.commit() has been forgotten and there may be an error to rollback. What we want is for there to be a warning if the type has not been properly disposed of.

A type can be disposed of by destructuring, or by passing it off to another function.

Some consequences:

1. mem::drop counts as disposal. It won't be infallible for the same reasons that Drop isn't infallible.
2. Traits like trait Foo { fn foo(self) {} } would expose a hole. And it could be a blanket implementation.
3. A method can ignore self by using let Self { .. } = self.

Result could be marked #[must_use(dispose)]. But I don't think it should be.

Alternatives

• Do nothing, and change fn inspect(&self) -> bool to fn inspect(self) -> (Self, bool).
• Do nothing.
• Implement with clippy instead.
• A different syntax, like #[must_dispose].
• Make #[must_use] function like the proposed #[must_use(dispose)].