`#[must_use]` for benchmarking components

[ggwpez]

Some faulty benchmarks ignore their complexity components as described in #400
To avoid this in the future, we can introduce a #[must_use] for complexity params.
This can obviously only be used in cases where the implementation would be faulty, if they are ignored.

Eg. the following benchmark result must depend on n, otherwise it is faulty:

#[must_use]
let n in 0..100;

for _ in 0..n {
    sleep(1 * SEC);
}

A error could be emitted when a weight is derived that does not depend on a #[must_use] component.

[ECJ222]

Hi @ggwpez can I attempt this issue?

[shawntabrizi]

I think we shouldn't tackle this until we transition the entire benchmarking macro into an attribute macro:

paritytech/substrate#10848

Are you good with macros @ECJ222? Do you think you can take this on?

[ECJ222]

Hi @shawntabrizi

I have not done much on macros yet, But I will attempt the issue it would be good for experience.

Do you want me to make the migrations in all the benchmark files or do you have any in mind I should start with?

[shawntabrizi]

This is going to be quite a large issue unless you are familiar with macro development. But yeah, I would start buy building something that works with pallet balances benchmarks as a start.

[ECJ222]

Okay @shawntabrizi, I will jump on it.

[shawntabrizi]

@ggwpez do you think this is still needed given the improvements to the benchmarking pipeline accuracy?

[ggwpez]

do you think this is still needed given the improvements to the benchmarking pipeline accuracy?

This is more of a Dev-UX thing; but I'm not sure anymore how much sense it makes.
Annotating all benchmark components with #[must_use] or #[maybe_unused] is also annoying.
Just printing a warning when a component is not used would also work.

[shawntabrizi]

ill leave it open. doesn't sound like something that would be bad to have

[ECJ222]

do you think this is still needed given the improvements to the benchmarking pipeline accuracy?

This is more of a Dev-UX thing; but I'm not sure anymore how much sense it makes. Annotating all benchmark components with #[must_use] or #[maybe_unused] is also annoying. Just printing a warning when a component is not used would also work.

Is this still needed @ggwpez?