Add standard Rust attributes.

[yskopets]

Summary

• add #[non_exhaustive] attribute to enums to reserve an option to add more values in a backwards-compatible way
• add #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]

[PiotrSikora]

While technically correct, I'm wondering why do you need #[non_exhaustive]?

Also, once we move to the new ABI, those values will be broken in non-backwards-compatible way, so I'm not sure if adding those guarantees and attributes now is such a good idea.

[yskopets]

It's about reserving a room for changes that otherwise would be backwards incompatible.

The problem comes form match statements.

Without #[non_exhaustive], if a user creates a match statement with all values of Status, then adding a new Status value will be a breaking change.

You will have to do a major release of the library to stick to semantic versioning.

[lizan]

@yskopets I don't think we need non-exaustive for all enums, for some of them it doesn't make sense. If ABI changes, those match statements need to be rewritten or it will break at runtime.

[PiotrSikora]

Regarding #[non_exhaustive], I think that we could add it for now (but we should remove it once the ABI is frozen), though it doesn't really makes sense to do an exhaustive match on any of the enums defined here (other than the LogLevel).

Regarding the other traits, Copy and Clone are fine, but I'm a bit confused as to why do we need PartialEq, Eq and Hash. Could you elaborate on each one?

[yskopets]

to why do we need PartialEq, Eq and Hash

Overall, implementing these traits is advised by the Rust API Guidelines (interoperability).

Practically, Eq and PartialEq come in pair and necessary for assertions like

#[test]
fn test_log_level_eq() {
    assert_ne!(LogLevel::Critical, LogLevel::Debug);
}

All 3 Eq, PartialEq, Hash are mostly necessary in the context of user-defined composite types, which are common in unit testing.

[PiotrSikora]

Thanks!

FWIW, I still think that #[non_exhaustive] shouldn't be necessary long-term, but the gRPC PRs (#100, #101) added new values, so I'm going to merge this to avoid breaking existing plugins.