Forwarding the `rustls` provider settings

[LecrisUT]

It would be good to use a design of the features similar to axum-server, i.e.:

tls-rustls = ["tls-rustls-no-provider", "rustls/aws-lc-rs"]
tls-rustls-no-provider = [...]

This would make it easier to forward these options down the chain of dependencies.

[djc]

It is pretty unclear what you are trying to achieve. What's the use case here?

[LecrisUT]

The issue is with propagationg the choice of rustls/ring vs rustls/aws-lc-rs that needs to be propagated to all dependencies until the leaf package. E.g. in atuin it has dependencies on metrics-exporter-prometheus and axum-server, the former having a dependency on hyper-rustls. axum-server allows to import the tls-rustls-no-provider feature in which case you can manually add rustls/aws-lc-rs or rustls/ring avoiding conflicts of each package having a different default tls provider. In the case of atuin after rustls switched the default provider, their CI is no longer buildable and it blocks the upgrade path because of this.

[djc]

So why can't you depend on hyper-rustls with default-features = false? hyper-rustls unconditionally depends on rustls already, so the setup in axum-server doesn't necessarily translate well to this crate.

[LecrisUT]

Of course that's possible, but then we would have to manage the non-aws-lc-rs feature, i.e. we would have to manually inlcude ["http1", "tls12", "logging"]. The proposal is to move all of the non-provider features into a group so that downstream can more easily compose it.

[djc]

Honestly I don't think this makes much sense. Just repeat the features downstream where it makes sense.

[cpu]

This feels like a place where cargo could be more helpful, allowing expressing something like "defaults minus feature X". In absence of that, and for a crate like hyper-rustls where the default features seldom change, I think I concur with Djc that repeating the features you want from the default set, without the ones you don't, is likely the best solution.

[djc]

This feels like a place where cargo could be more helpful, allowing expressing something like "defaults minus feature X".

That would be:

• Ability to disable individual default features rust-lang/cargo#3126