refactor(dns): unify symbol naming

[whtsht]

Description

Renamed the following

• dns::GenDnsConfig -> dns::Config
• dns::DnsConfig -> dns::async_std::Config
• dns::TokioDnsConfig -> dns::tokio::Config

If async-std feature is enable, use dns::async_std::Config. When using tokio, import dns::tokio::Config . There is no need to use dns::Config directly.

Resolves #4486.
Related: #2217.

Links to any relevant issues

Tracking issue for renaming symbols across the repository #2217

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[thomaseizinger]

Thanks! To make this an easier transition for our users, we usually keep the old symbols but deprecate them and mention in the deprecation message, what they have been renamed to.

You can do that by creating a type-alias with the old name in place of the old symbol!

That would also make this a non-breaking change which means we can release it immediately and don't have to wait for the next breaking release.

Can you add those types please? :)

See https://github.com/libp2p/rust-libp2p/pull/3852/files#diff-8afb61a90391b0558bf7653cf3ddaba5dec55a51ddac2eeb1d499d9af84b6b7d for an example!

[thomaseizinger]

That would also make this a non-breaking change

A good way to test this is to temporarily undo all changes in other crates in the workspace. They should still compile after that! :)

[whtsht]

I made the following changes based on the reviews.

• Rename DnsErr to Error
• Add type alias such as type TokioDnsConfig<T> = Config<T> to make the change non-breaking.

I also temporarily reverted all changes to other crates in the workspace and checked to see if the test passed.

[thomaseizinger]

Thank you! I've left a few more comments :)

[whtsht]

The version in this branch has been changed to 0.40.1. Also, the since attribute in the deprecated macro has been deleted. I postponed the documentation update.

[thomaseizinger]

Thanks for making the changes!

I am happy to delay the documentation update but it just occurred to me that we should actually name the main struct here Transport to be consistent with others.

libp2p-tcp for example has a Transport AND a Config so naming this one here Config would be a bit confusing. Sorry for not noticing this earlier.

[thomaseizinger]

Great work! This is ready modulo a few errors in the documentation :)

[thomaseizinger]

modulo a few errors in the documentation

See CI failures.

[thomaseizinger]

Thanks for this work! :)