Add prelude for blanket and extension traits across sub-crates

[Danil-Grigorev]

Motivation

Slight follow up on proposed changes in #1511 (comment)

Solution

Include prelude into kube crate, exporting all blanket implementations, such as:

• client::ConfigExt - client configuration options.
• client::scope::NamespacedRef - namespace scoped resource fetching via client.fetch (under unstable-client feature).
• core::PartialObjectMetaExt - useful for cache size reduction in cases when only watched object type and metadata are required.
• core::crd::CustomResourceExt - providing methods such as .crd() for custom resource generation.
• core::crd::{Resource, ResourceExt} - base and extension functionality on top of any valid kubernetes resource.
• runtime::utils::WatchStreamExt - utility methods for watcher streams, providing predicate capabilities, stream sharing with reflect and reflect_shared (under runtime feature)

[clux]

Thanks for starting this, I was about to write an issue for this!

Couple of things of-the-top of my head that could be useful:

• https://docs.rs/kube/latest/kube/trait.ResourceExt.html
• https://docs.rs/kube/latest/kube/trait.Resource.html
• https://docs.rs/kube/latest/kube/trait.CustomResourceExt.html with derive feature
• https://docs.rs/kube/latest/kube/runtime/trait.WatchStreamExt.htmlwith runtime feature

[clux]

I see people are importing traits in prelude using pub use ExplicitScope as _; to presumably avoid warnings
https://github.com/tokio-rs/tracing/blob/master/tracing-subscriber/src/prelude.rs

ideally people should not need to opt-in to unused_imports

[SOF3]

Are you sure adding feature gates in a prelude is a good idea? People doing a wildcard import on prelude crate may get their symbols conditionally shadowed if another crate enabled this feature.

[clux]

I think the shadowing is a bigger problem than the feature gates, and the shadowing can be avoided by use X as _;. It limits the prelude to extension trait stuff, but maybe that is a better way forward?

[Danil-Grigorev]

So as an update - I added all blanket implemented traits and extension traits to the prelude, while keeping those under feature gates separately - as prelude_unstable. I'm not sure that 2 preludes are needed, but went with separate so far. Also removed all struct, to avoid opt-in for unused imports. It would be perfect to have an option to say - prelude can be used but not re-exported (as in lib.rs), but I don't know if it is possible 🙂

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.2%. Comparing base (7a10e24) to head (a2527ef).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1527   +/-   ##
=====================================
  Coverage   75.2%   75.2%           
=====================================
  Files         78      78           
  Lines       6989    6989           
=====================================
  Hits        5249    5249           
  Misses      1740    1740           

Files	Coverage Δ
kube-client/src/client/client_ext.rs	84.5% <ø> (ø)
kube-runtime/src/utils/watch_ext.rs	22.3% <ø> (ø)
kube/src/lib.rs	88.5% <ø> (ø)

[clux]

Some concerns.

[Danil-Grigorev]

@clux Should be fixed now, I removed everything causing a concern, leaving only subset of trait extensions. Also moved it to kube crate.

[clux]

I think this looks more appropriate. Two lines that can be avoided, but the exports there now are mostly sensible to me.

[Danil-Grigorev]

Added some better description, JIC someone returns to this. Thanks for the review @clux