wip(stackable-versioned): impl ApplyResource for CustomResourceDefinition

NOTE: Just added comments to describe the next steps.
NOTE: We will need to move to async, since the kube api and discovery is async.

Author: NickLarsenNZ

crates/stackable-versioned/src/flux_converter/apply_crd.rs

@@ -0,0 +1,33 @@
+use std::convert::Infallible;
+
+use k8s_openapi::apiextensions_apiserver::pkg::apis::apiextensions::v1::CustomResourceDefinition;
+
+use crate::apply_resource::ApplyResource;
+
+impl ApplyResource for CustomResourceDefinition {
+    type Error = Infallible;
+
+    fn apply(&self, _kube_client: kube::Client) -> Result<(), Self::Error> {
+        // 1. Using the kube::Client, check if the CRD already exists.
+        //    If it does not exist, then simple apply.
+        //
+        // 2. If the CRD already exists, then get it, and check...
+        //    - spec.conversion (this is likely to change, which is fine)
+        //    - spec.group (this should probably never change)
+        //    - spec.names (it is ok to add names, probably not great to remove them)
+        //    - spec.preserve_unknown_fields (is this ok to change?)
+        //    - spec.scope (this should probably never change)
+        //
+        // 3. For spec.versions, where "A" is the sert of versions applied to the server,
+        //    and "B" is the set of versions to be applied...
+        //    - A - B: These versions are candidates for removal
+        //    - B - A: These versions can be safely appended
+        //    - A ∩ B: These versions are likely to change in the following ways:
+        //      - New fields added (safe for vXalphaY, vXbetaY, and vX)
+        //      - Fields changed (can happen in vXalphaY, vXbetaY, but shouldn't in vX)
+        //      - Fields removed (can happen in vXalphaY, vXbetaY, but shouldn't in vX)
+        //
+        // Complete the rest of the owl...
+        Ok(())
+    }
+}

crates/stackable-versioned/src/flux_converter/mod.rs

@@ -9,6 +9,8 @@ use snafu::Snafu;
 
 use crate::ParseResourceVersionError;
 
+mod apply_crd;
+
 #[cfg(test)]
 mod tests;