Merge pull request #62234 from liggitt/apigroup-partial-discovery

Automatic merge from submit-queue (batch tested with PRs 61306, 60270, 62496, 62181, 62234). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Handle partial group and resource responses consistently

GetAPIGroupResources tolerates partial discovery responses to provide as much information to the caller as possible.

Before skipping a particular error response, check whether the response was accompanied by partial group or resource data.

There's an existing TODO to propagate partial errors that I plan to address in a follow-up, but that had more ripples and I wanted to correct this first.

```release-note
NONE
```

staging/src/k8s.io/client-go/discovery/restmapper.go

@@ -144,7 +144,10 @@ func NewRESTMapper(groupResources []*APIGroupResources, versionInterfaces meta.V
 func GetAPIGroupResources(cl DiscoveryInterface) ([]*APIGroupResources, error) {
 	apiGroups, err := cl.ServerGroups()
 	if err != nil {
-		return nil, err
+		if apiGroups == nil || len(apiGroups.Groups) == 0 {
+			return nil, err
+		}
+		// TODO track the errors and update callers to handle partial errors.
 	}
 	var result []*APIGroupResources
 	for _, group := range apiGroups.Groups {
@@ -157,7 +160,9 @@ func GetAPIGroupResources(cl DiscoveryInterface) ([]*APIGroupResources, error) {
 			if err != nil {
 				// continue as best we can
 				// TODO track the errors and update callers to handle partial errors.
-				continue
+				if resources == nil || len(resources.APIResources) == 0 {
+					continue
+				}
 			}
 			groupResources.VersionedResources[version.Version] = resources.APIResources
 		}