Merge pull request #52545 from liggitt/automated-cherry-pick-of-#5001…

…2-upstream-release-1.7

Automatic merge from submit-queue.

Automated cherry pick of #50012

Cherry pick of #50012 on release-1.7.

#50012: use specified discovery information if possible

```release-note
custom resources that use unconventional pluralization now work properly with kubectl
```

staging/src/k8s.io/apimachinery/pkg/api/meta/restmapper.go

@@ -117,7 +117,10 @@ func NewDefaultRESTMapper(defaultGroupVersions []schema.GroupVersion, f VersionI
 
 func (m *DefaultRESTMapper) Add(kind schema.GroupVersionKind, scope RESTScope) {
 	plural, singular := UnsafeGuessKindToResource(kind)
+	m.AddSpecific(kind, plural, singular, scope)
+}
 
+func (m *DefaultRESTMapper) AddSpecific(kind schema.GroupVersionKind, plural, singular schema.GroupVersionResource, scope RESTScope) {
 	m.singularToPlural[singular] = plural
 	m.pluralToSingular[plural] = singular
 

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

@@ -96,8 +96,19 @@ func NewRESTMapper(groupResources []*APIGroupResources, versionInterfaces meta.V
 				if !resource.Namespaced {
 					scope = meta.RESTScopeRoot
 				}
-				versionMapper.Add(gv.WithKind(resource.Kind), scope)
-				// TODO only do this if it supports listing
+
+				// this is for legacy resources and servers which don't list singular forms.  For those we must still guess.
+				if len(resource.SingularName) == 0 {
+					versionMapper.Add(gv.WithKind(resource.Kind), scope)
+					// TODO this is producing unsafe guesses that don't actually work, but it matches previous behavior
+					versionMapper.Add(gv.WithKind(resource.Kind+"List"), scope)
+					continue
+				}
+
+				plural := gv.WithResource(resource.Name)
+				singular := gv.WithResource(resource.SingularName)
+				versionMapper.AddSpecific(gv.WithKind(resource.Kind), plural, singular, scope)
+				// TODO this is producing unsafe guesses that don't actually work, but it matches previous behavior
 				versionMapper.Add(gv.WithKind(resource.Kind+"List"), scope)
 			}
 			// TODO why is this type not in discovery (at least for "v1")