Refactor depends-on code

- Move from pkg/object to pkg/object/dependson
- Add DependencySet type to abstract some complexity
- Add Marshal/Unmarshal funcs for ObjMetadata and DependencySet
- Refactor primary API to ReadAnnotation and WriteAnnotation
- Move Write/Marshal behavior from testutil into dependson pkg
- Make constants private to encourage using functions as primary API

pkg/object/dependson/annotation.go

@@ -0,0 +1,74 @@
+// Copyright 2021 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package dependson
+
+import (
+	"errors"
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"k8s.io/klog/v2"
+)
+
+const (
+	Annotation = "config.kubernetes.io/depends-on"
+)
+
+// HasAnnotation returns true if the config.kubernetes.io/depends-on annotation
+// is present, false if not.
+func HasAnnotation(u *unstructured.Unstructured) bool {
+	if u == nil {
+		return false
+	}
+	_, found := u.GetAnnotations()[Annotation]
+	return found
+}
+
+// ReadAnnotation reads the depends-on annotation and parses the the set of
+// object references.
+func ReadAnnotation(u *unstructured.Unstructured) (DependencySet, error) {
+	depSet := DependencySet{}
+	if u == nil {
+		return depSet, nil
+	}
+	depSetStr, found := u.GetAnnotations()[Annotation]
+	if !found {
+		return depSet, nil
+	}
+	klog.V(5).Infof("depends-on annotation found for %s/%s: %q",
+		u.GetNamespace(), u.GetName(), depSetStr)
+
+	depSet, err := UnmarshalDependencySet(depSetStr)
+	if err != nil {
+		return depSet, fmt.Errorf("failed to parse dependency set: %w", err)
+	}
+	return depSet, nil
+}
+
+// WriteAnnotation updates the supplied unstructured object to add the
+// depends-on annotation. The value is a string of objmetas delimited by commas.
+// Each objmeta is formatted as "${group}/${kind}/${name}" if cluster-scoped or
+// "${group}/namespaces/${namespace}/${kind}/${name}" if namespace-scoped.
+func WriteAnnotation(obj *unstructured.Unstructured, depSet DependencySet) error {
+	if obj == nil {
+		return errors.New("object is nil")
+	}
+	if depSet.Equal(DependencySet{}) {
+		return errors.New("dependency set is empty")
+	}
+
+	depSetStr, err := MarshalDependencySet(depSet)
+	if err != nil {
+		return fmt.Errorf("failed to format dependency set: %w", err)
+	}
+
+	a := obj.GetAnnotations()
+	if a == nil {
+		a = map[string]string{}
+	}
+	a[Annotation] = depSetStr
+	obj.SetAnnotations(a)
+	return nil
+}