Expand the Conditions duck type to also encompass ObservedGeneration. (…

…#324)

With this, the expectation is that folks can embed the following in
the status of their resource:

```go
type FooStatus struct {
	duckv1alpha1.Status `json:",inline"`

	// other fields
}
```

`ObservedGeneration` is important to the usefulness of our standard
conditions because `{Ready,Succeeded}: True` is only meaningful when
`.status.observedGeneration == .metadata.generation`.

When `.status.observedGeneration != .metadata.generation` it indicates
that the controller has not yet attempted to reconcile a change in the
desired state of the world (aka `spec:`).

apis/duck/v1alpha1/condition_set_test.go

@@ -90,7 +90,7 @@ func TestNewBatchConditionSet(t *testing.T) {
 
 func TestNonTerminalCondition(t *testing.T) {
 	set := NewLivingConditionSet("Foo")
-	status := &KResourceStatus{}
+	status := &Status{}
 
 	manager := set.Manage(status)
 	manager.InitializeConditions()

apis/duck/v1alpha1/conditions_types.go

@@ -129,26 +129,21 @@ type KResource struct {
 	metav1.TypeMeta   `json:",inline"`
 	metav1.ObjectMeta `json:"metadata,omitempty"`
 
-	Status KResourceStatus `json:"status"`
+	Status Status `json:"status"`
 }
 
-// KResourceStatus shows how we expect folks to embed Conditions in
+// Status shows how we expect folks to embed Conditions in
 // their Status field.
-type KResourceStatus struct {
-	Conditions Conditions `json:"conditions,omitempty"`
-}
-
-func (krs *KResourceStatus) GetConditions() Conditions {
-	return krs.Conditions
-}
+type Status struct {
+	// ObservedGeneration is the 'Generation' of the Service that
+	// was last processed by the controller.
+	// +optional
+	ObservedGeneration int64 `json:"observedGeneration,omitempty"`
 
-func (krs *KResourceStatus) SetConditions(conditions Conditions) {
-	krs.Conditions = conditions
+	// +optional
+	Conditions Conditions `json:"conditions,omitempty"`
 }
 
-// Ensure KResourceStatus satisfies ConditionsAccessor
-var _ ConditionsAccessor = (*KResourceStatus)(nil)
-
 // In order for Conditions to be Implementable, KResource must be Populatable.
 var _ duck.Populatable = (*KResource)(nil)
 
@@ -162,6 +157,7 @@ func (_ *Conditions) GetFullType() duck.Populatable {
 
 // Populate implements duck.Populatable
 func (t *KResource) Populate() {
+	t.Status.ObservedGeneration = 42
 	t.Status.Conditions = Conditions{{
 		// Populate ALL fields
 		Type:               "Birthday",