merge: Apply returns nil object if unchanged

We need to know when the apply operation isn't changing the object, so
that we can update the timestamp of the operation. The simplest way to
do so it to return nil.

Author: Antoine Pelisse

internal/fixture/state.go

@@ -150,9 +150,10 @@ func (s *State) ApplyObject(tv *typed.TypedValue, version fieldpath.APIVersion,
 	if err != nil {
 		return err
 	}
-	s.Live = new
 	s.Managers = managers
-
+	if new != nil {
+		s.Live = new
+	}
 	return nil
 }
 

merge/update.go

@@ -148,7 +148,8 @@ func (s *Updater) Update(liveObject, newObject *typed.TypedValue, version fieldp
 
 // Apply should be called when Apply is run, given the current object as
 // well as the configuration that is applied. This will merge the object
-// and return it.
+// and return it. If the object hasn't changed, nil is returned (the
+// managers can still have changed though).
 func (s *Updater) Apply(liveObject, configObject *typed.TypedValue, version fieldpath.APIVersion, managers fieldpath.ManagedFields, manager string, force bool) (*typed.TypedValue, fieldpath.ManagedFields, error) {
 	managers = shallowCopyManagers(managers)
 	var err error
@@ -178,10 +179,13 @@ func (s *Updater) Apply(liveObject, configObject *typed.TypedValue, version fiel
 	if err != nil {
 		return nil, fieldpath.ManagedFields{}, fmt.Errorf("failed to prune fields: %v", err)
 	}
-	managers, _, err = s.update(liveObject, newObject, version, managers, manager, force)
+	managers, compare, err := s.update(liveObject, newObject, version, managers, manager, force)
 	if err != nil {
 		return nil, fieldpath.ManagedFields{}, err
 	}
+	if compare.IsSame() {
+		newObject = nil
+	}
 	return newObject, managers, nil
 }