Fixes internal bug for modified selector (open-telemetry#2874)

* fixes bug

* chlog

.chloggen/fix-selector-bug.yaml

@@ -0,0 +1,16 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. collector, target allocator, auto-instrumentation, opamp, github action)
+component: collector
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: resolves a bug that would create a junk selector for the service by merging rather than overriding.
+
+# One or more tracking issues related to the change
+issues: [2873]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

controllers/reconcile_test.go

@@ -152,9 +152,16 @@ func TestOpenTelemetryCollectorReconciler_Reconcile(t *testing.T) {
 							// confirm the initial strategy is unset
 							assert.Equal(t, d.Spec.Strategy.RollingUpdate.MaxUnavailable.IntVal, int32(0))
 							assert.Equal(t, d.Spec.Strategy.RollingUpdate.MaxSurge.IntVal, int32(0))
-							exists, err = populateObjectIfExists(t, &v1.Service{}, namespacedObjectName(naming.Service(params.Name), params.Namespace))
+							svc := &v1.Service{}
+							exists, err = populateObjectIfExists(t, svc, namespacedObjectName(naming.Service(params.Name), params.Namespace))
 							assert.NoError(t, err)
 							assert.True(t, exists)
+							assert.Equal(t, svc.Spec.Selector, map[string]string{
+								"app.kubernetes.io/component":  "opentelemetry-collector",
+								"app.kubernetes.io/instance":   "default.test",
+								"app.kubernetes.io/managed-by": "opentelemetry-operator",
+								"app.kubernetes.io/part-of":    "opentelemetry",
+							})
 							exists, err = populateObjectIfExists(t, &v1.ServiceAccount{}, namespacedObjectName(naming.ServiceAccount(params.Name), params.Namespace))
 							assert.NoError(t, err)
 							assert.True(t, exists)
@@ -183,6 +190,12 @@ func TestOpenTelemetryCollectorReconciler_Reconcile(t *testing.T) {
 							assert.NoError(t, err)
 							assert.True(t, exists)
 							assert.Contains(t, actual.Spec.Ports, extraPorts.ServicePort)
+							assert.Equal(t, actual.Spec.Selector, map[string]string{
+								"app.kubernetes.io/component":  "opentelemetry-collector",
+								"app.kubernetes.io/instance":   "default.test",
+								"app.kubernetes.io/managed-by": "opentelemetry-operator",
+								"app.kubernetes.io/part-of":    "opentelemetry",
+							})
 						},
 					},
 					wantErr:     assert.NoError,

internal/manifests/mutate.go

@@ -89,7 +89,7 @@ func MutateFuncFor(existing, desired client.Object) controllerutil.MutateFn {
 		case *corev1.Service:
 			svc := existing.(*corev1.Service)
 			wantSvc := desired.(*corev1.Service)
-			return mutateService(svc, wantSvc)
+			mutateService(svc, wantSvc)
 
 		case *corev1.ServiceAccount:
 			sa := existing.(*corev1.ServiceAccount)
@@ -256,12 +256,9 @@ func mutatePodMonitor(existing, desired *monitoringv1.PodMonitor) {
 	existing.Spec = desired.Spec
 }
 
-func mutateService(existing, desired *corev1.Service) error {
+func mutateService(existing, desired *corev1.Service) {
 	existing.Spec.Ports = desired.Spec.Ports
-	if err := mergeWithOverride(&existing.Spec.Selector, desired.Spec.Selector); err != nil {
-		return err
-	}
-	return nil
+	existing.Spec.Selector = desired.Spec.Selector
 }
 
 func mutateDaemonset(existing, desired *appsv1.DaemonSet) error {