Allow controller to watch a specified namespace

Add a command line option to optionally watch a specific namespace. The
default is to watch all namespaces.

cmd/controller/main.go

@@ -22,7 +22,10 @@ import (
 	"github.com/tektoncd/pipeline/pkg/apis/pipeline"
 	"github.com/tektoncd/pipeline/pkg/reconciler/pipelinerun"
 	"github.com/tektoncd/pipeline/pkg/reconciler/taskrun"
+	corev1 "k8s.io/api/core/v1"
+	"knative.dev/pkg/injection"
 	"knative.dev/pkg/injection/sharedmain"
+	"knative.dev/pkg/signals"
 )
 
 const (
@@ -49,6 +52,7 @@ var (
 		"The container image containing our PR binary.")
 	imageDigestExporterImage = flag.String("imagedigest-exporter-image", "override-with-imagedigest-exporter-image:latest",
 		"The container image containing our image digest exporter binary.")
+	namespace = flag.String("namespace", corev1.NamespaceAll, "Namespace to restrict informer to. Optional, defaults to all namespaces.")
 )
 
 func main() {
@@ -65,7 +69,7 @@ func main() {
 		PRImage:                  *prImage,
 		ImageDigestExporterImage: *imageDigestExporterImage,
 	}
-	sharedmain.Main(ControllerLogKey,
+	sharedmain.MainWithContext(injection.WithNamespaceScope(signals.NewContext(), *namespace), ControllerLogKey,
 		taskrun.NewController(images),
 		pipelinerun.NewController(images),
 	)