Add IfNotFound option to the ResourceReconciler

This can be optionally set and will be used if the resource doesn’t
exist yet. When reconciliations are triggered from the outside the
user can create the resource. This is useful if the ChildReconciler
cannot be used, i.e. if there’s no explicit parent resource.

Signed-off-by: Daniel Lohse <info@asapdesign.de>

Author: annismckenzie

reconcilers/resource.go

@@ -131,6 +131,12 @@ type ResourceReconciler[Type client.Object] struct {
 	// +optional
 	SkipResource func(ctx context.Context, resource Type) bool
 
+	// IfNotFound is called if the resource doesn't exist yet. Return nil if the reconcile should
+	// be aborted.
+	//
+	// +optional
+	IfNotFound func(ctx context.Context, req Request) Type
+
 	Config Config
 
 	lazyInit sync.Once
@@ -142,6 +148,12 @@ func (r *ResourceReconciler[T]) init() {
 			var nilT T
 			r.Type = newEmpty(nilT).(T)
 		}
+		if r.IfNotFound == nil {
+			r.IfNotFound = func(ctx context.Context, req Request) T {
+				var nilT T
+				return nilT
+			}
+		}
 		if r.Name == "" {
 			r.Name = fmt.Sprintf("%sResourceReconciler", typeName(r.Type))
 		}
@@ -320,13 +332,18 @@ func (r *ResourceReconciler[T]) reconcileOuter(ctx context.Context, req Request)
 
 	originalResource := r.Type.DeepCopyObject().(T)
 
-	if err := c.Get(ctx, req.NamespacedName, originalResource); err != nil {
-		if apierrs.IsNotFound(err) {
-			// we'll ignore not-found errors, since they can't be fixed by an immediate
-			// requeue (we'll need to wait for a new notification), and we can get them
-			// on deleted requests.
+	err := c.Get(ctx, req.NamespacedName, originalResource)
+	switch {
+	case err == nil:
+		// all good, continue
+	case apierrs.IsNotFound(err):
+		// we'll ignore not-found errors, since they can't be fixed by an immediate
+		// requeue (we'll need to wait for a new notification), and we can get them
+		// on deleted requests – except if `IfNotFound` returns a new resource
+		if originalResource = r.IfNotFound(ctx, req); internal.IsNil(originalResource) {
 			return Result{}, nil
 		}
+	default:
 		if !errors.Is(err, ErrQuiet) {
 			log.Error(err, "unable to fetch resource")
 		}