Move config into context (#209)

Reconcilers and sub reconcilers use the config object to centralize
common api operations. Previously this config was passed to each
reconciler when it was initialized. However, this makes it harder to
dynamically swap the config at runtime based on the content of a
resource. For example, a resource may specify a service account to use
when creating other resources with least privilege.

The ChildReconciler and SyncReconciler no long allow the Config to be
specified directly. It must be passed in via the context. So that the
RetrieveConfig method can return the Config.

SubReconcilers that need to interact with the parent resource should use
the parent config via RetrieveParentConfig method. In many cases the
config and parent config are one in the same, however, the WithConfig
sub reconciler can inject an alternate config for the nested sub
reconcilers.

Signed-off-by: Scott Andrews <andrewssc@vmware.com>

README.md

@@ -16,6 +16,7 @@
 	- [Higher-order Reconcilers](#higher-order-reconcilers)
 		- [CastParent](#castparent)
 		- [Sequence](#sequence)
+		- [WithConfig](#withconfig)
 - [Testing](#testing)
 	- [ReconcilerTestSuite](#reconcilertestsuite)
 	- [SubReconcilerTestSuite](#subreconcilertestsuite)
@@ -93,8 +94,6 @@ func FunctionTargetImageReconciler(c reconcilers.Config) reconcilers.SubReconcil
 			parent.Status.TargetImage = targetImage
 			return nil
 		},
-
-		Config: c,
 	}
 }
 ```
@@ -192,8 +191,6 @@ func FunctionChildImageReconciler(c reconcilers.Config) reconcilers.SubReconcile
 			// up in our logs
 			return child.Spec
 		},
-
-		Config:     c,
 	}
 }
 ```
@@ -224,7 +221,6 @@ func FunctionReconciler(c reconcilers.Config) *reconcilers.ParentReconciler {
 						// do something with the duckv1alpha1.ImageRef instead of a buildv1alpha1.Function
 						return nil
 					},
-					Config: c,
 				},
 			},
 			FunctionChildImageReconciler(c),
@@ -259,6 +255,31 @@ func FunctionReconciler(c reconcilers.Config) *reconcilers.ParentReconciler {
 ```
 [full source](https://github.com/projectriff/system/blob/4c3b75327bf99cc37b57ba14df4c65d21dc79d28/pkg/controllers/build/function_reconciler.go#L39-L51)
 
+#### WithConfig
+
+[`WithConfig`](https://pkg.go.dev/github.com/vmware-labs/reconciler-runtime/reconcilers#WithConfig) overrides the config that nested reconcilers consume. The config can be retrieved from the context via [`RetrieveConfig`](https://pkg.go.dev/github.com/vmware-labs/reconciler-runtime/reconcilers#RetrieveConfig). The config used to load the parent resource should be used for interactions with the parent resource, which can be retrieved from the context via [`RetrieveParentConfig`](https://pkg.go.dev/github.com/vmware-labs/reconciler-runtime/reconcilers#RetrieveParentConfig).
+
+**Example:**
+
+`WithConfig` can be used to change the REST Config backing the clients. This could be to make requests to the same cluster with a user defined service account, or target an entirely different Kubernetes cluster.
+
+```go
+func SwapRESTConfig(c reconciler.Config, rc *rest.Config) (*reconcilers.SubReconciler, error) {
+	cl, err := clusters.New(rc)
+	if err != nil {
+		return nil, err
+	}
+
+	return &reconcilers.WithConfig{
+		Reconciler: reconcilers.Sequence{
+			LookupReferenceDataReconciler(),
+			DoSomethingChildReconciler(),
+		},
+
+		Config: c.WithCluster(cl),
+	}, nil
+}
+```
 
 ## Testing
 
@@ -395,8 +416,6 @@ func StashExampleSubReconciler(c reconcilers.Config) reconcilers.SubReconciler {
 			reconcilers.StashValue(ctx, exampleStashKey, *value)
 			return nil
 		},
-
-		Config: c,
 	}
 }
 
@@ -411,8 +430,6 @@ func StashExampleSubReconciler(c reconcilers.Config) reconcilers.SubReconciler {
 			}
 			... // do something with the value
 		},
-
-		Config: c,
 	}
 }
 ```
@@ -431,6 +448,7 @@ func InMemoryGatewaySyncConfigReconciler(c reconcilers.Config, namespace string)
 		Name: "SyncConfig",
 		Sync: func(ctx context.Context, parent *streamingv1alpha1.InMemoryGateway) error {
 			log := logr.FromContextOrDiscard(ctx)
+			c := reconciler.RetrieveConfig(ctx)
 
 			var config corev1.ConfigMap
 			key := types.NamespacedName{Namespace: namespace, Name: inmemoryGatewayImages}
@@ -451,14 +469,13 @@ func InMemoryGatewaySyncConfigReconciler(c reconcilers.Config, namespace string)
 			return nil
 		},
 
-		Config: c,
 		Setup: func(ctx context.Context, mgr reconcilers.Manager, bldr *reconcilers.Builder) error {
 			// enqueue the tracking resource for reconciliation from changes to
 			// tracked ConfigMaps. Internally `EnqueueTracked` sets up an 
 			// Informer to watch to changes of the target resource. When the
 			// informer emits an event, the tracking resources are looked up
 			// from the tracker and enqueded for reconciliation.
-			bldr.Watches(&source.Kind{Type: &corev1.ConfigMap{}}, reconcilers.EnqueueTracked(ctx, &corev1.ConfigMap{}, c.Tracker, c.Scheme))
+			bldr.Watches(&source.Kind{Type: &corev1.ConfigMap{}}, reconcilers.EnqueueTracked(ctx, &corev1.ConfigMap{}))
 			return nil
 		},
 	}

reconcilers/enqueuer.go

@@ -8,7 +8,6 @@ package reconcilers
 import (
 	"context"
 
-	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/types"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 	"sigs.k8s.io/controller-runtime/pkg/handler"
@@ -17,12 +16,13 @@ import (
 	"github.com/vmware-labs/reconciler-runtime/tracker"
 )
 
-func EnqueueTracked(ctx context.Context, by client.Object, t tracker.Tracker, s *runtime.Scheme) handler.EventHandler {
+func EnqueueTracked(ctx context.Context, by client.Object) handler.EventHandler {
+	c := RetrieveConfigOrDie(ctx)
 	return handler.EnqueueRequestsFromMapFunc(
 		func(a client.Object) []reconcile.Request {
 			var requests []reconcile.Request
 
-			gvks, _, err := s.ObjectKinds(by)
+			gvks, _, err := c.Scheme().ObjectKinds(by)
 			if err != nil {
 				panic(err)
 			}
@@ -31,7 +31,7 @@ func EnqueueTracked(ctx context.Context, by client.Object, t tracker.Tracker, s
 				gvks[0],
 				types.NamespacedName{Namespace: a.GetNamespace(), Name: a.GetName()},
 			)
-			for _, item := range t.Lookup(ctx, key) {
+			for _, item := range c.Tracker.Lookup(ctx, key) {
 				requests = append(requests, reconcile.Request{NamespacedName: item})
 			}
 

reconcilers/patch.go

@@ -62,5 +62,7 @@ func (p *Patch) Apply(rebase client.Object) error {
 	if err != nil {
 		return err
 	}
+	// reset rebase to its empty value before unmarshaling into it
+	replaceWithEmpty(rebase)
 	return json.Unmarshal(patchedBytes, rebase)
 }