split source and destination config for RR's, everything else is just confusing

This is because now, with support for label selectors, we need explicit naming on the destination
side, which means the old idea of "the same thing is done on both sides to figure out the names on
origin and destination" doesn't apply anymore, because the logic is now slightly different between
both sides. To not ack this in the CRD will just create endless confusion.

On-behalf-of: @SAP [email protected]

Author: xrstf

deploy/crd/kcp.io/syncagent.kcp.io_publishedresources.yaml

@@ -171,38 +171,29 @@ type RelatedResourceSpec struct {
 	// ConfigMap or Secret
 	Kind string `json:"kind"`
 
-	// Source describes how the related resource can be found. The source expression is evaluated
-	// on both source and destination side of the sync.
+	// Source describes how the related resource can be found on the side where it originates.
 	Source RelatedResourceSource `json:"source"`
 
-	// Naming is used when a label selector is used in the source expression. Since the labels do
-	// not dictate how the actual object shall be named on the destination side, and the agent also
-	// does not simply want to re-use the source side's name/namespace (these could contain private
-	// information and leak details about how the service is structured), explicit naming rules need
-	// to be provided. These naming rules are used to form the destination name/namespace for the
-	// related object.
-	// When reference-based sources are used, this field is optional as the destination name/namespace
-	// are read from the main object.
-	Naming *ResourceNaming `json:"naming"`
+	// Destination describes where to place the copy of the object on the destination side.
+	Destination RelatedResourceDestination `json:"destination"`
 
 	// Mutation configures optional transformation rules for the related resource.
 	// Status mutations are only performed when the related resource originates in kcp.
 	Mutation *ResourceMutationSpec `json:"mutation,omitempty"`
 }
 
-// RelatedResourceSource configures how a related object can be found.
+// RelatedResourceSource configures how a related object can be found on its origin side.
 type RelatedResourceSource struct {
-	// Name configures how the related object's name can be constructed or
-	// found. This must always be configured for a related resource.
-	Name RelatedResourceSourceSpec `json:"name"`
+	RelatedResourceSourceSpec `json:",inline"`
+
 	// Namespace configures in what namespace the related object resides in. If
 	// not specified, the same namespace as the main object is assumed. If the
 	// main object is cluster-scoped, an error will be raised during syncing.
 	Namespace *RelatedResourceSourceSpec `json:"namespace,omitempty"`
 }
 
-// RelatedResourceSourceSpec configures how the related object itself or its
-// namespace can be found. Selector and Reference are mutally exclusive.
+// RelatedResourceSourceSpec configures different ways an object can be located.
+// All fields are mutually exclusive.
 type RelatedResourceSourceSpec struct {
 	// Selector is a label selector that is useful if no reference is in the
 	// main resource (i.e. if the related object links back to its parent, instead
@@ -211,8 +202,36 @@ type RelatedResourceSourceSpec struct {
 	// Reference points to a field inside the main object. This reference is
 	// evaluated on both source and destination sides to find the related object.
 	Reference *RelatedResourceReference `json:"reference,omitempty"`
+	// Expression is a Go templated string that can make use of variables to
+	// construct the resulting string.
+	Expression string `json:"expression,omitempty"`
+}
+
+// RelatedResourceDestination configures where the copy of the related object on the
+// destination side should be created.
+type RelatedResourceDestination struct {
+	RelatedResourceDestinationSpec `json:",inline"`
+
+	// Namespace configures in what namespace the related object should be created
+	// in. If not specified, the same namespace as the main object is assumed.
+	// If the main object is cluster-scoped, an error will be raised during
+	// syncing.
+	Namespace *RelatedResourceDestinationSpec `json:"namespace,omitempty"`
+}
+
+// RelatedResourceDestinationSpec configures different ways an object can be located.
+// All fields are mutually exclusive.
+type RelatedResourceDestinationSpec struct {
+	// Reference points to a field inside the main object. This reference is
+	// evaluated on both source and destination sides to find the related object.
+	Reference *RelatedResourceReference `json:"reference,omitempty"`
+	// Expression is a Go templated string that can make use of variables to
+	// construct the resulting string.
+	Expression string `json:"expression,omitempty"`
 }
 
+// RelatedResourceReference describes a path expression that is evaluated inside
+// a JSON-marshalled Kubernetes object, yielding a string when evaluated.
 type RelatedResourceReference struct {
 	// Path is a simplified JSONPath expression like "metadata.name". A reference
 	// must always select at least _something_ in the object, even if the value