refactor: apply metadata render interface to oras discover command

cmd/oras/internal/display/metadata/interface.go

@@ -42,13 +42,13 @@ type AttachHandler interface {
 
 // DiscoverHandler handles metadata output for discover events.
 type DiscoverHandler interface {
+	Renderer
+
 	// MultiLevelSupported returns true if the handler supports multi-level
 	// discovery.
 	MultiLevelSupported() bool
 	// OnDiscovered is called after a referrer is discovered.
 	OnDiscovered(referrer, subject ocispec.Descriptor) error
-	// OnCompleted is called when referrer discovery is completed.
-	OnCompleted() error
 }
 
 // ManifestFetchHandler handles metadata output for manifest fetch events.

cmd/oras/internal/display/metadata/json/discover.go

@@ -57,7 +57,7 @@ func (h *discoverHandler) OnDiscovered(referrer, subject ocispec.Descriptor) err
 	return nil
 }
 
-// OnCompleted implements metadata.DiscoverHandler.
-func (h *discoverHandler) OnCompleted() error {
+// Render implements metadata.DiscoverHandler.
+func (h *discoverHandler) Render() error {
 	return output.PrintPrettyJSON(h.out, model.NewDiscover(h.path, h.referrers))
 }

cmd/oras/internal/display/metadata/table/discover.go

@@ -59,8 +59,8 @@ func (h *discoverHandler) OnDiscovered(referrer, subject ocispec.Descriptor) err
 	return nil
 }
 
-// OnCompleted implements metadata.DiscoverHandler.
-func (h *discoverHandler) OnCompleted() error {
+// Render implements metadata.DiscoverHandler.
+func (h *discoverHandler) Render() error {
 	if n := len(h.referrers); n > 1 {
 		fmt.Fprintln(h.out, "Discovered", n, "artifacts referencing", h.rawReference)
 	} else {

cmd/oras/internal/display/metadata/template/discover.go

@@ -59,7 +59,7 @@ func (h *discoverHandler) OnDiscovered(referrer, subject ocispec.Descriptor) err
 	return nil
 }
 
-// OnCompleted implements metadata.DiscoverHandler.
-func (h *discoverHandler) OnCompleted() error {
+// Render implements metadata.DiscoverHandler.
+func (h *discoverHandler) Render() error {
 	return output.ParseAndWrite(h.out, model.NewDiscover(h.path, h.referrers), h.template)
 }

cmd/oras/internal/display/metadata/tree/discover.go

@@ -78,7 +78,7 @@ func (h *discoverHandler) OnDiscovered(referrer, subject ocispec.Descriptor) err
 	return nil
 }
 
-// OnCompleted implements metadata.DiscoverHandler.
-func (h *discoverHandler) OnCompleted() error {
+// Render implements metadata.DiscoverHandler.
+func (h *discoverHandler) Render() error {
 	return tree.NewPrinter(h.out).Print(h.root)
 }

cmd/oras/root/discover.go

@@ -151,7 +151,7 @@ func runDiscover(cmd *cobra.Command, opts *discoverOptions) error {
 			}
 		}
 	}
-	return handler.OnCompleted()
+	return handler.Render()
 }
 
 func fetchAllReferrers(ctx context.Context, repo oras.ReadOnlyGraphTarget, desc ocispec.Descriptor, artifactType string, handler metadata.DiscoverHandler) error {