feat: validate stability degradation for pluginRef dependencies

Signed-off-by: Cong Liu <conliu@google.com>

Author: liu-cong

pkg/epp/config/loader/configloader.go

@@ -259,6 +259,10 @@ func buildPluginDAG(configuredPlugins []configapi.PluginSpec, handle fwkplugin.H
 	pluginMap := map[string]configapi.PluginSpec{}
 	orderedPlugins := []configapi.PluginSpec{}
 
+	for _, spec := range configuredPlugins {
+		pluginMap[spec.Name] = spec
+	}
+
 	for _, spec := range configuredPlugins {
 		if parserFunc, ok := fwkplugin.PluginsWithPluginDependencies[spec.Type]; !ok {
 			// Add plugins that don't have dependencies to the graph
@@ -269,9 +273,20 @@ func buildPluginDAG(configuredPlugins []configapi.PluginSpec, handle fwkplugin.H
 			if err != nil {
 				return nil, fmt.Errorf("failed to parse plugin parameters for %s (type: %s): %w", spec.Name, spec.Type, err)
 			}
-			graph[spec.Name] = findPluginDependencies(configStruct)
+			deps := findPluginDependencies(configStruct)
+			graph[spec.Name] = deps
+
+			parentStability := fwkplugin.GetPluginStability(spec.Type)
+			for _, depName := range deps {
+				if depSpec, ok := pluginMap[depName]; ok {
+					childStability := fwkplugin.GetPluginStability(depSpec.Type)
+					if childStability.Rank() < parentStability.Rank() {
+						return nil, fmt.Errorf("stability degradation detected: plugin %s (%s, %s) depends on plugin %s (%s, %s)",
+							spec.Name, spec.Type, parentStability, depSpec.Name, depSpec.Type, childStability)
+					}
+				}
+			}
 		}
-		pluginMap[spec.Name] = spec
 	}
 
 	sortedGraph, err := util.TopologicalSort(graph)

pkg/epp/config/loader/configloader_test.go

@@ -1316,3 +1316,43 @@ func TestExperimentalPluginsFeatureGate(t *testing.T) {
 	_, err = InstantiateAndConfigure(rawConfigWithGate, testutils.NewTestHandle(context.Background()), logger)
 	require.NoError(t, err)
 }
+
+func TestPluginRefStabilityDegradation(t *testing.T) {
+	parentType := "test-beta-parent-plugin"
+	childType := "test-alpha-child-plugin"
+
+	fwkplugin.RegisterWithPluginDependencies(parentType, fwkplugin.StabilityBeta,
+		func(name string, _ *json.Decoder, _ fwkplugin.Handle) (fwkplugin.Plugin, error) {
+			return &mockPlugin{t: fwkplugin.TypedName{Name: name, Type: parentType}}, nil
+		},
+		func(dec *json.Decoder, _ fwkplugin.Handle) (any, error) {
+			type config struct {
+				ChildRef string `json:"childRef" pluginRef:"true"`
+			}
+			var cfg config
+			if dec != nil {
+				if err := dec.Decode(&cfg); err != nil {
+					return nil, err
+				}
+			}
+			return cfg, nil
+		},
+	)
+	fwkplugin.Register(childType, fwkplugin.StabilityAlpha, func(name string, _ *json.Decoder, _ fwkplugin.Handle) (fwkplugin.Plugin, error) {
+		return &mockPlugin{t: fwkplugin.TypedName{Name: name, Type: childType}}, nil
+	})
+
+	rawConfig := &configapi.EndpointPickerConfig{
+		FeatureGates: configapi.FeatureGates{fwkplugin.ExperimentalPluginsFeatureGate},
+		Plugins: []configapi.PluginSpec{
+			{Name: "child", Type: childType},
+			{Name: "parent", Type: parentType, Parameters: json.RawMessage(`{"childRef":"child"}`)},
+		},
+	}
+
+	logger := logging.NewTestLogger()
+	handle := testutils.NewTestHandle(context.Background())
+	_, err := InstantiateAndConfigure(rawConfig, handle, logger)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "stability degradation detected")
+}

pkg/epp/datalayer/data_graph.go

@@ -155,28 +155,20 @@ func ValidatePluginStabilityDependencies(plugins []plugin.Plugin, logger logr.Lo
 		}
 	}
 
-	stabilityRank := map[plugin.StabilityLevel]int{
-		plugin.StabilityStable: 3,
-		plugin.StabilityBeta:   2,
-		plugin.StabilityAlpha:  1,
-	}
-
 	for _, p := range plugins {
 		consumer, ok := p.(plugin.ConsumerPlugin)
 		if !ok {
 			continue
 		}
 		consumerType := consumer.TypedName().Type
 		consumerStability := plugin.GetPluginStability(consumerType)
-		consumerRank := stabilityRank[consumerStability]
 
 		for key := range consumer.Consumes().Required {
 			if producer, found := producerKeyMap[key.String()]; found {
 				producerType := producer.TypedName().Type
 				producerStability := plugin.GetPluginStability(producerType)
-				producerRank := stabilityRank[producerStability]
 
-				if producerRank < consumerRank {
+				if producerStability.Rank() < consumerStability.Rank() {
 					return fmt.Errorf("stability degradation detected: consumer %s (%s) depends on producer %s (%s) for dataKey %s",
 						consumer.TypedName().String(), consumerStability,
 						producer.TypedName().String(), producerStability,

pkg/epp/framework/interface/plugin/stability.go

@@ -40,3 +40,17 @@ type PluginMetadata struct {
 	ScheduledRemovalIn string
 	ReplacementType    string
 }
+
+// Rank returns an integer representing the stability level ordering (Stable: 3, Beta: 2, Alpha: 1).
+func (s StabilityLevel) Rank() int {
+	switch s {
+	case StabilityStable:
+		return 3
+	case StabilityBeta:
+		return 2
+	case StabilityAlpha:
+		return 1
+	default:
+		return 0
+	}
+}