[Multi_K8s-Plugin] Implement plan preview

pkg/app/pipedv1/plugin/kubernetes_multicluster/main.go

@@ -25,6 +25,7 @@ import (
 	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/config"
 	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/deployment"
 	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/livestate"
+	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/planpreview"
 	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/provider"
 	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/toolregistry"
 )
@@ -72,6 +73,7 @@ func main() {
 		sdk.WithInitializer[config.KubernetesApplicationSpec](&initializer{}),
 		sdk.WithDeploymentPlugin(&deployment.Plugin{}),
 		sdk.WithLivestatePlugin(&livestate.Plugin{}),
+		sdk.WithPlanPreviewPlugin(&planpreview.Plugin{}),
 	)
 	if err != nil {
 		log.Fatalln(err)

pkg/app/pipedv1/plugin/kubernetes_multicluster/planpreview/plugin.go

@@ -0,0 +1,203 @@
+// Copyright 2026 The PipeCD Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package planpreview
+
+import (
+	"context"
+	"fmt"
+
+	sdk "github.com/pipe-cd/piped-plugin-sdk-go"
+	"github.com/pipe-cd/piped-plugin-sdk-go/diff"
+
+	kubeconfig "github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/config"
+	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/provider"
+	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/plugin/kubernetes_multicluster/toolregistry"
+)
+
+var (
+	_ sdk.PlanPreviewPlugin[kubeconfig.KubernetesPluginConfig, kubeconfig.KubernetesDeployTargetConfig, kubeconfig.KubernetesApplicationSpec] = (*Plugin)(nil)
+)
+
+// Plugin implements the sdk.PlanPreviewPlugin interface for the kubernetes_multicluster plugin.
+type Plugin struct{}
+
+// GetPlanPreview returns the plan preview result showing what will change across all deploy targets.
+func (p *Plugin) GetPlanPreview(ctx context.Context, _ *kubeconfig.KubernetesPluginConfig, dts []*sdk.DeployTarget[kubeconfig.KubernetesDeployTargetConfig], input *sdk.GetPlanPreviewInput[kubeconfig.KubernetesApplicationSpec]) (*sdk.GetPlanPreviewResponse, error) {
+	toolRegistry := toolregistry.NewRegistry(input.Client.ToolRegistry())
+	loader := provider.NewLoader(toolRegistry)
+
+	targetDS := input.Request.TargetDeploymentSource
+	targetAppCfg, err := targetDS.AppConfig()
+	if err != nil {
+		return nil, err
+	}
+	targetSpec := targetAppCfg.Spec
+
+	runningDS := input.Request.RunningDeploymentSource
+
+	multiTargets := targetSpec.Input.MultiTargets
+
+	// Single-target fallback: no multiTargets configured — load manifests once and return one result.
+	if len(multiTargets) == 0 {
+		newManifests, err := loadManifests(ctx, loader, input, &targetDS, targetSpec, nil)
+		if err != nil {
+			return nil, err
+		}
+
+		var oldManifests []provider.Manifest
+		if runningDS.CommitHash != "" {
+			runningAppCfg, err := runningDS.AppConfig()
+			if err != nil {
+				return nil, err
+			}
+			oldManifests, err = loadManifests(ctx, loader, input, &runningDS, runningAppCfg.Spec, nil)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		result, err := provider.DiffList(
+			oldManifests,
+			newManifests,
+			input.Logger,
+			diff.WithEquateEmpty(),
+			diff.WithCompareNumberAndNumericString(),
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		deployTargetName := ""
+		if len(dts) > 0 {
+			deployTargetName = dts[0].Name
+		}
+		return &sdk.GetPlanPreviewResponse{
+			Results: []sdk.PlanPreviewResult{toResult(result, deployTargetName)},
+		}, nil
+	}
+
+	// Multi-target: produce one PlanPreviewResult per deploy target.
+	results := make([]sdk.PlanPreviewResult, 0, len(dts))
+	for _, dt := range dts {
+		// Find the matching KubernetesMultiTarget config for this deploy target.
+		var mt *kubeconfig.KubernetesMultiTarget
+		for i := range multiTargets {
+			if multiTargets[i].Target.Name == dt.Name {
+				mt = &multiTargets[i]
+				break
+			}
+		}
+
+		newManifests, err := loadManifests(ctx, loader, input, &targetDS, targetSpec, mt)
+		if err != nil {
+			results = append(results, sdk.PlanPreviewResult{
+				DeployTarget: dt.Name,
+				NoChange:     false,
+				Summary:      fmt.Sprintf("Failed to load target manifests: %v", err),
+				DiffLanguage: "diff",
+			})
+			continue
+		}
+
+		var oldManifests []provider.Manifest
+		if runningDS.CommitHash != "" {
+			runningAppCfg, err := runningDS.AppConfig()
+			if err != nil {
+				return nil, err
+			}
+			oldManifests, err = loadManifests(ctx, loader, input, &runningDS, runningAppCfg.Spec, mt)
+			if err != nil {
+				results = append(results, sdk.PlanPreviewResult{
+					DeployTarget: dt.Name,
+					NoChange:     false,
+					Summary:      fmt.Sprintf("Failed to load running manifests: %v", err),
+					DiffLanguage: "diff",
+				})
+				continue
+			}
+		}
+
+		result, err := provider.DiffList(
+			oldManifests,
+			newManifests,
+			input.Logger,
+			diff.WithEquateEmpty(),
+			diff.WithCompareNumberAndNumericString(),
+		)
+		if err != nil {
+			results = append(results, sdk.PlanPreviewResult{
+				DeployTarget: dt.Name,
+				NoChange:     false,
+				Summary:      fmt.Sprintf("Failed to diff manifests: %v", err),
+				DiffLanguage: "diff",
+			})
+			continue
+		}
+
+		results = append(results, toResult(result, dt.Name))
+	}
+
+	return &sdk.GetPlanPreviewResponse{Results: results}, nil
+}
+
+// loadManifests loads manifests from the given deployment source, optionally overriding
+// the manifest paths from the multiTarget config.
+func loadManifests(ctx context.Context, loader *provider.Loader, input *sdk.GetPlanPreviewInput[kubeconfig.KubernetesApplicationSpec], ds *sdk.DeploymentSource[kubeconfig.KubernetesApplicationSpec], spec *kubeconfig.KubernetesApplicationSpec, mt *kubeconfig.KubernetesMultiTarget) ([]provider.Manifest, error) {
+	manifestPaths := spec.Input.Manifests
+	if mt != nil && len(mt.Manifests) > 0 {
+		manifestPaths = mt.Manifests
+	}
+
+	return loader.LoadManifests(ctx, provider.LoaderInput{
+		PipedID:          input.Request.PipedID,
+		AppID:            input.Request.ApplicationID,
+		CommitHash:       ds.CommitHash,
+		AppName:          input.Request.ApplicationName,
+		AppDir:           ds.ApplicationDirectory,
+		ConfigFilename:   ds.ApplicationConfigFilename,
+		Manifests:        manifestPaths,
+		Namespace:        spec.Input.Namespace,
+		KustomizeVersion: spec.Input.KustomizeVersion,
+		KustomizeOptions: spec.Input.KustomizeOptions,
+		HelmVersion:      spec.Input.HelmVersion,
+		HelmChart:        spec.Input.HelmChart,
+		HelmOptions:      spec.Input.HelmOptions,
+		Logger:           input.Logger,
+	})
+}
+
+// toResult converts a DiffListResult into a PlanPreviewResult for the given deploy target.
+func toResult(result *provider.DiffListResult, deployTarget string) sdk.PlanPreviewResult {
+	if result.NoChanges() {
+		return sdk.PlanPreviewResult{
+			DeployTarget: deployTarget,
+			NoChange:     true,
+			Summary:      "No changes were detected",
+			DiffLanguage: "diff",
+		}
+	}
+
+	details := result.Render(provider.DiffRenderOptions{
+		MaskSecret: true,
+	})
+
+	return sdk.PlanPreviewResult{
+		DeployTarget: deployTarget,
+		NoChange:     false,
+		Summary:      fmt.Sprintf("%d added manifests, %d changed manifests, %d deleted manifests", len(result.Adds), len(result.Changes), len(result.Deletes)),
+		DiffLanguage: "diff",
+		Details:      []byte(details),
+	}
+}