Report a malformed config instead of panicking in pipectl migrate

pkg/app/pipectl/cmd/migrate/application_config.go

@@ -139,7 +139,12 @@ func (c *applicationConfig) migrateApplicationConfig(_ context.Context, configFi
 		"driftDetection",
 	}
 
-	oldSpec := cfg["spec"].(map[string]any)
+	oldSpec, ok := cfg["spec"].(map[string]any)
+	if !ok {
+		err := fmt.Errorf("spec must be a mapping, got %T", cfg["spec"])
+		logger.Error("invalid application config", zap.String("config-file", configFile), zap.Error(err))
+		return err
+	}
 	for _, key := range keys {
 		if _, ok := oldSpec[key]; ok {
 			spec[key] = oldSpec[key]
@@ -151,7 +156,19 @@ func (c *applicationConfig) migrateApplicationConfig(_ context.Context, configFi
 	if oldPipelineCfg, ok := oldSpec["pipeline"]; ok {
 		pipelineCfg := make(map[string][]any)
 
-		for _, oldStage := range oldPipelineCfg.(map[string]any)["stages"].([]any) {
+		oldPipeline, ok := oldPipelineCfg.(map[string]any)
+		if !ok {
+			err := fmt.Errorf("spec.pipeline must be a mapping, got %T", oldPipelineCfg)
+			logger.Error("invalid application config", zap.String("config-file", configFile), zap.Error(err))
+			return err
+		}
+		oldStages, ok := oldPipeline["stages"].([]any)
+		if !ok && oldPipeline["stages"] != nil {
+			err := fmt.Errorf("spec.pipeline.stages must be a list, got %T", oldPipeline["stages"])
+			logger.Error("invalid application config", zap.String("config-file", configFile), zap.Error(err))
+			return err
+		}
+		for _, oldStage := range oldStages {
 			if oldStageCfg, ok := oldStage.(map[string]any); ok {
 				// Check if the stage is the analysis stage to determine if we need to fill plugins.analysis config
 				if oldStageCfg["name"] == string(model.StageAnalysis) {
@@ -177,7 +194,13 @@ func (c *applicationConfig) migrateApplicationConfig(_ context.Context, configFi
 		spec["pipeline"] = pipelineCfg
 	}
 
-	switch config.Kind(cfg["kind"].(string)) {
+	kind, ok := cfg["kind"].(string)
+	if !ok {
+		err := fmt.Errorf("kind must be a string, got %T", cfg["kind"])
+		logger.Error("invalid application config", zap.String("config-file", configFile), zap.Error(err))
+		return err
+	}
+	switch config.Kind(kind) {
 	case config.KindKubernetesApp:
 		logger.Info("migrating kubernetes application config", zap.String("config-file", configFile))
 		keys := []string{
@@ -272,8 +295,8 @@ func (c *applicationConfig) migrateApplicationConfig(_ context.Context, configFi
 		}
 		spec["plugins"] = pluginCfg
 	default:
-		logger.Error("unsupported application kind", zap.String("config-file", configFile), zap.String("kind", cfg["kind"].(string)))
-		return fmt.Errorf("unsupported application kind: %s", cfg["kind"])
+		logger.Error("unsupported application kind", zap.String("config-file", configFile), zap.String("kind", kind))
+		return fmt.Errorf("unsupported application kind: %s", kind)
 	}
 
 	migrated["spec"] = spec

pkg/app/pipectl/cmd/migrate/malformed_config_test.go

@@ -0,0 +1,56 @@
+// Copyright 2024 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 migrate
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"go.uber.org/zap"
+)
+
+// migrateApplicationConfig reads a user-supplied YAML file into map[string]any,
+// so every lookup out of it can hold something other than the expected shape.
+// A malformed file has to be reported, not panic the CLI.
+func TestMigrateApplicationConfigMalformed(t *testing.T) {
+	cases := map[string]string{
+		"spec is a string":   "apiVersion: pipecd.dev/v1beta1\nkind: KubernetesApp\nspec: oops\n",
+		"spec missing":       "apiVersion: pipecd.dev/v1beta1\nkind: KubernetesApp\n",
+		"kind missing":       "apiVersion: pipecd.dev/v1beta1\nspec:\n  name: x\n",
+		"kind is a number":   "apiVersion: pipecd.dev/v1beta1\nkind: 42\nspec:\n  name: x\n",
+		"pipeline is a list": "apiVersion: pipecd.dev/v1beta1\nkind: KubernetesApp\nspec:\n  pipeline:\n    - a\n",
+		"stages is a string": "apiVersion: pipecd.dev/v1beta1\nkind: KubernetesApp\nspec:\n  pipeline:\n    stages: nope\n",
+	}
+	for name, body := range cases {
+		t.Run(name, func(t *testing.T) {
+			dir := t.TempDir()
+			f := filepath.Join(dir, "app.pipecd.yaml")
+			if err := os.WriteFile(f, []byte(body), 0o600); err != nil {
+				t.Fatal(err)
+			}
+			c := &applicationConfig{}
+			defer func() {
+				if r := recover(); r != nil {
+					t.Fatalf("panicked on a user-supplied config: %v", r)
+				}
+			}()
+			if err := c.migrateApplicationConfig(context.Background(), f, zap.NewNop()); err == nil {
+				t.Error("expected an error for a malformed config, got nil")
+			}
+		})
+	}
+}