feat(gen2-migration): allow generate to skip non-JS Lambda functions

docs/packages/amplify-cli/src/commands/gen2-migration/assess.md

@@ -45,7 +45,7 @@ Standalone class (not a step). `assess()` returns an `Assessment` instance. `run
 
 [`src/commands/gen2-migration/assess/assessment.ts`](../../../../packages/amplify-cli/src/commands/gen2-migration/assess/assessment.ts)
 
-Collector that assessors contribute to. Exposes `validFor('generate' | 'refactor')` for step validation, and `render()` for terminal output. Each entry uses the `Support` type with `level` and optional `note`.
+Collector that assessors contribute to. Exposes `validFor('generate' | 'refactor')` for step validation, `of(resource, step)` for per-resource support lookup, and `render()` for terminal output. Each entry uses the `Support` type with `level` and optional `note`.
 
 ### `Support`
 
@@ -70,22 +70,23 @@ Produced by `Gen1App.discover()`. The `key` field is a typed `category:service`
 
 ## Supported Resources
 
-| Category  | Service                 | Generate | Refactor    |
-| --------- | ----------------------- | -------- | ----------- |
-| auth      | Cognito                 | ✔        | ✔           |
-| auth      | Cognito-UserPool-Groups | ✔        | ✔           |
-| storage   | S3                      | ✔        | ✔           |
-| storage   | DynamoDB                | ✔        | ✔           |
-| api       | AppSync                 | ✔        | n/a         |
-| api       | API Gateway             | ✔        | n/a         |
-| analytics | Kinesis                 | ✔        | ✔           |
-| function  | Lambda                  | ✔        | ✔           |
-| geo       | Map                     | ✔        | ✔           |
-| geo       | PlaceIndex              | ✔        | ✔           |
-| geo       | GeofenceCollection      | ✔        | unsupported |
+| Category  | Service                 | Generate         | Refactor    |
+| --------- | ----------------------- | ---------------- | ----------- |
+| auth      | Cognito                 | ✔                | ✔           |
+| auth      | Cognito-UserPool-Groups | ✔                | ✔           |
+| storage   | S3                      | ✔                | ✔           |
+| storage   | DynamoDB                | ✔                | ✔           |
+| api       | AppSync                 | ✔                | n/a         |
+| api       | API Gateway             | ✔                | n/a         |
+| analytics | Kinesis                 | ✔                | ✔           |
+| function  | Lambda                  | ✔ (Node.js only) | ✔           |
+| geo       | Map                     | ✔                | ✔           |
+| geo       | PlaceIndex              | ✔                | ✔           |
+| geo       | GeofenceCollection      | ✔                | unsupported |
 
 ## AI Development Notes
 
 - Adding a new resource type: add the pair to `KNOWN_RESOURCE_KEYS` in `gen1-app.ts`, create an assessor, handle the case in `assess.ts`, and in the generate/refactor steps. The compiler enforces exhaustiveness.
-- The `Assessment` is also used by generate and refactor steps for validation — `validFor(step)` returns false if any resource or feature is unsupported for that step.
+- The `Assessment` is also used by generate and refactor steps for validation — `validFor(step)` returns false if any resource or feature is unsupported for that step. The `of(resource, step)` method returns the `Support` for a specific resource, used by the generate orchestrator to skip unsupported resources before instantiating generators.
 - Feature detection (overrides, custom policies) is assessor-specific. Each assessor checks for files in the cloud backend directory via `gen1App.fileExists()`.
+- `FunctionAssessor` reads the Lambda runtime from the local CloudFormation template (`function/<name>/<name>-cloudformation-template.json`). Non-Node.js runtimes are marked as unsupported for generate, allowing `--skip-validations` to skip them.

docs/packages/amplify-cli/src/commands/gen2-migration/generate.md

@@ -69,10 +69,12 @@ The pipeline has two layers plus an orchestrator:
 - **Orchestrator** (`generate.ts`) — Uses `Gen1App.discover()` to iterate
   all resources from `amplify-meta.json`, dispatches by `resource.key`
   (a typed `ResourceKey`) via an exhaustive switch statement, and
-  instantiates one generator per resource. Collects all operations and
-  appends final operations for folder replacement + npm install. The same
-  switch is used by the `assess()` method to record support into an
-  `Assessment` collector.
+  instantiates one generator per resource. Resources marked as unsupported
+  by the assessment are skipped before the switch — no generator is
+  instantiated for them. Collects all operations and appends final
+  operations for folder replacement + npm install. The same switch is used
+  by the `assess()` method to record support into an `Assessment`
+  collector.
 
 ## Key Abstractions
 

packages/amplify-cli/src/__tests__/commands/gen2-migration/assess.test.ts

@@ -14,6 +14,10 @@ function mockGen1App(resources: DiscoveredResource[], existingFiles: string[] =
   } as unknown as Gen1App;
 }
 
+const NODEJS_TEMPLATE = {
+  Resources: { LambdaFunction: { Properties: { Runtime: 'nodejs18.x' } } },
+};
+
 describe('AmplifyMigrationAssessor', () => {
   describe('assess()', () => {
     it('returns empty assessment when no resources discovered', () => {
@@ -31,7 +35,10 @@ describe('AmplifyMigrationAssessor', () => {
       const gen1App = mockGen1App(
         [{ category: 'function', resourceName: 'myFunc', service: 'Lambda', key: 'function:Lambda' }],
         ['function/myFunc/custom-policies.json'],
-        { 'function/myFunc/custom-policies.json': [{ Action: ['s3:GetObject'], Resource: ['arn:aws:s3:::my-bucket/*'] }] },
+        {
+          'function/myFunc/myFunc-cloudformation-template.json': NODEJS_TEMPLATE,
+          'function/myFunc/custom-policies.json': [{ Action: ['s3:GetObject'], Resource: ['arn:aws:s3:::my-bucket/*'] }],
+        },
       );
       const assessor = new AmplifyMigrationAssessor(gen1App);
       const assessment = assessor.assess();
@@ -56,7 +63,10 @@ describe('AmplifyMigrationAssessor', () => {
       const gen1App = mockGen1App(
         [{ category: 'function', resourceName: 'myFunc', service: 'Lambda', key: 'function:Lambda' }],
         ['function/myFunc/custom-policies.json'],
-        { 'function/myFunc/custom-policies.json': [{ Action: [], Resource: [] }] },
+        {
+          'function/myFunc/myFunc-cloudformation-template.json': NODEJS_TEMPLATE,
+          'function/myFunc/custom-policies.json': [{ Action: [], Resource: [] }],
+        },
       );
       const assessor = new AmplifyMigrationAssessor(gen1App);
       const assessment = assessor.assess();
@@ -73,6 +83,26 @@ describe('AmplifyMigrationAssessor', () => {
       expect(assessment.resources[0].generate.level).toBe('unsupported');
       expect(assessment.resources[0].refactor.level).toBe('unsupported');
     });
+
+    it('marks function with non-JS runtime as unsupported for generate', () => {
+      const gen1App = mockGen1App(
+        [{ category: 'function', resourceName: 'myPythonFunc', service: 'Lambda', key: 'function:Lambda' }],
+        ['function/myPythonFunc/myPythonFunc-cloudformation-template.json'],
+        {
+          'function/myPythonFunc/myPythonFunc-cloudformation-template.json': {
+            Resources: { LambdaFunction: { Properties: { Runtime: 'python3.11' } } },
+          },
+        },
+      );
+      const assessor = new AmplifyMigrationAssessor(gen1App);
+      const assessment = assessor.assess();
+
+      expect(assessment.resources).toHaveLength(1);
+      expect(assessment.resources[0].generate.level).toBe('unsupported');
+      expect(assessment.resources[0].refactor.level).toBe('supported');
+      expect(assessment.validFor('generate')).toBe(false);
+      expect(assessment.validFor('refactor')).toBe(true);
+    });
   });
 
   describe('run()', () => {

packages/amplify-cli/src/__tests__/commands/gen2-migration/assess/function/function.assessor.test.ts

@@ -10,12 +10,18 @@ function mockGen1App(existingFiles: string[] = [], jsonFiles: Record<string, unk
   } as unknown as Gen1App;
 }
 
+const NODEJS_TEMPLATE_PATH = 'function/myFunc/myFunc-cloudformation-template.json';
+const NODEJS_TEMPLATE = {
+  Resources: { LambdaFunction: { Properties: { Runtime: 'nodejs18.x' } } },
+};
+
 const RESOURCE: DiscoveredResource = { category: 'function', resourceName: 'myFunc', service: 'Lambda', key: 'function:Lambda' };
 
 describe('FunctionAssessor', () => {
   it('records resource as supported', () => {
+    const gen1App = mockGen1App([], { [NODEJS_TEMPLATE_PATH]: NODEJS_TEMPLATE });
     const assessment = new Assessment('app', 'dev');
-    new FunctionAssessor(mockGen1App(), RESOURCE).record(assessment);
+    new FunctionAssessor(gen1App, RESOURCE).record(assessment);
 
     const entry = assessment.resources[0];
     expect(entry!.generate.level).toBe('supported');
@@ -24,6 +30,7 @@ describe('FunctionAssessor', () => {
 
   it('detects non-empty custom-policies.json', () => {
     const gen1App = mockGen1App(['function/myFunc/custom-policies.json'], {
+      [NODEJS_TEMPLATE_PATH]: NODEJS_TEMPLATE,
       'function/myFunc/custom-policies.json': [{ Action: ['s3:GetObject'], Resource: ['arn:aws:s3:::bucket/*'] }],
     });
     const assessment = new Assessment('app', 'dev');
@@ -39,6 +46,7 @@ describe('FunctionAssessor', () => {
 
   it('ignores empty custom-policies.json', () => {
     const gen1App = mockGen1App(['function/myFunc/custom-policies.json'], {
+      [NODEJS_TEMPLATE_PATH]: NODEJS_TEMPLATE,
       'function/myFunc/custom-policies.json': [{ Action: [], Resource: [] }],
     });
     const assessment = new Assessment('app', 'dev');
@@ -48,9 +56,45 @@ describe('FunctionAssessor', () => {
   });
 
   it('records no features when custom-policies.json is absent', () => {
+    const gen1App = mockGen1App([], { [NODEJS_TEMPLATE_PATH]: NODEJS_TEMPLATE });
     const assessment = new Assessment('app', 'dev');
-    new FunctionAssessor(mockGen1App(), RESOURCE).record(assessment);
+    new FunctionAssessor(gen1App, RESOURCE).record(assessment);
 
     expect(assessment.features).toHaveLength(0);
   });
+
+  describe('non-JS runtime detection', () => {
+    it('marks resource as unsupported for generate when runtime is Python', () => {
+      const gen1App = mockGen1App([], {
+        [NODEJS_TEMPLATE_PATH]: { Resources: { LambdaFunction: { Properties: { Runtime: 'python3.11' } } } },
+      });
+      const assessment = new Assessment('app', 'dev');
+      new FunctionAssessor(gen1App, RESOURCE).record(assessment);
+
+      const entry = assessment.resources[0];
+      expect(entry!.generate.level).toBe('unsupported');
+      expect(entry!.generate.note).toContain('python3.11');
+      expect(entry!.refactor.level).toBe('supported');
+    });
+
+    it('fails assessment validFor generate when runtime is non-JS', () => {
+      const gen1App = mockGen1App([], {
+        [NODEJS_TEMPLATE_PATH]: { Resources: { LambdaFunction: { Properties: { Runtime: 'dotnet8' } } } },
+      });
+      const assessment = new Assessment('app', 'dev');
+      new FunctionAssessor(gen1App, RESOURCE).record(assessment);
+
+      expect(assessment.validFor('generate')).toBe(false);
+      expect(assessment.validFor('refactor')).toBe(true);
+    });
+
+    it('treats nodejs runtimes as supported', () => {
+      const gen1App = mockGen1App([], { [NODEJS_TEMPLATE_PATH]: NODEJS_TEMPLATE });
+      const assessment = new Assessment('app', 'dev');
+      new FunctionAssessor(gen1App, RESOURCE).record(assessment);
+
+      expect(assessment.resources[0]!.generate.level).toBe('supported');
+      expect(assessment.features).toHaveLength(0);
+    });
+  });
 });

packages/amplify-cli/src/__tests__/commands/gen2-migration/generate.test.ts

@@ -152,5 +152,28 @@ describe('AmplifyMigrationGenerateStep', () => {
       lockSpy.mockRestore();
       wdSpy.mockRestore();
     });
+
+    it('skips unsupported resources without instantiating generators', async () => {
+      const gen1 = mockGen1App({
+        discover: () => [{ category: 'function', resourceName: 'myPythonFunc', service: 'Lambda', key: 'function:Lambda' as const }],
+        json: (p: string) => {
+          if (p.endsWith('-cloudformation-template.json')) {
+            return { Resources: { LambdaFunction: { Properties: { Runtime: 'python3.11' } } } };
+          }
+          return undefined;
+        },
+      });
+      const logger = new SpinningLogger('generate', { debug: true });
+
+      const plan = await new AmplifyMigrationGenerateStep(logger, gen1, {} as $TSContext, {} as AmplifyGen2MigrationValidations).forward();
+
+      // 3 validation ops (lock, working dir, assessment)
+      // 1 delete amplify dir
+      // 6 infrastructure generators (backend, root package.json, backend package.json, tsconfig, amplify.yml, gitignore)
+      // 2 post-generation ops (replace folder, install deps)
+      // = 12 total — the unsupported function contributes zero operations.
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any -- accessing private field to assert operation count
+      expect((plan as any).operations).toHaveLength(12);
+    });
   });
 });

packages/amplify-cli/src/commands/gen2-migration/assess/assessment.ts

@@ -98,6 +98,25 @@ export class Assessment {
     return this._features;
   }
 
+  /**
+   * Returns the support level for a specific resource in the given step.
+   */
+  // eslint-disable-next-line consistent-return -- exhaustive switch; compiler enforces all cases
+  public of(resource: DiscoveredResource, step: 'generate' | 'refactor'): Support {
+    const entry = this._resources.find(
+      (ra) => ra.resource.category === resource.category && ra.resource.resourceName === resource.resourceName,
+    );
+    if (!entry) {
+      throw new Error(`No assessment recorded for resource '${resource.category}/${resource.resourceName}'`);
+    }
+    switch (step) {
+      case 'generate':
+        return entry.generate;
+      case 'refactor':
+        return entry.refactor;
+    }
+  }
+
   /**
    * Returns true if all resources and features are supported for the given step.
    */

packages/amplify-cli/src/commands/gen2-migration/assess/function/function.assessor.ts

@@ -4,7 +4,7 @@ import { Gen1App, DiscoveredResource, KNOWN_FEATURES } from '../../generate/_inf
 
 /**
  * Assesses migration readiness for a single Lambda function resource.
- * Detects custom-policies.json usage.
+ * Detects non-JS runtimes and custom-policies.json usage.
  */
 export class FunctionAssessor implements Assessor {
   public constructor(private readonly gen1App: Gen1App, private readonly resource: DiscoveredResource) {}
@@ -13,9 +13,13 @@ export class FunctionAssessor implements Assessor {
    * Records resource-level and feature-level support for this function.
    */
   public record(assessment: Assessment): void {
+    const templatePath = `function/${this.resource.resourceName}/${this.resource.resourceName}-cloudformation-template.json`;
+    const template = this.gen1App.json(templatePath);
+    const runtime = template.Resources.LambdaFunction.Properties.Runtime;
+
     assessment.recordResource({
       resource: this.resource,
-      generate: supported(),
+      generate: this.isNonJsRuntime(runtime) ? unsupported(`uses non-JS runtime '${runtime}'`) : supported(),
       refactor: supported(),
     });
 
@@ -30,6 +34,13 @@ export class FunctionAssessor implements Assessor {
     }
   }
 
+  /**
+   * Returns true if the runtime is present and is not a Node.js variant.
+   */
+  private isNonJsRuntime(runtime: string): boolean {
+    return !runtime.startsWith('nodejs');
+  }
+
   /**
    * Returns true if the function has non-empty custom policies.
    * The file always exists but defaults to `[{"Action":[],"Resource":[]}]`.

packages/amplify-cli/src/commands/gen2-migration/generate.ts

@@ -71,6 +71,12 @@ export class AmplifyMigrationGenerateStep extends AmplifyMigrationStep {
     const discovered = this.gen1App.discover();
 
     for (const resource of discovered) {
+      // skip resources the assessment did not mark as supported.
+      // these will show up as validation errors the user has to acknowledge.
+      if (assessment.of(resource, 'generate').level !== 'supported') {
+        continue;
+      }
+
       switch (resource.key) {
         case 'auth:Cognito': {
           const isReferenceAuth = discovered