feat(gen2-migration): support overriding default resolvers

packages/amplify-cli/.amplify/refactor.operations/update.gen1-auth-stack.parameters.json

@@ -0,0 +1 @@
+[]

packages/amplify-cli/.amplify/refactor.operations/update.gen1-auth-stack.template.json

@@ -0,0 +1,19 @@
+{
+  "AWSTemplateFormatVersion": "2010-09-09",
+  "Description": "{\"stackType\":\"auth-Cognito\"}",
+  "Resources": {
+    "UserPool": {
+      "Type": "AWS::Cognito::UserPool",
+      "Properties": {}
+    }
+  },
+  "Outputs": {},
+  "Parameters": {
+    "hostedUIProviderMeta": {
+      "Type": "String"
+    },
+    "hostedUIProviderCreds": {
+      "Type": "String"
+    }
+  }
+}

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

@@ -24,9 +24,18 @@ jest.mock('../../../../../../commands/gen2-migration/generate/_infra/ts', () =>
 
 const mockMkdir = jest.fn().mockResolvedValue(undefined);
 const mockWriteFile = jest.fn().mockResolvedValue(undefined);
+const mockCopyFile = jest.fn().mockResolvedValue(undefined);
 jest.mock('node:fs/promises', () => ({
   mkdir: (...args: unknown[]) => mockMkdir(...args),
   writeFile: (...args: unknown[]) => mockWriteFile(...args),
+  copyFile: (...args: unknown[]) => mockCopyFile(...args),
+}));
+
+const mockExistsSync = jest.fn().mockReturnValue(false);
+const mockReaddirSync = jest.fn().mockReturnValue([]);
+jest.mock('node:fs', () => ({
+  existsSync: (...args: unknown[]) => mockExistsSync(...args),
+  readdirSync: (...args: unknown[]) => mockReaddirSync(...args),
 }));
 
 function createMockGen1App(overrides?: Record<string, unknown>): Gen1App {
@@ -324,5 +333,125 @@ describe('DataGenerator', () => {
 
       expect(addStatementSpy).not.toHaveBeenCalled();
     });
+
+    describe('resolver overrides', () => {
+      it('does not add resolver operations when no resolvers directory exists', async () => {
+        mockExistsSync.mockReturnValue(false);
+
+        const generator = new DataGenerator(gen1App, backendGenerator, outputDir, {
+          category: 'api',
+          resourceName: 'testApi',
+          service: 'AppSync',
+          key: 'api:AppSync',
+        });
+        const ops = await generator.plan();
+
+        expect(ops).toHaveLength(1);
+        const addStatementSpy = jest.spyOn(backendGenerator, 'addStatement');
+        await ops[0].execute();
+        expect(addStatementSpy).not.toHaveBeenCalled();
+      });
+
+      it('does not add resolver operations when resolvers directory has no vtl files', async () => {
+        mockExistsSync.mockReturnValue(true);
+        mockReaddirSync.mockReturnValue(['readme.txt', 'notes.md']);
+
+        const generator = new DataGenerator(gen1App, backendGenerator, outputDir, {
+          category: 'api',
+          resourceName: 'testApi',
+          service: 'AppSync',
+          key: 'api:AppSync',
+        });
+        const ops = await generator.plan();
+
+        expect(ops).toHaveLength(1);
+      });
+
+      it('adds a copy operation when vtl files exist', async () => {
+        mockExistsSync.mockReturnValue(true);
+        mockReaddirSync.mockReturnValue(['Query.listProducts.res.vtl']);
+
+        const generator = new DataGenerator(gen1App, backendGenerator, outputDir, {
+          category: 'api',
+          resourceName: 'testApi',
+          service: 'AppSync',
+          key: 'api:AppSync',
+        });
+        const ops = await generator.plan();
+
+        expect(ops).toHaveLength(2);
+        const descriptions = await ops[1].describe();
+        expect(descriptions[0]).toContain('1 VTL resolver file(s)');
+      });
+
+      it('copies vtl files to amplify/data/resolvers/', async () => {
+        mockExistsSync.mockReturnValue(true);
+        mockReaddirSync.mockReturnValue(['Query.listProducts.res.vtl', 'Mutation.createProduct.req.vtl']);
+
+        const generator = new DataGenerator(gen1App, backendGenerator, outputDir, {
+          category: 'api',
+          resourceName: 'testApi',
+          service: 'AppSync',
+          key: 'api:AppSync',
+        });
+        const ops = await generator.plan();
+        await ops[1].execute();
+
+        expect(mockMkdir).toHaveBeenCalledWith(expect.stringContaining('resolvers'), { recursive: true });
+        expect(mockCopyFile).toHaveBeenCalledTimes(2);
+        expect(mockCopyFile).toHaveBeenCalledWith(
+          expect.stringContaining('Query.listProducts.res.vtl'),
+          expect.stringContaining('Query.listProducts.res.vtl'),
+        );
+        expect(mockCopyFile).toHaveBeenCalledWith(
+          expect.stringContaining('Mutation.createProduct.req.vtl'),
+          expect.stringContaining('Mutation.createProduct.req.vtl'),
+        );
+      });
+
+      it('contributes resolver override imports and statements to backendGenerator', async () => {
+        mockExistsSync.mockReturnValue(true);
+        mockReaddirSync.mockReturnValue(['Query.listProducts.res.vtl']);
+
+        const addImportSpy = jest.spyOn(backendGenerator, 'addImport');
+        const addNamespaceImportSpy = jest.spyOn(backendGenerator, 'addNamespaceImport');
+        const addStatementSpy = jest.spyOn(backendGenerator, 'addStatement');
+
+        const generator = new DataGenerator(gen1App, backendGenerator, outputDir, {
+          category: 'api',
+          resourceName: 'testApi',
+          service: 'AppSync',
+          key: 'api:AppSync',
+        });
+        const ops = await generator.plan();
+        await ops[0].execute();
+
+        // Resolver imports: fs (readdirSync only), path, url
+        expect(addImportSpy).toHaveBeenCalledWith('fs', ['readdirSync']);
+        expect(addImportSpy).toHaveBeenCalledWith('path', ['join', 'dirname']);
+        expect(addImportSpy).toHaveBeenCalledWith('url', ['fileURLToPath']);
+        expect(addNamespaceImportSpy).toHaveBeenCalledWith('aws-cdk-lib/aws-s3-assets', 'assets');
+
+        // 4 statements: __dirname, resolversDir, resolverFiles, for-of loop
+        expect(addStatementSpy).toHaveBeenCalledTimes(4);
+      });
+
+      it('handles multiple vtl files of both req and res types', async () => {
+        mockExistsSync.mockReturnValue(true);
+        mockReaddirSync.mockReturnValue(['Query.listProducts.res.vtl', 'Query.listProducts.req.vtl', 'Mutation.createProduct.res.vtl']);
+
+        const generator = new DataGenerator(gen1App, backendGenerator, outputDir, {
+          category: 'api',
+          resourceName: 'testApi',
+          service: 'AppSync',
+          key: 'api:AppSync',
+        });
+        const ops = await generator.plan();
+
+        expect(ops).toHaveLength(2);
+        const descriptions = await ops[1].describe();
+        expect(descriptions[0]).toContain('3 VTL resolver file(s)');
+      });
+    });
   });
 });

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

@@ -18,6 +18,7 @@ const factory = ts.factory;
  */
 export class BackendGenerator implements Planner {
   private readonly imports: Array<{ readonly source: string; readonly identifiers: string[] }> = [];
+  private readonly namespaceImports: Array<{ readonly source: string; readonly alias: string }> = [];
   private readonly defineBackendProperties: ts.ObjectLiteralElementLike[] = [];
   private readonly postDefineStatements: ts.Statement[] = [];
   private readonly earlyStatements: ts.Statement[] = [];
@@ -46,6 +47,15 @@ export class BackendGenerator implements Planner {
     }
   }
 
+  /**
+   * Adds a namespace import (`import * as alias from 'source'`) to backend.ts.
+   */
+  public addNamespaceImport(source: string, alias: string): void {
+    if (!this.namespaceImports.some((i) => i.source === source)) {
+      this.namespaceImports.push({ source, alias });
+    }
+  }
+
   /**
    * Adds a property to the `defineBackend({ ... })` call.
    */
@@ -122,6 +132,12 @@ export class BackendGenerator implements Planner {
             nodes.push(createImportDeclaration(imp.source, imp.identifiers));
           }
 
+          // Namespace imports (import * as X from 'source'), sorted by importOrder
+          const sortedNamespaceImports = [...this.namespaceImports].sort((a, b) => importOrder(a.source) - importOrder(b.source));
+          for (const ns of sortedNamespaceImports) {
+            nodes.push(createNamespaceImportDeclaration(ns.source, ns.alias));
+          }
+
           // Sort defineBackend properties: auth first, then data, storage, then functions
           const sortedProperties = [...this.defineBackendProperties].sort((a, b) => {
             const getName = (prop: ts.ObjectLiteralElementLike): string => {
@@ -186,6 +202,14 @@ function createImportDeclaration(source: string, identifiers: string[]): ts.Impo
   );
 }
 
+function createNamespaceImportDeclaration(source: string, alias: string): ts.ImportDeclaration {
+  return factory.createImportDeclaration(
+    undefined,
+    factory.createImportClause(false, undefined, factory.createNamespaceImport(factory.createIdentifier(alias))),
+    factory.createStringLiteral(source),
+  );
+}
+
 /**
  * Returns a numeric sort key for import source paths.
  *