Solution

{
  "presets": [
    "@babel/preset-typescript"
  ],
  "plugins": [
    [
      "@babel/plugin-proposal-decorators",
      {
        "legacy": true
      }
    ]
  ]
}

Original Issue

As of 1.48.0, lambda functions with decorators are broken.

Error: Failed to run bundling Docker image for asset cognito/customMessage/Code/Stage: Error: [Status 1] stdout: Building custom-message.ts...

SyntaxError: Support for the experimental syntax 'decorators-legacy' isn't currently enabled

Reproduction Steps

If it’s not a repro, what the hell is repro?

• custom-message.ts

import * as lambda from 'aws-lambda'
import { boundMethod } from 'autobind-decorator'

type TEvent = lambda.CognitoUserPoolTriggerEvent

/**
 * [UserPool Lambda Triggers](https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-lambda-custom-message.html)
 */
class CustomMessageHandler {
  constructor(/* ...dependencies */) {
    // ...
  }
  
  @boundMethod
  public async handle(event: TEvent): Promise<TEvent> {
    switch (event.triggerSource) {
      case 'CustomMessage_SignUp':
        return this.handleSignUp(event)
      case 'CustomMessage_ResendCode':
        return this.handleResendCode(event)
      case 'CustomMessage_ForgotPassword':
        return this.handleForgotPassword(event)
      default:
        throw new Error('Unhandled Trigger')
    }
  }

  ...

  @boundMethod
  protected async handleForgotPassword(event: TEvent): Promise<TEvent> {
    const givenName = event.request.userAttributes['given_name']
    const familyName = event.request.userAttributes['family_name']

    event.response = {
      ...event.response,
      emailSubject: 'Confirmation Code for Forgot Password',
      emailMessage: `
      <div>
        <p>Dear ${givenName} ${familyName},</p>
        <br/>
        <p>Confirmation Code is:</p>
        <p>${event.request.codeParameter}</p>
        <br/>
        <p>Thank you!</p>
      </div>
      `,
    }
    return event
  }
}

export const handle = new CustomMessageHandler(/* ...dependencies */).handle

• stack.ts

import * as cognito from '@aws-cdk/aws-cognito'
import * as lambda from '@aws-cdk/aws-lambda-nodejs'
import * as path from 'path'

const userPool = new cognito.UserPool(this, 'userPool', {
  ...,
  lambdaTriggers: {
    customMessage: new lambda.NodejsFunction(this, 'customMessage', {
      entry: path.resolve(__dirname, 'custom-message.ts'),
      handler: 'handle',
    }),
  },
}

Error Log

$ cdk synth

Error: Failed to run bundling Docker image for asset cognito/customMessage/Code/Stage: Error: [Status 1] stdout: Building custom-message.ts...
🚨 Build failed.


stderr: @parcel/transformer-babel: Support for the experimental syntax 'decorators-legacy' isn't currently enabled (11:3):
SyntaxError: Support for the experimental syntax 'decorators-legacy' isn't currently enabled (11:3):
    at Object._raise (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:757:17)
    at Object.raiseWithData (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:750:17)
    at Object.expectOnePlugin (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:8849:18)
    at Object.parseDecorator (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:11385:10)
    at /usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:11995:32
    at Object.withTopicForbiddingContext (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:11078:14)
    at Object.parseClassBody (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:11984:10)
    at Object.parseClass (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:11958:22)
    at Object.parseStatementContent (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:11245:21)
    at Object.parseStatementContent (/usr/local/share/.config/yarn/global/node_modules/@babel/parser/lib/index.js:6585:18)
/asset-input/packages/.../lib/cognito/custom-message.ts:11:2
  10 | class CustomMessageHandler {
> 11 |   @boundMethod
>    |  ^
  12 |   public async handle(event: TEvent): Promise<TEvent> {
  13 |     switch (event.triggerSource) {
    at AssetStaging.bundle (/Users/civilizeddev/GitHub/.../node_modules/@aws-cdk/core/lib/asset-staging.ts:182:13)
    at new AssetStaging (/Users/civilizeddev/GitHub/.../node_modules/@aws-cdk/core/lib/asset-staging.ts:92:29)
    at new Asset (/Users/civilizeddev/GitHub/.../node_modules/@aws-cdk/aws-s3-assets/lib/asset.ts:117:21)
    at AssetCode.bind (/Users/civilizeddev/GitHub/.../node_modules/@aws-cdk/aws-lambda/lib/code.ts:180:20)
    at new Function (/Users/civilizeddev/GitHub/.../node_modules/@aws-cdk/aws-lambda/lib/function.ts:502:29)
    at new NodejsFunction (/Users/civilizeddev/GitHub/.../node_modules/@aws-cdk/aws-lambda-nodejs/lib/function.ts:62:7)
    at CognitoStack.get userPool (/Users/civilizeddev/GitHub/.../lib/cognito/index.ts:23:24)
Subprocess exited with error 1
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Environment

• CLI Version : aws-cli/2.0.27 Python/3.8.3 Darwin/19.5.0 botocore/2.0.0dev31
• Framework Version: 1.49.1, 1.49.0, 1.48.0
• Node.js Version: 14.5.0
• OS : macos 10.15.5
• Language (Version): TypeScript (3.9.6)

Other

• Parcel 2 should require less manual configuration of Babel to build Typescript (with decorators)

---

This is 🐛 Bug Report