Summary

When using our built-in schema with zod, developers can infer the types with type SqsEvent = z.infer<typeof SqsSchema> and use it in their Lambda handler. Another popular option is to use @types/aws-lambda package wich has 3M downloads per week. We need to make sure that both types are compatible, so there is no confusion or unexpected behaviour.

Why is this needed?

If either @types/aws-lambda or our schema is updated, we want to have a reliable test to verify that they are both compatible and if not to fix one them.

Which area does this relate to?

Parser

Solution

I have checked the first idea that worked:

import { z } from 'zod';
import { ALBEvent, APIGatewayProxyEvent } from 'aws-lambda';
import { AlbSchema } from '../../src/schemas/alb';
import { APIGatewayProxyEventSchema } from '../../src/schemas/apigw';

type AlbType = z.infer<typeof AlbSchema>;
type ApiGatewayType = z.infer<typeof APIGatewayProxyEventSchema>;
describe('Types compatibility', () => {
  it('ALBEvent types are compatible', () => {
    // These functions will fail to compile if A and B are not structurally identical
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    const A = (value: AlbType): ALBEvent => value;
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    const B = (value: ALBEvent): AlbType => value;
  });

  it('ApiGatewayEvent types are compatible', () => {
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    const A = (value: ApiGatewayType): APIGatewayProxyEvent => value;
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    const B = (value: APIGatewayProxyEvent): ApiGatewayType => value;
  });
});

The compiler will fail if the structure does not match and will tell exactly which properties are not compatible.

Alternatively research more about https://github.com/fabien0102/ts-to-zod. If we can convert @types/aws-lambda to schemas, we might directly compare the schemas to find the differences.

Acknowledgment

• This request meets Powertools for AWS Lambda (TypeScript) Tenets
• Should this be considered in other Powertools for AWS Lambda languages? i.e. Python, Java, and .NET

Future readers

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