ts-alias-transformer

TypeScript AST transformer to resolve type aliases into fully formed interfaces

Blog post with more context.

Usage

• npm install -g ts-alias-transformer
• ts-alias-transformer -m [path to model root] -o [generated output]

Problem I'm trying to solve

I am using GraphQL at work and would like to add some type-safety around resolvers. Type safety in GQL is a bit weird to conceptualize, because resolvers are pretty dynamic by nature. Luckily I came across graphqlgen, which solved a lot of these problems I was having with its concept of models.

At work we run gRPC microservices, and GQL mostly serves as a nice fanout layer for our UI consumers. We already publish TypeScript interfaces that match our published proto contracts. I wanted to consume these types in graphqlgen, but ran into some issues due to type export support and with the way our TypeScript interfaces published (heavily namespaced, lots of references). Additionally, because graphqlgen is using babel-parser to do it's introspection and generation, it's quite limited as far as working with imported types (leads to parsing hell).

This repo is a mixture of me solving my narrow problem for work (and hopefully by extension graphqlgen), as well as demonstrating some of the power of the TypeScript compiler API. Utilizing the Checker API and a custom transformer, I was able to solve my problem without too much hassle.

Problem Visualized

// my_protos in node_modules
export namespace protos {
  export namespace user {
    export interface User {
      username: string;
      info: UserInfo;
    }
    
    export interface UserInfo {
      firstName: string;
      lastName: string;
    }
  }
  
  export namespace todo {
    export interface Todo {
      createdBy: protos.user.User;
      text: string;
    }
  }
}


// src/models.ts <-- models for graphqlgen (models returned from Query resolvers)
import { protos } from 'my_protos';

export type User = protos.user.User;
export type Todo = protos.todo.Todo;

// Run my program here pointing at src/models file

// generated/output.ts
export interface User {
  username: string;
  info: {
    firstName: string;
    lastName: string;
  }
}

export interface Todo {
  createdBy: {
    username: string;
    info: {
      firstName: string;
      lastName: string;
    }
  },
  text: string;
}