Trying to augment a module causes @parcel/transformer-typescript-types to output a mostly blank .d.ts file

[astegmaier]

🐛 bug report

If you try to use the module augmentation feature of typescript in the context of a library project that is using @parcel/transformer-typescript-types to generate a .d.ts file, parcel will output an incorrect .d.ts file with many elements missing.

🎛 Configuration (.babelrc, package.json, cli command)

Create a library-original package with the following export:

export class Person {
    constructor(public name: string) {}
}

Build a library-augmenter package with parcel:

package.json

{
  "name": "library-augmenter",
  "types": "dist/index.d.ts",
  "source": "src/index.ts",
  "main": "dist/index.js",
  "scripts": {
    "build": "parcel build",
  },
  "dependencies": {
    "library-original": "1.0.0"
  },
  "devDependencies": {
    "@parcel/packager-ts": "^2.0.1",
    "@parcel/transformer-typescript-types": "^2.0.1",
    "parcel": "^2.0.1",
  }
}

src/index.ts

import { Person } from "library-original";
Person.prototype.greet = function() { return `Hello ${this.name}!` }

// This will be present in the .d.ts file generated by parcel:
export const anotherThing: string = "hello";

// This will get dropped:
declare module "library-original" {
  interface Person {
    greet(): string;
  }
}

// This will also get dropped, if the "declare module" statement above is present:
export const somethingElse: string = "goodbye";

🤔 Expected Behavior

Parcel should ouput a complete .d.ts file, similar to tsc:

export declare const anotherThing: string;
declare module "library-original" {
    interface Person {
        greet(): string;
    }
}
export declare const somethingElse: string;

😯 Current Behavior

Parcel outputs a .d.ts file that is missing both the module augmentation code and any other exports that are declared after it:

export const anotherThing: string;

💁 Possible Solution

It looks like we're doing some tree shaking of the .d.ts file in these lines, and we probably didn't account for this case.

parcel/packages/transformers/typescript-types/src/TSTypesTransformer.js

Lines 58 to 69 in 145bfb8

	let emitResult = program.emit(undefined, undefined, undefined, true, {
	afterDeclarations: [
	// 1. Build module graph
	context => sourceFile => {
	return collect(moduleGraph, context, sourceFile);
	},
	// 2. Tree shake and rename types
	context => sourceFile => {
	return shake(moduleGraph, context, sourceFile);
	},
	],
	});

🔦 Context

I was trying to help answer this question on stackoverflow

💻 Code Sample

See this repo for a reproduction of the issue.

🌍 Your Environment

Software	Version(s)
Parcel	2.0.1
Node	14.17.5
Yarn	1.22.15
Operating System	MacOS Monterey 12.0.1