Parcel v2.12.0 is very slow while building ts [HIGHLY CRITICAL]

[iamyoki]

I've created a repo to reproduce this problem https://github.com/iamyoki/try-parcel.

By controlling the variable method, it can be determined that 2.12.0 will be hundreds of times slower than previous versions when building ts.

🐛 bug report

parcel watch is very slow while building ts while types being generated. It only slows on version 2.12.0, not 2.11.0 or lower. It only slows when "types": "dist/index.d.ts" configured. But even types not being configured, version 2.12.0 is slower than 2.11.0.

The below demo shows a very basic and simplified ts package.

You can clone my repo to reproduce, source code in https://github.com/iamyoki/try-parcel/tree/main/parcel-2.12.0-ts

The below demo shows the same code and config but in version 2.11.0, very fast, working perfectly.

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

{
  "name": "parcel-2.12.0-ts",
  "version": "1.0.0",
  "description": "",
  "main": "dist/index.js",
  "types": "dist/index.d.ts",
  "source": "src/index.ts",
  "scripts": {
    "dev": "parcel watch"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "packageManager": "[email protected]+sha512.0a203ffaed5a3f63242cd064c8fb5892366c103e328079318f78062f24ea8c9d50bc6a47aa3567cabefd824d170e78fa2745ed1f16b132e16436146b7688f19b",
  "devDependencies": {
    "@parcel/packager-ts": "2.12.0",
    "@parcel/transformer-typescript-types": "2.12.0",
    "parcel": "^2.12.0",
    "typescript": ">=3.0.0"
  }
}

🤔 Expected Behavior

v2.12.0 should as fast as v2.11.0. Under 10ms per build (caching) should be good.

😯 Current Behavior

200-400ms per build.

💁 Possible Solution

I was able to determine that the build was slow due to the types generation.

Maybe "@parcel/transformer-typescript-types" ?
Maybe "@parcel/packager-ts"?

🔦 Context

Full comparison see https://github.com/iamyoki/try-parcel

Build time comparison

My env:

env	version
os	macos 14
pnpm	9.11
node	20.17
parcel	2.12.0 vs 2.11.0

My results:

parcel watch (with cache, hmr on), cmd+s source file.

project	parcel version	build time
ts	2.12.0	200-300ms
ts	2.11.0	2-8ms
js	2.12.0	10-20ms
react	2.12.0	10-15ms
react	2.11.0	2-8ms

💻 Code Sample

https://github.com/iamyoki/try-parcel

🌍 Your Environment

Software	Version(s)
Parcel	2.12.0
Node	20.17.0
npm/Yarn	9.10.0
Operating System	macos 14