Build introduces overlapping variable names

[zawys]

🐛 Bug report

parcel build produces invalid JS.

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

.babelrc: not present

package.json:

{
  "name": "parcel_minification_bug_demo",
  "version": "1",
  "main": "dist/extension.js",
  "targets": {
    "main": {
      "includeNodeModules": {
        "vscode": false
      }
    }
  },
  "scripts": {
    "clean": "rm -rf out packages dist .parcel-cache",
    "bundle": "parcel build --target main --no-cache --no-optimize src/extension.ts",
    "build": "yarn run clean && yarn run bundle"
  },
  "devDependencies": {
    "@parcel/transformer-typescript-tsc": "^2.0.0-nightly.599",
    "@types/vscode": "^1.48.0",
    "parcel": "^2.0.0-nightly.597",
    "typescript": "^4.0.2"
  },
  "dependencies": {}
}

.parcelrc:

{
  "extends": "@parcel/config-default",
  "transformers": {
    "*.{ts,tsx}": ["@parcel/transformer-typescript-tsc"]
  }
}

src/extension.ts

import * as vscode from "vscode";

export function register(): void {
  const commands: any[] = [];
  for (const x of commands) {
    vscode.commands.registerCommand("", () => { });
  }
}

CLI command: yarn run build

🤔 Expected behavior

Working code.

😯 Current behavior

Following is produced in dist/extension.js:

var commands = require("vscode").commands;
function register() {
  var commands = [];
  for (var _i = 0, commands_1 = commands; _i < commands_1.length; _i++) {
    var x = commands_1[_i];
    commands.registerCommand("", function () {});
  }
}
exports.register = register;

//# sourceMappingURL=extension.js.map

The import commands is overlapped by the variable in the function while the TypeScript code is valid. This causes an exception at runtime (undefined is no function).

🔦 Context

I can reproduce the bug with parcel 2.0.0-beta.1 and @parcel/transformer-typescript-tsc 2.0.0-nightly.1. However, the code worked previously so it might be due to a change in a dependency of parcel.

💻 Code sample

See above and parcel_bug_demo.zip (contains the files above + yarn.lock).

🌍 Your Environment

Software	Version(s)
Parcel	2.0.0-nightly.597
Node	14.15.4
npm/Yarn	Yarn 1.22.5
Operating System	Fedora 33

🔗 Possibly related issues

#5746 #5657 #5091

[zawys]

From a developer perspective, a workaround would be to avoid star imports and instead choose explicitly what to import (import { commands } from "vscode";). Then no latent variables are introduced during build for that.

[devongovett]

I don't think this should be an issue anymore in beta 3 and later