Tree shaking completely broken?

updated with the latest versions (29.06.2017) Webpack - 3.0.0 Babel-preset-env - 1.5.2 Node - 8.1.2 OS X - 10.12.5

Current

Tree shaking is not removing imports, not used in the app.

Expected

Tree shaking, removing not used imports.

---

The test case is a simple app with React & React Router v4. Link component is not used, but the whole router package is bundled.

import React from 'react'
import ReactDOM from 'react-dom'
import { Link } from 'react-router-dom'

ReactDOM.render(
  <p>Hey</p>,
  document.getElementById('app')
)

Webpack & Rollup test repo

[danbucholtz]

Tree shaking should occur independently from minification/dead code removal IMO if possible. Otherwise it really doesn’t rely on Webpack, it relies on a different 3rd party tool.

For example, when I run Rollup to produce a bundle, it’s tree shaken without any sort of minification or dead code removal.

This is important for the Ionic Framework team because in order to support Webpack, Closure Compiler and Rollup independently, we run minification/dead code removal as a separate step independent from the bundling process.

Thanks, Dan

[TheLarkInn]

Thank you everyone for keeping this issue up to date. I have to apologize for not communicating the update on how we plan to tackle this issue.

So after we have finished our 2.3 regression milestone for bugfixes for webpack 2(.2) final, we start on features.

Therefore I’m going to add this to our feature milestone.

So tl;dr https://github.com/mishoo/UglifyJS2/issues/1261 is the biggest hurdle on solving this problem. So we either have to:

See if implement scope hoisting (rollup features) or build a new general purpose optimizer that supports a level of program flow analysis.

We would really appreciate as much brainstorming as possible to how we could solve this.