Switch to terser-webpack-plugin

[edmorley]

Since the webpack 4 default of uglifyjs-webpack-plugin uses uglify-es, which has been deprecated in favour of terser. webpack 5 is due to use terser-webpack-plugin, at which point we can remove this.

terser includes multiple correctness and performance fixes not present in uglify-es.

Fixes #1146.

[edmorley]

I've intentionally removed this reference to babel-minify-webpack-plugin, since it's still virtually unmaintained/buggy/slow. If that changes in the future we can re-add.

[eliperelman]

LGTM!

[edmorley]

I was thinking about this PR some more today. Since we manually configure terser-webpack-plugin, we have to choose whether to set sourceMaps to true/false. This is fine if people use the in-built web preset devtool option, however for Neutrino 8 upgraders it's likely they may have:

module.exports = {
  use: [
    ['@neutrinojs/react', {
      // ...
    }],
    (neutrino) => {
      if (process.env.NODE_ENV === 'production') {
        neutrino.config.devtool('source-map');
      }
    },
  ]
};

In this case, we'll pass sourceMaps: false to terser-webpack-plugin.

The only thing I think we can do, is to perhaps add a warning (or throw) in the webpack() handler, like we do for the vendor entrypoint check, which checks whether devtool and sourceMap are out of sync (if the terser plugin found).

@eliperelman, thoughts?

[eliperelman]

@edmorley I think that solution will work, but we should probably use a warning since it may be desired by the user to have them out of sync for some reason.

[edmorley]

I've updated the PR:

• rebased on master's webpack-chain v5 upgrade
• added a check for misconfiguration in handlers.js (see comment there for why throwing rather than a console.error())
• added migration guide changes