Fix build with/without npm ln, match scratch-gui

Match the versions of Webpack, Babel, and related plugins as used in
scratch-gui. That plus a few other tweaks means that this repository
builds the same with or without `npm ln scratch-gui`, and also means
that all syntax used in scratch-gui should build the same here.

electron-webpack.json5

@@ -1,4 +1,7 @@
 {
+    "main": {
+        "webpackConfig": "webpack.main.additions.js"
+    },
     "renderer": {
         "webpackConfig": "webpack.renderer.additions.js"
     }

package.json

@@ -14,12 +14,17 @@
     "source-map-support": "^0.5.9"
   },
   "devDependencies": {
+    "@babel/core": "^7.1.2",
     "@babel/plugin-proposal-object-rest-spread": "^7.0.0",
+    "@babel/plugin-syntax-dynamic-import": "^7.0.0",
+    "@babel/plugin-transform-async-to-generator": "^7.1.0",
+    "@babel/preset-env": "^7.1.0",
     "@babel/preset-react": "^7.0.0",
     "async": "^2.6.1",
-    "babel-eslint": "^10.0.0",
-    "babel-plugin-react-intl": "^3.0.1",
-    "copy-webpack-plugin": "^4.5.2",
+    "babel-eslint": "^10.0.1",
+    "babel-loader": "^8.0.4",
+    "babel-plugin-react-intl": "^2.3.1",
+    "copy-webpack-plugin": "^4.5.1",
     "electron": "^3.0.2",
     "electron-builder": "^20.28.1",
     "electron-devtools-installer": "^2.2.4",
@@ -35,7 +40,8 @@
     "react-redux": "5.0.7",
     "redux": "3.7.2",
     "scratch-gui": "0.1.0-prerelease.20180927141400",
-    "webpack": "^4.21.0"
+    "uglifyjs-webpack-plugin": "^1.2.5",
+    "webpack": "^4.6.0"
   },
   "resolutions": {
     "upath": "^1.0.5"

src/renderer/index.jsx

@@ -1,7 +1,7 @@
 import React from 'react';
 import ReactDOM from 'react-dom';
 
-import GUI, {AppStateHOC} from 'scratch-gui/dist/scratch-gui';
+import GUI, {AppStateHOC} from 'scratch-gui';
 import styles from 'scratch-gui/src/playground/index.css';
 
 // Register "base" page view

webpack.main.additions.js

@@ -0,0 +1,46 @@
+const UglifyJsPlugin = require('uglifyjs-webpack-plugin');
+
+const babelOptions = {
+    // Explicitly disable babelrc so we don't catch various config
+    // in much lower dependencies.
+    babelrc: false,
+    plugins: [
+        '@babel/plugin-syntax-dynamic-import',
+        '@babel/plugin-transform-async-to-generator',
+        '@babel/plugin-proposal-object-rest-spread'
+    ],
+    presets: [
+        ['@babel/preset-env', {targets: {electron: '3.0.2'}}]
+    ]
+};
+
+module.exports = {
+    devtool: 'cheap-module-source-map',
+    module: {
+        rules: [
+            // Override the *.js defaults from electron-webpack
+            // The test/include/exclude must match the defaults exactly for webpack-merge to do the override
+            {
+                test: /\.js$/,
+                exclude: /(node_modules|bower_components)/,
+                loader: 'babel-loader',
+                options: babelOptions
+            }
+        ]
+    },
+    optimization: {
+        // Use `--env.minify=false` to disable the UglifyJsPlugin instance automatically injected by electron-webpack.
+        // Otherwise it will do double-duty with this one.
+        minimizer: [new UglifyJsPlugin({
+            cache: true,
+            parallel: true,
+            sourceMap: true // disable this if UglifyJSPlugin takes too long and/or runs out of memory
+        })],
+        splitChunks: {
+            chunks: 'all'
+        }
+    },
+    resolve: {
+        symlinks: false
+    }
+};

webpack.renderer.additions.js

@@ -8,16 +8,16 @@ const babelOptions = {
     // in much lower dependencies.
     babelrc: false,
     plugins: [
-        '@babel/proposal-object-rest-spread',
-        // 'syntax-dynamic-import',
-        // 'transform-async-to-generator',
+        '@babel/plugin-syntax-dynamic-import',
+        '@babel/plugin-transform-async-to-generator',
+        '@babel/plugin-proposal-object-rest-spread',
         ['react-intl', {
             messagesDir: './translations/messages/'
         }]
     ],
     presets: [
-        ['@babel/env', {targets: {electron: '3.0.2'}}],
-        '@babel/react'
+        ['@babel/preset-env', {targets: {electron: '3.0.2'}}],
+        '@babel/preset-react'
     ]
 };
 
@@ -51,7 +51,7 @@ module.exports = {
         minimizer: [new UglifyJsPlugin({
             cache: true,
             parallel: true,
-            sourceMap: false // takes too long and runs out of memory :(
+            sourceMap: false // disable this if UglifyJSPlugin takes too long and/or runs out of memory
         })],
         splitChunks: {
             chunks: 'all'