Remove resolve: { symlinks: false }, fix fallout

Turning off symlink resolution in webpack was a quick fix but
complicates things by making webpack act less like Node.js than it
otherwise would. This change restores default symlink resolution
behavior for webpack, which matches Node.

In order to make Babel work with `npm link`ed modules even when symlink
resolution is enabled, the include paths for `babel-loader` are now
being run through `fs.realpathSync`.

Author: Christopher Willis-Ford

webpack.config.js

@@ -1,8 +1,27 @@
 var CopyWebpackPlugin = require('copy-webpack-plugin');
 var defaultsDeep = require('lodash.defaultsdeep');
+var fs = require('fs');
 var path = require('path');
 var webpack = require('webpack');
 
+/**
+ * Resolve a babel plugin or preset to a real path, resolving symlinks the way that Node.js would.
+ * Helps work around the differences between webpack's module lookup and Node's when `npm link` is in use.
+ * @param {string} prefix - 'babel-plugin' for a plugin, 'babel-preset' for a preset, etc.
+ * @param {string|Array} item - either a plugin/preset name or path or an array with such a string at index 0.
+ * @returns {string|Array} - the same type as `item` but the name/path will be replaced with an absolute path.
+ */
+const babelRealPath = function (prefix, item) {
+    if (typeof item === 'string') {
+        if (item.indexOf(prefix) !== 0) {
+            item = [prefix, item].join('-');
+        }
+        return fs.realpathSync(require.resolve(item));
+    }
+    item[0] = babelRealPath(prefix, item[0]);
+    return item;
+};
+
 var base = {
     devServer: {
         contentBase: false,
@@ -18,11 +37,13 @@ var base = {
                     path.resolve(__dirname, 'node_modules', 'scratch-render', 'src'),
                     path.resolve(__dirname, 'node_modules', 'scratch-storage', 'src'),
                     path.resolve(__dirname, 'src')
-                ],
+                ].map(x => fs.realpathSync(x)),
                 test: /\.js$/,
                 loader: 'babel-loader',
                 options: {
-                    presets: ['es2015']
+                    presets: [
+                        'es2015'
+                    ].map(x => babelRealPath('babel-preset', x))
                 }
             }
         ]
@@ -32,10 +53,7 @@ var base = {
             include: /\.min\.js$/,
             minimize: true
         })
-    ],
-    resolve: {
-        symlinks: false
-    }
+    ]
 };
 
 module.exports = [
@@ -102,15 +120,15 @@ module.exports = [
                     loader: 'expose-loader?Blockly'
                 },
                 {
-                    test: path.resolve(__dirname, 'node_modules', 'scratch-audio', 'src', 'index.js'),
+                    test: require.resolve('scratch-audio'),
                     loader: 'expose-loader?AudioEngine'
                 },
                 {
-                    test: path.resolve(__dirname, 'node_modules', 'scratch-render', 'src', 'index.js'),
+                    test: require.resolve('scratch-render'),
                     loader: 'expose-loader?RenderWebGL'
                 },
                 {
-                    test: path.resolve(__dirname, 'node_modules', 'scratch-storage', 'src', 'index.js'),
+                    test: require.resolve('scratch-storage'),
                     loader: 'expose-loader?Scratch.Storage'
                 }
             ])