feat: Enable the option to overwrite Webpack config by using 'elmapp.config.js' configuration file

Author: halfzebra

config/paths.js

@@ -15,6 +15,9 @@ const resolveApp = relativePath => path.resolve(appDirectory, relativePath);
 const explorer = cosmiconfig('elmapp');
 const result = explorer.searchSync(appDirectory);
 const config = result ? result.config : loadElmJson();
+const id = x => x;
+const configureWebpack =
+  typeof config.configureWebpack === 'function' ? config.configureWebpack : id;
 
 // WARNING:
 // We support config in elm.json only for legacy reasons.
@@ -76,5 +79,6 @@ module.exports = {
   elm: require.resolve('elm/bin/elm'),
   publicUrl: getPublicUrl(config),
   servedPath: getServedPath(config),
-  proxy: config.proxy
+  proxy: config.proxy,
+  configureWebpack
 };

scripts/build.js

@@ -94,7 +94,9 @@ function build(previousFileSizes) {
     console.log(`Creating an optimized ${process.env.NODE_ENV} build...`);
   }
 
-  const compiler = webpack(config);
+  const compiler = webpack(
+    paths.configureWebpack(config, process.env.NODE_ENV)
+  );
   return new Promise((resolve, reject) => {
     compiler.run((err, stats) => {
       if (err) {

scripts/start.js

@@ -160,7 +160,12 @@ choosePort(HOST, DEFAULT_PORT)
     const appName = path.basename(path.dirname(paths.elmJson));
     const urls = prepareUrls(protocol, HOST, port);
     // Create a webpack compiler that is configured with custom messages.
-    const compiler = createCompiler(webpack, config, appName, urls);
+    const compiler = createCompiler(
+      webpack,
+      paths.configureWebpack(config, process.env.NODE_ENV),
+      appName,
+      urls
+    );
     // Load proxy config
     const proxyConfig = prepareProxy(paths.proxy, paths.appPublic);
     // Serve webpack assets generated by the compiler over a web sever.