Add back in --stats output from webpack. (facebook#8790)

Author: samccone

packages/react-scripts/package.json

@@ -38,6 +38,7 @@
     "babel-loader": "8.1.0",
     "babel-plugin-named-asset-import": "^0.3.6",
     "babel-preset-react-app": "^9.1.2",
+    "bfj": "^7.0.2",
     "camelcase": "^5.3.1",
     "case-sensitive-paths-webpack-plugin": "2.3.0",
     "css-loader": "3.5.3",

packages/react-scripts/scripts/build.js

@@ -34,6 +34,7 @@ verifyTypeScriptSetup();
 const path = require('path');
 const chalk = require('react-dev-utils/chalk');
 const fs = require('fs-extra');
+const bfj = require('bfj');
 const webpack = require('webpack');
 const configFactory = require('../config/webpack.config');
 const paths = require('../config/paths');
@@ -59,6 +60,9 @@ if (!checkRequiredFiles([paths.appHtml, paths.appIndexJs])) {
   process.exit(1);
 }
 
+const argv = process.argv.slice(2);
+const writeStatsJson = argv.indexOf('--stats') !== -1;
+
 // Generate configuration
 const config = configFactory('production');
 
@@ -210,11 +214,20 @@ function build(previousFileSizes) {
         return reject(new Error(messages.warnings.join('\n\n')));
       }
 
-      return resolve({
+      const resolveArgs = {
         stats,
         previousFileSizes,
         warnings: messages.warnings,
-      });
+      };
+
+      if (writeStatsJson) {
+        return bfj
+          .write(paths.appBuild + '/bundle-stats.json', stats.toJson())
+          .then(() => resolve(resolveArgs))
+          .catch(error => reject(new Error(error)));
+      }
+
+      return resolve(resolveArgs);
     });
   });
 }