fix(client): add cache-busting hashes to chunks (#37746)

* fix(client): add cache-busting hashes to chunks

* fix: create cache-busting names for the workers

Prior to this PR the first webpack compilation gave the workers static
names.  This can cause caching problems, so this PR adds hashes to
their names to invalidate the cache.

In order for Gatsby to find them, the names are added to the
config directory.

client/.gitignore

@@ -4,6 +4,9 @@ node_modules
 yarn-error.log
 
 config/env.json
+config/frame-runner.json
+config/sass-compile.json
+config/test-evaluator.json
 
 # Build directory
 /public

client/src/templates/Challenges/rechallenge/transformers.js

@@ -18,6 +18,10 @@ import protect from 'loop-protect';
 import * as vinyl from '../utils/polyvinyl.js';
 import createWorker from '../utils/worker-executor';
 
+// the config files are created during the build, but not before linting
+// eslint-disable-next-line import/no-unresolved
+import { filename as sassCompile } from '../../../../config/sass-compile';
+
 const protectTimeout = 100;
 Babel.registerPlugin('loopProtection', protect(protectTimeout));
 
@@ -89,7 +93,7 @@ export const babelTransformer = cond([
   [stubTrue, identity]
 ]);
 
-const sassWorker = createWorker('sass-compile');
+const sassWorker = createWorker(sassCompile);
 async function transformSASS(element) {
   const styleTags = element.querySelectorAll('style[type="text/sass"]');
   await Promise.all(

client/src/templates/Challenges/utils/build.js

@@ -8,9 +8,15 @@ import {
   createMainFramer
 } from './frame';
 
+// the config files are created during the build, but not before linting
+// eslint-disable-next-line import/no-unresolved
+import { filename as runner } from '../../../../config/frame-runner';
+// eslint-disable-next-line import/no-unresolved
+import { filename as testEvaluator } from '../../../../config/test-evaluator';
+
 const frameRunner = [
   {
-    src: '/js/frame-runner.js'
+    src: `/js/${runner}.js`
   }
 ];
 
@@ -91,7 +97,7 @@ export function getTestRunner(buildData, proxyLogger, document) {
 function getJSTestRunner({ build, sources }, proxyLogger) {
   const code = sources && 'index' in sources ? sources['index'] : '';
 
-  const testWorker = createWorker('test-evaluator', { terminateWorker: true });
+  const testWorker = createWorker(testEvaluator, { terminateWorker: true });
 
   return (testString, testTimeout) => {
     return testWorker

client/webpack-workers.js

@@ -1,8 +1,11 @@
 const path = require('path');
 const CopyWebpackPlugin = require('copy-webpack-plugin');
+const { writeFileSync } = require('fs');
 
 module.exports = (env = {}) => {
   const __DEV__ = env.production !== true;
+  const staticPath = path.join(__dirname, './static/js');
+  const configPath = path.join(__dirname, './config');
   return {
     mode: __DEV__ ? 'development' : 'production',
     entry: {
@@ -13,8 +16,18 @@ module.exports = (env = {}) => {
     devtool: __DEV__ ? 'inline-source-map' : 'source-map',
     output: {
       publicPath: '/js/',
-      chunkFilename: '[name].js',
+      filename: chunkData => {
-      path: path.join(__dirname, './static/js')
+        // construct and output the filename here, so the client can use the
+        // json to find the file.
+        const filename = `${chunkData.chunk.name}.${chunkData.chunk.contentHash.javascript}`;
+        writeFileSync(
+          path.join(configPath, `${chunkData.chunk.name}.json`),
+          `{"filename": "${filename}"}`
+        );
+        return filename + '.js';
+      },
+      chunkFilename: '[name].[contenthash].js',
+      path: staticPath
     },
     stats: {
       // Display bailout reasons

curriculum/test/test-challenges.js

@@ -49,6 +49,8 @@ const {
   createPoly
 } = require('../../client/src/templates/Challenges/utils/polyvinyl');
 
+const testEvaluator = require('../../client/config/test-evaluator').filename;
+
 const oldRunnerFail = Mocha.Runner.prototype.fail;
 Mocha.Runner.prototype.fail = function(test, err) {
   if (err instanceof AssertionError) {
@@ -327,7 +329,7 @@ async function createTestRunnerForJSChallenge({ files }, solution) {
   const { build, sources } = await buildJSChallenge({ files });
   const code = sources && 'index' in sources ? sources['index'] : '';
 
-  const testWorker = createWorker('test-evaluator', { terminateWorker: true });
+  const testWorker = createWorker(testEvaluator, { terminateWorker: true });
   return async ({ text, testString }) => {
     try {
       const { pass, err } = await testWorker.execute(