title: Symfony Webpack: Could not find the entrypoints file from Webpack
body: <p>A relatively fresh Symfony 4.1.7 project after installing Webpack Encore throws the error</p>
  
  <blockquote>
    <p>An exception has been thrown during the rendering of a template
    ("Could not find the entrypoints file from Webpack: the file
    ".../public/build/entrypoints.json" does not exist.")</p>
  </blockquote>
  
  <p>where the template includes
  <code>{{ encore_entry_link_tags('app') }}</code>
  when launching <code>http://127.0.0.1:8000/</code></p>
  
  <p>What have I missed?</p>
  
  <pre><code>$ yarn encore dev
  Running webpack ...
  
   DONE  Compiled successfully in 1974ms
  
   I  3 files written to public\build
  Done in 3.33s.
  </code></pre>
  
  <p><code>.../public/build</code> contains </p>
  
  <pre><code>app.css
  app.js
  manifest.json
  </code></pre>
  
  <p>local Symfony versions:</p>
  
  <pre><code>symfony/webpack-encore-bundle       v1.0.0
  symfony/webpack-encore-pack         v1.0.3
  </code></pre>
  
  <p>webpack.config.js:</p>
  
  <pre><code>var Encore = require('@symfony/webpack-encore');
  
  Encore
      // the project directory where compiled assets will be stored
      .setOutputPath('public/build/')
      // the public path used by the web server to access the previous directory
      .setPublicPath('/build')
      .cleanupOutputBeforeBuild()
      .enableSourceMaps(!Encore.isProduction())
      // uncomment to create hashed filenames (e.g. app.abc123.css)
      // .enableVersioning(Encore.isProduction())
  
      // uncomment to define the assets of the project
      .addEntry('app', './assets/js/app.js')
  //     .addEntry('js/app', './assets/js/app.js')
  //     .addStyleEntry('css/app')
  //     .addStyleEntry('css/app', './assets/css/app.scss')
  
      // uncomment if you use Sass/SCSS files
      // .enableSassLoader()
  
      // uncomment for legacy applications that require $/jQuery as a global variable
       .autoProvidejQuery()
  ;
  
  module.exports = Encore.getWebpackConfig();
  </code></pre>