title: sourceMap with sass-loader and postcss-loader in Webpack
body: <p>I'm trying to enable sourceMaps in webpack but there seems to be a problem with sass-loader and postcss-loader combination.</p>
  
  <p>With both sass-loader and postcss-loader enabled my console shows "no source":</p>
  
  <p><a href="https://i.stack.imgur.com/cVuSy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cVuSy.png" alt="nosource"></a></p>
  
  <p>But when I disable postcss-loader the sourceMap works fine and points to "typography" file:</p>
  
  <p><a href="https://i.stack.imgur.com/ZDM9h.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZDM9h.png" alt="typography"></a></p>
  
  <p><strong>webpack.config.js</strong></p>
  
  <pre><code>const path = require('path');
  const ExtractTextPlugin = require('extract-text-webpack-plugin');
  
  module.exports = {
      mode: 'development',
      entry: './src/index.js',
      output: {
          path: path.resolve(__dirname, 'dist'),
          publicPath: '/dist',
          filename: 'js/bundle.js',
      },
      devtool: 'inline-source-map',
      module: {
          rules: [{
                  test: /\.css$/i,
                  use: ExtractTextPlugin.extract({
                      fallback: 'style-loader',
                      use: ['css-loader', 'postcss-loader']
                  })
              },
              {
                  test: /\.scss$/i,
                  use: ExtractTextPlugin.extract({
                      fallback: 'style-loader',
                      use: [{
                              loader: 'css-loader',
                              options: {
                                  sourceMap: true
                              }
                          },
                          {
                              loader: 'postcss-loader',
                              options: {
                                  sourceMap: true
                              }
                          },
                          {
                              loader: 'sass-loader',
                              options: {
                                  sourceMap: true
                              }
                          }
                      ]
                  })
              },
              {
                  test: /\.js$/i,
                  exclude: /node_modules/,
                  loader: 'babel-loader'
              }
          ]
      },
      plugins: [
          new ExtractTextPlugin('css/style.css')
      ]
  };
  </code></pre>
  
  <p><strong>main.scss</strong></p>
  
  <pre><code>@import 'typography';
  </code></pre>
  
  <p><strong>typography.scss</strong></p>
  
  <pre><code>p {
      font-size: responsive 12px 18px;
  }
  </code></pre>