CSS sourcemap using Extract Text Plugin /CSS-loader Webpack

Question

I am trying to generate a css sourcemap from webpack. However, currently the css.map file that is generate is largely empty.

{"version":3,"sources":[],"names":[],"mappings":"","file":"si-styles.css","sourceRoot":""}

I understand that I need to add something similar to the below

css-loader?sourceMap

But I am unsure how I chain this with importLoaders = 1, which I currently have within my webpack.config.js.

const webpack = require('webpack');
const path = require('path');
//post css
var precss       = require('precss');
var autoprefixer = require('autoprefixer');
var ExtractTextPlugin = require("extract-text-webpack-plugin");
var postcssImport = require('postcss-import');

module.exports = {

  context: __dirname + '/frontend',
  devtool: 'source-map',
  entry: "./index.js",
  output: {
    filename: 'bundle.js',
    path: path.join(__dirname, './static')
},
  module: {
    loaders: [
      {
        test: /\.js$/,
        loader: 'babel',
        exclude: /node_modules/,
        query: {
          presets: ['es2015']
        }
      },
      {
        test:   /\.css$/,
        loader: ExtractTextPlugin.extract('style-loader', '!css-loader?importLoaders=1!postcss-loader')
      }
    ]
  },
  plugins: [
    new ExtractTextPlugin("si-styles.css")
  ],
  // postcss: [
  //             precss,
  //             autoprefixer({ browsers: ['last 2 versions']  })
  // ]
   postcss: function(webpack) {
        return [
            postcssImport({ addDependencyTo: webpack }), // Must be first item in list
            precss,
            autoprefixer({ browsers: ['last 2 versions']  })
        ];
    },

}

Answer 1

I just found an example with the correct way to do this. I have used '&' to chain together ie

 {
    test:   /\.css$/,
    loader: ExtractTextPlugin.extract('style-loader', '!css-loader?sourceMap&importLoaders=1!postcss-loader')
  }