title: webpack source maps are anonymous
body: <p>I am attempting to use the <code>devtool</code> feature of <a href="http://webpack.github.io/docs/" rel="nofollow">webpack</a>, I have set up my configuration like so:</p>
  
  <pre><code>{
      devtool: 'eval-source-map'
  }
  </code></pre>
  
  <p>This appears to work fine and I can see that my source code is being wrapped within <code>eval()</code> functions and that a base64 source map is appended to the end.</p>
  
  <p>However my errors are not being mapped to the source (Chrome developer tools), instead I am getting errors like the following: </p>
  
  <pre><code>ReferenceError: _ is not defined
      at eval (eval at &lt;anonymous&gt; (http://localhost:8080/build/abc.js:78:2), &lt;anonymous&gt;:125:21)
  </code></pre>
  
  <p>Where <code>abc.js</code> is the name of my built and concatenated file. Clicking the error to the view the source just takes me to the <code>eval</code> function like so:</p>
  
  <pre><code>eval("var __WEBPACK_AMD_DEFINE_RESULT__;!(__WEBPACK_AMD_DEFINE_RESULT__ = (function() {\n  /** @type {angular.Module} */\n  return angular.module('utils', []);\n}.call(exports, __webpack_require__, exports, module)), __WEBPACK_AMD_DEFINE_RESULT__ !== undefined &amp;&amp; (module.exports = __WEBPACK_AMD_DEFINE_RESULT__));\n\n// Load exports\n__webpack_require__(6);\n//@ sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbIi4vbW9kdWxlcy91dGlscy9zcmMvbW9kdWxlLmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJrQ0FBQTtBQUNBLGFBQWEsZUFBZTtBQUM1QjtBQUNBLENBQUM7O0FBRUQ7QUFDQSIsInNvdXJjZXNDb250ZW50IjpbImRlZmluZShmdW5jdGlvbigpIHtcbiAgLyoqIEB0eXBlIHthbmd1bGFyLk1vZHVsZX0gKi9cbiAgcmV0dXJuIGFuZ3VsYXIubW9kdWxlKCd1dGlscycsIFtdKTtcbn0pO1xuXG4vLyBMb2FkIGV4cG9ydHNcbnJlcXVpcmUoJy4vZXhwb3J0cy9jb3JlJyk7XG4iXSwic291cmNlUm9vdCI6IndlYnBhY2stbW9kdWxlOi8vIn0=");
  </code></pre>
  
  <p>If I decode the base64 I can see that the source maps it is generating appear to be valid:</p>
  
  <pre><code>{  
     "version":3,
     "sources":[  
        "./modules/utils/src/module.js"
     ],
     "names":[  
  
     ],
     "mappings":"kCAAA;AACA,aAAa,eAAe;AAC5B;AACA,CAAC;;AAED;AACA",
     "sourcesContent":[  
        "define(function() {\n  /** @type {angular.Module} */\n  return angular.module('utils', []);\n});\n\n// Load exports\nrequire('./exports/core');\n"
     ],
     "sourceRoot":"webpack-module://"
  }
  </code></pre>
  
  <p>Does anyone know why these source maps don't appear to be working? The webpack documentation is still a bit ambiguous in areas.</p>
  
  <p>Please not I am only using <code>eval-source-map</code> in development and a seperate map file is generated for production (which also does not work).</p>