code: function mixin(compiler) {
    compiler._comment = compiler.comment;
    compiler.map = new SourceMap();
    compiler.position = { line: 1, column: 1 };
    compiler.files = {};
    for (var k in exports) compiler[k] = exports[k];
  }
docs: Mixin source map support into `compiler`.
  
  @param {Compiler} compiler
  @api public