code: function(nodePath) {
          createdGlobals = {};
          filenameNoExtCache = null;
  
          var node = nodePath.node;
          var contents = node.body;
          node.body = [t.expressionStatement(t.callExpression(
            t.memberExpression(
              t.functionExpression(null, [], t.blockStatement(contents)),
              t.identifier('call'),
              false
            ),
            [t.identifier('this')]
          ))];
        }
docs: Wraps the program body in a closure, protecting local variables.
  @param {!NodePath} nodePath