code: function renameFunctionName(ast, oldName, newName) {
    // Summary:
    //  Rename the name of the function first found. Usually used by
    //  flat function definition file.
  
    let defNode = null;
    // Find the definition node of the class
    traverse(ast, {
      FunctionDeclaration(path) {
        if (path.node.id && path.node.id.name === oldName) {
          defNode = path.node.id;
        }
      }
    });
  
    if (defNode) {
      return identifier.renameIdentifier(ast, oldName, newName, defNode);
    }
    return [];
  }
docs: Rename a function name in a module.
  @param {string} ast - Which module to rename function.
  @param {string} oldName - The old function name.
  @index {number} newName - The new function name.
  @alias module:refactor.renameFunctionName
  @example
  // function MyFunc() {
  //   ...
  // }
  const refactor = require('rekit-core').refactor;
  refactor.renameFunctionName(file, 'MyFunc', 'NewMyFunc');
  // => function NewMyFunc {
  // =>   ...
  // => }