Function validateUsage

build-system/task-runner/amp-task-runner.js:250–262

* Validates usage by examining task and flag invocation. * @param {object} task * @param {string} taskName * @param {TaskFuncDef} taskFunc

(task, taskName, taskFunc)

 * @param {TaskFuncDef} taskFunc
 */
function validateUsage(task, taskName, taskFunc) {
  const tasks = argv._;
  const invalidTasks = tasks.filter((task) => task != taskName);

  const flags = Object.keys(argv).slice(1); // Everything after '_'
  const validFlags = taskFunc.flags ? Object.keys(taskFunc.flags) : [];
  const invalidFlags = flags.filter((flag) => !validFlags.includes(flag));

  if (invalidTasks.length > 0 || invalidFlags.length > 0) {
    task.addHelpText('before', red('ERROR: ') + 'Invalid usage');
    task.help({error: true});
  }
}

/**
 * Finalizes the task runner by doing special-case setup for `amp --help`,