Function createTask

build-system/task-runner/amp-task-runner.js:211–242

* Helper that creates the tasks in AMP's toolchain based on the invocation: * - For `amp --help`, load all task descriptions so a list can be printed. * - For `amp --help`, load and print just the task description + flags. * - When a task is actually run, update root packages, load the ent

(
  taskName,
  taskFuncName = taskName,
  taskSourceFileName = taskName
)

 * @param {string=} taskSourceFileName
 */
function createTask(
  taskName,
  taskFuncName = taskName,
  taskSourceFileName = taskName
) {
  const isInvokedTask = argv._.includes(taskName); // `amp <task>`
  const isDefaultTask =
    argv._.length === 0 && taskName == 'default' && !isHelpTask; // `amp`

  if (isHelpTask) {
    const task = program.command(cyan(taskName));
    const description = getTaskDescription(taskSourceFileName, taskFuncName);
    task.description(description);
  }
  if (isInvokedTask || isDefaultTask) {
    startAtRepoRoot();
    ensureUpdatedPackages(taskSourceFileName);
    const taskFunc = getTaskFunc(taskSourceFileName, taskFuncName);
    const task = program.command(taskName, {isDefault: isDefaultTask});
    task.description(green(taskFunc.description));
    task.allowUnknownOption(); // Fall through to validateUsage()
    task.helpOption('--help', 'Print this list of flags');
    task.usage('<flags>');
    for (const [flag, description] of Object.entries(taskFunc.flags ?? {})) {
      task.option(`--${cyan(flag)}`, description);
    }
    task.action(async () => {
      validateUsage(task, taskName, taskFunc);
      await runTask(taskName, taskFunc);
    });
  }
}

/**
 * Validates usage by examining task and flag invocation.