func EnsureDirectoryExists(path string) (action.Action, error) {
	// Check whether the directory exists already.
	task := fmt.Sprintf("Check whether '%v' exists and is a directory", path)
	info, err := os.Stat(path)
	if err != nil {
		if !os.IsNotExist(err) {
			return nil, errs.NewError(task, err)
		}
	} else {
		// In case the path exists, make sure it is a directory.
		if !info.IsDir() {
			return nil, errs.NewError(task, errors.New("not a directory: "+path))
		}
		// We are done.
		return action.Noop, nil
	}

	// Now we know that path does not exist, so we need to create it.
	createTask := fmt.Sprintf("Create directory '%v'", path)
	log.Run(createTask)
	if err := os.MkdirAll(path, 0755); err != nil {
		return nil, errs.NewError(createTask, err)
	}

	return action.ActionFunc(func() error {
		log.Rollback(createTask)
		task := fmt.Sprintf("Remove directory '%v'", path)
		if err := os.RemoveAll(path); err != nil {
			return errs.NewError(task, err)
		}
		return nil
	}), nil
}

func (tool *codeReviewTool) FinaliseRelease(v *version.Version) (action.Action, error) {
	// Get a GitHub client.
	config, err := LoadConfig()
	if err != nil {
		return nil, err
	}
	client := ghutil.NewClient(config.Token())

	owner, repo, err := git.ParseUpstreamURL()
	if err != nil {
		return nil, err
	}

	// Get the relevant review milestone.
	releaseString := v.BaseString()
	task := fmt.Sprintf("Get GitHub review milestone for release %v", releaseString)
	log.Run(task)
	milestone, err := milestoneForVersion(config, owner, repo, v)
	if err != nil {
		return nil, errs.NewError(task, err)
	}
	if milestone == nil {
		log.Warn(fmt.Sprintf(
			"Weird, GitHub review milestone for release %v not found", releaseString))
		return nil, nil
	}

	// Close the milestone unless there are some issues open.
	task = fmt.Sprintf(
		"Make sure the review milestone for release %v can be closed", releaseString)
	if num := *milestone.OpenIssues; num != 0 {
		return nil, errs.NewError(
			task,
			fmt.Errorf(
				"review milestone for release %v cannot be closed: %v issue(s) open",
				releaseString, num))
	}

	milestoneTask := fmt.Sprintf("Close GitHub review milestone for release %v", releaseString)
	log.Run(milestoneTask)
	milestone, _, err = client.Issues.EditMilestone(owner, repo, *milestone.Number, &github.Milestone{
		State: github.String("closed"),
	})
	if err != nil {
		return nil, errs.NewError(milestoneTask, err)
	}

	// Return a rollback function.
	return action.ActionFunc(func() error {
		log.Rollback(milestoneTask)
		task := fmt.Sprintf("Reopen GitHub review milestone for release %v", releaseString)
		_, _, err := client.Issues.EditMilestone(owner, repo, *milestone.Number, &github.Milestone{
			State: github.String("open"),
		})
		if err != nil {
			return errs.NewError(task, err)
		}
		return nil
	}), nil
}

func CreateMilestone(
	client *github.Client,
	owner string,
	repo string,
	title string,
) (*github.Milestone, action.Action, error) {

	// Create the milestone.
	milestoneTask := fmt.Sprintf("Create GitHub milestone '%v'", title)
	log.Run(milestoneTask)
	milestone, _, err := client.Issues.CreateMilestone(owner, repo, &github.Milestone{
		Title: github.String(title),
	})
	if err != nil {
		return nil, nil, errs.NewError(milestoneTask, err)
	}

	// Return a rollback function.
	return milestone, action.ActionFunc(func() error {
		log.Rollback(milestoneTask)
		task := fmt.Sprintf("Delete GitHub milestone '%v'", title)
		_, err := client.Issues.DeleteMilestone(owner, repo, *milestone.Number)
		if err != nil {
			return errs.NewError(task, err)
		}
		return nil
	}), nil
}

func (release *nextRelease) Start() (action.Action, error) {
	// In case there are no additional stories, we are done.
	if len(release.additionalStories) == 0 {
		return action.Noop, nil
	}

	// Add release labels to the relevant stories.
	var (
		config    = release.tracker.config
		client    = pivotal.NewClient(config.UserToken)
		projectId = config.ProjectId
	)

	task := "Label the stories with the release label"
	log.Run(task)
	releaseLabel := getReleaseLabel(release.trunkVersion)
	stories, err := addLabel(client, projectId,
		release.additionalStories, releaseLabel)
	if err != nil {
		return nil, errs.NewError(task, err)
	}
	release.additionalStories = nil

	// Return the rollback action, which removes the release labels that were appended.
	return action.ActionFunc(func() error {
		log.Rollback(task)
		_, err := removeLabel(client, projectId, stories, releaseLabel)
		if err != nil {
			return errs.NewError("Remove the release label from the stories", err)
		}
		return nil
	}), nil
}

func (release *nextRelease) Start() (action.Action, error) {
	var (
		client         = release.client
		productId      = release.tracker.config.ProductId()
		itemReleaseTag = getItemReleaseTag(release.trunkVersion)
	)

	// Add the release tag to the relevant Sprintly items.
	task := "Tag relevant items with the release tag"
	log.Run(task)
	items, err := addTag(client, productId, release.additionalItems, itemReleaseTag)
	if err != nil {
		return nil, errs.NewError(task, err)
	}
	release.additionalItems = nil

	// Return the rollback action, which removes the release tags that were added.
	return action.ActionFunc(func() error {
		log.Rollback(task)
		_, err := removeTag(client, productId, items, itemReleaseTag)
		if err != nil {
			return errs.NewError("Remove the release tag from relevant items", err, nil)
		}
		return nil
	}), nil
}

func (release *runningRelease) Stage() (action.Action, error) {

	var (
		api           = newClient(release.tracker.config)
		versionString = release.releaseVersion.BaseString()
		stageTask     = fmt.Sprintf("Stage JIRA issues associated with release %v", versionString)
	)
	log.Run(stageTask)

	// Make sure we only try to stage the issues that are in Tested.
	var issuesToStage []*jira.Issue
	for _, issue := range release.issues {
		if issue.Fields.Status.Id == stateIdTested {
			issuesToStage = append(issuesToStage, issue)
		}
	}

	// Perform the transition.
	err := performBulkTransition(api, issuesToStage, transitionIdStage, transitionIdUnstage)
	if err != nil {
		return nil, errs.NewError(stageTask, err)
	}

	return action.ActionFunc(func() error {
		log.Rollback(stageTask)
		unstageTask := fmt.Sprintf("Unstage JIRA issues associated with release %v", versionString)
		if err := performBulkTransition(api, issuesToStage, transitionIdUnstage, ""); err != nil {
			return errs.NewError(unstageTask, err)
		}
		return nil
	}), nil
}

func createMilestone(
	config Config,
	owner string,
	repo string,
	v *version.Version,
) (*github.Milestone, action.Action, error) {

	// Create the review milestone.
	var (
		title         = milestoneTitle(v)
		milestoneTask = fmt.Sprintf("Create GitHub review milestone '%v'", title)
		client        = ghutil.NewClient(config.Token())
	)
	log.Run(milestoneTask)
	milestone, _, err := client.Issues.CreateMilestone(owner, repo, &github.Milestone{
		Title: github.String(title),
	})
	if err != nil {
		return nil, nil, errs.NewError(milestoneTask, err)
	}

	// Return a rollback function.
	return milestone, action.ActionFunc(func() error {
		log.Rollback(milestoneTask)
		task := fmt.Sprintf("Delete GitHub review milestone '%v'", title)
		_, err := client.Issues.DeleteMilestone(owner, repo, *milestone.Number)
		if err != nil {
			return errs.NewError(task, err)
		}
		return nil
	}), nil
}

func createBranch(branch, target string) (action.Action, error) {
	// Create the branch.
	if err := Branch(branch, target); err != nil {
		return nil, err
	}

	return action.ActionFunc(func() error {
		// On rollback, delete the branch.
		return Branch("-D", branch)
	}), nil
}

func (release *runningRelease) Stage() (action.Action, error) {
	stageTask := fmt.Sprintf(
		"Mark the stories as %v in Pivotal Tracker", pivotal.StoryStateDelivered)
	log.Run(stageTask)

	// Load the assigned stories.
	stories, err := release.loadStories()
	if err != nil {
		return nil, errs.NewError(stageTask, err)
	}

	// Pick only the stories that are in the right state.
	ss := make([]*pivotal.Story, 0, len(stories))
	for _, s := range stories {
		if release.tracker.canStoryBeStaged(s) {
			ss = append(ss, s)
		}
	}
	stories = ss

	// Mark the selected stories as delivered. Leave the labels as they are.
	updateRequest := &pivotal.StoryRequest{State: pivotal.StoryStateDelivered}
	updateFunc := func(story *pivotal.Story) *pivotal.StoryRequest {
		return updateRequest
	}
	// On rollback, set the story state to finished again.
	rollbackFunc := func(story *pivotal.Story) *pivotal.StoryRequest {
		return &pivotal.StoryRequest{State: pivotal.StoryStateFinished}
	}

	// Update the stories.
	updatedStories, err := release.tracker.updateStories(stories, updateFunc, rollbackFunc)
	if err != nil {
		return nil, errs.NewError(stageTask, err)
	}
	release.stories = updatedStories

	// Return the rollback function.
	return action.ActionFunc(func() error {
		// On error, set the states back to the original ones.
		log.Rollback(stageTask)
		task := fmt.Sprintf("Reset the story states back to %v", pivotal.StoryStateFinished)
		updatedStories, err := release.tracker.updateStories(release.stories, rollbackFunc, nil)
		if err != nil {
			return errs.NewError(task, err)
		}
		release.stories = updatedStories
		return nil
	}), nil
}

func resetBranch(branch, target string) (action.Action, error) {
	// Remember the current position.
	current, err := Hexsha("refs/heads/" + branch)
	if err != nil {
		return nil, err
	}

	// Reset the branch.
	if err := SetBranch(branch, target); err != nil {
		return nil, err
	}

	return action.ActionFunc(func() error {
		// On rollback, reset the branch to the original position.
		return SetBranch(branch, current)
	}), nil
}

func (r *release) Close() (action.Action, error) {
	// Make sure EnsureClosable has been called.
	if r.closingMilestone == nil {
		if err := r.EnsureClosable(); err != nil {
			return nil, err
		}
	}

	// Prepare for API calls.
	client, owner, repo, err := r.prepareForApiCalls()
	if err != nil {
		return nil, err
	}

	// Close the milestone.
	releaseString := r.v.BaseString()
	milestoneTask := fmt.Sprintf("Close GitHub review milestone for release %v", releaseString)
	log.Run(milestoneTask)
	milestone, _, err := client.Issues.EditMilestone(
		owner, repo, *r.closingMilestone.Number, &github.Milestone{
			State: github.String("closed"),
		})
	if err != nil {
		return nil, errs.NewError(milestoneTask, err)
	}
	r.closingMilestone = milestone

	// Return a rollback function.
	return action.ActionFunc(func() error {
		log.Rollback(milestoneTask)
		task := fmt.Sprintf("Reopen GitHub review milestone for release %v", releaseString)
		milestone, _, err := client.Issues.EditMilestone(
			owner, repo, *r.closingMilestone.Number, &github.Milestone{
				State: github.String("open"),
			})
		if err != nil {
			return errs.NewError(task, err)
		}
		r.closingMilestone = milestone
		return nil
	}), nil
}

func (story *story) MarkAsImplemented() (action.Action, error) {
	// Make sure the story is started.
	switch story.Story.State {
	case pivotal.StoryStateStarted:
		// Continue further to set the state to finished.
	case pivotal.StoryStateFinished:
		// Nothing to do here.
		return nil, nil
	default:
		// Foobar, an unexpected story state encountered.
		return nil, fmt.Errorf("unexpected story state: %v", story.State)
	}

	// Set the story state to finished.
	var (
		config    = story.tracker.config
		client    = pivotal.NewClient(config.UserToken)
		projectId = config.ProjectId
	)

	updateTask := fmt.Sprintf("Update Pivotal Tracker story (id = %v)", story.Story.Id)
	updateRequest := &pivotal.StoryRequest{State: pivotal.StoryStateFinished}
	updatedStory, _, err := client.Stories.Update(projectId, story.Story.Id, updateRequest)
	if err != nil {
		return nil, errs.NewError(updateTask, err)
	}
	originalStory := story.Story
	story.Story = updatedStory

	return action.ActionFunc(func() error {
		log.Rollback(updateTask)
		updateRequest := &pivotal.StoryRequest{State: originalStory.State}
		updatedStory, _, err := client.Stories.Update(projectId, story.Story.Id, updateRequest)
		if err != nil {
			return err
		}
		story.Story = updatedStory
		return nil
	}), nil
}

func ensureLocalConfigDirectoryExists() (action.Action, error) {
	task := "Make sure the local configuration directory exists"

	// Get the directory absolute path.
	localConfigDir, err := config.LocalConfigDirectoryAbsolutePath()
	if err != nil {
		return nil, errs.NewError(task, err)
	}

	// In case the path exists, make sure it is a directory.
	info, err := os.Stat(localConfigDir)
	if err != nil {
		if !os.IsNotExist(err) {
			return nil, errs.NewError(task, err)
		}
	} else {
		if !info.IsDir() {
			return nil, errs.NewError(task, fmt.Errorf("not a directory: %v", localConfigDir))
		}
		return action.Noop, nil
	}

	// Otherwise create the directory.
	if err := os.MkdirAll(localConfigDir, 0755); err != nil {
		return nil, errs.NewError(task, err)
	}

	// Return the rollback function.
	act := action.ActionFunc(func() error {
		// Delete the directory.
		log.Rollback(task)
		task := "Delete the local configuration directory"
		if err := os.RemoveAll(localConfigDir); err != nil {
			return errs.NewError(task, err)
		}
		return nil
	})
	return act, nil
}

func CloseMilestone(
	client *github.Client,
	owner string,
	repo string,
	milestone *github.Milestone,
) (*github.Milestone, action.Action, error) {

	// Copy the milestone to have it stored locally for the rollback closure.
	mstone := *milestone

	// A helper closure.
	setState := func(milestone *github.Milestone, state string) (*github.Milestone, error) {
		task := fmt.Sprintf("Mark GitHub milestone '%v' as %v", *milestone.Title, state)
		log.Run(task)
		m, _, err := client.Issues.EditMilestone(owner, repo, *milestone.Number, &github.Milestone{
			State: &state,
		})
		if err != nil {
			return nil, errs.NewError(task, err)
		}
		return m, nil
	}

	// Close the chosen milestone.
	m, err := setState(&mstone, "closed")
	if err != nil {
		return nil, nil, err
	}

	// Return the rollback function.
	act := action.ActionFunc(func() error {
		_, err := setState(&mstone, "open")
		return err
	})
	return m, act, nil
}

func Stage(options *StageOptions) (act action.Action, err error) {
	// Rollback machinery.
	chain := action.NewActionChain()
	defer chain.RollbackOnError(&err)

	// Make sure opts are not nil.
	if options == nil {
		options = DefaultStageOptions
	}

	// Load git config.
	gitConfig, err := git.LoadConfig()
	if err != nil {
		return nil, err
	}
	var (
		remoteName    = gitConfig.RemoteName
		releaseBranch = gitConfig.ReleaseBranchName
		stagingBranch = gitConfig.StagingBranchName
	)

	// Instantiate the issue tracker.
	tracker, err := modules.GetIssueTracker()
	if err != nil {
		return nil, err
	}

	// Get the current branch.
	task := "Get the current branch"
	currentBranch, err := gitutil.CurrentBranch()
	if err != nil {
		return nil, err
	}

	// Cannot be on the release branch, it will be deleted.
	task = fmt.Sprintf("Make sure that branch '%v' is not checked out", releaseBranch)
	if currentBranch == releaseBranch {
		return nil, errs.NewError(
			task, fmt.Errorf("cannot stage the release while on branch '%v'", releaseBranch))
	}

	// Fetch the remote repository.
	if !options.SkipFetch {
		task = "Fetch the remote repository"
		log.Run(task)
		if err := git.UpdateRemotes(remoteName); err != nil {
			return nil, errs.NewError(task, err)
		}
	}

	// Make sure that the local release branch exists and is up to date.
	task = fmt.Sprintf("Make sure that branch '%v' is up to date", releaseBranch)
	log.Run(task)
	if err := git.CheckOrCreateTrackingBranch(releaseBranch, remoteName); err != nil {
		return nil, errs.NewError(task, err)
	}

	// Read the current release version.
	task = "Read the current release version"
	releaseVersion, err := version.GetByBranch(releaseBranch)
	if err != nil {
		return nil, errs.NewError(task, err)
	}

	// Make sure the release is stageable.
	release := tracker.RunningRelease(releaseVersion)
	if err := release.EnsureStageable(); err != nil {
		return nil, err
	}

	// Make sure there are no commits being left behind,
	// e.g. make sure no commits are forgotten on the trunk branch,
	// i.e. make sure that everything necessary was cherry-picked.
	if err := checkCommits(tracker, release, releaseBranch); err != nil {
		return nil, err
	}

	// Reset the staging branch to point to the newly created tag.
	task = fmt.Sprintf("Reset branch '%v' to point to branch '%v'", stagingBranch, releaseBranch)
	log.Run(task)
	act, err = git.CreateOrResetBranch(stagingBranch, releaseBranch)
	if err != nil {
		return nil, errs.NewError(task, err)
	}
	chain.PushTask(task, act)

	// Delete the local release branch.
	task = fmt.Sprintf("Delete branch '%v'", releaseBranch)
	log.Run(task)
	if err := git.Branch("-D", releaseBranch); err != nil {
		return nil, errs.NewError(task, err)
	}
	chain.PushTask(task, action.ActionFunc(func() error {
		task := fmt.Sprintf("Recreate branch '%v'", releaseBranch)

		// In case the release branch exists locally, do nothing.
		// This might look like an extra and useless check, but it looks like
		// the final git push at the end of the command function actually creates
		// the release branch locally when it is aborted from the pre-push hook.
		// Not sure why and how that is happening.
//.........这里部分代码省略.........

func (s *story) setStateLabel(label string) (action.Action, error) {
	// A helper function for setting issue labels.
	setLabels := func(labels []string) error {
		var (
			client   = s.tracker.newClient()
			owner    = s.tracker.config.GitHubOwner
			repo     = s.tracker.config.GitHubRepository
			issueNum = *s.issue.Number

			updatedLabels []github.Label
			err           error
		)
		withRequestAllocated(func() {
			updatedLabels, _, err = client.Issues.ReplaceLabelsForIssue(
				owner, repo, issueNum, labels)
		})
		if err != nil {
			return err
		}
		s.issue.Labels = updatedLabels
		return nil
	}

	// A helper function for appending label names.
	appendLabelNames := func(names []string, labels []github.Label) []string {
		for _, label := range labels {
			names = append(names, *label.Name)
		}
		return names
	}

	// Set the state labels.
	task := fmt.Sprintf("Set state label to '%v' for issue %v", label, s.ReadableId())

	// Get the right label list.
	otherLabels, prunedLabels := pruneStateLabels(s.tracker.config, s.issue.Labels)
	newLabels := make([]string, 0, len(otherLabels)+1)
	newLabels = appendLabelNames(newLabels, otherLabels)
	newLabels = append(newLabels, label)

	// Update the issue.
	if err := setLabels(newLabels); err != nil {
		return nil, errs.NewError(task, err)
	}

	// Return a rollback function.
	return action.ActionFunc(func() error {
		// Append the pruned labels.
		newLabels := make([]string, 0, len(otherLabels)+len(prunedLabels))
		newLabels = appendLabelNames(newLabels, prunedLabels)

		// Generate the task string.
		task := fmt.Sprintf("Set the state labels to [%v] for issue %v",
			strings.Join(newLabels, ", "), s.ReadableId())

		// Append the other labels as well, thus getting the original label list.
		newLabels = appendLabelNames(newLabels, otherLabels)

		// Update the issue.
		if err := setLabels(newLabels); err != nil {
			return errs.NewError(task, err)
		}
		return nil
	}), nil
}

//.........这里部分代码省略.........
	line, err := prompt.Prompt(`
Please insert the branch slug now.
Insert an empty string to skip the branch creation step: `)
	if err != nil && err != prompt.ErrCanceled {
		return nil, errs.NewError(task, err)
	}

	sluggedLine := slug.Slug(line)
	if sluggedLine == "" {
		fmt.Println()
		log.Log("Not creating any feature branch")
		return nil, nil
	}

	branchName := "story/" + sluggedLine
	ok, err := prompt.Confirm(
		fmt.Sprintf(
			"\nThe branch that is going to be created will be called '%s'.\nIs that alright?",
			branchName),
		true)
	if err != nil {
		return nil, errs.NewError(task, err)
	}
	if !ok {
		panic(prompt.ErrCanceled)
	}
	fmt.Println()

	createTask := fmt.Sprintf(
		"Create branch '%v' on top of branch '%v'", branchName, baseBranch)
	log.Run(createTask)
	if err := git.Branch(branchName, baseBranch); err != nil {
		return nil, errs.NewError(createTask, err)
	}

	deleteTask := fmt.Sprintf("Delete branch '%v'", branchName)
	deleteBranch := func() error {
		// Roll back and delete the newly created branch.
		log.Rollback(createTask)
		if err := git.Branch("-D", branchName); err != nil {
			return errs.NewError(deleteTask, err)
		}
		return nil
	}

	// Checkout the newly created branch.
	checkoutTask := fmt.Sprintf("Checkout branch '%v'", branchName)
	log.Run(checkoutTask)
	if err := git.Checkout(branchName); err != nil {
		if err := deleteBranch(); err != nil {
			errs.Log(err)
		}
		return nil, errs.NewError(checkoutTask, err)
	}

	// Push the newly created branch unless -no_push.
	pushTask := fmt.Sprintf("Push branch '%v' to remote '%v'", branchName, remoteName)
	if flagPush {
		log.Run(pushTask)
		if err := git.Push(remoteName, branchName); err != nil {
			if err := deleteBranch(); err != nil {
				errs.Log(err)
			}
			return nil, errs.NewError(pushTask, err)
		}
	}

	return action.ActionFunc(func() error {
		// Checkout the original branch.
		log.Rollback(checkoutTask)
		if err := git.Checkout(originalBranch); err != nil {
			return errs.NewError(
				fmt.Sprintf("Checkout the original branch '%v'", originalBranch), err)
		}

		// Delete the newly created branch.
		deleteErr := deleteBranch()

		// In case we haven't pushed anything, we are done.
		if !flagPush {
			return deleteErr
		}

		// Delete the branch from the remote repository.
		log.Rollback(pushTask)
		if _, err := git.Run("push", "--delete", remoteName, branchName); err != nil {
			// In case deleteBranch failed, tell the user now
			// since we are not going to return that error.
			if deleteErr != nil {
				errs.Log(deleteErr)
			}

			return errs.NewError(
				fmt.Sprintf("Delete branch '%v' from remote '%v'", branchName, remoteName), err)
		}

		// Return deleteErr to make sure it propagates up.
		return deleteErr
	}), nil
}

func runMain() (err error) {
	tracker, err := modules.GetIssueTracker()
	if err != nil {
		return err
	}

	// Fetch stories from the issue tracker.
	task := "Fetch stories from the issue tracker"
	log.Run(task)
	stories, err := tracker.StartableStories()
	if err != nil {
		return errs.NewError(task, err)
	}
	if len(stories) == 0 {
		return errs.NewError(task, errors.New("no startable stories found"))
	}

	// Filter out the stories that are not relevant,
	// i.e. not owned by the current user or assigned to someone else.
	task = "Fetch the current user record from the issue tracker"
	user, err := tracker.CurrentUser()
	if err != nil {
		return errs.NewError(task, err)
	}

	var filteredStories []common.Story
StoryLoop:
	for _, story := range stories {
		assignees := story.Assignees()
		// Include the story in case there is no assignee set yet.
		if len(assignees) == 0 {
			filteredStories = append(filteredStories, story)
			continue StoryLoop
		}
		// Include the story in case the current user is assigned.
		for _, assignee := range assignees {
			if assignee.Id() == user.Id() {
				filteredStories = append(filteredStories, story)
				continue StoryLoop
			}
		}
	}
	stories = filteredStories

	// Prompt the user to select a story.
	story, err := dialog(
		"\nYou can start working on one of the following stories:", stories)
	if err != nil {
		switch err {
		case prompt.ErrNoStories:
			return errors.New("no startable stories found")
		case prompt.ErrCanceled:
			prompt.PanicCancel()
		default:
			return err
		}
	}
	fmt.Println()

	// Create the story branch, optionally.
	if flagNoBranch {
		log.Log("Not creating any feature branch")
	} else {
		var act action.Action
		act, err = createBranch()
		if err != nil {
			return err
		}
		// Roll back on error.
		defer action.RollbackTaskOnError(&err, task, act)
	}

	// Add the current user to the list of story assignees.
	task = "Amend the list of story assignees"
	log.Run(task)
	originalAssignees := story.Assignees()
	if err := story.AddAssignee(user); err != nil {
		return errs.NewError(task, err)
	}
	defer action.RollbackTaskOnError(&err, task, action.ActionFunc(func() error {
		task := "Reset the list of story assignees"
		if err := story.SetAssignees(originalAssignees); err != nil {
			return errs.NewError(task, err)
		}
		return nil
	}))

	// Start the selected story. No need to roll back.
	task = "Start the selected story"
	log.Run(task)
	return errs.Wrap(task, story.Start())
}

func merge(mergeTask, current, parent string) (act action.Action, err error) {
	// Remember the current branch hash.
	currentSHA, err := git.BranchHexsha(current)
	if err != nil {
		return nil, err
	}

	// Checkout the parent branch so that we can perform the merge.
	if err := git.Checkout(parent); err != nil {
		return nil, err
	}
	// Checkout the current branch on return to be consistent.
	defer func() {
		if ex := git.Checkout(current); ex != nil {
			if err == nil {
				err = ex
			} else {
				errs.Log(ex)
			}
		}
	}()

	// Perform the merge.
	// Use --no-ff in case -merge_no_ff is set.
	if flagMergeNoFF {
		err = git.Merge(current, "--no-ff")
	} else {
		err = git.Merge(current)
	}
	if err != nil {
		return nil, err
	}

	// Return a rollback action.
	return action.ActionFunc(func() (err error) {
		log.Rollback(mergeTask)
		task := fmt.Sprintf("Reset branch '%v' to the original position", current)

		// Get the branch is the current branch now.
		currentNow, err := gitutil.CurrentBranch()
		if err != nil {
			return errs.NewError(task, err)
		}

		// Checkout current in case it is not the same as the current branch now.
		if currentNow != current {
			if err := git.Checkout(current); err != nil {
				return errs.NewError(task, err)
			}
			defer func() {
				if ex := git.Checkout(currentNow); ex != nil {
					if err == nil {
						err = ex
					} else {
						errs.Log(ex)
					}
				}
			}()
		}

		// Reset the branch to the original position.
		if err := git.Reset("--keep", currentSHA); err != nil {
			return errs.NewError(task, err)
		}
		return nil
	}), nil
}

//.........这里部分代码省略.........
	log.Run(task)
	if err = git.EnsureBranchSynchronized(currentBranch, remoteName); err != nil {
		return errs.NewError(task, err)
	}

	// Get the commits to be posted
	task = "Get the commits to be posted for code review"
	commits, err := git.ShowCommitRange(parentBranch + "..")
	if err != nil {
		return errs.NewError(task, err)
	}

	// Make sure there are no merge commits.
	if err := ensureNoMergeCommits(commits); err != nil {
		return err
	}

	// Prompt the user to confirm.
	if err := promptUserToConfirmCommits(commits); err != nil {
		return err
	}

	// Rebase the current branch on top the parent branch.
	if !flagNoRebase {
		commits, err = rebase(currentBranch, parentBranch)
		if err != nil {
			return err
		}
	}

	// Ensure the Story-Id tag is there.
	commits, _, err = ensureStoryId(commits)
	if err != nil {
		return err
	}

	// Get data on the current branch.
	task = fmt.Sprintf("Get data on branch '%v'", currentBranch)
	remoteCurrentExists, err := git.RemoteBranchExists(currentBranch, remoteName)
	if err != nil {
		return errs.NewError(task, err)
	}
	currentUpToDate, err := git.IsBranchSynchronized(currentBranch, remoteName)
	if err != nil {
		return errs.NewError(task, err)
	}

	// Merge the current branch into the parent branch unless -no_merge.
	pushTask := "Push the current branch"
	if flagNoMerge {
		// In case the user doesn't want to merge,
		// we need to push the current branch.
		if !remoteCurrentExists || !currentUpToDate {
			if err := push(remoteName, currentBranch); err != nil {
				return errs.NewError(pushTask, err)
			}
		}
	} else {
		// Still push the current branch if necessary.
		if remoteCurrentExists && !currentUpToDate {
			if err := push(remoteName, currentBranch); err != nil {
				return errs.NewError(pushTask, err)
			}
		}

		// Merge the branch into the parent branch
		mergeTask := fmt.Sprintf("Merge branch '%v' into branch '%v'", currentBranch, parentBranch)
		log.Run(mergeTask)
		act, err := merge(mergeTask, currentBranch, parentBranch)
		if err != nil {
			return err
		}

		// Push the parent branch.
		if err := push(remoteName, parentBranch); err != nil {
			// In case the push fails, we revert the merge as well.
			if err := act.Rollback(); err != nil {
				errs.Log(err)
			}
			return errs.NewError(mergeTask, err)
		}

		// Register a rollback function that just says that
		// a pushed merge cannot be reverted.
		defer action.RollbackOnError(&err, action.ActionFunc(func() error {
			log.Rollback(mergeTask)
			hint := "\nCannot revert merge that has already been pushed.\n"
			return errs.NewErrorWithHint(
				"Revert the merge", errors.New("merge commit already pushed"), hint)
		}))
	}

	// Post the review requests.
	if err := postCommitsForReview(commits); err != nil {
		return err
	}

	// In case there is no error, tell the user they can do next.
	return printFollowup()
}