internal/branch/helper.go - chromiumos/infra/go - Git at Google

 // Copyright 2019 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 package branch

 import (
 	"context"
 	"fmt"
 	"net/url"
 	"os"
 	"regexp"
 	"strings"
 	"sync"
 	"time"

 	mv "go.chromium.org/chromiumos/infra/go/internal/chromeos_version"
 	"go.chromium.org/chromiumos/infra/go/internal/git"
 	"go.chromium.org/chromiumos/infra/go/internal/repo"
 	"go.chromium.org/chromiumos/infra/go/internal/shared"
 	"go.chromium.org/luci/common/errors"
 )

 const (
 	gitRetries = 3
 	gitTimeout = 30 * time.Second
 )

 var (
 	ManifestProjects = map[string]bool{
 		"chromiumos/manifest":        true,
 		"chromeos/manifest-internal": true,
 	}
 	// A Chrome OS branch name as a prefix to a string, starting with a dash.
 	// e.g. -release-R77-12371.B
 	BranchPrefix = regexp.MustCompile("^-.*[.]B")
 )

 // ProjectBranch is a project and a branch.
 type ProjectBranch struct {
 	Project    repo.Project
 	BranchName string
 }

 // branchMapEntry is a struct for manual branch mapping
 type branchMapEntry struct {
 	name        string
 	path        string
 	suffix      string
 	replacement string
 }

 // branchMap is a map that defines branch suffix replacements
 var branchMap = map[string]branchMapEntry{
 	"chromiumos/third_party/coreboot": {
 		name:        "chromiumos/third_party/coreboot",
 		path:        "src/third_party/coreboot",
 		suffix:      "-chromeos-2016.05",
 		replacement: "",
 	},
 }

 // canBranchProject retuns true if the Project can be branched.
 func canBranchProject(manifest repo.Manifest, project repo.Project) bool {
 	return manifest.ProjectBranchMode(project) == repo.Create
 }

 // projectBranchName determines the git branch name for the Project.
 func projectBranchName(br string, project repo.Project, original string) string {
 	// If the Project has only one checkout, then the base branch name is fine.
 	var checkouts []string
 	for _, proj := range WorkingManifest.Projects {
 		if proj.Name == project.Name {
 			checkouts = append(checkouts, proj.Name)
 		}
 	}

 	if len(checkouts) == 1 {
 		return br
 	}

 	// Otherwise, the project name needs a suffix. We append its upstream or
 	// revision to distinguish it from other checkouts. We grab the suffix
 	// from git using the Upstream or Revision. We then trim and replace
 	// any unneeded info from the suffix.
 	suffix := "-"
 	if project.Upstream != "" {
 		suffix += git.StripRefs(project.Upstream)
 	} else {
 		suffix += git.StripRefs(project.Revision)
 	}

 	// If the revision is itself a branch, we need to strip the old branch name
 	// from the suffix to keep naming consistent.
 	if original != "" {
 		if strings.HasPrefix(suffix, "-"+original+"-") {
 			suffix = strings.TrimPrefix(suffix, "-"+original)
 		}
 	}
 	if BranchPrefix.MatchString(suffix) {
 		// If the suffix already has a version in it, trim that.
 		// e.g. -release-R77-12371.B-wpa_supplicant-2.6 --> -wpa_supplicant-2.6
 		suffix = BranchPrefix.ReplaceAllString(suffix, "")
 	}
 	// Remove the "/" character, since those don't belong in branch names.
 	suffix = strings.ReplaceAll(suffix, "/", "-")

 	// Check if a branch naming override exist
 	entry, ok := branchMap[project.Name]

 	// Replace suffix
 	if ok && (suffix == entry.suffix && project.Path == entry.path) {
 		suffix = entry.replacement
 	}

 	return br + suffix
 }

 // ProjectBranches returns a list of ProjectBranch structs:
 // one for each branchable project.
 // The original parameter is the CrOS branch from which the current checkout stems.
 func ProjectBranches(br, original string) []ProjectBranch {
 	var projectBranches []ProjectBranch
 	for _, project := range WorkingManifest.Projects {
 		if canBranchProject(WorkingManifest, project) {
 			projectBranches = append(projectBranches,
 				ProjectBranch{
 					Project:    project,
 					BranchName: projectBranchName(br, project, original),
 				})
 		}
 	}
 	return projectBranches
 }

 // BranchExists checks that a branch matching the given pattern exists in a particular project.
 func BranchExists(branchPattern *regexp.Regexp, buildNumber string, branchType string, remoteBranches []string) (bool, error) {
 	for _, branch := range remoteBranches {
 		// Failing cases
 		switch {
 		case branchPattern.Match([]byte(branch)):
 			return true, nil
 		case strings.Contains(branch, buildNumber):

 			// Check that major version collision is on other branch type
 			if !strings.Contains(branch, branchType) {
 				err := errors.New("ERROR: Major version collision on branch " + branch)
 				return true, err
 			}
 		}
 	}

 	return false, nil
 }

 // branchExistsExplicit checks that the given branch exists in the project.
 // It is a good bit faster than BranchExists.
 func branchExistsExplicit(project repo.Project, br string) (bool, error) {
 	remoteUrl, err := ProjectFetchUrl(project.Path)
 	if err != nil {
 		return false, errors.Annotate(err, "failed to get remote project url").Err()
 	}

 	ch := make(chan bool, 1)

 	ctx, cancel := context.WithTimeout(context.Background(), gitTimeout)
 	defer cancel()
 	opts := shared.DefaultOpts
 	opts.Retries = gitRetries
 	err = shared.DoWithRetry(ctx, opts, func() error {
 		// If we give a full URL, don't need to run the command in a git repo.
 		output, err := git.RemoteHasBranch("", remoteUrl, br)
 		if err != nil {
 			return err
 		}
 		ch <- output
 		return nil
 	})
 	if err != nil {
 		return false, errors.Annotate(err, "failed to list remote branches for %s", remoteUrl).Err()
 	}

 	return <-ch, nil
 }

 func assertBranchesDoNotExistWorker(
 	wg *sync.WaitGroup, projectBranches <-chan ProjectBranch, errs chan<- error) {
 	for projectBranch := range projectBranches {
 		LogOut("...checking that %s does not exist in %s.\n",
 			projectBranch.BranchName,
 			projectBranch.Project.Name)
 		exists, err := branchExistsExplicit(projectBranch.Project, projectBranch.BranchName)
 		if err == nil {
 			if exists {
 				errs <- fmt.Errorf("branch %s exists for %s. Please rerun with --force to proceed.",
 					projectBranch.BranchName, projectBranch.Project.Name)
 			}
 		} else {
 			errs <- err
 		}
 		wg.Done()
 	}
 }

 // AssertBranchesDoNotExist checks that branches do not already exist.
 func AssertBranchesDoNotExist(branches []ProjectBranch, workerCount int) error {
 	projectBranches := make(chan ProjectBranch, len(branches))
 	errs := make(chan error, len(branches))

 	var wg sync.WaitGroup
 	for i := 1; i <= workerCount; i++ {
 		go assertBranchesDoNotExistWorker(&wg, projectBranches, errs)
 	}

 	for _, projectBranch := range branches {
 		projectBranches <- projectBranch
 		wg.Add(1)
 	}
 	close(projectBranches)

 	wg.Wait()

 	select {
 	case err := <-errs:
 		return err
 	default:
 	}
 	return nil
 }

 // GerritProjectBranches creates a slice of GerritProjectBranch objects, which
 // are representations of ProjectBranches that are useful for API based
 // branching.
 func GerritProjectBranches(pbs []ProjectBranch) ([]GerritProjectBranch, error) {
 	var result []GerritProjectBranch
 	for _, pb := range pbs {
 		remote := WorkingManifest.GetRemoteByName(pb.Project.RemoteName)
 		if remote == nil {
 			return result, fmt.Errorf("remote %s does not exist in working manifest", pb.Project.RemoteName)
 		}
 		remoteURL, err := url.Parse(remote.Fetch)
 		if err != nil {
 			return result, errors.Annotate(err, "failed to parse fetch location for remote %s", remote.Name).Err()
 		}
 		remoteStr := remoteURL.String()
 		remoteStr = strings.ReplaceAll(remoteStr,
 			"chromium.googlesource.com", "chromium-review.googlesource.com")
 		remoteStr = strings.ReplaceAll(remoteStr,
 			"chrome-internal.googlesource.com", "chrome-internal-review.googlesource.com")
 		result = append(result, GerritProjectBranch{
 			GerritURL: remoteStr,
 			Project:   pb.Project.Name,
 			Branch:    pb.BranchName,
 			SrcRef:    pb.Project.Revision,
 		})
 	}
 	return result, nil
 }

 // getBranchesByPath returns a map mapping project paths to git branch names.
 func getBranchesByPath(branches []ProjectBranch) map[string]string {
 	branchesByPath := make(map[string]string)
 	for _, branch := range branches {
 		branchesByPath[branch.Project.Path] = branch.BranchName
 	}
 	return branchesByPath
 }

 // getOriginRef returns the equivalent of the specified Ref for the "origin" remote.
 func getOriginRef(ref string) string {
 	// If the revision starts with refs/heads/, make it start with
 	// refs/remotes/origin instead.
 	if git.StripRefsHead(ref) != ref {
 		return "refs/remotes/origin/" + git.StripRefsHead(ref)
 	}
 	// If the revision is a SHA, let it be.
 	return ref
 }

 // GetNonManifestBranches filters out non-Manifest branches.
 func GetNonManifestBranches(branches []GerritProjectBranch) []GerritProjectBranch {
 	var result []GerritProjectBranch
 	for _, pb := range branches {
 		if _, ok := ManifestProjects[pb.Project]; ok {
 			continue
 		}
 		result = append(result, pb)
 	}
 	return result
 }

 // RepairManifestRepositories repairs all manifests in all manifest repositories
 // on the current branch and commits the changes. It then pushes the state of
 // the local git branches to remote.
 func RepairManifestRepositories(branches []ProjectBranch, dryRun, force bool) error {
 	manifestBranchNames := make(map[string]string)

 	// Find names of manifest project branches so that we can push changes.
 	for _, projectBranch := range branches {
 		if _, ok := ManifestProjects[projectBranch.Project.Name]; ok {
 			manifestBranchNames[projectBranch.Project.Name] = projectBranch.BranchName
 		}
 	}

 	for projectName := range ManifestProjects {
 		manifestProject, err := WorkingManifest.GetUniqueProject(projectName)
 		if err != nil {
 			return err
 		}
 		opts := &CheckoutOptions{
 			Depth: 1,
 			Ref:   manifestProject.Revision,
 		}
 		manifestCheckout, err := GetProjectCheckout(manifestProject.Path, opts)

 		defer os.RemoveAll(manifestCheckout)

 		if err != nil {
 			return errors.Annotate(err, "failed to checkout project %s", manifestProject.Path).Err()
 		}

 		manifestRepo := ManifestRepo{
 			ProjectCheckout: manifestCheckout,
 			Project:         manifestProject,
 		}
 		if err := manifestRepo.RepairManifestsOnDisk(getBranchesByPath(branches)); err != nil {
 			return errors.Annotate(err, "failed to repair manifest project %s", projectName).Err()
 		}
 		if output, err := git.RunGit(manifestCheckout,
 			[]string{"commit", "-a", "-m", "commit repaired manifests"}); err != nil {
 			return fmt.Errorf("error committing repaired manifests: %s", output.Stdout)
 		}

 		remoteRef := git.RemoteRef{
 			Remote: "origin",
 			Ref:    git.NormalizeRef(manifestBranchNames[manifestProject.Name]),
 		}
 		gitOpts := git.GitOpts{
 			DryRun: dryRun,
 			Force:  force,
 		}
 		if err := git.PushRef(manifestCheckout, "HEAD", remoteRef, gitOpts); err != nil {
 			return errors.Annotate(err, "could not push branches to remote").Err()
 		}
 	}
 	return nil
 }

 func createRemoteBranchesWorker(
 	wg *sync.WaitGroup,
 	branches <-chan ProjectBranch,
 	errs chan<- error,
 	dryRun, force bool) {
 	for projectBranch := range branches {
 		opts := &CheckoutOptions{
 			Depth: 1,
 			Ref:   projectBranch.Project.Revision,
 		}
 		projectCheckout, err := GetProjectCheckout(projectBranch.Project.Path, opts)
 		defer os.RemoveAll(projectCheckout)
 		if err != nil {
 			errs <- errors.Annotate(err, "could not checkout %s:%s",
 				projectBranch.Project.Path, projectBranch.BranchName).Err()
 			wg.Done()
 			continue
 		}

 		branchName := git.NormalizeRef(projectBranch.BranchName)
 		refspec := fmt.Sprintf("%s:%s", getOriginRef(projectBranch.Project.Revision), branchName)

 		logMode := "Pushing"
 		cmd := []string{"push", "origin", refspec}
 		if dryRun {
 			cmd = append(cmd, "--dry-run")
 			logMode = "Dry run"
 		}
 		if force {
 			cmd = append(cmd, "--force")
 			logMode += " (with --force flag)"
 		}
 		LogOut("%s ref %s for project %s\n", logMode, branchName, projectBranch.Project.Path)

 		ctx, cancel := context.WithTimeout(context.Background(), gitTimeout)
 		defer cancel()
 		retryOpts := shared.DefaultOpts
 		retryOpts.Retries = gitRetries
 		err = shared.DoWithRetry(ctx, retryOpts, func() error {
 			return git.RunGitIgnoreOutput(projectCheckout, cmd)
 		})
 		if err != nil {
 			errs <- errors.Annotate(err, "could not push branches to remote").Err()
 			wg.Done()
 			continue
 		}
 		wg.Done()
 	}

 	return
 }

 // CreateRemoteBranches makes the requested branches on the remote Gerrit hosts
 // using git checkouts and pushes.
 func CreateRemoteBranches(branches []ProjectBranch, dryRun, force bool, workerCount int) error {
 	branchChan := make(chan ProjectBranch, len(branches))
 	errs := make(chan error, len(branches))

 	var wg sync.WaitGroup
 	for i := 1; i <= workerCount; i++ {
 		go createRemoteBranchesWorker(&wg, branchChan, errs, dryRun, force)
 	}

 	// Push the local git branches to remote.
 	for _, projectBranch := range branches {
 		// Don't push the manifest repos because that already happened in RepairManifestRepositories.
 		if _, ok := ManifestProjects[projectBranch.Project.Name]; ok {
 			continue
 		}

 		branchChan <- projectBranch
 		wg.Add(1)
 	}
 	close(branchChan)

 	wg.Wait()

 	select {
 	case err := <-errs:
 		return err
 	default:
 	}
 	return nil
 }

 // WhichVersionShouldBump returns which version is incremented by builds on a new branch.
 func WhichVersionShouldBump(vinfo mv.VersionInfo) (mv.VersionComponent, error) {
 	if vinfo.PatchNumber != 0 {
 		return mv.Unspecified, fmt.Errorf("cannot bump version with nonzero patch number")
 	}
 	if vinfo.BranchBuildNumber != 0 {
 		return mv.Patch, nil
 	} else {
 		return mv.Branch, nil
 	}
 }

 // BranchType determines the type of branch to be created.
 func BranchType(release, factory, firmware, stabilize bool, custom string) (string, bool) {
 	var branchType string
 	branchTypesSelected := 0
 	if release {
 		branchTypesSelected++
 		branchType = "release"
 	}
 	if factory {
 		branchTypesSelected++
 		branchType = "factory"
 	}
 	if firmware {
 		branchTypesSelected++
 		branchType = "firmware"
 	}
 	if stabilize {
 		branchTypesSelected++
 		branchType = "stabilize"
 	}
 	if custom != "" {
 		branchTypesSelected++
 		branchType = "custom"
 	}
 	if branchTypesSelected != 1 {
 		return "", false
 	}

 	return branchType, true
 }

 // Determine the name for a new branch.
 // By convention, standard branch names must end with the stripped version
 // string from which they were created, followed by '.B'.
 //
 // For example:
 //	- A branch created from 1.0.0 must end with -1.B
 //	- A branch created from 1.2.0 must end with -1.2.B
 //
 // Release branches have a slightly different naming scheme. They include
 //  the milestone from which they were created. Example: release-R12-1.2.B
 func NewBranchName(vinfo mv.VersionInfo, custom, descriptor string, release, factory, firmware, stabilize bool) string {
 	if custom != "" {
 		return custom
 	}
 	branchType, _ := BranchType(release, factory, firmware, stabilize, custom)
 	branchNameParts := []string{branchType}
 	if branchType == "release" {
 		branchNameParts = append(branchNameParts, fmt.Sprintf("R%d", vinfo.ChromeBranch))
 	}
 	if descriptor != "" {
 		branchNameParts = append(branchNameParts, descriptor)
 	}
 	branchNameParts = append(branchNameParts, vinfo.StrippedVersionString()+".B")
 	return strings.Join(branchNameParts, "-")
 }

 // CheckIfAlreadyBranched checks if there's already a branch for the desired new
 // branch to create on the manifest-internal repo.
 func CheckIfAlreadyBranched(vinfo mv.VersionInfo, manifestInternal repo.Project, force bool, branchType string) error {
 	// Check that we did not already branch from this version.
 	// manifest-internal serves as the sentinel project.
 	pattern := regexp.MustCompile(fmt.Sprintf(`.*-%s.B$`, vinfo.StrippedVersionString()))

 	// Verify that a major-minor version collision won't occur
 	majorMinor := fmt.Sprintf("%v.%v", vinfo.BuildNumber, vinfo.BranchBuildNumber)

 	// Fetch remoteUrl
 	remoteUrl, err := ProjectFetchUrl(manifestInternal.Path)
 	if err != nil {
 		err = errors.Annotate(err, "failed to get remote project url").Err()
 	}

 	// If we give a full URL, don't need to run the command in a git repo.
 	remoteBranches, err := git.RemoteBranches("", remoteUrl)
 	if err != nil {
 		err = errors.Annotate(err, "failed to list remote branches for %s", remoteUrl).Err()
 	}

 	exists, err := BranchExists(pattern, majorMinor, branchType, remoteBranches)
 	if err != nil {
 		return err
 	}
 	if exists {
 		if !force {
 			return fmt.Errorf("already branched %s. Please rerun with --force if you "+
 				"would like to proceed", vinfo.VersionString())
 		} else {
 			LogOut("Overwriting branch with version %s (--force was set).\n", vinfo.VersionString())
 		}
 	} else {
 		LogOut("No branch exists for version %s. Continuing...\n", vinfo.VersionString())
 	}
 	return nil
 }
	// Copyright 2019 The Chromium OS Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	package branch

	import (
	"context"
	"fmt"
	"net/url"
	"os"
	"regexp"
	"strings"
	"sync"
	"time"

	mv "go.chromium.org/chromiumos/infra/go/internal/chromeos_version"
	"go.chromium.org/chromiumos/infra/go/internal/git"
	"go.chromium.org/chromiumos/infra/go/internal/repo"
	"go.chromium.org/chromiumos/infra/go/internal/shared"
	"go.chromium.org/luci/common/errors"
	)

	const (
	gitRetries = 3
	gitTimeout = 30 * time.Second
	)

	var (
	ManifestProjects = map[string]bool{
	"chromiumos/manifest": true,
	"chromeos/manifest-internal": true,
	}
	// A Chrome OS branch name as a prefix to a string, starting with a dash.
	// e.g. -release-R77-12371.B
	BranchPrefix = regexp.MustCompile("^-.*[.]B")
	)

	// ProjectBranch is a project and a branch.
	type ProjectBranch struct {
	Project repo.Project
	BranchName string
	}

	// branchMapEntry is a struct for manual branch mapping
	type branchMapEntry struct {
	name string
	path string
	suffix string
	replacement string
	}

	// branchMap is a map that defines branch suffix replacements
	var branchMap = map[string]branchMapEntry{
	"chromiumos/third_party/coreboot": {
	name: "chromiumos/third_party/coreboot",
	path: "src/third_party/coreboot",
	suffix: "-chromeos-2016.05",
	replacement: "",
	},
	}

	// canBranchProject retuns true if the Project can be branched.
	func canBranchProject(manifest repo.Manifest, project repo.Project) bool {
	return manifest.ProjectBranchMode(project) == repo.Create
	}

	// projectBranchName determines the git branch name for the Project.
	func projectBranchName(br string, project repo.Project, original string) string {
	// If the Project has only one checkout, then the base branch name is fine.
	var checkouts []string
	for _, proj := range WorkingManifest.Projects {
	if proj.Name == project.Name {
	checkouts = append(checkouts, proj.Name)
	}
	}

	if len(checkouts) == 1 {
	return br
	}

	// Otherwise, the project name needs a suffix. We append its upstream or
	// revision to distinguish it from other checkouts. We grab the suffix
	// from git using the Upstream or Revision. We then trim and replace
	// any unneeded info from the suffix.
	suffix := "-"
	if project.Upstream != "" {
	suffix += git.StripRefs(project.Upstream)
	} else {
	suffix += git.StripRefs(project.Revision)
	}

	// If the revision is itself a branch, we need to strip the old branch name
	// from the suffix to keep naming consistent.
	if original != "" {
	if strings.HasPrefix(suffix, "-"+original+"-") {
	suffix = strings.TrimPrefix(suffix, "-"+original)
	}
	}
	if BranchPrefix.MatchString(suffix) {
	// If the suffix already has a version in it, trim that.
	// e.g. -release-R77-12371.B-wpa_supplicant-2.6 --> -wpa_supplicant-2.6
	suffix = BranchPrefix.ReplaceAllString(suffix, "")
	}
	// Remove the "/" character, since those don't belong in branch names.
	suffix = strings.ReplaceAll(suffix, "/", "-")

	// Check if a branch naming override exist
	entry, ok := branchMap[project.Name]

	// Replace suffix
	if ok && (suffix == entry.suffix && project.Path == entry.path) {
	suffix = entry.replacement
	}

	return br + suffix
	}

	// ProjectBranches returns a list of ProjectBranch structs:
	// one for each branchable project.
	// The original parameter is the CrOS branch from which the current checkout stems.
	func ProjectBranches(br, original string) []ProjectBranch {
	var projectBranches []ProjectBranch
	for _, project := range WorkingManifest.Projects {
	if canBranchProject(WorkingManifest, project) {
	projectBranches = append(projectBranches,
	ProjectBranch{
	Project: project,
	BranchName: projectBranchName(br, project, original),
	})
	}
	}
	return projectBranches
	}

	// BranchExists checks that a branch matching the given pattern exists in a particular project.
	func BranchExists(branchPattern *regexp.Regexp, buildNumber string, branchType string, remoteBranches []string) (bool, error) {
	for _, branch := range remoteBranches {
	// Failing cases
	switch {
	case branchPattern.Match([]byte(branch)):
	return true, nil
	case strings.Contains(branch, buildNumber):

	// Check that major version collision is on other branch type
	if !strings.Contains(branch, branchType) {
	err := errors.New("ERROR: Major version collision on branch " + branch)
	return true, err
	}
	}
	}

	return false, nil
	}

	// branchExistsExplicit checks that the given branch exists in the project.
	// It is a good bit faster than BranchExists.
	func branchExistsExplicit(project repo.Project, br string) (bool, error) {
	remoteUrl, err := ProjectFetchUrl(project.Path)
	if err != nil {
	return false, errors.Annotate(err, "failed to get remote project url").Err()
	}

	ch := make(chan bool, 1)

	ctx, cancel := context.WithTimeout(context.Background(), gitTimeout)
	defer cancel()
	opts := shared.DefaultOpts
	opts.Retries = gitRetries
	err = shared.DoWithRetry(ctx, opts, func() error {
	// If we give a full URL, don't need to run the command in a git repo.
	output, err := git.RemoteHasBranch("", remoteUrl, br)
	if err != nil {
	return err
	}
	ch <- output
	return nil
	})
	if err != nil {
	return false, errors.Annotate(err, "failed to list remote branches for %s", remoteUrl).Err()
	}

	return <-ch, nil
	}

	func assertBranchesDoNotExistWorker(
	wg *sync.WaitGroup, projectBranches <-chan ProjectBranch, errs chan<- error) {
	for projectBranch := range projectBranches {
	LogOut("...checking that %s does not exist in %s.\n",
	projectBranch.BranchName,
	projectBranch.Project.Name)
	exists, err := branchExistsExplicit(projectBranch.Project, projectBranch.BranchName)
	if err == nil {
	if exists {
	errs <- fmt.Errorf("branch %s exists for %s. Please rerun with --force to proceed.",
	projectBranch.BranchName, projectBranch.Project.Name)
	}
	} else {
	errs <- err
	}
	wg.Done()
	}
	}

	// AssertBranchesDoNotExist checks that branches do not already exist.
	func AssertBranchesDoNotExist(branches []ProjectBranch, workerCount int) error {
	projectBranches := make(chan ProjectBranch, len(branches))
	errs := make(chan error, len(branches))

	var wg sync.WaitGroup
	for i := 1; i <= workerCount; i++ {
	go assertBranchesDoNotExistWorker(&wg, projectBranches, errs)
	}

	for _, projectBranch := range branches {
	projectBranches <- projectBranch
	wg.Add(1)
	}
	close(projectBranches)

	wg.Wait()

	select {
	case err := <-errs:
	return err
	default:
	}
	return nil
	}

	// GerritProjectBranches creates a slice of GerritProjectBranch objects, which
	// are representations of ProjectBranches that are useful for API based
	// branching.
	func GerritProjectBranches(pbs []ProjectBranch) ([]GerritProjectBranch, error) {
	var result []GerritProjectBranch
	for _, pb := range pbs {
	remote := WorkingManifest.GetRemoteByName(pb.Project.RemoteName)
	if remote == nil {
	return result, fmt.Errorf("remote %s does not exist in working manifest", pb.Project.RemoteName)
	}
	remoteURL, err := url.Parse(remote.Fetch)
	if err != nil {
	return result, errors.Annotate(err, "failed to parse fetch location for remote %s", remote.Name).Err()
	}
	remoteStr := remoteURL.String()
	remoteStr = strings.ReplaceAll(remoteStr,
	"chromium.googlesource.com", "chromium-review.googlesource.com")
	remoteStr = strings.ReplaceAll(remoteStr,
	"chrome-internal.googlesource.com", "chrome-internal-review.googlesource.com")
	result = append(result, GerritProjectBranch{
	GerritURL: remoteStr,
	Project: pb.Project.Name,
	Branch: pb.BranchName,
	SrcRef: pb.Project.Revision,
	})
	}
	return result, nil
	}

	// getBranchesByPath returns a map mapping project paths to git branch names.
	func getBranchesByPath(branches []ProjectBranch) map[string]string {
	branchesByPath := make(map[string]string)
	for _, branch := range branches {
	branchesByPath[branch.Project.Path] = branch.BranchName
	}
	return branchesByPath
	}

	// getOriginRef returns the equivalent of the specified Ref for the "origin" remote.
	func getOriginRef(ref string) string {
	// If the revision starts with refs/heads/, make it start with
	// refs/remotes/origin instead.
	if git.StripRefsHead(ref) != ref {
	return "refs/remotes/origin/" + git.StripRefsHead(ref)
	}
	// If the revision is a SHA, let it be.
	return ref
	}

	// GetNonManifestBranches filters out non-Manifest branches.
	func GetNonManifestBranches(branches []GerritProjectBranch) []GerritProjectBranch {
	var result []GerritProjectBranch
	for _, pb := range branches {
	if _, ok := ManifestProjects[pb.Project]; ok {
	continue
	}
	result = append(result, pb)
	}
	return result
	}

	// RepairManifestRepositories repairs all manifests in all manifest repositories
	// on the current branch and commits the changes. It then pushes the state of
	// the local git branches to remote.
	func RepairManifestRepositories(branches []ProjectBranch, dryRun, force bool) error {
	manifestBranchNames := make(map[string]string)

	// Find names of manifest project branches so that we can push changes.
	for _, projectBranch := range branches {
	if _, ok := ManifestProjects[projectBranch.Project.Name]; ok {
	manifestBranchNames[projectBranch.Project.Name] = projectBranch.BranchName
	}
	}

	for projectName := range ManifestProjects {
	manifestProject, err := WorkingManifest.GetUniqueProject(projectName)
	if err != nil {
	return err
	}
	opts := &CheckoutOptions{
	Depth: 1,
	Ref: manifestProject.Revision,
	}
	manifestCheckout, err := GetProjectCheckout(manifestProject.Path, opts)

	defer os.RemoveAll(manifestCheckout)

	if err != nil {
	return errors.Annotate(err, "failed to checkout project %s", manifestProject.Path).Err()
	}

	manifestRepo := ManifestRepo{
	ProjectCheckout: manifestCheckout,
	Project: manifestProject,
	}
	if err := manifestRepo.RepairManifestsOnDisk(getBranchesByPath(branches)); err != nil {
	return errors.Annotate(err, "failed to repair manifest project %s", projectName).Err()
	}
	if output, err := git.RunGit(manifestCheckout,
	[]string{"commit", "-a", "-m", "commit repaired manifests"}); err != nil {
	return fmt.Errorf("error committing repaired manifests: %s", output.Stdout)
	}

	remoteRef := git.RemoteRef{
	Remote: "origin",
	Ref: git.NormalizeRef(manifestBranchNames[manifestProject.Name]),
	}
	gitOpts := git.GitOpts{
	DryRun: dryRun,
	Force: force,
	}
	if err := git.PushRef(manifestCheckout, "HEAD", remoteRef, gitOpts); err != nil {
	return errors.Annotate(err, "could not push branches to remote").Err()
	}
	}
	return nil
	}

	func createRemoteBranchesWorker(
	wg *sync.WaitGroup,
	branches <-chan ProjectBranch,
	errs chan<- error,
	dryRun, force bool) {
	for projectBranch := range branches {
	opts := &CheckoutOptions{
	Depth: 1,
	Ref: projectBranch.Project.Revision,
	}
	projectCheckout, err := GetProjectCheckout(projectBranch.Project.Path, opts)
	defer os.RemoveAll(projectCheckout)
	if err != nil {
	errs <- errors.Annotate(err, "could not checkout %s:%s",
	projectBranch.Project.Path, projectBranch.BranchName).Err()
	wg.Done()
	continue
	}

	branchName := git.NormalizeRef(projectBranch.BranchName)
	refspec := fmt.Sprintf("%s:%s", getOriginRef(projectBranch.Project.Revision), branchName)

	logMode := "Pushing"
	cmd := []string{"push", "origin", refspec}
	if dryRun {
	cmd = append(cmd, "--dry-run")
	logMode = "Dry run"
	}
	if force {
	cmd = append(cmd, "--force")
	logMode += " (with --force flag)"
	}
	LogOut("%s ref %s for project %s\n", logMode, branchName, projectBranch.Project.Path)

	ctx, cancel := context.WithTimeout(context.Background(), gitTimeout)
	defer cancel()
	retryOpts := shared.DefaultOpts
	retryOpts.Retries = gitRetries
	err = shared.DoWithRetry(ctx, retryOpts, func() error {
	return git.RunGitIgnoreOutput(projectCheckout, cmd)
	})
	if err != nil {
	errs <- errors.Annotate(err, "could not push branches to remote").Err()
	wg.Done()
	continue
	}
	wg.Done()
	}

	return
	}

	// CreateRemoteBranches makes the requested branches on the remote Gerrit hosts
	// using git checkouts and pushes.
	func CreateRemoteBranches(branches []ProjectBranch, dryRun, force bool, workerCount int) error {
	branchChan := make(chan ProjectBranch, len(branches))
	errs := make(chan error, len(branches))

	var wg sync.WaitGroup
	for i := 1; i <= workerCount; i++ {
	go createRemoteBranchesWorker(&wg, branchChan, errs, dryRun, force)
	}

	// Push the local git branches to remote.
	for _, projectBranch := range branches {
	// Don't push the manifest repos because that already happened in RepairManifestRepositories.
	if _, ok := ManifestProjects[projectBranch.Project.Name]; ok {
	continue
	}

	branchChan <- projectBranch
	wg.Add(1)
	}
	close(branchChan)

	wg.Wait()

	select {
	case err := <-errs:
	return err
	default:
	}
	return nil
	}

	// WhichVersionShouldBump returns which version is incremented by builds on a new branch.
	func WhichVersionShouldBump(vinfo mv.VersionInfo) (mv.VersionComponent, error) {
	if vinfo.PatchNumber != 0 {
	return mv.Unspecified, fmt.Errorf("cannot bump version with nonzero patch number")
	}
	if vinfo.BranchBuildNumber != 0 {
	return mv.Patch, nil
	} else {
	return mv.Branch, nil
	}
	}

	// BranchType determines the type of branch to be created.
	func BranchType(release, factory, firmware, stabilize bool, custom string) (string, bool) {
	var branchType string
	branchTypesSelected := 0
	if release {
	branchTypesSelected++
	branchType = "release"
	}
	if factory {
	branchTypesSelected++
	branchType = "factory"
	}
	if firmware {
	branchTypesSelected++
	branchType = "firmware"
	}
	if stabilize {
	branchTypesSelected++
	branchType = "stabilize"
	}
	if custom != "" {
	branchTypesSelected++
	branchType = "custom"
	}
	if branchTypesSelected != 1 {
	return "", false
	}

	return branchType, true
	}

	// Determine the name for a new branch.
	// By convention, standard branch names must end with the stripped version
	// string from which they were created, followed by '.B'.
	//
	// For example:
	// - A branch created from 1.0.0 must end with -1.B
	// - A branch created from 1.2.0 must end with -1.2.B
	//
	// Release branches have a slightly different naming scheme. They include
	// the milestone from which they were created. Example: release-R12-1.2.B
	func NewBranchName(vinfo mv.VersionInfo, custom, descriptor string, release, factory, firmware, stabilize bool) string {
	if custom != "" {
	return custom
	}
	branchType, _ := BranchType(release, factory, firmware, stabilize, custom)
	branchNameParts := []string{branchType}
	if branchType == "release" {
	branchNameParts = append(branchNameParts, fmt.Sprintf("R%d", vinfo.ChromeBranch))
	}
	if descriptor != "" {
	branchNameParts = append(branchNameParts, descriptor)
	}
	branchNameParts = append(branchNameParts, vinfo.StrippedVersionString()+".B")
	return strings.Join(branchNameParts, "-")
	}

	// CheckIfAlreadyBranched checks if there's already a branch for the desired new
	// branch to create on the manifest-internal repo.
	func CheckIfAlreadyBranched(vinfo mv.VersionInfo, manifestInternal repo.Project, force bool, branchType string) error {
	// Check that we did not already branch from this version.
	// manifest-internal serves as the sentinel project.
	pattern := regexp.MustCompile(fmt.Sprintf(`.*-%s.B$`, vinfo.StrippedVersionString()))

	// Verify that a major-minor version collision won't occur
	majorMinor := fmt.Sprintf("%v.%v", vinfo.BuildNumber, vinfo.BranchBuildNumber)

	// Fetch remoteUrl
	remoteUrl, err := ProjectFetchUrl(manifestInternal.Path)
	if err != nil {
	err = errors.Annotate(err, "failed to get remote project url").Err()
	}

	// If we give a full URL, don't need to run the command in a git repo.
	remoteBranches, err := git.RemoteBranches("", remoteUrl)
	if err != nil {
	err = errors.Annotate(err, "failed to list remote branches for %s", remoteUrl).Err()
	}

	exists, err := BranchExists(pattern, majorMinor, branchType, remoteBranches)
	if err != nil {
	return err
	}
	if exists {
	if !force {
	return fmt.Errorf("already branched %s. Please rerun with --force if you "+
	"would like to proceed", vinfo.VersionString())
	} else {
	LogOut("Overwriting branch with version %s (--force was set).\n", vinfo.VersionString())
	}
	} else {
	LogOut("No branch exists for version %s. Continuing...\n", vinfo.VersionString())
	}
	return nil
	}