feat(third_party): Check in git-appraise r/10

1 files changed, 987 insertions, 0 deletions

diff --git a/third_party/go/git-appraise/repository/git.go b/third_party/go/git-appraise/repository/git.go
new file mode 100644
index 000000000000..31d27ea6d2ec
--- /dev/null
+++ b/third_party/go/git-appraise/repository/git.go
@@ -0,0 +1,987 @@
+/*
+Copyright 2015 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package repository contains helper methods for working with the Git repo.
+package repository
+
+import (
+	"bufio"
+	"bytes"
+	"crypto/sha1"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+)
+
+const branchRefPrefix = "refs/heads/"
+
+// GitRepo represents an instance of a (local) git repository.
+type GitRepo struct {
+	Path string
+}
+
+// Run the given git command with the given I/O reader/writers, returning an error if it fails.
+func (repo *GitRepo) runGitCommandWithIO(stdin io.Reader, stdout, stderr io.Writer, args ...string) error {
+	cmd := exec.Command("git", args...)
+	cmd.Dir = repo.Path
+	cmd.Stdin = stdin
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
+	return cmd.Run()
+}
+
+// Run the given git command and return its stdout, or an error if the command fails.
+func (repo *GitRepo) runGitCommandRaw(args ...string) (string, string, error) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	err := repo.runGitCommandWithIO(nil, &stdout, &stderr, args...)
+	return strings.TrimSpace(stdout.String()), strings.TrimSpace(stderr.String()), err
+}
+
+// Run the given git command and return its stdout, or an error if the command fails.
+func (repo *GitRepo) runGitCommand(args ...string) (string, error) {
+	stdout, stderr, err := repo.runGitCommandRaw(args...)
+	if err != nil {
+		if stderr == "" {
+			stderr = "Error running git command: " + strings.Join(args, " ")
+		}
+		err = fmt.Errorf(stderr)
+	}
+	return stdout, err
+}
+
+// Run the given git command using the same stdin, stdout, and stderr as the review tool.
+func (repo *GitRepo) runGitCommandInline(args ...string) error {
+	return repo.runGitCommandWithIO(os.Stdin, os.Stdout, os.Stderr, args...)
+}
+
+// NewGitRepo determines if the given working directory is inside of a git repository,
+// and returns the corresponding GitRepo instance if it is.
+func NewGitRepo(path string) (*GitRepo, error) {
+	repo := &GitRepo{Path: path}
+	_, _, err := repo.runGitCommandRaw("rev-parse")
+	if err == nil {
+		return repo, nil
+	}
+	if _, ok := err.(*exec.ExitError); ok {
+		return nil, err
+	}
+	return nil, err
+}
+
+// GetPath returns the path to the repo.
+func (repo *GitRepo) GetPath() string {
+	return repo.Path
+}
+
+// GetRepoStateHash returns a hash which embodies the entire current state of a repository.
+func (repo *GitRepo) GetRepoStateHash() (string, error) {
+	stateSummary, error := repo.runGitCommand("show-ref")
+	return fmt.Sprintf("%x", sha1.Sum([]byte(stateSummary))), error
+}
+
+// GetUserEmail returns the email address that the user has used to configure git.
+func (repo *GitRepo) GetUserEmail() (string, error) {
+	return repo.runGitCommand("config", "user.email")
+}
+
+// GetUserSigningKey returns the key id the user has configured for
+// sigining git artifacts.
+func (repo *GitRepo) GetUserSigningKey() (string, error) {
+	return repo.runGitCommand("config", "user.signingKey")
+}
+
+// GetCoreEditor returns the name of the editor that the user has used to configure git.
+func (repo *GitRepo) GetCoreEditor() (string, error) {
+	return repo.runGitCommand("var", "GIT_EDITOR")
+}
+
+// GetSubmitStrategy returns the way in which a review is submitted
+func (repo *GitRepo) GetSubmitStrategy() (string, error) {
+	submitStrategy, _ := repo.runGitCommand("config", "appraise.submit")
+	return submitStrategy, nil
+}
+
+// HasUncommittedChanges returns true if there are local, uncommitted changes.
+func (repo *GitRepo) HasUncommittedChanges() (bool, error) {
+	out, err := repo.runGitCommand("status", "--porcelain")
+	if err != nil {
+		return false, err
+	}
+	if len(out) > 0 {
+		return true, nil
+	}
+	return false, nil
+}
+
+// VerifyCommit verifies that the supplied hash points to a known commit.
+func (repo *GitRepo) VerifyCommit(hash string) error {
+	out, err := repo.runGitCommand("cat-file", "-t", hash)
+	if err != nil {
+		return err
+	}
+	objectType := strings.TrimSpace(string(out))
+	if objectType != "commit" {
+		return fmt.Errorf("Hash %q points to a non-commit object of type %q", hash, objectType)
+	}
+	return nil
+}
+
+// VerifyGitRef verifies that the supplied ref points to a known commit.
+func (repo *GitRepo) VerifyGitRef(ref string) error {
+	_, err := repo.runGitCommand("show-ref", "--verify", ref)
+	return err
+}
+
+// GetHeadRef returns the ref that is the current HEAD.
+func (repo *GitRepo) GetHeadRef() (string, error) {
+	return repo.runGitCommand("symbolic-ref", "HEAD")
+}
+
+// GetCommitHash returns the hash of the commit pointed to by the given ref.
+func (repo *GitRepo) GetCommitHash(ref string) (string, error) {
+	return repo.runGitCommand("show", "-s", "--format=%H", ref)
+}
+
+// ResolveRefCommit returns the commit pointed to by the given ref, which may be a remote ref.
+//
+// This differs from GetCommitHash which only works on exact matches, in that it will try to
+// intelligently handle the scenario of a ref not existing locally, but being known to exist
+// in a remote repo.
+//
+// This method should be used when a command may be performed by either the reviewer or the
+// reviewee, while GetCommitHash should be used when the encompassing command should only be
+// performed by the reviewee.
+func (repo *GitRepo) ResolveRefCommit(ref string) (string, error) {
+	if err := repo.VerifyGitRef(ref); err == nil {
+		return repo.GetCommitHash(ref)
+	}
+	if strings.HasPrefix(ref, "refs/heads/") {
+		// The ref is a branch. Check if it exists in exactly one remote
+		pattern := strings.Replace(ref, "refs/heads", "**", 1)
+		matchingOutput, err := repo.runGitCommand("for-each-ref", "--format=%(refname)", pattern)
+		if err != nil {
+			return "", err
+		}
+		matchingRefs := strings.Split(matchingOutput, "\n")
+		if len(matchingRefs) == 1 && matchingRefs[0] != "" {
+			// There is exactly one match
+			return repo.GetCommitHash(matchingRefs[0])
+		}
+		return "", fmt.Errorf("Unable to find a git ref matching the pattern %q", pattern)
+	}
+	return "", fmt.Errorf("Unknown git ref %q", ref)
+}
+
+// GetCommitMessage returns the message stored in the commit pointed to by the given ref.
+func (repo *GitRepo) GetCommitMessage(ref string) (string, error) {
+	return repo.runGitCommand("show", "-s", "--format=%B", ref)
+}
+
+// GetCommitTime returns the commit time of the commit pointed to by the given ref.
+func (repo *GitRepo) GetCommitTime(ref string) (string, error) {
+	return repo.runGitCommand("show", "-s", "--format=%ct", ref)
+}
+
+// GetLastParent returns the last parent of the given commit (as ordered by git).
+func (repo *GitRepo) GetLastParent(ref string) (string, error) {
+	return repo.runGitCommand("rev-list", "--skip", "1", "-n", "1", ref)
+}
+
+// GetCommitDetails returns the details of a commit's metadata.
+func (repo GitRepo) GetCommitDetails(ref string) (*CommitDetails, error) {
+	var err error
+	show := func(formatString string) (result string) {
+		if err != nil {
+			return ""
+		}
+		result, err = repo.runGitCommand("show", "-s", ref, fmt.Sprintf("--format=tformat:%s", formatString))
+		return result
+	}
+
+	jsonFormatString := "{\"tree\":\"%T\", \"time\": \"%at\"}"
+	detailsJSON := show(jsonFormatString)
+	if err != nil {
+		return nil, err
+	}
+	var details CommitDetails
+	err = json.Unmarshal([]byte(detailsJSON), &details)
+	if err != nil {
+		return nil, err
+	}
+	details.Author = show("%an")
+	details.AuthorEmail = show("%ae")
+	details.Summary = show("%s")
+	parentsString := show("%P")
+	details.Parents = strings.Split(parentsString, " ")
+	if err != nil {
+		return nil, err
+	}
+	return &details, nil
+}
+
+// MergeBase determines if the first commit that is an ancestor of the two arguments.
+func (repo *GitRepo) MergeBase(a, b string) (string, error) {
+	return repo.runGitCommand("merge-base", a, b)
+}
+
+// IsAncestor determines if the first argument points to a commit that is an ancestor of the second.
+func (repo *GitRepo) IsAncestor(ancestor, descendant string) (bool, error) {
+	_, _, err := repo.runGitCommandRaw("merge-base", "--is-ancestor", ancestor, descendant)
+	if err == nil {
+		return true, nil
+	}
+	if _, ok := err.(*exec.ExitError); ok {
+		return false, nil
+	}
+	return false, fmt.Errorf("Error while trying to determine commit ancestry: %v", err)
+}
+
+// Diff computes the diff between two given commits.
+func (repo *GitRepo) Diff(left, right string, diffArgs ...string) (string, error) {
+	args := []string{"diff"}
+	args = append(args, diffArgs...)
+	args = append(args, fmt.Sprintf("%s..%s", left, right))
+	return repo.runGitCommand(args...)
+}
+
+// Show returns the contents of the given file at the given commit.
+func (repo *GitRepo) Show(commit, path string) (string, error) {
+	return repo.runGitCommand("show", fmt.Sprintf("%s:%s", commit, path))
+}
+
+// SwitchToRef changes the currently-checked-out ref.
+func (repo *GitRepo) SwitchToRef(ref string) error {
+	// If the ref starts with "refs/heads/", then we have to trim that prefix,
+	// or else we will wind up in a detached HEAD state.
+	if strings.HasPrefix(ref, branchRefPrefix) {
+		ref = ref[len(branchRefPrefix):]
+	}
+	_, err := repo.runGitCommand("checkout", ref)
+	return err
+}
+
+// mergeArchives merges two archive refs.
+func (repo *GitRepo) mergeArchives(archive, remoteArchive string) error {
+	remoteHash, err := repo.GetCommitHash(remoteArchive)
+	if err != nil {
+		return err
+	}
+	if remoteHash == "" {
+		// The remote archive does not exist, so we have nothing to do
+		return nil
+	}
+
+	archiveHash, err := repo.GetCommitHash(archive)
+	if err != nil {
+		return err
+	}
+	if archiveHash == "" {
+		// The local archive does not exist, so we merely need to set it
+		_, err := repo.runGitCommand("update-ref", archive, remoteHash)
+		return err
+	}
+
+	isAncestor, err := repo.IsAncestor(archiveHash, remoteHash)
+	if err != nil {
+		return err
+	}
+	if isAncestor {
+		// The archive can simply be fast-forwarded
+		_, err := repo.runGitCommand("update-ref", archive, remoteHash, archiveHash)
+		return err
+	}
+
+	// Create a merge commit of the two archives
+	refDetails, err := repo.GetCommitDetails(remoteArchive)
+	if err != nil {
+		return err
+	}
+	newArchiveHash, err := repo.runGitCommand("commit-tree", "-p", remoteHash, "-p", archiveHash, "-m", "Merge local and remote archives", refDetails.Tree)
+	if err != nil {
+		return err
+	}
+	newArchiveHash = strings.TrimSpace(newArchiveHash)
+	_, err = repo.runGitCommand("update-ref", archive, newArchiveHash, archiveHash)
+	return err
+}
+
+// ArchiveRef adds the current commit pointed to by the 'ref' argument
+// under the ref specified in the 'archive' argument.
+//
+// Both the 'ref' and 'archive' arguments are expected to be the fully
+// qualified names of git refs (e.g. 'refs/heads/my-change' or
+// 'refs/devtools/archives/reviews').
+//
+// If the ref pointed to by the 'archive' argument does not exist
+// yet, then it will be created.
+func (repo *GitRepo) ArchiveRef(ref, archive string) error {
+	refHash, err := repo.GetCommitHash(ref)
+	if err != nil {
+		return err
+	}
+	refDetails, err := repo.GetCommitDetails(ref)
+	if err != nil {
+		return err
+	}
+
+	commitTreeArgs := []string{"commit-tree"}
+	archiveHash, err := repo.GetCommitHash(archive)
+	if err != nil {
+		archiveHash = ""
+	} else {
+		commitTreeArgs = append(commitTreeArgs, "-p", archiveHash)
+	}
+	commitTreeArgs = append(commitTreeArgs, "-p", refHash, "-m", fmt.Sprintf("Archive %s", refHash), refDetails.Tree)
+	newArchiveHash, err := repo.runGitCommand(commitTreeArgs...)
+	if err != nil {
+		return err
+	}
+	newArchiveHash = strings.TrimSpace(newArchiveHash)
+	updateRefArgs := []string{"update-ref", archive, newArchiveHash}
+	if archiveHash != "" {
+		updateRefArgs = append(updateRefArgs, archiveHash)
+	}
+	_, err = repo.runGitCommand(updateRefArgs...)
+	return err
+}
+
+// MergeRef merges the given ref into the current one.
+//
+// The ref argument is the ref to merge, and fastForward indicates that the
+// current ref should only move forward, as opposed to creating a bubble merge.
+// The messages argument(s) provide text that should be included in the default
+// merge commit message (separated by blank lines).
+func (repo *GitRepo) MergeRef(ref string, fastForward bool, messages ...string) error {
+	args := []string{"merge"}
+	if fastForward {
+		args = append(args, "--ff", "--ff-only")
+	} else {
+		args = append(args, "--no-ff")
+	}
+	if len(messages) > 0 {
+		commitMessage := strings.Join(messages, "\n\n")
+		args = append(args, "-e", "-m", commitMessage)
+	}
+	args = append(args, ref)
+	return repo.runGitCommandInline(args...)
+}
+
+// MergeAndSignRef merges the given ref into the current one and signs the
+// merge.
+//
+// The ref argument is the ref to merge, and fastForward indicates that the
+// current ref should only move forward, as opposed to creating a bubble merge.
+// The messages argument(s) provide text that should be included in the default
+// merge commit message (separated by blank lines).
+func (repo *GitRepo) MergeAndSignRef(ref string, fastForward bool,
+	messages ...string) error {
+
+	args := []string{"merge"}
+	if fastForward {
+		args = append(args, "--ff", "--ff-only", "-S")
+	} else {
+		args = append(args, "--no-ff", "-S")
+	}
+	if len(messages) > 0 {
+		commitMessage := strings.Join(messages, "\n\n")
+		args = append(args, "-e", "-m", commitMessage)
+	}
+	args = append(args, ref)
+	return repo.runGitCommandInline(args...)
+}
+
+// RebaseRef rebases the current ref onto the given one.
+func (repo *GitRepo) RebaseRef(ref string) error {
+	return repo.runGitCommandInline("rebase", "-i", ref)
+}
+
+// RebaseAndSignRef rebases the current ref onto the given one and signs the
+// result.
+func (repo *GitRepo) RebaseAndSignRef(ref string) error {
+	return repo.runGitCommandInline("rebase", "-S", "-i", ref)
+}
+
+// ListCommits returns the list of commits reachable from the given ref.
+//
+// The generated list is in chronological order (with the oldest commit first).
+//
+// If the specified ref does not exist, then this method returns an empty result.
+func (repo *GitRepo) ListCommits(ref string) []string {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	if err := repo.runGitCommandWithIO(nil, &stdout, &stderr, "rev-list", "--reverse", ref); err != nil {
+		return nil
+	}
+
+	byteLines := bytes.Split(stdout.Bytes(), []byte("\n"))
+	var commits []string
+	for _, byteLine := range byteLines {
+		commits = append(commits, string(byteLine))
+	}
+	return commits
+}
+
+// ListCommitsBetween returns the list of commits between the two given revisions.
+//
+// The "from" parameter is the starting point (exclusive), and the "to"
+// parameter is the ending point (inclusive).
+//
+// The "from" commit does not need to be an ancestor of the "to" commit. If it
+// is not, then the merge base of the two is used as the starting point.
+// Admittedly, this makes calling these the "between" commits is a bit of a
+// misnomer, but it also makes the method easier to use when you want to
+// generate the list of changes in a feature branch, as it eliminates the need
+// to explicitly calculate the merge base. This also makes the semantics of the
+// method compatible with git's built-in "rev-list" command.
+//
+// The generated list is in chronological order (with the oldest commit first).
+func (repo *GitRepo) ListCommitsBetween(from, to string) ([]string, error) {
+	out, err := repo.runGitCommand("rev-list", "--reverse", from+".."+to)
+	if err != nil {
+		return nil, err
+	}
+	if out == "" {
+		return nil, nil
+	}
+	return strings.Split(out, "\n"), nil
+}
+
+// GetNotes uses the "git" command-line tool to read the notes from the given ref for a given revision.
+func (repo *GitRepo) GetNotes(notesRef, revision string) []Note {
+	var notes []Note
+	rawNotes, err := repo.runGitCommand("notes", "--ref", notesRef, "show", revision)
+	if err != nil {
+		// We just assume that this means there are no notes
+		return nil
+	}
+	for _, line := range strings.Split(rawNotes, "\n") {
+		notes = append(notes, Note([]byte(line)))
+	}
+	return notes
+}
+
+func stringsReader(s []*string) io.Reader {
+	var subReaders []io.Reader
+	for _, strPtr := range s {
+		subReader := strings.NewReader(*strPtr)
+		subReaders = append(subReaders, subReader, strings.NewReader("\n"))
+	}
+	return io.MultiReader(subReaders...)
+}
+
+// splitBatchCheckOutput parses the output of a 'git cat-file --batch-check=...' command.
+//
+// The output is expected to be formatted as a series of entries, with each
+// entry consisting of:
+// 1. The SHA1 hash of the git object being output, followed by a space.
+// 2. The git "type" of the object (commit, blob, tree, missing, etc), followed by a newline.
+//
+// To generate this format, make sure that the 'git cat-file' command includes
+// the argument '--batch-check=%(objectname) %(objecttype)'.
+//
+// The return value is a map from object hash to a boolean indicating if that object is a commit.
+func splitBatchCheckOutput(out *bytes.Buffer) (map[string]bool, error) {
+	isCommit := make(map[string]bool)
+	reader := bufio.NewReader(out)
+	for {
+		nameLine, err := reader.ReadString(byte(' '))
+		if err == io.EOF {
+			return isCommit, nil
+		}
+		if err != nil {
+			return nil, fmt.Errorf("Failure while reading the next object name: %v", err)
+		}
+		nameLine = strings.TrimSuffix(nameLine, " ")
+		typeLine, err := reader.ReadString(byte('\n'))
+		if err != nil && err != io.EOF {
+			return nil, fmt.Errorf("Failure while reading the next object type: %q - %v", nameLine, err)
+		}
+		typeLine = strings.TrimSuffix(typeLine, "\n")
+		if typeLine == "commit" {
+			isCommit[nameLine] = true
+		}
+	}
+}
+
+// splitBatchCatFileOutput parses the output of a 'git cat-file --batch=...' command.
+//
+// The output is expected to be formatted as a series of entries, with each
+// entry consisting of:
+// 1. The SHA1 hash of the git object being output, followed by a newline.
+// 2. The size of the object's contents in bytes, followed by a newline.
+// 3. The objects contents.
+//
+// To generate this format, make sure that the 'git cat-file' command includes
+// the argument '--batch=%(objectname)\n%(objectsize)'.
+func splitBatchCatFileOutput(out *bytes.Buffer) (map[string][]byte, error) {
+	contentsMap := make(map[string][]byte)
+	reader := bufio.NewReader(out)
+	for {
+		nameLine, err := reader.ReadString(byte('\n'))
+		if strings.HasSuffix(nameLine, "\n") {
+			nameLine = strings.TrimSuffix(nameLine, "\n")
+		}
+		if err == io.EOF {
+			return contentsMap, nil
+		}
+		if err != nil {
+			return nil, fmt.Errorf("Failure while reading the next object name: %v", err)
+		}
+		sizeLine, err := reader.ReadString(byte('\n'))
+		if strings.HasSuffix(sizeLine, "\n") {
+			sizeLine = strings.TrimSuffix(sizeLine, "\n")
+		}
+		if err != nil {
+			return nil, fmt.Errorf("Failure while reading the next object size: %q - %v", nameLine, err)
+		}
+		size, err := strconv.Atoi(sizeLine)
+		if err != nil {
+			return nil, fmt.Errorf("Failure while parsing the next object size: %q - %v", nameLine, err)
+		}
+		contentBytes := make([]byte, size, size)
+		readDest := contentBytes
+		len := 0
+		err = nil
+		for err == nil && len < size {
+			nextLen := 0
+			nextLen, err = reader.Read(readDest)
+			len += nextLen
+			readDest = contentBytes[len:]
+		}
+		contentsMap[nameLine] = contentBytes
+		if err == io.EOF {
+			return contentsMap, nil
+		}
+		if err != nil {
+			return nil, err
+		}
+		for bs, err := reader.Peek(1); err == nil && bs[0] == byte('\n'); bs, err = reader.Peek(1) {
+			reader.ReadByte()
+		}
+	}
+}
+
+// notesMapping represents the association between a git object and the notes for that object.
+type notesMapping struct {
+	ObjectHash *string
+	NotesHash  *string
+}
+
+// notesOverview represents a high-level overview of all the notes under a single notes ref.
+type notesOverview struct {
+	NotesMappings      []*notesMapping
+	ObjectHashesReader io.Reader
+	NotesHashesReader  io.Reader
+}
+
+// notesOverview returns an overview of the git notes stored under the given ref.
+func (repo *GitRepo) notesOverview(notesRef string) (*notesOverview, error) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	if err := repo.runGitCommandWithIO(nil, &stdout, &stderr, "notes", "--ref", notesRef, "list"); err != nil {
+		return nil, err
+	}
+
+	var notesMappings []*notesMapping
+	var objHashes []*string
+	var notesHashes []*string
+	outScanner := bufio.NewScanner(&stdout)
+	for outScanner.Scan() {
+		line := outScanner.Text()
+		lineParts := strings.Split(line, " ")
+		if len(lineParts) != 2 {
+			return nil, fmt.Errorf("Malformed output line from 'git-notes list': %q", line)
+		}
+		objHash := &lineParts[1]
+		notesHash := &lineParts[0]
+		notesMappings = append(notesMappings, &notesMapping{
+			ObjectHash: objHash,
+			NotesHash:  notesHash,
+		})
+		objHashes = append(objHashes, objHash)
+		notesHashes = append(notesHashes, notesHash)
+	}
+	err := outScanner.Err()
+	if err != nil && err != io.EOF {
+		return nil, fmt.Errorf("Failure parsing the output of 'git-notes list': %v", err)
+	}
+	return &notesOverview{
+		NotesMappings:      notesMappings,
+		ObjectHashesReader: stringsReader(objHashes),
+		NotesHashesReader:  stringsReader(notesHashes),
+	}, nil
+}
+
+// getIsCommitMap returns a mapping of all the annotated objects that are commits.
+func (overview *notesOverview) getIsCommitMap(repo *GitRepo) (map[string]bool, error) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	if err := repo.runGitCommandWithIO(overview.ObjectHashesReader, &stdout, &stderr, "cat-file", "--batch-check=%(objectname) %(objecttype)"); err != nil {
+		return nil, fmt.Errorf("Failure performing a batch file check: %v", err)
+	}
+	isCommit, err := splitBatchCheckOutput(&stdout)
+	if err != nil {
+		return nil, fmt.Errorf("Failure parsing the output of a batch file check: %v", err)
+	}
+	return isCommit, nil
+}
+
+// getNoteContentsMap returns a mapping from all the notes hashes to their contents.
+func (overview *notesOverview) getNoteContentsMap(repo *GitRepo) (map[string][]byte, error) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	if err := repo.runGitCommandWithIO(overview.NotesHashesReader, &stdout, &stderr, "cat-file", "--batch=%(objectname)\n%(objectsize)"); err != nil {
+		return nil, fmt.Errorf("Failure performing a batch file read: %v", err)
+	}
+	noteContentsMap, err := splitBatchCatFileOutput(&stdout)
+	if err != nil {
+		return nil, fmt.Errorf("Failure parsing the output of a batch file read: %v", err)
+	}
+	return noteContentsMap, nil
+}
+
+// GetAllNotes reads the contents of the notes under the given ref for every commit.
+//
+// The returned value is a mapping from commit hash to the list of notes for that commit.
+//
+// This is the batch version of the corresponding GetNotes(...) method.
+func (repo *GitRepo) GetAllNotes(notesRef string) (map[string][]Note, error) {
+	// This code is unfortunately quite complicated, but it needs to be so.
+	//
+	// Conceptually, this is equivalent to:
+	//   result := make(map[string][]Note)
+	//   for _, commit := range repo.ListNotedRevisions(notesRef) {
+	//     result[commit] = repo.GetNotes(notesRef, commit)
+	//   }
+	//   return result, nil
+	//
+	// However, that logic would require separate executions of the 'git'
+	// command for every annotated commit. For a repo with 10s of thousands
+	// of reviews, that would mean calling Cmd.Run(...) 10s of thousands of
+	// times. That, in turn, would take so long that the tool would be unusable.
+	//
+	// This method avoids that by taking advantage of the 'git cat-file --batch="..."'
+	// command. That allows us to use a single invocation of Cmd.Run(...) to
+	// inspect multiple git objects at once.
+	//
+	// As such, regardless of the number of reviews in a repo, we can get all
+	// of the notes using a total of three invocations of Cmd.Run(...):
+	//  1. One to list all the annotated objects (and their notes hash)
+	//  2. A second one to filter out all of the annotated objects that are not commits.
+	//  3. A final one to get the contents of all of the notes blobs.
+	overview, err := repo.notesOverview(notesRef)
+	if err != nil {
+		return nil, err
+	}
+	isCommit, err := overview.getIsCommitMap(repo)
+	if err != nil {
+		return nil, fmt.Errorf("Failure building the set of commit objects: %v", err)
+	}
+	noteContentsMap, err := overview.getNoteContentsMap(repo)
+	if err != nil {
+		return nil, fmt.Errorf("Failure building the mapping from notes hash to contents: %v", err)
+	}
+	commitNotesMap := make(map[string][]Note)
+	for _, notesMapping := range overview.NotesMappings {
+		if !isCommit[*notesMapping.ObjectHash] {
+			continue
+		}
+		noteBytes := noteContentsMap[*notesMapping.NotesHash]
+		byteSlices := bytes.Split(noteBytes, []byte("\n"))
+		var notes []Note
+		for _, slice := range byteSlices {
+			notes = append(notes, Note(slice))
+		}
+		commitNotesMap[*notesMapping.ObjectHash] = notes
+	}
+
+	return commitNotesMap, nil
+}
+
+// AppendNote appends a note to a revision under the given ref.
+func (repo *GitRepo) AppendNote(notesRef, revision string, note Note) error {
+	_, err := repo.runGitCommand("notes", "--ref", notesRef, "append", "-m", string(note), revision)
+	return err
+}
+
+// ListNotedRevisions returns the collection of revisions that are annotated by notes in the given ref.
+func (repo *GitRepo) ListNotedRevisions(notesRef string) []string {
+	var revisions []string
+	notesListOut, err := repo.runGitCommand("notes", "--ref", notesRef, "list")
+	if err != nil {
+		return nil
+	}
+	notesList := strings.Split(notesListOut, "\n")
+	for _, notePair := range notesList {
+		noteParts := strings.SplitN(notePair, " ", 2)
+		if len(noteParts) == 2 {
+			objHash := noteParts[1]
+			objType, err := repo.runGitCommand("cat-file", "-t", objHash)
+			// If a note points to an object that we do not know about (yet), then err will not
+			// be nil. We can safely just ignore those notes.
+			if err == nil && objType == "commit" {
+				revisions = append(revisions, objHash)
+			}
+		}
+	}
+	return revisions
+}
+
+// PushNotes pushes git notes to a remote repo.
+func (repo *GitRepo) PushNotes(remote, notesRefPattern string) error {
+	refspec := fmt.Sprintf("%s:%s", notesRefPattern, notesRefPattern)
+
+	// The push is liable to fail if the user forgot to do a pull first, so
+	// we treat errors as user errors rather than fatal errors.
+	err := repo.runGitCommandInline("push", remote, refspec)
+	if err != nil {
+		return fmt.Errorf("Failed to push to the remote '%s': %v", remote, err)
+	}
+	return nil
+}
+
+// PushNotesAndArchive pushes the given notes and archive refs to a remote repo.
+func (repo *GitRepo) PushNotesAndArchive(remote, notesRefPattern, archiveRefPattern string) error {
+	notesRefspec := fmt.Sprintf("%s:%s", notesRefPattern, notesRefPattern)
+	archiveRefspec := fmt.Sprintf("%s:%s", archiveRefPattern, archiveRefPattern)
+	err := repo.runGitCommandInline("push", remote, notesRefspec, archiveRefspec)
+	if err != nil {
+		return fmt.Errorf("Failed to push the local archive to the remote '%s': %v", remote, err)
+	}
+	return nil
+}
+
+func getRemoteNotesRef(remote, localNotesRef string) string {
+	relativeNotesRef := strings.TrimPrefix(localNotesRef, "refs/notes/")
+	return "refs/notes/" + remote + "/" + relativeNotesRef
+}
+
+// MergeNotes merges in the remote's state of the notes reference into the
+// local repository's.
+func (repo *GitRepo) MergeNotes(remote, notesRefPattern string) error {
+	remoteRefs, err := repo.runGitCommand("ls-remote", remote, notesRefPattern)
+	if err != nil {
+		return err
+	}
+	for _, line := range strings.Split(remoteRefs, "\n") {
+		lineParts := strings.Split(line, "\t")
+		if len(lineParts) == 2 {
+			ref := lineParts[1]
+			remoteRef := getRemoteNotesRef(remote, ref)
+			_, err := repo.runGitCommand("notes", "--ref", ref, "merge", remoteRef, "-s", "cat_sort_uniq")
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// PullNotes fetches the contents of the given notes ref from a remote repo,
+// and then merges them with the corresponding local notes using the
+// "cat_sort_uniq" strategy.
+func (repo *GitRepo) PullNotes(remote, notesRefPattern string) error {
+	remoteNotesRefPattern := getRemoteNotesRef(remote, notesRefPattern)
+	fetchRefSpec := fmt.Sprintf("+%s:%s", notesRefPattern, remoteNotesRefPattern)
+	err := repo.runGitCommandInline("fetch", remote, fetchRefSpec)
+	if err != nil {
+		return err
+	}
+
+	return repo.MergeNotes(remote, notesRefPattern)
+}
+
+func getRemoteArchiveRef(remote, archiveRefPattern string) string {
+	relativeArchiveRef := strings.TrimPrefix(archiveRefPattern, "refs/devtools/archives/")
+	return "refs/devtools/remoteArchives/" + remote + "/" + relativeArchiveRef
+}
+
+// MergeArchives merges in the remote's state of the archives reference into
+// the local repository's.
+func (repo *GitRepo) MergeArchives(remote, archiveRefPattern string) error {
+	remoteRefs, err := repo.runGitCommand("ls-remote", remote, archiveRefPattern)
+	if err != nil {
+		return err
+	}
+	for _, line := range strings.Split(remoteRefs, "\n") {
+		lineParts := strings.Split(line, "\t")
+		if len(lineParts) == 2 {
+			ref := lineParts[1]
+			remoteRef := getRemoteArchiveRef(remote, ref)
+			if err := repo.mergeArchives(ref, remoteRef); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func (repo *GitRepo) fetchNotes(remote, notesRefPattern,
+	archiveRefPattern string) error {
+
+	remoteArchiveRef := getRemoteArchiveRef(remote, archiveRefPattern)
+	archiveFetchRefSpec := fmt.Sprintf("+%s:%s", archiveRefPattern, remoteArchiveRef)
+
+	remoteNotesRefPattern := getRemoteNotesRef(remote, notesRefPattern)
+	notesFetchRefSpec := fmt.Sprintf("+%s:%s", notesRefPattern, remoteNotesRefPattern)
+
+	return repo.runGitCommandInline("fetch", remote, notesFetchRefSpec, archiveFetchRefSpec)
+}
+
+// PullNotesAndArchive fetches the contents of the notes and archives refs from
+// a remote repo, and merges them with the corresponding local refs.
+//
+// For notes refs, we assume that every note can be automatically merged using
+// the 'cat_sort_uniq' strategy (the git-appraise schemas fit that requirement),
+// so we automatically merge the remote notes into the local notes.
+//
+// For "archive" refs, they are expected to be used solely for maintaining
+// reachability of commits that are part of the history of any reviews,
+// so we do not maintain any consistency with their tree objects. Instead,
+// we merely ensure that their history graph includes every commit that we
+// intend to keep.
+func (repo *GitRepo) PullNotesAndArchive(remote, notesRefPattern, archiveRefPattern string) error {
+	err := repo.fetchNotes(remote, notesRefPattern, archiveRefPattern)
+	if err != nil {
+		return err
+	}
+
+	err = repo.MergeNotes(remote, notesRefPattern)
+	if err != nil {
+		return err
+	}
+	return repo.MergeArchives(remote, archiveRefPattern)
+}
+
+// FetchAndReturnNewReviewHashes fetches the notes "branches" and then susses
+// out the IDs (the revision the review points to) of any new reviews, then
+// returns that list of IDs.
+//
+// This is accomplished by determining which files in the notes tree have
+// changed because the _names_ of these files correspond to the revisions they
+// point to.
+func (repo *GitRepo) FetchAndReturnNewReviewHashes(remote, notesRefPattern,
+	archiveRefPattern string) ([]string, error) {
+
+	// Record the current state of the reviews and comments refs.
+	var (
+		getAllRevs, getAllComs    bool
+		reviewsList, commentsList []string
+	)
+	reviewBeforeHash, err := repo.GetCommitHash(
+		"notes/" + remote + "/devtools/reviews")
+	getAllRevs = err != nil
+
+	commentBeforeHash, err := repo.GetCommitHash(
+		"notes/" + remote + "/devtools/discuss")
+	getAllComs = err != nil
+
+	// Update them from the remote.
+	err = repo.fetchNotes(remote, notesRefPattern, archiveRefPattern)
+	if err != nil {
+		return nil, err
+	}
+
+	// Now, if either of these are new refs, we just use the whole tree at that
+	// new ref. Otherwise we see which reviews or comments changed and collect
+	// them into a list.
+	if getAllRevs {
+		hash, err := repo.GetCommitHash(
+			"notes/" + remote + "/devtools/reviews")
+		// It is possible that even after we've pulled that this ref still
+		// isn't present (because there are no reviews yet).
+		if err == nil {
+			rvws, err := repo.runGitCommand("ls-tree", "-r", "--name-only",
+				hash)
+			if err != nil {
+				return nil, err
+			}
+			reviewsList = strings.Split(strings.Replace(rvws, "/", "", -1),
+				"\n")
+		}
+	} else {
+		reviewAfterHash, err := repo.GetCommitHash(
+			"notes/" + remote + "/devtools/reviews")
+		if err != nil {
+			return nil, err
+		}
+
+		// Only run through this if the fetch fetched new revisions.
+		// Otherwise leave reviewsList as its default value, an empty slice
+		// of strings.
+		if reviewBeforeHash != reviewAfterHash {
+			newReviewsRaw, err := repo.runGitCommand("diff", "--name-only",
+				reviewBeforeHash, reviewAfterHash)
+			if err != nil {
+				return nil, err
+			}
+			reviewsList = strings.Split(strings.Replace(newReviewsRaw,
+				"/", "", -1), "\n")
+		}
+	}
+
+	if getAllComs {
+		hash, err := repo.GetCommitHash(
+			"notes/" + remote + "/devtools/discuss")
+		// It is possible that even after we've pulled that this ref still
+		// isn't present (because there are no comments yet).
+		if err == nil {
+			rvws, err := repo.runGitCommand("ls-tree", "-r", "--name-only",
+				hash)
+			if err != nil {
+				return nil, err
+			}
+			commentsList = strings.Split(strings.Replace(rvws, "/", "", -1),
+				"\n")
+		}
+	} else {
+		commentAfterHash, err := repo.GetCommitHash(
+			"notes/" + remote + "/devtools/discuss")
+		if err != nil {
+			return nil, err
+		}
+
+		// Only run through this if the fetch fetched new revisions.
+		// Otherwise leave commentsList as its default value, an empty slice
+		// of strings.
+		if commentBeforeHash != commentAfterHash {
+			newCommentsRaw, err := repo.runGitCommand("diff", "--name-only",
+				commentBeforeHash, commentAfterHash)
+			if err != nil {
+				return nil, err
+			}
+			commentsList = strings.Split(strings.Replace(newCommentsRaw,
+				"/", "", -1), "\n")
+		}
+	}
+
+	// Now that we have our two lists, we need to merge them.
+	updatedReviewSet := make(map[string]struct{})
+	for _, hash := range append(reviewsList, commentsList...) {
+		updatedReviewSet[hash] = struct{}{}
+	}
+
+	updatedReviews := make([]string, 0, len(updatedReviewSet))
+	for key, _ := range updatedReviewSet {
+		updatedReviews = append(updatedReviews, key)
+	}
+	return updatedReviews, nil
+}