tools/src/cmd/git-stats/main.go - dawn - Git at Google

 // Copyright 2022 The Dawn & Tint Authors
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are met:
 //
 // 1. Redistributions of source code must retain the above copyright notice, this
 //    list of conditions and the following disclaimer.
 //
 // 2. Redistributions in binary form must reproduce the above copyright notice,
 //    this list of conditions and the following disclaimer in the documentation
 //    and/or other materials provided with the distribution.
 //
 // 3. Neither the name of the copyright holder nor the names of its
 //    contributors may be used to endorse or promote products derived from
 //    this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 // git-stats gathers statistics about changes made to a git repo.
 package main

 import (
 	"flag"
 	"fmt"
 	"os"
 	"os/exec"
 	"regexp"
 	"runtime"
 	"sort"
 	"strings"
 	"sync"
 	"text/tabwriter"
 	"time"

 	"dawn.googlesource.com/dawn/tools/src/container"
 	"dawn.googlesource.com/dawn/tools/src/git"
 )

 // Flags
 var (
 	repo       = flag.String("repo", ".", "path to git directory")
 	afterFlag  = flag.String("after", "", "start date")
 	beforeFlag = flag.String("before", "", "end date")
 	daysFlag   = flag.Int("days", 182, "interval in days (used if --after is not specified)")
 )

 // main entry point
 func main() {
 	flag.Parse()
 	if err := run(); err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)
 	}
 }

 // Date format strings
 const (
 	yyyymmdd = "2006-01-02"
 	yyyymm   = "2006-01"
 )

 // Returns true if the file with the given path should be included for addition / deletion stats.
 func shouldConsiderLinesOfFile(path string) bool {
 	for _, ignore := range []string{
 		"Doxyfile",
 		"package-lock.json",
 		"src/tint/builtin_table.inl",
 		"src/tint/lang/core/intrinsic/table.inl",
 		"src/tint/lang/core/*.cc",
 		"src/tint/lang/core/*.h",
 		"test/tint/",
 		"third_party/gn/webgpu-cts/test_list.txt",
 		"third_party/khronos/",
 		"webgpu-cts/",
 		"src/external/petamoriken",
 	} {
 		if strings.HasPrefix(path, ignore) {
 			return false
 		}
 	}
 	return true
 }

 // Returns true if the commit with the given hash should be included for addition / deletion stats.
 func shouldConsiderLinesOfCommit(hash string) bool {
 	for _, ignore := range []string{
 		"41e4d9a34c1d9dcb2eef3ff39ff9c1f987bfa02a", // Consistent formatting for Dawn/Tint.
 		"e87ac76f7ddf9237f3022cda90224bd0691fb318", // Merge tint -> dawn
 		"b0acbd436dbd499505a3fa8bf89e69231ec4d1e0", // Fix build/namespaces issues
 	} {
 		if hash == ignore {
 			return false
 		}
 	}
 	return true
 }

 // Regular expression used to parse the email from an author string. Example:
 // Bob Bobson <bob@bobmail.com>
 // ____________^^^^^^^^^^^^^^^_
 var reEmail = regexp.MustCompile(`<([^>]+)>`)

 func run() error {
 	// Parse the --after and --before flags
 	var after, before time.Time
 	var err error
 	if *beforeFlag != "" {
 		before, err = time.Parse(yyyymmdd, *beforeFlag)
 		if err != nil {
 			return fmt.Errorf("Couldn't parse before date: %w", err)
 		}
 	} else {
 		before = time.Now()
 	}
 	if *afterFlag != "" {
 		after, err = time.Parse(yyyymmdd, *afterFlag)
 		if err != nil {
 			return fmt.Errorf("Couldn't parse after date: %w", err)
 		}
 	} else {
 		after = before.Add(-time.Hour * time.Duration(24**daysFlag))
 	}

 	// Find 'git'
 	gitExe, err := exec.LookPath("git")
 	if err != nil {
 		return err
 	}

 	// Create the git.Git wrapper
 	g, err := git.New(gitExe)
 	if err != nil {
 		return err
 	}

 	// Open the repo
 	r, err := g.Open(*repo)
 	if err != nil {
 		return err
 	}

 	// Information obtained about a single commit
 	type CommitStat struct {
 		author     string
 		commit     *git.CommitInfo
 		insertions int
 		deletions  int
 		fileDeltas container.Map[string, int]
 	}

 	// Kick a goroutine to gather all the commits in the git log between
 	// 'after' and 'before', streaming the commits to the 'commits' chan.
 	// This chan will be closed by the goroutine when all commits have been
 	// gathered.
 	commits := make(chan git.CommitInfo, 256)
 	go func() {
 		log, err := r.LogBetween(after, before, &git.LogBetweenOptions{})
 		if err != nil {
 			panic(fmt.Errorf("failed to gather commits: %w", err))
 		}
 		for _, commit := range log {
 			commits <- commit
 		}
 		close(commits)
 	}()

 	// Kick 'numWorkers' goroutines to gather the commit statistics of the
 	// commits in the 'commits' chan, streaming the commit statistics to the
 	// 'commitStats' chan.
 	commitStats := make(chan CommitStat, 256)
 	numWorkers := runtime.NumCPU()
 	wg := sync.WaitGroup{}
 	wg.Add(numWorkers)
 	for worker := 0; worker < numWorkers; worker++ {
 		go func() {
 			defer wg.Done()
 			for commit := range commits {
 				commit := commit
 				email := reEmail.FindStringSubmatch(commit.Author)[1]
 				stats, err := r.Stats(commit, nil)
 				if err != nil {
 					panic(fmt.Errorf("failed to get stats for commit '%v': %w", commit.Hash, err))
 				}

 				s := CommitStat{
 					author:     email,
 					commit:     &commit,
 					fileDeltas: container.NewMap[string, int](),
 				}
 				if shouldConsiderLinesOfCommit(commit.Hash.String()) {
 					for file, stats := range stats {
 						if shouldConsiderLinesOfFile(file) {
 							s.insertions += stats.Insertions
 							s.deletions += stats.Deletions
 							s.fileDeltas[file] = stats.Insertions + stats.Deletions
 						}
 					}
 				}
 				commitStats <- s
 			}
 		}()
 	}

 	// Kick a helper goroutine that waits for all the goroutines that feed the
 	// 'commitStats' chan to complete, and then closes the 'commitStats' chan.
 	go func() {
 		wg.Wait()
 		close(commitStats)
 	}()

 	// CommitDelta holds the sum of line additions and deletions for a given
 	// commit.
 	type CommitDelta struct {
 		commit *git.CommitInfo
 		delta  int
 	}

 	// Stream in the commit statistics from the 'commitStats' chan, and collect
 	// statistics by author and by file.
 	statsByAuthor := container.NewMap[string, AuthorStats]()
 	fileDeltas := container.NewMap[string, int]()
 	commitDeltas := []CommitDelta{}
 	for cs := range commitStats {
 		as := statsByAuthor[cs.author]
 		as.insertions += cs.insertions
 		as.deletions += cs.deletions
 		as.commits++
 		if as.commitsByMonth == nil {
 			as.commitsByMonth = container.NewMap[string, int]()
 		}
 		month := cs.commit.Date.Format(yyyymm)
 		as.commitsByMonth[month] = as.commitsByMonth[month] + 1
 		statsByAuthor[cs.author] = as

 		commitDelta := 0
 		for path, delta := range cs.fileDeltas {
 			fileDeltas[path] = fileDeltas[path] + delta
 			commitDelta += delta
 		}
 		commitDeltas = append(commitDeltas, CommitDelta{cs.commit, commitDelta})
 	}

 	// Transform the 'statsByAuthor' map, so that authors that have statistics
 	// for both a @google.com and @chromium.org account have all their
 	// statistics merged into the @google.com account.
 	for google, g := range statsByAuthor {
 		if strings.HasSuffix(google, "@google.com") {
 			combined := strings.TrimSuffix(google, "@google.com")
 			chromium := combined + "@chromium.org"
 			if c, hasChromium := statsByAuthor[chromium]; hasChromium {
 				statsByAuthor[google] = combine(g, c)
 				delete(statsByAuthor, chromium)
 			}
 		}
 	}

 	// Print those stats!

 	fmt.Printf("Between %v and %v:\n", after, before)

 	// Print the top 10 most modified files.
 	// This is helpful to identify files that are automatically generated, which
 	// we should exclude from the statistics.
 	{
 		type FileDelta struct {
 			file  string
 			delta int
 		}
 		l := make([]FileDelta, 0, len(fileDeltas))
 		for file, delta := range fileDeltas {
 			l = append(l, FileDelta{file, delta})
 		}
 		sort.Slice(l, func(i, j int) bool { return l[i].delta > l[j].delta })
 		n := len(l)
 		if n > 10 {
 			n = 10
 		}
 		fmt.Println()
 		fmt.Printf("Top %v most modified files:\n", n)
 		fmt.Println()
 		tw := tabwriter.NewWriter(os.Stdout, 0, 0, 0, ' ', 0)
 		fmt.Fprintln(tw, "  delta\t | file")
 		for _, fd := range l[:n] {
 			fmt.Fprintln(tw,
 				" ", fd.delta,
 				"\t |", fd.file)
 		}
 		tw.Flush()
 	}

 	// Print the top 10 largest commits.
 	// This is helpful to identify commits that may contain a large bulk
 	// refactor, which we should exclude from the statistics.
 	{
 		sort.Slice(commitDeltas, func(i, j int) bool {
 			return commitDeltas[i].delta > commitDeltas[j].delta
 		})
 		n := len(commitDeltas)
 		if n > 10 {
 			n = 10
 		}
 		fmt.Println()
 		fmt.Printf("Top %v largest commits:\n", n)
 		fmt.Println()
 		tw := tabwriter.NewWriter(os.Stdout, 0, 0, 0, ' ', 0)
 		fmt.Fprintln(tw,
 			"  delta\t | author\t | hash\t | description")
 		for _, fd := range commitDeltas[:n] {
 			fmt.Fprintln(tw,
 				" ", fd.delta,
 				"\t |", fd.commit.Author,
 				"\t |", fd.commit.Hash.String()[:6],
 				"\t |", fd.commit.Subject)
 		}
 		tw.Flush()
 	}

 	// Print the contributions by author.
 	{
 		fmt.Println()
 		fmt.Println("Total contributions by author:")
 		tw := tabwriter.NewWriter(os.Stdout, 0, 0, 0, ' ', 0)
 		fmt.Println()
 		fmt.Fprintln(tw, "  author\t | commits\t | added\t | removed")
 		for _, author := range statsByAuthor.Keys() {
 			s := statsByAuthor[author]
 			fmt.Fprintln(tw,
 				"  "+author,
 				"\t |", s.commits,
 				"\t |", s.insertions,
 				"\t |", s.deletions)
 		}
 		tw.Flush()
 	}

 	// Print the per-author contributions by month.
 	{
 		allMonths := container.NewSet[string]()
 		for _, author := range statsByAuthor {
 			for month := range author.commitsByMonth {
 				allMonths.Add(month)
 			}
 		}

 		months := allMonths.List()

 		fmt.Println()
 		fmt.Println("Commits by author by month:")
 		tw := tabwriter.NewWriter(os.Stdout, 0, 0, 0, ' ', 0)
 		fmt.Println()
 		fmt.Fprintf(tw, "  author")
 		for _, month := range months {
 			fmt.Fprint(tw, "\t | ", month)
 		}
 		fmt.Fprintln(tw)

 		for _, author := range statsByAuthor.Keys() {
 			fmt.Fprint(tw, "  ", author)
 			cbm := statsByAuthor[author].commitsByMonth
 			for _, month := range months {
 				fmt.Fprint(tw, "\t | ", cbm[month])
 			}
 			fmt.Fprintln(tw)
 		}
 		tw.Flush()
 	}

 	return nil
 }

 type AuthorStats struct {
 	commits        int
 	commitsByMonth container.Map[string, int]
 	insertions     int
 	deletions      int
 }

 // combine returns a new AuthorStats, with the summed statistics of 'a' and 'b'.
 func combine(a, b AuthorStats) AuthorStats {
 	out := AuthorStats{
 		commits:    a.commits + b.commits,
 		insertions: a.insertions + b.insertions,
 		deletions:  a.deletions + b.deletions,
 	}
 	out.commitsByMonth = container.NewMap[string, int]()
 	for month, commits := range a.commitsByMonth {
 		out.commitsByMonth[month] = commits
 	}
 	for month, commits := range b.commitsByMonth {
 		out.commitsByMonth[month] = out.commitsByMonth[month] + commits
 	}
 	return out
 }

 func today() time.Time {
 	return time.Now()
 }

 func date(t time.Time) string {
 	return t.Format(yyyymmdd)
 }
	// Copyright 2022 The Dawn & Tint Authors
	//
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are met:
	//
	// 1. Redistributions of source code must retain the above copyright notice, this
	// list of conditions and the following disclaimer.
	//
	// 2. Redistributions in binary form must reproduce the above copyright notice,
	// this list of conditions and the following disclaimer in the documentation
	// and/or other materials provided with the distribution.
	//
	// 3. Neither the name of the copyright holder nor the names of its
	// contributors may be used to endorse or promote products derived from
	// this software without specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
	// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
	// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
	// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
	// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	// git-stats gathers statistics about changes made to a git repo.
	package main

	import (
	"flag"
	"fmt"
	"os"
	"os/exec"
	"regexp"
	"runtime"
	"sort"
	"strings"
	"sync"
	"text/tabwriter"
	"time"

	"dawn.googlesource.com/dawn/tools/src/container"
	"dawn.googlesource.com/dawn/tools/src/git"
	)

	// Flags
	var (
	repo = flag.String("repo", ".", "path to git directory")
	afterFlag = flag.String("after", "", "start date")
	beforeFlag = flag.String("before", "", "end date")
	daysFlag = flag.Int("days", 182, "interval in days (used if --after is not specified)")
	)

	// main entry point
	func main() {
	flag.Parse()
	if err := run(); err != nil {
	fmt.Fprintln(os.Stderr, err)
	os.Exit(1)
	}
	}

	// Date format strings
	const (
	yyyymmdd = "2006-01-02"
	yyyymm = "2006-01"
	)

	// Returns true if the file with the given path should be included for addition / deletion stats.
	func shouldConsiderLinesOfFile(path string) bool {
	for _, ignore := range []string{
	"Doxyfile",
	"package-lock.json",
	"src/tint/builtin_table.inl",
	"src/tint/lang/core/intrinsic/table.inl",
	"src/tint/lang/core/*.cc",
	"src/tint/lang/core/*.h",
	"test/tint/",
	"third_party/gn/webgpu-cts/test_list.txt",
	"third_party/khronos/",
	"webgpu-cts/",
	"src/external/petamoriken",
	} {
	if strings.HasPrefix(path, ignore) {
	return false
	}
	}
	return true
	}

	// Returns true if the commit with the given hash should be included for addition / deletion stats.
	func shouldConsiderLinesOfCommit(hash string) bool {
	for _, ignore := range []string{
	"41e4d9a34c1d9dcb2eef3ff39ff9c1f987bfa02a", // Consistent formatting for Dawn/Tint.
	"e87ac76f7ddf9237f3022cda90224bd0691fb318", // Merge tint -> dawn
	"b0acbd436dbd499505a3fa8bf89e69231ec4d1e0", // Fix build/namespaces issues
	} {
	if hash == ignore {
	return false
	}
	}
	return true
	}

	// Regular expression used to parse the email from an author string. Example:
	// Bob Bobson <bob@bobmail.com>
	// ____________^^^^^^^^^^^^^^^_
	var reEmail = regexp.MustCompile(`<([^>]+)>`)

	func run() error {
	// Parse the --after and --before flags
	var after, before time.Time
	var err error
	if *beforeFlag != "" {
	before, err = time.Parse(yyyymmdd, *beforeFlag)
	if err != nil {
	return fmt.Errorf("Couldn't parse before date: %w", err)
	}
	} else {
	before = time.Now()
	}
	if *afterFlag != "" {
	after, err = time.Parse(yyyymmdd, *afterFlag)
	if err != nil {
	return fmt.Errorf("Couldn't parse after date: %w", err)
	}
	} else {
	after = before.Add(-time.Hour * time.Duration(24**daysFlag))
	}

	// Find 'git'
	gitExe, err := exec.LookPath("git")
	if err != nil {
	return err
	}

	// Create the git.Git wrapper
	g, err := git.New(gitExe)
	if err != nil {
	return err
	}

	// Open the repo
	r, err := g.Open(*repo)
	if err != nil {
	return err
	}

	// Information obtained about a single commit
	type CommitStat struct {
	author string
	commit *git.CommitInfo
	insertions int
	deletions int
	fileDeltas container.Map[string, int]
	}

	// Kick a goroutine to gather all the commits in the git log between
	// 'after' and 'before', streaming the commits to the 'commits' chan.
	// This chan will be closed by the goroutine when all commits have been
	// gathered.
	commits := make(chan git.CommitInfo, 256)
	go func() {
	log, err := r.LogBetween(after, before, &git.LogBetweenOptions{})
	if err != nil {
	panic(fmt.Errorf("failed to gather commits: %w", err))
	}
	for _, commit := range log {
	commits <- commit
	}
	close(commits)
	}()

	// Kick 'numWorkers' goroutines to gather the commit statistics of the
	// commits in the 'commits' chan, streaming the commit statistics to the
	// 'commitStats' chan.
	commitStats := make(chan CommitStat, 256)
	numWorkers := runtime.NumCPU()
	wg := sync.WaitGroup{}
	wg.Add(numWorkers)
	for worker := 0; worker < numWorkers; worker++ {
	go func() {
	defer wg.Done()
	for commit := range commits {
	commit := commit
	email := reEmail.FindStringSubmatch(commit.Author)[1]
	stats, err := r.Stats(commit, nil)
	if err != nil {
	panic(fmt.Errorf("failed to get stats for commit '%v': %w", commit.Hash, err))
	}

	s := CommitStat{
	author: email,
	commit: &commit,
	fileDeltas: container.NewMap[string, int](),
	}
	if shouldConsiderLinesOfCommit(commit.Hash.String()) {
	for file, stats := range stats {
	if shouldConsiderLinesOfFile(file) {
	s.insertions += stats.Insertions
	s.deletions += stats.Deletions
	s.fileDeltas[file] = stats.Insertions + stats.Deletions
	}
	}
	}
	commitStats <- s
	}
	}()
	}

	// Kick a helper goroutine that waits for all the goroutines that feed the
	// 'commitStats' chan to complete, and then closes the 'commitStats' chan.
	go func() {
	wg.Wait()
	close(commitStats)
	}()

	// CommitDelta holds the sum of line additions and deletions for a given
	// commit.
	type CommitDelta struct {
	commit *git.CommitInfo
	delta int
	}

	// Stream in the commit statistics from the 'commitStats' chan, and collect
	// statistics by author and by file.
	statsByAuthor := container.NewMap[string, AuthorStats]()
	fileDeltas := container.NewMap[string, int]()
	commitDeltas := []CommitDelta{}
	for cs := range commitStats {
	as := statsByAuthor[cs.author]
	as.insertions += cs.insertions
	as.deletions += cs.deletions
	as.commits++
	if as.commitsByMonth == nil {
	as.commitsByMonth = container.NewMap[string, int]()
	}
	month := cs.commit.Date.Format(yyyymm)
	as.commitsByMonth[month] = as.commitsByMonth[month] + 1
	statsByAuthor[cs.author] = as

	commitDelta := 0
	for path, delta := range cs.fileDeltas {
	fileDeltas[path] = fileDeltas[path] + delta
	commitDelta += delta
	}
	commitDeltas = append(commitDeltas, CommitDelta{cs.commit, commitDelta})
	}

	// Transform the 'statsByAuthor' map, so that authors that have statistics
	// for both a @google.com and @chromium.org account have all their
	// statistics merged into the @google.com account.
	for google, g := range statsByAuthor {
	if strings.HasSuffix(google, "@google.com") {
	combined := strings.TrimSuffix(google, "@google.com")
	chromium := combined + "@chromium.org"
	if c, hasChromium := statsByAuthor[chromium]; hasChromium {
	statsByAuthor[google] = combine(g, c)
	delete(statsByAuthor, chromium)
	}
	}
	}

	// Print those stats!

	fmt.Printf("Between %v and %v:\n", after, before)

	// Print the top 10 most modified files.
	// This is helpful to identify files that are automatically generated, which
	// we should exclude from the statistics.
	{
	type FileDelta struct {
	file string
	delta int
	}
	l := make([]FileDelta, 0, len(fileDeltas))
	for file, delta := range fileDeltas {
	l = append(l, FileDelta{file, delta})
	}
	sort.Slice(l, func(i, j int) bool { return l[i].delta > l[j].delta })
	n := len(l)
	if n > 10 {
	n = 10
	}
	fmt.Println()
	fmt.Printf("Top %v most modified files:\n", n)
	fmt.Println()
	tw := tabwriter.NewWriter(os.Stdout, 0, 0, 0, ' ', 0)
	fmt.Fprintln(tw, " delta\t \| file")
	for _, fd := range l[:n] {
	fmt.Fprintln(tw,
	" ", fd.delta,
	"\t \|", fd.file)
	}
	tw.Flush()
	}

	// Print the top 10 largest commits.
	// This is helpful to identify commits that may contain a large bulk
	// refactor, which we should exclude from the statistics.
	{
	sort.Slice(commitDeltas, func(i, j int) bool {
	return commitDeltas[i].delta > commitDeltas[j].delta
	})
	n := len(commitDeltas)
	if n > 10 {
	n = 10
	}
	fmt.Println()
	fmt.Printf("Top %v largest commits:\n", n)
	fmt.Println()
	tw := tabwriter.NewWriter(os.Stdout, 0, 0, 0, ' ', 0)
	fmt.Fprintln(tw,
	" delta\t \| author\t \| hash\t \| description")
	for _, fd := range commitDeltas[:n] {
	fmt.Fprintln(tw,
	" ", fd.delta,
	"\t \|", fd.commit.Author,
	"\t \|", fd.commit.Hash.String()[:6],
	"\t \|", fd.commit.Subject)
	}
	tw.Flush()
	}

	// Print the contributions by author.
	{
	fmt.Println()
	fmt.Println("Total contributions by author:")
	tw := tabwriter.NewWriter(os.Stdout, 0, 0, 0, ' ', 0)
	fmt.Println()
	fmt.Fprintln(tw, " author\t \| commits\t \| added\t \| removed")
	for _, author := range statsByAuthor.Keys() {
	s := statsByAuthor[author]
	fmt.Fprintln(tw,
	" "+author,
	"\t \|", s.commits,
	"\t \|", s.insertions,
	"\t \|", s.deletions)
	}
	tw.Flush()
	}

	// Print the per-author contributions by month.
	{
	allMonths := container.NewSet[string]()
	for _, author := range statsByAuthor {
	for month := range author.commitsByMonth {
	allMonths.Add(month)
	}
	}

	months := allMonths.List()

	fmt.Println()
	fmt.Println("Commits by author by month:")
	tw := tabwriter.NewWriter(os.Stdout, 0, 0, 0, ' ', 0)
	fmt.Println()
	fmt.Fprintf(tw, " author")
	for _, month := range months {
	fmt.Fprint(tw, "\t \| ", month)
	}
	fmt.Fprintln(tw)

	for _, author := range statsByAuthor.Keys() {
	fmt.Fprint(tw, " ", author)
	cbm := statsByAuthor[author].commitsByMonth
	for _, month := range months {
	fmt.Fprint(tw, "\t \| ", cbm[month])
	}
	fmt.Fprintln(tw)
	}
	tw.Flush()
	}

	return nil
	}

	type AuthorStats struct {
	commits int
	commitsByMonth container.Map[string, int]
	insertions int
	deletions int
	}

	// combine returns a new AuthorStats, with the summed statistics of 'a' and 'b'.
	func combine(a, b AuthorStats) AuthorStats {
	out := AuthorStats{
	commits: a.commits + b.commits,
	insertions: a.insertions + b.insertions,
	deletions: a.deletions + b.deletions,
	}
	out.commitsByMonth = container.NewMap[string, int]()
	for month, commits := range a.commitsByMonth {
	out.commitsByMonth[month] = commits
	}
	for month, commits := range b.commitsByMonth {
	out.commitsByMonth[month] = out.commitsByMonth[month] + commits
	}
	return out
	}

	func today() time.Time {
	return time.Now()
	}

	func date(t time.Time) string {
	return t.Format(yyyymmdd)
	}