Automate the Hugo release process

This commit adds a work flow aroung GoReleaser to get the Hugo release process automated and more uniform:

* It can be run fully automated or in two steps to allow for manual edits of the relase notes.
* It supports both patch and full releases.
* It fetches author, issue, repo info. etc. for the release notes from GitHub.
* The file names produced are mainly the same as before, but we no use tar.gz as archive for all Unix versions.
* There isn't a fully automated CI setup in place yet, but the release tag is marked in the commit message with "[ci deploy]"

Fixes #3358

8 files changed, 1123 insertions, 0 deletions

diff --git a/releaser/git.go b/releaser/git.go
new file mode 100644
index 000000000..d8b5bef31
--- /dev/null
+++ b/releaser/git.go
@@ -0,0 +1,265 @@
+// Copyright 2017-present The Hugo Authors. 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 releaser
+
+import (
+	"fmt"
+	"os/exec"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+var issueRe = regexp.MustCompile(`(?i)[Updates?|Closes?|Fix.*|See] #(\d+)`)
+
+const (
+	templateChanges = "templateChanges"
+	coreChanges     = "coreChanges"
+	outChanges      = "outChanges"
+	docsChanges     = "docsChanges"
+	otherChanges    = "otherChanges"
+)
+
+type changeLog struct {
+	Version      string
+	Enhancements map[string]gitInfos
+	Fixes        map[string]gitInfos
+	All          gitInfos
+
+	// Overall stats
+	Repo             *gitHubRepo
+	ContributorCount int
+	ThemeCount       int
+}
+
+func newChangeLog(infos gitInfos) changeLog {
+	return changeLog{
+		Enhancements: make(map[string]gitInfos),
+		Fixes:        make(map[string]gitInfos),
+		All:          infos,
+	}
+}
+
+func (l changeLog) addGitInfo(isFix bool, info gitInfo, category string) {
+	var (
+		infos   gitInfos
+		found   bool
+		segment map[string]gitInfos
+	)
+
+	if isFix {
+		segment = l.Fixes
+	} else {
+		segment = l.Enhancements
+	}
+
+	infos, found = segment[category]
+	if !found {
+		infos = gitInfos{}
+	}
+
+	infos = append(infos, info)
+	segment[category] = infos
+}
+
+func gitInfosToChangeLog(infos gitInfos) changeLog {
+	log := newChangeLog(infos)
+	for _, info := range infos {
+		los := strings.ToLower(info.Subject)
+		isFix := strings.Contains(los, "fix")
+		var category = otherChanges
+
+		// TODO(bep) improve
+		if regexp.MustCompile("(?i)tpl:|tplimpl:|layout").MatchString(los) {
+			category = templateChanges
+		} else if regexp.MustCompile("(?i)docs?:|documentation:").MatchString(los) {
+			category = docsChanges
+		} else if regexp.MustCompile("(?i)hugolib:").MatchString(los) {
+			category = coreChanges
+		} else if regexp.MustCompile("(?i)out(put)?:|media:|Output|Media").MatchString(los) {
+			category = outChanges
+		}
+
+		// Trim package prefix.
+		colonIdx := strings.Index(info.Subject, ":")
+		if colonIdx != -1 && colonIdx < (len(info.Subject)/2) {
+			info.Subject = info.Subject[colonIdx+1:]
+		}
+
+		info.Subject = strings.TrimSpace(info.Subject)
+
+		log.addGitInfo(isFix, info, category)
+	}
+
+	return log
+}
+
+type gitInfo struct {
+	Hash    string
+	Author  string
+	Subject string
+	Body    string
+
+	GitHubCommit *gitHubCommit
+}
+
+func (g gitInfo) Issues() []int {
+	return extractIssues(g.Body)
+}
+
+func (g gitInfo) AuthorID() string {
+	if g.GitHubCommit != nil {
+		return g.GitHubCommit.Author.Login
+	}
+	return g.Author
+}
+
+func extractIssues(body string) []int {
+	var i []int
+	m := issueRe.FindAllStringSubmatch(body, -1)
+	for _, mm := range m {
+		issueID, err := strconv.Atoi(mm[1])
+		if err != nil {
+			continue
+		}
+		i = append(i, issueID)
+	}
+	return i
+}
+
+type gitInfos []gitInfo
+
+func git(args ...string) (string, error) {
+	cmd := exec.Command("git", args...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return "", fmt.Errorf("git failed: %q: %q", err, out)
+	}
+	return string(out), nil
+}
+
+func getGitInfos(remote bool) (gitInfos, error) {
+	return getGitInfosBefore("HEAD", remote)
+}
+
+type countribCount struct {
+	Author       string
+	GitHubAuthor gitHubAuthor
+	Count        int
+}
+
+func (c countribCount) AuthorLink() string {
+	if c.GitHubAuthor.HtmlURL != "" {
+		return fmt.Sprintf("[@%s](%s)", c.GitHubAuthor.Login, c.GitHubAuthor.HtmlURL)
+	}
+
+	if !strings.Contains(c.Author, "@") {
+		return c.Author
+	}
+
+	return c.Author[:strings.Index(c.Author, "@")]
+
+}
+
+type contribCounts []countribCount
+
+func (c contribCounts) Less(i, j int) bool { return c[i].Count > c[j].Count }
+func (c contribCounts) Len() int           { return len(c) }
+func (c contribCounts) Swap(i, j int)      { c[i], c[j] = c[j], c[i] }
+
+func (g gitInfos) ContribCountPerAuthor() contribCounts {
+	var c contribCounts
+
+	counters := make(map[string]countribCount)
+
+	for _, gi := range g {
+		authorID := gi.AuthorID()
+		if count, ok := counters[authorID]; ok {
+			count.Count = count.Count + 1
+			counters[authorID] = count
+		} else {
+			var ghA gitHubAuthor
+			if gi.GitHubCommit != nil {
+				ghA = gi.GitHubCommit.Author
+			}
+			authorCount := countribCount{Count: 1, Author: gi.Author, GitHubAuthor: ghA}
+			counters[authorID] = authorCount
+		}
+	}
+
+	for _, v := range counters {
+		c = append(c, v)
+	}
+
+	sort.Sort(c)
+	return c
+}
+
+func getGitInfosBefore(ref string, remote bool) (gitInfos, error) {
+
+	var g gitInfos
+
+	log, err := gitLogBefore(ref)
+	if err != nil {
+		return g, err
+	}
+
+	log = strings.Trim(log, "\n\x1e'")
+	entries := strings.Split(log, "\x1e")
+
+	for _, entry := range entries {
+		items := strings.Split(entry, "\x1f")
+		gi := gitInfo{
+			Hash:    items[0],
+			Author:  items[1],
+			Subject: items[2],
+			Body:    items[3],
+		}
+		if remote {
+			gc, err := fetchCommit(gi.Hash)
+			if err == nil {
+				gi.GitHubCommit = &gc
+			}
+		}
+		g = append(g, gi)
+	}
+
+	return g, nil
+}
+
+// Ignore autogenerated commits etc. in change log. This is a regexp.
+const ignoredCommits = "release:|vendor:|snapcraft:"
+
+func gitLogBefore(ref string) (string, error) {
+	prevTag, err := gitShort("describe", "--tags", "--abbrev=0", "--always", ref+"^")
+	if err != nil {
+		return "", err
+	}
+	log, err := git("log", "-E", fmt.Sprintf("--grep=%s", ignoredCommits), "--invert-grep", "--pretty=format:%x1e%h%x1f%aE%x1f%s%x1f%b", "--abbrev-commit", prevTag+".."+ref)
+	if err != nil {
+		return ",", err
+	}
+
+	return log, err
+}
+
+func gitLog() (string, error) {
+	return gitLogBefore("HEAD")
+}
+
+func gitShort(args ...string) (output string, err error) {
+	output, err = git(args...)
+	return strings.Replace(strings.Split(output, "\n")[0], "'", "", -1), err
+}
diff --git a/releaser/git_test.go b/releaser/git_test.go
new file mode 100644
index 000000000..dc1db5dc7
--- /dev/null
+++ b/releaser/git_test.go
@@ -0,0 +1,53 @@
+// Copyright 2017-present The Hugo Authors. 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 releaser
+
+import (
+	"testing"
+
+	"runtime"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGitInfos(t *testing.T) {
+	if runtime.GOOS == "linux" {
+		// Travis has an ancient git with no --invert-grep: https://github.com/travis-ci/travis-ci/issues/6328
+		t.Skip("Skip git test on Linux to make Travis happy.")
+	}
+	infos, err := getGitInfos(false)
+
+	require.NoError(t, err)
+	require.True(t, len(infos) > 0)
+
+}
+
+func TestIssuesRe(t *testing.T) {
+
+	body := `
+This is a commit message.
+
+Updates #123
+Fix #345
+closes #543
+See #456
+	`
+
+	issues := extractIssues(body)
+
+	require.Len(t, issues, 4)
+	require.Equal(t, 123, issues[0])
+	require.Equal(t, 543, issues[2])
+
+}
diff --git a/releaser/github.go b/releaser/github.go
new file mode 100644
index 000000000..0dbb1bca1
--- /dev/null
+++ b/releaser/github.go
@@ -0,0 +1,129 @@
+package releaser
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"os"
+)
+
+var (
+	gitHubCommitsApi      = "https://api.github.com/repos/spf13/hugo/commits/%s"
+	gitHubRepoApi         = "https://api.github.com/repos/spf13/hugo"
+	gitHubContributorsApi = "https://api.github.com/repos/spf13/hugo/contributors"
+)
+
+type gitHubCommit struct {
+	Author  gitHubAuthor `json:"author"`
+	HtmlURL string       `json:"html_url"`
+}
+
+type gitHubAuthor struct {
+	ID        int    `json:"id"`
+	Login     string `json:"login"`
+	HtmlURL   string `json:"html_url"`
+	AvatarURL string `json:"avatar_url"`
+}
+
+type gitHubRepo struct {
+	ID           int    `json:"id"`
+	Name         string `json:"name"`
+	Description  string `json:"description"`
+	HtmlURL      string `json:"html_url"`
+	Stars        int    `json:"stargazers_count"`
+	Contributors []gitHubContributor
+}
+
+type gitHubContributor struct {
+	ID            int    `json:"id"`
+	Login         string `json:"login"`
+	HtmlURL       string `json:"html_url"`
+	Contributions int    `json:"contributions"`
+}
+
+func fetchCommit(ref string) (gitHubCommit, error) {
+	var commit gitHubCommit
+
+	u := fmt.Sprintf(gitHubCommitsApi, ref)
+
+	req, err := http.NewRequest("GET", u, nil)
+	if err != nil {
+		return commit, err
+	}
+
+	err = doGitHubRequest(req, &commit)
+
+	return commit, err
+}
+
+func fetchRepo() (gitHubRepo, error) {
+	var repo gitHubRepo
+
+	req, err := http.NewRequest("GET", gitHubRepoApi, nil)
+	if err != nil {
+		return repo, err
+	}
+
+	err = doGitHubRequest(req, &repo)
+	if err != nil {
+		return repo, err
+	}
+
+	var contributors []gitHubContributor
+	page := 0
+	for {
+		page++
+		var currPage []gitHubContributor
+		url := fmt.Sprintf(gitHubContributorsApi+"?page=%d", page)
+
+		req, err = http.NewRequest("GET", url, nil)
+		if err != nil {
+			return repo, err
+		}
+
+		err = doGitHubRequest(req, &currPage)
+		if err != nil {
+			return repo, err
+		}
+		if len(currPage) == 0 {
+			break
+		}
+
+		contributors = append(contributors, currPage...)
+
+	}
+
+	repo.Contributors = contributors
+
+	return repo, err
+
+}
+
+func doGitHubRequest(req *http.Request, v interface{}) error {
+	addGitHubToken(req)
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if isError(resp) {
+		b, _ := ioutil.ReadAll(resp.Body)
+		return fmt.Errorf("GitHub lookup failed: %s", string(b))
+	}
+
+	return json.NewDecoder(resp.Body).Decode(v)
+}
+
+func isError(resp *http.Response) bool {
+	return resp.StatusCode < 200 || resp.StatusCode > 299
+}
+
+func addGitHubToken(req *http.Request) {
+	gitHubToken := os.Getenv("GITHUB_TOKEN")
+	if gitHubToken != "" {
+		req.Header.Add("Authorization", "token "+gitHubToken)
+	}
+}
diff --git a/releaser/github_test.go b/releaser/github_test.go
new file mode 100644
index 000000000..7feae75f5
--- /dev/null
+++ b/releaser/github_test.go
@@ -0,0 +1,42 @@
+// Copyright 2017-present The Hugo Authors. 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 releaser
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGitHubLookupCommit(t *testing.T) {
+	skipIfNoToken(t)
+	commit, err := fetchCommit("793554108763c0984f1a1b1a6ee5744b560d78d0")
+	require.NoError(t, err)
+	fmt.Println(commit)
+}
+
+func TestFetchRepo(t *testing.T) {
+	skipIfNoToken(t)
+	repo, err := fetchRepo()
+	require.NoError(t, err)
+	fmt.Println(">>", len(repo.Contributors))
+}
+
+func skipIfNoToken(t *testing.T) {
+	if os.Getenv("GITHUB_TOKEN") == "" {
+		t.Skip("Skip test against GitHub as no GITHUB_TOKEN set.")
+	}
+}
diff --git a/releaser/releasenotes_writer.go b/releaser/releasenotes_writer.go
new file mode 100644
index 000000000..3d48d9ae8
--- /dev/null
+++ b/releaser/releasenotes_writer.go
@@ -0,0 +1,245 @@
+// Copyright 2017-present The Hugo Authors. 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 release implements a set of utilities and a wrapper around Goreleaser
+// to help automate the Hugo release process.
+package releaser
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"text/template"
+	"time"
+)
+
+const (
+	issueLinkTemplate            = "[#%d](https://github.com/spf13/hugo/issues/%d)"
+	linkTemplate                 = "[%s](%s)"
+	releaseNotesMarkdownTemplate = `
+{{- $patchRelease := isPatch . -}}
+{{- $contribsPerAuthor := .All.ContribCountPerAuthor -}}
+
+{{- if $patchRelease }}
+{{ if eq (len .All) 1 }}
+This is a bug-fix release with one important fix.
+{{ else }}
+This is a bug-fix relase with a couple of important fixes.
+{{ end }}
+{{ else }}
+This release represents **{{ len .All }} contributions by {{ len $contribsPerAuthor }} contributors** to the main Hugo code base.
+{{ end -}}
+
+{{- if  gt (len $contribsPerAuthor) 3 -}}
+{{- $u1 := index $contribsPerAuthor 0 -}}
+{{- $u2 := index $contribsPerAuthor 1 -}}
+{{- $u3 := index $contribsPerAuthor 2 -}}
+{{- $u4 := index $contribsPerAuthor 3 -}}
+{{- $u1.AuthorLink }} leads the Hugo development with a significant amount of contributions, but also a big shoutout to {{ $u2.AuthorLink }}, {{ $u3.AuthorLink }}, and {{ $u4.AuthorLink }} for their ongoing contributions.
+And as always a big thanks to [@digitalcraftsman](https://github.com/digitalcraftsman) for his relentless work on keeping the documentation and the themes site in pristine condition.
+{{ end }}
+Hugo now has:
+
+{{ with .Repo -}}
+* {{ .Stars }}+ [stars](https://github.com/spf13/hugo/stargazers)
+* {{ len .Contributors }}+ [contributors](https://github.com/spf13/hugo/graphs/contributors)
+{{- end -}}
+{{ with .ThemeCount }}
+* 156+ [themes](http://themes.gohugo.io/)
+{{- end }}
+
+## Enhancements
+{{ template "change-headers"  .Enhancements -}}
+## Fixes
+{{ template "change-headers"  .Fixes -}}
+
+{{ define "change-headers" }}
+{{ $tmplChanges := index . "templateChanges" -}}
+{{- $outChanges := index . "outChanges" -}}
+{{- $coreChanges := index . "coreChanges" -}}
+{{- $docsChanges := index . "docsChanges" -}}
+{{- $otherChanges := index . "otherChanges" -}}
+{{- with $tmplChanges -}}
+### Templates
+{{ template "change-section" . }}
+{{- end -}}
+{{- with $outChanges -}}
+### Output
+{{- template "change-section"  . }}
+{{- end -}}
+{{- with $coreChanges -}}
+### Core
+{{ template "change-section" . }}
+{{- end -}}
+{{- with $docsChanges -}}
+### Docs
+{{- template "change-section"  . }}
+{{- end -}}
+{{- with $otherChanges -}}
+### Other
+{{ template "change-section"  . }}
+{{- end -}}
+{{ end }}
+
+
+{{ define "change-section" }}
+{{ range . }}
+{{- if .GitHubCommit -}}
+* {{ .Subject }} {{ . | commitURL }} {{ . | authorURL }} {{ range .Issues }}{{ . | issue }} {{ end }}
+{{ else -}}
+* {{ .Subject }} {{ range .Issues }}{{ . | issue }} {{ end }}
+{{ end -}}
+{{- end }}
+{{ end }}
+`
+)
+
+var templateFuncs = template.FuncMap{
+	"isPatch": func(c changeLog) bool {
+		return strings.Count(c.Version, ".") > 1
+	},
+	"issue": func(id int) string {
+		return fmt.Sprintf(issueLinkTemplate, id, id)
+	},
+	"commitURL": func(info gitInfo) string {
+		if info.GitHubCommit.HtmlURL == "" {
+			return ""
+		}
+		return fmt.Sprintf(linkTemplate, info.Hash, info.GitHubCommit.HtmlURL)
+	},
+	"authorURL": func(info gitInfo) string {
+		if info.GitHubCommit.Author.Login == "" {
+			return ""
+		}
+		return fmt.Sprintf(linkTemplate, "@"+info.GitHubCommit.Author.Login, info.GitHubCommit.Author.HtmlURL)
+	},
+}
+
+func writeReleaseNotes(version string, infos gitInfos, to io.Writer) error {
+	changes := gitInfosToChangeLog(infos)
+	changes.Version = version
+	repo, err := fetchRepo()
+	if err == nil {
+		changes.Repo = &repo
+	}
+	themeCount, err := fetchThemeCount()
+	if err == nil {
+		changes.ThemeCount = themeCount
+	}
+
+	tmpl, err := template.New("").Funcs(templateFuncs).Parse(releaseNotesMarkdownTemplate)
+	if err != nil {
+		return err
+	}
+
+	err = tmpl.Execute(to, changes)
+	if err != nil {
+		return err
+	}
+
+	return nil
+
+}
+
+func fetchThemeCount() (int, error) {
+	resp, err := http.Get("https://github.com/spf13/hugoThemes/blob/master/.gitmodules")
+	if err != nil {
+		return 0, err
+	}
+	defer resp.Body.Close()
+
+	b, _ := ioutil.ReadAll(resp.Body)
+	return bytes.Count(b, []byte("submodule")), nil
+}
+
+func writeReleaseNotesToTmpFile(version string, infos gitInfos) (string, error) {
+	f, err := ioutil.TempFile("", "hugorelease")
+	if err != nil {
+		return "", err
+	}
+
+	defer f.Close()
+
+	if err := writeReleaseNotes(version, infos, f); err != nil {
+		return "", err
+	}
+
+	return f.Name(), nil
+}
+
+func getRelaseNotesDocsTempDirAndName(version string) (string, string) {
+	return hugoFilepath("docs/temp"), fmt.Sprintf("%s-relnotes.md", version)
+}
+
+func getRelaseNotesDocsTempFilename(version string) string {
+	return filepath.Join(getRelaseNotesDocsTempDirAndName(version))
+}
+
+func writeReleaseNotesToDocsTemp(version string, infos gitInfos) (string, error) {
+	docsTempPath, name := getRelaseNotesDocsTempDirAndName(version)
+	os.Mkdir(docsTempPath, os.ModePerm)
+
+	f, err := os.Create(filepath.Join(docsTempPath, name))
+	if err != nil {
+		return "", err
+	}
+
+	defer f.Close()
+
+	if err := writeReleaseNotes(version, infos, f); err != nil {
+		return "", err
+	}
+
+	return f.Name(), nil
+
+}
+
+func writeReleaseNotesToDocs(title, sourceFilename string) (string, error) {
+	targetFilename := filepath.Base(sourceFilename)
+	contentDir := hugoFilepath("docs/content/release-notes")
+	targetFullFilename := filepath.Join(contentDir, targetFilename)
+	os.Mkdir(contentDir, os.ModePerm)
+
+	b, err := ioutil.ReadFile(sourceFilename)
+	if err != nil {
+		return "", err
+	}
+
+	f, err := os.Create(targetFullFilename)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	if _, err := f.WriteString(fmt.Sprintf(`
+---
+date: %s
+title: %s
+---
+
+	`, time.Now().Format("2006-01-02"), title)); err != nil {
+		return "", err
+	}
+
+	if _, err := f.Write(b); err != nil {
+		return "", err
+	}
+
+	return targetFullFilename, nil
+
+}
diff --git a/releaser/releasenotes_writer_test.go b/releaser/releasenotes_writer_test.go
new file mode 100644
index 000000000..d1151bffc
--- /dev/null
+++ b/releaser/releasenotes_writer_test.go
@@ -0,0 +1,44 @@
+// Copyright 2017-present The Hugo Authors. 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 commands defines and implements command-line commands and flags
+// used by Hugo. Commands and flags are implemented using Cobra.
+
+package releaser
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+
+	"runtime"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestReleaseNotesWriter(t *testing.T) {
+	if runtime.GOOS == "linux" {
+		// Travis has an ancient git with no --invert-grep: https://github.com/travis-ci/travis-ci/issues/6328
+		t.Skip("Skip git test on Linux to make Travis happy.")
+	}
+
+	var b bytes.Buffer
+
+	// TODO(bep) consider to query GitHub directly for the gitlog with author info, probably faster.
+	infos, err := getGitInfosBefore("v0.20", false)
+	require.NoError(t, err)
+
+	require.NoError(t, writeReleaseNotes("0.20", infos, &b))
+
+	fmt.Println(">>>", b.String())
+}
diff --git a/releaser/releaser.go b/releaser/releaser.go
new file mode 100644
index 000000000..b6e9bfde1
--- /dev/null
+++ b/releaser/releaser.go
@@ -0,0 +1,267 @@
+// Copyright 2017-present The Hugo Authors. 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 releaser implements a set of utilities and a wrapper around Goreleaser
+// to help automate the Hugo release process.
+package releaser
+
+import (
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"strings"
+
+	"github.com/spf13/hugo/helpers"
+)
+
+const commitPrefix = "releaser:"
+
+type ReleaseHandler struct {
+	patch       int
+	step        int
+	skipPublish bool
+}
+
+func (r ReleaseHandler) shouldRelease() bool {
+	return r.step < 1 || r.shouldContinue()
+}
+
+func (r ReleaseHandler) shouldContinue() bool {
+	return r.step == 2
+}
+
+func (r ReleaseHandler) shouldPrepare() bool {
+	return r.step < 1 || r.step == 1
+}
+
+func (r ReleaseHandler) calculateVersions(current helpers.HugoVersion) (helpers.HugoVersion, helpers.HugoVersion) {
+	var (
+		newVersion   = current
+		finalVersion = current
+	)
+
+	newVersion.Suffix = ""
+
+	if r.shouldContinue() {
+		// The version in the current code base is in the state we want for
+		// the release.
+		if r.patch == 0 {
+			finalVersion = newVersion.Next()
+		}
+	} else if r.patch > 0 {
+		newVersion = helpers.CurrentHugoVersion.NextPatchLevel(r.patch)
+	} else {
+		finalVersion = newVersion.Next()
+	}
+
+	finalVersion.Suffix = "-DEV"
+
+	return newVersion, finalVersion
+}
+
+func New(patch, step int, skipPublish bool) *ReleaseHandler {
+	return &ReleaseHandler{patch: patch, step: step, skipPublish: skipPublish}
+}
+
+func (r *ReleaseHandler) Run() error {
+	if os.Getenv("GITHUB_TOKEN") == "" {
+		return errors.New("GITHUB_TOKEN not set, create one here with the repo scope selected: https://github.com/settings/tokens/new")
+	}
+
+	newVersion, finalVersion := r.calculateVersions(helpers.CurrentHugoVersion)
+
+	version := newVersion.String()
+	tag := "v" + version
+
+	// Exit early if tag already exists
+	out, err := git("tag", "-l", tag)
+
+	if err != nil {
+		return err
+	}
+
+	if strings.Contains(out, tag) {
+		return fmt.Errorf("Tag %q already exists", tag)
+	}
+
+	var gitCommits gitInfos
+
+	if r.shouldPrepare() || r.shouldRelease() {
+		gitCommits, err = getGitInfos(true)
+		if err != nil {
+			return err
+		}
+	}
+
+	if r.shouldPrepare() {
+		if err := bumpVersions(newVersion); err != nil {
+			return err
+		}
+
+		if _, err := git("commit", "-a", "-m", fmt.Sprintf("%s Bump versions for release of %s\n\n[ci skip]", commitPrefix, newVersion)); err != nil {
+			return err
+		}
+
+		releaseNotesFile, err := writeReleaseNotesToDocsTemp(version, gitCommits)
+		if err != nil {
+			return err
+		}
+
+		if _, err := git("add", releaseNotesFile); err != nil {
+			return err
+		}
+		if _, err := git("commit", "-m", fmt.Sprintf("%s Add relase notes draft for release of %s\n\n[ci skip]", commitPrefix, newVersion)); err != nil {
+			return err
+		}
+	}
+
+	if !r.shouldRelease() {
+		fmt.Println("Skip release ... Use --state=2 to continue.")
+		return nil
+	}
+
+	releaseNotesFile := getRelaseNotesDocsTempFilename(version)
+
+	// Write the release notes to the docs site as well.
+	docFile, err := writeReleaseNotesToDocs(version, releaseNotesFile)
+	if err != nil {
+		return err
+	}
+
+	if _, err := git("add", docFile); err != nil {
+		return err
+	}
+	if _, err := git("commit", "-m", fmt.Sprintf("%s Add relase notes to /docs for release of %s\n\n[ci skip]", commitPrefix, newVersion)); err != nil {
+		return err
+	}
+
+	if _, err := git("tag", "-a", tag, "-m", fmt.Sprintf("%s %s [ci deploy]", commitPrefix, newVersion)); err != nil {
+		return err
+	}
+
+	if err := r.release(releaseNotesFile); err != nil {
+		return err
+	}
+
+	if err := bumpVersions(finalVersion); err != nil {
+		return err
+	}
+
+	// No longer needed.
+	if err := os.Remove(releaseNotesFile); err != nil {
+		return err
+	}
+
+	if _, err := git("commit", "-a", "-m", fmt.Sprintf("%s Prepare repository for %s\n\n[ci skip]", commitPrefix, finalVersion)); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (r *ReleaseHandler) release(releaseNotesFile string) error {
+	cmd := exec.Command("goreleaser", "--release-notes", releaseNotesFile, "--skip-publish="+fmt.Sprint(r.skipPublish))
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	if err != nil {
+		return fmt.Errorf("goreleaser failed: %s", err)
+	}
+	return nil
+}
+
+func bumpVersions(ver helpers.HugoVersion) error {
+	fromDev := ""
+	toDev := ""
+
+	if ver.Suffix != "" {
+		toDev = "-DEV"
+	} else {
+		fromDev = "-DEV"
+	}
+
+	if err := replaceInFile("helpers/hugo.go",
+		`Number:(\s{4,})(.*),`, fmt.Sprintf(`Number:${1}%.2f,`, ver.Number),
+		`PatchLevel:(\s*)(.*),`, fmt.Sprintf(`PatchLevel:${1}%d,`, ver.PatchLevel),
+		fmt.Sprintf(`Suffix:(\s{4,})"%s",`, fromDev), fmt.Sprintf(`Suffix:${1}"%s",`, toDev)); err != nil {
+		return err
+	}
+
+	snapcraftGrade := "stable"
+	if ver.Suffix != "" {
+		snapcraftGrade = "devel"
+	}
+	if err := replaceInFile("snapcraft.yaml",
+		`version: "(.*)"`, fmt.Sprintf(`version: "%s"`, ver),
+		`grade: (.*) #`, fmt.Sprintf(`grade: %s #`, snapcraftGrade)); err != nil {
+		return err
+	}
+
+	var minVersion string
+	if ver.Suffix != "" {
+		// People use the DEV version in daily use, and we cannot create new themes
+		// with the next version before it is released.
+		minVersion = ver.Prev().String()
+	} else {
+		minVersion = ver.String()
+	}
+
+	if err := replaceInFile("commands/new.go",
+		`min_version = "(.*)"`, fmt.Sprintf(`min_version = "%s"`, minVersion)); err != nil {
+		return err
+	}
+
+	// docs/config.toml
+	if err := replaceInFile("docs/config.toml",
+		`release = "(.*)"`, fmt.Sprintf(`release = "%s"`, ver)); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func replaceInFile(filename string, oldNew ...string) error {
+	fullFilename := hugoFilepath(filename)
+	fi, err := os.Stat(fullFilename)
+	if err != nil {
+		return err
+	}
+
+	b, err := ioutil.ReadFile(fullFilename)
+	if err != nil {
+		return err
+	}
+	newContent := string(b)
+
+	for i := 0; i < len(oldNew); i += 2 {
+		re := regexp.MustCompile(oldNew[i])
+		newContent = re.ReplaceAllString(newContent, oldNew[i+1])
+	}
+
+	return ioutil.WriteFile(fullFilename, []byte(newContent), fi.Mode())
+
+	return nil
+}
+
+func hugoFilepath(filename string) string {
+	pwd, err := os.Getwd()
+	if err != nil {
+		log.Fatal(err)
+	}
+	return filepath.Join(pwd, filename)
+}
diff --git a/releaser/releaser_test.go b/releaser/releaser_test.go
new file mode 100644
index 000000000..641600545
--- /dev/null
+++ b/releaser/releaser_test.go
@@ -0,0 +1,78 @@
+// Copyright 2017-present The Hugo Authors. 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 commands defines and implements command-line commands and flags
+// used by Hugo. Commands and flags are implemented using Cobra.
+
+package releaser
+
+import (
+	"testing"
+
+	"github.com/spf13/hugo/helpers"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCalculateVersions(t *testing.T) {
+	startVersion := helpers.HugoVersion{Number: 0.20, Suffix: "-DEV"}
+
+	tests := []struct {
+		handler *ReleaseHandler
+		version helpers.HugoVersion
+		v1      string
+		v2      string
+	}{
+		{
+			New(0, 0, true),
+			startVersion,
+			"0.20",
+			"0.21-DEV",
+		},
+		{
+			New(2, 0, true),
+			startVersion,
+			"0.20.2",
+			"0.20-DEV",
+		},
+		{
+			New(0, 1, true),
+			startVersion,
+			"0.20",
+			"0.21-DEV",
+		},
+		{
+			New(0, 2, true),
+			startVersion,
+			"0.20",
+			"0.21-DEV",
+		},
+		{
+			New(3, 1, true),
+			startVersion,
+			"0.20.3",
+			"0.20-DEV",
+		},
+		{
+			New(3, 2, true),
+			startVersion.Next(),
+			"0.21",
+			"0.21-DEV",
+		},
+	}
+
+	for _, test := range tests {
+		v1, v2 := test.handler.calculateVersions(test.version)
+		require.Equal(t, test.v1, v1.String(), "Release version")
+		require.Equal(t, test.v2, v2.String(), "Final version")
+	}
+}