Add Contributed backport command (#22643)

This PR provides a contributed backport command to help create backports
for Gitea.

It represents a significant improvement on my previously described
shell-script.

It can be installed using `go install contrib/backport/backport.go`.

Signed-off-by: Andrew Thornton <art27@cantab.net>

2 files changed, 479 insertions, 0 deletions

diff --git a/contrib/backport/README b/contrib/backport/README
new file mode 100644
index 000000000..1e84c1bb9
--- /dev/null
+++ b/contrib/backport/README
@@ -0,0 +1,41 @@
+`backport`
+==========
+
+`backport` is a command to help create backports of PRs. It backports a
+provided PR from main on to a released version.
+
+It will create a backport branch, cherry-pick the PR's merge commit, adjust
+the commit message and then push this back up to your fork's remote.
+
+The default version will read from `docs/config.yml`. You can override this
+using the option `--version`.
+
+The upstream branches will be fetched, using the remote `origin`. This can
+be overrided using `--upstream`, and fetching can be avoided using
+`--no-fetch`.
+
+By default the branch created will be called `backport-$PR-$VERSION`. You
+can override this using the option `--backport-branch`. This branch will
+be created from `--release-branch` which is `release/$(VERSION)`
+by default and will be pulled from `$(UPSTREAM)`.
+
+The merge-commit as determined by the github API will be used as the SHA to
+cherry-pick. You can override this using `--cherry-pick`.
+
+The commit message will be amended to add the `Backport` header.
+`--no-amend-message` can be set to stop this from happening.
+
+If cherry-pick is successful the backported branch will be pushed up to your
+fork using your remote. These will be determined using `git remote -v`. You
+can set your fork name using `--fork-user` and your remote name using
+`--remote`. You can avoid pushing using `--no-push`.
+
+If the push is successful, `xdg-open` will be called to open a backport url.
+You can stop this using `--no-xdg-open`.
+
+Installation
+============
+
+```bash
+go install contrib/backport/backport.go
+```
diff --git a/contrib/backport/backport.go b/contrib/backport/backport.go
new file mode 100644
index 000000000..c35bf9e30
--- /dev/null
+++ b/contrib/backport/backport.go
@@ -0,0 +1,438 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"os/signal"
+	"path"
+	"strconv"
+	"strings"
+	"syscall"
+
+	"github.com/google/go-github/v45/github"
+	"github.com/urfave/cli"
+	"gopkg.in/yaml.v3"
+)
+
+const defaultVersion = "v1.18" // to backport to
+
+func main() {
+	app := cli.NewApp()
+	app.Name = "backport"
+	app.Usage = "Backport provided PR-number on to the current or previous released version"
+	app.Description = `Backport will look-up the PR in Gitea's git log and attempt to cherry-pick it on the current version`
+	app.ArgsUsage = "<PR-to-backport>"
+
+	app.Flags = []cli.Flag{
+		cli.StringFlag{
+			Name:  "version",
+			Usage: "Version branch to backport on to",
+		},
+		cli.StringFlag{
+			Name:  "upstream",
+			Value: "origin",
+			Usage: "Upstream remote for the Gitea upstream",
+		},
+		cli.StringFlag{
+			Name:  "release-branch",
+			Value: "",
+			Usage: "Release branch to backport on. Will default to release/<version>",
+		},
+		cli.StringFlag{
+			Name:  "cherry-pick",
+			Usage: "SHA to cherry-pick as backport",
+		},
+		cli.StringFlag{
+			Name:  "backport-branch",
+			Usage: "Backport branch to backport on to (default: backport-<pr>-<version>",
+		},
+		cli.StringFlag{
+			Name:  "remote",
+			Value: "",
+			Usage: "Remote for your fork of the Gitea upstream",
+		},
+		cli.StringFlag{
+			Name:  "fork-user",
+			Value: "",
+			Usage: "Forked user name on Github",
+		},
+		cli.BoolFlag{
+			Name:  "no-fetch",
+			Usage: "Set this flag to prevent fetch of remote branches",
+		},
+		cli.BoolFlag{
+			Name:  "no-amend-message",
+			Usage: "Set this flag to prevent automatic amendment of the commit message",
+		},
+		cli.BoolFlag{
+			Name:  "no-push",
+			Usage: "Set this flag to prevent pushing the backport up to your fork",
+		},
+		cli.BoolFlag{
+			Name:  "no-xdg-open",
+			Usage: "Set this flag to not use xdg-open to open the PR URL",
+		},
+	}
+	cli.AppHelpTemplate = `NAME:
+	{{.Name}} - {{.Usage}}
+USAGE:
+	{{.HelpName}} {{if .VisibleFlags}}[options]{{end}} {{if .ArgsUsage}}{{.ArgsUsage}}{{else}}[arguments...]{{end}}
+	{{if len .Authors}}
+AUTHOR:
+	{{range .Authors}}{{ . }}{{end}}
+	{{end}}{{if .Commands}}
+OPTIONS:
+	{{range .VisibleFlags}}{{.}}
+	{{end}}{{end}}
+`
+
+	app.Action = runBackport
+
+	if err := app.Run(os.Args); err != nil {
+		fmt.Fprintf(os.Stderr, "Unable to backport: %v\n", err)
+	}
+}
+
+func runBackport(c *cli.Context) error {
+	ctx, cancel := installSignals()
+	defer cancel()
+
+	version := c.String("version")
+	if version == "" {
+		version = readVersion()
+	}
+	if version == "" {
+		version = defaultVersion
+	}
+
+	upstream := c.String("upstream")
+	if upstream == "" {
+		upstream = "origin"
+	}
+
+	forkUser := c.String("fork-user")
+	remote := c.String("remote")
+	if remote == "" && !c.Bool("--no-push") {
+		var err error
+		remote, forkUser, err = determineRemote(ctx, forkUser)
+		if err != nil {
+			return err
+		}
+	}
+
+	upstreamReleaseBranch := c.String("release-branch")
+	if upstreamReleaseBranch == "" {
+		upstreamReleaseBranch = path.Join("release", version)
+	}
+
+	localReleaseBranch := path.Join(upstream, upstreamReleaseBranch)
+
+	args := c.Args()
+	if len(args) == 0 {
+		return fmt.Errorf("no PR number provided\nProvide a PR number to backport")
+	} else if len(args) != 1 {
+		return fmt.Errorf("multiple PRs provided %v\nOnly a single PR can be backported at a time", args)
+	}
+
+	pr := args[0]
+
+	backportBranch := c.String("backport-branch")
+	if backportBranch == "" {
+		backportBranch = "backport-" + pr + "-" + version
+	}
+
+	fmt.Printf("* Backporting %s to %s as %s\n", pr, localReleaseBranch, backportBranch)
+
+	sha := c.String("cherry-pick")
+	if sha == "" {
+		var err error
+		sha, err = determineSHAforPR(ctx, pr)
+		if err != nil {
+			return err
+		}
+	}
+	if sha == "" {
+		return fmt.Errorf("unable to determine sha for cherry-pick of %s", pr)
+	}
+
+	if !c.Bool("no-fetch") {
+		if err := fetchRemoteAndMain(ctx, upstream, upstreamReleaseBranch); err != nil {
+			return err
+		}
+	}
+
+	if err := checkoutBackportBranch(ctx, backportBranch, localReleaseBranch); err != nil {
+		return err
+	}
+
+	if err := cherrypick(ctx, sha); err != nil {
+		return err
+	}
+
+	if !c.Bool("no-amend-message") {
+		if err := amendCommit(ctx, pr); err != nil {
+			return err
+		}
+	}
+
+	if !c.Bool("no-push") {
+		url := "https://github.com/go-gitea/gitea/compare/" + upstreamReleaseBranch + "..." + forkUser + ":" + backportBranch
+
+		if err := gitPushUp(ctx, remote, backportBranch); err != nil {
+			return err
+		}
+
+		if !c.Bool("no-xdg-open") {
+			if err := xdgOpen(ctx, url); err != nil {
+				return err
+			}
+		} else {
+			fmt.Printf("* Navigate to %s to open PR\n", url)
+		}
+	}
+	return nil
+}
+
+func xdgOpen(ctx context.Context, url string) error {
+	fmt.Printf("* `xdg-open %s`\n", url)
+	out, err := exec.CommandContext(ctx, "xdg-open", url).Output()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%s", string(out))
+		return fmt.Errorf("unable to xdg-open to %s: %w", url, err)
+	}
+	return nil
+}
+
+func gitPushUp(ctx context.Context, remote, backportBranch string) error {
+	fmt.Printf("* `git push -u %s %s`\n", remote, backportBranch)
+	out, err := exec.CommandContext(ctx, "git", "push", "-u", remote, backportBranch).Output()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%s", string(out))
+		return fmt.Errorf("unable to push up to %s: %w", remote, err)
+	}
+	return nil
+}
+
+func amendCommit(ctx context.Context, pr string) error {
+	fmt.Printf("* Amending commit to prepend `Backport #%s` to body\n", pr)
+	out, err := exec.CommandContext(ctx, "git", "log", "-1", "--pretty=format:%B").Output()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%s", string(out))
+		return fmt.Errorf("unable to get last log message: %w", err)
+	}
+
+	parts := strings.SplitN(string(out), "\n", 2)
+
+	if len(parts) != 2 {
+		return fmt.Errorf("unable to interpret log message:\n%s", string(out))
+	}
+	subject, body := parts[0], parts[1]
+	if !strings.HasSuffix(subject, " (#"+pr+")") {
+		subject = subject + " (#" + pr + ")"
+	}
+
+	out, err = exec.CommandContext(ctx, "git", "commit", "--amend", "-m", subject+"\n\nBackport #"+pr+"\n"+body).Output()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%s", string(out))
+		return fmt.Errorf("unable to amend last log message: %w", err)
+	}
+	return nil
+}
+
+func cherrypick(ctx context.Context, sha string) error {
+	// Check if a CHERRY_PICK_HEAD exists
+	if _, err := os.Stat(".git/CHERRY_PICK_HEAD"); err == nil {
+		// Assume that we are in the middle of cherry-pick - continue it
+		fmt.Println("* Attempting git cherry-pick --continue")
+		out, err := exec.CommandContext(ctx, "git", "cherry-pick", "--continue").Output()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "git cherry-pick --continue failed:\n%s\n", string(out))
+			return fmt.Errorf("unable to continue cherry-pick: %w", err)
+		}
+		return nil
+	}
+
+	fmt.Printf("* Attempting git cherry-pick %s\n", sha)
+	out, err := exec.CommandContext(ctx, "git", "cherry-pick", sha).Output()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "git cherry-pick %s failed:\n%s\n", sha, string(out))
+		return fmt.Errorf("git cherry-pick %s failed: %w", sha, err)
+	}
+	return nil
+}
+
+func checkoutBackportBranch(ctx context.Context, backportBranch, releaseBranch string) error {
+	out, err := exec.CommandContext(ctx, "git", "branch", "--show-current").Output()
+	if err != nil {
+		return fmt.Errorf("unable to check current branch %w", err)
+	}
+
+	currentBranch := strings.TrimSpace(string(out))
+	fmt.Printf("* Current branch is %s\n", currentBranch)
+	if currentBranch == backportBranch {
+		fmt.Printf("* Current branch is %s - not checking out\n", currentBranch)
+		return nil
+	}
+
+	if _, err := exec.CommandContext(ctx, "git", "rev-list", "-1", backportBranch).Output(); err == nil {
+		fmt.Printf("* Branch %s already exists. Checking it out...\n", backportBranch)
+		return exec.CommandContext(ctx, "git", "checkout", "-f", backportBranch).Run()
+	}
+
+	fmt.Printf("* `git checkout -b %s %s`\n", backportBranch, releaseBranch)
+	return exec.CommandContext(ctx, "git", "checkout", "-b", backportBranch, releaseBranch).Run()
+}
+
+func fetchRemoteAndMain(ctx context.Context, remote, releaseBranch string) error {
+	fmt.Printf("* `git fetch %s main`\n", remote)
+	out, err := exec.CommandContext(ctx, "git", "fetch", remote, "main").Output()
+	if err != nil {
+		fmt.Println(string(out))
+		return fmt.Errorf("unable to fetch %s from %s: %w", "main", remote, err)
+	}
+	fmt.Println(string(out))
+
+	fmt.Printf("* `git fetch %s %s`\n", remote, releaseBranch)
+	out, err = exec.CommandContext(ctx, "git", "fetch", remote, releaseBranch).Output()
+	if err != nil {
+		fmt.Println(string(out))
+		return fmt.Errorf("unable to fetch %s from %s: %w", releaseBranch, remote, err)
+	}
+	fmt.Println(string(out))
+
+	return nil
+}
+
+func determineRemote(ctx context.Context, forkUser string) (string, string, error) {
+	out, err := exec.CommandContext(ctx, "git", "remote", "-v").Output()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Unable to list git remotes:\n%s\n", string(out))
+		return "", "", fmt.Errorf("unable to determine forked remote: %w", err)
+	}
+	lines := strings.Split(string(out), "\n")
+	for _, line := range lines {
+		fields := strings.Split(line, "\t")
+		name, remote := fields[0], fields[1]
+		// only look at pushers
+		if !strings.HasSuffix(remote, " (push)") {
+			continue
+		}
+		// only look at github.com pushes
+		if !strings.Contains(remote, "github.com") {
+			continue
+		}
+		// ignore go-gitea/gitea
+		if strings.Contains(remote, "go-gitea/gitea") {
+			continue
+		}
+		if !strings.Contains(remote, forkUser) {
+			continue
+		}
+		if strings.HasPrefix(remote, "git@github.com:") {
+			forkUser = strings.TrimPrefix(remote, "git@github.com:")
+		} else if strings.HasPrefix(remote, "https://github.com/") {
+			forkUser = strings.TrimPrefix(remote, "https://github.com/")
+		} else if strings.HasPrefix(remote, "https://www.github.com/") {
+			forkUser = strings.TrimPrefix(remote, "https://www.github.com/")
+		} else if forkUser == "" {
+			return "", "", fmt.Errorf("unable to extract forkUser from remote %s: %s", name, remote)
+		}
+		idx := strings.Index(forkUser, "/")
+		if idx >= 0 {
+			forkUser = forkUser[:idx]
+		}
+		return name, forkUser, nil
+	}
+	return "", "", fmt.Errorf("unable to find appropriate remote in:\n%s", string(out))
+}
+
+func readVersion() string {
+	bs, err := os.ReadFile("docs/config.yaml")
+	if err != nil {
+		if err == os.ErrNotExist {
+			log.Println("`docs/config.yaml` not present")
+			return ""
+		}
+		fmt.Fprintf(os.Stderr, "Unable to read `docs/config.yaml`: %v\n", err)
+		return ""
+	}
+
+	type params struct {
+		Version string
+	}
+	type docConfig struct {
+		Params params
+	}
+	dc := &docConfig{}
+	if err := yaml.Unmarshal(bs, dc); err != nil {
+		fmt.Fprintf(os.Stderr, "Unable to read `docs/config.yaml`: %v\n", err)
+		return ""
+	}
+
+	if dc.Params.Version == "" {
+		fmt.Fprintf(os.Stderr, "No version in `docs/config.yaml`")
+		return ""
+	}
+
+	version := dc.Params.Version
+	if version[0] != 'v' {
+		version = "v" + version
+	}
+
+	split := strings.SplitN(version, ".", 3)
+
+	return strings.Join(split[:2], ".")
+}
+
+func determineSHAforPR(ctx context.Context, prStr string) (string, error) {
+	prNum, err := strconv.Atoi(prStr)
+	if err != nil {
+		return "", err
+	}
+
+	client := github.NewClient(http.DefaultClient)
+
+	pr, _, err := client.PullRequests.Get(ctx, "go-gitea", "gitea", prNum)
+	if err != nil {
+		return "", err
+	}
+
+	if pr.Merged == nil || !*pr.Merged {
+		return "", fmt.Errorf("PR #%d is not yet merged - cannot determine sha to backport", prNum)
+	}
+
+	if pr.MergeCommitSHA != nil {
+		return *pr.MergeCommitSHA, nil
+	}
+
+	return "", nil
+}
+
+func installSignals() (context.Context, context.CancelFunc) {
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		// install notify
+		signalChannel := make(chan os.Signal, 1)
+
+		signal.Notify(
+			signalChannel,
+			syscall.SIGINT,
+			syscall.SIGTERM,
+		)
+		select {
+		case <-signalChannel:
+		case <-ctx.Done():
+		}
+		cancel()
+		signal.Reset()
+	}()
+
+	return ctx, cancel
+}