feat: allow to PR homebrew taps (#3903)

closes #3485

also fixed a bug in file creation for github: it was always searching
for the file in the default branch

also, we don't need to create the file first, update does both create
and update.

TODO: implement the for krew, scoop, etc...

---------

Signed-off-by: Carlos A Becker <caarlos0@users.noreply.github.com>

internal/client/github.go

@@ -21,12 +21,24 @@ import (
 
 const DefaultGitHubDownloadURL = "https://github.com"
 
+var (
+	_ Client                = &githubClient{}
+	_ ReleaseNotesGenerator = &githubClient{}
+	_ PullRequestOpener     = &githubClient{}
+)
+
 type githubClient struct {
 	client *github.Client
 }
 
-// NewGitHub returns a github client implementation.
-func NewGitHub(ctx *context.Context, token string) (GitHubClient, error) {
+// NewGitHubReleaseNotesGenerator returns a GitHub client that can generate
+// changelogs.
+func NewGitHubReleaseNotesGenerator(ctx *context.Context, token string) (ReleaseNotesGenerator, error) {
+	return newGitHub(ctx, token)
+}
+
+// newGitHub returns a github client implementation.
+func newGitHub(ctx *context.Context, token string) (*githubClient, error) {
 	ts := oauth2.StaticTokenSource(
 		&oauth2.Token{AccessToken: token},
 	)
@@ -89,8 +101,8 @@ func (c *githubClient) Changelog(ctx *context.Context, repo Repo, prev, current
 	return strings.Join(log, "\n"), nil
 }
 
-// GetDefaultBranch returns the default branch of a github repo
-func (c *githubClient) GetDefaultBranch(ctx *context.Context, repo Repo) (string, error) {
+// getDefaultBranch returns the default branch of a github repo
+func (c *githubClient) getDefaultBranch(ctx *context.Context, repo Repo) (string, error) {
 	p, res, err := c.client.Repositories.Get(ctx, repo.Owner, repo.Name)
 	if err != nil {
 		log.WithFields(log.Fields{
@@ -128,6 +140,35 @@ func (c *githubClient) CloseMilestone(ctx *context.Context, repo Repo, title str
 	return err
 }
 
+func (c *githubClient) OpenPullRequest(
+	ctx *context.Context,
+	repo Repo,
+	base, title string,
+) error {
+	if base == "" {
+		def, err := c.getDefaultBranch(ctx, repo)
+		if err != nil {
+			return err
+		}
+		base = def
+	}
+	pr, res, err := c.client.PullRequests.Create(ctx, repo.Owner, repo.Name, &github.NewPullRequest{
+		Title: github.String(title),
+		Head:  github.String(repo.Branch),
+		Base:  github.String(base),
+		Body:  github.String("Automatically generated by [GoReleaser](https://goreleaser.com)"),
+	})
+	if err != nil {
+		if res.StatusCode == 422 {
+			log.Warn("PR already exists, doing nothing...")
+			return nil
+		}
+		return fmt.Errorf("could not create pull request: %w", err)
+	}
+	log.WithField("url", pr.GetHTMLURL()).Info("opened")
+	return nil
+}
+
 func (c *githubClient) CreateFile(
 	ctx *context.Context,
 	commitAuthor config.CommitAuthor,
@@ -136,22 +177,16 @@ func (c *githubClient) CreateFile(
 	path,
 	message string,
 ) error {
-	var branch string
-	var err error
-	if repo.Branch != "" {
-		branch = repo.Branch
-	} else {
-		branch, err = c.GetDefaultBranch(ctx, repo)
-		if err != nil {
-			// Fall back to sdk default
-			log.WithFields(log.Fields{
-				"fileName":        path,
-				"projectID":       repo.String(),
-				"requestedBranch": branch,
-				"err":             err.Error(),
-			}).Warn("error checking for default branch, using master")
-		}
+	defBranch, err := c.getDefaultBranch(ctx, repo)
+	if err != nil {
+		return fmt.Errorf("could not get default branch: %w", err)
 	}
+
+	branch := repo.Branch
+	if branch == "" {
+		branch = defBranch
+	}
+
 	options := &github.RepositoryContentFileOptions{
 		Committer: &github.CommitAuthor{
 			Name:  github.String(commitAuthor.Name),
@@ -167,36 +202,53 @@ func (c *githubClient) CreateFile(
 		options.Branch = &branch
 	}
 
+	if defBranch != branch && branch != "" {
+		_, res, err := c.client.Repositories.GetBranch(ctx, repo.Owner, repo.Name, branch, true)
+		if err != nil && (res == nil || res.StatusCode != 404) {
+			return fmt.Errorf("could not get branch %q: %w", branch, err)
+		}
+
+		if res.StatusCode == 404 {
+			defRef, _, err := c.client.Git.GetRef(ctx, repo.Owner, repo.Name, "refs/heads/"+defBranch)
+			if err != nil {
+				return fmt.Errorf("could not get ref %q: %w", "refs/heads/"+defBranch, err)
+			}
+
+			if _, _, err := c.client.Git.CreateRef(ctx, repo.Owner, repo.Name, &github.Reference{
+				Ref: github.String("refs/heads/" + branch),
+				Object: &github.GitObject{
+					SHA: defRef.Object.SHA,
+				},
+			}); err != nil {
+				return fmt.Errorf("could not create ref %q from %q: %w", "refs/heads/"+branch, defRef.Object.GetSHA(), err)
+			}
+		}
+	}
+
 	file, _, res, err := c.client.Repositories.GetContents(
 		ctx,
 		repo.Owner,
 		repo.Name,
 		path,
-		&github.RepositoryContentGetOptions{},
+		&github.RepositoryContentGetOptions{
+			Ref: branch,
+		},
 	)
 	if err != nil && (res == nil || res.StatusCode != 404) {
-		return err
+		return fmt.Errorf("could not get %q: %w", path, err)
 	}
 
-	if res.StatusCode == 404 {
-		_, _, err = c.client.Repositories.CreateFile(
-			ctx,
-			repo.Owner,
-			repo.Name,
-			path,
-			options,
-		)
-		return err
-	}
-	options.SHA = file.SHA
-	_, _, err = c.client.Repositories.UpdateFile(
+	options.SHA = github.String(file.GetSHA())
+	if _, _, err := c.client.Repositories.UpdateFile(
 		ctx,
 		repo.Owner,
 		repo.Name,
 		path,
 		options,
-	)
-	return err
+	); err != nil {
+		return fmt.Errorf("could not update %q: %w", path, err)
+	}
+	return nil
 }
 
 func (c *githubClient) CreateRelease(ctx *context.Context, body string) (string, error) {