pull: add an option to use rebase for merging pull requests

For DVCS, either merge or rebase works for getting new code in a pull
request in the main branch.

The rebase workflow produces a linear history which is cleaner, and
more bisect-able.

This commit adds a repo-level option to enable the rebase workflow. Once
enabled, "Merge Pull Request" will be replaced by
"Rebase and Merge Pull Request" which does exactly what the user wants.
It's unlikely a project wants a mixed-use of both rebase and merge
workflows, therefore the feature is not implemented as a drop-down
button like what GitHub does
(https://github.com/blog/2243-rebase-and-merge-pull-requests).

conf/locale/locale_en-US.ini

@@ -633,6 +633,7 @@ pulls.can_auto_merge_desc = This pull request can be merged automatically.
 pulls.cannot_auto_merge_desc = This pull request can't be merged automatically because there are conflicts.
 pulls.cannot_auto_merge_helper = Please merge manually in order to resolve the conflicts.
 pulls.merge_pull_request = Merge Pull Request
+pulls.rebase_merge_pull_request = Rebase and Merge Pull Request
 pulls.open_unmerged_pull_exists = `You can't perform reopen operation because there is already an open pull request (#%d) from same repository with same merge information and is waiting for merging.`
 pulls.delete_branch = Delete Branch
 pulls.delete_branch_has_new_commits = Branch cannot be deleted because it has new commits after mergence.
@@ -737,6 +738,7 @@ settings.tracker_issue_style.numeric = Numeric
 settings.tracker_issue_style.alphanumeric = Alphanumeric
 settings.tracker_url_format_desc = You can use placeholder <code>{user} {repo} {index}</code> for user name, repository name and issue index.
 settings.pulls_desc = Enable pull requests to accept public contributions
+settings.use_rebase_desc = Use rebase to merge pull requests
 settings.danger_zone = Danger Zone
 settings.cannot_fork_to_same_owner = You cannot fork a repository to its original owner.
 settings.new_owner_has_same_repo = The new owner already has a repository with same name. Please choose another name.

models/pull.go

@@ -233,13 +233,21 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository) (err error
 		return fmt.Errorf("git remote add [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
 	}
 
-	// Merge commits.
 	if _, stderr, err = process.ExecDir(-1, tmpBasePath,
 		fmt.Sprintf("PullRequest.Merge (git fetch): %s", tmpBasePath),
 		"git", "fetch", "head_repo"); err != nil {
 		return fmt.Errorf("git fetch [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
 	}
 
+	if (pr.BaseRepo.PullUseRebase) {
+		// Rebase.
+		if _, stderr, err = process.ExecDir(-1, tmpBasePath,
+			fmt.Sprintf("PullRequest.Rebase (git rebase): %s", tmpBasePath),
+			"git", "rebase", "-q", pr.BaseBranch, "head_repo/"+pr.HeadBranch); err != nil {
+			return fmt.Errorf("git rebase [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
+		}
+	} else {
+		// Merge commits.
 		if _, stderr, err = process.ExecDir(-1, tmpBasePath,
 			fmt.Sprintf("PullRequest.Merge (git merge --no-ff --no-commit): %s", tmpBasePath),
 			"git", "merge", "--no-ff", "--no-commit", "head_repo/"+pr.HeadBranch); err != nil {
@@ -253,11 +261,12 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository) (err error
 			"-m", fmt.Sprintf("Merge branch '%s' of %s/%s into %s", pr.HeadBranch, pr.HeadUserName, pr.HeadRepo.Name, pr.BaseBranch)); err != nil {
 			return fmt.Errorf("git commit [%s]: %v - %s", tmpBasePath, err, stderr)
 		}
+	}
 
 	// Push back to upstream.
 	if _, stderr, err = process.ExecDir(-1, tmpBasePath,
 		fmt.Sprintf("PullRequest.Merge (git push): %s", tmpBasePath),
-		"git", "push", baseGitRepo.Path, pr.BaseBranch); err != nil {
+		"git", "push", "head_repo", "HEAD:"+pr.BaseBranch); err != nil {
 		return fmt.Errorf("git push: %s", stderr)
 	}
 

models/repo.go

@@ -184,6 +184,7 @@ type Repository struct {
 	ExternalTrackerStyle  string
 	ExternalMetas         map[string]string `xorm:"-"`
 	EnablePulls           bool              `xorm:"NOT NULL DEFAULT true"`
+	PullUseRebase         bool              `xorm:"NOT NULL DEFAULT false"`
 
 	IsFork   bool `xorm:"NOT NULL DEFAULT false"`
 	ForkID   int64

pkg/form/repo.go

@@ -102,6 +102,7 @@ type RepoSetting struct {
 	TrackerURLFormat      string
 	TrackerIssueStyle     string
 	EnablePulls           bool
+	PullUseRebase         bool
 }
 
 func (f *RepoSetting) Validate(ctx *macaron.Context, errs binding.Errors) binding.Errors {

routes/repo/setting.go

@@ -147,6 +147,7 @@ func SettingsPost(c *context.Context, f form.RepoSetting) {
 		repo.ExternalTrackerFormat = f.TrackerURLFormat
 		repo.ExternalTrackerStyle = f.TrackerIssueStyle
 		repo.EnablePulls = f.EnablePulls
+		repo.PullUseRebase = f.PullUseRebase
 
 		if err := models.UpdateRepository(repo, false); err != nil {
 			c.ServerError("UpdateRepository", err)

templates/repo/issue/view_content.tmpl

@@ -196,7 +196,11 @@
 										<form class="ui form" action="{{.Link}}/merge" method="post">
 											{{.CSRFTokenHTML}}
 											<button class="ui green button">
+												{{if .Issue.Repo.PullUseRebase }}
+													<span class="octicon octicon-git-pull-request"></span> {{$.i18n.Tr "repo.pulls.rebase_merge_pull_request"}}
+												{{else}}
 													<span class="octicon octicon-git-merge"></span> {{$.i18n.Tr "repo.pulls.merge_pull_request"}}
+												{{end}}
 											</button>
 										</form>
 									</div>

templates/repo/settings/options.tmpl

@@ -193,10 +193,16 @@
 							<div class="inline field">
 								<label>{{.i18n.Tr "repo.pulls"}}</label>
 								<div class="ui checkbox">
-									<input name="enable_pulls" type="checkbox" {{if .Repository.EnablePulls}}checked{{end}}>
+									<input class="enable-system" name="enable_pulls" type="checkbox" data-target="#pull_box" {{if .Repository.EnablePulls}}checked{{end}}>
 									<label>{{.i18n.Tr "repo.settings.pulls_desc"}}</label>
 								</div>
 							</div>
+							<div class="ui segment field {{if not .Repository.EnablePulls}}disabled{{end}}" id="pull_box">
+								<div class="ui checkbox">
+									<input name="pull_use_rebase" type="checkbox" {{if .Repository.PullUseRebase}}checked{{end}}>
+									<label>{{.i18n.Tr "repo.settings.use_rebase_desc"}}</label>
+								</div>
+							</div>
 						{{end}}
 
 						<div class="field">