Add Pull Request merge options - Ignore white-space for conflict checking, Rebase, Squash merge (#3188)

* Pull request options migration and UI in settings

* Add ignore whitespace functionality

* Fix settings if pull requests are disabled

* Fix migration transaction

* Merge with Rebase functionality

* UI changes and related functionality for pull request merging button

* Implement squash functionality

* Fix rebase merging

* Fix pull request merge tests

* Add squash and rebase tests

* Fix API method to reuse default message functions

* Some refactoring and small fixes

* Remove more hardcoded values from tests

* Remove unneeded check from API method

* Fix variable name and comment typo

* Fix reset commit count after PR merge

20 files changed, 529 insertions, 44 deletions

diff --git a/integrations/pull_merge_test.go b/integrations/pull_merge_test.go
index 65ccc93f95..b123239331 100644
--- a/integrations/pull_merge_test.go
+++ b/integrations/pull_merge_test.go
@@ -11,21 +11,23 @@ import (
 	"strings"
 	"testing"
 
+	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/test"
 
 	"github.com/stretchr/testify/assert"
 )
 
-func testPullMerge(t *testing.T, session *TestSession, user, repo, pullnum string) *httptest.ResponseRecorder {
+func testPullMerge(t *testing.T, session *TestSession, user, repo, pullnum string, mergeStyle models.MergeStyle) *httptest.ResponseRecorder {
 	req := NewRequest(t, "GET", path.Join(user, repo, "pulls", pullnum))
 	resp := session.MakeRequest(t, req, http.StatusOK)
 
 	// Click the little green button to create a pull
 	htmlDoc := NewHTMLParser(t, resp.Body)
-	link, exists := htmlDoc.doc.Find("form.ui.form>button.ui.green.button").Parent().Attr("action")
+	link, exists := htmlDoc.doc.Find(".ui.form." + string(mergeStyle) + "-fields > form").Attr("action")
 	assert.True(t, exists, "The template has changed")
 	req = NewRequestWithValues(t, "POST", link, map[string]string{
 		"_csrf": htmlDoc.GetCSRF(),
+		"do":    string(mergeStyle),
 	})
 	resp = session.MakeRequest(t, req, http.StatusFound)
 
@@ -58,7 +60,34 @@ func TestPullMerge(t *testing.T) {
 
 	elem := strings.Split(test.RedirectURL(resp), "/")
 	assert.EqualValues(t, "pulls", elem[3])
-	testPullMerge(t, session, elem[1], elem[2], elem[4])
+	testPullMerge(t, session, elem[1], elem[2], elem[4], models.MergeStyleMerge)
+}
+
+func TestPullRebase(t *testing.T) {
+	prepareTestEnv(t)
+	session := loginUser(t, "user1")
+	testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
+	testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
+
+	resp := testPullCreate(t, session, "user1", "repo1", "master")
+
+	elem := strings.Split(test.RedirectURL(resp), "/")
+	assert.EqualValues(t, "pulls", elem[3])
+	testPullMerge(t, session, elem[1], elem[2], elem[4], models.MergeStyleRebase)
+}
+
+func TestPullSquash(t *testing.T) {
+	prepareTestEnv(t)
+	session := loginUser(t, "user1")
+	testRepoFork(t, session, "user2", "repo1", "user1", "repo1")
+	testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited)\n")
+	testEditFile(t, session, "user1", "repo1", "master", "README.md", "Hello, World (Edited!)\n")
+
+	resp := testPullCreate(t, session, "user1", "repo1", "master")
+
+	elem := strings.Split(test.RedirectURL(resp), "/")
+	assert.EqualValues(t, "pulls", elem[3])
+	testPullMerge(t, session, elem[1], elem[2], elem[4], models.MergeStyleSquash)
 }
 
 func TestPullCleanUpAfterMerge(t *testing.T) {
@@ -71,7 +100,7 @@ func TestPullCleanUpAfterMerge(t *testing.T) {
 
 	elem := strings.Split(test.RedirectURL(resp), "/")
 	assert.EqualValues(t, "pulls", elem[3])
-	testPullMerge(t, session, elem[1], elem[2], elem[4])
+	testPullMerge(t, session, elem[1], elem[2], elem[4], models.MergeStyleMerge)
 
 	// Check PR branch deletion
 	resp = testPullCleanUp(t, session, elem[1], elem[2], elem[4])
diff --git a/integrations/repo_activity_test.go b/integrations/repo_activity_test.go
index d3d2de4a2c..40983cbe1a 100644
--- a/integrations/repo_activity_test.go
+++ b/integrations/repo_activity_test.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 	"testing"
 
+	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/test"
 
 	"github.com/stretchr/testify/assert"
@@ -24,7 +25,7 @@ func TestRepoActivity(t *testing.T) {
 	resp := testPullCreate(t, session, "user1", "repo1", "master")
 	elem := strings.Split(test.RedirectURL(resp), "/")
 	assert.EqualValues(t, "pulls", elem[3])
-	testPullMerge(t, session, elem[1], elem[2], elem[4])
+	testPullMerge(t, session, elem[1], elem[2], elem[4], models.MergeStyleMerge)
 
 	testEditFileToNewBranch(t, session, "user1", "repo1", "master", "feat/better_readme", "README.md", "Hello, World (Edited Again)\n")
 	testPullCreate(t, session, "user1", "repo1", "feat/better_readme")
diff --git a/models/error.go b/models/error.go
index fceee21fdf..765b8fa6ca 100644
--- a/models/error.go
+++ b/models/error.go
@@ -878,6 +878,23 @@ func (err ErrPullRequestAlreadyExists) Error() string {
 		err.ID, err.IssueID, err.HeadRepoID, err.BaseRepoID, err.HeadBranch, err.BaseBranch)
 }
 
+// ErrInvalidMergeStyle represents an error if merging with disabled merge strategy
+type ErrInvalidMergeStyle struct {
+	ID    int64
+	Style MergeStyle
+}
+
+// IsErrInvalidMergeStyle checks if an error is a ErrInvalidMergeStyle.
+func IsErrInvalidMergeStyle(err error) bool {
+	_, ok := err.(ErrInvalidMergeStyle)
+	return ok
+}
+
+func (err ErrInvalidMergeStyle) Error() string {
+	return fmt.Sprintf("merge strategy is not allowed or is invalid [repo_id: %d, strategy: %s]",
+		err.ID, err.Style)
+}
+
 // _________                                       __
 // \_   ___ \  ____   _____   _____   ____   _____/  |_
 // /    \  \/ /  _ \ /     \ /     \_/ __ \ /    \   __\
diff --git a/models/fixtures/repo_unit.yml b/models/fixtures/repo_unit.yml
index e9931453ad..45229cce37 100644
--- a/models/fixtures/repo_unit.yml
+++ b/models/fixtures/repo_unit.yml
@@ -30,7 +30,7 @@
   id: 5
   repo_id: 1
   type: 3
-  config: "{}"
+  config: "{\"IgnoreWhitespaceConflicts\":false,\"AllowMerge\":true,\"AllowRebase\":true,\"AllowSquash\":true}"
   created_unix: 946684810
 
 -
@@ -51,7 +51,7 @@
   id: 8
   repo_id: 3
   type: 3
-  config: "{}"
+  config: "{\"IgnoreWhitespaceConflicts\":true,\"AllowMerge\":true,\"AllowRebase\":false,\"AllowSquash\":false}"
   created_unix: 946684810
 
 -
diff --git a/models/migrations/migrations.go b/models/migrations/migrations.go
index cbd09afabf..90f286056f 100644
--- a/models/migrations/migrations.go
+++ b/models/migrations/migrations.go
@@ -160,6 +160,8 @@ var migrations = []Migration{
 	NewMigration("add lfs lock table", addLFSLock),
 	// v53 -> v54
 	NewMigration("add reactions", addReactions),
+	// v54 -> v55
+	NewMigration("add pull request options", addPullRequestOptions),
 }
 
 // Migrate database to current version
diff --git a/models/migrations/v54.go b/models/migrations/v54.go
new file mode 100644
index 0000000000..96c26739c6
--- /dev/null
+++ b/models/migrations/v54.go
@@ -0,0 +1,57 @@
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"fmt"
+
+	"code.gitea.io/gitea/modules/util"
+
+	"github.com/go-xorm/xorm"
+)
+
+func addPullRequestOptions(x *xorm.Engine) error {
+	// RepoUnit describes all units of a repository
+	type RepoUnit struct {
+		ID          int64
+		RepoID      int64                  `xorm:"INDEX(s)"`
+		Type        int                    `xorm:"INDEX(s)"`
+		Config      map[string]interface{} `xorm:"JSON"`
+		CreatedUnix util.TimeStamp         `xorm:"INDEX CREATED"`
+	}
+
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	//Updating existing issue units
+	units := make([]*RepoUnit, 0, 100)
+	if err := sess.Where("`type` = ?", V16UnitTypePRs).Find(&units); err != nil {
+		return fmt.Errorf("Query repo units: %v", err)
+	}
+	for _, unit := range units {
+		if unit.Config == nil {
+			unit.Config = make(map[string]interface{})
+		}
+		if _, ok := unit.Config["IgnoreWhitespaceConflicts"]; !ok {
+			unit.Config["IgnoreWhitespaceConflicts"] = false
+		}
+		if _, ok := unit.Config["AllowMerge"]; !ok {
+			unit.Config["AllowMerge"] = true
+		}
+		if _, ok := unit.Config["AllowRebase"]; !ok {
+			unit.Config["AllowRebase"] = true
+		}
+		if _, ok := unit.Config["AllowSquash"]; !ok {
+			unit.Config["AllowSquash"] = true
+		}
+		if _, err := sess.ID(unit.ID).Cols("config").Update(unit); err != nil {
+			return err
+		}
+	}
+	return sess.Commit()
+}
diff --git a/models/pull.go b/models/pull.go
index 47fc1dfb61..c9357e9130 100644
--- a/models/pull.go
+++ b/models/pull.go
@@ -16,6 +16,7 @@ import (
 
 	"code.gitea.io/git"
 	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/cache"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/process"
 	"code.gitea.io/gitea/modules/setting"
@@ -109,6 +110,28 @@ func (pr *PullRequest) loadIssue(e Engine) (err error) {
 	return err
 }
 
+// GetDefaultMergeMessage returns default message used when merging pull request
+func (pr *PullRequest) GetDefaultMergeMessage() string {
+	if pr.HeadRepo == nil {
+		var err error
+		pr.HeadRepo, err = GetRepositoryByID(pr.HeadRepoID)
+		if err != nil {
+			log.Error(4, "GetRepositoryById[%d]: %v", pr.HeadRepoID, err)
+			return ""
+		}
+	}
+	return fmt.Sprintf("Merge branch '%s' of %s/%s into %s", pr.HeadBranch, pr.HeadUserName, pr.HeadRepo.Name, pr.BaseBranch)
+}
+
+// GetDefaultSquashMessage returns default message used when squash and merging pull request
+func (pr *PullRequest) GetDefaultSquashMessage() string {
+	if err := pr.LoadIssue(); err != nil {
+		log.Error(4, "LoadIssue: %v", err)
+		return ""
+	}
+	return fmt.Sprintf("%s (#%d)", pr.Issue.Title, pr.Issue.Index)
+}
+
 // APIFormat assumes following fields have been assigned with valid values:
 // Required - Issue
 // Optional - Merger
@@ -232,15 +255,38 @@ func (pr *PullRequest) CanAutoMerge() bool {
 	return pr.Status == PullRequestStatusMergeable
 }
 
+// MergeStyle represents the approach to merge commits into base branch.
+type MergeStyle string
+
+const (
+	// MergeStyleMerge create merge commit
+	MergeStyleMerge MergeStyle = "merge"
+	// MergeStyleRebase rebase before merging
+	MergeStyleRebase MergeStyle = "rebase"
+	// MergeStyleSquash squash commits into single commit before merging
+	MergeStyleSquash MergeStyle = "squash"
+)
+
 // Merge merges pull request to base repository.
 // FIXME: add repoWorkingPull make sure two merges does not happen at same time.
-func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository) (err error) {
+func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository, mergeStyle MergeStyle, message string) (err error) {
 	if err = pr.GetHeadRepo(); err != nil {
 		return fmt.Errorf("GetHeadRepo: %v", err)
 	} else if err = pr.GetBaseRepo(); err != nil {
 		return fmt.Errorf("GetBaseRepo: %v", err)
 	}
 
+	prUnit, err := pr.BaseRepo.GetUnit(UnitTypePullRequests)
+	if err != nil {
+		return err
+	}
+	prConfig := prUnit.PullRequestsConfig()
+
+	// Check if merge style is correct and allowed
+	if !prConfig.IsMergeStyleAllowed(mergeStyle) {
+		return ErrInvalidMergeStyle{pr.BaseRepo.ID, mergeStyle}
+	}
+
 	defer func() {
 		go HookQueue.Add(pr.BaseRepo.ID)
 		go AddTestPullRequestTask(doer, pr.BaseRepo.ID, pr.BaseBranch, false)
@@ -289,18 +335,62 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository) (err error
 		return fmt.Errorf("git fetch [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
 	}
 
-	if _, stderr, err = process.GetManager().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 {
-		return fmt.Errorf("git merge --no-ff --no-commit [%s]: %v - %s", tmpBasePath, err, stderr)
-	}
+	switch mergeStyle {
+	case MergeStyleMerge:
+		if _, stderr, err = process.GetManager().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 {
+			return fmt.Errorf("git merge --no-ff --no-commit [%s]: %v - %s", tmpBasePath, err, stderr)
+		}
 
-	sig := doer.NewGitSig()
-	if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
-		fmt.Sprintf("PullRequest.Merge (git merge): %s", tmpBasePath),
-		"git", "commit", fmt.Sprintf("--author='%s <%s>'", sig.Name, sig.Email),
-		"-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)
+		sig := doer.NewGitSig()
+		if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+			fmt.Sprintf("PullRequest.Merge (git merge): %s", tmpBasePath),
+			"git", "commit", fmt.Sprintf("--author='%s <%s>'", sig.Name, sig.Email),
+			"-m", message); err != nil {
+			return fmt.Errorf("git commit [%s]: %v - %s", tmpBasePath, err, stderr)
+		}
+	case MergeStyleRebase:
+		// Checkout head branch
+		if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+			fmt.Sprintf("PullRequest.Merge (git checkout): %s", tmpBasePath),
+			"git", "checkout", "-b", "head_repo_"+pr.HeadBranch, "head_repo/"+pr.HeadBranch); err != nil {
+			return fmt.Errorf("git checkout: %s", stderr)
+		}
+		// Rebase before merging
+		if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+			fmt.Sprintf("PullRequest.Merge (git rebase): %s", tmpBasePath),
+			"git", "rebase", "-q", pr.BaseBranch); err != nil {
+			return fmt.Errorf("git rebase [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
+		}
+		// Checkout base branch again
+		if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+			fmt.Sprintf("PullRequest.Merge (git checkout): %s", tmpBasePath),
+			"git", "checkout", pr.BaseBranch); err != nil {
+			return fmt.Errorf("git checkout: %s", stderr)
+		}
+		// Merge fast forward
+		if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+			fmt.Sprintf("PullRequest.Merge (git rebase): %s", tmpBasePath),
+			"git", "merge", "--ff-only", "-q", "head_repo_"+pr.HeadBranch); err != nil {
+			return fmt.Errorf("git merge --ff-only [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
+		}
+	case MergeStyleSquash:
+		// Merge with squash
+		if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+			fmt.Sprintf("PullRequest.Merge (git squash): %s", tmpBasePath),
+			"git", "merge", "-q", "--squash", "head_repo/"+pr.HeadBranch); err != nil {
+			return fmt.Errorf("git merge --squash [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
+		}
+		sig := pr.Issue.Poster.NewGitSig()
+		if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+			fmt.Sprintf("PullRequest.Merge (git squash): %s", tmpBasePath),
+			"git", "commit", fmt.Sprintf("--author='%s <%s>'", sig.Name, sig.Email),
+			"-m", message); err != nil {
+			return fmt.Errorf("git commit [%s]: %v - %s", tmpBasePath, err, stderr)
+		}
+	default:
+		return ErrInvalidMergeStyle{pr.BaseRepo.ID, mergeStyle}
 	}
 
 	// Push back to upstream.
@@ -327,6 +417,9 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository) (err error
 		log.Error(4, "MergePullRequestAction [%d]: %v", pr.ID, err)
 	}
 
+	// Reset cached commit count
+	cache.Remove(pr.Issue.Repo.GetCommitsCountCacheKey(pr.BaseBranch, true))
+
 	// Reload pull request information.
 	if err = pr.LoadAttributes(); err != nil {
 		log.Error(4, "LoadAttributes: %v", err)
@@ -349,7 +442,6 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository) (err error
 		return nil
 	}
 
-	// TODO: when squash commits, no need to append merge commit.
 	// It is possible that head branch is not fully sync with base branch for merge commits,
 	// so we need to get latest head commit and append merge commit manually
 	// to avoid strange diff commits produced.
@@ -358,12 +450,14 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository) (err error
 		log.Error(4, "GetBranchCommit: %v", err)
 		return nil
 	}
-	l.PushFront(mergeCommit)
+	if mergeStyle == MergeStyleMerge {
+		l.PushFront(mergeCommit)
+	}
 
 	p := &api.PushPayload{
 		Ref:        git.BranchPrefix + pr.BaseBranch,
 		Before:     pr.MergeBase,
-		After:      pr.MergedCommitID,
+		After:      mergeCommit.ID.String(),
 		CompareURL: setting.AppURL + pr.BaseRepo.ComposeCompareURL(pr.MergeBase, pr.MergedCommitID),
 		Commits:    ListToPushCommits(l).ToAPIPayloadCommits(pr.BaseRepo.HTMLURL()),
 		Repo:       pr.BaseRepo.APIFormat(AccessModeNone),
@@ -563,9 +657,21 @@ func (pr *PullRequest) testPatch() (err error) {
 		return fmt.Errorf("git read-tree --index-output=%s %s: %v - %s", indexTmpPath, pr.BaseBranch, err, stderr)
 	}
 
+	prUnit, err := pr.BaseRepo.GetUnit(UnitTypePullRequests)
+	if err != nil {
+		return err
+	}
+	prConfig := prUnit.PullRequestsConfig()
+
+	args := []string{"apply", "--check", "--cached"}
+	if prConfig.IgnoreWhitespaceConflicts {
+		args = append(args, "--ignore-whitespace")
+	}
+	args = append(args, patchPath)
+
 	_, stderr, err = process.GetManager().ExecDirEnv(-1, "", fmt.Sprintf("testPatch (git apply --check): %d", pr.BaseRepo.ID),
 		[]string{"GIT_INDEX_FILE=" + indexTmpPath, "GIT_DIR=" + pr.BaseRepo.RepoPath()},
-		"git", "apply", "--check", "--cached", patchPath)
+		"git", args...)
 	if err != nil {
 		for i := range patchConflicts {
 			if strings.Contains(stderr, patchConflicts[i]) {
diff --git a/models/repo.go b/models/repo.go
index 29fd39ca99..a9e116d6bd 100644
--- a/models/repo.go
+++ b/models/repo.go
@@ -427,6 +427,11 @@ func (repo *Repository) MustGetUnit(tp UnitType) *RepoUnit {
 			Type:   tp,
 			Config: new(ExternalTrackerConfig),
 		}
+	} else if tp == UnitTypePullRequests {
+		return &RepoUnit{
+			Type:   tp,
+			Config: new(PullRequestsConfig),
+		}
 	}
 	return &RepoUnit{
 		Type:   tp,
diff --git a/models/repo_unit.go b/models/repo_unit.go
index 5100ca1ce2..49b62ec9cd 100644
--- a/models/repo_unit.go
+++ b/models/repo_unit.go
@@ -85,18 +85,44 @@ func (cfg *IssuesConfig) ToDB() ([]byte, error) {
 	return json.Marshal(cfg)
 }
 
+// PullRequestsConfig describes pull requests config
+type PullRequestsConfig struct {
+	IgnoreWhitespaceConflicts bool
+	AllowMerge                bool
+	AllowRebase               bool
+	AllowSquash               bool
+}
+
+// FromDB fills up a PullRequestsConfig from serialized format.
+func (cfg *PullRequestsConfig) FromDB(bs []byte) error {
+	return json.Unmarshal(bs, &cfg)
+}
+
+// ToDB exports a PullRequestsConfig to a serialized format.
+func (cfg *PullRequestsConfig) ToDB() ([]byte, error) {
+	return json.Marshal(cfg)
+}
+
+// IsMergeStyleAllowed returns if merge style is allowed
+func (cfg *PullRequestsConfig) IsMergeStyleAllowed(mergeStyle MergeStyle) bool {
+	return mergeStyle == MergeStyleMerge && cfg.AllowMerge ||
+		mergeStyle == MergeStyleRebase && cfg.AllowRebase ||
+		mergeStyle == MergeStyleSquash && cfg.AllowSquash
+}
+
 // BeforeSet is invoked from XORM before setting the value of a field of this object.
 func (r *RepoUnit) BeforeSet(colName string, val xorm.Cell) {
 	switch colName {
 	case "type":
 		switch UnitType(Cell2Int64(val)) {
-		case UnitTypeCode, UnitTypePullRequests, UnitTypeReleases,
-			UnitTypeWiki:
+		case UnitTypeCode, UnitTypeReleases, UnitTypeWiki:
 			r.Config = new(UnitConfig)
 		case UnitTypeExternalWiki:
 			r.Config = new(ExternalWikiConfig)
 		case UnitTypeExternalTracker:
 			r.Config = new(ExternalTrackerConfig)
+		case UnitTypePullRequests:
+			r.Config = new(PullRequestsConfig)
 		case UnitTypeIssues:
 			r.Config = new(IssuesConfig)
 		default:
@@ -116,8 +142,8 @@ func (r *RepoUnit) CodeConfig() *UnitConfig {
 }
 
 // PullRequestsConfig returns config for UnitTypePullRequests
-func (r *RepoUnit) PullRequestsConfig() *UnitConfig {
-	return r.Config.(*UnitConfig)
+func (r *RepoUnit) PullRequestsConfig() *PullRequestsConfig {
+	return r.Config.(*PullRequestsConfig)
 }
 
 // ReleasesConfig returns config for UnitTypeReleases
diff --git a/modules/auth/repo_form.go b/modules/auth/repo_form.go
index 221f7221a4..634274c4e8 100644
--- a/modules/auth/repo_form.go
+++ b/modules/auth/repo_form.go
@@ -107,6 +107,10 @@ type RepoSettingForm struct {
 	TrackerURLFormat                 string
 	TrackerIssueStyle                string
 	EnablePulls                      bool
+	PullsIgnoreWhitespace            bool
+	PullsAllowMerge                  bool
+	PullsAllowRebase                 bool
+	PullsAllowSquash                 bool
 	EnableTimetracker                bool
 	AllowOnlyContributorsToTrackTime bool
 }
@@ -326,6 +330,25 @@ func (f *InitializeLabelsForm) Validate(ctx *macaron.Context, errs binding.Error
 	return validate(errs, ctx.Data, f, ctx.Locale)
 }
 
+// __________      .__  .__    __________                                     __
+// \______   \__ __|  | |  |   \______   \ ____  ________ __   ____   _______/  |_
+//  |     ___/  |  \  | |  |    |       _// __ \/ ____/  |  \_/ __ \ /  ___/\   __\
+//  |    |   |  |  /  |_|  |__  |    |   \  ___< <_|  |  |  /\  ___/ \___ \  |  |
+//  |____|   |____/|____/____/  |____|_  /\___  >__   |____/  \___  >____  > |__|
+//                                     \/     \/   |__|           \/     \/
+
+// MergePullRequestForm form for merging Pull Request
+type MergePullRequestForm struct {
+	Do                string `binding:"Required;In(merge,rebase,squash)"`
+	MergeTitleField   string
+	MergeMessageField string
+}
+
+// Validate validates the fields
+func (f *MergePullRequestForm) Validate(ctx *macaron.Context, errs binding.Errors) binding.Errors {
+	return validate(errs, ctx.Data, f, ctx.Locale)
+}
+
 // __________       .__
 // \______   \ ____ |  |   ____ _____    ______ ____
 //  |       _// __ \|  | _/ __ \\__  \  /  ___// __ \
diff --git a/options/locale/locale_en-US.ini b/options/locale/locale_en-US.ini
index 4e1cf42ddb..4344a65774 100644
--- a/options/locale/locale_en-US.ini
+++ b/options/locale/locale_en-US.ini
@@ -755,7 +755,12 @@ pulls.is_checking = "The conflict checking is still in progress; please refresh
 pulls.can_auto_merge_desc = This pull request can be merged automatically.
 pulls.cannot_auto_merge_desc = This pull request cannot be merged automatically because there are conflicts.
 pulls.cannot_auto_merge_helper = Please merge manually in order to resolve the conflicts.
+pulls.no_merge_desc = This pull request can not be merged as no merge options are enabled.
+pulls.no_merge_helper = To merge this pull request enable at least one merge option in repository settings or merge pull request manually.
 pulls.merge_pull_request = Merge Pull Request
+pulls.rebase_merge_pull_request = Rebase and Merge
+pulls.squash_merge_pull_request = Squash and Merge
+pulls.invalid_merge_option = You can not use this merge option for this pull request
 pulls.open_unmerged_pull_exists = `You cannot perform reopen operation because there is already an open pull request (#%d) from same repository with same merge information and is waiting for merging.`
 
 milestones.new = New Milestone
@@ -894,6 +899,10 @@ settings.tracker_url_format_desc = You can use placeholder <code>{user} {repo} {
 settings.enable_timetracker = Enable time tracker
 settings.allow_only_contributors_to_track_time = Allow only contributors to track time
 settings.pulls_desc = Enable pull requests to accept public contributions
+settings.pulls.ignore_whitespace = Ignore changes in whitespace when checking conflicts
+settings.pulls.allow_merge_commits = Allow merge commits
+settings.pulls.allow_rebase_merge = Allow rebase to merge commits
+settings.pulls.allow_squash_commits = Allow to squash commits before merging
 settings.danger_zone = Danger Zone
 settings.new_owner_has_same_repo = The new owner already has a repository with same name. Please choose another name.
 settings.convert = Convert To Regular Repository
diff --git a/public/js/index.js b/public/js/index.js
index 9104bf6400..160be5b684 100644
--- a/public/js/index.js
+++ b/public/js/index.js
@@ -649,6 +649,28 @@ function initRepository() {
             $('#status').val($statusButton.data('status-val'));
             $('#comment-form').submit();
         });
+
+        // Pull Request merge button
+        var $mergeButton = $('.merge-button > button');
+        $mergeButton.on('click', function(e) {
+            e.preventDefault();
+            $('.' + $(this).data('do') + '-fields').show();
+            $(this).parent().hide();
+        });
+        $('.merge-button > .dropdown').dropdown({
+            onChange: function (text, value, $choice) {
+                if ($choice.data('do')) {
+                    $mergeButton.find('.button-text').text($choice.text());
+                    $mergeButton.data('do', $choice.data('do'));
+                }
+            }
+        });
+        $('.merge-cancel').on('click', function(e) {
+            e.preventDefault();
+            $(this).closest('.form').hide();
+            $mergeButton.parent().show();
+        });
+
         initReactionSelector();
     }
 
diff --git a/routers/api/v1/api.go b/routers/api/v1/api.go
index 588a763616..8a300f9958 100644
--- a/routers/api/v1/api.go
+++ b/routers/api/v1/api.go
@@ -477,7 +477,7 @@ func RegisterRoutes(m *macaron.Macaron) {
 						m.Combo("").Get(repo.GetPullRequest).
 							Patch(reqToken(), reqRepoWriter(), bind(api.EditPullRequestOption{}), repo.EditPullRequest)
 						m.Combo("/merge").Get(repo.IsPullRequestMerged).
-							Post(reqToken(), reqRepoWriter(), repo.MergePullRequest)
+							Post(reqToken(), reqRepoWriter(), bind(auth.MergePullRequestForm{}), repo.MergePullRequest)
 					})
 
 				}, mustAllowPulls, context.ReferencesGitRepo())
diff --git a/routers/api/v1/repo/pull.go b/routers/api/v1/repo/pull.go
index 50b864e323..7e011219be 100644
--- a/routers/api/v1/repo/pull.go
+++ b/routers/api/v1/repo/pull.go
@@ -10,6 +10,7 @@ import (
 
 	"code.gitea.io/git"
 	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/auth"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/log"
 
@@ -434,7 +435,7 @@ func IsPullRequestMerged(ctx *context.APIContext) {
 }
 
 // MergePullRequest merges a PR given an index
-func MergePullRequest(ctx *context.APIContext) {
+func MergePullRequest(ctx *context.APIContext, form auth.MergePullRequestForm) {
 	// swagger:operation POST /repos/{owner}/{repo}/pulls/{index}/merge repository repoMergePullRequest
 	// ---
 	// summary: Merge a pull request
@@ -497,7 +498,30 @@ func MergePullRequest(ctx *context.APIContext) {
 		return
 	}
 
-	if err := pr.Merge(ctx.User, ctx.Repo.GitRepo); err != nil {
+	if len(form.Do) == 0 {
+		form.Do = string(models.MergeStyleMerge)
+	}
+
+	message := strings.TrimSpace(form.MergeTitleField)
+	if len(message) == 0 {
+		if models.MergeStyle(form.Do) == models.MergeStyleMerge {
+			message = pr.GetDefaultMergeMessage()
+		}
+		if models.MergeStyle(form.Do) == models.MergeStyleSquash {
+			message = pr.GetDefaultSquashMessage()
+		}
+	}
+
+	form.MergeMessageField = strings.TrimSpace(form.MergeMessageField)
+	if len(form.MergeMessageField) > 0 {
+		message += "\n\n" + form.MergeMessageField
+	}
+
+	if err := pr.Merge(ctx.User, ctx.Repo.GitRepo, models.MergeStyle(form.Do), message); err != nil {
+		if models.IsErrInvalidMergeStyle(err) {
+			ctx.Status(405)
+			return
+		}
 		ctx.Error(500, "Merge", err)
 		return
 	}
diff --git a/routers/repo/issue.go b/routers/repo/issue.go
index 530586a143..e4aecf152e 100644
--- a/routers/repo/issue.go
+++ b/routers/repo/issue.go
@@ -727,6 +727,26 @@ func ViewIssue(ctx *context.Context) {
 			}
 		}
 
+		prUnit, err := repo.GetUnit(models.UnitTypePullRequests)
+		if err != nil {
+			ctx.Handle(500, "GetUnit", err)
+			return
+		}
+		prConfig := prUnit.PullRequestsConfig()
+
+		// Check correct values and select default
+		if ms, ok := ctx.Data["MergeStyle"].(models.MergeStyle); !ok ||
+			!prConfig.IsMergeStyleAllowed(ms) {
+			if prConfig.AllowMerge {
+				ctx.Data["MergeStyle"] = models.MergeStyleMerge
+			} else if prConfig.AllowRebase {
+				ctx.Data["MergeStyle"] = models.MergeStyleRebase
+			} else if prConfig.AllowSquash {
+				ctx.Data["MergeStyle"] = models.MergeStyleSquash
+			} else {
+				ctx.Data["MergeStyle"] = ""
+			}
+		}
 		ctx.Data["IsPullBranchDeletable"] = canDelete && pull.HeadRepo != nil && git.IsBranchExist(pull.HeadRepo.RepoPath(), pull.HeadBranch)
 	}
 
diff --git a/routers/repo/pull.go b/routers/repo/pull.go
index 6162df9651..9de8268957 100644
--- a/routers/repo/pull.go
+++ b/routers/repo/pull.go
@@ -495,7 +495,7 @@ func ViewPullFiles(ctx *context.Context) {
 }
 
 // MergePullRequest response for merging pull request
-func MergePullRequest(ctx *context.Context) {
+func MergePullRequest(ctx *context.Context, form auth.MergePullRequestForm) {
 	issue := checkPullInfo(ctx)
 	if ctx.Written() {
 		return
@@ -514,15 +514,42 @@ func MergePullRequest(ctx *context.Context) {
 		}
 		return
 	}
+	pr.Issue = issue
 
 	if !pr.CanAutoMerge() || pr.HasMerged {
 		ctx.Handle(404, "MergePullRequest", nil)
 		return
 	}
 
+	if ctx.HasError() {
+		ctx.Flash.Error(ctx.Data["ErrorMsg"].(string))
+		ctx.Redirect(ctx.Repo.RepoLink + "/pulls/" + com.ToStr(pr.Index))
+		return
+	}
+
+	message := strings.TrimSpace(form.MergeTitleField)
+	if len(message) == 0 {
+		if models.MergeStyle(form.Do) == models.MergeStyleMerge {
+			message = pr.GetDefaultMergeMessage()
+		}
+		if models.MergeStyle(form.Do) == models.MergeStyleSquash {
+			message = pr.GetDefaultSquashMessage()
+		}
+	}
+
+	form.MergeMessageField = strings.TrimSpace(form.MergeMessageField)
+	if len(form.MergeMessageField) > 0 {
+		message += "\n\n" + form.MergeMessageField
+	}
+
 	pr.Issue = issue
 	pr.Issue.Repo = ctx.Repo.Repository
-	if err = pr.Merge(ctx.User, ctx.Repo.GitRepo); err != nil {
+	if err = pr.Merge(ctx.User, ctx.Repo.GitRepo, models.MergeStyle(form.Do), message); err != nil {
+		if models.IsErrInvalidMergeStyle(err) {
+			ctx.Flash.Error(ctx.Tr("repo.pulls.invalid_merge_option"))
+			ctx.Redirect(ctx.Repo.RepoLink + "/pulls/" + com.ToStr(pr.Index))
+			return
+		}
 		ctx.Handle(500, "Merge", err)
 		return
 	}
diff --git a/routers/repo/setting.go b/routers/repo/setting.go
index 8cb551707c..342451b8ad 100644
--- a/routers/repo/setting.go
+++ b/routers/repo/setting.go
@@ -211,7 +211,12 @@ func SettingsPost(ctx *context.Context, form auth.RepoSettingForm) {
 			units = append(units, models.RepoUnit{
 				RepoID: repo.ID,
 				Type:   models.UnitTypePullRequests,
-				Config: new(models.UnitConfig),
+				Config: &models.PullRequestsConfig{
+					IgnoreWhitespaceConflicts: form.PullsIgnoreWhitespace,
+					AllowMerge:                form.PullsAllowMerge,
+					AllowRebase:               form.PullsAllowRebase,
+					AllowSquash:               form.PullsAllowSquash,
+				},
 			})
 		}
 
diff --git a/routers/routes/routes.go b/routers/routes/routes.go
index 4293cca6c9..3e00f55ebf 100644
--- a/routers/routes/routes.go
+++ b/routers/routes/routes.go
@@ -627,7 +627,7 @@ func RegisterRoutes(m *macaron.Macaron) {
 			m.Get(".diff", repo.DownloadPullDiff)
 			m.Get("/commits", context.RepoRef(), repo.ViewPullCommits)
 			m.Get("/files", context.RepoRef(), repo.SetEditorconfigIfExists, repo.SetDiffViewStyle, repo.ViewPullFiles)
-			m.Post("/merge", reqRepoWriter, repo.MergePullRequest)
+			m.Post("/merge", reqRepoWriter, bindIgnErr(auth.MergePullRequestForm{}), repo.MergePullRequest)
 			m.Post("/cleanup", context.RepoRef(), repo.CleanUpPullRequest)
 		}, repo.MustAllowPulls)
 
diff --git a/templates/repo/issue/view_content/pull.tmpl b/templates/repo/issue/view_content/pull.tmpl
index 87de9c508b..9bd51b7c3e 100644
--- a/templates/repo/issue/view_content/pull.tmpl
+++ b/templates/repo/issue/view_content/pull.tmpl
@@ -38,15 +38,100 @@
 					{{$.i18n.Tr "repo.pulls.can_auto_merge_desc"}}
 				</div>
 				{{if .IsRepositoryWriter}}
-					<div class="ui divider"></div>
-					<div>
-						<form class="ui form" action="{{.Link}}/merge" method="post">
-							{{.CsrfTokenHtml}}
-							<button class="ui green button">
-								<span class="octicon octicon-git-merge"></span> {{$.i18n.Tr "repo.pulls.merge_pull_request"}}
+					{{$prUnit := .Repository.MustGetUnit $.UnitTypePullRequests}}
+					{{if or $prUnit.PullRequestsConfig.AllowMerge $prUnit.PullRequestsConfig.AllowRebase $prUnit.PullRequestsConfig.AllowSquash}}
+						<div class="ui divider"></div>
+						{{if $prUnit.PullRequestsConfig.AllowMerge}}
+						<div class="ui form merge-fields" style="display: none">
+							<form action="{{.Link}}/merge" method="post">
+								{{.CsrfTokenHtml}}
+								<div class="field">
+									<input type="text" name="merge_title_field" value="{{.Issue.PullRequest.GetDefaultMergeMessage}}">
+								</div>
+								<div class="field">
+									<textarea name="merge_message_field" rows="5" placeholder="{{$.i18n.Tr "repo.editor.commit_message_desc"}}"></textarea>
+								</div>
+								<button class="ui green button" type="submit" name="do" value="merge">
+									{{$.i18n.Tr "repo.pulls.merge_pull_request"}}
+								</button>
+								<button class="ui button merge-cancel">
+									{{$.i18n.Tr "cancel"}}
+								</button>
+							</form>
+						</div>
+						{{end}}
+						{{if $prUnit.PullRequestsConfig.AllowRebase}}
+						<div class="ui form rebase-fields" style="display: none">
+							<form action="{{.Link}}/merge" method="post">
+								{{.CsrfTokenHtml}}
+								<button class="ui green button" type="submit" name="do" value="rebase">
+									{{$.i18n.Tr "repo.pulls.rebase_merge_pull_request"}}
+								</button>
+								<button class="ui button merge-cancel">
+									{{$.i18n.Tr "cancel"}}
+								</button>
+							</form>
+						</div>
+						{{end}}
+						{{if $prUnit.PullRequestsConfig.AllowSquash}}
+						<div class="ui form squash-fields" style="display: none">
+							<form action="{{.Link}}/merge" method="post">
+								{{.CsrfTokenHtml}}
+								<div class="field">
+									<input type="text" name="merge_title_field" value="{{.Issue.PullRequest.GetDefaultSquashMessage}}">
+								</div>
+								<div class="field">
+									<textarea name="merge_message_field" rows="5" placeholder="{{$.i18n.Tr "repo.editor.commit_message_desc"}}"></textarea>
+								</div>
+								<button class="ui green button" type="submit" name="do" value="squash">
+									{{$.i18n.Tr "repo.pulls.squash_merge_pull_request"}}
+								</button>
+								<button class="ui button merge-cancel">
+									{{$.i18n.Tr "cancel"}}
+								</button>
+							</form>
+						</div>
+						{{end}}
+						<div class="ui green buttons merge-button">
+							<button class="ui button" data-do="{{.MergeStyle}}">
+								<span class="octicon octicon-git-merge"></span>
+								<span class="button-text">
+								{{if eq .MergeStyle "merge"}}
+									{{$.i18n.Tr "repo.pulls.merge_pull_request"}}
+								{{end}}
+								{{if eq .MergeStyle "rebase"}}
+									{{$.i18n.Tr "repo.pulls.rebase_merge_pull_request"}}
+								{{end}}
+								{{if eq .MergeStyle "squash"}}
+									{{$.i18n.Tr "repo.pulls.squash_merge_pull_request"}}
+								{{end}}
+								</span>
 							</button>
-						</form>
-					</div>
+							<div class="ui dropdown icon button">
+								<i class="dropdown icon"></i>
+								<div class="menu">
+									{{if $prUnit.PullRequestsConfig.AllowMerge}}
+									<div class="item{{if eq .MergeStyle "merge"}} active selected{{end}}" data-do="merge">{{$.i18n.Tr "repo.pulls.merge_pull_request"}}</div>
+									{{end}}
+									{{if $prUnit.PullRequestsConfig.AllowRebase}}
+									<div class="item{{if eq .MergeStyle "rebase"}} active selected{{end}}" data-do="rebase">{{$.i18n.Tr "repo.pulls.rebase_merge_pull_request"}}</div>
+									{{end}}
+									{{if $prUnit.PullRequestsConfig.AllowSquash}}
+									<div class="item{{if eq .MergeStyle "squash"}} active selected{{end}}" data-do="squash">{{$.i18n.Tr "repo.pulls.squash_merge_pull_request"}}</div>
+									{{end}}
+								</div>
+							</div>
+						</div>
+					{{else}}
+						<div class="item text red">
+							<span class="octicon octicon-x"></span>
+							{{$.i18n.Tr "repo.pulls.no_merge_desc"}}
+						</div>
+						<div class="item text grey">
+							<span class="octicon octicon-info"></span>
+							{{$.i18n.Tr "repo.pulls.no_merge_helper"}}
+						</div>
+					{{end}}
 				{{end}}
 			{{else}}
 				<div class="item text red">
diff --git a/templates/repo/settings/options.tmpl b/templates/repo/settings/options.tmpl
index 41a91ea26e..3bc1a209f0 100644
--- a/templates/repo/settings/options.tmpl
+++ b/templates/repo/settings/options.tmpl
@@ -192,14 +192,41 @@
 
 				{{if .Repository.CanEnablePulls}}
 					<div class="ui divider"></div>
-
+					{{$pullRequestEnabled := .Repository.UnitEnabled $.UnitTypePullRequests}}
+					{{$prUnit := .Repository.MustGetUnit $.UnitTypePullRequests}}
 					<div class="inline field">
 						<label>{{.i18n.Tr "repo.pulls"}}</label>
 						<div class="ui checkbox">
-							<input name="enable_pulls" type="checkbox" {{if .Repository.UnitEnabled $.UnitTypePullRequests}}checked{{end}}>
+							<input class="enable-system" name="enable_pulls" type="checkbox" data-target="#pull_box" {{if $pullRequestEnabled}}checked{{end}}>
 							<label>{{.i18n.Tr "repo.settings.pulls_desc"}}</label>
 						</div>
 					</div>
+					<div class="field{{if not $pullRequestEnabled}} disabled{{end}}" id="pull_box">
+						<div class="field">
+							<div class="ui checkbox">
+								<input name="pulls_ignore_whitespace" type="checkbox" {{if and $pullRequestEnabled ($prUnit.PullRequestsConfig.IgnoreWhitespaceConflicts)}}checked{{end}}>
+								<label>{{.i18n.Tr "repo.settings.pulls.ignore_whitespace"}}</label>
+							</div>
+						</div>
+						<div class="field">
+							<div class="ui checkbox">
+								<input name="pulls_allow_merge" type="checkbox" {{if or (not $pullRequestEnabled) ($prUnit.PullRequestsConfig.AllowMerge)}}checked{{end}}>
+								<label>{{.i18n.Tr "repo.settings.pulls.allow_merge_commits"}}</label>
+							</div>
+						</div>
+						<div class="field">
+							<div class="ui checkbox">
+								<input name="pulls_allow_rebase" type="checkbox" {{if or (not $pullRequestEnabled) ($prUnit.PullRequestsConfig.AllowRebase)}}checked{{end}}>
+								<label>{{.i18n.Tr "repo.settings.pulls.allow_rebase_merge"}}</label>
+							</div>
+						</div>
+						<div class="field">
+							<div class="ui checkbox">
+								<input name="pulls_allow_squash" type="checkbox" {{if or (not $pullRequestEnabled) ($prUnit.PullRequestsConfig.AllowSquash)}}checked{{end}}>
+								<label>{{.i18n.Tr "repo.settings.pulls.allow_squash_commits"}}</label>
+							</div>
+						</div>
+					</div>
 				{{end}}
 
 				<div class="ui divider"></div>