Remove SavePatch and generate patches on the fly (#9302)

* Save patches to temporary files

* Remove SavePatch and generate patches on the fly

* Use ioutil.TempDir

* fixup! Use ioutil.TempDir

* fixup! fixup! Use ioutil.TempDir

* RemoveAll LocalCopyPath() in initIntergrationTest

* Default to status checking on PR creation

* Remove unnecessary set to StatusChecking

* Protect against unable to load repo

* Handle conflicts

* Restore original conflict setting

* In TestPullRequests update status to StatusChecking before running TestPatch

16 files changed, 430 insertions, 404 deletions

diff --git a/integrations/integration_test.go b/integrations/integration_test.go
index 4177493930..5da9e04c78 100644
--- a/integrations/integration_test.go
+++ b/integrations/integration_test.go
@@ -125,6 +125,7 @@ func initIntegrationTest() {
 
 	setting.SetCustomPathAndConf("", "", "")
 	setting.NewContext()
+	os.RemoveAll(models.LocalCopyPath())
 	setting.CheckLFSVersion()
 	setting.InitDBConfig()
 
@@ -182,7 +183,6 @@ func prepareTestEnv(t testing.TB, skip ...int) func() {
 	deferFn := PrintCurrentTest(t, ourSkip)
 	assert.NoError(t, models.LoadFixtures())
 	assert.NoError(t, os.RemoveAll(setting.RepoRootPath))
-	assert.NoError(t, os.RemoveAll(models.LocalCopyPath()))
 
 	assert.NoError(t, com.CopyDir(path.Join(filepath.Dir(setting.AppPath), "integrations/gitea-repositories-meta"),
 		setting.RepoRootPath))
diff --git a/models/helper_directory.go b/models/helper_directory.go
index 813f0577bc..8119ec91a3 100644
--- a/models/helper_directory.go
+++ b/models/helper_directory.go
@@ -6,15 +6,13 @@ package models
 
 import (
 	"fmt"
+	"io/ioutil"
 	"os"
 	"path"
 	"path/filepath"
-	"time"
 
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
-
-	"github.com/unknwon/com"
 )
 
 // LocalCopyPath returns the local repository temporary copy path.
@@ -27,11 +25,15 @@ func LocalCopyPath() string {
 
 // CreateTemporaryPath creates a temporary path
 func CreateTemporaryPath(prefix string) (string, error) {
-	timeStr := com.ToStr(time.Now().Nanosecond()) // SHOULD USE SOMETHING UNIQUE
-	basePath := path.Join(LocalCopyPath(), prefix+"-"+timeStr+".git")
-	if err := os.MkdirAll(filepath.Dir(basePath), os.ModePerm); err != nil {
-		log.Error("Unable to create temporary directory: %s (%v)", basePath, err)
-		return "", fmt.Errorf("Failed to create dir %s: %v", basePath, err)
+	if err := os.MkdirAll(LocalCopyPath(), os.ModePerm); err != nil {
+		log.Error("Unable to create localcopypath directory: %s (%v)", LocalCopyPath(), err)
+		return "", fmt.Errorf("Failed to create localcopypath directory %s: %v", LocalCopyPath(), err)
+	}
+	basePath, err := ioutil.TempDir(LocalCopyPath(), prefix+".git")
+	if err != nil {
+		log.Error("Unable to create temporary directory: %s-*.git (%v)", prefix, err)
+		return "", fmt.Errorf("Failed to create dir %s-*.git: %v", prefix, err)
+
 	}
 	return basePath, nil
 }
diff --git a/models/issue_xref_test.go b/models/issue_xref_test.go
index c13577e905..d8defd99c6 100644
--- a/models/issue_xref_test.go
+++ b/models/issue_xref_test.go
@@ -142,8 +142,8 @@ func testCreatePR(t *testing.T, repo, doer int64, title, content string) *PullRe
 	r := AssertExistsAndLoadBean(t, &Repository{ID: repo}).(*Repository)
 	d := AssertExistsAndLoadBean(t, &User{ID: doer}).(*User)
 	i := &Issue{RepoID: r.ID, PosterID: d.ID, Poster: d, Title: title, Content: content, IsPull: true}
-	pr := &PullRequest{HeadRepoID: repo, BaseRepoID: repo, HeadBranch: "head", BaseBranch: "base"}
-	assert.NoError(t, NewPullRequest(r, i, nil, nil, pr, nil))
+	pr := &PullRequest{HeadRepoID: repo, BaseRepoID: repo, HeadBranch: "head", BaseBranch: "base", Status: PullRequestStatusMergeable}
+	assert.NoError(t, NewPullRequest(r, i, nil, nil, pr))
 	pr.Issue = i
 	return pr
 }
diff --git a/models/pull.go b/models/pull.go
index 2bd79202f0..33adc3214f 100644
--- a/models/pull.go
+++ b/models/pull.go
@@ -6,22 +6,16 @@
 package models
 
 import (
-	"bufio"
 	"fmt"
 	"os"
 	"path"
-	"path/filepath"
-	"strconv"
 	"strings"
-	"time"
 
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	api "code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/timeutil"
-
-	"github.com/unknwon/com"
 )
 
 // PullRequestType defines pull request type
@@ -481,125 +475,12 @@ func (pr *PullRequest) SetMerged() (err error) {
 	return nil
 }
 
-// patchConflicts is a list of conflict description from Git.
-var patchConflicts = []string{
-	"patch does not apply",
-	"already exists in working directory",
-	"unrecognized input",
-	"error:",
-}
-
-// TestPatch checks if patch can be merged to base repository without conflict.
-func (pr *PullRequest) TestPatch() error {
-	return pr.testPatch(x)
-}
-
-// testPatch checks if patch can be merged to base repository without conflict.
-func (pr *PullRequest) testPatch(e Engine) (err error) {
-	if pr.BaseRepo == nil {
-		pr.BaseRepo, err = getRepositoryByID(e, pr.BaseRepoID)
-		if err != nil {
-			return fmt.Errorf("GetRepositoryByID: %v", err)
-		}
-	}
-
-	patchPath, err := pr.BaseRepo.patchPath(e, pr.Index)
-	if err != nil {
-		return fmt.Errorf("BaseRepo.PatchPath: %v", err)
-	}
-
-	// Fast fail if patch does not exist, this assumes data is corrupted.
-	if !com.IsFile(patchPath) {
-		log.Trace("PullRequest[%d].testPatch: ignored corrupted data", pr.ID)
-		return nil
-	}
-
-	RepoWorkingPool.CheckIn(com.ToStr(pr.BaseRepoID))
-	defer RepoWorkingPool.CheckOut(com.ToStr(pr.BaseRepoID))
-
-	log.Trace("PullRequest[%d].testPatch (patchPath): %s", pr.ID, patchPath)
-
-	pr.Status = PullRequestStatusChecking
-
-	indexTmpPath := filepath.Join(os.TempDir(), "gitea-"+pr.BaseRepo.Name+"-"+strconv.Itoa(time.Now().Nanosecond()))
-	defer os.Remove(indexTmpPath)
-
-	_, err = git.NewCommand("read-tree", pr.BaseBranch).RunInDirWithEnv("", []string{"GIT_DIR=" + pr.BaseRepo.RepoPath(), "GIT_INDEX_FILE=" + indexTmpPath})
-	if err != nil {
-		return fmt.Errorf("git read-tree --index-output=%s %s: %v", indexTmpPath, pr.BaseBranch, err)
-	}
-
-	prUnit, err := pr.BaseRepo.getUnit(e, 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)
-	pr.ConflictedFiles = []string{}
-
-	stderrBuilder := new(strings.Builder)
-	err = git.NewCommand(args...).RunInDirTimeoutEnvPipeline(
-		[]string{"GIT_INDEX_FILE=" + indexTmpPath, "GIT_DIR=" + pr.BaseRepo.RepoPath()},
-		-1,
-		"",
-		nil,
-		stderrBuilder)
-	stderr := stderrBuilder.String()
-
-	if err != nil {
-		for i := range patchConflicts {
-			if strings.Contains(stderr, patchConflicts[i]) {
-				log.Trace("PullRequest[%d].testPatch (apply): has conflict: %s", pr.ID, stderr)
-				const prefix = "error: patch failed:"
-				pr.Status = PullRequestStatusConflict
-				pr.ConflictedFiles = make([]string, 0, 5)
-				scanner := bufio.NewScanner(strings.NewReader(stderr))
-				for scanner.Scan() {
-					line := scanner.Text()
-
-					if strings.HasPrefix(line, prefix) {
-						var found bool
-						var filepath = strings.TrimSpace(strings.Split(line[len(prefix):], ":")[0])
-						for _, f := range pr.ConflictedFiles {
-							if f == filepath {
-								found = true
-								break
-							}
-						}
-						if !found {
-							pr.ConflictedFiles = append(pr.ConflictedFiles, filepath)
-						}
-					}
-					// only list 10 conflicted files
-					if len(pr.ConflictedFiles) >= 10 {
-						break
-					}
-				}
-
-				if len(pr.ConflictedFiles) > 0 {
-					log.Trace("Found %d files conflicted: %v", len(pr.ConflictedFiles), pr.ConflictedFiles)
-				}
-
-				return nil
-			}
-		}
-
-		return fmt.Errorf("git apply --check: %v - %s", err, stderr)
-	}
-	return nil
-}
-
 // NewPullRequest creates new pull request with labels for repository.
-func NewPullRequest(repo *Repository, pull *Issue, labelIDs []int64, uuids []string, pr *PullRequest, patch []byte) (err error) {
+func NewPullRequest(repo *Repository, pull *Issue, labelIDs []int64, uuids []string, pr *PullRequest) (err error) {
 	// Retry several times in case INSERT fails due to duplicate key for (repo_id, index); see #7887
 	i := 0
 	for {
-		if err = newPullRequestAttempt(repo, pull, labelIDs, uuids, pr, patch); err == nil {
+		if err = newPullRequestAttempt(repo, pull, labelIDs, uuids, pr); err == nil {
 			return nil
 		}
 		if !IsErrNewIssueInsert(err) {
@@ -613,7 +494,7 @@ func NewPullRequest(repo *Repository, pull *Issue, labelIDs []int64, uuids []str
 	return fmt.Errorf("NewPullRequest: too many errors attempting to insert the new issue. Last error was: %v", err)
 }
 
-func newPullRequestAttempt(repo *Repository, pull *Issue, labelIDs []int64, uuids []string, pr *PullRequest, patch []byte) (err error) {
+func newPullRequestAttempt(repo *Repository, pull *Issue, labelIDs []int64, uuids []string, pr *PullRequest) (err error) {
 	sess := x.NewSession()
 	defer sess.Close()
 	if err = sess.Begin(); err != nil {
@@ -635,20 +516,6 @@ func newPullRequestAttempt(repo *Repository, pull *Issue, labelIDs []int64, uuid
 
 	pr.Index = pull.Index
 	pr.BaseRepo = repo
-	pr.Status = PullRequestStatusChecking
-	if len(patch) > 0 {
-		if err = repo.savePatch(sess, pr.Index, patch); err != nil {
-			return fmt.Errorf("SavePatch: %v", err)
-		}
-
-		if err = pr.testPatch(sess); err != nil {
-			return fmt.Errorf("testPatch: %v", err)
-		}
-	}
-	// No conflict appears after test means mergeable.
-	if pr.Status == PullRequestStatusChecking {
-		pr.Status = PullRequestStatusMergeable
-	}
 
 	pr.IssueID = pull.ID
 	if _, err = sess.Insert(pr); err != nil {
@@ -764,54 +631,6 @@ func (pr *PullRequest) UpdateCols(cols ...string) error {
 	return err
 }
 
-// UpdatePatch generates and saves a new patch.
-func (pr *PullRequest) UpdatePatch() (err error) {
-	if err = pr.GetHeadRepo(); err != nil {
-		return fmt.Errorf("GetHeadRepo: %v", err)
-	} else if pr.HeadRepo == nil {
-		log.Trace("PullRequest[%d].UpdatePatch: ignored corrupted data", pr.ID)
-		return nil
-	}
-
-	if err = pr.GetBaseRepo(); err != nil {
-		return fmt.Errorf("GetBaseRepo: %v", err)
-	}
-
-	headGitRepo, err := git.OpenRepository(pr.HeadRepo.RepoPath())
-	if err != nil {
-		return fmt.Errorf("OpenRepository: %v", err)
-	}
-	defer headGitRepo.Close()
-
-	// Add a temporary remote.
-	tmpRemote := com.ToStr(time.Now().UnixNano())
-	if err = headGitRepo.AddRemote(tmpRemote, RepoPath(pr.BaseRepo.MustOwner().Name, pr.BaseRepo.Name), true); err != nil {
-		return fmt.Errorf("AddRemote: %v", err)
-	}
-	defer func() {
-		if err := headGitRepo.RemoveRemote(tmpRemote); err != nil {
-			log.Error("UpdatePatch: RemoveRemote: %s", err)
-		}
-	}()
-	pr.MergeBase, _, err = headGitRepo.GetMergeBase(tmpRemote, pr.BaseBranch, pr.HeadBranch)
-	if err != nil {
-		return fmt.Errorf("GetMergeBase: %v", err)
-	} else if err = pr.Update(); err != nil {
-		return fmt.Errorf("Update: %v", err)
-	}
-
-	patch, err := headGitRepo.GetPatch(pr.MergeBase, pr.HeadBranch)
-	if err != nil {
-		return fmt.Errorf("GetPatch: %v", err)
-	}
-
-	if err = pr.BaseRepo.SavePatch(pr.Index, patch); err != nil {
-		return fmt.Errorf("BaseRepo.SavePatch: %v", err)
-	}
-
-	return nil
-}
-
 // PushToBaseRepo pushes commits from branches of head repository to
 // corresponding branches of base repository.
 // FIXME: Only push branches that are actually updates?
diff --git a/models/pull_test.go b/models/pull_test.go
index 4971ff2e52..6f799c1c82 100644
--- a/models/pull_test.go
+++ b/models/pull_test.go
@@ -190,8 +190,6 @@ func TestPullRequest_UpdateCols(t *testing.T) {
 	CheckConsistencyFor(t, pr)
 }
 
-// TODO TestPullRequest_UpdatePatch
-
 // TODO TestPullRequest_PushToBaseRepo
 
 func TestPullRequestList_LoadAttributes(t *testing.T) {
diff --git a/models/repo.go b/models/repo.go
index c904449bbd..09735bd2c2 100644
--- a/models/repo.go
+++ b/models/repo.go
@@ -887,42 +887,6 @@ func (repo *Repository) DescriptionHTML() template.HTML {
 	return template.HTML(markup.Sanitize(string(desc)))
 }
 
-// PatchPath returns corresponding patch file path of repository by given issue ID.
-func (repo *Repository) PatchPath(index int64) (string, error) {
-	return repo.patchPath(x, index)
-}
-
-func (repo *Repository) patchPath(e Engine, index int64) (string, error) {
-	if err := repo.getOwner(e); err != nil {
-		return "", err
-	}
-
-	return filepath.Join(RepoPath(repo.Owner.Name, repo.Name), "pulls", com.ToStr(index)+".patch"), nil
-}
-
-// SavePatch saves patch data to corresponding location by given issue ID.
-func (repo *Repository) SavePatch(index int64, patch []byte) error {
-	return repo.savePatch(x, index, patch)
-}
-
-func (repo *Repository) savePatch(e Engine, index int64, patch []byte) error {
-	patchPath, err := repo.patchPath(e, index)
-	if err != nil {
-		return fmt.Errorf("PatchPath: %v", err)
-	}
-	dir := filepath.Dir(patchPath)
-
-	if err := os.MkdirAll(dir, os.ModePerm); err != nil {
-		return fmt.Errorf("Failed to create dir %s: %v", dir, err)
-	}
-
-	if err = ioutil.WriteFile(patchPath, patch, 0644); err != nil {
-		return fmt.Errorf("WriteFile: %v", err)
-	}
-
-	return nil
-}
-
 func isRepositoryExist(e Engine, u *User, repoName string) (bool, error) {
 	has, err := e.Get(&Repository{
 		OwnerID:   u.ID,
diff --git a/modules/git/repo_compare.go b/modules/git/repo_compare.go
index 677201c5e0..53b8af4bb4 100644
--- a/modules/git/repo_compare.go
+++ b/modules/git/repo_compare.go
@@ -6,7 +6,6 @@
 package git
 
 import (
-	"bytes"
 	"container/list"
 	"fmt"
 	"io"
@@ -94,19 +93,22 @@ func (repo *Repository) GetCompareInfo(basePath, baseBranch, headBranch string)
 	return compareInfo, nil
 }
 
-// GetPatch generates and returns patch data between given revisions.
-func (repo *Repository) GetPatch(base, head string) ([]byte, error) {
-	return NewCommand("diff", "-p", "--binary", base, head).RunInDirBytes(repo.Path)
+// GetDiffOrPatch generates either diff or formatted patch data between given revisions
+func (repo *Repository) GetDiffOrPatch(base, head string, w io.Writer, formatted bool) error {
+	if formatted {
+		return repo.GetPatch(base, head, w)
+	}
+	return repo.GetDiff(base, head, w)
 }
 
-// GetFormatPatch generates and returns format-patch data between given revisions.
-func (repo *Repository) GetFormatPatch(base, head string) (io.Reader, error) {
-	stdout := new(bytes.Buffer)
-	stderr := new(bytes.Buffer)
+// GetDiff generates and returns patch data between given revisions.
+func (repo *Repository) GetDiff(base, head string, w io.Writer) error {
+	return NewCommand("diff", "-p", "--binary", base, head).
+		RunInDirPipeline(repo.Path, w, nil)
+}
 
-	if err := NewCommand("format-patch", "--binary", "--stdout", base+"..."+head).
-		RunInDirPipeline(repo.Path, stdout, stderr); err != nil {
-		return nil, concatenateError(err, stderr.String())
-	}
-	return stdout, nil
+// GetPatch generates and returns format-patch data between given revisions.
+func (repo *Repository) GetPatch(base, head string, w io.Writer) error {
+	return NewCommand("format-patch", "--binary", "--stdout", base+"..."+head).
+		RunInDirPipeline(repo.Path, w, nil)
 }
diff --git a/modules/git/repo_compare_test.go b/modules/git/repo_compare_test.go
index def67fa87b..bf4631d853 100644
--- a/modules/git/repo_compare_test.go
+++ b/modules/git/repo_compare_test.go
@@ -5,6 +5,7 @@
 package git
 
 import (
+	"bytes"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -21,7 +22,8 @@ func TestGetFormatPatch(t *testing.T) {
 	repo, err := OpenRepository(clonedPath)
 	assert.NoError(t, err)
 	defer repo.Close()
-	rd, err := repo.GetFormatPatch("8d92fc95^", "8d92fc95")
+	rd := &bytes.Buffer{}
+	err = repo.GetPatch("8d92fc95^", "8d92fc95", rd)
 	assert.NoError(t, err)
 	patchb, err := ioutil.ReadAll(rd)
 	assert.NoError(t, err)
diff --git a/routers/api/v1/repo/pull.go b/routers/api/v1/repo/pull.go
index 9abcaa0496..93fa6ad276 100644
--- a/routers/api/v1/repo/pull.go
+++ b/routers/api/v1/repo/pull.go
@@ -244,12 +244,6 @@ func CreatePullRequest(ctx *context.APIContext, form api.CreatePullRequestOption
 		milestoneID = milestone.ID
 	}
 
-	patch, err := headGitRepo.GetPatch(compareInfo.MergeBase, headBranch)
-	if err != nil {
-		ctx.Error(500, "GetPatch", err)
-		return
-	}
-
 	var deadlineUnix timeutil.TimeStamp
 	if form.Deadline != nil {
 		deadlineUnix = timeutil.TimeStamp(form.Deadline.Unix())
@@ -306,7 +300,7 @@ func CreatePullRequest(ctx *context.APIContext, form api.CreatePullRequestOption
 		}
 	}
 
-	if err := pull_service.NewPullRequest(repo, prIssue, labelIDs, []string{}, pr, patch, assigneeIDs); err != nil {
+	if err := pull_service.NewPullRequest(repo, prIssue, labelIDs, []string{}, pr, assigneeIDs); err != nil {
 		if models.IsErrUserDoesNotHaveAccessToRepo(err) {
 			ctx.Error(400, "UserDoesNotHaveAccessToRepo", err)
 			return
diff --git a/routers/repo/issue.go b/routers/repo/issue.go
index 5d5aaca253..adafb64eb3 100644
--- a/routers/repo/issue.go
+++ b/routers/repo/issue.go
@@ -1282,11 +1282,6 @@ func NewComment(ctx *context.Context, form auth.CreateCommentForm) {
 
 				// Regenerate patch and test conflict.
 				if pr == nil {
-					if err = issue.PullRequest.UpdatePatch(); err != nil {
-						ctx.ServerError("UpdatePatch", err)
-						return
-					}
-
 					pull_service.AddToTaskQueue(issue.PullRequest)
 				}
 			}
diff --git a/routers/repo/pull.go b/routers/repo/pull.go
index 78406de8ac..c791bc55d9 100644
--- a/routers/repo/pull.go
+++ b/routers/repo/pull.go
@@ -11,7 +11,6 @@ import (
 	"crypto/subtle"
 	"fmt"
 	"html"
-	"io"
 	"path"
 	"strings"
 
@@ -785,12 +784,6 @@ func CompareAndPullRequestPost(ctx *context.Context, form auth.CreateIssueForm)
 		return
 	}
 
-	patch, err := headGitRepo.GetPatch(prInfo.MergeBase, headBranch)
-	if err != nil {
-		ctx.ServerError("GetPatch", err)
-		return
-	}
-
 	pullIssue := &models.Issue{
 		RepoID:      repo.ID,
 		Title:       form.Title,
@@ -813,7 +806,7 @@ func CompareAndPullRequestPost(ctx *context.Context, form auth.CreateIssueForm)
 	// FIXME: check error in the case two people send pull request at almost same time, give nice error prompt
 	// instead of 500.
 
-	if err := pull_service.NewPullRequest(repo, pullIssue, labelIDs, attachments, pullRequest, patch, assigneeIDs); err != nil {
+	if err := pull_service.NewPullRequest(repo, pullIssue, labelIDs, attachments, pullRequest, assigneeIDs); err != nil {
 		if models.IsErrUserDoesNotHaveAccessToRepo(err) {
 			ctx.Error(400, "UserDoesNotHaveAccessToRepo", err.Error())
 			return
@@ -981,44 +974,16 @@ func CleanUpPullRequest(ctx *context.Context) {
 
 // DownloadPullDiff render a pull's raw diff
 func DownloadPullDiff(ctx *context.Context) {
-	issue, err := models.GetIssueByIndex(ctx.Repo.Repository.ID, ctx.ParamsInt64(":index"))
-	if err != nil {
-		if models.IsErrIssueNotExist(err) {
-			ctx.NotFound("GetIssueByIndex", err)
-		} else {
-			ctx.ServerError("GetIssueByIndex", err)
-		}
-		return
-	}
-
-	// Return not found if it's not a pull request
-	if !issue.IsPull {
-		ctx.NotFound("DownloadPullDiff",
-			fmt.Errorf("Issue is not a pull request"))
-		return
-	}
-
-	if err = issue.LoadPullRequest(); err != nil {
-		ctx.ServerError("LoadPullRequest", err)
-		return
-	}
-
-	pr := issue.PullRequest
-	if err = pr.GetBaseRepo(); err != nil {
-		ctx.ServerError("GetBaseRepo", err)
-		return
-	}
-	patch, err := pr.BaseRepo.PatchPath(pr.Index)
-	if err != nil {
-		ctx.ServerError("PatchPath", err)
-		return
-	}
-
-	ctx.ServeFileContent(patch)
+	DownloadPullDiffOrPatch(ctx, false)
 }
 
 // DownloadPullPatch render a pull's raw patch
 func DownloadPullPatch(ctx *context.Context) {
+	DownloadPullDiffOrPatch(ctx, true)
+}
+
+// DownloadPullDiffOrPatch render a pull's raw diff or patch
+func DownloadPullDiffOrPatch(ctx *context.Context, patch bool) {
 	issue, err := models.GetIssueByIndex(ctx.Repo.Repository.ID, ctx.ParamsInt64(":index"))
 	if err != nil {
 		if models.IsErrIssueNotExist(err) {
@@ -1042,27 +1007,9 @@ func DownloadPullPatch(ctx *context.Context) {
 	}
 
 	pr := issue.PullRequest
-	if err = pr.GetHeadRepo(); err != nil {
-		ctx.ServerError("GetHeadRepo", err)
-		return
-	}
-
-	headGitRepo, err := git.OpenRepository(pr.HeadRepo.RepoPath())
-	if err != nil {
-		ctx.ServerError("OpenRepository", err)
-		return
-	}
-	defer headGitRepo.Close()
-
-	patch, err := headGitRepo.GetFormatPatch(pr.MergeBase, pr.HeadBranch)
-	if err != nil {
-		ctx.ServerError("GetFormatPatch", err)
-		return
-	}
 
-	_, err = io.Copy(ctx, patch)
-	if err != nil {
-		ctx.ServerError("io.Copy", err)
+	if err := pull_service.DownloadDiffOrPatch(pr, ctx, patch); err != nil {
+		ctx.ServerError("DownloadDiffOrPatch", err)
 		return
 	}
 }
diff --git a/services/pull/check.go b/services/pull/check.go
index 0fd3e2a76f..fc2ac927b8 100644
--- a/services/pull/check.go
+++ b/services/pull/check.go
@@ -170,7 +170,7 @@ func TestPullRequests() {
 		if manuallyMerged(pr) {
 			continue
 		}
-		if err := pr.TestPatch(); err != nil {
+		if err := TestPatch(pr); err != nil {
 			log.Error("testPatch: %v", err)
 			continue
 		}
@@ -194,7 +194,13 @@ func TestPullRequests() {
 			continue
 		} else if manuallyMerged(pr) {
 			continue
-		} else if err = pr.TestPatch(); err != nil {
+		}
+		pr.Status = models.PullRequestStatusChecking
+		if err := pr.Update(); err != nil {
+			log.Error("testPatch[%d]: Unable to update status to Checking Status %v", pr.ID, err)
+			continue
+		}
+		if err = TestPatch(pr); err != nil {
 			log.Error("testPatch[%d]: %v", pr.ID, err)
 			continue
 		}
diff --git a/services/pull/merge.go b/services/pull/merge.go
index e5563a89b9..9b75c5ffda 100644
--- a/services/pull/merge.go
+++ b/services/pull/merge.go
@@ -68,95 +68,23 @@ func Merge(pr *models.PullRequest, doer *models.User, baseGitRepo *git.Repositor
 	}()
 
 	// Clone base repo.
-	tmpBasePath, err := models.CreateTemporaryPath("merge")
+	tmpBasePath, err := createTemporaryRepo(pr)
 	if err != nil {
 		log.Error("CreateTemporaryPath: %v", err)
 		return err
 	}
-
 	defer func() {
 		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
 			log.Error("Merge: RemoveTemporaryPath: %s", err)
 		}
 	}()
 
-	headRepoPath := pr.HeadRepo.RepoPath()
-
-	if err := git.InitRepository(tmpBasePath, false); err != nil {
-		log.Error("git init tmpBasePath: %v", err)
-		return err
-	}
-
-	remoteRepoName := "head_repo"
 	baseBranch := "base"
-
-	// Add head repo remote.
-	addCacheRepo := func(staging, cache string) error {
-		p := filepath.Join(staging, ".git", "objects", "info", "alternates")
-		f, err := os.OpenFile(p, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0600)
-		if err != nil {
-			log.Error("Could not create .git/objects/info/alternates file in %s: %v", staging, err)
-			return err
-		}
-		defer f.Close()
-		data := filepath.Join(cache, "objects")
-		if _, err := fmt.Fprintln(f, data); err != nil {
-			log.Error("Could not write to .git/objects/info/alternates file in %s: %v", staging, err)
-			return err
-		}
-		return nil
-	}
-
-	if err := addCacheRepo(tmpBasePath, baseGitRepo.Path); err != nil {
-		log.Error("Unable to add base repository to temporary repo [%s -> %s]: %v", pr.BaseRepo.FullName(), tmpBasePath, err)
-		return fmt.Errorf("Unable to add base repository to temporary repo [%s -> tmpBasePath]: %v", pr.BaseRepo.FullName(), err)
-	}
-
-	var outbuf, errbuf strings.Builder
-	if err := git.NewCommand("remote", "add", "-t", pr.BaseBranch, "-m", pr.BaseBranch, "origin", baseGitRepo.Path).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
-		log.Error("Unable to add base repository as origin [%s -> %s]: %v\n%s\n%s", pr.BaseRepo.FullName(), tmpBasePath, err, outbuf.String(), errbuf.String())
-		return fmt.Errorf("Unable to add base repository as origin [%s -> tmpBasePath]: %v\n%s\n%s", pr.BaseRepo.FullName(), err, outbuf.String(), errbuf.String())
-	}
-	outbuf.Reset()
-	errbuf.Reset()
-
-	if err := git.NewCommand("fetch", "origin", "--no-tags", pr.BaseBranch+":"+baseBranch, pr.BaseBranch+":original_"+baseBranch).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
-		log.Error("Unable to fetch origin base branch [%s:%s -> base, original_base in %s]: %v:\n%s\n%s", pr.BaseRepo.FullName(), pr.BaseBranch, tmpBasePath, err, outbuf.String(), errbuf.String())
-		return fmt.Errorf("Unable to fetch origin base branch [%s:%s -> base, original_base in tmpBasePath]: %v\n%s\n%s", pr.BaseRepo.FullName(), pr.BaseBranch, err, outbuf.String(), errbuf.String())
-	}
-	outbuf.Reset()
-	errbuf.Reset()
-
-	if err := git.NewCommand("symbolic-ref", "HEAD", git.BranchPrefix+baseBranch).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
-		log.Error("Unable to set HEAD as base branch [%s]: %v\n%s\n%s", tmpBasePath, err, outbuf.String(), errbuf.String())
-		return fmt.Errorf("Unable to set HEAD as base branch [tmpBasePath]: %v\n%s\n%s", err, outbuf.String(), errbuf.String())
-	}
-	outbuf.Reset()
-	errbuf.Reset()
-
-	if err := addCacheRepo(tmpBasePath, headRepoPath); err != nil {
-		log.Error("Unable to add head repository to temporary repo [%s -> %s]: %v", pr.HeadRepo.FullName(), tmpBasePath, err)
-		return fmt.Errorf("Unable to head base repository to temporary repo [%s -> tmpBasePath]: %v", pr.HeadRepo.FullName(), err)
-	}
-
-	if err := git.NewCommand("remote", "add", remoteRepoName, headRepoPath).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
-		log.Error("Unable to add head repository as head_repo [%s -> %s]: %v\n%s\n%s", pr.HeadRepo.FullName(), tmpBasePath, err, outbuf.String(), errbuf.String())
-		return fmt.Errorf("Unable to add head repository as head_repo [%s -> tmpBasePath]: %v\n%s\n%s", pr.HeadRepo.FullName(), err, outbuf.String(), errbuf.String())
-	}
-	outbuf.Reset()
-	errbuf.Reset()
-
 	trackingBranch := "tracking"
-	// Fetch head branch
-	if err := git.NewCommand("fetch", "--no-tags", remoteRepoName, pr.HeadBranch+":"+trackingBranch).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
-		log.Error("Unable to fetch head_repo head branch [%s:%s -> tracking in %s]: %v:\n%s\n%s", pr.HeadRepo.FullName(), pr.HeadBranch, tmpBasePath, err, outbuf.String(), errbuf.String())
-		return fmt.Errorf("Unable to fetch head_repo head branch [%s:%s -> tracking in tmpBasePath]: %v\n%s\n%s", pr.HeadRepo.FullName(), pr.HeadBranch, err, outbuf.String(), errbuf.String())
-	}
-	outbuf.Reset()
-	errbuf.Reset()
-
 	stagingBranch := "staging"
 
+	var outbuf, errbuf strings.Builder
+
 	// Enable sparse-checkout
 	sparseCheckoutList, err := getDiffTree(tmpBasePath, baseBranch, trackingBranch)
 	if err != nil {
diff --git a/services/pull/patch.go b/services/pull/patch.go
new file mode 100644
index 0000000000..cb8d014486
--- /dev/null
+++ b/services/pull/patch.go
@@ -0,0 +1,216 @@
+// Copyright 2019 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 pull
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"strings"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+)
+
+// DownloadDiff will write the patch for the pr to the writer
+func DownloadDiff(pr *models.PullRequest, w io.Writer, patch bool) error {
+	return DownloadDiffOrPatch(pr, w, false)
+}
+
+// DownloadPatch will write the patch for the pr to the writer
+func DownloadPatch(pr *models.PullRequest, w io.Writer, patch bool) error {
+	return DownloadDiffOrPatch(pr, w, true)
+}
+
+// DownloadDiffOrPatch will write the patch for the pr to the writer
+func DownloadDiffOrPatch(pr *models.PullRequest, w io.Writer, patch bool) error {
+	// Clone base repo.
+	tmpBasePath, err := createTemporaryRepo(pr)
+	if err != nil {
+		log.Error("CreateTemporaryPath: %v", err)
+		return err
+	}
+	defer func() {
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("DownloadDiff: RemoveTemporaryPath: %s", err)
+		}
+	}()
+
+	gitRepo, err := git.OpenRepository(tmpBasePath)
+	if err != nil {
+		return fmt.Errorf("OpenRepository: %v", err)
+	}
+	defer gitRepo.Close()
+
+	pr.MergeBase, err = git.NewCommand("merge-base", "--", "base", "tracking").RunInDir(tmpBasePath)
+	if err != nil {
+		pr.MergeBase = "base"
+	}
+	pr.MergeBase = strings.TrimSpace(pr.MergeBase)
+	if err := gitRepo.GetDiffOrPatch(pr.MergeBase, "tracking", w, patch); err != nil {
+		log.Error("Unable to get patch file from %s to %s in %s/%s Error: %v", pr.MergeBase, pr.HeadBranch, pr.BaseRepo.MustOwner().Name, pr.BaseRepo.Name, err)
+		return fmt.Errorf("Unable to get patch file from %s to %s in %s/%s Error: %v", pr.MergeBase, pr.HeadBranch, pr.BaseRepo.MustOwner().Name, pr.BaseRepo.Name, err)
+	}
+	return nil
+}
+
+var patchErrorSuffices = []string{
+	": already exists in index",
+	": patch does not apply",
+	": already exists in working directory",
+	"unrecognized input",
+}
+
+// TestPatch will test whether a simple patch will apply
+func TestPatch(pr *models.PullRequest) error {
+	// Clone base repo.
+	tmpBasePath, err := createTemporaryRepo(pr)
+	if err != nil {
+		log.Error("CreateTemporaryPath: %v", err)
+		return err
+	}
+	defer func() {
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("Merge: RemoveTemporaryPath: %s", err)
+		}
+	}()
+
+	gitRepo, err := git.OpenRepository(tmpBasePath)
+	if err != nil {
+		return fmt.Errorf("OpenRepository: %v", err)
+	}
+	defer gitRepo.Close()
+
+	pr.MergeBase, err = git.NewCommand("merge-base", "--", "base", "tracking").RunInDir(tmpBasePath)
+	if err != nil {
+		var err2 error
+		pr.MergeBase, err2 = gitRepo.GetRefCommitID(git.BranchPrefix + "base")
+		if err2 != nil {
+			return fmt.Errorf("GetMergeBase: %v and can't find commit ID for base: %v", err, err2)
+		}
+	}
+	pr.MergeBase = strings.TrimSpace(pr.MergeBase)
+	tmpPatchFile, err := ioutil.TempFile("", "patch")
+	if err != nil {
+		log.Error("Unable to create temporary patch file! Error: %v", err)
+		return fmt.Errorf("Unable to create temporary patch file! Error: %v", err)
+	}
+	defer func() {
+		_ = os.Remove(tmpPatchFile.Name())
+	}()
+
+	if err := gitRepo.GetDiff(pr.MergeBase, "tracking", tmpPatchFile); err != nil {
+		tmpPatchFile.Close()
+		log.Error("Unable to get patch file from %s to %s in %s/%s Error: %v", pr.MergeBase, pr.HeadBranch, pr.BaseRepo.MustOwner().Name, pr.BaseRepo.Name, err)
+		return fmt.Errorf("Unable to get patch file from %s to %s in %s/%s Error: %v", pr.MergeBase, pr.HeadBranch, pr.BaseRepo.MustOwner().Name, pr.BaseRepo.Name, err)
+	}
+	stat, err := tmpPatchFile.Stat()
+	if err != nil {
+		tmpPatchFile.Close()
+		return fmt.Errorf("Unable to stat patch file: %v", err)
+	}
+	patchPath := tmpPatchFile.Name()
+	tmpPatchFile.Close()
+
+	if stat.Size() == 0 {
+		log.Debug("PullRequest[%d]: Patch is empty - ignoring", pr.ID)
+		pr.Status = models.PullRequestStatusMergeable
+		pr.ConflictedFiles = []string{}
+		return nil
+	}
+
+	log.Trace("PullRequest[%d].testPatch (patchPath): %s", pr.ID, patchPath)
+
+	pr.Status = models.PullRequestStatusChecking
+
+	_, err = git.NewCommand("read-tree", "base").RunInDir(tmpBasePath)
+	if err != nil {
+		return fmt.Errorf("git read-tree %s: %v", pr.BaseBranch, err)
+	}
+
+	prUnit, err := pr.BaseRepo.GetUnit(models.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)
+	pr.ConflictedFiles = make([]string, 0, 5)
+
+	stderrReader, stderrWriter, err := os.Pipe()
+	if err != nil {
+		log.Error("Unable to open stderr pipe: %v", err)
+		return fmt.Errorf("Unable to open stderr pipe: %v", err)
+	}
+	defer func() {
+		_ = stderrReader.Close()
+		_ = stderrWriter.Close()
+	}()
+	conflict := false
+	err = git.NewCommand(args...).
+		RunInDirTimeoutEnvFullPipelineFunc(
+			nil, -1, tmpBasePath,
+			nil, stderrWriter, nil,
+			func(ctx context.Context, cancel context.CancelFunc) {
+				_ = stderrWriter.Close()
+				const prefix = "error: patch failed:"
+				const errorPrefix = "error: "
+				conflictMap := map[string]bool{}
+
+				scanner := bufio.NewScanner(stderrReader)
+				for scanner.Scan() {
+					line := scanner.Text()
+					fmt.Printf("%s\n", line)
+					if strings.HasPrefix(line, prefix) {
+						conflict = true
+						filepath := strings.TrimSpace(strings.Split(line[len(prefix):], ":")[0])
+						conflictMap[filepath] = true
+					} else if strings.HasPrefix(line, errorPrefix) {
+						conflict = true
+						for _, suffix := range patchErrorSuffices {
+							if strings.HasSuffix(line, suffix) {
+								filepath := strings.TrimSpace(strings.TrimSuffix(line[len(errorPrefix):], suffix))
+								if filepath != "" {
+									conflictMap[filepath] = true
+								}
+								break
+							}
+						}
+					}
+					// only list 10 conflicted files
+					if len(conflictMap) >= 10 {
+						break
+					}
+				}
+				if len(conflictMap) > 0 {
+					pr.ConflictedFiles = make([]string, 0, len(conflictMap))
+					for key := range conflictMap {
+						pr.ConflictedFiles = append(pr.ConflictedFiles, key)
+					}
+				}
+				_ = stderrReader.Close()
+			})
+
+	if err != nil {
+		if conflict {
+			pr.Status = models.PullRequestStatusConflict
+			log.Trace("Found %d files conflicted: %v", len(pr.ConflictedFiles), pr.ConflictedFiles)
+			return nil
+		}
+		return fmt.Errorf("git apply --check: %v", err)
+	}
+	pr.Status = models.PullRequestStatusMergeable
+
+	return nil
+}
diff --git a/services/pull/pull.go b/services/pull/pull.go
index 2650dacc11..df44402ad8 100644
--- a/services/pull/pull.go
+++ b/services/pull/pull.go
@@ -15,8 +15,12 @@ import (
 )
 
 // NewPullRequest creates new pull request with labels for repository.
-func NewPullRequest(repo *models.Repository, pull *models.Issue, labelIDs []int64, uuids []string, pr *models.PullRequest, patch []byte, assigneeIDs []int64) error {
-	if err := models.NewPullRequest(repo, pull, labelIDs, uuids, pr, patch); err != nil {
+func NewPullRequest(repo *models.Repository, pull *models.Issue, labelIDs []int64, uuids []string, pr *models.PullRequest, assigneeIDs []int64) error {
+	if err := TestPatch(pr); err != nil {
+		return err
+	}
+
+	if err := models.NewPullRequest(repo, pull, labelIDs, uuids, pr); err != nil {
 		return err
 	}
 
@@ -56,10 +60,7 @@ func checkForInvalidation(requests models.PullRequestList, repoID int64, doer *m
 func addHeadRepoTasks(prs []*models.PullRequest) {
 	for _, pr := range prs {
 		log.Trace("addHeadRepoTasks[%d]: composing new test task", pr.ID)
-		if err := pr.UpdatePatch(); err != nil {
-			log.Error("UpdatePatch: %v", err)
-			continue
-		} else if err := pr.PushToBaseRepo(); err != nil {
+		if err := pr.PushToBaseRepo(); err != nil {
 			log.Error("PushToBaseRepo: %v", err)
 			continue
 		}
diff --git a/services/pull/temp_repo.go b/services/pull/temp_repo.go
new file mode 100644
index 0000000000..bb6ce2921e
--- /dev/null
+++ b/services/pull/temp_repo.go
@@ -0,0 +1,152 @@
+// Copyright 2019 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 pull
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+)
+
+func createTemporaryRepo(pr *models.PullRequest) (string, error) {
+	if err := pr.GetHeadRepo(); err != nil {
+		log.Error("GetHeadRepo: %v", err)
+		return "", fmt.Errorf("GetHeadRepo: %v", err)
+	} else if pr.HeadRepo == nil {
+		log.Error("Pr %d HeadRepo %d does not exist", pr.ID, pr.HeadRepoID)
+		return "", &models.ErrRepoNotExist{
+			ID: pr.HeadRepoID,
+		}
+	} else if err := pr.GetBaseRepo(); err != nil {
+		log.Error("GetBaseRepo: %v", err)
+		return "", fmt.Errorf("GetBaseRepo: %v", err)
+	} else if pr.BaseRepo == nil {
+		log.Error("Pr %d BaseRepo %d does not exist", pr.ID, pr.BaseRepoID)
+		return "", &models.ErrRepoNotExist{
+			ID: pr.BaseRepoID,
+		}
+	} else if err := pr.HeadRepo.GetOwner(); err != nil {
+		log.Error("HeadRepo.GetOwner: %v", err)
+		return "", fmt.Errorf("HeadRepo.GetOwner: %v", err)
+	} else if err := pr.BaseRepo.GetOwner(); err != nil {
+		log.Error("BaseRepo.GetOwner: %v", err)
+		return "", fmt.Errorf("BaseRepo.GetOwner: %v", err)
+	}
+
+	// Clone base repo.
+	tmpBasePath, err := models.CreateTemporaryPath("pull")
+	if err != nil {
+		log.Error("CreateTemporaryPath: %v", err)
+		return "", err
+	}
+
+	baseRepoPath := pr.BaseRepo.RepoPath()
+	headRepoPath := pr.HeadRepo.RepoPath()
+
+	if err := git.InitRepository(tmpBasePath, false); err != nil {
+		log.Error("git init tmpBasePath: %v", err)
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
+		}
+		return "", err
+	}
+
+	remoteRepoName := "head_repo"
+	baseBranch := "base"
+
+	// Add head repo remote.
+	addCacheRepo := func(staging, cache string) error {
+		p := filepath.Join(staging, ".git", "objects", "info", "alternates")
+		f, err := os.OpenFile(p, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0600)
+		if err != nil {
+			log.Error("Could not create .git/objects/info/alternates file in %s: %v", staging, err)
+			return err
+		}
+		defer f.Close()
+		data := filepath.Join(cache, "objects")
+		if _, err := fmt.Fprintln(f, data); err != nil {
+			log.Error("Could not write to .git/objects/info/alternates file in %s: %v", staging, err)
+			return err
+		}
+		return nil
+	}
+
+	if err := addCacheRepo(tmpBasePath, baseRepoPath); err != nil {
+		log.Error("Unable to add base repository to temporary repo [%s -> %s]: %v", pr.BaseRepo.FullName(), tmpBasePath, err)
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
+		}
+		return "", fmt.Errorf("Unable to add base repository to temporary repo [%s -> tmpBasePath]: %v", pr.BaseRepo.FullName(), err)
+	}
+
+	var outbuf, errbuf strings.Builder
+	if err := git.NewCommand("remote", "add", "-t", pr.BaseBranch, "-m", pr.BaseBranch, "origin", baseRepoPath).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
+		log.Error("Unable to add base repository as origin [%s -> %s]: %v\n%s\n%s", pr.BaseRepo.FullName(), tmpBasePath, err, outbuf.String(), errbuf.String())
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
+		}
+		return "", fmt.Errorf("Unable to add base repository as origin [%s -> tmpBasePath]: %v\n%s\n%s", pr.BaseRepo.FullName(), err, outbuf.String(), errbuf.String())
+	}
+	outbuf.Reset()
+	errbuf.Reset()
+
+	if err := git.NewCommand("fetch", "origin", "--no-tags", pr.BaseBranch+":"+baseBranch, pr.BaseBranch+":original_"+baseBranch).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
+		log.Error("Unable to fetch origin base branch [%s:%s -> base, original_base in %s]: %v:\n%s\n%s", pr.BaseRepo.FullName(), pr.BaseBranch, tmpBasePath, err, outbuf.String(), errbuf.String())
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
+		}
+		return "", fmt.Errorf("Unable to fetch origin base branch [%s:%s -> base, original_base in tmpBasePath]: %v\n%s\n%s", pr.BaseRepo.FullName(), pr.BaseBranch, err, outbuf.String(), errbuf.String())
+	}
+	outbuf.Reset()
+	errbuf.Reset()
+
+	if err := git.NewCommand("symbolic-ref", "HEAD", git.BranchPrefix+baseBranch).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
+		log.Error("Unable to set HEAD as base branch [%s]: %v\n%s\n%s", tmpBasePath, err, outbuf.String(), errbuf.String())
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
+		}
+		return "", fmt.Errorf("Unable to set HEAD as base branch [tmpBasePath]: %v\n%s\n%s", err, outbuf.String(), errbuf.String())
+	}
+	outbuf.Reset()
+	errbuf.Reset()
+
+	if err := addCacheRepo(tmpBasePath, headRepoPath); err != nil {
+		log.Error("Unable to add head repository to temporary repo [%s -> %s]: %v", pr.HeadRepo.FullName(), tmpBasePath, err)
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
+		}
+		return "", fmt.Errorf("Unable to head base repository to temporary repo [%s -> tmpBasePath]: %v", pr.HeadRepo.FullName(), err)
+	}
+
+	if err := git.NewCommand("remote", "add", remoteRepoName, headRepoPath).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
+		log.Error("Unable to add head repository as head_repo [%s -> %s]: %v\n%s\n%s", pr.HeadRepo.FullName(), tmpBasePath, err, outbuf.String(), errbuf.String())
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
+		}
+		return "", fmt.Errorf("Unable to add head repository as head_repo [%s -> tmpBasePath]: %v\n%s\n%s", pr.HeadRepo.FullName(), err, outbuf.String(), errbuf.String())
+	}
+	outbuf.Reset()
+	errbuf.Reset()
+
+	trackingBranch := "tracking"
+	// Fetch head branch
+	if err := git.NewCommand("fetch", "--no-tags", remoteRepoName, pr.HeadBranch+":"+trackingBranch).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
+		log.Error("Unable to fetch head_repo head branch [%s:%s -> tracking in %s]: %v:\n%s\n%s", pr.HeadRepo.FullName(), pr.HeadBranch, tmpBasePath, err, outbuf.String(), errbuf.String())
+		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
+		}
+		return "", fmt.Errorf("Unable to fetch head_repo head branch [%s:%s -> tracking in tmpBasePath]: %v\n%s\n%s", pr.HeadRepo.FullName(), pr.HeadBranch, err, outbuf.String(), errbuf.String())
+	}
+	outbuf.Reset()
+	errbuf.Reset()
+
+	return tmpBasePath, nil
+}