Optimize pulls merging (#4921)

* Optimize pulls merging By utilizing `git clone -s --no-checkout` rather than cloning the whole repo. * Use sparse-checkout to speedup pulls merge * Use bytes.Buffer instead of strings.Builder for backward compatibility * Fix empty diff-tree output for repos with only the initial commit * Fix missing argument for the format string * Rework diff-tree-list generation * Remove logging code * File list for sparse-checkout must be prefix with / Otherwise, they would match all files with the same name under subdirectories. * Update onto the rebased head * Use referecen repo to avoid fetching objects

Author: typeless

models/pull.go

@@ -5,6 +5,8 @@
 package models
 
 import (
+"bufio"
+"bytes"
 "fmt"
 "io/ioutil"
 "os"
@@ -328,6 +330,34 @@ func (pr *PullRequest) CheckUserAllowedToMerge(doer *User) (err error) {
 return nil
 }
 
+func getDiffTree(repoPath, baseBranch, headBranch string) (string, error) {
+getDiffTreeFromBranch := func(repoPath, baseBranch, headBranch string) (string, error) {
+var stdout, stderr string
+// Compute the diff-tree for sparse-checkout
+// The branch argument must be enclosed with double-quotes ("") in case it contains slashes (e.g "feature/test")
+stdout, stderr, err := process.GetManager().ExecDir(-1, repoPath,
+fmt.Sprintf("PullRequest.Merge (git diff-tree): %s", repoPath),
+"git", "diff-tree", "--no-commit-id", "--name-only", "-r", "--root", baseBranch, headBranch)
+if err != nil {
+return "", fmt.Errorf("git diff-tree [%s base:%s head:%s]: %s", repoPath, baseBranch, headBranch, stderr)
+}
+return stdout, nil
+}
+
+list, err := getDiffTreeFromBranch(repoPath, baseBranch, headBranch)
+if err != nil {
+return "", err
+}
+
+// Prefixing '/' for each entry, otherwise all files with the same name in subdirectories would be matched.
+out := bytes.Buffer{}
+scanner := bufio.NewScanner(strings.NewReader(list))
+for scanner.Scan() {
+fmt.Fprintf(&out, "/%s\n", scanner.Text())
+}
+return out.String(), nil
+}
+
 // 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, mergeStyle MergeStyle, message string) (err error) {
@@ -371,36 +401,76 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository, mergeStyle
 var stderr string
 if _, stderr, err = process.GetManager().ExecTimeout(5*time.Minute,
 fmt.Sprintf("PullRequest.Merge (git clone): %s", tmpBasePath),
-"git", "clone", baseGitRepo.Path, tmpBasePath); err != nil {
+"git", "clone", "-s", "--no-checkout", "-b", pr.BaseBranch, baseGitRepo.Path, tmpBasePath); err != nil {
 return fmt.Errorf("git clone: %s", stderr)
 }
 
-// Check out base branch.
-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)
-}
+remoteRepoName := "head_repo"
 
 // 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_WRONLY, 0600)
+if err != nil {
+return err
+}
+defer f.Close()
+data := filepath.Join(cache, "objects")
+if _, err := fmt.Fprintln(f, data); err != nil {
+return err
+}
+return nil
+}
+
+if err := addCacheRepo(tmpBasePath, headRepoPath); err != nil {
+return fmt.Errorf("addCacheRepo [%s -> %s]: %v", headRepoPath, tmpBasePath, err)
+}
 if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
 fmt.Sprintf("PullRequest.Merge (git remote add): %s", tmpBasePath),
-"git", "remote", "add", "head_repo", headRepoPath); err != nil {
+"git", "remote", "add", remoteRepoName, headRepoPath); err != nil {
 return fmt.Errorf("git remote add [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
 }
 
-// Merge commits.
+// Fetch head branch
 if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
 fmt.Sprintf("PullRequest.Merge (git fetch): %s", tmpBasePath),
-"git", "fetch", "head_repo"); err != nil {
+"git", "fetch", remoteRepoName); err != nil {
 return fmt.Errorf("git fetch [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
 }
 
+trackingBranch := path.Join(remoteRepoName, pr.HeadBranch)
+stagingBranch := fmt.Sprintf("%s_%s", remoteRepoName, pr.HeadBranch)
+
+// Enable sparse-checkout
+sparseCheckoutList, err := getDiffTree(tmpBasePath, pr.BaseBranch, trackingBranch)
+if err != nil {
+return fmt.Errorf("getDiffTree: %v", err)
+}
+
+sparseCheckoutListPath := filepath.Join(tmpBasePath, ".git", "info", "sparse-checkout")
+if err := ioutil.WriteFile(sparseCheckoutListPath, []byte(sparseCheckoutList), 0600); err != nil {
+return fmt.Errorf("Writing sparse-checkout file to %s: %v", sparseCheckoutListPath, err)
+}
+
+if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+fmt.Sprintf("PullRequest.Merge (git config): %s", tmpBasePath),
+"git", "config", "--local", "core.sparseCheckout", "true"); err != nil {
+return fmt.Errorf("git config [core.sparsecheckout -> true]: %v", stderr)
+}
+
+// Read base branch index
+if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
+fmt.Sprintf("PullRequest.Merge (git read-tree): %s", tmpBasePath),
+"git", "read-tree", "HEAD"); err != nil {
+return fmt.Errorf("git read-tree HEAD: %s", stderr)
+}
+
+// Merge commits.
 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 {
+"git", "merge", "--no-ff", "--no-commit", trackingBranch); err != nil {
 return fmt.Errorf("git merge --no-ff --no-commit [%s]: %v - %s", tmpBasePath, err, stderr)
 }
 
@@ -415,7 +485,7 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository, mergeStyle
 // 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 {
+"git", "checkout", "-b", stagingBranch, trackingBranch); err != nil {
 return fmt.Errorf("git checkout: %s", stderr)
 }
 // Rebase before merging
@@ -433,14 +503,14 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository, mergeStyle
 // 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 {
+"git", "merge", "--ff-only", "-q", stagingBranch); err != nil {
 return fmt.Errorf("git merge --ff-only [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
 }
 case MergeStyleRebaseMerge:
 // 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 {
+"git", "checkout", "-b", stagingBranch, trackingBranch); err != nil {
 return fmt.Errorf("git checkout: %s", stderr)
 }
 // Rebase before merging
@@ -458,7 +528,7 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository, mergeStyle
 // Prepare merge with commit
 if _, stderr, err = process.GetManager().ExecDir(-1, tmpBasePath,
 fmt.Sprintf("PullRequest.Merge (git merge): %s", tmpBasePath),
-"git", "merge", "--no-ff", "--no-commit", "-q", "head_repo_"+pr.HeadBranch); err != nil {
+"git", "merge", "--no-ff", "--no-commit", "-q", stagingBranch); err != nil {
 return fmt.Errorf("git merge --no-ff [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
 }
 
@@ -475,7 +545,7 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository, mergeStyle
 // 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 {
+"git", "merge", "-q", "--squash", trackingBranch); err != nil {
 return fmt.Errorf("git merge --squash [%s -> %s]: %s", headRepoPath, tmpBasePath, stderr)
 }
 sig := pr.Issue.Poster.NewGitSig()