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Use merge tree to detect conflicts when possible (#36400)

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In Git 2.38, the `merge-tree` command introduced the `--write-tree`
option, which works directly on bare repositories. In Git 2.40, a new parameter `--merge-base` introduced so we require Git 2.40 to use the merge tree feature.

This option produces the merged tree object ID, allowing us to perform
diffs between commits without creating a temporary repository. By
avoiding the overhead of setting up and tearing down temporary repos,
this approach delivers a notable performance improvement.

It also fixes a possible situation that conflict files might be empty
but it's a conflict status according to
https://git-scm.com/docs/git-merge-tree#_mistakes_to_avoid

Replace #35542

---------

Signed-off-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
This commit is contained in:
Lunny Xiao
2026-01-27 11:57:20 -08:00
committed by GitHub
parent 125257eacf
commit 1463426a27
29 changed files with 607 additions and 126 deletions
Download Patch File Download Diff File Expand all files Collapse all files
services/pull/merge_prepare.go
+7 -20
View File
@@ -5,7 +5,6 @@ package pull
import (
"bufio"
"bytes"
"context"
"fmt"
"io"
@@ -21,6 +20,7 @@ import (
"code.gitea.io/gitea/modules/git/gitcmd"
"code.gitea.io/gitea/modules/gitrepo"
"code.gitea.io/gitea/modules/log"
"code.gitea.io/gitea/modules/util"
asymkey_service "code.gitea.io/gitea/services/asymkey"
)
@@ -76,7 +76,7 @@ func createTemporaryRepoForMerge(ctx context.Context, pr *issues_model.PullReque
if expectedHeadCommitID != "" {
trackingCommitID, _, err := gitcmd.NewCommand("show-ref", "--hash").
AddDynamicArguments(git.BranchPrefix + trackingBranch).
AddDynamicArguments(git.BranchPrefix + tmpRepoTrackingBranch).
WithEnv(mergeCtx.env).
WithDir(mergeCtx.tmpBasePath).
RunStdString(ctx)
@@ -152,8 +152,8 @@ func prepareTemporaryRepoForMerge(ctx *mergeContext) error {
}
defer sparseCheckoutListFile.Close() // we will close it earlier but we need to ensure it is closed if there is an error
if err := getDiffTree(ctx, ctx.tmpBasePath, baseBranch, trackingBranch, sparseCheckoutListFile); err != nil {
log.Error("%-v getDiffTree(%s, %s, %s): %v", ctx.pr, ctx.tmpBasePath, baseBranch, trackingBranch, err)
if err := getDiffTree(ctx, ctx.tmpBasePath, tmpRepoBaseBranch, tmpRepoTrackingBranch, sparseCheckoutListFile); err != nil {
log.Error("%-v getDiffTree(%s, %s, %s): %v", ctx.pr, ctx.tmpBasePath, tmpRepoBaseBranch, tmpRepoTrackingBranch, err)
return fmt.Errorf("getDiffTree: %w", err)
}
@@ -206,19 +206,6 @@ func prepareTemporaryRepoForMerge(ctx *mergeContext) error {
// getDiffTree returns a string containing all the files that were changed between headBranch and baseBranch
// the filenames are escaped so as to fit the format required for .git/info/sparse-checkout
func getDiffTree(ctx context.Context, repoPath, baseBranch, headBranch string, out io.Writer) error {
scanNullTerminatedStrings := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
if atEOF && len(data) == 0 {
return 0, nil, nil
}
if i := bytes.IndexByte(data, '\x00'); i >= 0 {
return i + 1, data[0:i], nil
}
if atEOF {
return len(data), data, nil
}
return 0, nil, nil
}
cmd := gitcmd.NewCommand("diff-tree", "--no-commit-id", "--name-only", "-r", "-r", "-z", "--root")
diffOutReader, diffOutReaderClose := cmd.MakeStdoutPipe()
defer diffOutReaderClose()
@@ -227,7 +214,7 @@ func getDiffTree(ctx context.Context, repoPath, baseBranch, headBranch string, o
WithPipelineFunc(func(ctx gitcmd.Context) error {
// Now scan the output from the command
scanner := bufio.NewScanner(diffOutReader)
scanner.Split(scanNullTerminatedStrings)
scanner.Split(util.BufioScannerSplit(0))
for scanner.Scan() {
treePath := scanner.Text()
// escape '*', '?', '[', spaces and '!' prefix
@@ -266,14 +253,14 @@ func (err ErrRebaseConflicts) Error() string {
// if there is a conflict it will return an ErrRebaseConflicts
func rebaseTrackingOnToBase(ctx *mergeContext, mergeStyle repo_model.MergeStyle) error {
// Checkout head branch
if err := ctx.PrepareGitCmd(gitcmd.NewCommand("checkout", "-b").AddDynamicArguments(stagingBranch, trackingBranch)).
if err := ctx.PrepareGitCmd(gitcmd.NewCommand("checkout", "-b").AddDynamicArguments(tmpRepoStagingBranch, tmpRepoTrackingBranch)).
RunWithStderr(ctx); err != nil {
return fmt.Errorf("unable to git checkout tracking as staging in temp repo for %v: %w\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), err.Stderr())
}
ctx.outbuf.Reset()
// Rebase before merging
if err := ctx.PrepareGitCmd(gitcmd.NewCommand("rebase").AddDynamicArguments(baseBranch)).
if err := ctx.PrepareGitCmd(gitcmd.NewCommand("rebase").AddDynamicArguments(tmpRepoBaseBranch)).
RunWithStderr(ctx); err != nil {
// Rebase will leave a REBASE_HEAD file in .git if there is a conflict
if _, statErr := os.Stat(filepath.Join(ctx.tmpBasePath, ".git", "REBASE_HEAD")); statErr == nil {