add git v2.28.0 support

modules/git/repo_compare.go

@@ -71,10 +71,16 @@ func (repo *Repository) GetCompareInfo(basePath, baseBranch, headBranch string)
 		// We have a common base
 		logs, err := NewCommand("log", compareInfo.MergeBase+"..."+headBranch, prettyLogFormat).RunInDirBytes(repo.Path)
 		if err != nil {
+			if strings.HasSuffix(strings.TrimSpace(err.Error()), "no merge base") {
+				return compareInfo, nil
+			}
 			return nil, err
 		}
 		compareInfo.Commits, err = repo.parsePrettyFormatLogToList(logs)
 		if err != nil {
+			if strings.HasSuffix(strings.TrimSpace(err.Error()), "no merge base") {
+				return compareInfo, nil
+			}
 			return nil, fmt.Errorf("parsePrettyFormatLogToList: %v", err)
 		}
 	} else {
@@ -90,6 +96,9 @@ func (repo *Repository) GetCompareInfo(basePath, baseBranch, headBranch string)
 	// Now there is git diff --shortstat but this appears to be slower than simply iterating with --nameonly
 	compareInfo.NumFiles, err = repo.GetDiffNumChangedFiles(remoteBranch, headBranch)
 	if err != nil {
+		if strings.HasSuffix(strings.TrimSpace(err.Error()), "no merge base") {
+			return compareInfo, nil
+		}
 		return nil, err
 	}
 	return compareInfo, nil
@@ -115,6 +124,15 @@ func (repo *Repository) GetDiffNumChangedFiles(base, head string) (int, error) {
 
 	if err := NewCommand("diff", "-z", "--name-only", base+"..."+head).
 		RunInDirPipeline(repo.Path, w, stderr); err != nil {
+		if strings.HasSuffix(strings.TrimSpace(err.Error()), "no merge base") {
+			// git >= 2.28 now returns an error if base and head have become unrelated.
+			// previously it would return the results of git diff -z --name-only base head so let's try that...
+			w = &lineCountWriter{}
+			stderr.Reset()
+			if err = NewCommand("diff", "-z", "--name-only", base, head).RunInDirPipeline(repo.Path, w, stderr); err == nil {
+				return w.numLines, nil
+			}
+		}
 		return 0, fmt.Errorf("%v: Stderr: %s", err, stderr)
 	}
 	return w.numLines, nil

routers/repo/compare.go

@@ -443,10 +443,13 @@ func PrepareCompareDiff(
 	diff, err := gitdiff.GetDiffRange(models.RepoPath(headUser.Name, headRepo.Name),
 		compareInfo.MergeBase, headCommitID, setting.Git.MaxGitDiffLines,
 		setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles)
-	if err != nil {
+	if err != nil && !strings.HasSuffix(strings.TrimSpace(err.Error()), "no merge base") {
 		ctx.ServerError("GetDiffRange", err)
 		return false
 	}
+	if diff == nil {
+		diff = &gitdiff.Diff{}
+	}
 	ctx.Data["Diff"] = diff
 	ctx.Data["DiffNotAvailable"] = diff.NumFiles == 0