fix(pulls): respect diff.orderFile in diff file tree (#38566)

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/config.go

@@ -91,7 +91,7 @@ func syncGitConfig(ctx context.Context) (err error) {
 		}
 	}
 
-	// By default partial clones are disabled, enable them from git v2.22
+	// By default, partial clones are disabled, enable them from git v2.22
 	if !setting.Git.DisablePartialClone && DefaultFeatures().CheckVersionAtLeast("2.22") {
 		if err = configSet(ctx, "uploadpack.allowfilter", "true"); err != nil {
 			return err
@@ -114,9 +114,23 @@ func syncGitConfig(ctx context.Context) (err error) {
 		}
 	}
 
+	GlobalConfig = &GlobalConfigStruct{}
+	// HINT: GIT-DIFF-TREE-UI-CONFIG: Git's bug: git-diff-tree loads config with /* no "diff" UI options */ (since 20 years ago).
+	// https://github.com/git/git/blame/5d2e7709234afea1b6ddb25cd4f60d3d5fb3c200/builtin/diff-tree.c#L127
+	// Although document and manual say that "git-diff-tree" supports "diff.orderfile" option, but it is not actually supported.
+	// So we need to apply the diff.orderfile explicitly in our code.
+	GlobalConfig.DiffOrderFile, _ = configGet(ctx, "diff.orderfile")
 	return nil
 }
 
+func configGet(ctx context.Context, key string) (string, error) {
+	stdout, _, err := gitcmd.NewCommand("config", "--global", "--get").AddDynamicArguments(key).RunStdString(ctx)
+	if err != nil && !gitcmd.IsErrorExitCode(err, 1) {
+		return "", fmt.Errorf("failed to get git config %s, err: %w", key, err)
+	}
+	return strings.TrimRight(stdout, "\r\n"), nil
+}
+
 func configSet(ctx context.Context, key, value string) error {
 	stdout, _, err := gitcmd.NewCommand("config", "--global", "--get").
 		AddDynamicArguments(key).

modules/git/git.go

@@ -37,7 +37,14 @@ type Features struct {
 	SupportGitMergeTree        bool           // >= 2.40 // we also need "--merge-base"
 }
 
-var defaultFeatures *Features
+type GlobalConfigStruct struct {
+	DiffOrderFile string
+}
+
+var (
+	defaultFeatures *Features
+	GlobalConfig    *GlobalConfigStruct
+)
 
 func (f *Features) CheckVersionAtLeast(atLeast string) bool {
 	return f.gitVersion.Compare(version.Must(version.NewVersion(atLeast))) >= 0

services/gitdiff/git_diff_tree.go

@@ -60,6 +60,11 @@ func runGitDiffTree(ctx context.Context, gitRepo *git.Repository, useMergeBase b
 	cmd := gitcmd.NewCommand("diff-tree", "--raw", "-r", "--root").
 		AddOptionFormat("--find-renames=%s", setting.Git.DiffRenameSimilarityThreshold)
 
+	// HINT: GIT-DIFF-TREE-UI-CONFIG: apply the diff.orderfile explicitly
+	if git.GlobalConfig.DiffOrderFile != "" {
+		cmd.AddOptionFormat("-O%s", git.GlobalConfig.DiffOrderFile)
+	}
+
 	if useMergeBase {
 		cmd.AddArguments("--merge-base")
 	}

services/gitdiff/git_diff_tree_test.go

@@ -4,10 +4,13 @@
 package gitdiff
 
 import (
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
 	"gitea.dev/modules/git"
+	"gitea.dev/modules/git/gitcmd"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -217,6 +220,43 @@ func TestGitDiffTree(t *testing.T) {
 	}
 }
 
+func TestGitDiffTreeRespectsDiffOrderFile(t *testing.T) {
+	gitRepo, err := git.OpenRepositoryLocal("../../modules/git/tests/repos/repo5_pulls")
+	require.NoError(t, err)
+	defer gitRepo.Close()
+
+	testDiffTree := func(t *testing.T) (filePaths []string) {
+		t.Helper()
+		diffTree, err := GetDiffTree(t.Context(), gitRepo, false, "72866af952e98d02a73003501836074b286a78f6", "d8e0bbb45f200e67d9a784ce55bd90821af45ebd")
+		require.NoError(t, err)
+		for _, f := range diffTree.Files {
+			filePaths = append(filePaths, f.HeadPath)
+		}
+		return filePaths
+	}
+
+	t.Run("NoDiffOrderFile", func(t *testing.T) {
+		assert.Equal(t, []string{"LICENSE", "README.md"}, testDiffTree(t))
+	})
+
+	t.Run("GlobalDiffOrderFile", func(t *testing.T) {
+		diffOrderFilePath := filepath.Join(t.TempDir(), "test-diff-order.txt")
+		err = os.WriteFile(diffOrderFilePath, []byte("README.md\nLICENSE\n"), 0o644)
+		require.NoError(t, err)
+
+		_, _, err = gitcmd.NewCommand("config", "set", "--global").AddDynamicArguments("diff.orderFile", diffOrderFilePath).RunStdString(t.Context())
+		require.NoError(t, err)
+		require.NoError(t, git.InitFull())
+		defer func() {
+			_, _, err = gitcmd.NewCommand("config", "unset", "--global").AddDynamicArguments("diff.orderFile").RunStdString(t.Context())
+			require.NoError(t, err)
+			require.NoError(t, git.InitFull())
+		}()
+
+		assert.Equal(t, []string{"README.md", "LICENSE"}, testDiffTree(t))
+	})
+}
+
 func TestParseGitDiffTree(t *testing.T) {
 	test := []struct {
 		Name      string