Refactor Git Attribute & performance optimization (#34154)

This PR moved git attributes related code to `modules/git/attribute` sub
package and moved language stats related code to
`modules/git/languagestats` sub package to make it easier to maintain.

And it also introduced a performance improvement which use the `git
check-attr --source` which can be run in a bare git repository so that
we don't need to create a git index file. The new parameter need a git
version >= 2.40 . If git version less than 2.40, it will fall back to
previous implementation.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: yp05327 <576951401@qq.com>

modules/git/attribute/checker_test.go

@@ -0,0 +1,74 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package attribute
+
+import (
+	"path/filepath"
+	"testing"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/test"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_Checker(t *testing.T) {
+	setting.AppDataPath = t.TempDir()
+	repoPath := "../tests/repos/language_stats_repo"
+	gitRepo, err := git.OpenRepository(t.Context(), repoPath)
+	require.NoError(t, err)
+	defer gitRepo.Close()
+
+	commitID := "8fee858da5796dfb37704761701bb8e800ad9ef3"
+
+	t.Run("Create index file to run git check-attr", func(t *testing.T) {
+		defer test.MockVariableValue(&git.DefaultFeatures().SupportCheckAttrOnBare, false)()
+		attrs, err := CheckAttributes(t.Context(), gitRepo, commitID, CheckAttributeOpts{
+			Filenames:  []string{"i-am-a-python.p"},
+			Attributes: LinguistAttributes,
+		})
+		assert.NoError(t, err)
+		assert.Len(t, attrs, 1)
+		assert.Equal(t, expectedAttrs(), attrs["i-am-a-python.p"])
+	})
+
+	// run git check-attr on work tree
+	t.Run("Run git check-attr on git work tree", func(t *testing.T) {
+		dir := filepath.Join(t.TempDir(), "test-repo")
+		err := git.Clone(t.Context(), repoPath, dir, git.CloneRepoOptions{
+			Shared: true,
+			Branch: "master",
+		})
+		assert.NoError(t, err)
+
+		tempRepo, err := git.OpenRepository(t.Context(), dir)
+		assert.NoError(t, err)
+		defer tempRepo.Close()
+
+		attrs, err := CheckAttributes(t.Context(), tempRepo, "", CheckAttributeOpts{
+			Filenames:  []string{"i-am-a-python.p"},
+			Attributes: LinguistAttributes,
+		})
+		assert.NoError(t, err)
+		assert.Len(t, attrs, 1)
+		assert.Equal(t, expectedAttrs(), attrs["i-am-a-python.p"])
+	})
+
+	if !git.DefaultFeatures().SupportCheckAttrOnBare {
+		t.Skip("git version 2.40 is required to support run check-attr on bare repo")
+		return
+	}
+
+	t.Run("Run git check-attr in bare repository", func(t *testing.T) {
+		attrs, err := CheckAttributes(t.Context(), gitRepo, commitID, CheckAttributeOpts{
+			Filenames:  []string{"i-am-a-python.p"},
+			Attributes: LinguistAttributes,
+		})
+		assert.NoError(t, err)
+		assert.Len(t, attrs, 1)
+		assert.Equal(t, expectedAttrs(), attrs["i-am-a-python.p"])
+	})
+}