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>

1 files changed, 96 insertions, 0 deletions

diff --git a/modules/git/attribute/checker.go b/modules/git/attribute/checker.go
new file mode 100644
index 0000000000..c17006a154
--- /dev/null
+++ b/modules/git/attribute/checker.go
@@ -0,0 +1,96 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package attribute
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"os"
+
+	"code.gitea.io/gitea/modules/git"
+)
+
+func checkAttrCommand(gitRepo *git.Repository, treeish string, filenames, attributes []string) (*git.Command, []string, func(), error) {
+	cancel := func() {}
+	envs := []string{"GIT_FLUSH=1"}
+	cmd := git.NewCommand("check-attr", "-z")
+	if len(attributes) == 0 {
+		cmd.AddArguments("--all")
+	}
+
+	// there is treeish, read from bare repo or temp index created by "read-tree"
+	if treeish != "" {
+		if git.DefaultFeatures().SupportCheckAttrOnBare {
+			cmd.AddArguments("--source")
+			cmd.AddDynamicArguments(treeish)
+		} else {
+			indexFilename, worktree, deleteTemporaryFile, err := gitRepo.ReadTreeToTemporaryIndex(treeish)
+			if err != nil {
+				return nil, nil, nil, err
+			}
+
+			cmd.AddArguments("--cached")
+			envs = append(envs,
+				"GIT_INDEX_FILE="+indexFilename,
+				"GIT_WORK_TREE="+worktree,
+			)
+			cancel = deleteTemporaryFile
+		}
+	} // else: no treeish, assume it is a not a bare repo, read from working directory
+
+	cmd.AddDynamicArguments(attributes...)
+	if len(filenames) > 0 {
+		cmd.AddDashesAndList(filenames...)
+	}
+	return cmd, envs, cancel, nil
+}
+
+type CheckAttributeOpts struct {
+	Filenames  []string
+	Attributes []string
+}
+
+// CheckAttributes return the attributes of the given filenames and attributes in the given treeish.
+// If treeish is empty, then it will use current working directory, otherwise it will use the provided treeish on the bare repo
+func CheckAttributes(ctx context.Context, gitRepo *git.Repository, treeish string, opts CheckAttributeOpts) (map[string]*Attributes, error) {
+	cmd, envs, cancel, err := checkAttrCommand(gitRepo, treeish, opts.Filenames, opts.Attributes)
+	if err != nil {
+		return nil, err
+	}
+	defer cancel()
+
+	stdOut := new(bytes.Buffer)
+	stdErr := new(bytes.Buffer)
+
+	if err := cmd.Run(ctx, &git.RunOpts{
+		Env:    append(os.Environ(), envs...),
+		Dir:    gitRepo.Path,
+		Stdout: stdOut,
+		Stderr: stdErr,
+	}); err != nil {
+		return nil, fmt.Errorf("failed to run check-attr: %w\n%s\n%s", err, stdOut.String(), stdErr.String())
+	}
+
+	fields := bytes.Split(stdOut.Bytes(), []byte{'\000'})
+	if len(fields)%3 != 1 {
+		return nil, errors.New("wrong number of fields in return from check-attr")
+	}
+
+	attributesMap := make(map[string]*Attributes)
+	for i := 0; i < (len(fields) / 3); i++ {
+		filename := string(fields[3*i])
+		attribute := string(fields[3*i+1])
+		info := string(fields[3*i+2])
+		attribute2info, ok := attributesMap[filename]
+		if !ok {
+			attribute2info = NewAttributes()
+			attributesMap[filename] = attribute2info
+		}
+		attribute2info.m[attribute] = Attribute(info)
+	}
+
+	return attributesMap, nil
+}