Move repofiles from modules/repofiles to services/repository/files (#17774)

* Move repofiles from modules to services

* rename services/repository/repofiles -> services/repository/files

* Fix test

Co-authored-by: 6543 <6543@obermui.de>

services/repository/files/diff.go

@@ -0,0 +1,42 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package files
+
+import (
+	"strings"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/services/gitdiff"
+)
+
+// GetDiffPreview produces and returns diff result of a file which is not yet committed.
+func GetDiffPreview(repo *models.Repository, branch, treePath, content string) (*gitdiff.Diff, error) {
+	if branch == "" {
+		branch = repo.DefaultBranch
+	}
+	t, err := NewTemporaryUploadRepository(repo)
+	if err != nil {
+		return nil, err
+	}
+	defer t.Close()
+	if err := t.Clone(branch); err != nil {
+		return nil, err
+	}
+	if err := t.SetDefaultIndex(); err != nil {
+		return nil, err
+	}
+
+	// Add the object to the database
+	objectHash, err := t.HashObject(strings.NewReader(content))
+	if err != nil {
+		return nil, err
+	}
+
+	// Add the object to the index
+	if err := t.AddObjectToIndex("100644", objectHash, treePath); err != nil {
+		return nil, err
+	}
+	return t.DiffIndex()
+}