Add a simple way to rename branch like gh (#15870)

- Update default branch if needed
- Update protected branch if needed
- Update all not merged pull request base branch name
- Rename git branch
- Record this rename work and auto redirect for old branch on ui

Signed-off-by: a1012112796 <1012112796@qq.com>
Co-authored-by: delvh <dev.lh@web.de>

integrations/rename_branch_test.go

@@ -0,0 +1,44 @@
+// Copyright 2021 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 integrations
+
+import (
+	"net/http"
+	"testing"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/models/db"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRenameBranch(t *testing.T) {
+	// get branch setting page
+	session := loginUser(t, "user2")
+	req := NewRequest(t, "GET", "/user2/repo1/settings/branches")
+	resp := session.MakeRequest(t, req, http.StatusOK)
+	htmlDoc := NewHTMLParser(t, resp.Body)
+
+	postData := map[string]string{
+		"_csrf": htmlDoc.GetCSRF(),
+		"from":  "master",
+		"to":    "main",
+	}
+	req = NewRequestWithValues(t, "POST", "/user2/repo1/settings/rename_branch", postData)
+	session.MakeRequest(t, req, http.StatusFound)
+
+	// check new branch link
+	req = NewRequestWithValues(t, "GET", "/user2/repo1/src/branch/main/README.md", postData)
+	session.MakeRequest(t, req, http.StatusOK)
+
+	// check old branch link
+	req = NewRequestWithValues(t, "GET", "/user2/repo1/src/branch/master/README.md", postData)
+	resp = session.MakeRequest(t, req, http.StatusFound)
+	location := resp.HeaderMap.Get("Location")
+	assert.Equal(t, "/user2/repo1/src/branch/main/README.md", location)
+
+	// check db
+	repo1 := db.AssertExistsAndLoadBean(t, &models.Repository{ID: 1}).(*models.Repository)
+	assert.Equal(t, "main", repo1.DefaultBranch)
+}