[BUG] Detect protected branch on branch rename

- If a branch cannot be renamed due to a protected branch rule, show
this error in the UI instead of throwing an internal server error.
- Add integration test (also simplify the existing one).
- Resolves #2751

options/locale/locale_en-US.ini

@@ -2513,6 +2513,7 @@ settings.lfs_pointers.inRepo=In Repo
 settings.lfs_pointers.exists=Exists in store
 settings.lfs_pointers.accessible=Accessible to User
 settings.lfs_pointers.associateAccessible=Associate accessible %d OIDs
+settings.rename_branch_failed_protected=Cannot rename branch %s because it is a protected branch.
 settings.rename_branch_failed_exist=Cannot rename branch because target branch %s exists.
 settings.rename_branch_failed_not_exist=Cannot rename branch %s because it does not exist.
 settings.rename_branch_success =Branch %s was successfully renamed to %s.

routers/web/repo/setting/protected_branch.go

@@ -4,6 +4,7 @@
 package setting
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -316,7 +317,12 @@ func RenameBranchPost(ctx *context.Context) {
 
 	msg, err := repository.RenameBranch(ctx, ctx.Repo.Repository, ctx.Doer, ctx.Repo.GitRepo, form.From, form.To)
 	if err != nil {
+		if errors.Is(err, git_model.ErrBranchIsProtected) {
+			ctx.Flash.Error(ctx.Tr("repo.settings.rename_branch_failed_protected", form.To))
+			ctx.Redirect(fmt.Sprintf("%s/branches", ctx.Repo.RepoLink))
+		} else {
 			ctx.ServerError("RenameBranch", err)
+		}
 		return
 	}
 

tests/integration/rename_branch_test.go

@@ -10,6 +10,7 @@ import (
 	git_model "code.gitea.io/gitea/models/git"
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unittest"
+	gitea_context "code.gitea.io/gitea/services/context"
 	"code.gitea.io/gitea/tests"
 
 	"github.com/stretchr/testify/assert"
@@ -18,33 +19,63 @@ import (
 func TestRenameBranch(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
 
-	unittest.AssertExistsAndLoadBean(t, &git_model.Branch{RepoID: 1, Name: "master"})
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+	unittest.AssertExistsAndLoadBean(t, &git_model.Branch{RepoID: repo.ID, Name: "master"})
 
 	// 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)
+	t.Run("Normal", func(t *testing.T) {
+		defer tests.PrintCurrentTest(t)()
 
-	postData := map[string]string{
-		"_csrf": htmlDoc.GetCSRF(),
+		req := NewRequestWithValues(t, "POST", "/user2/repo1/settings/rename_branch", map[string]string{
+			"_csrf": GetCSRF(t, session, "/user2/repo1/settings/branches"),
 			"from":  "master",
 			"to":    "main",
-	}
-	req = NewRequestWithValues(t, "POST", "/user2/repo1/settings/rename_branch", postData)
+		})
 		session.MakeRequest(t, req, http.StatusSeeOther)
 
 		// check new branch link
-	req = NewRequestWithValues(t, "GET", "/user2/repo1/src/branch/main/README.md", postData)
+		req = NewRequest(t, "GET", "/user2/repo1/src/branch/main/README.md")
 		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.StatusSeeOther)
+		req = NewRequest(t, "GET", "/user2/repo1/src/branch/master/README.md")
+		resp := session.MakeRequest(t, req, http.StatusSeeOther)
 		location := resp.Header().Get("Location")
 		assert.Equal(t, "/user2/repo1/src/branch/main/README.md", location)
 
 		// check db
 		repo1 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
 		assert.Equal(t, "main", repo1.DefaultBranch)
+	})
+
+	t.Run("Protected branch", func(t *testing.T) {
+		defer tests.PrintCurrentTest(t)()
+
+		// Add protected branch
+		req := NewRequestWithValues(t, "POST", "/user2/repo1/settings/branches/edit", map[string]string{
+			"_csrf":       GetCSRF(t, session, "/user2/repo1/settings/branches/edit"),
+			"rule_name":   "*",
+			"enable_push": "true",
+		})
+		session.MakeRequest(t, req, http.StatusSeeOther)
+
+		// Verify it was added.
+		unittest.AssertExistsIf(t, true, &git_model.ProtectedBranch{RuleName: "*", RepoID: repo.ID})
+
+		req = NewRequestWithValues(t, "POST", "/user2/repo1/settings/rename_branch", map[string]string{
+			"_csrf": GetCSRF(t, session, "/user2/repo1/settings/branches"),
+			"from":  "main",
+			"to":    "main2",
+		})
+		session.MakeRequest(t, req, http.StatusSeeOther)
+
+		flashCookie := session.GetCookie(gitea_context.CookieNameFlash)
+		assert.NotNil(t, flashCookie)
+		assert.EqualValues(t, "error%3DCannot%2Brename%2Bbranch%2Bmain2%2Bbecause%2Bit%2Bis%2Ba%2Bprotected%2Bbranch.", flashCookie.Value)
+
+		// Verify it didn't change.
+		repo1 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+		assert.Equal(t, "main", repo1.DefaultBranch)
+	})
 }