Get rules by id when editing branch protection rule (#22932)

When users rename an existing branch protection rule, a new rule with
the new name will be created and the old rule will still exist.

![image](https://user-images.githubusercontent.com/15528715/219276442-d3c001ad-e693-44ec-9ad2-b33f2666b49b.png)

---

![image](https://user-images.githubusercontent.com/15528715/219276478-547c3b93-b3f1-4292-a1ef-c1b7747fe1bb.png)

The reason is that the `SettingsProtectedBranchPost` function only get
branch protection rule by name before updating or creating a rule. When
the rule name changes, the function cannot find the existing rule so it
will create a new rule rather than update the existing rule. To fix the
bug, the function should get rule by id first.

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

options/locale/locale_en-US.ini

@@ -2152,6 +2152,7 @@ settings.choose_branch = Choose a branch…
 settings.no_protected_branch = There are no protected branches.
 settings.edit_protected_branch = Edit
 settings.protected_branch_required_rule_name = Required rule name
+settings.protected_branch_duplicate_rule_name = Duplicate rule name
 settings.protected_branch_required_approvals_min = Required approvals cannot be negative.
 settings.tags = Tags
 settings.tags.protection = Tag Protection

routers/web/repo/setting_protected_branch.go

@@ -166,11 +166,37 @@ func SettingsProtectedBranchPost(ctx *context.Context) {
 	}
 
 	var err error
+	if f.RuleID > 0 {
+		// If the RuleID isn't 0, it must be an edit operation. So we get rule by id.
+		protectBranch, err = git_model.GetProtectedBranchRuleByID(ctx, ctx.Repo.Repository.ID, f.RuleID)
+		if err != nil {
+			ctx.ServerError("GetProtectBranchOfRepoByID", err)
+			return
+		}
+		if protectBranch != nil && protectBranch.RuleName != f.RuleName {
+			// RuleName changed. We need to check if there is a rule with the same name.
+			// If a rule with the same name exists, an error should be returned.
+			sameNameProtectBranch, err := git_model.GetProtectedBranchRuleByName(ctx, ctx.Repo.Repository.ID, f.RuleName)
+			if err != nil {
+				ctx.ServerError("GetProtectBranchOfRepoByName", err)
+				return
+			}
+			if sameNameProtectBranch != nil {
+				ctx.Flash.Error(ctx.Tr("repo.settings.protected_branch_duplicate_rule_name"))
+				ctx.Redirect(fmt.Sprintf("%s/settings/branches/edit?rule_name=%s", ctx.Repo.RepoLink, protectBranch.RuleName))
+				return
+			}
+		}
+	} else {
+		// FIXME: If a new ProtectBranch has a duplicate RuleName, an error should be returned.
+		// Currently, if a new ProtectBranch with a duplicate RuleName is created, the existing ProtectBranch will be updated.
+		// But we cannot modify this logic now because many unit tests rely on it.
 		protectBranch, err = git_model.GetProtectedBranchRuleByName(ctx, ctx.Repo.Repository.ID, f.RuleName)
 		if err != nil {
 			ctx.ServerError("GetProtectBranchOfRepoByName", err)
 			return
 		}
+	}
 	if protectBranch == nil {
 		// No options found, create defaults.
 		protectBranch = &git_model.ProtectedBranch{

services/forms/repo_form.go

@@ -190,6 +190,7 @@ func (f *RepoSettingForm) Validate(req *http.Request, errs binding.Errors) bindi
 // ProtectBranchForm form for changing protected branch settings
 type ProtectBranchForm struct {
 	RuleName                      string `binding:"Required"`
+	RuleID                        int64
 	EnablePush                    string
 	WhitelistUsers                string
 	WhitelistTeams                string