Alerting: Allow rules with same title across folders (#35270)

* Alerting: Allow rules with same title across folders

* Add test

pkg/services/ngalert/models/alert_rule.go

@@ -17,6 +17,8 @@ var (
 	ErrRuleGroupNamespaceNotFound = errors.New("rule group not found under this namespace")
 	// ErrAlertRuleFailedValidation
 	ErrAlertRuleFailedValidation = errors.New("invalid alert rule")
+	// ErrAlertRuleUniqueConstraintViolation
+	ErrAlertRuleUniqueConstraintViolation = errors.New("a conflicting alert rule is found: rule title under the same organisation and folder should be unique")
 )
 
 type NoDataState string

pkg/services/ngalert/store/alert_rule.go

@@ -522,6 +522,9 @@ func (st DBstore) UpdateRuleGroup(cmd UpdateRuleGroupCmd) error {
 		}
 
 		if err := st.UpsertAlertRules(upsertRules); err != nil {
+			if st.SQLStore.Dialect.IsUniqueConstraintViolation(err) {
+				return ngmodels.ErrAlertRuleUniqueConstraintViolation
+			}
 			return err
 		}