alerting: propagate alert validation issues to the user instead of just 'invalid alert data' message

pkg/api/dashboard.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path"
 
+	"github.com/grafana/grafana/pkg/services/alerting"
 	"github.com/grafana/grafana/pkg/services/dashboards"
 
 	"github.com/grafana/grafana/pkg/api/dtos"
@@ -251,8 +252,8 @@ func PostDashboard(c *m.ReqContext, cmd m.SaveDashboardCommand) Response {
 		return Error(403, err.Error(), err)
 	}
 
-	if err == m.ErrDashboardContainsInvalidAlertData {
-		return Error(500, "Invalid alert data. Cannot save dashboard", err)
+	if validationErr, ok := err.(alerting.ValidationError); ok {
+		return Error(422, validationErr.Error(), nil)
 	}
 
 	if err != nil {

pkg/api/dashboard_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/grafana/grafana/pkg/bus"
 	"github.com/grafana/grafana/pkg/components/simplejson"
 	m "github.com/grafana/grafana/pkg/models"
+	"github.com/grafana/grafana/pkg/services/alerting"
 	"github.com/grafana/grafana/pkg/services/dashboards"
 	"github.com/grafana/grafana/pkg/setting"
 
@@ -725,7 +726,7 @@ func TestDashboardApiEndpoint(t *testing.T) {
 				{SaveError: m.ErrDashboardVersionMismatch, ExpectedStatusCode: 412},
 				{SaveError: m.ErrDashboardTitleEmpty, ExpectedStatusCode: 400},
 				{SaveError: m.ErrDashboardFolderCannotHaveParent, ExpectedStatusCode: 400},
-				{SaveError: m.ErrDashboardContainsInvalidAlertData, ExpectedStatusCode: 500},
+				{SaveError: alerting.ValidationError{Reason: "Mu"}, ExpectedStatusCode: 422},
 				{SaveError: m.ErrDashboardFailedToUpdateAlertData, ExpectedStatusCode: 500},
 				{SaveError: m.ErrDashboardFailedGenerateUniqueUid, ExpectedStatusCode: 500},
 				{SaveError: m.ErrDashboardTypeMismatch, ExpectedStatusCode: 400},