Alerting: Improve validation of query and expressions on rule submit (#53258)

* Improve error messages of server-side expression 
* move validation of alert queries and a condition to eval package

pkg/services/ngalert/api/api_ruler.go

@@ -10,10 +10,10 @@ import (
 
 	"github.com/grafana/grafana/pkg/services/accesscontrol"
 	"github.com/grafana/grafana/pkg/services/dashboards"
-	"github.com/grafana/grafana/pkg/services/datasources"
 	"github.com/grafana/grafana/pkg/services/ngalert/provisioning"
 	"github.com/grafana/grafana/pkg/services/ngalert/store"
 	"github.com/grafana/grafana/pkg/services/quota"
+	"github.com/grafana/grafana/pkg/services/user"
 	"github.com/grafana/grafana/pkg/setting"
 
 	"github.com/prometheus/common/model"
@@ -28,16 +28,21 @@ import (
 	"github.com/grafana/grafana/pkg/util"
 )
 
+type ConditionValidator interface {
+	// Validate validates that the condition is correct. Returns nil if the condition is correct. Otherwise, error that describes the failure
+	Validate(ctx context.Context, user *user.SignedInUser, condition ngmodels.Condition) error
+}
+
 type RulerSrv struct {
-	xactManager     provisioning.TransactionManager
-	provenanceStore provisioning.ProvisioningStore
-	store           store.RuleStore
-	DatasourceCache datasources.CacheService
-	QuotaService    quota.Service
-	scheduleService schedule.ScheduleService
-	log             log.Logger
-	cfg             *setting.UnifiedAlertingSettings
-	ac              accesscontrol.AccessControl
+	xactManager        provisioning.TransactionManager
+	provenanceStore    provisioning.ProvisioningStore
+	store              store.RuleStore
+	QuotaService       quota.Service
+	scheduleService    schedule.ScheduleService
+	log                log.Logger
+	cfg                *setting.UnifiedAlertingSettings
+	ac                 accesscontrol.AccessControl
+	conditionValidator ConditionValidator
 }
 
 var (
@@ -302,7 +307,9 @@ func (srv RulerSrv) RoutePostNameRulesConfig(c *models.ReqContext, ruleGroupConf
 		return toNamespaceErrorResponse(err)
 	}
 
-	rules, err := validateRuleGroup(&ruleGroupConfig, c.SignedInUser.OrgID, namespace, conditionValidator(c, srv.DatasourceCache), srv.cfg)
+	rules, err := validateRuleGroup(&ruleGroupConfig, c.SignedInUser.OrgID, namespace, func(condition ngmodels.Condition) error {
+		return srv.conditionValidator.Validate(c.Req.Context(), c.SignedInUser, condition)
+	}, srv.cfg)
 	if err != nil {
 		return ErrResp(http.StatusBadRequest, err, "")
 	}