Alerting: Fix rule API to accept 0 duration of field For (#50992)

* make 'for' pointer to distinguish between missing field and 0
* set 'for' to -1 if the value is missing but not allow negative in the request + path -1 with the value from original rule
* update store validation to not allow negative 'for'
* update usages to use pointer

pkg/services/ngalert/api/api_ruler.go

@@ -484,8 +484,9 @@ func toGettableExtendedRuleNode(r ngmodels.AlertRule, namespaceID int64, provena
 			Provenance:      provenance,
 		},
 	}
+	forDuration := model.Duration(r.For)
 	gettableExtendedRuleNode.ApiRuleNode = &apimodels.ApiRuleNode{
-		For:         model.Duration(r.For),
+		For:         &forDuration,
 		Annotations: r.Annotations,
 		Labels:      r.Labels,
 	}

pkg/services/ngalert/api/api_ruler_validation.go

@@ -110,8 +110,13 @@ func validateRuleNode(
 		ExecErrState:    errorState,
 	}
 
+	var err error
+	newAlertRule.For, err = validateForInterval(ruleNode)
+	if err != nil {
+		return nil, err
+	}
+
 	if ruleNode.ApiRuleNode != nil {
-		newAlertRule.For = time.Duration(ruleNode.ApiRuleNode.For)
 		newAlertRule.Annotations = ruleNode.ApiRuleNode.Annotations
 		newAlertRule.Labels = ruleNode.ApiRuleNode.Labels
 
@@ -131,10 +136,24 @@ func validateRuleNode(
 			newAlertRule.PanelID = &panelIDValue
 		}
 	}
-
 	return &newAlertRule, nil
 }
 
+// validateForInterval validates ApiRuleNode.For and converts it to time.Duration. If the field is not specified returns 0 if GrafanaManagedAlert.UID is empty and -1 if it is not.
+func validateForInterval(ruleNode *apimodels.PostableExtendedRuleNode) (time.Duration, error) {
+	if ruleNode.ApiRuleNode == nil || ruleNode.ApiRuleNode.For == nil {
+		if ruleNode.GrafanaManagedAlert.UID != "" {
+			return -1, nil // will be patched later with the real value of the current version of the rule
+		}
+		return 0, nil // if it's a new rule, use the 0 as the default
+	}
+	duration := time.Duration(*ruleNode.ApiRuleNode.For)
+	if duration < 0 {
+		return 0, fmt.Errorf("field `for` cannot be negative [%v]. 0 or any positive duration are allowed", *ruleNode.ApiRuleNode.For)
+	}
+	return duration, nil
+}
+
 // validateRuleGroup validates API model (definitions.PostableRuleGroupConfig) and converts it to a collection of models.AlertRule.
 // Returns a slice that contains all rules described by API model or error if either group specification or an alert definition is not valid.
 func validateRuleGroup(

pkg/services/ngalert/api/api_ruler_validation_test.go

@@ -42,9 +42,10 @@ func config(t *testing.T) *setting.UnifiedAlertingSettings {
 }
 
 func validRule() apimodels.PostableExtendedRuleNode {
+	forDuration := model.Duration(rand.Int63n(1000))
 	return apimodels.PostableExtendedRuleNode{
 		ApiRuleNode: &apimodels.ApiRuleNode{
-			For: model.Duration(rand.Int63n(1000)),
+			For: &forDuration,
 			Labels: map[string]string{
 				"test-label": "data",
 			},
@@ -240,7 +241,7 @@ func TestValidateRuleNode_NoUID(t *testing.T) {
 				require.Equal(t, name, alert.RuleGroup)
 				require.Equal(t, models.NoDataState(api.GrafanaManagedAlert.NoDataState), alert.NoDataState)
 				require.Equal(t, models.ExecutionErrorState(api.GrafanaManagedAlert.ExecErrState), alert.ExecErrState)
-				require.Equal(t, time.Duration(api.ApiRuleNode.For), alert.For)
+				require.Equal(t, time.Duration(*api.ApiRuleNode.For), alert.For)
 				require.Equal(t, api.ApiRuleNode.Annotations, alert.Annotations)
 				require.Equal(t, api.ApiRuleNode.Labels, alert.Labels)
 			},

pkg/services/ngalert/api/tooling/definitions/cortex-ruler.go

@@ -257,7 +257,7 @@ type ApiRuleNode struct {
 	Record      string            `yaml:"record,omitempty" json:"record,omitempty"`
 	Alert       string            `yaml:"alert,omitempty" json:"alert,omitempty"`
 	Expr        string            `yaml:"expr" json:"expr"`
-	For         model.Duration    `yaml:"for,omitempty" json:"for,omitempty"`
+	For         *model.Duration   `yaml:"for,omitempty" json:"for,omitempty"`
 	Labels      map[string]string `yaml:"labels,omitempty" json:"labels,omitempty"`
 	Annotations map[string]string `yaml:"annotations,omitempty" json:"annotations,omitempty"`
 }

pkg/services/ngalert/api/tooling/definitions/cortex-ruler_test.go

@@ -50,7 +50,7 @@ func Test_Rule_Marshaling(t *testing.T) {
 			desc: "grafana with for, annotation and label properties",
 			input: PostableExtendedRuleNode{
 				ApiRuleNode: &ApiRuleNode{
-					For:         dur,
+					For:         &dur,
 					Annotations: map[string]string{"foo": "bar"},
 					Labels:      map[string]string{"label1": "val1"}},
 				GrafanaManagedAlert: &PostableGrafanaRule{},
@@ -136,7 +136,7 @@ func Test_Rule_Group_Marshaling(t *testing.T) {
 				Rules: []PostableExtendedRuleNode{
 					{
 						ApiRuleNode: &ApiRuleNode{
-							For:         dur,
+							For:         &dur,
 							Annotations: map[string]string{"foo": "bar"},
 							Labels:      map[string]string{"label1": "val1"},
 						},