alerting: support `for` on execution errors and notdata

pkg/services/alerting/eval_context.go

@@ -118,21 +118,13 @@ func (c *EvalContext) GetRuleUrl() (string, error) {
 	return fmt.Sprintf(urlFormat, m.GetFullDashboardUrl(ref.Uid, ref.Slug), c.Rule.PanelId, c.Rule.OrgId), nil
 }
 
+// GetNewState returns the new state from the alert rule evaluation
 func (c *EvalContext) GetNewState() m.AlertStateType {
-	if c.Error != nil {
-		c.log.Error("Alert Rule Result Error",
-			"ruleId", c.Rule.Id,
-			"name", c.Rule.Name,
-			"error", c.Error,
-			"changing state to", c.Rule.ExecutionErrorState.ToAlertState())
-
-		if c.Rule.ExecutionErrorState == m.ExecutionErrorKeepState {
-			return c.PrevAlertState
-		}
-		return c.Rule.ExecutionErrorState.ToAlertState()
+	ns := getNewStateInternal(c)
+	if ns != m.AlertStateAlerting || c.Rule.For == 0 {
+		return ns
 	}
 
-	if c.Firing && c.Rule.For != 0 {
 	since := time.Now().Sub(c.Rule.LastStateChange)
 	if since > c.Rule.For {
 		return m.AlertStateAlerting
@@ -143,6 +135,20 @@ func (c *EvalContext) GetNewState() m.AlertStateType {
 	}
 
 	return m.AlertStatePending
+}
+
+func getNewStateInternal(c *EvalContext) m.AlertStateType {
+	if c.Error != nil {
+		c.log.Error("Alert Rule Result Error",
+			"ruleId", c.Rule.Id,
+			"name", c.Rule.Name,
+			"error", c.Error,
+			"changing state to", c.Rule.ExecutionErrorState.ToAlertState())
+
+		if c.Rule.ExecutionErrorState == m.ExecutionErrorKeepState {
+			return c.PrevAlertState
+		}
+		return c.Rule.ExecutionErrorState.ToAlertState()
 	}
 
 	if c.Firing {