Fix failover problem by having weighted_target report TF

Author: zasweq

balancer/weightedtarget/weightedaggregator/aggregator.go

@@ -178,6 +178,12 @@ func (wbsa *Aggregator) ResumeStateUpdates() {
 	}
 }
 
+// NeedUpdateStateOnResume sets the UpdateStateOnResume bool to true, letting a
+// picker update be sent once ResumeStateUpdates is called.
+func (wbsa *Aggregator) NeedUpdateStateOnResume() {
+	wbsa.needUpdateStateOnResume = true
+}
+
 // UpdateState is called to report a balancer state change from sub-balancer.
 // It's usually called by the balancer group.
 //

balancer/weightedtarget/weightedtarget.go

@@ -143,6 +143,12 @@ func (b *weightedTargetBalancer) UpdateClientConnState(s balancer.ClientConnStat
 
 	b.targets = newConfig.Targets
 
+	// To send a TF state update in the case of a configuration with no targets
+	// passed in.
+	if len(b.targets) == 0 {
+		b.stateAggregator.NeedUpdateStateOnResume()
+	}
+
 	return nil
 }