Precondition not checked in ReactiveSequence

[mrjogo]

Describe the bug

In the following behavior tree, AlwaysRunning never succeeds even when _successIf="my_var != 0" evaluates to true. (AlwaysRunning is a StatefulActionNode that always returns RUNNING; Echo just prints the variable; full repro below):

<root BTCPP_format="4">
  <BehaviorTree ID="MainTree">
    <Sequence name="root">
      <Script code="my_var := 0; loop := 0"/>
      <ReactiveSequence>
        <Script code="loop += 1; my_var = (loop &gt;= 3) ? 42 : 0"/>
        <Echo message="{my_var}"/>
        <AlwaysRunning _successIf="my_var != 0"/>
      </ReactiveSequence>
    </Sequence>
  </BehaviorTree>
</root>

I would expect AlwaysRunning to return SUCCESS on the 3rd iteration, once my_var is set to 42, but the precondition never hits:

[1738296607.060]: root                      IDLE -> RUNNING
[1738296607.060]: Script                    IDLE -> SUCCESS
[1738296607.060]: ReactiveSequence          IDLE -> RUNNING
[1738296607.060]: Script                    IDLE -> SUCCESS
ECHO: 0
[1738296607.060]: Echo                      IDLE -> SUCCESS
[1738296607.060]: AlwaysRunning             IDLE -> RUNNING
[1738296607.060]: Script                    SUCCESS -> IDLE
[1738296607.060]: Echo                      SUCCESS -> IDLE
[1738296607.070]: Script                    IDLE -> SUCCESS
ECHO: 0
[1738296607.070]: Echo                      IDLE -> SUCCESS
[1738296607.070]: Script                    SUCCESS -> IDLE
[1738296607.070]: Echo                      SUCCESS -> IDLE
[1738296607.081]: Script                    IDLE -> SUCCESS
ECHO: 42
[1738296607.081]: Echo                      IDLE -> SUCCESS
[1738296607.081]: Script                    SUCCESS -> IDLE
[1738296607.081]: Echo                      SUCCESS -> IDLE
[1738296607.091]: Script                    IDLE -> SUCCESS
ECHO: 42
[1738296607.091]: Echo                      IDLE -> SUCCESS
[1738296607.091]: Script                    SUCCESS -> IDLE
[1738296607.091]: Echo                      SUCCESS -> IDLE
ad nauseam

How to Reproduce

#include <behaviortree_cpp/action_node.h>
#include <behaviortree_cpp/bt_factory.h>
#include <behaviortree_cpp/loggers/bt_cout_logger.h>

static const char* xml_text = R"(
 <root BTCPP_format="4">
 
   <BehaviorTree ID="MainTree">
     <Sequence name="root">
       <Script code="my_var := 0; loop := 0"/>
       <ReactiveSequence>
         <Script code="loop += 1; my_var = (loop &gt;= 3) ? 42 : 0"/>
         <Echo message="{my_var}"/>
         <AlwaysRunning _successIf="my_var != 0"/>
       </ReactiveSequence>
     </Sequence>
   </BehaviorTree>
 
 </root>
 )";

class AlwaysRunning : public BT::StatefulActionNode
{
public:
  AlwaysRunning(const std::string& name) : StatefulActionNode(name, {})
  {
  }

private:
  BT::NodeStatus onStart() override
  {
    return BT::NodeStatus::RUNNING;
  }
  BT::NodeStatus onRunning() override
  {
    return BT::NodeStatus::RUNNING;
  }
  void onHalted() override
  {
  }
};

class Echo : public BT::SyncActionNode
{
public:
  Echo(const std::string& name, const BT::NodeConfig& config) : BT::SyncActionNode(name, config)
  {
  }

  static BT::PortsList providedPorts()
  {
    return { BT::InputPort<std::string>("message") };
  }

  BT::NodeStatus tick() override
  {
    auto msg = getInput<int>("message");
    if (!msg)
    {
      throw BT::RuntimeError("missing required input [message]: ", msg.error());
    }

    std::cout << "ECHO: " << msg.value() << std::endl;
    return BT::NodeStatus::SUCCESS;
  }
};

int main()
{
  BT::BehaviorTreeFactory factory;
  factory.registerNodeType<AlwaysRunning>("AlwaysRunning");
  factory.registerNodeType<Echo>("Echo");

  auto tree = factory.createTreeFromText(xml_text);
  BT::StdCoutLogger logger(tree);
  tree.tickWhileRunning();

  return 0;
}

[mrjogo]

Here is a workaround to get the same behavior:

<root BTCPP_format="4">

  <BehaviorTree ID="MainTree">
    <Sequence name="root">
      <Script code="my_var := 0; loop := 0"/>
      <ReactiveSequence>
        <Script code="loop += 1; my_var = (loop &gt;= 3) ? 42 : 0"/>
        <Echo message="{my_var}"/>
        <Precondition else="RUNNING" if="my_var != 0">
          <AlwaysSuccess/>
        </Precondition>
      </ReactiveSequence>
    </Sequence>
  </BehaviorTree>

</root>