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Detect recursive subtree cycles at parse time (fixes #979) #1085

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Merged
facontidavide merged 2 commits into from
Feb 1, 2026
+96 −9
Merged

Detect recursive subtree cycles at parse time (fixes #979) #1085

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b4e217e
Detect recursive subtree cycles at parse time (fixes #979)
facontidavide Feb 1, 2026
1d11a40
Pass ancestors set by reference instead of by value
facontidavide Feb 1, 2026
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25 changes: 16 additions & 9 deletions src/xml_parsing.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
#include <string>
#include <tuple>
#include <typeindex>
#include <unordered_set>

#if defined(_MSVC_LANG) && !defined(__clang__)
#define __bt_cplusplus (_MSC_VER == 1900 ? 201103L : _MSVC_LANG)
Expand Down Expand Up @@ -196,7 +197,8 @@ struct XMLParser::PImpl
void recursivelyCreateSubtree(const std::string& tree_ID, const std::string& tree_path,
const std::string& prefix_path, Tree& output_tree,
Blackboard::Ptr blackboard,
const TreeNode::Ptr& root_node);
const TreeNode::Ptr& root_node,
std::unordered_set<std::string>& ancestors);

void getPortsRecursively(const XMLElement* element,
std::vector<std::string>& output_ports);
Expand Down Expand Up @@ -703,8 +705,9 @@ Tree XMLParser::instantiateTree(const Blackboard::Ptr& root_blackboard,
"root_blackboard");
}

std::unordered_set<std::string> ancestors;
_p->recursivelyCreateSubtree(main_tree_ID, {}, {}, output_tree, root_blackboard,
TreeNode::Ptr());
TreeNode::Ptr(), ancestors);
output_tree.initialize();
return output_tree;
}
Expand Down Expand Up @@ -1000,13 +1003,16 @@ TreeNode::Ptr XMLParser::PImpl::createNodeFromXML(const XMLElement* element,
return new_node;
}

void BT::XMLParser::PImpl::recursivelyCreateSubtree(const std::string& tree_ID,
const std::string& tree_path,
const std::string& prefix_path,
Tree& output_tree,
Blackboard::Ptr blackboard,
const TreeNode::Ptr& root_node)
void BT::XMLParser::PImpl::recursivelyCreateSubtree(
const std::string& tree_ID, const std::string& tree_path,
const std::string& prefix_path, Tree& output_tree, Blackboard::Ptr blackboard,
const TreeNode::Ptr& root_node, std::unordered_set<std::string>& ancestors)
{
if(!ancestors.insert(tree_ID).second)
{
throw RuntimeError("Recursive behavior tree cycle detected: tree '", tree_ID,
"' references itself (directly or indirectly)");
}
std::function<void(const TreeNode::Ptr&, Tree::Subtree::Ptr, std::string,
const XMLElement*)>
recursiveStep;
Expand Down Expand Up @@ -1135,7 +1141,7 @@ void BT::XMLParser::PImpl::recursivelyCreateSubtree(const std::string& tree_ID,
recursivelyCreateSubtree(subtree_ID,
subtree_path, // name
subtree_path + "/", //prefix
output_tree, new_bb, node);
output_tree, new_bb, node, ancestors);
}
};

Expand All @@ -1157,6 +1163,7 @@ void BT::XMLParser::PImpl::recursivelyCreateSubtree(const std::string& tree_ID,
output_tree.subtrees.push_back(new_tree);

recursiveStep(root_node, new_tree, prefix_path, root_element);
ancestors.erase(tree_ID);
}

void XMLParser::PImpl::getPortsRecursively(const XMLElement* element,
Expand Down
80 changes: 80 additions & 0 deletions tests/gtest_subtree.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -732,6 +732,86 @@ TEST(SubTree, SubtreeNameNotRegistered)
ASSERT_ANY_THROW(factory.registerBehaviorTreeFromText(xml_text));
}

TEST(SubTree, RecursiveSubtree)
{
// clang-format off

static const char* xml_text = R"(
<root BTCPP_format="4" >
<BehaviorTree ID="MainTree">
<Sequence name="root">
<AlwaysSuccess/>
<SubTree ID="MainTree" />
</Sequence>
</BehaviorTree>
</root>
)";

// clang-format on
BehaviorTreeFactory factory;

ASSERT_ANY_THROW(auto tree = factory.createTreeFromText(xml_text));
}

TEST(SubTree, RecursiveCycle)
{
// clang-format off

static const char* xml_text = R"(
<root BTCPP_format="4" main_tree_to_execute="MainTree">
<BehaviorTree ID="MainTree">
<Sequence name="root">
<AlwaysSuccess/>
<SubTree ID="TreeA" />
</Sequence>
</BehaviorTree>
<BehaviorTree ID="TreeA">
<Sequence name="root">
<AlwaysSuccess/>
<SubTree ID="TreeB" />
</Sequence>
</BehaviorTree>
<BehaviorTree ID="TreeB">
<Sequence name="root">
<AlwaysSuccess/>
<SubTree ID="MainTree" />
</Sequence>
</BehaviorTree>
</root>
)";

// clang-format on
BehaviorTreeFactory factory;

ASSERT_ANY_THROW(auto tree = factory.createTreeFromText(xml_text));
}

TEST(SubTree, SubstringTreeIDsAreNotRecursive)
{
// Verify that tree IDs which are substrings of each other do NOT
// incorrectly trigger the recursive cycle detection.
// clang-format off

static const char* xml_text = R"(
<root BTCPP_format="4" main_tree_to_execute="Tree">
<BehaviorTree ID="Tree">
<SubTree ID="TreeABC" />
</BehaviorTree>
<BehaviorTree ID="TreeABC">
<AlwaysSuccess/>
</BehaviorTree>
</root>
)";

// clang-format on
BehaviorTreeFactory factory;

ASSERT_NO_THROW(auto tree = factory.createTreeFromText(xml_text));
}

// Test for Groot2 issue #56: duplicate _fullpath when multiple subtrees have the same name
// https://github.com/BehaviorTree/Groot2/issues/56
//
Expand Down
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