TreeObserver: don't throw when two nodes have the same path

fullPath() is the subtree prefix plus the node name, so two nodes with
the same explicit name in the same subtree, e.g.

  <Sequence>
    <AlwaysSuccess name="step"/>
    <AlwaysSuccess name="step"/>
  </Sequence>

share a path, and the TreeObserver constructor threw
"TreeObserver not built correctly. Report issue" for a valid tree.

Register every node by UID, and keep the first node in depth-first
order for a duplicated path in pathToUID() / getStatistics(path).
No API or ABI change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: facontidavide

include/behaviortree_cpp/loggers/bt_observer.h

@@ -50,7 +50,8 @@ class TreeObserver : public StatusChangeLogger
     Duration last_timestamp = {};
   };
 
-  // find the statistics of a node, based on its path
+  // find the statistics of a node, based on its path.
+  // If more nodes have the same path, this is the first one in depth-first order.
   const NodeStatistics& getStatistics(const std::string& path) const;
 
   // find the statistics of a node, based on its TreeNode::UID()

src/loggers/bt_observer.cpp

@@ -25,23 +25,17 @@ TreeObserver::TreeObserver(const BT::Tree& tree) : StatusChangeLogger(tree.rootN
       }
     }
 
-    if(_path_to_uid.count(node.fullPath()) != 0)
-    {
-      throw LogicError("TreeObserver not built correctly. Report issue");
-    }
-    _path_to_uid[node.fullPath()] = node.UID();
+    // Nodes with the same name in the same subtree share the same path:
+    // keep the first one, the others can be found by UID.
+    _path_to_uid.emplace(node.fullPath(), node.UID());
+    _uid_to_path[node.UID()] = node.fullPath();
+    _statistics[node.UID()] = {};
   };
 
   for(const auto& subtree : tree.subtrees)
   {
     recursiveStep(*subtree->nodes.front());
   }
-
-  for(const auto& [path, uid] : _path_to_uid)
-  {
-    _statistics[uid] = {};
-    _uid_to_path[uid] = path;
-  }
 }
 
 TreeObserver::~TreeObserver()

tests/gtest_loggers.cpp

@@ -14,6 +14,7 @@
 #include "behaviortree_cpp/loggers/bt_cout_logger.h"
 #include "behaviortree_cpp/loggers/bt_file_logger_v2.h"
 #include "behaviortree_cpp/loggers/bt_minitrace_logger.h"
+#include "behaviortree_cpp/loggers/bt_observer.h"
 #include "behaviortree_cpp/loggers/bt_sqlite_logger.h"
 
 #include <array>
@@ -620,3 +621,35 @@ TEST_F(LoggerTest, Logger_DisabledDuringExecution)
 
   ASSERT_TRUE(std::filesystem::exists(filepath));
 }
+
+TEST(TreeObserverTest, NodesWithTheSameName)
+{
+  // Two siblings with the same name have the same fullPath()
+  static const char* xml_text = R"(
+    <root BTCPP_format="4">
+      <BehaviorTree ID="MainTree">
+        <Sequence>
+          <AlwaysSuccess name="step"/>
+          <AlwaysSuccess name="step"/>
+        </Sequence>
+      </BehaviorTree>
+    </root>)";
+
+  BehaviorTreeFactory factory;
+  auto tree = factory.createTreeFromText(xml_text);
+
+  std::unique_ptr<TreeObserver> observer;
+  ASSERT_NO_THROW(observer = std::make_unique<TreeObserver>(tree));
+  ASSERT_EQ(tree.tickWhileRunning(), NodeStatus::SUCCESS);
+
+  const auto& nodes = tree.subtrees.front()->nodes;
+  ASSERT_EQ(nodes.size(), 3u);
+  EXPECT_EQ(observer->statistics().size(), 3u);
+  EXPECT_EQ(observer->uidToPath().size(), 3u);
+  for(const auto& node : nodes)
+  {
+    EXPECT_EQ(observer->uidToPath().at(node->UID()), node->fullPath());
+    EXPECT_EQ(observer->getStatistics(node->UID()).success_count, 1u);
+  }
+  EXPECT_EQ(observer->pathToUID().at("step"), nodes[1]->UID());
+}