Fix subtree reuse

samples/subsys/zephyrbt/subtree_reuse/CMakeLists.txt

@@ -0,0 +1,27 @@
+# Copyright (c) 2026 O.S. Systems Software LTDA.
+# Copyright (c) 2026 Freedom Veiculos Eletricos
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+include(${ZEPHYR_ZEPHYRBT_MODULE_DIR}/cmake/zephyrbt-from-behaviourtreecpp-xml.cmake)
+
+project(zephyrbt_subtree_reuse)
+
+zephyr_include_directories(
+	${CMAKE_CURRENT_SOURCE_DIR}/include
+)
+
+target_sources(app PRIVATE
+	src/main.c
+)
+
+zephyrbt_define_from_behaviourtreecpp_xml(app
+	models/subtree_reuse.xml
+	${CMAKE_BINARY_DIR}/include
+	${CMAKE_BINARY_DIR}/src
+	1024
+	0
+	yes
+)

samples/subsys/zephyrbt/subtree_reuse/README.rst

@@ -0,0 +1,75 @@
+.. Copyright (c) 2026 O.S. Systems Software LTDA.
+.. Copyright (c) 2026 Freedom Veiculos Eletricos
+.. SPDX-License-Identifier: Apache-2.0
+.. _zephyrbt_subtree_reuse:
+
+Zephyr Behaviour Tree - Subtree Reuse
+#####################################
+
+Overview
+********
+
+This sample validates the correct behavior tree traversal when a subtree is
+used multiple times. It reproduces the scenario from `GitHub issue #28`_ where
+incorrect indices caused nodes to be skipped during execution.
+
+The behavior tree structure is:
+
+.. code-block:: text
+
+   Sequence
+   ├── SubTree (btree_subtree) → sub
+   ├── A
+   ├── SubTree (btree_subtree) → sub
+   └── B
+
+The expected execution order is: sub → A → sub → B
+
+Prior to the fix, the second instance of the subtree had incorrect sibling
+indices, causing node A to be skipped entirely.
+
+.. _GitHub issue #28: https://github.com/OSSystems/ZephyrBT/issues/28
+
+Building and Running
+********************
+
+This application can be built and executed on ``qemu_cortex_m3`` as follows:
+
+.. code-block:: console
+
+   west build -p -b qemu_cortex_m3 samples/subsys/zephyrbt/subtree_reuse -t run
+
+To build for another board, change "qemu_cortex_m3" above to that board's name.
+
+Sample Output
+=============
+
+.. code-block:: console
+
+   *** Booting Zephyr OS ***
+   D: zephyrbt_action_sub_init stub function
+   D: zephyrbt_action_a_init stub function
+   D: zephyrbt_action_sub_init stub function
+   D: zephyrbt_action_b_init stub function
+   D: tick
+   D: eval sequence [control, 4]
+   D: Deep: 1
+   D: sequence [control, 4]
+   D: eval sub [action, 3]
+   D: Deep: 2
+   D: zephyrbt_action_sub stub function
+   D: eval a [action, 2]
+   D: Deep: 2
+   D: zephyrbt_action_a stub function
+   D: eval sub [action, 1]
+   D: Deep: 2
+   D: zephyrbt_action_sub stub function
+   D: eval b [action, 0]
+   D: Deep: 2
+   D: zephyrbt_action_b stub function
+
+The key verification points are:
+
+1. All four nodes (sub, a, sub, b) are evaluated in the correct order
+2. Node 'a' is not skipped (which was the bug symptom)
+3. Each subtree instance has a unique index (3 and 1)

samples/subsys/zephyrbt/subtree_reuse/include/zephyrbt_user.h

@@ -0,0 +1,11 @@
+/*
+ * Copyright (c) 2026 O.S. Systems Software LTDA.
+ * Copyright (c) 2026 Freedom Veiculos Eletricos
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYRBT_USER_H
+#define ZEPHYRBT_USER_H
+
+#endif /* ZEPHYRBT_USER_H */

samples/subsys/zephyrbt/subtree_reuse/models/subtree_reuse.xml

@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<root BTCPP_format="4"
+      main_tree_to_execute="btree_debug">
+  <BehaviorTree ID="btree_debug">
+    <Sequence>
+      <SubTree ID="btree_subtree"
+               _autoremap="true"/>
+      <A/>
+      <SubTree ID="btree_subtree"
+               _autoremap="true"/>
+      <B/>
+    </Sequence>
+  </BehaviorTree>
+
+  <BehaviorTree ID="btree_subtree">
+    <sub/>
+  </BehaviorTree>
+
+  <!-- Description of Node Models (used by Groot) -->
+  <TreeNodesModel>
+    <Action ID="A"
+            editable="true"/>
+    <Action ID="B"
+            editable="true"/>
+    <Action ID="sub"
+            editable="true"/>
+  </TreeNodesModel>
+
+</root>

samples/subsys/zephyrbt/subtree_reuse/prj.conf

@@ -0,0 +1,20 @@
+# Copyright (c) 2026 O.S. Systems Software LTDA.
+# Copyright (c) 2026 Freedom Veiculos Eletricos
+# SPDX-License-Identifier: Apache-2.0
+
+CONFIG_LOG=y
+CONFIG_LOG_MODE_MINIMAL=y
+
+CONFIG_ZEPHYR_BEHAVIOUR_TREE=y
+CONFIG_ZEPHYR_BEHAVIOUR_TREE_DYNAMIC=y
+CONFIG_ZEPHYR_BEHAVIOUR_TREE_NODE_INFO=y
+CONFIG_ZEPHYR_BEHAVIOUR_TREE_NODE_INIT=y
+CONFIG_ZEPHYR_BEHAVIOUR_TREE_NODE_CONTEXT=y
+CONFIG_ZEPHYR_BEHAVIOUR_TREE_LOG_LEVEL_DBG=y
+
+CONFIG_DYNAMIC_THREAD=y
+CONFIG_DYNAMIC_THREAD_POOL_SIZE=10
+CONFIG_THREAD_STACK_INFO=y
+
+CONFIG_KERNEL_MEM_POOL=y
+CONFIG_HEAP_MEM_POOL_SIZE=8192

samples/subsys/zephyrbt/subtree_reuse/sample.yaml

@@ -0,0 +1,37 @@
+# Copyright (c) 2026 O.S. Systems Software LTDA.
+# Copyright (c) 2026 Freedom Veiculos Eletricos
+# SPDX-License-Identifier: Apache-2.0
+
+sample:
+  name: Zephyr Behaviour Tree - Subtree Reuse (Issue #28)
+  description: |
+    This sample validates correct traversal when a subtree is used multiple
+    times in the same behavior tree. It reproduces the scenario from issue #28
+    where incorrect indices caused nodes to be skipped during execution.
+common:
+  tags: zephyrbt
+tests:
+  samples.zephyrbt.subtree_reuse:
+    platform_allow:
+      - qemu_cortex_m3
+      - nucleo_f767zi
+    harness: console
+    harness_config:
+      type: multi_line
+      regex:
+        - "D: tick"
+        - "D: eval sequence \\[control, 4\\]"
+        - "D: Deep: 1"
+        - "D: sequence \\[control, 4\\]"
+        - "D: eval sub \\[action, 3\\]"
+        - "D: Deep: 2"
+        - "D: zephyrbt_action_sub stub function"
+        - "D: eval a \\[action, 2\\]"
+        - "D: Deep: 2"
+        - "D: zephyrbt_action_a stub function"
+        - "D: eval sub \\[action, 1\\]"
+        - "D: Deep: 2"
+        - "D: zephyrbt_action_sub stub function"
+        - "D: eval b \\[action, 0\\]"
+        - "D: Deep: 2"
+        - "D: zephyrbt_action_b stub function"

samples/subsys/zephyrbt/subtree_reuse/src/main.c

@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) 2026 O.S. Systems Software LTDA.
+ * Copyright (c) 2026 Freedom Veiculos Eletricos
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/kernel.h>
+
+int main(void)
+{
+	return 0;
+}

scripts/generate-zephyrbt-from-behaviourtreecpp-xml

@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
-# Copyright (c) 2024-2025 O.S. Systems Software LTDA.
-# Copyright (c) 2024-2025 Freedom Veiculos Eletricos
+# Copyright (c) 2024-2026 O.S. Systems Software LTDA.
+# Copyright (c) 2024-2026 Freedom Veiculos Eletricos
 # SPDX-License-Identifier: Apache-2.0
 
 """
@@ -20,6 +20,7 @@ import struct
 
 from natsort import natsorted
 import xml.etree.ElementTree as ET
+import copy
 
 REPO_ROOT = Path(__file__).absolute().parents[1]
 HEADER = """/*
@@ -422,6 +423,34 @@ def addBlackboardVariables(idx_nodes_set, blackboard_set):
             index = loadBlackboardVariables(index, str(blackboard[0][1]), blackboard_set)
 
 
+def expand_subtrees(elem, root):
+    """
+    Recursively expand SubTree nodes by replacing them with deep copies
+    of their referenced tree content. This ensures each subtree instance
+    has unique element IDs when a subtree is used multiple times.
+    """
+    i = 0
+    while i < len(elem):
+        child = elem[i]
+        if child.tag == 'SubTree':
+            subtree_id = child.get('ID')
+            for tree in root.iter('BehaviorTree'):
+                if tree.attrib.get('ID') == subtree_id:
+                    # Create a deep copy of the subtree content
+                    subtree_content = copy.deepcopy(tree[0])
+                    # Remove the SubTree placeholder
+                    elem.remove(child)
+                    # Insert the expanded content
+                    elem.insert(i, subtree_content)
+                    # Recursively expand any nested subtrees in the copy
+                    expand_subtrees(subtree_content, root)
+                    break
+        else:
+            # Recursively process non-SubTree children
+            expand_subtrees(child, root)
+        i += 1
+
+
 def build_bt_set(builtin, root):
     main = root.attrib.get('main_tree_to_execute')
 
@@ -438,8 +467,14 @@ def build_bt_set(builtin, root):
         if elem.attrib.get('ID') != main:
             continue
 
-        parseNodes(builtin, idx_nodes_set, custom_set, 0, elem[0], root)
-        assemblyBT(builtin, idx_nodes_set, bt_set, 0, elem[0], elem[0], root)
+        # Deep copy and expand the main tree before processing.
+        # This ensures each subtree instance has unique element IDs
+        # when a subtree is used multiple times (fixes issue #28).
+        main_tree = copy.deepcopy(elem[0])
+        expand_subtrees(main_tree, root)
+
+        parseNodes(builtin, idx_nodes_set, custom_set, 0, main_tree, root)
+        assemblyBT(builtin, idx_nodes_set, bt_set, 0, main_tree, main_tree, root)
         break
 
     addBuiltinBlackboard(idx_nodes_set, blackboard_set, builtin)