Fix broken ROS2 C++ build in CI due to ament

[lsk567]

Summary

Fixes the ROS2 C++ build integration by correcting how reactor-cpp exports its CMake configuration for the ament/colcon ecosystem. Also fixes a pre-existing bug in the C++ coverage collection CI step.

Problem

The ROS2 C++ test was failing because downstream packages (the generated LF ROS2 packages) could not find the reactor-cpp library via CMake's find_package(reactor-cpp REQUIRED).

Root cause: The reactor-cpp library was being built and installed correctly by colcon, but its CMake export configuration wasn't set up properly for the ament/colcon ecosystem. Specifically:

• The install(EXPORT ...) command was in lib/CMakeLists.txt, but ament requires it to be in the root CMakeLists.txt alongside ament_package() for proper integration
• The export lacked a NAMESPACE, which meant the generated CMake config file didn't create proper imported targets
• The LF code generator's find_package(reactor-cpp) couldn't locate the package because ament_auto_find_build_dependencies() doesn't automatically find packages installed in sibling directories of a colcon workspace

Fix

Three coordinated changes were needed:

A. reactor-cpp CMakeLists.txt (root):

if (REACTOR_CPP_USE_AMENT)
  # Moved from lib/CMakeLists.txt - must be here for ament compatibility
  install(EXPORT ${LIB_TARGET} DESTINATION share/${LIB_TARGET}/cmake NAMESPACE ${LIB_TARGET}::)
  ament_export_targets(${LIB_TARGET} HAS_LIBRARY_TARGET)
  ament_export_include_directories(include)
  ament_export_libraries(${LIB_TARGET})
  ament_package()
endif()

B. reactor-cpp lib/CMakeLists.txt:

• Removed the install(EXPORT ...) call (moved to root)

C. CppRos2PackageGenerator.kt (LF code generator):

// Added HINTS to find reactor-cpp in the colcon workspace install directory
find_package(reactor-cpp REQUIRED HINTS ${CMAKE_INSTALL_PREFIX}/../reactor-cpp/share/reactor-cpp/cmake)

// Changed to use namespaced target
target_link_libraries(${LF_MAIN_TARGET} reactor-cpp::reactor-cpp)

The key insight was that ament's build system requires the export installation and ament_package() to be in the same CMakeLists.txt file, and using namespaced targets (reactor-cpp::reactor-cpp) ensures proper linkage through CMake's imported target mechanism.

Additional Fix: C++ Coverage Collection

Fixed a pre-existing bug in the CI workflow where the coverage extraction step was looking for the wrong directory path:

• Was: test/Cpp/src-gen/reactor-cpp-default/*
• Now: test/Cpp/src-gen/reactor-cpp/*

Test plan

• ROS2 C++ integration tests pass in CI
• Regular C++ integration tests pass in CI
• C++ coverage collection works correctly

🤖 Generated with Claude Code

[edwardalee]

Wow, this was a complicated one. Thanks for fixing!