added an EXPORT arg to allow for exporting for other packages to use

dbc_gen_cpp/cmake/generate_dbc_cpp.cmake

@@ -1,57 +1,84 @@
 # SPDX-FileCopyrightText: 2026 Polymath Robotics, Inc.
 # SPDX-License-Identifier: Apache-2.0
-function(generate_dbc_cpp library_name)
+#
+# generate_dbc_cpp(<library_name> DBC <path/to/file.dbc>)
+#
+# Generates C/C++ CAN message types from a DBC file and builds them into a static
+# library named <library_name> (C++ namespace and C-symbol prefix also <library_name>,
+# headers at include/<library_name>/<library_name>.hpp).
+#
+# The library is ALWAYS installed and exported, so a downstream package that does
+# find_package(<this_package>) can link it as the imported target
+# <this_package>::<library_name>. Within the generating package it is also usable by
+# its plain local name.
+#
+# NOTE: this is a macro, not a function, on purpose. It calls ament_export_targets()
+# and ament_export_dependencies(), whose bookkeeping is stored in ordinary variables
+# in the current scope; ament_package() reads them from the package's top-level scope,
+# so they must not be trapped inside a function scope.
+macro(generate_dbc_cpp library_name)
   find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
-  set(one_value_args DBC)
-  cmake_parse_arguments(ARG "" "${one_value_args}" "" ${ARGN})
-  if(NOT ARG_DBC)
+  cmake_parse_arguments(_dbc_arg "" "DBC" "" ${ARGN})
+  if(NOT _dbc_arg_DBC)
     message(FATAL_ERROR "generate_dbc_cpp: Missing required keyword argument DBC")
   endif()
 
-  set(gen_basedir ${CMAKE_CURRENT_BINARY_DIR}/dbc_gen_cpp)
-  set(gen_dir ${gen_basedir}/${library_name})
+  set(_dbc_gen_basedir ${CMAKE_CURRENT_BINARY_DIR}/dbc_gen_cpp)
+  set(_dbc_gen_dir ${_dbc_gen_basedir}/${library_name})
 
-  set(generated_c ${gen_dir}/${library_name}.c)
-  set(generated_h ${gen_dir}/${library_name}.h)
-  set(generated_hpp ${gen_dir}/${library_name}.hpp)
-  set(generated_files ${generated_c} ${generated_h} ${generated_hpp})
+  set(_dbc_generated_c ${_dbc_gen_dir}/${library_name}.c)
+  set(_dbc_generated_h ${_dbc_gen_dir}/${library_name}.h)
+  set(_dbc_generated_hpp ${_dbc_gen_dir}/${library_name}.hpp)
 
-  # Kind of awkward, but makes the sources get regenerated if the generator tool changes, by depending on the generator sources.
-  # Finds the python module directory via Python3 import
+  # Kind of awkward, but makes the sources get regenerated if the generator tool
+  # changes, by depending on the generator sources. Finds the python module directory.
   execute_process(
     COMMAND ${Python3_EXECUTABLE} -c "import dbc_gen_cpp, os; print(os.path.dirname(dbc_gen_cpp.__file__))"
-    OUTPUT_VARIABLE GENERATOR_DIR
+    OUTPUT_VARIABLE _dbc_generator_dir
     OUTPUT_STRIP_TRAILING_WHITESPACE
   )
-  file(GLOB_RECURSE GENERATOR_SOURCES CONFIGURE_DEPENDS
-    "${GENERATOR_DIR}/*.py"
-    "${GENERATOR_DIR}/templates/*.j2"
+  file(GLOB_RECURSE _dbc_generator_sources CONFIGURE_DEPENDS
+    "${_dbc_generator_dir}/*.py"
+    "${_dbc_generator_dir}/templates/*.j2"
   )
 
-  # Generate the source files
+  # Generate the source files.
   add_custom_command(
-    OUTPUT ${generated_files}
-    COMMAND ${Python3_EXECUTABLE} -m dbc_gen_cpp ${ARG_DBC} -o ${gen_dir} -n ${library_name}
-    DEPENDS ${ARG_DBC} ${GENERATOR_SOURCES}
-    COMMENT "Generating C source from DBC ${ARG_DBC} with cantools"
+    OUTPUT ${_dbc_generated_c} ${_dbc_generated_h} ${_dbc_generated_hpp}
+    COMMAND ${Python3_EXECUTABLE} -m dbc_gen_cpp ${_dbc_arg_DBC} -o ${_dbc_gen_dir} -n ${library_name}
+    DEPENDS ${_dbc_arg_DBC} ${_dbc_generator_sources}
+    COMMENT "Generating C source from DBC ${_dbc_arg_DBC} with cantools"
     VERBATIM
   )
   add_custom_target(${library_name}_c_sources
-    DEPENDS ${generated_c} ${generated_h}
+    DEPENDS ${_dbc_generated_c} ${_dbc_generated_h}
   )
 
-  # Create the library target from generated sources
-  add_library(${library_name} STATIC ${generated_c})
+  # Create the library target from generated sources.
+  add_library(${library_name} STATIC ${_dbc_generated_c})
   add_dependencies(${library_name} ${library_name}_c_sources)
   target_link_libraries(${library_name} PUBLIC dbc_gen_cpp::dbc_gen_cpp)
   target_include_directories(${library_name}
-    PUBLIC ${gen_basedir}
+    PUBLIC
+      $<BUILD_INTERFACE:${_dbc_gen_basedir}>
+      $<INSTALL_INTERFACE:include>
   )
 
-  # Install the generated files to the install space, just in case they're included in public headers
+  # Install + export the target and its headers so other packages can link it as
+  # <this_package>::${library_name}.
   install(
-    FILES ${generated_h} ${generated_hpp}
+    TARGETS ${library_name}
+    EXPORT ${library_name}Targets
+    ARCHIVE DESTINATION lib
+    LIBRARY DESTINATION lib
+    RUNTIME DESTINATION bin
+    INCLUDES DESTINATION include
+  )
+  install(
+    FILES ${_dbc_generated_h} ${_dbc_generated_hpp}
     DESTINATION include/${library_name}
   )
-endfunction()
+  ament_export_targets(${library_name}Targets HAS_LIBRARY_TARGET)
+  ament_export_dependencies(dbc_gen_cpp)
+endmacro()

test_dbc_gen_cpp/CMakeLists.txt

@@ -48,6 +48,20 @@ if(BUILD_TESTING)
     ENV CATCH_CONFIG_CONSOLE_WIDTH=120
     WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
   )
+
+  # Verify that generate_dbc_cpp() installs the generated headers into the export
+  # location (include/<library_name>/) so downstream packages can consume them.
+  # This exercises the install/export path, which the compiled test above does not:
+  # that test links the libraries in-tree via their BUILD_INTERFACE include dirs.
+  ament_add_test(
+    test_dbc_exported_headers
+    GENERATE_RESULT_FOR_RETURN_CODE_ZERO
+    COMMAND ${CMAKE_COMMAND}
+      -DINSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
+      "-DLIBRARIES=fake_vehicle_can;fake_j1939_can"
+      -P ${CMAKE_CURRENT_SOURCE_DIR}/test/check_exported_headers.cmake
+    WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
+  )
 endif()
 
 ament_package()

test_dbc_gen_cpp/test/check_exported_headers.cmake

@@ -0,0 +1,31 @@
+# SPDX-FileCopyrightText: 2026 Polymath Robotics, Inc.
+# SPDX-License-Identifier: Apache-2.0
+#
+# Verifies that generate_dbc_cpp() exports the generated headers into the install
+# space so downstream packages can include them as <library_name>/<library_name>.hpp.
+#
+# Invoked with -DINSTALL_PREFIX=<prefix> -DLIBRARIES=<lib1;lib2>.
+
+if(NOT DEFINED INSTALL_PREFIX)
+  message(FATAL_ERROR "check_exported_headers: INSTALL_PREFIX not set")
+endif()
+if(NOT DEFINED LIBRARIES)
+  message(FATAL_ERROR "check_exported_headers: LIBRARIES not set")
+endif()
+
+set(_missing "")
+foreach(_lib IN LISTS LIBRARIES)
+  foreach(_ext h hpp)
+    set(_header "${INSTALL_PREFIX}/include/${_lib}/${_lib}.${_ext}")
+    if(EXISTS "${_header}")
+      message(STATUS "Found exported header: ${_header}")
+    else()
+      message(WARNING "Missing exported header: ${_header}")
+      list(APPEND _missing "${_header}")
+    endif()
+  endforeach()
+endforeach()
+
+if(_missing)
+  message(FATAL_ERROR "generate_dbc_cpp did not export the expected headers:\n  ${_missing}")
+endif()