Packaging a mid-size (pure) CMake project

May 6, 2023

This article describes how to organize structure and write CMakeList files in middle scaled project. Repository is also available where a ROS wrapper uses the packaged CMake project.

Project description

You can find the project repo here (opens in a new tab).

File structure

I have three modules: obstacle_manager, target_manager, and wrapper. Each module has module_name.cc and module_name.h files.

my_package
├── CMakeLists.txt
├── include
│   └── my_package
├── src
│   ├── obstacle_manager
│   ├── target_manager
│   └── wrapper
└── test
    ├── obstacle_manager_test.cc
    ├── target_manager_test.cc
    └── wrapper_test.cc

Include graph

Each module is dependent on each other. wrapper is on the top of the hierarchy.

wrapper.h

#ifndef HEADER_WRAPPER
#define HEADER_WRAPPER
 
#include <string>
 
#include "my_package/obstacle_manager/obstacle_manager.h"
#include "my_package/target_manager/target_manager.h"
 
namespace my_package {
class Wrapper {
private:
  std::string name_{"Wrapper"};
  ObstacleManager obstacle_manager_;
  TargetManager target_manager_;
 
public:
  bool Plan() const;
};
} // namespace my_package
 
#endif /* HEADER_WRAPPER */

How to deliver this project

Each module is hardly used as a separate library. That is, I do not expect module obstacle_manager to be used as a separate library for other consumer library. I will compile all the sources and headers into a single library, as Cartographer (opens in a new tab) did.
I want each module of this project will include headers using prefix my_package as the below:
wrapper.h
```
...
#include "my_package/obstacle_manager/obstacle_manager.h"
#include "my_package/target_manager/target_manager.h"
...
```
Why? The consumer library (my_package_ros2 in the repo) will also include the headers such as below:
server.h (consumer)
```
#ifndef HEADER_SERVER
#define HEADER_SERVER
#include "my_package/wrapper/wrapper.h"
#include <rclcpp/rclcpp.hpp>
...
```
To have the consistency, my_package should have a folder my_package inside root directory!
The consumer library (my_package_ros2) should be able to find my headers and link against my library by only find_package and target_link_libraries:
consumer/CMakeLists.txt
```
find_package(my_package REQUIRED)
add_library(server src/server/server.cc)
ament_target_dependencies(server rclcpp)
target_include_directories(
  server PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
                $<INSTALL_INTERFACE:include>)
target_link_libraries(server my_package)
```
I prefer this way as Open3D did (opens in a new tab), rather than exporting variables such as XXX_INCLUDE_DIR and XXX_LIBRARIES. The latter requires extra files such as XXXConfig.cmake.in as this (opens in a new tab).

How to write `CMakeLists.txt`

This is all my CMakeLists.txt got: (quite concise, isn't it? 😊)

 
cmake_minimum_required(VERSION 3.5)
project(my_package)
 
find_package(Eigen3 REQUIRED)
find_package(PCL REQUIRED COMPONENTS common)
 
file(GLOB_RECURSE LIBRARY_HDRS "include/my_package/*.h")
file(GLOB_RECURSE LIBRARY_SRCS "src/*.cc")
file(GLOB TEST_SRCS "test/*.cc")
 
add_library(${PROJECT_NAME} STATIC ${LIBRARY_SRCS} ${LIBRARY_HDRS})
target_link_libraries(${PROJECT_NAME} ${PCL_LIBRARIES})
target_include_directories(
  ${PROJECT_NAME}
  PUBLIC ${EIGEN_INCLUDE_DIR} ${PCL_INCLUDE_DIRS}
         $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/include>
         $<INSTALL_INTERFACE:include>)
 
install(DIRECTORY ${CMAKE_SOURCE_DIR}/include DESTINATION .)
install(TARGETS ${PROJECT_NAME} EXPORT ${PROJECT_NAME}Config)
install(EXPORT ${PROJECT_NAME}Config DESTINATION share/${PROJECT_NAME}/cmake)
 
enable_testing()
find_package(GTest REQUIRED)
foreach(TEST_SRC ${TEST_SRCS})
  get_filename_component(TEST_NAME ${TEST_SRC} NAME_WE)
  add_executable(${TEST_NAME} ${TEST_SRC})
  target_link_libraries(${TEST_NAME} ${PROJECT_NAME} GTest::GTest GTest::Main)
  add_test(${TEST_NAME} ${TEST_NAME})
endforeach()

1. Single `CMakeLists.txt` in `my_package` root directory

I did not put CMakeLists.txt to each module folder. If I put it on individual folders, and add_library individually, every CMakeLists.txt should reflect dependency on other modules inside a package when target_link_libraries. For example,

obstacle_manager/CMakeList.txt

target_link_libraries(obstacle_manager PUBLIC ${PCL_LIBRARIES})
 
target_include_directories(
  obstacle_manager
  PUBLIC $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}>
  ...

target_manager/CMakeLists.txt

target_link_libraries(target_manager PUBLIC obstacle_manager)

I found that this is not an elegant way unless I have concluded the module dependency tree, and working with others who have a solid background in CMake.

2. GLOB to compile all sources and headers into a single library

...
file(GLOB_RECURSE LIBRARY_HDRS "include/my_package/*.h")
file(GLOB_RECURSE LIBRARY_SRCS "src/*.cc")
file(GLOB TEST_SRCS "test/*.cc")
 
add_library(${PROJECT_NAME} STATIC ${LIBRARY_SRCS} ${LIBRARY_HDRS})
...

I was motivated by that: Cartographer collects all source files (opens in a new tab) and compile them into a single library (opens in a new tab).

3. Carry all dependency (Eigen / PCL) for consumer

...
target_link_libraries(${PROJECT_NAME} ${PCL_LIBRARIES})
target_include_directories(
  ${PROJECT_NAME}
  PUBLIC ${EIGEN_INCLUDE_DIR} ${PCL_INCLUDE_DIRS}
         $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/include>
         $<INSTALL_INTERFACE:include>)
...

I want to the consumer of my_package to use directly external headers (pcl / eigen) and all the headers of my_package, by linking my_package. For the purpose, I put PUBLIC keyword. What happens if I change it into PRIVATE? First problem is test executables are not compiled which would included headers of my_package by linking my_pacakge (${PROJECT_NAME})!

CMakeLists.txt

  ...
  add_executable(${TEST_NAME} ${TEST_SRC})
  target_link_libraries(${TEST_NAME} ${PROJECT_NAME} GTest::GTest GTest::Main)
  ...

The compiler complains about headers of my_package not found:

/home/jbs/ros2_ws/src/simple-ros2-package/my_package/test/wrapper_test.cc:1:10: fatal error: my_package/wrapper/wrapper.h: No such file or directory
    1 | #include "my_package/wrapper/wrapper.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/wrapper_test.dir/build.make:63: CMakeFiles/wrapper_test.dir/test/wrapper_test.cc.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:82: CMakeFiles/wrapper_test.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
/home/jbs/ros2_ws/src/simple-ros2-package/my_package/test/target_manager_test.cc:1:10: fatal error: my_package/target_manager/target_manager.h: No such file or directory
    1 | #include "my_package/target_manager/target_manager.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/target_manager_test.dir/build.make:63: CMakeFiles/target_manager_test.dir/test/target_manager_test.cc.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:109: CMakeFiles/target_manager_test.dir/all] Error 2
/home/jbs/ros2_ws/src/simple-ros2-package/my_package/test/obstacle_manager_test.cc:1:10: fatal error: my_package/obstacle_manager/obstacle_manager.h: No such file or directory
    1 | #include "my_package/obstacle_manager/obstacle_manager.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

4. Install full include folder

...
install(DIRECTORY ${CMAKE_SOURCE_DIR}/include DESTINATION .)
...

Preliminary

${CMAKE_SOURCE_DIR}: directory where CMakeLists.txt is located. In this case, my_package folder.
${CMAKE_INSTALL_PREFIX}: root directory of installation when invoking install process. This is normally set by users or upstream CMakeLists.txt. When we do colcon build, it is /home/jbs/ros2_ws/install/my_package.

I already gathered all headers in my_package/include. This will be installed into ${CMAKE_INSTALL_PREFIX}.

Installation of include folder

Assuming my_package in installed in ~/ros2_ws/src/simple-ros2-package/my_package, ~/ros2_ws$ colcon build --packages-select my_package will install

~/ros2_ws/install$ tree my_package/include -L 3
my_package/include
└── my_package
    ├── obstacle_manager
    │   └── obstacle_manager.h
    ├── target_manager
    │   └── target_manager.h
    └── wrapper
        └── wrapper.h

5. Help headers of `my_package` can find each other even after Install

target_include_directories(
  ${PROJECT_NAME}
  PUBLIC ${EIGEN_INCLUDE_DIR} ${PCL_INCLUDE_DIRS}
         $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/include>
         $<INSTALL_INTERFACE:include>)

Preliminary

Official documents here (opens in a new tab).

In $<BUILD_INTERFACE:<blah-blah>>, blah-blah will be effective only when build process. When install process, it is treated as an empty. It applies same for $<INSTALL_INTERFACE:<blah-blah>>
It is very common to delete all the sources and build outputs after installation. (consider that sudo apt-get install some_package does not have all sources and build outputs.) Thus, you should understand that ${CMAKE_SOURCE_DIR}/include can be deleted, and the installed targets (in this case, installation_path/lib/my_package.a) cannot use ~/ros2_ws/src/simple-ros2-package/my_package/include. Read this thread (opens in a new tab).

When building `my_package`

When building the sources into library, all the header-search should refer $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/include> which is ~/ros2_ws/src/simple_ros2_package/include if I cloned the repo into ~/ros2_ws/src/

When installing `my_pacakge`

This process installed header files into ${CMAKE_INSTALL_PREFIX}/include. So we should make sure that: library my_package should refer the folder when searching for headers. That is, $<INSTALL_INTERFACE:include> is needed.

6. Install Config.cmake shipping library

...
install(TARGETS ${PROJECT_NAME} EXPORT ${PROJECT_NAME}Config)
install(EXPORT ${PROJECT_NAME}Config DESTINATION share/${PROJECT_NAME}/cmake)
...

Last part. we make ${PROJECT_NAME}Config file (or some object?) hold the property (opens in a new tab) of target ${PROJECT_NAME}. Then we install the file ${PROJECT_NAME}Config.cmake into ${CMAKE_INSTALL_PREFIX}/share/my_package/cmake so that other projects can find the target:

my_package_ros2/CMakeLists.txt

 
find_package(los_keeper REQUIRED)
 
add_library(los_server src/los_server/los_server.cc)
ament_target_dependencies(los_server rclcpp)
target_include_directories(
  los_server PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
                    $<INSTALL_INTERFACE:include>)
target_link_libraries(los_server los_keeper)

Packaging a mid-size (pure) CMake project

Project description

File structure

Include graph

How to deliver this project

How to write CMakeLists.txt

1. Single CMakeLists.txt in my_package root directory

2. GLOB to compile all sources and headers into a single library

3. Carry all dependency (Eigen / PCL) for consumer

4. Install full include folder

Preliminary

Installation of include folder

5. Help headers of my_package can find each other even after Install

Preliminary

When building my_package

When installing my_pacakge

6. Install Config.cmake shipping library

How to write `CMakeLists.txt`

1. Single `CMakeLists.txt` in `my_package` root directory

5. Help headers of `my_package` can find each other even after Install

When building `my_package`

When installing `my_pacakge`