Enable capability to build with pedantic flags.

[leander-dsouza]

Description

• Let's say we have a demo_pkg as follows:

  .
  ├── CMakeLists.txt
  ├── msg
  │   └── Demo.msg
  └── package.xml

  CMakeLists.txt:

  cmake_minimum_required(VERSION 3.8)
  project(demo_pkg)
  
  find_package(ament_cmake REQUIRED)
  find_package(rosidl_default_generators REQUIRED)
  
  rosidl_generate_interfaces(${PROJECT_NAME}
    "msg/Demo.msg"
  )
  
  ament_package()

  package.xml:

  <?xml version="1.0"?>
  <package format="3">
   <name>demo_pkg</name>
   <version>0.0.1</version>
   <description>Demo messages for testing -Wpedantic</description>
   <maintainer email="test@test.com">test</maintainer>
   <license>Apache-2.0</license>
  
   <buildtool_depend>ament_cmake</buildtool_depend>
   <buildtool_depend>rosidl_default_generators</buildtool_depend>
  
   <exec_depend>rosidl_default_runtime</exec_depend>
  
   <member_of_group>rosidl_interface_packages</member_of_group>
  </package>

  Demo.msg:

  string name

• Building with the -Wpedantic flag causes the following errors:

  $ colcon build --packages-select demo_pkg --cmake-args -DCMAKE_C_FLAGS="-Wpedantic -Werror"
  
  /ros2_ws/build/demo_msgs/rosidl_generator_py/demo_msgs/_demo_msgs_s.ep.rosidl_typesupport_c.c:59:5: warning: ISO C forbids conversion of function pointer to object pointer type [-Wpedantic]
    59 |     (void *)&demo_msgs__msg__demo__create_ros_message,
       |     ^
  /ros2_ws/build/demo_msgs/rosidl_generator_py/demo_msgs/_demo_msgs_s.ep.rosidl_typesupport_c.c:78:5: warning: ISO C forbids conversion of function pointer to object pointer type [-Wpedantic]
    78 |     (void *)&demo_msgs__msg__demo__destroy_ros_message,
       |     ^
  /ros2_ws/build/demo_msgs/rosidl_generator_py/demo_msgs/_demo_msgs_s.ep.rosidl_typesupport_c.c:97:5: warning: ISO C forbids conversion of function pointer to object pointer type [-Wpedantic]
    97 |     (void *)&demo_msgs__msg__demo__convert_from_py,
       |     ^
  /ros2_ws/build/demo_msgs/rosidl_generator_py/demo_msgs/_demo_msgs_s.ep.rosidl_typesupport_c.c:116:5: warning: ISO C forbids conversion of function pointer to object pointer type [-Wpedantic]
   116 |     (void *)&demo_msgs__msg__demo__convert_to_py,

• This is because -Wpedantic prevents casting a function pointer directly to void *.

• Therefore, instead of casting, the bytes of the function pointer are copied into a void * via memcpy through the added contribution.

• To test this fix, rosidl and rosidl_typesupport_fastrps needs to compiled from source.

Fixes # (issue)

• This enables the capability to build packages with the pedantic warning flag enabled.

Is this user-facing behavior change?

Yes, it is a user-facing behavior change, as now new packages can be passed with - --cmake-args -DCMAKE_C_FLAGS="-Wpedantic"

Did you use Generative AI?

• N/A

Additional Information

• N/A