[Build fails] rosapi: targets with same name

[ShivamPR21]

Hi! all,
I am facing some problems with the build of rosapi with colcon.

Command used

cd <rosbridge_suite_ws>
colcon build

Errors

--- stderr: rosapi
CMake Error at /home/shivam/ros2_galactic/install/ament_cmake_python/share/ament_cmake_python/cmake/ament_python_install_package.cmake:108 (add_custom_target):
  add_custom_target cannot create target "ament_cmake_python_symlink_rosapi"
  because another target with the same name already exists.  The existing
  target is a custom target created in source directory
  "/home/shivam/autoware/tmp/src/rosbridge_suite/rosapi".  See documentation
  for policy CMP0002 for more details.
Call Stack (most recent call first):
  /home/shivam/ros2_galactic/install/ament_cmake_python/share/ament_cmake_python/cmake/ament_python_install_package.cmake:39 (_ament_cmake_python_install_package)
  /home/shivam/ros2_galactic/install/rosidl_generator_py/share/rosidl_generator_py/cmake/rosidl_generator_py_generate_interfaces.cmake:124 (ament_python_install_package)
  /home/shivam/ros2_galactic/install/ament_cmake_core/share/ament_cmake_core/cmake/core/ament_execute_extensions.cmake:48 (include)
  /home/shivam/ros2_galactic/install/rosidl_cmake/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:292 (ament_execute_extensions)
  CMakeLists.txt:15 (rosidl_generate_interfaces)


---
Failed   <<< rosapi [8.45s, exited with code 1]

I am not able to intercept/interpret this problem, I have checked, and there isn't any other previous install for such packages.

Specifications

• ROS Version (echo $ROS_DISTRO): rolling/galactic
• OS Version (grep DISTRIB_CODENAME /etc/lsb-release): Ubuntu 20.04
• Rosbridge Version (roscat rosbridge_server package.xml | grep '<version>'): ros2
• Twisted Version (python -c 'import twisted; print twisted.version'): 18.9.0
• Installation type: Source (ROS & ROSbridge)

[ShivamPR21]

This is the problem with all new CMake versions, and according to the docs it has to be taken care of because it's going to be removed soon.
Even setting CMP0002 policy to OLD doesn't seem to work.

cmake_policy(SET CMP0002 OLD)

Also tried setting ALLOW_DUPLICATE_CUSTOM_TARGETS

set_property(GLOBAL PROPERTY ALLOW_DUPLICATE_CUSTOM_TARGETS 1)

This also not working, I think these properties have to be set by the core packages.

[jtbandes]

I also noticed this problem in rolling when we tried to add it to CI, so we'll need to resolve it in order to do this: #598 #602 I don't know why it would fail in rolling but it works for galactic/foxy in CI and on my machine.

cc @nuclearsandwich

[jtbandes]

This issue is caused by ros2/rosidl_python#131 / ros2/rosidl_python#141.