I am cross-compiling ROS2 Eloquent for a FreeBSD-based research system. My cmake toolchain file is here.

When building rosidl_typesupport_fastrtps_cpp (and also rmw_fastrtps), I get the following error:

--- stderr: rosidl_typesupport_fastrtps_cpp                                                                                                        
CMake Error at /usr/local/share/cmake-3.17/Modules/FindPackageHandleStandardArgs.cmake:164 (message):
  Could NOT find FastRTPS (missing: FastRTPS_INCLUDE_DIR FastRTPS_LIBRARIES)
Call Stack (most recent call first):
  /usr/local/share/cmake-3.17/Modules/FindPackageHandleStandardArgs.cmake:445 (_FPHSA_FAILURE_MESSAGE)
  /home/broomstick/cheri/ros2_eloquent_min/install/fastrtps_cmake_module/share/fastrtps_cmake_module/cmake/Modules/FindFastRTPS.cmake:106 (find_package_handle_standard_args)
  CMakeLists.txt:27 (find_package)
---
Failed   <<< rosidl_typesupport_fastrtps_cpp    [ Exited with code 1 ]

The CMakeList.txt file for rosidl_typesupport_fastrtps_cpp includes the following lines:

find_package(fastrtps REQUIRED CONFIG)
find_package(FastRTPS REQUIRED MODULE)

It's the second of these that appears to find FindFastRTPS.cmake here:

/home/broomstick/cheri/ros2_eloquent_min/install/fastrtps_cmake_module/share/fastrtps_cmake_module/cmake/Modules/FindFastRTPS.cmake

FindFastRTPS.cmake has the following lines:

find_path(FastRTPS_INCLUDE_DIR
  NAMES fastrtps/)

find_package(fastcdr REQUIRED CONFIG)
find_package(fastrtps REQUIRED CONFIG)

I've instrumented the CMakeList.txt and FindFastRTPS.cmake files to print all cached variables to the log, and the latter does not find anything to assign to FastRTPS_INCLUDE_DIR.

I've similarly instrumented my natively built ROS2 Eloquent distribution. Those cmake files find the include directory in <prefix>/install/fastrtps.

I added -DCMAKE_PREFIX_PATH=<prefix>/install/fastrtps. I tried the same for CMAKE_INCLUDE_PATH. Neither helped.

My build invocation is the following:

colcon build \
    --packages-skip-build-finished \
    --cmake-args \
        -DCMAKE_TOOLCHAIN_FILE=/home/broomstick/cheri/ros2_eloquent_min/CrossToolchain.cmake \
        -DBUILD_TESTING=NO \
        -DTHIRDPARTY=ON \
        -DCMAKE_PREFIX_PATH="/home/broomstick/cheri/ros2_eloquent_min/install" \
    --no-warn-unused-cli

Admittedly, I've removed several packages from the vanilla Eloquent distribution, but fastrtps seems to build just fine and there is a <prefix>/install/fastrtps which has the same cmake files as my native build.

This seems like it should be straightforward, but I didn't find any similar issues on ROS answers. The closest had similar answers, but they were building packages in their own workspaces after successfully building ROS2 (dashing, in this case).