（1）colcon build ERROR: Unknown CMake command "rosidl_get_typesupport_target"
demos： GitHub - ros2/demos
ROS2在demos执行colcon build的时候报错，
> colcon build
--- stderr: logging_demo CMake Error at CMakeLists.txt:34 (rosidl_get_typesupport_target): Unknown CMake command "rosidl_get_typesupport_target".
原因，
忘记添加版本信息，版本错误。
解决办法，
重新下载，
git clone -b galactic-devel https://github.com/ros2/demos.git或
git checkout galactic-devel
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（2）colcon build ERROR: Could not find a package configuration file provided by "ament_cmake" with any ...
--- stderr: rclpy CMake Error at CMakeLists.txt:26 (find_package): By not providing "Findament_cmake.cmake" in CMAKE_MODULE_PATH this project has asked CMake to find a package configuration file provided by "ament_cmake", but CMake did not find one.
Could not find a package configuration file provided by "ament_cmake" with any of the following names:
ament_cmakeConfig.cmake ament_cmake-config.cmake
Add the installation prefix of "ament_cmake" to CMAKE_PREFIX_PATH or set "ament_cmake_DIR" to a directory containing one of the above files. If "ament_cmake" provides a separate development package or SDK, be sure it has been installed.
原因，
忘记导入启动信息
解决办法，
call C:\opt\ros\galactic\x64\setup.bat
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