I've been trying to build for desktop per the README and ran into this error:
/home/kevin/Projects/ros2_java_ws/build_isolated/action_msgs/rosidl_generator_c/action_msgs/msg/goal_info__struct.h:18:10: fatal error: unique_identifier_msgs/msg/uuid__struct.h: No such file or directory
18 | #include "unique_identifier_msgs/msg/uuid__struct.h"
Similar message for uuid_functions.h.
I found the actual file in the foxy installation as:
/opt/ros/foxy/include/unique_identifier_msgs/msg/detail/uuid__struct.h
/opt/ros/foxy/include/unique_identifier_msgs/msg/detail/uuid__functions.h
It appears someone has moved those files recently.