Descripción del problema:
CMake Error at CMakeLists.txt:1:
Parse error. Expected a command name, got unquoted argument with text
"/opt/ros/melodic/share/catkin/cmake/toplevel.cmake".
-- Configuring incomplete, errors occurred!
Invoking "cmake" failed
Solución:
elimine el archivo CMakeLists.txt en src y vuelva a catkin_init_workspace