While programs/executables and libraries are sufficient in most cases, Arduino introduced the concept of Sketches which combines both into a single structure, usually even a single file.

For Arduino-CMake, Sketches are indeed a single file having the .ino or .pde extension. Sketches are popular among Arduino IDE users especially since Arduino-CMake doesn't have the ability to create those - It treats all source files as standard C++ files, usually having the .cpp extension. In other words, sketch support exists mostly for compatibility issues, so that users of Arduino IDE won't have a hard time switching platforms.

From the above, we can infer that Arduino Sketches can only be used, not created. Thus, we can only accept them as parameters to various generation functions, mostly the generate_arduino_firmware function.

So to include a sketch in your program, you should pass the sketch's parent directory path to the SKETCH parameter of the generation function.

For example, if you would like to include the built-in Blink sketch, you would do the following:

set(blink_SKETCH  ${ARDUINO_SDK_PATH}/examples/1.Basics/Blink) # Path to sketch directory
set(blink_BOARD uno)

generate_arduino_firmware(blink)

This will create a perfectly valid target using either the .ino or .pde file existing inside the given directory.