Why wouldn't the compiler access nuttx/drivers/ioexpander/pcf8575.h?
Access to internal driver files by applications is specifically
forbidden. This is part of the enforcement of the modular design to
assure that people do not do that kind of thing: Applications must
not have access to the internal implementation of drivers.
Never mind, I misread the ultra tiny fonts in the image.
include/nuttx/ holds the public interface to the driver (vs. the
internal private definitions for the driver in drivers/). Anything
under include/ should be include-able by your application.
Actually, the problem is very simple. This file does not exist.
#include <nuttx/drivers/ioexpander/pcf8575.h>
You probably wanted
#include <nuttx/ioexpander/pcf8575.h>
