This directory contains C++ language bindings for the Mojo Public API.
A number of subdirectories provide wrappers for the lower-level C APIs (in subdirectories of the same name, under mojo/public/c/). Typically, these wrappers provide increased convenience and/or type-safety.
Other subdirectories provide support (static) libraries of various sorts. In this case, the organization is to have the public interface for the library defined in header files in the subdirectory itself and the implementation of the library at a lower level, under a lib (sub)subdirectory. A developer should be able to substitute their own implementation of any such support library, and expect other support libraries, which may depend on that library, to work properly.
The bindings/ subdirectory contains a support (static) library needed by the code generated by the bindings generator tool (in mojo/public/tools/bindings/), which translates Mojo IDL (.mojom) files into idiomatic C++ (among other languages).
The system/ subdirectory contains C++ wrappers (and some additional helpers) of the API defined in mojo/public/c/system/, which defines the basic, “core” API, especially used to communicate with Mojo services.
The test_support/ subdirectory contains C++ wrappers of the test-only API defined in mojo/public/c/test_support/. It is not meant for general use by Mojo applications.