Developing custom preprocessor plugins and callbacks
As flexible as other parts of LLVM and Clang, Clang's preprocessing framework also provides a way to insert custom logic via plugins. More specifically, it allows developers to write plugins to handle custom pragma directives (that is, allowing users to write something such as #pragma my_awesome_feature). In addition, the Preprocessor class also provides a more general way to define custom callback functions in reaction to arbitrary preprocessing events— such as when a macro is expanded or a #include directive is resolved, to name but a couple of examples. In this section, we're going to use a simple project that leverages both techniques to demonstrate their usage.
The project goal and preparation
Macros in C/C++ have always been notorious for poor design hygiene that could easily lead to coding errors when used without care. Have a look at the following code snippet for an example of this:
#define PRINT...