Just my 2 cents:

The _external_ way of doing introspection (a parser like yours) is generally very limiting in real life, as you will have to interpret all the preprocessor directives that your code follows.

e.g.:

    struct Foo {
    #ifdef ...
        int a;
    #else
        float b;
    #endif
    }

Not only will you have to feed your parser the exact same inputs as your build system, but also some directives are built-in the compiler and may be hard to replicate.

The easiest way to do introspection is _intrusive_, even though it pollute the code a bit.

e.g.

    DECL_STRUCT(Foo)
    {
        DECL_ATTR(int, a);
    }
    END_DECL_STRUCT

A long time ago, Qt had a sort of hybrid intrusive parser like this (MOC?), that was 20y ago though things may have changed.

Regarding pre-processing, I feed the result of `clang -E` to the code-generator. Since I use a unity build (single translation unit), it works out fine. In fact, the parser treats pre-processor directives as comments (to work around #line and `-dD`, etc.)

Regarding external and intrusive, I used to do it in the intrusive way but found it too limiting. Here, I not only generate code but can also (potentially) add whole new extensions to the language. This was the reason I wrote a new parser instead of just using libclang's JSON AST dump. Well, that and the fact that libclang is a multi-MB dependency while my parser is ~3000 lines of C code.