parsec doesn't generate a symbol when the target of a macro is a field within a union.

[dimenus]

This format is common within OpenGL loaders.

typedef unsigned int GLbitfield;
typedef void (*PFNGLCLEARPROC) (GLbitfield mask);

typedef void(*OpenGLProc)(void);
union OpenGLProcs {
    OpenGLProc ptr[1];
    struct {
        PFNGLCLEARPROC Clear;
    } gl;
};

extern union OpenGLProcs glProcs;
#define glClearUnion glProcs.gl.Clear
#define glClearPFN PFNGLCLEARPROC

zig output:

pub const GLbitfield = c_uint;
pub const PFNGLCLEARPROC = ?extern fn(GLbitfield);
pub const OpenGLProc = ?extern fn();
pub const glClearPFN = PFNGLCLEARPROC;