Example of declaring C.INPUT that uses an anonymous union inside, by just ignoring it.

input_windows.v

#include <windows.h>

[typedef]
struct C.MOUSEINPUT {
	dx          i64
	dy          i64
	mouseData   u32
	dwFlags     u32
	time        u32
	dwExtraInfo &u64 = unsafe { nil }
}

[typedef]
struct C.KEYBDINPUT {
	wVk         u16
	wScam       u16
	dwFlags     u32
	time        u32
	dwExtraInfo &u64 = unsafe { nil }
}

[typedef]
struct C.HARDWAREINPUT {
	uMsg    u32
	wParamL u16
	wParamH u16
}

[typedef]
struct C.INPUT {
	@type u32
	mi    C.MOUSEINPUT
	ki    C.KEYBDINPUT
	hi    C.HARDWAREINPUT
}

fn main() {
	a := unsafe { C.INPUT{} }
	unsafe { dump(a.mi.dx) }
}