bindgen is not aware of std::atomic

[nwoods-cimpress]

Input C/C++ Header

#include <atomic>

struct StructWithAtomics
{
	std::atomic<uint32_t>	m_x;
	uint32_t		m_a, m_b, m_c;
};

StructWithAtomics frob();

Bindgen Invocation

$ bindgen foo.h --allowlist-function=frob --no-layout-tests -- -x c++

Actual Results

/* automatically generated by rust-bindgen 0.59.1 */

#[repr(C)]
#[derive(Debug)]
pub struct std_atomic<_Tp> {
    pub _M_i: _Tp,
    pub _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<_Tp>>,
}
pub type std_atomic_value_type<_Tp> = _Tp;
pub type __uint32_t = ::std::os::raw::c_uint;
#[repr(C)]
#[derive(Debug)]
pub struct StructWithAtomics {
    pub m_x: std_atomic<u32>,
    pub m_a: u32,
    pub m_b: u32,
    pub m_c: u32,
}
extern "C" {
    #[link_name = "\u{1}_Z4frobv"]
    pub fn frob() -> StructWithAtomics;
}

With the System V AMD64 ABI (used on x86-64 pretty much everywhere except for Windows), this can actually create a calling convention mismatch because the bindings generated by Rust will expect StructWithAtomics to be returned in RAX/RDX, whereas the C++ code will actually use a hidden return parameter. This can be demonstrated here: https://godbolt.org/z/4ErhEjb1v

Expected Results

/* automatically generated by rust-bindgen 0.59.1 */

#[repr(C)]
#[derive(Debug)]
pub struct StructWithAtomics {
    pub m_x: std::sync::atomic::AtomicU32,
    pub m_a: u32,
    pub m_b: u32,
    pub m_c: u32,
}
extern "C" {
    #[link_name = "\u{1}_Z4frobv"]
    pub fn frob() -> StructWithAtomics;
}

[pvdrz]

duplicated of #2151