Different layout in C++'s composition and inheritance

[not-fl3]

Input C/C++ Header

class A {
  double X;
  int Y;
};

class B : public A {
  int Z;
};

Bindgen Invocation

bindgen test.hpp

Actual Results

ERROR:bindgen::codegen::struct_layout: Calculated wrong layout for B, too more 4 bytes

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct B {
    pub _base: A,
    pub Y: ::std::os::raw::c_int,
}
#[test]
fn bindgen_test_layout_B() {
    assert_eq!(
        ::std::mem::size_of::<B>(),
        16usize,
        concat!("Size of: ", stringify!(B))
    );

C++ demonstration:
https://gist.github.com/not-fl3/1e2d478b6c74230c313fb4e1716b937b
Size of class is different for composition and inheritance, also with different field's visibility.

Expected Results

Probably, correct represntation of c++ memory layout will be with embedded public fields from base class to derived class. Not actually sure about this.

[emilio]

Dupe of #380, thanks for the report though!

See there for details and a bit more analysis.