bindgen doesn't handle mozilla::AlignedStorage correctly

Input C/C++ Header

typedef unsigned long long uint64_t;

template<typename T>
struct AlignedStorage2 {
  union U {
    char mBytes[sizeof(T)];
    uint64_t mDummy;
  } u;
};

struct Foo {
  uint64_t a;
  uint64_t b;
};

class Bar {
  AlignedStorage2<Foo> m;
};

Bindgen Invocation

$ bindgen input.hpp

Actual Results

#[repr(C)]
pub struct __BindgenUnionField<T>(::std::marker::PhantomData<T>);
impl <T> __BindgenUnionField<T> {
    #[inline]
    pub fn new() -> Self { __BindgenUnionField(::std::marker::PhantomData) }
    #[inline]
    pub unsafe fn as_ref(&self) -> &T { ::std::mem::transmute(self) }
    #[inline]
    pub unsafe fn as_mut(&mut self) -> &mut T { ::std::mem::transmute(self) }
}
impl <T> ::std::default::Default for __BindgenUnionField<T> {
    #[inline]
    fn default() -> Self { Self::new() }
}
impl <T> ::std::clone::Clone for __BindgenUnionField<T> {
    #[inline]
    fn clone(&self) -> Self { Self::new() }
}
impl <T> ::std::marker::Copy for __BindgenUnionField<T> { }
impl <T> ::std::fmt::Debug for __BindgenUnionField<T> {
    fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        fmt.write_str("__BindgenUnionField")
    }
}
#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct AlignedStorage2 {
    pub u: AlignedStorage2_U,
}
#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct AlignedStorage2_U {
    pub mBytes: __BindgenUnionField<*mut ::std::os::raw::c_char>,
    pub mDummy: __BindgenUnionField<u64>,
    pub bindgen_union_field: u64,
}
#[repr(C)]
#[derive(Debug, Copy)]
pub struct Foo {
    pub a: u64,
    pub b: u64,
}
#[test]
fn bindgen_test_layout_Foo() {
    assert_eq!(::std::mem::size_of::<Foo>() , 16usize , concat ! (
               "Size of: " , stringify ! ( Foo ) ));
    assert_eq! (::std::mem::align_of::<Foo>() , 8usize , concat ! (
                "Alignment of " , stringify ! ( Foo ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const Foo ) ) . a as * const _ as usize } ,
                0usize , concat ! (
                "Alignment of field: " , stringify ! ( Foo ) , "::" ,
                stringify ! ( a ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const Foo ) ) . b as * const _ as usize } ,
                8usize , concat ! (
                "Alignment of field: " , stringify ! ( Foo ) , "::" ,
                stringify ! ( b ) ));
}
impl Clone for Foo {
    fn clone(&self) -> Self { *self }
}
#[repr(C)]
#[derive(Debug, Copy)]
pub struct Bar {
    pub m: AlignedStorage2,
}
#[test]
fn bindgen_test_layout_Bar() {
    assert_eq!(::std::mem::size_of::<Bar>() , 16usize , concat ! (
               "Size of: " , stringify ! ( Bar ) ));
    assert_eq! (::std::mem::align_of::<Bar>() , 8usize , concat ! (
                "Alignment of " , stringify ! ( Bar ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const Bar ) ) . m as * const _ as usize } ,
                0usize , concat ! (
                "Alignment of field: " , stringify ! ( Bar ) , "::" ,
                stringify ! ( m ) ));
}
impl Clone for Bar {
    fn clone(&self) -> Self { *self }
}
#[test]
fn __bindgen_test_layout_AlignedStorage2_open0_Foo_close0_instantiation() {
    assert_eq!(::std::mem::size_of::<AlignedStorage2>() , 16usize , concat ! (
               "Size of template specialization: " , stringify ! (
               AlignedStorage2 ) ));
    assert_eq!(::std::mem::align_of::<AlignedStorage2>() , 8usize , concat ! (
               "Alignment of template specialization: " , stringify ! (
               AlignedStorage2 ) ));
}

Expected Results

In the generated code above, the size of AlignedStorage2 is 8 bytes, but in the layout test, it asserts the size is 16 bytes, which is the correct size for the original C++ struct.

I'm not sure what should we do here. I guess it is possible for bindgen to generate the correct size for AlignedStorage2.

Reproduce the case with the C++ header shown in input.hpp and the bindgen input.hpp invocation. Compare the generated AlignedStorage2 definition with __bindgen_test_layout_AlignedStorage2_open0_Foo_close0_instantiation; done means the generated layout represents the C++ size of 16 bytes and the layout test passes.