repr(align(0)) for std::basic_string causing build error

[bengl]

Input C/C++ Header

#include <string>
using namespace std;
basic_string<char> simple(basic_string<char> str);

Bindgen Invocation

bindgen::Builder::default()
    .header("simple.hpp")
    .clang_arg("-x")
    .clang_arg("c++")
    .opaque_type("std::.*")
    .whitelist_function("simple")
    .generate()
    .unwrap()

Actual Results

Generating the binding.rs works fine, but when compiling....

cargo build
  Compiling simple-bindgen v0.1.0 (simple-bindgen)
error[E0589]: invalid `repr(align)` attribute: not a power of two
 --> simple-bindgen/target/debug/build/simple-bindgen-0af4d98c1d10abb2/out/bindings.rs:73:8
  |
73 | #[repr(align(0))]
  |        ^^^^^^^^

error[E0589]: invalid `repr(align)` attribute: not a power of two
 --> simple-bindgen/target/debug/build/simple-bindgen-0af4d98c1d10abb2/out/bindings.rs:90:8
  |
90 | #[repr(align(0))]
  |        ^^^^^^^^

The offending lines in the binding.rs look like:

#[repr(C)]
#[repr(align(0))]
pub union std_basic_string___ulx {
    pub _bindgen_opaque_blob: [u8; 0usize],
}

and

#[repr(C)]
#[repr(align(0))]
pub union std_basic_string___rep__bindgen_ty_1 {
    pub _bindgen_opaque_blob: [u8; 0usize],
}

Expected Results

While this works just fine on our linux machines, on our Macs, we get the error provided. Here's a sample uname -a from one of our Macs:

Darwin computer.local 18.5.0 Darwin Kernel Version 18.5.0: Mon Mar 11 20:40:32 PDT 2019; root:xnu-4903.251.3~3/RELEASE_X86_64 x86_64

[emilio]

Is there any chance to provide a test-case? Presumably we should be just min(align, 1) or such, but I'd rather land the fix with a test that reproduces the issue.

[bengl]

Here's a __bindgen.ii file (zipped to appease github).
__bindgen.ii.zip

[pmarks]

Bump. I'm also hitting this on Mac for a library that refers to std::string. Would a smaller test case help?

[emilio]

Yes, for sure. creducing this would be awesome.

[emilio]

This is not fixed per #1593, which has a more complex test-case.