Can't tell autocxx that the replaced type is POD and safe to use in other PODs

[RReverser]

Expected Behavior

I should be able to replace a C++ type autocxx doesn't understand with my custom Rust type, and tell autocxx that it's a POD so it can be used in generate_pod! for other types like this:

#include <Eigen/Dense>

struct MyStruct {
	Eigen::Vector2d vec;
};

(Eigen is a header-only library, so should be relatively easy to add for a repro, but I suppose this can be reproduced with simpler custom types too)

#[repr(transparent)]
pub struct Vector2d(pub nalgebra::Vector2<f64>);

impl cxx::ExternType for Vector2d {
    type Id = cxx::type_id!("Eigen::Vector2d");
    type Kind = cxx::kind::Trivial;
}

include_cpp! {
    #include "test.h"

    safety!(unsafe)

    extern_cpp_type!("Eigen::Vector2d", crate::Vector2d)
    pod!("Eigen::Vector2d")

    generate_pod!("MyStruct")
}

Actual Behavior

autocxx complains that MyStruct can't be generated as a POD because the dependency type "isn't known":

  --- stderr
  Error:
    × the include_cpp! macro couldn't be expanded into Rust bindings to C++:
    │ An item was requested using 'generate_pod' which was not safe to hold by
    │ value in Rust. Type MyStruct could not be POD because its dependent type
    │ Eigen::Vector2d isn't known

Specifications

• Version: 0.23.1

[adetaylor]

Thanks. I agree this is seems like a valid bug. It would be even better if you could raise a PR with a failing test case in integration-tests/src/integration_tests.rs (or at least it means I'm likely to look at fixing it quicker).

[RReverser]

I'll try to get to it, but have a bit much to unwrap locally at the moment.

[adetaylor]

Landed a fix in a branch, but it's made me realize this bit of the autocxx codebase is a bit... legacy. I might do some more thinking about it over the next week or so in case I think it merits a more substantial rewrite.

[ntorresalberto]

Hi, just commenting to say I'm interested in this use case, coming from the linear algebra and c++ world.