LNK2019 unresolved symbol for Vec<SharedStruct> using MSVC

[stery28]

Hello!

I'm trying to expose a function taking an opaque type as arugment and returning a Vec containing a shared struct type (fn get_inner_vec(some_outer: &SomeOuterOpaqueStruct) -> Vec<SomeInnerSharedStruct>):

// inner.rs
#[cxx::bridge(namespace = "cxx_test_vec::inner")]
pub(crate) mod ffi {
    #[derive(Clone)]
    pub(crate) struct SomeInnerSharedStruct {
        pub(crate) f1: i32,
        pub(crate) f2: i32,
    }
}

// lib.rs
use ffi::SomeInnerSharedStruct;

mod inner;

pub(crate) struct SomeOuterOpaqueStruct {
    pub(crate) inner_vec: Vec<SomeInnerSharedStruct>,
    pub(crate) some_flag: bool,
}

impl SomeOuterOpaqueStruct {
    fn new(inner_vec: Vec<SomeInnerSharedStruct>) -> Self {
        Self {
            inner_vec,
            some_flag: false,
        }
    }

}

fn get_inner_vec(some_outer: &SomeOuterOpaqueStruct) -> Vec<SomeInnerSharedStruct> {
    some_outer.inner_vec.to_owned()
}

pub(crate) fn make_inner_vec() -> Vec<SomeInnerSharedStruct> {
    vec![
        SomeInnerSharedStruct { f1: 1, f2: 2 },
        SomeInnerSharedStruct { f1: 4, f2: 5 },
    ]
}

pub(crate) fn new_outer() -> Box<SomeOuterOpaqueStruct> {
    Box::new(SomeOuterOpaqueStruct::new(make_inner_vec()))
}

#[cxx::bridge(namespace = "cxx_test_vec::outer")]
mod ffi {
    #[namespace = "cxx_test_vec::inner"]
    extern "C++" {
        include!("cxx-test-vec/src/inner.rs.h");
        type SomeInnerSharedStruct = crate::inner::ffi::SomeInnerSharedStruct;
    }

    extern "Rust" {
        type SomeOuterOpaqueStruct;
        fn new_outer() -> Box<SomeOuterOpaqueStruct>;
        fn get_inner_vec(some_outer: &SomeOuterOpaqueStruct) -> Vec<SomeInnerSharedStruct>;
    }
}

#[cfg(test)]
mod tests {
    use crate::{get_inner_vec, new_outer};


    #[test]
    fn test_fn() {
        let outer_struct = new_outer();
        let inner_vec = get_inner_vec(&outer_struct);

        assert_ne!(inner_vec.len(), 0);
    }
}

// build.rs
fn main() {
    let source_files = vec![
        "src/lib.rs",
        "src/inner.rs",
    ];

    cxx_build::bridges(source_files)
    .std("c++14")
    .compile("cxx-test-vec");

    println!("cargo:rerun-if-changed=src/lib.rs");
    println!("cargo:rerun-if-changed=src/inner.rs");
}

# Cargo.toml
[package]
name = "cxx-test-vec"
version = "0.1.0"
edition = "2021"


[lib]
crate-type = ["staticlib"]

[dependencies]
cxx = "1.0"

[build-dependencies]
cxx-build = "1.0"

cargo build runs fine, but I encounter an unresolved symbol error when running cargo test using the stable-x86_64-pc-windows-msvc toolchain. I'm getting the same error when actually linking the library in a C++ project, but I'll focus only on cargo test for now. I think it's something MSVC specific, because I didn't encounter any errors running cargo test on macOS, but unfortunately I need to use MSVC in this project.

The error:

note: cxx-test-vec.lib(1c4c8df760424d6e-lib.rs.o) : error LNK2019: unresolved external symbol 
"public: __cdecl rust::cxxbridge1::Vec<struct cxx_test_vec::inner::SomeInnerSharedStruct>::Vec<struct cxx_test_vec::inner::SomeInnerSharedStruct>(void)" 
(??0?$Vec@USomeInnerSharedStruct@inner@cxx_test_vec@@@cxxbridge1@rust@@QEAA@XZ) referenced in function 
"public: __cdecl rust::cxxbridge1::Vec<struct cxx_test_vec::inner::SomeInnerSharedStruct>::Vec<struct cxx_test_vec::inner::SomeInnerSharedStruct>(class rust::cxxbridge1::Vec<struct cxx_test_vec::inner::SomeInnerSharedStruct> &&)" 
(??0?$Vec@USomeInnerSharedStruct@inner@cxx_test_vec@@@cxxbridge1@rust@@QEAA@$$QEAV012@@Z)

This also doesn't happen if both the function returning Vec<SomeInnerSharedStruct> and SomeInnerSharedStruct's definition are in the same cxx::bridge module, so it might have something to do with "reimporting" the shared struct from another bridge.

Other details:
rustc 1.79.0 (129f3b996 2024-06-10)
Windows 11 22H2 build 22621.3880
Microsoft Visual Studio Community 2022, MSVC 14.34.31933 (link.exe version 14.34.31937.0, cl.exe version 19.34.31937 for x64)