tests/ffi: strange error with a function returning Vec<Buffer>

[naufraghi]

The error triggers a warning for the Buffer field in Array that was already there but somehow silent.

cargo:warning=.../out/cxxbridge/sources/tests/ffi/lib.rs.cc:1387:45:
    error: static assertion failed: type tests::Buffer should be trivially
           move constructible and trivially destructible in C++ to be used
           as a field of `Array` or vector element in Vec<Buffer> in Rust
cargo:warning= 1387 |     ::rust::IsRelocatable<::tests::Buffer>::value,

• Here the failing pipeline log for the error above (first commit c858291).
• The "fix" is not complete either, the plain Buffer struct code does not pass the tests on windows: msvc pipeline logs (second commit d0537c9)

[naufraghi]

Long story short, I'd like to use a trivial struct inside a Vec, but it did not work. I had to wrap it inside a struct as a field to have it work.

struct Foo {
   data: Vec<TrivialData>
}

does not link, missing Vec constructor.

struct DataWrapper {    // <--- shared
   d: TrivialData
}

struct Foo {
   data: Vec<DataWrapper>
}

So I dived into the code to understand if that case was covered, tried to add a test and found a strange error.

[naufraghi]

I'd like to help, either adding support for the use case or improving the error or the documentation or the tests, feel free to suggest some direction and I'll have a look in my spare time. Thanks anyway!

[dtolnay]

c858291 should work as of cxx 1.0.76.