Reuse of shared structs containing String

[alexeyr]

It seems I am still getting something wrong about #297. Here I am trying to reuse a shared struct instead of declaring it the second time and get

  running: "E:\\VisualStudio\\VC\\Tools\\MSVC\\14.26.28801\\bin\\HostX64\\x64\\cl.exe" "-nologo" "-MD" "-Z7" "-Brepro" "-I" "E:\\MyProgramming\\tokenizers\\bindings\\cpp\\target\\debug\\build\\tokenizers-cpp-348e1825e6b8d85d\\out\\cxxbridge\\include" "-I" "E:\\MyProgramming\\tokenizers\\bindings\\cpp\\target\\debug\\build\\tokenizers-cpp-348e1825e6b8d85d\\out\\cxxbridge\\crate" "-I" "." "-I" "target/cxxbridge/tokenizers-cpp" "-I" "thirdparty" "-W4" "/std:c++14" "/EHsc" "-FoE:\\MyProgramming\\tokenizers\\bindings\\cpp\\target\\debug\\build\\tokenizers-cpp-348e1825e6b8d85d\\out\\cxxbridge\\sources\\tokenizers-cpp\\tokenizers-cpp\\processors.rs.o" "-c" "E:\\MyProgramming\\tokenizers\\bindings\\cpp\\target\\debug\\build\\tokenizers-cpp-348e1825e6b8d85d\\out\\cxxbridge\\sources\\tokenizers-cpp\\tokenizers-cpp\\processors.rs.cc"
  processors.rs.cc
  E:\MyProgramming\tokenizers\bindings\cpp\target\cxxbridge\tokenizers-cpp\tokenizers-cpp/processors.rs.h(198): error C2338: type ::huggingface::tokenizers::ffi::KVStringU32 marked as Trivial in Rust is not trivially move constructible and trivially destructible in C++     
  E:\MyProgramming\tokenizers\bindings\cpp\target\debug\build\tokenizers-cpp-348e1825e6b8d85d\out\cxxbridge\sources\tokenizers-cpp\tokenizers-cpp\processors.rs.cc(251): error C2338: type ::huggingface::tokenizers::ffi::KVStringU32 marked as Trivial in Rust is not trivially 
move constructible and trivially destructible in C++
  exit code: 2

  --- stderr

  CXX include path:
    E:\MyProgramming\tokenizers\bindings\cpp\target\debug\build\tokenizers-cpp-348e1825e6b8d85d\out\cxxbridge\include
    E:\MyProgramming\tokenizers\bindings\cpp\target\debug\build\tokenizers-cpp-348e1825e6b8d85d\out\cxxbridge\crate

The only potentially significant difference from #465 that I can see on my own is that I include!("tokenizers-cpp/models.h"); and not .rs.h; but trying to change that adds a lot more errors and doesn't fix this one.

Hopefully the commit introducing the error is small enough; if not, I can try to create a smaller case reproducing it.

[alexeyr]

Ah, the problem is that it contains a String, and is never actually passed by value in models, but only in processors . Is that right?

[alexeyr]

It looks like the problem can be fixed by adding

template <>
struct IsRelocatable<MyStruct> : std::true_type {};

If I understand IsRelocatable, this should be safe, and can be generated for any shared struct containing String; and for shared structs containing Vec<SomethingElse>,

template <>
struct IsRelocatable<MyStruct> : IsRelocatable<SomethingElse>::value {};

(approximately). If this is correct, I can make a pull request.