compilation issue: no member named 'construct'

[hsdk123]

Hi, I'm seeing a new error in compilation:

In file included from D:/a/Light.vn-core/Light.vn-core/_deps/sol2/80081c33f3d3c0bc53deb21b682463e1ae98eef5/include\sol/sol.hpp:53:
In file included from D:/a/Light.vn-core/Light.vn-core/_deps/sol2/80081c33f3d3c0bc53deb21b682463e1ae98eef5/include\sol/stack.hpp:27:
In file included from D:/a/Light.vn-core/Light.vn-core/_deps/sol2/80081c33f3d3c0bc53deb21b682463e1ae98eef5/include\sol/trampoline.hpp:27:
In file included from D:/a/Light.vn-core/Light.vn-core/_deps/sol2/80081c33f3d3c0bc53deb21b682463e1ae98eef5/include\sol/types.hpp:28:
In file included from D:/a/Light.vn-core/Light.vn-core/_deps/sol2/80081c33f3d3c0bc53deb21b682463e1ae98eef5/include\sol/optional.hpp:33:

D:/a/Light.vn-core/Light.vn-core/_deps/sol2/80081c33f3d3c0bc53deb21b682463e1ae98eef5/include\sol/optional_implementation.hpp:2191:10: error: no member named 'construct' in 'optional<type-parameter-0-0 &>'

 2191 |                         this->construct(std::forward<Args>(args)...);

      |                         ~~~~  ^

1 error generated.

compiler: CMAKE_C_COMPILER: D:/a/Light.vn-core/Light.vn-core/emsdk/upstream/emscripten/emcc.bat

-- The CXX compiler identification is Clang 19.0.0
-- The C compiler identification is Clang 19.0.0

[tukss]

I'm getting the same error. Even a simple test program that just includes sol/sol.hpp fails with the same error on Clang 19 (current main) but compiles fine with version 18.1.6.

It boils down to the implementation of the emplace member function in class optional.

sol2/include/sol/optional_implementation.hpp

Line 2189 in e8e122e

template <class... Args>

At first glance it's strange why this ever worked. The construct member function is not part of optional.

Some further tests show that clang < 19 doesn't actually test for the existence of the member functions being called inside another member function of a templated type. Clang 19 changed that. This example might be instructive:

template<int i>
struct bar {
  void baz() {
    this->foo();
  }
};

int main(int argc, char**argv){

  bar<1> a;

  // uncommenting the code below makes it fail on every compiler
  // On clang >= 19 it even fails without the explicit call to baz but it works on g++ and clang < 19.
  //a.baz();

  return 0;
}

So I think this just worked before because emplace wasn't actually used. For my application I could get everything to work by just removing emplace entirely.

As a side note: The return type of emplace is T& but we don't actually return anything. This should probably be fixed as well.

[tukss]

#1606 fixes it for me.

It seems that this-> doesn't resolve to m_value as it's suggested by operator overloading.

[hsdk123]

Thanks @tukss! Hope the fix gets into main

[hsdk123]

1606 merged - confirming issue resolved!
Closing