[BUG] Constant static members not initialized inside class definition

[vladvrabie]

Describe the bug I have a Cpp1 class with some integral const static members initialized inside class. This allows me to use them to declare other members, notable std::array. Tried to port the class to Cpp2, but the static members are initialized outside the class, so I cannot use them to declare a std::array.

To Reproduce Steps to reproduce the behavior:

1. Sample code
   My original Cpp1 code

   class Piece {};
   class Board {
   public:
   static const size_t kWidth{ 4 };
   static const size_t kHeight{ 4 };
   static const size_t kSize{ kWidth * kHeight };
   private:  std::array<std::optional<Piece>, kSize> m_pieces;
   };

   Cpp2 code:

   Piece: type = {}
   Board: type = {
   kWidth: size_t == 4;
   kHeight: size_t == 4;
   kSize: size_t == kWidth * kHeight;
   
   m_pieces: std::array<std::optional<Piece>, kSize> = ();
   }
   
   main: () = {
   b: Board = ();
   }

2. Command lines including which C++ compiler you are using
   For Cpp2: cppfront.exe main.cpp2 -import-std
   Visual Studio Community 2022 (64-bit) Version 17.10.5
   Microsoft (R) C/C++ Optimizing Compiler Version 19.40.33813 for x86
   Project -> Properties -> Configuration Properties -> C/C++ -> Command Line:

   /JMC /experimental:module /permissive- /MP /ifcOutput "x64\Debug\" /GS /W3 /Zc:wchar_t /ZI /Gm- /Od /sdl /Fd"x64\Debug\vc143.pdb" /Zc:inline /fp:precise /D "_DEBUG" /D "_CONSOLE" /D "_UNICODE" /D "UNICODE" /errorReport:prompt /WX- /Zc:forScope /RTC1 /Gd /MDd /std:c++latest /FC /Fa"x64\Debug\" /EHsc /nologo /Fo"x64\Debug\" /Fp"x64\Debug\GameCpp2.pch" /diagnostics:column 

3. Expected result To compile to my original code or to compile to
   static constexpr size_t kWidth{ 4 }; // omitting the rest for brevity

4. Actual result/error
   Error: Code C2975, '_Size': invalid template argument for 'std::array', expected compile-time constant expression
   Generated Cpp1 code (normally i don't use -clean, but I'm pasting here the clean version)

   #define CPP2_IMPORT_STD          Yes
   #include "cpp2util.h"
   
   class Piece;
   class Board;
   
   class Piece {
   public: Piece() = default;
   public: Piece(Piece const&) = delete; /* No 'that' constructor, suppress copy */
   public: auto operator=(Piece const&) -> void = delete;
   };
   
   class Board {
   public: static const size_t kWidth;
   public: static const size_t kHeight;
   public: static const size_t kSize;
   
   private: std::array<std::optional<Piece>,kSize> m_pieces {}; 
   public: Board() = default;
   public: Board(Board const&) = delete; /* No 'that' constructor, suppress copy */
   public: auto operator=(Board const&) -> void = delete;
   };
   
   auto main() -> int;
   
   inline CPP2_CONSTEXPR size_t Board::kWidth{ 4 };
   inline CPP2_CONSTEXPR size_t Board::kHeight{ 4 };
   inline CPP2_CONSTEXPR size_t Board::kSize{ kWidth * kHeight };
   
   auto main() -> int{
   Board b {}; 
   }

Additional context cppreference.com static members

[JohelEGP]

706 attempts to fix this.

See also #700.