compilation errors if include *<SDL3/SDL_vulkan.h>* before *<vulkan/vulkan.hpp>*

[feelamee]

The problem in compilation errors if <SDL3/SDL_vulkan.h> was included before <vulkan/vulkan.hpp>.
It reproducing only with vulkan C++ api, but not C.

compilation output

In file included from /home/missed/code/sdl-bug-with-vulkan-cpp-api/build/_deps/vulkan-headers-src/include/vulkan/vulkan.hpp:8681,
               from /home/missed/code/sdl-bug-with-vulkan-cpp-api/build/_deps/vulkan-headers-src/include/vulkan/vulkan_raii.hpp:11,
               from /home/missed/code/sdl-bug-with-vulkan-cpp-api/main.cpp:3:
/home/missed/code/sdl-bug-with-vulkan-cpp-api/build/_deps/vulkan-headers-src/include/vulkan/vulkan_handles.hpp:2613:46: error: conversion from ‘int’ to ‘VkSurfaceKHR_T*’ in a converted constant expression
 2613 |   struct CppType<VkSurfaceKHR, VK_NULL_HANDLE>
      |                                              ^
/home/missed/code/sdl-bug-with-vulkan-cpp-api/build/_deps/vulkan-headers-src/include/vulkan/vulkan_handles.hpp:2613:46: error: could not convert ‘0’ from ‘int’ to ‘VkSurfaceKHR_T*’
 2613 |   struct CppType<VkSurfaceKHR, VK_NULL_HANDLE>
      |                                              ^
      |                                              |
      |                                              int

As I explored, VK_NULL_HANDLE defined to 0 insted of nullptr in <vulkan/vulkan_core.h>

#ifndef VK_DEFINE_NON_DISPATCHABLE_HANDLE
    #if (VK_USE_64_BIT_PTR_DEFINES==1)
        #if (defined(__cplusplus) && (__cplusplus >= 201103L)) || (defined(_MSVC_LANG) && (_MSVC_LANG >= 201103L))
            #define VK_NULL_HANDLE nullptr
        #else
            #define VK_NULL_HANDLE ((void*)0)
        #endif
    #else
        #define VK_NULL_HANDLE 0ULL
    #endif
#endif
#ifndef VK_NULL_HANDLE
    #define VK_NULL_HANDLE 0
#endif

Because <SDL3/SDL_vulkan.h> defined VK_DEFINE_NON_DISPATCHABLE_HANDLE.

I also made a repo with minimal repoducible example.

So, I'm not sure that this is an SDL bug. But, probably, we need to provide workaround for this.
I'm ready to make PR, if someone will guide me to right solution/fix.

[Dv-Senna]

The issue is due to VK_NULL_HANDLE being defined to 0, which can't be implicitly converted to a pointer in C++. By looking at the way VK_NULL_HANDLE is defined, you have to not define VK_DEFINE_NON_DISPATCHABLE_HANDLE before including vulkan/vulkan_core.h, or else, #define VK_NULL_HANDLE 0 is forced. The issue is that SDL_vulkan.h need VK_DEFINE_NON_DISPATCHABLE_HANDLE and define it itself, but it's never undef. In #11361 , I added an #undef at the end of SDL_vulkan.h for VK_DEFINE_NON_DISPATCHABLE_HANDLE and one for VK_DEFINE_DISPATCHABLE (didn't check if it can work without the second one, but it's safer to add it anyway).

[Dv-Senna]

After check, #undef VK_DEFINE_DISPATCHABLE is not necessary to allow it to compile with gcc 14.2.1