Automatically generate macro functions

[Susko3]

Currently, macro functions need to be manually updated (and added), see 2590a72.

My idea for this

The manually written C# code would be the following, placed in the usual SDL_{name}.cs file:

public static partial class SDL3
{
    [Macro]
    [return: CastFrom("int")]
    public static partial SDL_PixelType SDL_PIXELTYPE([Cast("int")] SDL_PixelFormat X);
}

This will cause the source gen to generate the following code (this may be unnecessary):

    public static partial SDL_PixelType SDL_PIXELTYPE(SDL_PixelFormat X) => (SDL_PixelType)Unsafe_SDL_PIXELTYPE((int)X);

The python script would generate this C header file and add it to ClangSharp (the file is not saved to disk/repo):

#include <SDL3/SDL.h>

//      | taken from [CastFrom("int")]
//      ↓                        ↓ taken from [Cast("int")]
inline int Unsafe_SDL_PIXELTYPE(int X)
{
    return SDL_PIXELTYPE(X);
}

ClangSharp can convert inline functions to C# code, so calling the macro functions inside inline functions should work.

The generated C# code will be horrible, as it'll resolve all macros (and SDL code sometime nests a lot of macros).

[SaxxonPike]

@Susko3 I was thinking of looking into this during the weekend. Another alternative to this approach could be to update the C# source generators to handle these sorts of situations, what are your thoughts?

[Susko3]

Looking back at my idea, I think it's too complicated for no reason. A simpler approach would be to write the C header file manually and add it in ClangSharpPInvokeGenerator. --prefixStrip could be used to trick it into generating a method with the same name as the macro.

SDL3-CS/SDL3/SDL_pixels.h

#include <SDL3/SDL.h>

inline SDL_PixelType BindgenMacro_SDL_PIXELTYPE(SDL_PixelFormat X)
{
    return SDL_PIXELTYPE(X);
}

With --prefixStrip "BindgenMacro_" it should just work™.