include: Use `struct private_hwdata` incomplete type for API compat

Classic SDL 1.2 headers traditionally had this member as a pointer to
the incomplete type `struct private_hwdata`. For whatever reason
(presumably a sense of completeness) the SDLmm C++ binding[1] that is
bundled in Debian package 'asc' (Advanced Strategic Command) defines an
accessor for it, which is declared as returning `struct private_hwdata *`
and has the obvious trivial implementation[2].

Implicit conversion from `void *` to `struct private_hwdata *` is
allowed in C, but not in C++, so sdl12-classic's simplification of
changing this member from `struct private_hwdata *` to `void *`
breaks the build for SDLmm.

Arguably it's a bug that SDLmm has this accessor, because this member
is for internal use by SDL and its type has no public definition, so
there's no legitimate reason for third-party code to call the accessor;
but it does exist, so 100% source compatibility with classic SDL 1.2
would require it to have the same type it historically had.

[1] https://sourceforge.net/projects/sdlmm/
[2] https://sourceforge.net/p/sdlmm/code/HEAD/tree/trunk/SDLmm/src/sdlmm_basesurface.h#l141

Resolves: https://github.com/libsdl-org/sdl12-compat/issues/299
Signed-off-by: Simon McVittie <smcv@debian.org>
Forwarded: https://github.com/libsdl-org/sdl12-compat/pull/300
Applied-upstream: 1.2.66, commit:ed188b5e24fc33190e3eeada5e26f5d295f50948
Bug-Debian: https://bugs.debian.org/1039439

Gbp-Pq: Name include-Use-struct-private_hwdata-incomplete-type-for-API.patch

1 files changed, 1 insertions, 1 deletions

diff --git a/include/SDL/SDL_video.h b/include/SDL/SDL_video.h
index 67db723..d9e9069 100644
--- a/include/SDL/SDL_video.h
+++ b/include/SDL/SDL_video.h
@@ -89,7 +89,7 @@ typedef struct SDL_Surface
     Uint16 pitch;
     void *pixels;
     int offset;
-    void *hwdata;
+    struct private_hwdata *hwdata;
     SDL_Rect clip_rect;
     Uint32 unused1;
     Uint32 locked;