Platform: silence Sdl2App warning on <SDL.h>

[sthalik]

Magnum is otherwise clean on -Wold-style-cast. This warning is enabled by default on clang, but not presently enabled by default on GCC.

[mosra]

This warning is enabled by default on clang, but not presently enabled by default on GCC.

I'm enabling it on both, tho: https://github.com/mosra/corrade/blob/6f115b267502859c2d713c74f9843002c10b153b/modules/UseCorrade.cmake#L105

Does it mean you get the warning on Clang only, and not on GCC? Can you post the warning here, just so I'm aware which part of the header causes it? Thanks.

Also, this is due to SDL being a subproject, which means the include paths are not supplied with -isystem that'd suppress the warnings, right? In other words, if you'd use add_subdirectory(SYSTEM) from CMake 3.25, the warning would be gone, right?

[sthalik]

Here's the warning on clang,

In file included from F:/dev/game/external/magnum/src/Magnum/Platform/Sdl2Application.cpp:41:
In file included from F:/dev/game/build/external/sdl2/include/SDL.h:41:
F:/dev/game/build/external/sdl2/include/SDL_events.h:676:65: warning: use of old-style cast [-Wold-style-cast]
SDL_COMPILE_TIME_ASSERT(SDL_Event, sizeof(SDL_Event) == sizeof(((SDL_Event *)NULL)->padding));
                                                                ^            ~~~~
F:/dev/game/build/external/sdl2/include/SDL_stdinc.h:379:57: note: expanded from macro 'SDL_COMPILE_TIME_ASSERT'
#define SDL_COMPILE_TIME_ASSERT(name, x)  static_assert(x, #x)
                                                        ^
1 warning generated.

SDL_COMPILE_TIME_ASSERT(SDL_Event, sizeof(SDL_Event) == sizeof(((SDL_Event *)NULL)->padding));

GCC somehow doesn't emit a warning in that case.

[mosra]

As the warning doesn't happen with SDL included from a system location (where CMake uses -isystem), the solution here is to use add_subdirectory(SYSTEM) in CMake 3.25+ as mentioned above, or a corresponding equivalent with CMake's FetchContent and other alternatives.