Bug#909740: libsdl2-dev: No longer multi-arch co-installable

[Simon McVittie]

On Mon, 09 Dec 2019 at 19:08:05 +0100, Felix Geyer wrote:
> On a second though I fear having the include files of libsdl2 and libsdl2-*
> in different paths will break some build systems.
> 
> A random example I quickly found:
> https://sources.debian.org/src/neverball/1.6.0+git20180603-2/Makefile/

Good point. Build systems like this assume that sdl2-config is sufficient
to find all the SDL2_foo family, not just the main library.

> One option would be to add -I/usr/include/SDL2 to sdl2-config or pkg-config
> but I'm not sure if that would cover all cases.

If neverball was using `pkg-config --cflags SDL2_ttf` then that would just
give it -I/usr/include/SDL2, so it seems like that ought to be sufficient.

I suppose if one of the SDL2_foo family uses #include "SDL_bar.h"
and expects to find an adjacent SDL2 that way, or if
something tries to second-guess the compiler and read
header files directly, that might be a reason to revert
https://salsa.debian.org/sdl-team/libsdl2/merge_requests/5
(the one that goes via pkg-config) and apply
https://salsa.debian.org/sdl-team/libsdl2/merge_requests/3 (my original
proposal with a forwarding header) instead - that's the only solution
I could see that keeps most SDL headers in the same place they have
always been.

(Alternatively, you could switch all the SDL2_foo packages to use the
multiarch include directory "unnecessarily", just to make them consistent,
but that's more avoidable uploads and header duplication.)

    smcv