SDL2: Reinstate find-headers.patch

pkgs/development/libraries/SDL2/default.nix

@@ -65,6 +65,14 @@ stdenv.mkDerivation rec {
   outputs = [ "out" "dev" ];
   outputBin = "dev"; # sdl-config
 
+  patches = [
+    # `sdl2-config --cflags` from Nixpkgs returns include path to just SDL2.
+    # On a normal distro this is enough for includes from all SDL2* packages to work,
+    # but on NixOS they're spread across different paths.
+    # This patch + the setup-hook will ensure that `sdl2-config --cflags` works correctly.
+    ./find-headers.patch
+  ];
+
   depsBuildBuild = [ pkg-config ];
 
   nativeBuildInputs = [ pkg-config ] ++ optionals waylandSupport [ wayland ];

pkgs/development/libraries/SDL2/find-headers.patch

@@ -0,0 +1,34 @@
+diff --git a/sdl2-config.cmake.in b/sdl2-config.cmake.in
+index c570511fa..ca694f595 100644
+--- a/sdl2-config.cmake.in
++++ b/sdl2-config.cmake.in
+@@ -7,7 +7,8 @@ set(includedir "@includedir@")
+ set(SDL2_PREFIX "${prefix}")
+ set(SDL2_EXEC_PREFIX "${exec_prefix}")
+ set(SDL2_LIBDIR "${libdir}")
+-set(SDL2_INCLUDE_DIRS "${includedir}/SDL2")
++set(SDL2_INCLUDE_DIRS "${includedir}/SDL2" $ENV{SDL2_PATH})
++separate_arguments(SDL2_INCLUDE_DIRS)
+ set(SDL2_LIBRARIES "-L${SDL2_LIBDIR} @SDL_RLD_FLAGS@ @SDL_LIBS@")
+ string(STRIP "${SDL2_LIBRARIES}" SDL2_LIBRARIES)
+ 
+diff --git a/sdl2-config.in b/sdl2-config.in
+index 5a2aed292..7c55f0a28 100644
+--- a/sdl2-config.in
++++ b/sdl2-config.in
+@@ -42,7 +42,11 @@ while test $# -gt 0; do
+       echo @SDL_VERSION@
+       ;;
+     --cflags)
+-      echo -I@includedir@/SDL2 @SDL_CFLAGS@
++      SDL_CFLAGS=""
++      for i in @includedir@/SDL2 $SDL2_PATH; do
++        SDL_CFLAGS="$SDL_CFLAGS -I$i"
++      done
++      echo $SDL_CFLAGS @SDL_CFLAGS@
+       ;;
+ @ENABLE_SHARED_TRUE@    --libs)
+ @ENABLE_SHARED_TRUE@      echo -L@libdir@ @SDL_RLD_FLAGS@ @SDL_LIBS@
+-- 
+2.33.1
+