Add FindSDL2 to simplify main CML

* the FindSDL2 module forwards to CONFIG mode first
* if that fails (eg. no -version.cmake or config not even present) it
uses pkg-config
* exports SDL2::SDL2 and SDL2::SDL2main as targets
* fix missing IMPORTED_LOCATION for other build types in Vorbisfile

CMakeLists.txt

@@ -478,19 +478,15 @@ if(ENABLE_GAME OR ENABLE_TESTS)
 	find_package(VorbisFile REQUIRED)
 	find_package(PkgConfig REQUIRED)
 	find_package(Fontconfig REQUIRED)
+	find_package(SDL2 2.0.8 REQUIRED)
 	if(NOT MSVC)
 		# for everything else, use pkgconfig
-		# find_package can't be used for SDL2 since at least as of Ubuntu 20.04 they forgot to include the sdl2-config-version.cmake, so cmake can't tell if it's >= 2.0.8 and thus rejects using it
-		# meanwhile SDL2_image and SDL2_mixer don't seem to have any cmake configuration available at all
-		# the best I could find is that the more modern cmake module support is only available if you build SDL2 yourself instead of using a distro-packaged version
-		# still wouldn't help for SDL2_image and SDL2_mixer though
-		pkg_check_modules(SDL2 REQUIRED sdl2>=2.0.8)
+		# SDL2_image and SDL2_mixer don't seem to have any cmake configuration available at all
 		pkg_check_modules(SDL2IMAGE REQUIRED SDL2_image>=2.0.2)
 		pkg_check_modules(SDL2MIXER REQUIRED SDL2_mixer>=2.0.0)
 	else()
-		# for MSVC, vcpkg builds and provides SDL2-related modules for cmake to use, so use those
+		# for MSVC, vcpkg builds and provides custom SDL2-related modules for cmake to use, so use those
 		# this also fixes the issue with our previous FindSDL2* scripts incorrectly using the Release version of these libs instead of the Debug version
-		find_package(SDL2 2.0.8 CONFIG REQUIRED)
 		find_package(sdl2-image CONFIG REQUIRED)
 		find_package(sdl2-mixer CONFIG REQUIRED)
 	endif()

cmake/FindSDL2.cmake

@@ -0,0 +1,95 @@
+#[=======================================================================[.rst:
+FindSDL2
+--------
+
+Find the SDL2 includes and libraries.
+
+IMPORTED Targets
+^^^^^^^^^^^^^^^^
+
+This module defines the `IMPORTED` targets ``SDL2::SDL2`` and ``SDL2::SDL2main``, if
+SDL2 has been found.
+
+Result Variables
+^^^^^^^^^^^^^^^^
+
+This module defines the following variables:
+
+	SDL2_FOUND         - True if SDL2 found.
+	SDL2_INCLUDE_DIRS  - Where to find SDL2/SDL.h.
+	SDL2_LIBRARIES     - Libraries when using SDL2.
+
+#]=======================================================================]
+
+include(FindPackageHandleStandardArgs)
+
+# first specifically look for the CMake config version of SDL2 (either system or package manager)
+# provides two TARGETs SDL2::SDL2 and SDL2::SDL2Main
+find_package(SDL2 QUIET NO_MODULE)
+
+# after the CONFIG type `find_package` we get, if available, a SDL2_VERSION var
+# if we found the SDL2 cmake package then we are almost done
+# we still need to check the version for some edge cases where the -version.cmake file
+# is missing
+if(SDL2_FOUND)
+	find_package_handle_standard_args(SDL2 HANDLE_COMPONENTS CONFIG_MODE)
+
+	# in some cases the target is an ALIAS, we want the original
+	get_target_property(_SDL2_ORIGINAL_TARGET "SDL2::SDL2" ALIASED_TARGET)
+
+	# if it's a regular target, just set it to SDL2::SDL2
+	if(NOT _SDL2_ORIGINAL_TARGET)
+		set(_SDL2_ORIGINAL_TARGET "SDL2::SDL2")
+	endif()
+
+	get_target_property(_SDL2_INCLUDE_DIRS_FROM_CONFIG "${_SDL2_ORIGINAL_TARGET}" INTERFACE_INCLUDE_DIRECTORIES)
+	
+	# in the original sdl2-config.cmake we get only <path>/include/SDL2 and in vcpkg we that + <path>/include/
+	if(_SDL2_INCLUDE_DIRS_FROM_CONFIG MATCHES ".*/include/SDL2.*")
+		get_filename_component(_SDL2_INCLUDE_DIRS "${_SDL2_INCLUDE_DIRS_FROM_CONFIG}" DIRECTORY)
+		list(APPEND _SDL2_INCLUDE_DIRS_FROM_CONFIG "${_SDL2_INCLUDE_DIRS}")
+		# we can endup with a duplicate with vcpkg
+		list(REMOVE_DUPLICATES _SDL2_INCLUDE_DIRS_FROM_CONFIG)
+
+		set_property(TARGET "${_SDL2_ORIGINAL_TARGET}" PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${_SDL2_INCLUDE_DIRS_FROM_CONFIG}")
+	endif()
+
+	get_target_property(_SDL2_INCLUDE_DIRS_FROM_CONFIG "${_SDL2_ORIGINAL_TARGET}" INTERFACE_INCLUDE_DIRECTORIES)
+
+	mark_as_advanced(SDL2_INCLUDE_DIRS SDL2_LIBRARIES)
+
+	return()
+endif()
+
+# let's try pkg-config
+find_package(PkgConfig QUIET)
+if(PKG_CONFIG_FOUND)
+	pkg_check_modules(PC_SDL2 REQUIRED sdl2>=${SDL2_FIND_VERSION})
+endif()
+
+find_package_handle_standard_args(SDL2 DEFAULT_MSG PC_SDL2_INCLUDE_DIRS PC_SDL2_LIBRARIES)
+
+if(SDL2_FOUND)
+	if(NOT TARGET SDL2::SDL2)
+		# the .pc file for SDL2 contains `<prefix>/include/SDL2` which is different from the cmake version
+		# i.e. `<prefix>/include`
+		get_filename_component(SDL2_INCLUDE_DIRS ${PC_SDL2_INCLUDE_DIRS} DIRECTORY)
+
+		set(SDL2_INCLUDE_DIRS ${SDL2_INCLUDE_DIRS} CACHE STRING "SDL2 include directories")
+		set(SDL2_LIBRARIES ${PC_SDL2_LIBRARIES} CACHE STRING "SDL2 libraries")
+		
+		mark_as_advanced(SDL2_INCLUDE_DIRS SDL2_LIBRARIES)
+
+		add_library(SDL2::SDL2 INTERFACE IMPORTED)
+		set_target_properties(SDL2::SDL2 PROPERTIES
+			INTERFACE_INCLUDE_DIRECTORIES "${SDL2_INCLUDE_DIRS}"
+			INTERFACE_LINK_DIRECTORIES "${PC_SDL2_LIBDIR}"
+			INTERFACE_LINK_LIBRARIES "${SDL2_LIBRARIES}")
+	endif()
+
+	if(NOT TARGET SDL2::SDL2main)
+		# on *nix it seems that .pc files don't actually include libSDL2main, but for consistency's sake,
+		# let's add a phony library we can link with
+		add_library(SDL2::SDL2main INTERFACE IMPORTED)
+	endif()
+endif()

cmake/FindVorbisFile.cmake

@@ -115,7 +115,7 @@ if(VORBISFILE_FOUND AND (NOT TARGET VorbisFile::VorbisFile))
 	if(VORBISFILE_LIBRARY_DEBUG)
 		set_target_properties(VorbisFile::VorbisFile PROPERTIES IMPORTED_LOCATION_DEBUG "${VORBISFILE_LIBRARY_DEBUG}")
 		set_target_properties(VorbisFile::VorbisFile PROPERTIES IMPORTED_LOCATION_RELEASE "${VORBISFILE_LIBRARY}")
-	else()
-		set_target_properties(VorbisFile::VorbisFile PROPERTIES IMPORTED_LOCATION "${VORBISFILE_LIBRARY}")
 	endif()
+	# for the rest of build types
+	set_target_properties(VorbisFile::VorbisFile PROPERTIES IMPORTED_LOCATION "${VORBISFILE_LIBRARY}")
 endif()

src/CMakeLists.txt

@@ -17,7 +17,6 @@ include_directories(SYSTEM ${PANGOCAIRO_INCLUDE_DIRS})
 include_directories(SYSTEM ${GETTEXT_INCLUDE_DIR})
 include_directories(SYSTEM ${LIBDBUS_INCLUDE_DIRS})
 if(NOT MSVC)
-	include_directories(SYSTEM ${SDL2_INCLUDE_DIRS})
 	include_directories(SYSTEM ${SDL2IMAGE_INCLUDE_DIRS})
 	include_directories(SYSTEM ${SDL2MIXER_INCLUDE_DIRS})
 endif()
@@ -59,7 +58,6 @@ set(game-external-libs
 if(NOT MSVC)
 	set(game-external-libs
 		${game-external-libs}
-		${SDL2_LIBRARIES}
 		${SDL2IMAGE_LIBRARIES}
 		${SDL2MIXER_LIBRARIES}
 	)
@@ -248,10 +246,10 @@ if(ENABLE_GAME)
 		Boost::locale
 		Boost::filesystem
 		Fontconfig::Fontconfig
+		SDL2::SDL2
+		SDL2::SDL2main
 	)
 	if(MSVC)
-		target_link_libraries(wesnoth SDL2::SDL2)
-		target_link_libraries(wesnoth SDL2::SDL2main)
 		target_link_libraries(wesnoth SDL2::SDL2_image)
 		target_link_libraries(wesnoth SDL2::SDL2_mixer)
 	endif()
@@ -295,10 +293,10 @@ if(ENABLE_TESTS)
 		Boost::filesystem
 		Boost::unit_test_framework
 		Fontconfig::Fontconfig
+		SDL2::SDL2
+		SDL2::SDL2main
 	)
 	if(MSVC)
-		target_link_libraries(boost_unit_tests SDL2::SDL2)
-		target_link_libraries(boost_unit_tests SDL2::SDL2main)
 		target_link_libraries(boost_unit_tests SDL2::SDL2_image)
 		target_link_libraries(boost_unit_tests SDL2::SDL2_mixer)
 	endif()