Allow in-tree build

.gitignore

···
 *.rej
 
 # for CMake
+.cmake
 CMakeFiles/
 CMakeCache.txt
 cmake_install.cmake
 cmake_uninstall.cmake
-SDL3ConfigVersion.cmake
-.ninja_*
-*.ninja
+install_manifest.txt
+*Targets.cmake
+*Config.cmake
+*ConfigVersion.cmake
+CTestTestfile.cmake
+Testing
 compile_commands.json
 .cache/
+/include-config-*
+/include-revision
+/Makefile
+.ninja_*
+*.ninja
+*.pc
+test/*.test
+wayland-generated-protocols
 
 # for CLion
 .idea

CMakeLists.txt

···
 cmake_minimum_required(VERSION 3.16)
 
-if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_CURRENT_BINARY_DIR)
-  message(FATAL_ERROR "Prevented in-tree build. Please create a build directory outside of the SDL source code and run \"cmake -S ${CMAKE_SOURCE_DIR} -B .\" from there")
-endif()
-
 # See docs/release_checklist.md
 project(SDL3 LANGUAGES C VERSION "3.1.5")
 
···
 sdl_include_directories(
   PRIVATE
     "${SDL3_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/build_config"
-    "${SDL3_BINARY_DIR}/include"
+    "${SDL3_BINARY_DIR}/include-revision"
     "${SDL3_SOURCE_DIR}/include"
 )
 # Note: The clang toolset for Visual Studio does not support the '-idirafter' option.
···
 # config variables may contain generator expression, so we need to generate SDL_build_config.h in 2 steps:
 # 1. replace all `#cmakedefine`'s and `@abc@`
 configure_file("${SDL3_SOURCE_DIR}/include/build_config/SDL_build_config.h.cmake"
-  "${SDL3_BINARY_DIR}/SDL_build_config.h.intermediate")
+  "${SDL3_BINARY_DIR}/CMakeFiles/SDL_build_config.h.intermediate")
 # 2. generate SDL_build_config.h in an build_type-dependent folder (which should be first in the include search path)
 file(GENERATE
   OUTPUT "${SDL3_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/build_config/SDL_build_config.h"
-  INPUT "${SDL3_BINARY_DIR}/SDL_build_config.h.intermediate"
+  INPUT "${SDL3_BINARY_DIR}/CMakeFiles/SDL_build_config.h.intermediate"
 )
 
 file(GLOB SDL3_INCLUDE_FILES "${SDL3_SOURCE_DIR}/include/SDL3/*.h")
···
   set(SDL_REVISION "SDL3-${SDL_REVISION_CENTER}")
 endif()
 
-execute_process(COMMAND "${CMAKE_COMMAND}" -E make_directory "${SDL3_BINARY_DIR}/include/SDL3")
-configure_file(include/build_config/SDL_revision.h.cmake include/SDL3/SDL_revision.h @ONLY)
-list(APPEND SDL3_INCLUDE_FILES "${SDL3_BINARY_DIR}/include/SDL3/SDL_revision.h")
+execute_process(COMMAND "${CMAKE_COMMAND}" -E make_directory "${SDL3_BINARY_DIR}/include-revision/SDL3")
+configure_file(include/build_config/SDL_revision.h.cmake include-revision/SDL3/SDL_revision.h @ONLY)
+list(APPEND SDL3_INCLUDE_FILES "${SDL3_BINARY_DIR}/include-revision/SDL3/SDL_revision.h")
 
 if(SDL_FRAMEWORK)
   # With Apple frameworks, headers in the PUBLIC_HEADER property also need to be added as sources
···
 set_property(TARGET SDL3_Headers PROPERTY EXPORT_NAME "Headers")
 target_include_directories(SDL3_Headers
   INTERFACE
-    "$<BUILD_INTERFACE:${SDL3_BINARY_DIR}/include>"
+    "$<BUILD_INTERFACE:${SDL3_BINARY_DIR}/include-revision>"
     "$<BUILD_INTERFACE:${SDL3_SOURCE_DIR}/include>"
 )
 if(SDL_FRAMEWORK)

cmake/macros.cmake

···
     set(LINKER_SUPPORTS_VERSION_SCRIPT FALSE)
   else()
     cmake_push_check_state(RESET)
-    file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/dummy.sym" "n_0 {\n global:\n  func;\n local: *;\n};\n")
-    list(APPEND CMAKE_REQUIRED_LINK_OPTIONS "-Wl,--version-script=${CMAKE_CURRENT_BINARY_DIR}/dummy.sym")
+    file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/dummy.sym" "n_0 {\n global:\n  func;\n local: *;\n};\n")
+    list(APPEND CMAKE_REQUIRED_LINK_OPTIONS "-Wl,--version-script=${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/dummy.sym")
     check_c_source_compiles("int func(void) {return 0;} int main(int argc,char*argv[]){(void)argc;(void)argv;return func();}" LINKER_SUPPORTS_VERSION_SCRIPT FAIL_REGEX "(unsupported|syntax error|unrecognized option)")
     cmake_pop_check_state()
   endif()