cmake: Use standard CMAKE_INSTALL_INCLUDEDIR (#347)

* cmake: use standard `CMAKE_INSTALL_INCLUDEDIR`

Current code uses hard-coded `include` or `CMAKE_INSTALL_INCDIR` to specify included directories. It makes the installed target not work with Nix, which tries to split headers into a different package. `CMAKE_INSTALL_INCLUDEDIR` is CMake’s recommended standard for setting header location. It allows package maintainers like Nix to control the install destination by setting appropriate cache variables.

* Add changelog fragment

Author: KiruyaMomochi

CMakeLists.txt

@@ -78,7 +78,7 @@ elseif(ANDROID AND INSTALL_TO_ARCHITECTURE_PREFIXES)
     set(PREFAB_MODULE_INSTALL_DIR ${PREFAB_INSTALL_DIR}/modules/openxr_loader)
     set(CMAKE_INSTALL_LIBDIR ${PREFAB_MODULE_INSTALL_DIR}/libs/android.${ANDROID_ABI} CACHE STRING "Where to install libraries")
     set(CMAKE_INSTALL_BINDIR ${CMAKE_INSTALL_LIBDIR})
-    set(CMAKE_INSTALL_INCDIR ${PREFAB_MODULE_INSTALL_DIR}/include)
+    set(CMAKE_INSTALL_INCLUDEDIR ${PREFAB_MODULE_INSTALL_DIR}/include)
 
     unset(NDK_MAJOR_VERSION)
     if(CMAKE_ANDROID_NDK)

changes/sdk/pr.347.gh.OpenXR-SDK-Source.md

@@ -0,0 +1 @@
+cmake: Use standard `CMAKE_INSTALL_INCLUDEDIR` to specify included directories.

include/openxr/CMakeLists.txt

@@ -91,11 +91,11 @@ else()
     )
 endif()
 set_target_properties(generate_openxr_header PROPERTIES FOLDER ${CODEGEN_FOLDER})
-if(NOT CMAKE_INSTALL_INCDIR)
-    set(CMAKE_INSTALL_INCDIR include)
-endif()
+
+# make cache variables for install destinations
+include(GNUInstallDirs)
 
 INSTALL(FILES ${INSTALL_HEADERS}
-    DESTINATION ${CMAKE_INSTALL_INCDIR}/openxr
+    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/openxr
     COMPONENT Headers
 )

src/loader/CMakeLists.txt

@@ -28,6 +28,9 @@ if(NOT MSVC)
     set(CMAKE_CXX_VISIBILITY_PRESET hidden)
 endif()
 
+# make cache variables for install destinations
+include(GNUInstallDirs)
+
 # List of all files externally generated outside of the loader that the loader
 # needs to build with.
 set(LOADER_EXTERNAL_GEN_FILES ${COMMON_GENERATED_OUTPUT})
@@ -108,7 +111,7 @@ target_include_directories(
             # for target-specific generated files
             ${CMAKE_CURRENT_SOURCE_DIR}
             ${CMAKE_CURRENT_BINARY_DIR}
-    INTERFACE $<INSTALL_INTERFACE:include>
+    INTERFACE $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
 )
 
 if(Vulkan_FOUND)
@@ -277,7 +280,7 @@ if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID MATCHES "Clang")
 endif()
 
 add_library(headers INTERFACE)
-target_include_directories(headers INTERFACE $<INSTALL_INTERFACE:include>)
+target_include_directories(headers INTERFACE $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 
 # We will never actually install here, but it's easier to set something than block all install code.
 if(ANDROID AND NOT INSTALL_TO_ARCHITECTURE_PREFIXES)