generate_apple_*_selection_file: Save/restore PACKAGE_PREFIX_DIR

Issue: #25827

Modules/Internal/AppleArchitectureSelection.cmake.in

@@ -1,2 +1,23 @@
+# Save this now so we can restore it before returning
+if(NOT DEFINED PACKAGE_PREFIX_DIR)
+  list(APPEND _gasf_PACKAGE_PREFIX_DIR "<__CMAKE_UNDEFINED__>")
+elseif("${PACKAGE_PREFIX_DIR}" STREQUAL "")
+  list(APPEND _gasf_PACKAGE_PREFIX_DIR "<__CMAKE_EMPTY__>")
+else()
+  list(APPEND _gasf_PACKAGE_PREFIX_DIR "${PACKAGE_PREFIX_DIR}")
+endif()
+
 @PACKAGE_INIT@
 @_branch_code@
+
+# Restore PACKAGE_PREFIX_DIR
+list(LENGTH _gasf_PACKAGE_PREFIX_DIR _gasf_tmp)
+math(EXPR _gasf_tmp "${_gasf_tmp} - 1")
+list(GET _gasf_PACKAGE_PREFIX_DIR ${_gasf_tmp} PACKAGE_PREFIX_DIR)
+list(REMOVE_AT _gasf_PACKAGE_PREFIX_DIR ${_gasf_tmp})
+unset(_gasf_tmp)
+if("${PACKAGE_PREFIX_DIR}" STREQUAL "<__CMAKE_UNDEFINED__>")
+  unset(PACKAGE_PREFIX_DIR)
+elseif("${PACKAGE_PREFIX_DIR}" STREQUAL "<__CMAKE_EMPTY__>")
+  set(PACKAGE_PREFIX_DIR "")
+endif()

Modules/Internal/ApplePlatformSelection.cmake.in

@@ -1,3 +1,12 @@
+# Save this now so we can restore it before returning
+if(NOT DEFINED PACKAGE_PREFIX_DIR)
+  list(APPEND _gpsf_PACKAGE_PREFIX_DIR "<__CMAKE_UNDEFINED__>")
+elseif("${PACKAGE_PREFIX_DIR}" STREQUAL "")
+  list(APPEND _gpsf_PACKAGE_PREFIX_DIR "<__CMAKE_EMPTY__>")
+else()
+  list(APPEND _gpsf_PACKAGE_PREFIX_DIR "${PACKAGE_PREFIX_DIR}")
+endif()
+
 @PACKAGE_INIT@
 
 string(TOLOWER "${CMAKE_OSX_SYSROOT}" _CMAKE_OSX_SYSROOT_LOWER)
@@ -23,3 +32,15 @@ elseif(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
 else()
   @_branch_ELSE@
 endif()
+
+# Restore PACKAGE_PREFIX_DIR
+list(LENGTH _gpsf_PACKAGE_PREFIX_DIR _gpsf_tmp)
+math(EXPR _gpsf_tmp "${_gpsf_tmp} - 1")
+list(GET _gpsf_PACKAGE_PREFIX_DIR ${_gpsf_tmp} PACKAGE_PREFIX_DIR)
+list(REMOVE_AT _gpsf_PACKAGE_PREFIX_DIR ${_gpsf_tmp})
+unset(_gpsf_tmp)
+if("${PACKAGE_PREFIX_DIR}" STREQUAL "<__CMAKE_UNDEFINED__>")
+  unset(PACKAGE_PREFIX_DIR)
+elseif("${PACKAGE_PREFIX_DIR}" STREQUAL "<__CMAKE_EMPTY__>")
+  set(PACKAGE_PREFIX_DIR "")
+endif()

Tests/RunCMake/CMakePackage/ApplePlatformGenSubdir-stdout.txt

@@ -0,0 +1,3 @@
+(-- )?Hello from platform switch
+(-- )?Hello from arch switch
+(-- )?Hello from pkg_a

Tests/RunCMake/CMakePackage/ApplePlatformGenSubdir.cmake

@@ -0,0 +1,50 @@
+set(CMAKE_INSTALL_DATADIR share)
+set(SWITCH_DIR platform/cmake)
+
+include(CMakePackageConfigHelpers)
+
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/pkg_a-config.cmake.in [[
+@PACKAGE_INIT@
+include("@PACKAGE_SWITCH_DIR@/platform-switch.cmake")
+include("@PACKAGE_CMAKE_INSTALL_DATADIR@/pkg_a_included.cmake")
+]])
+configure_package_config_file(
+  ${CMAKE_CURRENT_BINARY_DIR}/pkg_a-config.cmake.in
+  ${CMAKE_CURRENT_BINARY_DIR}/install/pkg_a-config.cmake
+  INSTALL_DESTINATION .
+  PATH_VARS CMAKE_INSTALL_DATADIR SWITCH_DIR
+)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/install/${CMAKE_INSTALL_DATADIR}/pkg_a_included.cmake
+  [[message(STATUS "Hello from pkg_a")]]
+)
+
+# To expose re-using the same package prefix variable, we need to use a
+# different install prefix. This is really contrived and not representative of
+# what a package should do.
+generate_apple_platform_selection_file(
+  ${CMAKE_CURRENT_BINARY_DIR}/install/platform/cmake/platform-switch.cmake
+  INSTALL_PREFIX ${CMAKE_INSTALL_PREFIX}/platform
+  INSTALL_DESTINATION cmake
+  MACOS_INCLUDE_FILE cmake/switch_included.cmake  # relative to install prefix
+)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/install/platform/cmake/switch_included.cmake
+[[
+message(STATUS "Hello from platform switch")
+include("${CMAKE_CURRENT_LIST_DIR}/../arch/cmake/arch-switch.cmake")
+]]
+)
+
+generate_apple_architecture_selection_file(
+  ${CMAKE_CURRENT_BINARY_DIR}/install/platform/arch/cmake/arch-switch.cmake
+  INSTALL_PREFIX ${CMAKE_INSTALL_PREFIX}/platform/arch
+  INSTALL_DESTINATION cmake
+  UNIVERSAL_ARCHITECTURES i386 x86_64 arm64 $(ARCHS_STANDARD)
+  UNIVERSAL_INCLUDE_FILE cmake/switch_included.cmake  # relative to install prefix
+)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/install/platform/arch/cmake/switch_included.cmake
+  [[message(STATUS "Hello from arch switch")]]
+)
+
+find_package(pkg_a REQUIRED NO_DEFAULT_PATH
+  PATHS ${CMAKE_CURRENT_BINARY_DIR}/install
+)

Tests/RunCMake/CMakePackage/RunCMakeTest.cmake

@@ -75,6 +75,13 @@ if(APPLE AND CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
     set(enable_visionos 1)
   endif()
 
+  string(REPLACE ";" "\\;" macos_archs_for_cmd "${macos_archs}")
+  run_cmake_with_options(ApplePlatformGenSubdir
+    "-DCMAKE_OSX_ARCHITECTURES=${macos_archs_for_cmd}"
+    ${maybe_CMAKE_BUILD_TYPE}
+  )
+  unset(macos_archs_for_cmd)
+
   # Place all export/import steps in a single install prefix.
   set(apple_install ${RunCMake_BINARY_DIR}/apple-install)
   file(REMOVE_RECURSE "${apple_install}")