Tests: Cover macOS host architecture selection on Apple Silicon hosts

Add test cases verifying that `CMAKE_APPLE_SILICON_PROCESSOR` set as
either a cache or environment variable causes that to be selected as the
host architecture.  Also verify that sources compile using whatever is
selected as the host architecture, even when the explicit setting is not
used.

Issue: #21554

Tests/CMakeLists.txt

@@ -228,6 +228,22 @@ if(BUILD_TESTING)
     endif()
   endif()
 
+  if(CMAKE_SYSTEM_NAME STREQUAL "Darwin" AND NOT DEFINED CMake_TEST_APPLE_SILICON)
+    execute_process(COMMAND sysctl -q hw.optional.arm64
+      OUTPUT_VARIABLE _sysctl_stdout
+      ERROR_VARIABLE  _sysctl_stderr
+      RESULT_VARIABLE _sysctl_result
+      )
+    if(_sysctl_result EQUAL 0 AND _sysctl_stdout MATCHES "hw.optional.arm64: 1")
+      set(CMake_TEST_APPLE_SILICON 1)
+    else()
+      set(CMake_TEST_APPLE_SILICON 0)
+    endif()
+    unset(_sysctl_result)
+    unset(_sysctl_stderr)
+    unset(_sysctl_stdout)
+  endif()
+
   #---------------------------------------------------------------------------
   # Add tests below here.
 

Tests/RunCMake/AppleSilicon/CMakeLists.txt

@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.19)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)

Tests/RunCMake/AppleSilicon/RunCMakeTest.cmake

@@ -0,0 +1,27 @@
+include(RunCMake)
+
+# Isolate from caller's environment.
+set(ENV{CMAKE_APPLE_SILICON_PROCESSOR} "")
+set(ENV{CMAKE_OSX_ARCHITECTURES} "")
+
+function(run_arch case)
+  set(RunCMake_TEST_OPTIONS ${ARGN})
+  set(RunCMake_TEST_BINARY_DIR "${RunCMake_BINARY_DIR}/${case}-build")
+  run_cmake(${case})
+  unset(RunCMake_TEST_OPTIONS)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  run_cmake_command(${case}-build ${CMAKE_COMMAND} --build . --config Debug)
+endfunction()
+
+run_arch(default)
+
+run_arch(arm64-var -DCMAKE_APPLE_SILICON_PROCESSOR=arm64)
+run_arch(x86_64-var -DCMAKE_APPLE_SILICON_PROCESSOR=x86_64)
+
+set(ENV{CMAKE_APPLE_SILICON_PROCESSOR} "arm64")
+run_arch(arm64-env)
+
+set(ENV{CMAKE_APPLE_SILICON_PROCESSOR} "x86_64")
+run_arch(x86_64-env)
+
+set(ENV{CMAKE_APPLE_SILICON_PROCESSOR} "")

Tests/RunCMake/AppleSilicon/arm64-common.cmake

@@ -0,0 +1,10 @@
+enable_language(C)
+
+if(NOT CMAKE_HOST_SYSTEM_PROCESSOR STREQUAL "arm64")
+  message(FATAL_ERROR "CMAKE_HOST_SYSTEM_PROCESSOR is '${CMAKE_HOST_SYSTEM_PROCESSOR}', not 'arm64'")
+endif()
+if(NOT CMAKE_OSX_ARCHITECTURES STREQUAL "")
+  message(FATAL_ERROR "CMAKE_OSX_ARCHITECTURES is '${CMAKE_OSX_ARCHITECTURES}', not empty ''")
+endif()
+
+add_library(arm64 arm64.c)

Tests/RunCMake/AppleSilicon/arm64-env.cmake

@@ -0,0 +1 @@
+include(arm64-common.cmake)

Tests/RunCMake/AppleSilicon/arm64-var.cmake

@@ -0,0 +1 @@
+include(arm64-common.cmake)

Tests/RunCMake/AppleSilicon/arm64.c

@@ -0,0 +1,9 @@
+#ifndef __aarch64__
+#  error "Not compiling as arm64"
+#endif
+#ifdef __x86_64__
+#  error "Incorrectly compiling as x86_64"
+#endif
+void arm64_arch(void)
+{
+}

Tests/RunCMake/AppleSilicon/default.c

@@ -0,0 +1,14 @@
+#if defined(HOST_ARM64)
+#  if !defined(__aarch64__)
+#    error "Not compiling as host arm64"
+#  endif
+#elif defined(HOST_X86_64)
+#  if !defined(__x86_64__)
+#    error "Not compiling as host x86_64"
+#  endif
+#else
+#  error "One of HOST_ARM64 or HOST_X86_64 must be defined."
+#endif
+void default_arch(void)
+{
+}

Tests/RunCMake/AppleSilicon/default.cmake

@@ -0,0 +1,15 @@
+enable_language(C)
+
+if(CMAKE_HOST_SYSTEM_PROCESSOR STREQUAL "arm64")
+  set(host_def HOST_ARM64)
+elseif(CMAKE_HOST_SYSTEM_PROCESSOR STREQUAL "x86_64")
+  set(host_def HOST_X86_64)
+else()
+  message(FATAL_ERROR "CMAKE_HOST_SYSTEM_PROCESSOR is '${CMAKE_HOST_SYSTEM_PROCESSOR}', not 'arm64' or 'x86_64'")
+endif()
+if(NOT CMAKE_OSX_ARCHITECTURES STREQUAL "")
+  message(FATAL_ERROR "CMAKE_OSX_ARCHITECTURES is '${CMAKE_OSX_ARCHITECTURES}', not empty ''")
+endif()
+
+add_library(default default.c)
+target_compile_definitions(default PRIVATE ${host_def})

Tests/RunCMake/AppleSilicon/x86_64-common.cmake

@@ -0,0 +1,10 @@
+enable_language(C)
+
+if(NOT CMAKE_HOST_SYSTEM_PROCESSOR STREQUAL "x86_64")
+  message(FATAL_ERROR "CMAKE_HOST_SYSTEM_PROCESSOR is '${CMAKE_HOST_SYSTEM_PROCESSOR}', not 'x86_64'")
+endif()
+if(NOT CMAKE_OSX_ARCHITECTURES STREQUAL "")
+  message(FATAL_ERROR "CMAKE_OSX_ARCHITECTURES is '${CMAKE_OSX_ARCHITECTURES}', not empty ''")
+endif()
+
+add_library(x86_64 x86_64.c)

Tests/RunCMake/AppleSilicon/x86_64-env.cmake

@@ -0,0 +1 @@
+include(x86_64-common.cmake)

Tests/RunCMake/AppleSilicon/x86_64-var.cmake

@@ -0,0 +1 @@
+include(x86_64-common.cmake)

Tests/RunCMake/AppleSilicon/x86_64.c

@@ -0,0 +1,9 @@
+#ifndef __x86_64__
+#  error "Not compiling as x86_64"
+#endif
+#ifdef __aarch64__
+#  error "Incorrectly compiling as arm64"
+#endif
+void x86_64_arch(void)
+{
+}

Tests/RunCMake/CMakeLists.txt

@@ -176,6 +176,9 @@ if(NOT CMake_TEST_EXTERNAL_CMAKE)
 endif()
 
 add_RunCMake_test(AndroidTestUtilities)
+if(CMake_TEST_APPLE_SILICON)
+  add_RunCMake_test(AppleSilicon)
+endif()
 set(autogen_with_qt5 FALSE)
 if(CMake_TEST_Qt5)
   find_package(Qt5Widgets QUIET NO_MODULE)