generate_apple_*_selection_file: Add option to capture errors

Add an option to capture error messages in a variable instead of
terminating with a fatal error.

Fixes: #25778

Modules/CMakePackageConfigHelpers.cmake

@@ -210,6 +210,7 @@ Generating an Apple Platform Selection File
       [WATCHOS_SIMULATOR_INCLUDE_FILE <file>]
       [VISIONOS_INCLUDE_FILE <file>]
       [VISIONOS_SIMULATOR_INCLUDE_FILE <file>]
+      [ERROR_VARIABLE <variable>]
       )
 
   Write a file that includes an Apple-platform-specific ``.cmake`` file,
@@ -256,9 +257,16 @@ Generating an Apple Platform Selection File
   ``VISIONOS_SIMULATOR_INCLUDE_FILE <file>``
     File to include if the platform is visionOS Simulator.
 
+  ``ERROR_VARIABLE <variable>``
+    If the consuming project is built for an unsupported platform,
+    set ``<variable>`` to an error message.  The includer may use this
+    information to pretend the package was not found.  If this option
+    is not given, the default behavior is to issue a fatal error.
+
   If any of the optional include files is not specified, and the consuming
-  project is built for its corresponding platform, an error will be thrown
-  when including the generated file.
+  project is built for its corresponding platform, the generated file will
+  consider the platform to be unsupported.  The behavior is determined
+  by the ``ERROR_VARIABLE`` option.
 
 .. command:: generate_apple_architecture_selection_file
 
@@ -275,6 +283,7 @@ Generating an Apple Platform Selection File
        SINGLE_ARCHITECTURE_INCLUDE_FILES <file>...]
       [UNIVERSAL_ARCHITECTURES <arch>...
        UNIVERSAL_INCLUDE_FILE <file>]
+      [ERROR_VARIABLE <variable>]
       )
 
   Write a file that includes an Apple-architecture-specific ``.cmake`` file
@@ -313,6 +322,12 @@ Generating an Apple Platform Selection File
     a (non-strict) subset of the ``UNIVERSAL_ARCHITECTURES`` and
     does not match any one of the ``SINGLE_ARCHITECTURES``.
 
+  ``ERROR_VARIABLE <variable>``
+    If the consuming project is built for an unsupported architecture,
+    set ``<variable>`` to an error message.  The includer may use this
+    information to pretend the package was not found.  If this option
+    is not given, the default behavior is to issue a fatal error.
+
 Example Generating Package Files
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -486,6 +501,7 @@ function(generate_apple_platform_selection_file _output_file)
     INSTALL_DESTINATION
     INSTALL_PREFIX
     ${_config_file_options}
+    ERROR_VARIABLE
     )
   set(_multi)
   cmake_parse_arguments(PARSE_ARGV 0 _gpsf "${_options}" "${_single}" "${_multi}")
@@ -499,8 +515,15 @@ function(generate_apple_platform_selection_file _output_file)
     set(maybe_INSTALL_PREFIX "")
   endif()
 
+  if(_gpsf_ERROR_VARIABLE)
+    set(_branch_INIT "set(\"${_gpsf_ERROR_VARIABLE}\" \"\")")
+  else()
+    set(_branch_INIT "")
+  endif()
+
+  set(_else ELSE)
   set(_have_relative 0)
-  foreach(_opt IN LISTS _config_file_options)
+  foreach(_opt IN LISTS _config_file_options _else)
     if(_gpsf_${_opt})
       set(_config_file "${_gpsf_${_opt}}")
       if(NOT IS_ABSOLUTE "${_config_file}")
@@ -508,6 +531,8 @@ function(generate_apple_platform_selection_file _output_file)
         set(_have_relative 1)
       endif()
       set(_branch_${_opt} "include(\"${_config_file}\")")
+    elseif(_gpsf_ERROR_VARIABLE)
+      set(_branch_${_opt} "set(\"${_gpsf_ERROR_VARIABLE}\" \"Platform not supported\")")
     else()
       set(_branch_${_opt} "message(FATAL_ERROR \"Platform not supported\")")
     endif()
@@ -527,6 +552,7 @@ function(generate_apple_architecture_selection_file _output_file)
     INSTALL_DESTINATION
     INSTALL_PREFIX
     UNIVERSAL_INCLUDE_FILE
+    ERROR_VARIABLE
     )
   set(_multi
     SINGLE_ARCHITECTURES
@@ -552,6 +578,30 @@ function(generate_apple_architecture_selection_file _output_file)
 
   set(_branch_code "")
 
+  if(_gasf_ERROR_VARIABLE)
+    string(APPEND _branch_code
+      "set(\"${_gasf_ERROR_VARIABLE}\" \"\")\n"
+      )
+  endif()
+
+  string(APPEND _branch_code
+    "\n"
+    "if(NOT CMAKE_OSX_ARCHITECTURES)\n"
+    )
+  if(_gasf_ERROR_VARIABLE)
+    string(APPEND _branch_code
+      "  set(\"${_gasf_ERROR_VARIABLE}\" \"CMAKE_OSX_ARCHITECTURES must be explicitly set for this package\")\n"
+      "  return()\n"
+      )
+  else()
+    string(APPEND _branch_code
+      "  message(FATAL_ERROR \"CMAKE_OSX_ARCHITECTURES must be explicitly set for this package\")\n"
+      )
+  endif()
+  string(APPEND _branch_code
+    "endif()\n"
+    )
+
   foreach(pair IN ZIP_LISTS _gasf_SINGLE_ARCHITECTURES _gasf_SINGLE_ARCHITECTURE_INCLUDE_FILES)
     set(arch "${pair_0}")
     set(config_file "${pair_1}")
@@ -588,6 +638,13 @@ function(generate_apple_architecture_selection_file _output_file)
     message(FATAL_ERROR "UNIVERSAL_ARCHITECTURES requires UNIVERSAL_INCLUDE_FILE")
   endif()
 
+  string(APPEND _branch_code "\n")
+  if(_gasf_ERROR_VARIABLE)
+    string(APPEND _branch_code "set(\"${_gasf_ERROR_VARIABLE}\" \"Architecture not supported\")")
+  else()
+    string(APPEND _branch_code "message(FATAL_ERROR \"Architecture not supported\")")
+  endif()
+
   configure_package_config_file("${CMAKE_CURRENT_FUNCTION_LIST_DIR}/Internal/AppleArchitectureSelection.cmake.in" "${_output_file}"
     INSTALL_DESTINATION "${_gasf_INSTALL_DESTINATION}"
     ${maybe_INSTALL_PREFIX}

Modules/Internal/AppleArchitectureSelection.cmake.in

@@ -1,8 +1,2 @@
 @PACKAGE_INIT@
-
-if(NOT CMAKE_OSX_ARCHITECTURES)
-  message(FATAL_ERROR "CMAKE_OSX_ARCHITECTURES must be explicitly set for this package")
-endif()
 @_branch_code@
-
-message(FATAL_ERROR "Architecture not supported")

Modules/Internal/ApplePlatformSelection.cmake.in

@@ -1,6 +1,7 @@
 @PACKAGE_INIT@
 
 string(TOLOWER "${CMAKE_OSX_SYSROOT}" _CMAKE_OSX_SYSROOT_LOWER)
+@_branch_INIT@
 if(_CMAKE_OSX_SYSROOT_LOWER MATCHES "(^|/)iphonesimulator")
   @_branch_IOS_SIMULATOR_INCLUDE_FILE@
 elseif(_CMAKE_OSX_SYSROOT_LOWER MATCHES "(^|/)iphoneos")
@@ -20,5 +21,5 @@ elseif(_CMAKE_OSX_SYSROOT_LOWER MATCHES "(^|/)xros")
 elseif(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
   @_branch_MACOS_INCLUDE_FILE@
 else()
-  message(FATAL_ERROR "Platform not supported")
+  @_branch_ELSE@
 endif()

Tests/RunCMake/CMakePackage/RunCMakeTest.cmake

@@ -37,6 +37,9 @@ function(apple_import platform system_name archs sysroot)
     ${maybe_CMAKE_BUILD_TYPE}
     )
   set(RunCMake_TEST_NO_CLEAN 1)
+  if(apple_import_no_build)
+    return()
+  endif()
   run_cmake_command(apple-import-${platform}-build ${CMAKE_COMMAND} --build . --config Release)
 endfunction()
 
@@ -93,6 +96,8 @@ if(APPLE AND CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
     apple_export(visionos-simulator visionOS "${macos_archs}" xrsimulator)
   endif()
   apple_export(watchos-simulator watchOS "${watch_sim_archs}" watchsimulator)
+  apple_export(unsupported-capture Darwin "${macos_archs}" macosx)
+  apple_export(unsupported-fatal Darwin "${macos_archs}" macosx)
 
   apple_import(macos Darwin "${macos_archs}" macosx)
   apple_import(ios iOS "arm64" iphoneos)
@@ -115,4 +120,9 @@ if(APPLE AND CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
     apple_import(visionos-simulator visionOS "${macos_archs}" xrsimulator)
   endif()
   apple_import(watchos-simulator watchOS "${watch_sim_archs}" watchsimulator)
+  set(apple_import_no_build 1)
+  apple_import(unsupported-capture Darwin "${macos_archs}" macosx)
+  apple_import(unsupported-fatal-platform Darwin "${macos_archs}" macosx)
+  apple_import(unsupported-fatal-architecture Darwin "${macos_archs}" macosx)
+  unset(apple_import_no_build)
 endif()

Tests/RunCMake/CMakePackage/apple-export-unsupported-capture.cmake

@@ -0,0 +1,16 @@
+include(apple-common.cmake)
+
+include(CMakePackageConfigHelpers)
+generate_apple_platform_selection_file(bad-platform-capture-config-install.cmake
+  INSTALL_DESTINATION lib/cmake/bad-platform-capture
+  INSTALL_PREFIX ${CMAKE_INSTALL_PREFIX}
+  ERROR_VARIABLE bad-platform-capture_unsupported
+  )
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/bad-platform-capture-config-install.cmake DESTINATION lib/cmake/bad-platform-capture RENAME bad-platform-capture-config.cmake)
+
+generate_apple_architecture_selection_file(bad-arch-capture-config-install.cmake
+  INSTALL_DESTINATION lib/cmake/bad-arch-capture
+  INSTALL_PREFIX ${CMAKE_INSTALL_PREFIX}
+  ERROR_VARIABLE bad-arch-capture_unsupported
+  )
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/bad-arch-capture-config-install.cmake DESTINATION lib/cmake/bad-arch-capture RENAME bad-arch-capture-config.cmake)

Tests/RunCMake/CMakePackage/apple-export-unsupported-fatal.cmake

@@ -0,0 +1,14 @@
+include(apple-common.cmake)
+
+include(CMakePackageConfigHelpers)
+generate_apple_platform_selection_file(bad-platform-fatal-config-install.cmake
+  INSTALL_DESTINATION lib/cmake/bad-platform-fatal
+  INSTALL_PREFIX ${CMAKE_INSTALL_PREFIX}
+  )
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/bad-platform-fatal-config-install.cmake DESTINATION lib/cmake/bad-platform-fatal RENAME bad-platform-fatal-config.cmake)
+
+generate_apple_architecture_selection_file(bad-arch-fatal-config-install.cmake
+  INSTALL_DESTINATION lib/cmake/bad-arch-fatal
+  INSTALL_PREFIX ${CMAKE_INSTALL_PREFIX}
+  )
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/bad-arch-fatal-config-install.cmake DESTINATION lib/cmake/bad-arch-fatal RENAME bad-arch-fatal-config.cmake)

Tests/RunCMake/CMakePackage/apple-import-unsupported-capture-stdout.txt

@@ -0,0 +1,2 @@
+-- Platform not supported
+-- Architecture not supported

Tests/RunCMake/CMakePackage/apple-import-unsupported-capture.cmake

@@ -0,0 +1,11 @@
+include(apple-common.cmake)
+
+set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE NEVER)
+find_package(bad-platform-capture CONFIG REQUIRED)
+find_package(bad-arch-capture CONFIG REQUIRED)
+
+# The above packages capture their own error messages.
+# In real packages they would then set _FOUND to false.
+# For testing here, just print the messages.
+message(STATUS "${bad-platform-capture_unsupported}")
+message(STATUS "${bad-arch-capture_unsupported}")

Tests/RunCMake/CMakePackage/apple-import-unsupported-fatal-architecture-result.txt

@@ -0,0 +1 @@
+1

Tests/RunCMake/CMakePackage/apple-import-unsupported-fatal-architecture-stderr.txt

@@ -0,0 +1,6 @@
+^CMake Error at [^
+]*/Tests/RunCMake/CMakePackage/apple-install/lib/cmake/bad-arch-fatal/bad-arch-fatal-config.cmake:[0-9]+ \(message\):
+  Architecture not supported
+Call Stack \(most recent call first\):
+  apple-import-unsupported-fatal-architecture\.cmake:[0-9]+ \(find_package\)
+  CMakeLists\.txt:[0-9]+ \(include\)$

Tests/RunCMake/CMakePackage/apple-import-unsupported-fatal-architecture.cmake

@@ -0,0 +1,4 @@
+include(apple-common.cmake)
+
+set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE NEVER)
+find_package(bad-arch-fatal CONFIG REQUIRED)

Tests/RunCMake/CMakePackage/apple-import-unsupported-fatal-platform-result.txt

@@ -0,0 +1 @@
+1

Tests/RunCMake/CMakePackage/apple-import-unsupported-fatal-platform-stderr.txt

@@ -0,0 +1,6 @@
+^CMake Error at [^
+]*/Tests/RunCMake/CMakePackage/apple-install/lib/cmake/bad-platform-fatal/bad-platform-fatal-config.cmake:[0-9]+ \(message\):
+  Platform not supported
+Call Stack \(most recent call first\):
+  apple-import-unsupported-fatal-platform\.cmake:[0-9]+ \(find_package\)
+  CMakeLists\.txt:[0-9]+ \(include\)$

Tests/RunCMake/CMakePackage/apple-import-unsupported-fatal-platform.cmake

@@ -0,0 +1,4 @@
+include(apple-common.cmake)
+
+set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE NEVER)
+find_package(bad-platform-fatal CONFIG REQUIRED)