iOS: Fix detection of supported SDK architectures

Instead of relying on SDKSettings.plist which does not contain the
certain architectures, deduce the supported architectures by
inspecting libSystem.tbd and libSystem.dylib.

.tbd files are text files, so just parse out the archs string.
.dylib files can be fat or non-fat, so use lipo -info to extract
the architectures and parse lipo output.

Fixes: #20588

Modules/Platform/Darwin-Initialize.cmake

@@ -133,6 +133,80 @@ function(_apple_resolve_sdk_path sdk_name ret)
   )
   set(${ret} "${_stdout}" PARENT_SCOPE)
 endfunction()
+
+function(_apple_resolve_supported_archs_for_sdk_from_system_lib sdk_path ret ret_failed)
+  # Detect the supported SDK architectures by inspecting the main libSystem library.
+  set(common_lib_prefix "${sdk_path}/usr/lib/libSystem")
+  set(system_lib_dylib_path "${common_lib_prefix}.dylib")
+  set(system_lib_tbd_path "${common_lib_prefix}.tbd")
+
+  # Newer SDKs ship text based dylib stub files which contain the architectures supported by the
+  # library in text form.
+  if(EXISTS "${system_lib_tbd_path}")
+    file(STRINGS "${system_lib_tbd_path}" tbd_lines REGEX "^archs: +\\[.+\\]")
+    if(NOT tbd_lines)
+      set(${ret_failed} TRUE PARENT_SCOPE)
+      return()
+    endif()
+
+    # The tbd architectures line looks like the following:
+    # archs:           [ armv7, armv7s, arm64, arm64e ]
+    list(GET tbd_lines 0 first_arch_line)
+    string(REGEX REPLACE
+           "archs: +\\[ (.+) \\]" "\\1" arches_comma_separated "${first_arch_line}")
+    string(STRIP "${arches_comma_separated}" arches_comma_separated)
+    string(REPLACE "," ";" arch_list "${arches_comma_separated}")
+    string(REPLACE " " "" arch_list "${arch_list}")
+    if(NOT arch_list)
+      set(${ret_failed} TRUE PARENT_SCOPE)
+      return()
+    endif()
+    set(${ret} "${arch_list}" PARENT_SCOPE)
+  elseif(EXISTS "${system_lib_dylib_path}")
+    # Old SDKs (Xcode < 7) ship dylib files, use lipo to inspect the supported architectures.
+    # Can't use -archs because the option is not available in older Xcode versions.
+    execute_process(
+      COMMAND lipo -info ${system_lib_dylib_path}
+      OUTPUT_VARIABLE lipo_output
+      OUTPUT_STRIP_TRAILING_WHITESPACE
+      ERROR_VARIABLE _stderr
+      RESULT_VARIABLE _failed
+    )
+    if(_failed OR NOT lipo_output OR NOT lipo_output MATCHES "(Non-fat file:|Architectures in the fat file:)")
+      set(${ret_failed} TRUE PARENT_SCOPE)
+      return()
+    endif()
+
+    # The lipo output looks like the following:
+    # Non-fat file: <path> is architecture: i386
+    # Architectures in the fat file: <path> are: i386 x86_64
+    string(REGEX REPLACE
+           "^(.+)is architecture:(.+)" "\\2" arches_space_separated "${lipo_output}")
+    string(REGEX REPLACE
+            "^(.+)are:(.+)" "\\2" arches_space_separated "${arches_space_separated}")
+
+    # Need to clean up the arches, with Xcode 4.6.3 the output of lipo -info contains some
+    # additional info, e.g.
+    # Architectures in the fat file: <path> are: armv7 (cputype (12) cpusubtype (11))
+    string(REGEX REPLACE
+            "\\(.+\\)" "" arches_space_separated "${arches_space_separated}")
+
+    # The output is space separated.
+    string(STRIP "${arches_space_separated}" arches_space_separated)
+    string(REPLACE " " ";" arch_list "${arches_space_separated}")
+
+    if(NOT arch_list)
+      set(${ret_failed} TRUE PARENT_SCOPE)
+      return()
+    endif()
+    set(${ret} "${arch_list}" PARENT_SCOPE)
+  else()
+    # This shouldn't happen, but keep it for safety.
+    message(WARNING "No way to find architectures for given sdk_path '${sdk_path}'")
+    set(${ret_failed} TRUE PARENT_SCOPE)
+  endif()
+endfunction()
+
 # Handle multi-arch sysroots. Do this before CMAKE_OSX_SYSROOT is
 # transformed into a path, so that we know the sysroot name.
 function(_apple_resolve_multi_arch_sysroots)
@@ -166,13 +240,8 @@ function(_apple_resolve_multi_arch_sysroots)
       continue()
     endif()
 
-    execute_process(
+    _apple_resolve_supported_archs_for_sdk_from_system_lib(${_sdk_path} _sdk_archs _failed)
-      COMMAND plutil -extract SupportedTargets.${sdk}.Archs json ${_sdk_path}/SDKSettings.plist -o -
+
-      OUTPUT_VARIABLE _sdk_archs_json
-      OUTPUT_STRIP_TRAILING_WHITESPACE
-      ERROR_VARIABLE _stderr
-      RESULT_VARIABLE _failed
-      )
     if(_failed)
       # Failure to extract supported architectures for an SDK means that the installed SDK is old
       # and does not provide such information (SDKs that come with Xcode >= 10.x started providing
@@ -181,10 +250,6 @@ function(_apple_resolve_multi_arch_sysroots)
       return()
     endif()
 
-    # Poor man's JSON decoding
-    string(REGEX REPLACE "[]\\[\"]" "" _sdk_archs ${_sdk_archs_json})
-    string(REPLACE "," ";" _sdk_archs ${_sdk_archs})
-
     set(_sdk_archs_${sdk} ${_sdk_archs})
     set(_sdk_path_${sdk} ${_sdk_path})
   endforeach()