[CMake] [Darwin] Don't build the SDK overlays by default on Apple platforms

The Apple SDKs have been providing the Darwin overlay since macOS 10.14.4, iOS 12.2, et al. More recently the SDK version has diverged from the Swift version making them incompatible. Stop building the overlay from Swift.

rdar://115192929

Author: ian-twilightcoder

CMakeLists.txt

@@ -244,10 +244,17 @@ option(SWIFT_BUILD_CLANG_OVERLAYS
   "Build Swift overlays for the clang builtin modules"
   TRUE)
 
+# The SDK overlay is provided by the SDK itself on Darwin platforms.
+if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS)
+  set(SWIFT_BUILD_DYNAMIC_SDK_OVERLAY_default FALSE)
+else()
+  set(SWIFT_BUILD_DYNAMIC_SDK_OVERLAY_default TRUE)
+endif()
+
 option(SWIFT_BUILD_DYNAMIC_SDK_OVERLAY
     "Build dynamic variants of the Swift SDK overlay"
-    TRUE)
-
+    "${SWIFT_BUILD_DYNAMIC_SDK_OVERLAY_default}")
+  
 option(SWIFT_BUILD_STATIC_SDK_OVERLAY
     "Build static variants of the Swift SDK overlay"
     FALSE)

benchmark/cmake/modules/AddSwiftBenchmarkSuite.cmake

@@ -716,7 +716,7 @@ function(swift_benchmark_compile)
 
   if(NOT SWIFT_BENCHMARK_BUILT_STANDALONE)
     set(stdlib_dependencies "swift-frontend" "swiftCore-${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}")
-    if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS)
+    if((SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS) AND ${SWIFT_BUILD_SDK_OVERLAY})
       list(APPEND stdlib_dependencies "swiftDarwin-${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}")
     endif()
     foreach(stdlib_dependency ${UNIVERSAL_LIBRARY_NAMES_${SWIFT_BENCHMARK_COMPILE_PLATFORM}})

cmake/modules/DarwinSDKs.cmake

@@ -38,7 +38,11 @@ if(swift_build_freestanding AND (SWIFT_FREESTANDING_FLAVOR STREQUAL "apple"))
   configure_target_variant(FREESTANDING-R  "FREESTANDING Release"         FREESTANDING R  "Release")
   configure_target_variant(FREESTANDING-S  "FREESTANDING MinSizeRelease"  FREESTANDING S  "MinSizeRelease")
 
-  set(SWIFT_FREESTANDING_TEST_DEPENDENCIES "Darwin")
+  if(${SWIFT_BUILD_SDK_OVERLAY})
+    set(SWIFT_FREESTANDING_TEST_DEPENDENCIES "Darwin")
+  else()
+    set(SWIFT_FREESTANDING_TEST_DEPENDENCIES "")
+  endif()
 endif()
 
 # Compatible cross-compile SDKS for Darwin OSes: IOS, IOS_SIMULATOR, TVOS,

stdlib/public/CMakeLists.txt

@@ -315,7 +315,7 @@ if(SWIFT_BUILD_REMOTE_MIRROR)
   add_subdirectory(SwiftRemoteMirror)
 endif()
 
-if(SWIFT_BUILD_SDK_OVERLAY OR SWIFT_BUILD_TEST_SUPPORT_MODULES)
+if(SWIFT_BUILD_SDK_OVERLAY OR (SWIFT_BUILD_TEST_SUPPORT_MODULES AND SWIFT_BUILD_DYNAMIC_SDK_OVERLAY_default))
   add_subdirectory(Platform)
 endif()
 

utils/build_swift/build_swift/driver_arguments.py

@@ -8,6 +8,7 @@
 
 import multiprocessing
 import os
+import platform
 
 import android.adb.commands
 
@@ -1136,7 +1137,7 @@ def create_argument_parser():
            help='build static variants of the Swift standard library')
 
     option('--build-swift-dynamic-sdk-overlay', toggle_true,
-           default=True,
+           default=platform.system() != "Darwin",
            help='build dynamic variants of the Swift SDK overlay')
 
     option('--build-swift-static-sdk-overlay', toggle_true,

utils/build_swift/tests/expected_options.py

@@ -8,6 +8,7 @@
 
 
 import multiprocessing
+import platform
 
 from build_swift import argparse
 from build_swift import defaults
@@ -79,7 +80,7 @@
     'build_runtime_with_host_compiler': False,
     'build_stdlib_deployment_targets': ['all'],
     'build_subdir': None,
-    'build_swift_dynamic_sdk_overlay': True,
+    'build_swift_dynamic_sdk_overlay': platform.system() != "Darwin",
     'build_swift_dynamic_stdlib': True,
     'build_swift_inspect': False,
     'build_swift_private_stdlib': True,