Add a flag to build the stdlib without COMPATIBILITY_OVERRIDE (swiftlang#33438)

Author: kubamracek

stdlib/CMakeLists.txt

@@ -9,6 +9,18 @@ project(swift-stdlib LANGUAGES C CXX)
 list(APPEND CMAKE_MODULE_PATH
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
 
+#
+# User-configurable options for the standard library.
+#
+
+option(SWIFT_ENABLE_COMPATIBILITY_OVERRIDES
+  "Support back-deploying compatibility fixes for newer apps running on older runtimes."
+  TRUE)
+
+#
+# End of user-configurable options.
+#
+
 include(AddSwiftStdlib)
 
 # Create convenience targets for the Swift standard library.

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -333,6 +333,10 @@ function(_add_target_variant_c_compile_flags)
     list(APPEND result "-DSWIFT_OBJC_INTEROP=0")
   endif()
 
+  if(NOT SWIFT_ENABLE_COMPATIBILITY_OVERRIDES)
+    list(APPEND result "-DSWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES")
+  endif()
+
   set("${CFLAGS_RESULT_VAR_NAME}" "${result}" PARENT_SCOPE)
 endfunction()
 

stdlib/public/runtime/CompatibilityOverride.cpp

@@ -14,6 +14,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#ifndef SWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES
+
 #include "CompatibilityOverride.h"
 
 #include "ImageInspection.h"
@@ -68,3 +70,5 @@ static OverrideSection *getOverrideSectionPtr() {
     return Section->name;                                           \
   }
 #include "CompatibilityOverride.def"
+
+#endif // #ifndef SWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES

stdlib/public/runtime/CompatibilityOverride.h

@@ -24,6 +24,15 @@
 
 namespace swift {
 
+#ifdef SWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES
+
+#define COMPATIBILITY_OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
+  attrs ccAttrs ret namespace swift_ ## name typedArgs {                          \
+    return swift_ ## name ## Impl namedArgs; \
+  }
+
+#else // #ifdef SWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES
+
 #define COMPATIBILITY_UNPAREN(...) __VA_ARGS__
 
 #define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
@@ -56,6 +65,8 @@ namespace swift {
     return swift_ ## name ## Impl namedArgs; \
   }
 
+#endif // #else SWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES
+
 } /* end namespace swift */
 
 #endif /* COMPATIBILITY_OVERRIDE_H */

stdlib/public/runtime/ImageInspectionMachO.cpp

@@ -169,6 +169,8 @@ int swift::lookupSymbol(const void *address, SymbolInfo *info) {
   return 1;
 }
 
+#ifndef SWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES
+
 void *swift::lookupSection(const char *segment, const char *section, size_t *outSize) {
   unsigned long size;
   auto *executableHeader = static_cast<mach_header_platform *>(_NSGetMachExecuteHeader());
@@ -178,4 +180,6 @@ void *swift::lookupSection(const char *segment, const char *section, size_t *out
   return static_cast<void *>(data);
 }
 
+#endif // #ifndef SWIFT_RUNTIME_NO_COMPATIBILITY_OVERRIDES
+
 #endif // defined(__APPLE__) && defined(__MACH__)

utils/build-presets.ini

@@ -2390,6 +2390,7 @@ build-swift-dynamic-sdk-overlay=0
 build-swift-dynamic-stdlib=0
 build-swift-static-stdlib=1
 swift-objc-interop=0
+swift-enable-compatibility-overrides=0
 
 [preset: stdlib_S_standalone_minimal_macho_x86_64,build]
 mixin-preset=

utils/build-script-impl

@@ -193,6 +193,7 @@ KNOWN_SETTINGS=(
     sil-verify-all                                "0"               "If enabled, run the SIL verifier after each transform when building Swift files during this build process"
     stdlib-deployment-targets                     ""                "space-separated list of targets to configure the Swift standard library to be compiled or cross-compiled for"
     swift-objc-interop                            ""                "whether to enable interoperability with Objective-C, default is 1 on Apple platfors, 0 otherwise"
+    swift-enable-compatibility-overrides          "1"               "whether to support back-deploying compatibility fixes for newer apps running on older runtimes"
 
     ## FREESTANDING Stdlib Options
     swift-freestanding-sdk                      ""                "which SDK to use when building the FREESTANDING stdlib"
@@ -1763,6 +1764,7 @@ for host in "${ALL_HOSTS[@]}"; do
                     -DSWIFT_STDLIB_BUILD_TYPE:STRING="${SWIFT_STDLIB_BUILD_TYPE}"
                     -DSWIFT_STDLIB_ASSERTIONS:BOOL=$(true_false "${SWIFT_STDLIB_ENABLE_ASSERTIONS}")
                     -DSWIFT_STDLIB_USE_NONATOMIC_RC:BOOL=$(true_false "${SWIFT_STDLIB_USE_NONATOMIC_RC}")
+                    -DSWIFT_ENABLE_COMPATIBILITY_OVERRIDES:BOOL=$(true_false "${SWIFT_ENABLE_COMPATIBILITY_OVERRIDES}")
                     -DSWIFT_ENABLE_RUNTIME_FUNCTION_COUNTERS:BOOL=$(true_false "${SWIFT_ENABLE_RUNTIME_FUNCTION_COUNTERS}")
                     -DSWIFT_NATIVE_LLVM_TOOLS_PATH:STRING="${native_llvm_tools_path}"
                     -DSWIFT_NATIVE_CLANG_TOOLS_PATH:STRING="${native_clang_tools_path}"