Update the branch to build with Xcode 12.5

include/swift/Runtime/Bincompat.h

@@ -22,8 +22,18 @@ namespace bincompat {
 
 /// Whether protocol conformance iteration should be reversed, to prefer
 /// conformances from images that are later in the list over earlier ones.
+/// Default is false starting with Swift 5.4.
 bool workaroundProtocolConformanceReverseIteration();
 
+/// Whether we should crash when we encounter a non-nullable Obj-C
+/// reference with a null value as the source of a cast.
+/// Default is true starting with Swift 5.4.
+bool unexpectedObjCNullWhileCastingIsFatal();
+
+/// Whether we should use the legacy semantics for casting nil optionals
+/// to nested optionals
+bool useLegacyOptionalNilInjection();
+
 } // namespace bincompat
 
 } // namespace runtime

stdlib/public/runtime/Bincompat.cpp

@@ -15,14 +15,92 @@
 //===----------------------------------------------------------------------===//
 
 #include "swift/Runtime/Bincompat.h"
+#include <stdint.h>
+
+// If this is an Apple OS, use the Apple binary compatibility rules
+#if __has_include(<mach-o/dyld_priv.h>)
+  #include <mach-o/dyld_priv.h>
+  #ifndef BINARY_COMPATIBILITY_APPLE
+    #define BINARY_COMPATIBILITY_APPLE 1
+  #endif
+#else
+  #undef BINARY_COMPATIBILITY_APPLE
+#endif
 
 namespace swift {
 
 namespace runtime {
 
 namespace bincompat {
 
-bool workaroundProtocolConformanceReverseIteration() { return false; }
+// Should we mimic the old override behavior when scanning protocol conformance records?
+
+// Old apps expect protocol conformances to override each other in a particular
+// order.  Starting with Swift 5.4, that order has changed as a result of
+// significant performance improvements to protocol conformance scanning.  If
+// this returns `true`, the protocol conformance scan will do extra work to
+// mimic the old override behavior.
+bool workaroundProtocolConformanceReverseIteration() {
+#if BINARY_COMPATIBILITY_APPLE
+  // If this is a newer Apple OS ...
+  if (__builtin_available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *)) {
+    const dyld_build_version_t spring_2021_os_versions = {0xffffffff, 0x007e50301};
+    // ... but the app was compiled before Spring 2021, use the legacy behavior.
+    return !dyld_program_sdk_at_least(spring_2021_os_versions);
+  } else {
+    return false; // Use new (non-legacy) behavior on old Apple OSes
+  }
+#else
+  return false; // Never use the legacy behavior on non-Apple OSes
+#endif
+}
+
+// Should the dynamic cast operation crash when it sees
+// a non-nullable Obj-C pointer with a null value?
+
+// Obj-C does not strictly enforce non-nullability in all cases, so it is
+// possible for Obj-C code to pass null pointers into Swift code even when
+// declared non-nullable.  Such null pointers can lead to undefined behavior
+// later on.  Starting in Swift 5.4, these unexpected null pointers are fatal
+// runtime errors, but this is selectively disabled for old apps.
+bool unexpectedObjCNullWhileCastingIsFatal() {
+#if BINARY_COMPATIBILITY_APPLE
+  // If this is a new enough Apple OS ...
+  if (__builtin_available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *)) {
+    const dyld_build_version_t spring_2021_os_versions = {0xffffffff, 0x007e50301};
+    // ... use strict behavior for apps compiled on or after Spring 2021.
+    return dyld_program_sdk_at_least(spring_2021_os_versions);
+  } else {
+    return false; // Use permissive behavior on old Apple OS
+  }
+#else
+  return true;  // Always use the strict behavior on non-Apple OSes
+#endif
+}
+
+// Should casting a nil optional to another optional
+// use the legacy semantics?
+
+// For consistency, starting with Swift 5.4, casting Optional<Int> to
+// Optional<Optional<Int>> always wraps the source in another layer
+// of Optional.
+// Earlier versions of the Swift runtime did not do this if the source
+// optional was nil.  In that case, the outer target optional would be
+// set to nil.
+bool useLegacyOptionalNilInjection() {
+#if BINARY_COMPATIBILITY_APPLE
+  // If this is a new enough Apple OS ...
+  if (__builtin_available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *)) {
+    const dyld_build_version_t spring_2021_os_versions = {0xffffffff, 0x007e50301};
+    // It's using Spring 2021 or later SDK, so don't use the legacy behavior.
+    return !dyld_program_sdk_at_least(spring_2021_os_versions);
+  } else {
+    return true; // Use the legacy behavior on old Apple OS
+  }
+#else
+  return false;  // Always use the 5.4 behavior on non-Apple OSes
+#endif
+}
 
 } // namespace bincompat
 

stdlib/public/runtime/DynamicCast.cpp

@@ -20,6 +20,7 @@
 #include "SwiftHashableSupport.h"
 #include "swift/ABI/MetadataValues.h"
 #include "swift/Basic/Lazy.h"
+#include "swift/Runtime/Bincompat.h"
 #include "swift/Runtime/Casting.h"
 #include "swift/Runtime/Config.h"
 #include "swift/Runtime/ExistentialContainer.h"
@@ -110,12 +111,6 @@ extern "C" const StructDescriptor NOMINAL_TYPE_DESCR_SYM(Sh);
 /// Nominal type descriptor for Swift.String.
 extern "C" const StructDescriptor NOMINAL_TYPE_DESCR_SYM(SS);
 
-// If this returns `true`, then we will call `fatalError` when we encounter a
-// null reference in a storage locaation whose type does not allow null.
-static bool unexpectedNullIsFatal() {
-  return true;  // Placeholder for an upcoming check.
-}
-
 /// This issues a fatal error or warning if the srcValue contains a null object
 /// reference.  It is used when the srcType is a non-nullable reference type, in
 /// which case it is dangerous to continue with a null reference.  The null
@@ -134,7 +129,7 @@ static HeapObject * getNonNullSrcObject(OpaqueValue *srcValue,
   const char *msg = "Found unexpected null pointer value"
                     " while trying to cast value of type '%s' (%p)"
                     " to '%s' (%p)%s\n";
-  if (unexpectedNullIsFatal()) {
+  if (runtime::bincompat::unexpectedObjCNullWhileCastingIsFatal()) {
     // By default, Swift 5.4 and later issue a fatal error.
     swift::fatalError(/* flags = */ 0, msg,
                       srcTypeName.c_str(), srcType,
@@ -1044,7 +1039,7 @@ initializeToNilAtDepth(OpaqueValue *destLocation, const Metadata *destType, int
 }
 
 static void
-copyNil(OpaqueValue *destLocation, const Metadata *destType, const Metadata *srcType)
+copyNilPreservingDepth(OpaqueValue *destLocation, const Metadata *destType, const Metadata *srcType)
 {
   assert(srcType->getKind() == MetadataKind::Optional);
   assert(destType->getKind() == MetadataKind::Optional);
@@ -1087,7 +1082,13 @@ tryCastUnwrappingOptionalBoth(
     srcValue, /*emptyCases=*/1);
   auto sourceIsNil = (sourceEnumCase != 0);
   if (sourceIsNil) {
-    copyNil(destLocation, destType, srcType);
+    if (runtime::bincompat::useLegacyOptionalNilInjection()) {
+      auto destInnerType = cast<EnumMetadata>(destType)->getGenericArgs()[0];
+      // Set .none at the outer level
+      destInnerType->vw_storeEnumTagSinglePayload(destLocation, 1, 1);
+    } else {
+      copyNilPreservingDepth(destLocation, destType, srcType);
+    }
     return DynamicCastResult::SuccessViaCopy; // nil was essentially copied to dest
   } else {
     auto destEnumType = cast<EnumMetadata>(destType);

test/Casting/Casts.swift

@@ -342,7 +342,7 @@ CastsTests.test("Dynamic cast to ObjC protocol") {
 #endif
 
 // SR-6126
-if #available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, *) {
+if #available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *) {
 CastsTests.test("Nil handling for Optionals and Arrays (SR-6126)") {
   func check(_ arg: Int??) -> String {
     switch arg {
@@ -621,6 +621,7 @@ CastsTests.test("NSNull?.none -> Any? should set outer nil") {
 }
 #endif
 
+if #available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *) {
 CastsTests.test("Int??.some(nil) => Int??? should inject naturally") {
   let a: Int?? = .some(nil)
   let b = a as? Int???
@@ -629,7 +630,9 @@ CastsTests.test("Int??.some(nil) => Int??? should inject naturally") {
   let e = d!
   expectNil(e)
 }
+}
 
+if #available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *) {
 CastsTests.test("Int??.some(nil) => String??? should inject naturally") {
   let a: Int?? = .some(nil)
   let b = runtimeCast(a, to: String???.self)
@@ -638,7 +641,9 @@ CastsTests.test("Int??.some(nil) => String??? should inject naturally") {
   let e = d!
   expectNil(e)
 }
+}
 
+if #available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *) {
 CastsTests.test("Int??.some(nil) => Any??? should inject naturally") {
   let a: Int?? = .some(nil)
   let b = a as? Any???
@@ -647,6 +652,7 @@ CastsTests.test("Int??.some(nil) => Any??? should inject naturally") {
   let e = d!
   expectNil(e)
 }
+}
 
 #if _runtime(_ObjC)
 CastsTests.test("NSString -> String fast path") {

test/Runtime/protocol_conformance_collision.swift

@@ -16,8 +16,6 @@
 
 // UNSUPPORTED: use_os_stdlib
 
-// REQUIRES: rdar73049300
-
 import Accelerate
 import Foundation
 import StdlibUnittest
@@ -48,10 +46,7 @@ func firstHashValue(_ x: P) -> Int {
 }
 
 let osHasWorkaround: Bool
-// These are deliberately NOT version 9999, as we don't want to hit the special
-// case where development runtimes always return true for 9999. This check needs
-// to be false until real version numbers are put in.
-if #available(macOS 99990, iOS 99990, tvOS 99990, watchOS 99990, *) {
+if #available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *) {
   osHasWorkaround = true
 } else {
   osHasWorkaround = false

utils/find-overlay-deps-closure.sh

@@ -15,7 +15,7 @@
 set -o pipefail
 set -e
 
-OVERLAY_NAME_ALTERNATION="AppKit|AssetsLibrary|AVFoundation|CallKit|CloudKit|Compression|Contacts|CoreAudio|CoreData|CoreGraphics|CoreImage|CoreLocation|CoreMedia|CryptoTokenKit|dispatch|Foundation|GameplayKit|GLKit|HomeKit|IOKit|Intents|MapKit|objc|OpenCL|os|Photos|QuartzCore|SafariServices|SceneKit|simd|SpriteKit|UIKit|WatchKit|XCTest|xpc"
+OVERLAY_NAME_ALTERNATION="AppKit|AssetsLibrary|AVFoundation|CallKit|CloudKit|Compression|Contacts|CoreAudio|CoreData|CoreGraphics|CoreImage|CoreLocation|CoreMedia|CoreML|CryptoTokenKit|dispatch|Foundation|GameplayKit|GLKit|HomeKit|IOKit|Intents|MapKit|objc|OpenCL|os|Photos|QuartzCore|SafariServices|SceneKit|simd|SpriteKit|UIKit|WatchKit|XCTest|xpc"
 
 function find_deps() {
     local OVERLAY_ARG=$1