diff --git a/CMakeLists.txt b/CMakeLists.txt
index d181545c2ac58..931008da73ab6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -119,7 +119,7 @@ set(SWIFT_DARWIN_EMBEDDED_VARIANTS "^(iphoneos|iphonesimulator|appletvos|appletv
 #  if("${SWIFT_HOST_VARIANT_SDK}" IN_LIST SWIFT_DARWIN_PLATFORMS)
 #    ...
 #  endif()
-set(SWIFT_DARWIN_PLATFORMS "IOS" "IOS_SIMULATOR" "TVOS" "TVOS_SIMULATOR" "WATCHOS" "WATCHOS_SIMULATOR" "OSX")
+set(SWIFT_DARWIN_PLATFORMS "IOS" "IOS_SIMULATOR" "TVOS" "TVOS_SIMULATOR" "WATCHOS" "WATCHOS_SIMULATOR" "OSX" "XROS" "XROS_SIMULATOR")
 
 set(SWIFT_APPLE_PLATFORMS ${SWIFT_DARWIN_PLATFORMS})
 if(SWIFT_FREESTANDING_FLAVOR STREQUAL "apple")
@@ -542,6 +542,9 @@ set(SWIFT_DARWIN_DEPLOYMENT_VERSION_TVOS "11.0" CACHE STRING
 set(SWIFT_DARWIN_DEPLOYMENT_VERSION_WATCHOS "4.0" CACHE STRING
     "Minimum deployment target version for watchOS")
 
+set(SWIFT_DARWIN_DEPLOYMENT_VERSION_XROS "1.0" CACHE STRING
+    "Minimum deployment target version for xrOS")
+
 #
 #  Compatibility library deployment versions
 #
@@ -550,6 +553,7 @@ set(COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_OSX "10.9")
 set(COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_IOS "7.0")
 set(COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_TVOS "9.0")
 set(COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_WATCHOS "2.0")
+set(COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_XROS "1.0")
 set(COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_MACCATALYST "13.1")
 
 #
@@ -595,7 +599,7 @@ option(SWIFT_REPORT_STATISTICS
     FALSE)
 
 # Only Darwin platforms enable ObjC interop by default.
-if("${SWIFT_HOST_VARIANT_SDK}" MATCHES "(OSX|IOS*|TVOS*|WATCHOS*)")
+if("${SWIFT_HOST_VARIANT_SDK}" MATCHES "(OSX|IOS*|TVOS*|WATCHOS*|XROS*)")
   set(SWIFT_STDLIB_ENABLE_OBJC_INTEROP_default TRUE)
 else()
   set(SWIFT_STDLIB_ENABLE_OBJC_INTEROP_default FALSE)
@@ -1139,7 +1143,7 @@ elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "WASI")
   set(SWIFT_PRIMARY_VARIANT_SDK_default  "${SWIFT_HOST_VARIANT_SDK}")
   set(SWIFT_PRIMARY_VARIANT_ARCH_default "${SWIFT_HOST_VARIANT_ARCH}")
 
-elseif("${SWIFT_HOST_VARIANT_SDK}" MATCHES "(OSX|IOS*|TVOS*|WATCHOS*)")
+elseif("${SWIFT_HOST_VARIANT_SDK}" MATCHES "(OSX|IOS*|TVOS*|WATCHOS*|XROS*)")
 
   set(SWIFT_HOST_VARIANT "macosx" CACHE STRING
       "Deployment OS for Swift host tools (the compiler) [macosx, iphoneos].")
diff --git a/cmake/modules/DarwinSDKs.cmake b/cmake/modules/DarwinSDKs.cmake
index 32c020425747e..558771b1516db 100644
--- a/cmake/modules/DarwinSDKs.cmake
+++ b/cmake/modules/DarwinSDKs.cmake
@@ -15,6 +15,8 @@ set(SUPPORTED_TVOS_SIMULATOR_ARCHS "x86_64;arm64")
 set(SUPPORTED_WATCHOS_ARCHS "armv7k;arm64_32")
 set(SUPPORTED_WATCHOS_SIMULATOR_ARCHS "i386;x86_64;arm64")
 set(SUPPORTED_OSX_ARCHS "x86_64;arm64")
+set(SUPPORTED_XROS_ARCHS "arm64;arm64e")
+set(SUPPORTED_XROS_SIMULATOR_ARCHS "arm64")
 
 is_sdk_requested(OSX swift_build_osx)
 if(swift_build_osx)
@@ -50,7 +52,8 @@ if(swift_build_freestanding AND (SWIFT_FREESTANDING_FLAVOR STREQUAL "apple"))
 endif()
 
 # Compatible cross-compile SDKS for Darwin OSes: IOS, IOS_SIMULATOR, TVOS,
-#   TVOS_SIMULATOR, WATCHOS, WATCHOS_SIMULATOR (archs hardcoded below).
+#   TVOS_SIMULATOR, WATCHOS, WATCHOS_SIMULATOR, XROS, XROS_SIMULATOR
+#   (archs hardcoded below).
 
 is_sdk_requested(IOS swift_build_ios)
 if(swift_build_ios)
@@ -120,3 +123,28 @@ if(swift_build_watchos_simulator)
   configure_target_variant(WATCHOS_SIMULATOR-RA "watchOS Release+Asserts" WATCHOS_SIMULATOR RA "Release+Asserts")
   configure_target_variant(WATCHOS_SIMULATOR-R  "watchOS Release"         WATCHOS_SIMULATOR R "Release")
 endif()
+
+is_sdk_requested(XROS swift_build_xros)
+if(swift_build_xros)
+  configure_sdk_darwin(
+      XROS "xrOS" "${SWIFT_DARWIN_DEPLOYMENT_VERSION_XROS}"
+      xros xros xros "${SUPPORTED_XROS_ARCHS}")
+  configure_target_variant(XROS-DA "xrOS Debug+Asserts"   XROS DA "Debug+Asserts")
+  configure_target_variant(XROS-RA "xrOS Release+Asserts" XROS RA "Release+Asserts")
+  configure_target_variant(XROS-R  "xrOS Release"         XROS R "Release")
+endif()
+
+is_sdk_requested(XROS_SIMULATOR swift_build_xros_simulator)
+if(swift_build_xros_simulator)
+  configure_sdk_darwin(
+      XROS_SIMULATOR "xrOS Simulator" "${SWIFT_DARWIN_DEPLOYMENT_VERSION_XROS}"
+      xrsimulator xros xros-simulator
+      "${SUPPORTED_XROS_SIMULATOR_ARCHS}")
+
+  configure_target_variant(
+      XROS_SIMULATOR-DA "xrOS Simulator Debug+Asserts"   XROS_SIMULATOR DA "Debug+Asserts")
+  configure_target_variant(
+      XROS_SIMULATOR-RA "xrOS Simulator Release+Asserts" XROS_SIMULATOR RA "Release+Asserts")
+  configure_target_variant(
+      XROS_SIMULATOR-R  "xrOS Simulator Release"         XROS_SIMULATOR R "Release")
+endif()
diff --git a/cmake/modules/StandaloneOverlay.cmake b/cmake/modules/StandaloneOverlay.cmake
index debf5c543d8eb..0b75224f2112b 100644
--- a/cmake/modules/StandaloneOverlay.cmake
+++ b/cmake/modules/StandaloneOverlay.cmake
@@ -100,7 +100,7 @@ set(CMAKE_INSTALL_PREFIX
 
 
 set(SWIFT_DARWIN_PLATFORMS
-  OSX IOS IOS_SIMULATOR TVOS TVOS_SIMULATOR WATCHOS WATCHOS_SIMULATOR)
+  OSX IOS IOS_SIMULATOR TVOS TVOS_SIMULATOR WATCHOS WATCHOS_SIMULATOR XROS XROS_SIMULATOR)
 
 # Flags used to indicate we are building a standalone overlay.
 # FIXME: We should cut this down to a single flag.
diff --git a/include/swift/AST/ASTContext.h b/include/swift/AST/ASTContext.h
index f636aa382903f..4447782e8dc7f 100644
--- a/include/swift/AST/ASTContext.h
+++ b/include/swift/AST/ASTContext.h
@@ -34,6 +34,7 @@
 #include "swift/Basic/BlockList.h"
 #include "swift/SymbolGraphGen/SymbolGraphOptions.h"
 #include "clang/AST/DeclTemplate.h"
+#include "clang/Basic/DarwinSDKInfo.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
@@ -948,6 +949,12 @@ class ASTContext final {
     return getMultiPayloadEnumTagSinglePayloadAvailability();
   }
 
+  /// Test support utility for loading a platform remap file
+  /// in case an SDK is not specified to the compilation.
+  const clang::DarwinSDKInfo::RelatedTargetVersionMapping *
+  getAuxiliaryDarwinPlatformRemapInfo(
+      clang::DarwinSDKInfo::OSEnvPair Kind) const;
+
   //===--------------------------------------------------------------------===//
   // Diagnostics Helper functions
   //===--------------------------------------------------------------------===//
@@ -1511,6 +1518,9 @@ class ASTContext final {
   /// Provide context-level uniquing for SIL lowered type layouts and boxes.
   friend SILLayout;
   friend SILBoxType;
+
+public:
+  clang::DarwinSDKInfo *getDarwinSDKInfo() const;
 };
 
 } // end namespace swift
diff --git a/include/swift/AST/Availability.h b/include/swift/AST/Availability.h
index f1a4ce0475948..8e21d27137197 100644
--- a/include/swift/AST/Availability.h
+++ b/include/swift/AST/Availability.h
@@ -25,6 +25,7 @@
 namespace swift {
 class ASTContext;
 class AvailableAttr;
+class BackDeployedAttr;
 class Decl;
 
 /// A lattice of version ranges of the form [x.y.z, +Inf).
@@ -380,6 +381,39 @@ class AvailabilityInference {
 
   static AvailabilityContext
   annotatedAvailableRangeForAttr(const SpecializeAttr *attr, ASTContext &ctx);
+
+  /// For the attribute's introduction version, update the platform and version
+  /// values to the re-mapped platform's, if using a fallback platform.
+  /// Returns `true` if a remap occured.
+  static bool updateIntroducedPlatformForFallback(
+      const AvailableAttr *attr, const ASTContext &Ctx,
+      llvm::StringRef &Platform, llvm::VersionTuple &PlatformVer);
+
+  /// For the attribute's deprecation version, update the platform and version
+  /// values to the re-mapped platform's, if using a fallback platform.
+  /// Returns `true` if a remap occured.
+  static bool updateDeprecatedPlatformForFallback(
+      const AvailableAttr *attr, const ASTContext &Ctx,
+      llvm::StringRef &Platform, llvm::VersionTuple &PlatformVer);
+
+  /// For the attribute's obsoletion version, update the platform and version
+  /// values to the re-mapped platform's, if using a fallback platform.
+  /// Returns `true` if a remap occured.
+  static bool updateObsoletedPlatformForFallback(
+      const AvailableAttr *attr, const ASTContext &Ctx,
+      llvm::StringRef &Platform, llvm::VersionTuple &PlatformVer);
+
+  static void updatePlatformStringForFallback(
+      const AvailableAttr *attr, const ASTContext &Ctx,
+      llvm::StringRef &Platform);
+
+  /// For the attribute's before version, update the platform and version
+  /// values to the re-mapped platform's, if using a fallback platform.
+  /// Returns `true` if a remap occured.
+  static bool updateBeforePlatformForFallback(const BackDeployedAttr *attr,
+                                              const ASTContext &Ctx,
+                                              llvm::StringRef &Platform,
+                                              llvm::VersionTuple &PlatformVer);
 };
 
 /// Given a declaration upon which an availability attribute would appear in
diff --git a/include/swift/AST/PlatformKind.h b/include/swift/AST/PlatformKind.h
index cfc78467ccf31..cb59c440784d6 100644
--- a/include/swift/AST/PlatformKind.h
+++ b/include/swift/AST/PlatformKind.h
@@ -78,7 +78,7 @@ inline bool isApplicationExtensionPlatform(PlatformKind Platform) {
 /// triple will be used rather than the target to determine whether the
 /// platform is active.
 bool isPlatformActive(PlatformKind Platform, const LangOptions &LangOpts,
-                      bool ForTargetVariant = false);
+                      bool ForTargetVariant = false, bool ForRuntimeQuery = false);
 
 /// Returns the target platform for the given language options.
 PlatformKind targetPlatform(const LangOptions &LangOpts);
diff --git a/include/swift/AST/PlatformKinds.def b/include/swift/AST/PlatformKinds.def
index 017f09b7abe44..dd10bf495b65b 100644
--- a/include/swift/AST/PlatformKinds.def
+++ b/include/swift/AST/PlatformKinds.def
@@ -25,10 +25,12 @@
 AVAILABILITY_PLATFORM(iOS, "iOS")
 AVAILABILITY_PLATFORM(tvOS, "tvOS")
 AVAILABILITY_PLATFORM(watchOS, "watchOS")
+AVAILABILITY_PLATFORM(visionOS, "visionOS")
 AVAILABILITY_PLATFORM(macOS, "macOS")
 AVAILABILITY_PLATFORM(iOSApplicationExtension, "application extensions for iOS")
 AVAILABILITY_PLATFORM(tvOSApplicationExtension, "application extensions for tvOS")
 AVAILABILITY_PLATFORM(watchOSApplicationExtension, "application extensions for watchOS")
+AVAILABILITY_PLATFORM(visionOSApplicationExtension, "application extensions for visionOS")
 AVAILABILITY_PLATFORM(macOSApplicationExtension, "application extensions for macOS")
 AVAILABILITY_PLATFORM(macCatalyst, "Mac Catalyst")
 AVAILABILITY_PLATFORM(macCatalystApplicationExtension, "application extensions for Mac Catalyst")
diff --git a/include/swift/AST/RuntimeVersions.def b/include/swift/AST/RuntimeVersions.def
index 3223756a6dcb5..2aa07fee075e3 100644
--- a/include/swift/AST/RuntimeVersions.def
+++ b/include/swift/AST/RuntimeVersions.def
@@ -135,6 +135,7 @@ RUNTIME_VERSION(
   PLATFORM(macOS,   (14, 4, 0))
   PLATFORM(iOS,     (17, 4, 0))
   PLATFORM(watchOS, (10, 4, 0))
+  PLATFORM(xrOS, (1, 0, 0))
 )
 
 RUNTIME_VERSION(
diff --git a/include/swift/AST/SearchPathOptions.h b/include/swift/AST/SearchPathOptions.h
index dd7debcce1351..166107440504a 100644
--- a/include/swift/AST/SearchPathOptions.h
+++ b/include/swift/AST/SearchPathOptions.h
@@ -500,6 +500,10 @@ class SearchPathOptions {
   /// A file containing a list of protocols whose conformances require const value extraction.
   std::string ConstGatherProtocolListFilePath;
 
+  /// Path to the file that defines platform mapping for availability
+  /// version inheritance.
+  std::optional<std::string> PlatformAvailabilityInheritanceMapPath;
+
   /// Debug path mappings to apply to serialized search paths. These are
   /// specified in LLDB from the target.source-map entries.
   PathRemapper SearchPathRemapper;
diff --git a/include/swift/Basic/LangOptions.h b/include/swift/Basic/LangOptions.h
index 38aeb2ec20b7c..c2805ac1011b9 100644
--- a/include/swift/Basic/LangOptions.h
+++ b/include/swift/Basic/LangOptions.h
@@ -635,6 +635,8 @@ namespace swift {
         return Target.getiOSVersion();
       } else if (Target.isWatchOS()) {
         return Target.getOSVersion();
+      } else if (Target.isXROS()) {
+        return Target.getOSVersion();
       }
       return llvm::VersionTuple(/*Major=*/0, /*Minor=*/0, /*Subminor=*/0);
     }
diff --git a/include/swift/Basic/Platform.h b/include/swift/Basic/Platform.h
index 6eff7622ea2e2..2a1b984087e70 100644
--- a/include/swift/Basic/Platform.h
+++ b/include/swift/Basic/Platform.h
@@ -33,7 +33,9 @@ namespace swift {
     TvOS,
     TvOSSimulator,
     WatchOS,
-    WatchOSSimulator
+    WatchOSSimulator,
+    VisionOS,
+    VisionOSSimulator
   };
 
   /// Returns true if the given triple represents iOS running in a simulator.
@@ -48,6 +50,9 @@ namespace swift {
   /// Returns true if the given triple represents a macCatalyst environment.
   bool tripleIsMacCatalystEnvironment(const llvm::Triple &triple);
 
+  /// Returns true if the given triple represents visionOS running in a simulator.
+  bool tripleIsVisionSimulator(const llvm::Triple &triple);
+
   /// Determine whether the triple infers the "simulator" environment.
   bool tripleInfersSimulatorEnvironment(const llvm::Triple &triple);
 
diff --git a/include/swift/Frontend/Frontend.h b/include/swift/Frontend/Frontend.h
index 6531a2e07adcd..5c1d54f002375 100644
--- a/include/swift/Frontend/Frontend.h
+++ b/include/swift/Frontend/Frontend.h
@@ -233,6 +233,8 @@ class CompilerInvocation {
 
   void setRuntimeResourcePath(StringRef Path);
 
+  void setPlatformAvailabilityInheritanceMapPath(StringRef Path);
+
   /// Compute the default prebuilt module cache path for a given resource path
   /// and SDK version. This function is also used by LLDB.
   static std::string
diff --git a/include/swift/Option/FrontendOptions.td b/include/swift/Option/FrontendOptions.td
index 27098b7cd1a37..a80f5ea99b870 100644
--- a/include/swift/Option/FrontendOptions.td
+++ b/include/swift/Option/FrontendOptions.td
@@ -1343,4 +1343,8 @@ def module_load_mode: Separate<["-"], "module-load-mode">,
     MetaVarName<"only-interface|prefer-interface|prefer-serialized|only-serialized">,
     HelpText<"Module loading mode">;
 
+def platform_availability_inheritance_map_path
+  : Separate<["-"], "platform-availability-inheritance-map-path">, MetaVarName<"<path>">,
+    HelpText<"Path of the platform inheritance platform map">;
+
 } // end let Flags = [FrontendOption, NoDriverOption, HelpHidden]
diff --git a/include/swift/RemoteInspection/RuntimeHeaders/llvm/BinaryFormat/MachO.h b/include/swift/RemoteInspection/RuntimeHeaders/llvm/BinaryFormat/MachO.h
index 35b6bce574bab..ca4d9cdb99ff4 100644
--- a/include/swift/RemoteInspection/RuntimeHeaders/llvm/BinaryFormat/MachO.h
+++ b/include/swift/RemoteInspection/RuntimeHeaders/llvm/BinaryFormat/MachO.h
@@ -508,6 +508,8 @@ enum PlatformType {
   PLATFORM_TVOSSIMULATOR = 8,
   PLATFORM_WATCHOSSIMULATOR = 9,
   PLATFORM_DRIVERKIT = 10,
+  PLATFORM_XROS = 11,
+  PLATFORM_XROS_SIMULATOR = 12
 };
 
 // Values for tools enum in build_tool_version.
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index fce435171b1eb..dd8fbbdf5d29e 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -657,6 +657,8 @@ struct ASTContext::Implementation {
   /// The scratch context used to allocate intrinsic data on behalf of \c swift::IntrinsicInfo
   std::unique_ptr<llvm::LLVMContext> IntrinsicScratchContext;
 
+  mutable std::optional<std::unique_ptr<clang::DarwinSDKInfo>> SDKInfo;
+
   /// Memory allocation arena for the term rewriting system.
   std::unique_ptr<rewriting::RewriteContext> TheRewriteContext;
 
@@ -6399,6 +6401,44 @@ bool ASTContext::isASCIIString(StringRef s) const {
   return true;
 }
 
+clang::DarwinSDKInfo *ASTContext::getDarwinSDKInfo() const {
+  if (!getImpl().SDKInfo) {
+    auto SDKInfoOrErr = clang::parseDarwinSDKInfo(
+            *llvm::vfs::getRealFileSystem(),
+            SearchPathOpts.SDKPath);
+    if (!SDKInfoOrErr) {
+      llvm::handleAllErrors(SDKInfoOrErr.takeError(),
+                            [](const llvm::ErrorInfoBase &) {
+                              // Ignore the error for now..
+                            });
+      getImpl().SDKInfo.emplace();
+    } else if (!*SDKInfoOrErr) {
+      getImpl().SDKInfo.emplace();
+    } else {
+      getImpl().SDKInfo.emplace(std::make_unique<clang::DarwinSDKInfo>(**SDKInfoOrErr));
+    }
+  }
+
+  return getImpl().SDKInfo->get();
+}
+
+const clang::DarwinSDKInfo::RelatedTargetVersionMapping
+*ASTContext::getAuxiliaryDarwinPlatformRemapInfo(clang::DarwinSDKInfo::OSEnvPair Kind) const {
+  if (SearchPathOpts.PlatformAvailabilityInheritanceMapPath) {
+    auto SDKInfoOrErr = clang::parseDarwinSDKInfo(
+            *llvm::vfs::getRealFileSystem(),
+            *SearchPathOpts.PlatformAvailabilityInheritanceMapPath);
+    if (!SDKInfoOrErr || !*SDKInfoOrErr) {
+      llvm::handleAllErrors(SDKInfoOrErr.takeError(),
+                            [](const llvm::ErrorInfoBase &) {
+        // Ignore the error for now..
+      });
+    }
+    return (*SDKInfoOrErr)->getVersionMapping(Kind);
+  }
+  return nullptr;
+}
+
 /// The special Builtin.TheTupleType, which parents tuple extensions and
 /// conformances.
 BuiltinTupleDecl *ASTContext::getBuiltinTupleDecl() {
diff --git a/lib/AST/Attr.cpp b/lib/AST/Attr.cpp
index 631056e6675f3..f80257ff0d3a7 100644
--- a/lib/AST/Attr.cpp
+++ b/lib/AST/Attr.cpp
@@ -497,6 +497,13 @@ DeclAttributes::getDeprecated(const ASTContext &ctx) const {
         return AvAttr;
 
       std::optional<llvm::VersionTuple> DeprecatedVersion = AvAttr->Deprecated;
+
+      StringRef DeprecatedPlatform = AvAttr->prettyPlatformString();
+      llvm::VersionTuple RemappedDeprecatedVersion;
+      if (AvailabilityInference::updateDeprecatedPlatformForFallback(
+          AvAttr, ctx, DeprecatedPlatform, RemappedDeprecatedVersion))
+        DeprecatedVersion = RemappedDeprecatedVersion;
+
       if (!DeprecatedVersion.has_value())
         continue;
 
@@ -2335,18 +2342,32 @@ AvailableVersionComparison AvailableAttr::getVersionAvailability(
     return AvailableVersionComparison::Unavailable;
 
   llvm::VersionTuple queryVersion = getActiveVersion(ctx);
+  std::optional<llvm::VersionTuple> ObsoletedVersion = Obsoleted;
+
+  StringRef ObsoletedPlatform = prettyPlatformString();
+  llvm::VersionTuple RemappedObsoletedVersion;
+  if (AvailabilityInference::updateObsoletedPlatformForFallback(
+      this, ctx, ObsoletedPlatform, RemappedObsoletedVersion))
+    ObsoletedVersion = RemappedObsoletedVersion;
 
   // If this entity was obsoleted before or at the query platform version,
   // consider it obsolete.
-  if (Obsoleted && *Obsoleted <= queryVersion)
+  if (ObsoletedVersion && *ObsoletedVersion <= queryVersion)
     return AvailableVersionComparison::Obsoleted;
 
+  std::optional<llvm::VersionTuple> IntroducedVersion = Introduced;
+  StringRef IntroducedPlatform = prettyPlatformString();
+  llvm::VersionTuple RemappedIntroducedVersion;
+  if (AvailabilityInference::updateIntroducedPlatformForFallback(
+      this, ctx, IntroducedPlatform, RemappedIntroducedVersion))
+    IntroducedVersion = RemappedIntroducedVersion;
+
   // If this entity was introduced after the query version and we're doing a
   // platform comparison, true availability can only be determined dynamically;
   // if we're doing a _language_ version check, the query version is a
   // static requirement, so we treat "introduced later" as just plain
   // unavailable.
-  if (Introduced && *Introduced > queryVersion) {
+  if (IntroducedVersion && *IntroducedVersion > queryVersion) {
     if (isLanguageVersionSpecific() || isPackageDescriptionVersionSpecific())
       return AvailableVersionComparison::Unavailable;
     else
diff --git a/lib/AST/Availability.cpp b/lib/AST/Availability.cpp
index 80c118c205836..3a580c9bfd923 100644
--- a/lib/AST/Availability.cpp
+++ b/lib/AST/Availability.cpp
@@ -251,6 +251,123 @@ static bool isBetterThan(const AvailableAttr *newAttr,
                                           prevAttr->Platform);
 }
 
+static const clang::DarwinSDKInfo::RelatedTargetVersionMapping *
+getFallbackVersionMapping(const ASTContext &Ctx,
+                          clang::DarwinSDKInfo::OSEnvPair Kind) {
+  auto *SDKInfo = Ctx.getDarwinSDKInfo();
+  if (SDKInfo)
+    return SDKInfo->getVersionMapping(Kind);
+
+  return Ctx.getAuxiliaryDarwinPlatformRemapInfo(Kind);
+}
+
+static std::optional<clang::VersionTuple>
+getRemappedIntroducedVersionForFallbackPlatform(
+    const ASTContext &Ctx, const llvm::VersionTuple &Version) {
+  const auto *Mapping = getFallbackVersionMapping(
+      Ctx, clang::DarwinSDKInfo::OSEnvPair(
+               llvm::Triple::IOS, llvm::Triple::UnknownEnvironment,
+               llvm::Triple::XROS, llvm::Triple::UnknownEnvironment));
+  if (!Mapping)
+    return std::nullopt;
+  return Mapping->mapIntroducedAvailabilityVersion(Version);
+}
+
+static std::optional<clang::VersionTuple>
+getRemappedDeprecatedObsoletedVersionForFallbackPlatform(
+    const ASTContext &Ctx, const llvm::VersionTuple &Version) {
+  const auto *Mapping = getFallbackVersionMapping(
+      Ctx, clang::DarwinSDKInfo::OSEnvPair(
+               llvm::Triple::IOS, llvm::Triple::UnknownEnvironment,
+               llvm::Triple::XROS, llvm::Triple::UnknownEnvironment));
+  if (!Mapping)
+    return std::nullopt;
+  return Mapping->mapDeprecatedObsoletedAvailabilityVersion(Version);
+}
+
+bool AvailabilityInference::updateIntroducedPlatformForFallback(
+    const AvailableAttr *attr, const ASTContext &Ctx, llvm::StringRef &Platform,
+    llvm::VersionTuple &PlatformVer) {
+  std::optional<llvm::VersionTuple> IntroducedVersion = attr->Introduced;
+  if (attr->Platform == PlatformKind::iOS && IntroducedVersion.has_value() &&
+      isPlatformActive(PlatformKind::visionOS, Ctx.LangOpts)) {
+    // We re-map the iOS introduced version to the corresponding visionOS version
+    auto PotentiallyRemappedIntroducedVersion =
+        getRemappedIntroducedVersionForFallbackPlatform(Ctx,
+                                                        *IntroducedVersion);
+    if (PotentiallyRemappedIntroducedVersion.has_value()) {
+      Platform = swift::prettyPlatformString(PlatformKind::visionOS);
+      PlatformVer = PotentiallyRemappedIntroducedVersion.value();
+      return true;
+    }
+  }
+  return false;
+}
+
+bool AvailabilityInference::updateDeprecatedPlatformForFallback(
+    const AvailableAttr *attr, const ASTContext &Ctx, llvm::StringRef &Platform,
+    llvm::VersionTuple &PlatformVer) {
+  std::optional<llvm::VersionTuple> DeprecatedVersion = attr->Deprecated;
+  if (attr->Platform == PlatformKind::iOS && DeprecatedVersion.has_value() &&
+      isPlatformActive(PlatformKind::visionOS, Ctx.LangOpts)) {
+    // We re-map the iOS deprecated version to the corresponding visionOS version
+    auto PotentiallyRemappedDeprecatedVersion =
+        getRemappedDeprecatedObsoletedVersionForFallbackPlatform(
+            Ctx, *DeprecatedVersion);
+    if (PotentiallyRemappedDeprecatedVersion.has_value()) {
+      Platform = swift::prettyPlatformString(PlatformKind::visionOS);
+      PlatformVer = PotentiallyRemappedDeprecatedVersion.value();
+      return true;
+    }
+  }
+  return false;
+}
+
+bool AvailabilityInference::updateObsoletedPlatformForFallback(
+    const AvailableAttr *attr, const ASTContext &Ctx, llvm::StringRef &Platform,
+    llvm::VersionTuple &PlatformVer) {
+  std::optional<llvm::VersionTuple> ObsoletedVersion = attr->Obsoleted;
+  if (attr->Platform == PlatformKind::iOS && ObsoletedVersion.has_value() &&
+      isPlatformActive(PlatformKind::visionOS, Ctx.LangOpts)) {
+    // We re-map the iOS obsoleted version to the corresponding visionOS version
+    auto PotentiallyRemappedObsoletedVersion =
+        getRemappedDeprecatedObsoletedVersionForFallbackPlatform(
+            Ctx, *ObsoletedVersion);
+    if (PotentiallyRemappedObsoletedVersion.has_value()) {
+      Platform = swift::prettyPlatformString(PlatformKind::visionOS);
+      PlatformVer = PotentiallyRemappedObsoletedVersion.value();
+      return true;
+    }
+  }
+  return false;
+}
+
+void AvailabilityInference::updatePlatformStringForFallback(
+    const AvailableAttr *attr, const ASTContext &Ctx, llvm::StringRef &Platform) {
+  if (attr->Platform == PlatformKind::iOS &&
+      isPlatformActive(PlatformKind::visionOS, Ctx.LangOpts)) {
+    Platform = swift::prettyPlatformString(PlatformKind::visionOS);
+  }
+}
+
+bool AvailabilityInference::updateBeforePlatformForFallback(
+    const BackDeployedAttr *attr, const ASTContext &Ctx,
+    llvm::StringRef &Platform, llvm::VersionTuple &PlatformVer) {
+  auto BeforeVersion = attr->Version;
+  if (attr->Platform == PlatformKind::iOS &&
+      isPlatformActive(PlatformKind::visionOS, Ctx.LangOpts)) {
+    // We re-map the iOS before version to the corresponding visionOS version
+    auto PotentiallyRemappedIntroducedVersion =
+        getRemappedIntroducedVersionForFallbackPlatform(Ctx, BeforeVersion);
+    if (PotentiallyRemappedIntroducedVersion.has_value()) {
+      Platform = swift::prettyPlatformString(PlatformKind::visionOS);
+      PlatformVer = PotentiallyRemappedIntroducedVersion.value();
+      return true;
+    }
+  }
+  return false;
+}
+
 const AvailableAttr *
 AvailabilityInference::attrForAnnotatedAvailableRange(const Decl *D,
                                                       ASTContext &Ctx) {
@@ -369,6 +486,14 @@ getEffectiveUnavailableDeclOptimization(ASTContext &ctx) {
   if (ctx.LangOpts.UnavailableDeclOptimizationMode.has_value())
     return *ctx.LangOpts.UnavailableDeclOptimizationMode;
 
+  // FIXME: Allow unavailable decl optimization on visionOS.
+  // visionOS must be ABI compatible with iOS. Enabling unavailable declaration
+  // optimizations naively would break compatibility since declarations marked
+  // unavailable on visionOS would be optimized regardless of whether they are
+  // available on iOS. rdar://116742214
+  if (ctx.LangOpts.Target.isXROS())
+    return UnavailableDeclOptimization::None;
+
   return UnavailableDeclOptimization::None;
 }
 
@@ -456,7 +581,15 @@ AvailabilityContext
 AvailabilityInference::availableRange(const AvailableAttr *attr,
                                       ASTContext &Ctx) {
   assert(attr->isActivePlatform(Ctx));
-  return AvailabilityContext{VersionRange::allGTE(attr->Introduced.value()),
+
+  llvm::VersionTuple IntroducedVersion = attr->Introduced.value();
+  StringRef Platform = attr->prettyPlatformString();
+  llvm::VersionTuple RemappedIntroducedVersion;
+  if (AvailabilityInference::updateIntroducedPlatformForFallback(
+      attr, Ctx, Platform, RemappedIntroducedVersion))
+    IntroducedVersion = RemappedIntroducedVersion;
+
+  return AvailabilityContext{VersionRange::allGTE(IntroducedVersion),
                              attr->IsSPI};
 }
 
@@ -533,6 +666,7 @@ ASTContext::getSwiftAvailability(unsigned major, unsigned minor) const {
 #define PLATFORM_TEST_macOS     target.isMacOSX()
 #define PLATFORM_TEST_iOS       target.isiOS()
 #define PLATFORM_TEST_watchOS   target.isWatchOS()
+#define PLATFORM_TEST_xrOS      target.isXROS()
 
 #define _SECOND(A, B) B
 #define SECOND(T) _SECOND T
@@ -547,6 +681,7 @@ ASTContext::getSwiftAvailability(unsigned major, unsigned minor) const {
 #undef PLATFORM_TEST_macOS
 #undef PLATFORM_TEST_iOS
 #undef PLATFORM_TEST_watchOS
+#undef PLATFORM_TEST_xrOS
 #undef _SECOND
 #undef SECOND
 
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 28f98e37c1a09..2c211b80faa5b 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -567,6 +567,15 @@ std::optional<llvm::VersionTuple>
 Decl::getBackDeployedBeforeOSVersion(ASTContext &Ctx) const {
   if (auto *attr = getAttrs().getBackDeployed(Ctx)) {
     auto version = attr->Version;
+    StringRef ignoredPlatformString;
+    AvailabilityInference::updateBeforePlatformForFallback(
+        attr, getASTContext(), ignoredPlatformString, version);
+
+    // If the remap for fallback resulted in 1.0, then the
+    // backdeployment prior to that is not meaningful.
+    if (version == clang::VersionTuple(1, 0, 0, 0))
+      return std::nullopt;
+
     return version;
   }
 
diff --git a/lib/AST/PlatformKind.cpp b/lib/AST/PlatformKind.cpp
index e856a9e046e03..31af9b088a69d 100644
--- a/lib/AST/PlatformKind.cpp
+++ b/lib/AST/PlatformKind.cpp
@@ -107,11 +107,14 @@ swift::basePlatformForExtensionPlatform(PlatformKind Platform) {
     return PlatformKind::tvOS;
   case PlatformKind::watchOSApplicationExtension:
     return PlatformKind::watchOS;
+  case PlatformKind::visionOSApplicationExtension:
+    return PlatformKind::visionOS;
   case PlatformKind::macOS:
   case PlatformKind::iOS:
   case PlatformKind::macCatalyst:
   case PlatformKind::tvOS:
   case PlatformKind::watchOS:
+  case PlatformKind::visionOS:
   case PlatformKind::OpenBSD:
   case PlatformKind::Windows:
   case PlatformKind::none:
@@ -122,7 +125,8 @@ swift::basePlatformForExtensionPlatform(PlatformKind Platform) {
 
 static bool isPlatformActiveForTarget(PlatformKind Platform,
                                       const llvm::Triple &Target,
-                                      bool EnableAppExtensionRestrictions) {
+                                      bool EnableAppExtensionRestrictions,
+                                      bool ForRuntimeQuery) {
   if (Platform == PlatformKind::none)
     return true;
 
@@ -137,6 +141,9 @@ static bool isPlatformActiveForTarget(PlatformKind Platform,
       return Target.isMacOSX();
     case PlatformKind::iOS:
     case PlatformKind::iOSApplicationExtension:
+      if (!ForRuntimeQuery && Target.isXROS()) {
+        return true;
+      }
       return Target.isiOS() && !Target.isTvOS();
     case PlatformKind::macCatalyst:
     case PlatformKind::macCatalystApplicationExtension:
@@ -147,6 +154,9 @@ static bool isPlatformActiveForTarget(PlatformKind Platform,
     case PlatformKind::watchOS:
     case PlatformKind::watchOSApplicationExtension:
       return Target.isWatchOS();
+    case PlatformKind::visionOS:
+    case PlatformKind::visionOSApplicationExtension:
+      return Target.isXROS();
     case PlatformKind::OpenBSD:
       return Target.isOSOpenBSD();
     case PlatformKind::Windows:
@@ -158,15 +168,16 @@ static bool isPlatformActiveForTarget(PlatformKind Platform,
 }
 
 bool swift::isPlatformActive(PlatformKind Platform, const LangOptions &LangOpts,
-                             bool ForTargetVariant) {
+                             bool ForTargetVariant, bool ForRuntimeQuery) {
   if (ForTargetVariant) {
     assert(LangOpts.TargetVariant && "Must have target variant triple");
     return isPlatformActiveForTarget(Platform, *LangOpts.TargetVariant,
-                                     LangOpts.EnableAppExtensionRestrictions);
+                                     LangOpts.EnableAppExtensionRestrictions,
+                                     ForRuntimeQuery);
   }
 
   return isPlatformActiveForTarget(Platform, LangOpts.Target,
-                                   LangOpts.EnableAppExtensionRestrictions);
+                                   LangOpts.EnableAppExtensionRestrictions, ForRuntimeQuery);
 }
 
 PlatformKind swift::targetPlatform(const LangOptions &LangOpts) {
@@ -198,6 +209,12 @@ PlatformKind swift::targetPlatform(const LangOptions &LangOpts) {
                 : PlatformKind::iOS);
   }
 
+  if (LangOpts.Target.isXROS()) {
+    return (LangOpts.EnableAppExtensionRestrictions
+            ? PlatformKind::visionOSApplicationExtension
+            : PlatformKind::visionOS);
+  }
+
   return PlatformKind::none;
 }
 
@@ -218,6 +235,16 @@ bool swift::inheritsAvailabilityFromPlatform(PlatformKind Child,
     }
   }
 
+  if (Child == PlatformKind::visionOS && Parent == PlatformKind::iOS)
+    return true;
+
+  if (Child == PlatformKind::visionOSApplicationExtension) {
+    if (Parent == PlatformKind::iOS ||
+        Parent == PlatformKind::iOSApplicationExtension) {
+      return true;
+    }
+  }
+
   return false;
 }
 
diff --git a/lib/Basic/LangOptions.cpp b/lib/Basic/LangOptions.cpp
index 13441dc76ae50..5c9918dc1e577 100644
--- a/lib/Basic/LangOptions.cpp
+++ b/lib/Basic/LangOptions.cpp
@@ -72,6 +72,8 @@ static const SupportedConditionalValue SupportedConditionalCompilationOSs[] = {
   "tvOS",
   "watchOS",
   "iOS",
+  "visionOS",
+  "xrOS",
   "Linux",
   "FreeBSD",
   "OpenBSD",
@@ -440,6 +442,10 @@ std::pair<bool, bool> LangOptions::setTarget(llvm::Triple triple) {
   case llvm::Triple::IOS:
     addPlatformConditionValue(PlatformConditionKind::OS, "iOS");
     break;
+  case llvm::Triple::XROS:
+    addPlatformConditionValue(PlatformConditionKind::OS, "xrOS");
+    addPlatformConditionValue(PlatformConditionKind::OS, "visionOS");
+    break;
   case llvm::Triple::Linux:
     if (Target.getEnvironment() == llvm::Triple::Android)
       addPlatformConditionValue(PlatformConditionKind::OS, "Android");
diff --git a/lib/Basic/Platform.cpp b/lib/Basic/Platform.cpp
index 40b266caa0dd1..5916e5ad74352 100644
--- a/lib/Basic/Platform.cpp
+++ b/lib/Basic/Platform.cpp
@@ -37,6 +37,10 @@ bool swift::tripleIsMacCatalystEnvironment(const llvm::Triple &triple) {
       triple.getEnvironment() == llvm::Triple::MacABI;
 }
 
+bool swift::tripleIsVisionSimulator(const llvm::Triple &triple) {
+  return triple.isXROS() && triple.isSimulatorEnvironment();
+}
+
 bool swift::tripleInfersSimulatorEnvironment(const llvm::Triple &triple) {
   switch (triple.getOS()) {
   case llvm::Triple::IOS:
@@ -123,6 +127,10 @@ bool swift::tripleRequiresRPathForSwiftLibrariesInOS(
     return triple.isOSVersionLT(8, 0);
   }
 
+  if (triple.isXROS()) {
+    return triple.isOSVersionLT(1, 0);
+  }
+
   // Other platforms don't have Swift installed as part of the OS by default.
   return false;
 }
@@ -150,6 +158,12 @@ DarwinPlatformKind swift::getDarwinPlatformKind(const llvm::Triple &triple) {
   if (triple.isMacOSX())
     return DarwinPlatformKind::MacOS;
 
+  if (triple.isXROS()) {
+    if (tripleIsVisionSimulator(triple))
+      return DarwinPlatformKind::VisionOSSimulator;
+    return DarwinPlatformKind::VisionOS;
+  }
+
   llvm_unreachable("Unsupported Darwin platform");
 }
 
@@ -169,6 +183,10 @@ static StringRef getPlatformNameForDarwin(const DarwinPlatformKind platform) {
     return "watchos";
   case DarwinPlatformKind::WatchOSSimulator:
     return "watchsimulator";
+  case DarwinPlatformKind::VisionOS:
+    return "xros";
+  case DarwinPlatformKind::VisionOSSimulator:
+    return "xrsimulator";
   }
   llvm_unreachable("Unsupported Darwin platform");
 }
@@ -180,7 +198,6 @@ StringRef swift::getPlatformNameForTriple(const llvm::Triple &triple) {
   case llvm::Triple::CloudABI:
   case llvm::Triple::DragonFly:
   case llvm::Triple::DriverKit:
-  case llvm::Triple::XROS:
   case llvm::Triple::Emscripten:
   case llvm::Triple::Fuchsia:
   case llvm::Triple::KFreeBSD:
@@ -208,6 +225,7 @@ StringRef swift::getPlatformNameForTriple(const llvm::Triple &triple) {
   case llvm::Triple::IOS:
   case llvm::Triple::TvOS:
   case llvm::Triple::WatchOS:
+  case llvm::Triple::XROS:
     return getPlatformNameForDarwin(getDarwinPlatformKind(triple));
   case llvm::Triple::Linux:
     return triple.isAndroid() ? "android" : "linux";
@@ -513,6 +531,9 @@ swift::getSwiftRuntimeCompatibilityVersionForTarget(
       return floorFor64bits(llvm::VersionTuple(5, 7));
     }
   }
+  else if (Triple.isXROS()) {
+    return std::nullopt;
+  }
 
   return std::nullopt;
 }
diff --git a/lib/ClangImporter/ClangImporter.cpp b/lib/ClangImporter/ClangImporter.cpp
index ec580ce31c305..9028f5485f50a 100644
--- a/lib/ClangImporter/ClangImporter.cpp
+++ b/lib/ClangImporter/ClangImporter.cpp
@@ -616,6 +616,13 @@ importer::getNormalInvocationArguments(
     if (clangSupportsPragmaAttributeWithSwiftAttr())
       invocationArgStrs.push_back("-D__SWIFT_ATTR_SUPPORTS_SENDABLE_DECLS=1");
 
+    if (triple.isXROS()) {
+      // FIXME: This is a gnarly hack until some macros get adjusted in the SDK.
+      invocationArgStrs.insert(invocationArgStrs.end(), {
+        "-DOS_OBJECT_HAVE_OBJC_SUPPORT=1",
+      });
+    }
+
     // Get the version of this compiler and pass it to C/Objective-C
     // declarations.
     auto V = version::getCurrentCompilerVersion();
@@ -820,6 +827,9 @@ importer::addCommonInvocationArguments(
     else if (triple.isAArch64() && triple.isSimulatorEnvironment() &&
              (triple.isiOS() || triple.isWatchOS()))
       invocationArgStrs.push_back("-mcpu=apple-a12");
+    else if (triple.isAArch64() && triple.isSimulatorEnvironment() &&
+             triple.isXROS())
+      invocationArgStrs.push_back("-mcpu=apple-a12");
     else if (triple.getArch() == llvm::Triple::aarch64 ||
              triple.getArch() == llvm::Triple::aarch64_32 ||
              triple.getArch() == llvm::Triple::aarch64_be) {
@@ -2445,6 +2455,10 @@ PlatformAvailability::PlatformAvailability(const LangOptions &langOpts)
       "'async'";
     break;
 
+  case PlatformKind::visionOS:
+  case PlatformKind::visionOSApplicationExtension:
+    break;
+
   case PlatformKind::OpenBSD:
     deprecatedAsUnavailableMessage = "";
     break;
@@ -2486,6 +2500,12 @@ bool PlatformAvailability::isPlatformRelevant(StringRef name) const {
   case PlatformKind::watchOSApplicationExtension:
     return name == "watchos" || name == "watchos_app_extension";
 
+  case PlatformKind::visionOS:
+    return name == "xros" || name == "visionos";
+  case PlatformKind::visionOSApplicationExtension:
+    return name == "xros" || name == "xros_app_extension" ||
+           name == "visionos" || name == "visionos_app_extension";
+
   case PlatformKind::OpenBSD:
     return name == "openbsd";
 
@@ -2552,6 +2572,11 @@ bool PlatformAvailability::treatDeprecatedAsUnavailable(
     // No deprecation filter on watchOS
     return false;
 
+  case PlatformKind::visionOS:
+  case PlatformKind::visionOSApplicationExtension:
+    // No deprecation filter on xrOS
+    return false;
+
   case PlatformKind::OpenBSD:
     // No deprecation filter on OpenBSD
     return false;
diff --git a/lib/ClangImporter/ImportDecl.cpp b/lib/ClangImporter/ImportDecl.cpp
index 9e47837fc3931..c6b2efa143c91 100644
--- a/lib/ClangImporter/ImportDecl.cpp
+++ b/lib/ClangImporter/ImportDecl.cpp
@@ -8313,6 +8313,8 @@ void ClangImporter::Implementation::importAttributes(
               .Case("maccatalyst", PlatformKind::macCatalyst)
               .Case("tvos", PlatformKind::tvOS)
               .Case("watchos", PlatformKind::watchOS)
+              .Case("xros", PlatformKind::visionOS)
+              .Case("visionos", PlatformKind::visionOS)
               .Case("ios_app_extension", PlatformKind::iOSApplicationExtension)
               .Case("maccatalyst_app_extension",
                     PlatformKind::macCatalystApplicationExtension)
@@ -8322,6 +8324,8 @@ void ClangImporter::Implementation::importAttributes(
                     PlatformKind::tvOSApplicationExtension)
               .Case("watchos_app_extension",
                     PlatformKind::watchOSApplicationExtension)
+              .Case("xros_app_extension",
+                    PlatformKind::visionOSApplicationExtension)
               .Default(std::nullopt);
       if (!platformK)
         continue;
diff --git a/lib/Driver/DarwinToolChains.cpp b/lib/Driver/DarwinToolChains.cpp
index 432534ff0163c..727e8d56ecdca 100644
--- a/lib/Driver/DarwinToolChains.cpp
+++ b/lib/Driver/DarwinToolChains.cpp
@@ -112,6 +112,10 @@ getDarwinLibraryNameSuffixForTriple(const llvm::Triple &triple) {
     return "watchos";
   case DarwinPlatformKind::WatchOSSimulator:
     return "watchossim";
+  case DarwinPlatformKind::VisionOS:
+    return "xros";
+  case DarwinPlatformKind::VisionOSSimulator:
+    return "xrossim";
   }
   llvm_unreachable("Unsupported Darwin platform");
 }
@@ -502,6 +506,8 @@ toolchains::Darwin::addProfileGenerationArgs(ArgStringList &Arguments,
         RT = "ios";
     } else if (Triple.isWatchOS()) {
       RT = "watchos";
+    } else if (Triple.isXROS()) {
+      RT = "xros";
     } else {
       assert(Triple.isMacOSX());
       RT = "osx";
@@ -563,6 +569,12 @@ toolchains::Darwin::addDeploymentTargetArgs(ArgStringList &Arguments,
       case DarwinPlatformKind::WatchOSSimulator:
         platformName = "watchos-simulator";
         break;
+      case DarwinPlatformKind::VisionOS:
+        platformName = "xros";
+        break;
+      case DarwinPlatformKind::VisionOSSimulator:
+        platformName = "xros-simulator";
+        break;
       }
     }
 
@@ -611,6 +623,17 @@ toolchains::Darwin::addDeploymentTargetArgs(ArgStringList &Arguments,
       case DarwinPlatformKind::WatchOS:
       case DarwinPlatformKind::WatchOSSimulator:
         osVersion = triple.getOSVersion();
+        break;
+      case DarwinPlatformKind::VisionOS:
+      case DarwinPlatformKind::VisionOSSimulator:
+        osVersion = triple.getOSVersion();
+
+        // The first deployment of 64-bit xrOS simulator is version 1.0.
+        if (triple.isArch64Bit() && triple.isSimulatorEnvironment() &&
+            osVersion.getMajor() < 1) {
+          osVersion = llvm::VersionTuple(/*Major=*/1, /*Minor=*/0);
+        }
+
         break;
       }
     }
diff --git a/lib/Driver/Driver.cpp b/lib/Driver/Driver.cpp
index 1cedad0a2fc32..9e2544b181327 100644
--- a/lib/Driver/Driver.cpp
+++ b/lib/Driver/Driver.cpp
@@ -340,6 +340,7 @@ Driver::buildToolChain(const llvm::opt::InputArgList &ArgList) {
   }
 
   switch (target.getOS()) {
+  case llvm::Triple::XROS:
   case llvm::Triple::IOS:
   case llvm::Triple::TvOS:
   case llvm::Triple::WatchOS:
diff --git a/lib/DriverTool/swift_api_digester_main.cpp b/lib/DriverTool/swift_api_digester_main.cpp
index bf3e9faf4ac81..792219929ecd2 100644
--- a/lib/DriverTool/swift_api_digester_main.cpp
+++ b/lib/DriverTool/swift_api_digester_main.cpp
@@ -2177,6 +2177,8 @@ static StringRef getBaselineFilename(llvm::Triple Triple) {
     return "linux.json";
   else if (Triple.isOSWindows())
     return "windows.json";
+  else if (Triple.isXROS())
+    return "xros.json";
   else {
     llvm::errs() << "Unsupported triple target\n";
     exit(1);
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index a8d3f2547737b..7ed4e2e6d0a44 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -305,6 +305,10 @@ void CompilerInvocation::setRuntimeResourcePath(StringRef Path) {
   updateRuntimeLibraryPaths(SearchPathOpts, FrontendOpts, LangOpts);
 }
 
+void CompilerInvocation::setPlatformAvailabilityInheritanceMapPath(StringRef Path) {
+  SearchPathOpts.PlatformAvailabilityInheritanceMapPath = Path.str();
+}
+
 void CompilerInvocation::setTargetTriple(StringRef Triple) {
   setTargetTriple(llvm::Triple(Triple));
 }
@@ -1180,6 +1184,24 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Target = llvm::Triple(A->getValue());
     TargetArg = A->getValue();
 
+    const bool targetNeedsRemapping = Target.isXROS();
+    if (targetNeedsRemapping && Target.getOSMajorVersion() == 0) {
+      // FIXME(xrOS): Work around an LLVM-ism until we have something
+      // akin to Target::get*Version for this platform. The Clang driver
+      // also has to pull version numbers up to 1.0.0 when a triple for an
+      // unknown platform with no explicit version number is passed.
+      if (Target.getEnvironmentName().empty()) {
+        Target = llvm::Triple(Target.getArchName(),
+                              Target.getVendorName(),
+                              Target.getOSName() + "1.0");
+      } else {
+        Target = llvm::Triple(Target.getArchName(),
+                              Target.getVendorName(),
+                              Target.getOSName() + "1.0",
+                              Target.getEnvironmentName());
+      }
+    }
+
     // Backward compatibility hack: infer "simulator" environment for x86
     // iOS/tvOS/watchOS. The driver takes care of this for the frontend
     // most of the time, but loading of old .swiftinterface files goes
@@ -2015,6 +2037,9 @@ static bool ParseSearchPathArgs(SearchPathOptions &Opts, ArgList &Args,
   if (const Arg *A = Args.getLastArg(OPT_const_gather_protocols_file))
     Opts.ConstGatherProtocolListFilePath = A->getValue();
 
+  if (const Arg *A = Args.getLastArg(OPT_platform_availability_inheritance_map_path))
+    Opts.PlatformAvailabilityInheritanceMapPath = A->getValue();
+
   for (auto A : Args.getAllArgValues(options::OPT_serialized_path_obfuscate)) {
     auto SplitMap = StringRef(A).split('=');
     Opts.DeserializedPathRecoverer.addMapping(SplitMap.first, SplitMap.second);
diff --git a/lib/Frontend/ModuleInterfaceLoader.cpp b/lib/Frontend/ModuleInterfaceLoader.cpp
index d065f3837d1f6..952fa247afb4e 100644
--- a/lib/Frontend/ModuleInterfaceLoader.cpp
+++ b/lib/Frontend/ModuleInterfaceLoader.cpp
@@ -1690,6 +1690,12 @@ void InterfaceSubContextDelegateImpl::inheritOptionsForBuildingInterface(
     genericSubInvocation.setSDKPath(SearchPathOpts.getSDKPath().str());
   }
 
+  if (SearchPathOpts.PlatformAvailabilityInheritanceMapPath) {
+    GenericArgs.push_back("-platform-availability-inheritance-map-path");
+    GenericArgs.push_back(ArgSaver.save(*SearchPathOpts.PlatformAvailabilityInheritanceMapPath));
+    genericSubInvocation.setPlatformAvailabilityInheritanceMapPath(*SearchPathOpts.PlatformAvailabilityInheritanceMapPath);
+  }
+
   genericSubInvocation.getFrontendOptions().InputMode
       = FrontendOptions::ParseInputMode::SwiftModuleInterface;
   if (!SearchPathOpts.RuntimeResourcePath.empty()) {
diff --git a/lib/IDE/CodeCompletionDiagnostics.cpp b/lib/IDE/CodeCompletionDiagnostics.cpp
index d82484ff26420..6f8bae705a649 100644
--- a/lib/IDE/CodeCompletionDiagnostics.cpp
+++ b/lib/IDE/CodeCompletionDiagnostics.cpp
@@ -94,6 +94,11 @@ bool CodeCompletionDiagnostics::getDiagnosticForDeprecated(
   if (Attr->Deprecated)
     DeprecatedVersion = Attr->Deprecated.value();
 
+  llvm::VersionTuple RemappedDeprecatedVersion;
+  if (AvailabilityInference::updateDeprecatedPlatformForFallback(
+      Attr, Ctx, Platform, RemappedDeprecatedVersion))
+    DeprecatedVersion = RemappedDeprecatedVersion;
+
   if (!isSoftDeprecated) {
     if (Attr->Message.empty() && Attr->Rename.empty()) {
       getDiagnostics(severity, Out, diag::availability_deprecated,
diff --git a/lib/IRGen/IRGenFunction.cpp b/lib/IRGen/IRGenFunction.cpp
index e2baf08b3c703..463cf1d9a9084 100644
--- a/lib/IRGen/IRGenFunction.cpp
+++ b/lib/IRGen/IRGenFunction.cpp
@@ -290,6 +290,8 @@ static unsigned getBaseMachOPlatformID(const llvm::Triple &TT) {
     return llvm::MachO::PLATFORM_TVOS;
   case llvm::Triple::WatchOS:
     return llvm::MachO::PLATFORM_WATCHOS;
+  case llvm::Triple::XROS:
+    return llvm::MachO::PLATFORM_XROS;
   default:
     return /*Unknown platform*/ 0;
   }
diff --git a/lib/IRGen/TBDGen.cpp b/lib/IRGen/TBDGen.cpp
index 267c8b0f924aa..f265153e5e135 100644
--- a/lib/IRGen/TBDGen.cpp
+++ b/lib/IRGen/TBDGen.cpp
@@ -264,6 +264,10 @@ getLinkerPlatformId(OriginallyDefinedInAttr::ActiveVersion Ver,
   case swift::PlatformKind::macCatalyst:
   case swift::PlatformKind::macCatalystApplicationExtension:
     return LinkerPlatformId::macCatalyst;
+  case swift::PlatformKind::visionOS:
+  case swift::PlatformKind::visionOSApplicationExtension:
+    return isSimulator ? LinkerPlatformId::xrOS_sim:
+                         LinkerPlatformId::xrOS;
   }
   llvm_unreachable("invalid platform kind");
 }
diff --git a/lib/IRGen/ldPlatformKinds.def b/lib/IRGen/ldPlatformKinds.def
index 46ab4d99c7dc8..5f25cac1168d4 100644
--- a/lib/IRGen/ldPlatformKinds.def
+++ b/lib/IRGen/ldPlatformKinds.def
@@ -26,5 +26,7 @@ LD_PLATFORM(macCatalyst, 6)
 LD_PLATFORM(iOS_sim, 7)
 LD_PLATFORM(tvOS_sim, 8)
 LD_PLATFORM(watchOS_sim, 9)
+LD_PLATFORM(xrOS, 11)
+LD_PLATFORM(xrOS_sim, 12)
 
 #undef LD_PLATFORM
diff --git a/lib/PrintAsClang/DeclAndTypePrinter.cpp b/lib/PrintAsClang/DeclAndTypePrinter.cpp
index 165fb7b1787d7..bfdb64d212524 100644
--- a/lib/PrintAsClang/DeclAndTypePrinter.cpp
+++ b/lib/PrintAsClang/DeclAndTypePrinter.cpp
@@ -1715,6 +1715,9 @@ class DeclAndTypePrinter::Implementation
       case PlatformKind::watchOS:
         plat = "watchos";
         break;
+      case PlatformKind::visionOS:
+        plat = "visionos";
+        break;
       case PlatformKind::macOSApplicationExtension:
         plat = "macos_app_extension";
         break;
@@ -1730,6 +1733,9 @@ class DeclAndTypePrinter::Implementation
       case PlatformKind::watchOSApplicationExtension:
         plat = "watchos_app_extension";
         break;
+      case PlatformKind::visionOSApplicationExtension:
+        plat = "visionos_app_extension";
+        break;
       case PlatformKind::OpenBSD:
         plat = "openbsd";
         break;
diff --git a/lib/Sema/DerivedConformanceRawRepresentable.cpp b/lib/Sema/DerivedConformanceRawRepresentable.cpp
index 56824ea6f756d..ea960ef510257 100644
--- a/lib/Sema/DerivedConformanceRawRepresentable.cpp
+++ b/lib/Sema/DerivedConformanceRawRepresentable.cpp
@@ -249,6 +249,14 @@ checkAvailability(const EnumElementDecl *elt, ASTContext &C,
   if (!attr)
     return true;
 
+  // For type-checking purposes, iOS availability is inherited for visionOS
+  // targets. However, it is not inherited for the sake of code-generation
+  // of runtime availability queries, and is assumed to be available.
+  if ((attr->Platform == PlatformKind::iOS ||
+       attr->Platform == PlatformKind::iOSApplicationExtension) &&
+      C.LangOpts.Target.isXROS())
+    return true;
+
   AvailableVersionComparison availability = attr->getVersionAvailability(C);
 
   assert(availability != AvailableVersionComparison::Available &&
diff --git a/lib/Sema/TypeCheckAttr.cpp b/lib/Sema/TypeCheckAttr.cpp
index 7d115c2c5853b..c6c1cb6bf59ad 100644
--- a/lib/Sema/TypeCheckAttr.cpp
+++ b/lib/Sema/TypeCheckAttr.cpp
@@ -705,6 +705,9 @@ static bool iswatchOS(ASTContext &ctx) {
 }
 
 static bool isRelaxedIBAction(ASTContext &ctx) {
+  if (ctx.LangOpts.Target.isXROS())
+    return true;
+
   return isiOS(ctx) || iswatchOS(ctx);
 }
 
@@ -2055,6 +2058,13 @@ void AttributeChecker::visitAvailableAttr(AvailableAttr *attr) {
     }
   }
 
+  if (attr->Platform == PlatformKind::iOS &&
+      isPlatformActive(PlatformKind::visionOS, Ctx.LangOpts)) {
+    if (attr != D->getAttrs().findMostSpecificActivePlatform(Ctx)) {
+      return;
+    }
+  }
+
   SourceLoc attrLoc = attr->getLocation();
   auto versionAvailability = attr->getVersionAvailability(Ctx);
   if (versionAvailability == AvailableVersionComparison::Obsoleted ||
@@ -4588,6 +4598,11 @@ void AttributeChecker::checkBackDeployedAttrs(
                                             Attr->Platform)) {
         auto platformString = prettyPlatformString(Attr->Platform);
 
+        llvm::VersionTuple ignoredVersion;
+
+        AvailabilityInference::updateBeforePlatformForFallback(
+            Attr, Ctx, platformString, ignoredVersion);
+
         diagnose(AtLoc, diag::attr_has_no_effect_on_unavailable_decl, Attr, VD,
                  platformString);
         diagnose(unavailableAttr->AtLoc, diag::availability_marked_unavailable,
@@ -4607,6 +4622,11 @@ void AttributeChecker::checkBackDeployedAttrs(
       auto introVersion = availableAttr->Introduced.value();
       StringRef introPlatformString = availableAttr->prettyPlatformString();
 
+      AvailabilityInference::updateBeforePlatformForFallback(
+          Attr, Ctx, beforePlatformString, beforeVersion);
+      AvailabilityInference::updateIntroducedPlatformForFallback(
+          availableAttr, Ctx, introPlatformString, introVersion);
+
       if (Attr->Version <= introVersion) {
         diagnose(AtLoc, diag::attr_has_no_effect_decl_not_available_before,
                  Attr, VD, beforePlatformString, beforeVersion);
diff --git a/lib/Sema/TypeCheckAvailability.cpp b/lib/Sema/TypeCheckAvailability.cpp
index 1278e5495bdc7..74dd17fb4f95b 100644
--- a/lib/Sema/TypeCheckAvailability.cpp
+++ b/lib/Sema/TypeCheckAvailability.cpp
@@ -1212,7 +1212,7 @@ class TypeRefinementContextBuilder : private ASTWalker {
       // we want to chose the OS X spec unless there is an explicit
       // OSXApplicationExtension spec.
       if (isPlatformActive(VersionSpec->getPlatform(), Context.LangOpts,
-                           forTargetVariant)) {
+                           forTargetVariant, /* ForRuntimeQuery */ true)) {
         if (!BestSpec ||
             inheritsAvailabilityFromPlatform(VersionSpec->getPlatform(),
                                              BestSpec->getPlatform())) {
@@ -2674,6 +2674,11 @@ void TypeChecker::diagnoseIfDeprecated(SourceRange ReferenceRange,
     return;
   }
 
+  llvm::VersionTuple RemappedDeprecatedVersion;
+  if (AvailabilityInference::updateDeprecatedPlatformForFallback(
+      Attr, Context, Platform, RemappedDeprecatedVersion))
+    DeprecatedVersion = RemappedDeprecatedVersion;
+
   SmallString<32> newNameBuf;
   std::optional<ReplacementDeclKind> replacementDeclKind =
       describeRename(Context, Attr, /*decl*/ nullptr, newNameBuf);
@@ -2743,6 +2748,11 @@ bool TypeChecker::diagnoseIfDeprecated(SourceLoc loc,
   if (attr->Deprecated)
     deprecatedVersion = attr->Deprecated.value();
 
+  llvm::VersionTuple remappedDeprecatedVersion;
+  if (AvailabilityInference::updateDeprecatedPlatformForFallback(
+      attr, ctx, platform, remappedDeprecatedVersion))
+    deprecatedVersion = remappedDeprecatedVersion;
+
   if (attr->Message.empty()) {
     ctx.Diags.diagnose(
              loc, diag::conformance_availability_deprecated,
@@ -3245,10 +3255,12 @@ bool swift::diagnoseExplicitUnavailability(
     // Skip the note emitted below.
     return true;
   } else {
+    auto unavailableDiagnosticPlatform = platform;
+    AvailabilityInference::updatePlatformStringForFallback(Attr, ctx, unavailableDiagnosticPlatform);
     EncodedDiagnosticMessage EncodedMessage(Attr->Message);
     diags
         .diagnose(Loc, diag::availability_decl_unavailable, D, platform.empty(),
-                  platform, EncodedMessage.Message)
+                  unavailableDiagnosticPlatform, EncodedMessage.Message)
         .highlight(R)
         .limitBehavior(limit);
   }
diff --git a/lib/Sema/TypeCheckDeclObjC.cpp b/lib/Sema/TypeCheckDeclObjC.cpp
index 7f7ad956793bd..f3af12a9a06bc 100644
--- a/lib/Sema/TypeCheckDeclObjC.cpp
+++ b/lib/Sema/TypeCheckDeclObjC.cpp
@@ -505,6 +505,8 @@ static VersionRange getMinOSVersionForClassStubs(const llvm::Triple &target) {
     return VersionRange::allGTE(llvm::VersionTuple(13, 0, 0));
   if (target.isWatchOS())
     return VersionRange::allGTE(llvm::VersionTuple(6, 0, 0));
+  if (target.isXROS())
+    return VersionRange::allGTE(llvm::VersionTuple(1, 0, 0));
   return VersionRange::all();
 }
 
diff --git a/lib/Serialization/SerializedModuleLoader.cpp b/lib/Serialization/SerializedModuleLoader.cpp
index 6f888e8243cb9..a44ee0f19e41a 100644
--- a/lib/Serialization/SerializedModuleLoader.cpp
+++ b/lib/Serialization/SerializedModuleLoader.cpp
@@ -845,6 +845,8 @@ getOSAndVersionForDiagnostics(const llvm::Triple &triple) {
       osName = swift::prettyPlatformString(PlatformKind::tvOS);
     } else if (triple.isiOS()) {
       osName = swift::prettyPlatformString(PlatformKind::iOS);
+    }  else if (triple.isXROS()) {
+      osName = swift::prettyPlatformString(PlatformKind::visionOS);
     } else {
       assert(!triple.isOSDarwin() && "unknown Apple OS");
       // Fallback to the LLVM triple name. This isn't great (it won't be
diff --git a/lib/SymbolGraphGen/AvailabilityMixin.cpp b/lib/SymbolGraphGen/AvailabilityMixin.cpp
index 03b6e963bbb95..01bec91ccd2aa 100644
--- a/lib/SymbolGraphGen/AvailabilityMixin.cpp
+++ b/lib/SymbolGraphGen/AvailabilityMixin.cpp
@@ -47,6 +47,8 @@ StringRef getDomain(const AvailableAttr &AvAttr) {
       return { "tvOS" };
     case swift::PlatformKind::watchOS:
       return { "watchOS" };
+    case swift::PlatformKind::visionOS:
+      return { "visionOS" };
     case swift::PlatformKind::iOSApplicationExtension:
       return { "iOSAppExtension" };
     case swift::PlatformKind::macCatalystApplicationExtension:
@@ -57,6 +59,8 @@ StringRef getDomain(const AvailableAttr &AvAttr) {
       return { "tvOSAppExtension" };
     case swift::PlatformKind::watchOSApplicationExtension:
       return { "watchOSAppExtension" };
+    case swift::PlatformKind::visionOSApplicationExtension:
+      return { "visionOSAppExtension" };
     case swift::PlatformKind::OpenBSD:
       return { "OpenBSD" };
     case swift::PlatformKind::Windows:
diff --git a/stdlib/cmake/modules/AddSwiftStdlib.cmake b/stdlib/cmake/modules/AddSwiftStdlib.cmake
index ba6d9eb4547cd..d95ce397e7726 100644
--- a/stdlib/cmake/modules/AddSwiftStdlib.cmake
+++ b/stdlib/cmake/modules/AddSwiftStdlib.cmake
@@ -31,11 +31,13 @@ endfunction()
 #   DEPLOYMENT_VERSION_IOS version
 #   DEPLOYMENT_VERSION_TVOS version
 #   DEPLOYMENT_VERSION_WATCHOS version
+#   DEPLOYMENT_VERSION_XROS version
 #
 # )
 function(_add_target_variant_c_compile_link_flags)
   set(oneValueArgs SDK ARCH BUILD_TYPE RESULT_VAR_NAME ENABLE_LTO ANALYZE_CODE_COVERAGE
     DEPLOYMENT_VERSION_OSX DEPLOYMENT_VERSION_MACCATALYST DEPLOYMENT_VERSION_IOS DEPLOYMENT_VERSION_TVOS DEPLOYMENT_VERSION_WATCHOS
+    DEPLOYMENT_VERSION_XROS
     MACCATALYST_BUILD_FLAVOR
   )
   cmake_parse_arguments(CFLAGS
@@ -63,6 +65,8 @@ function(_add_target_variant_c_compile_link_flags)
       set(DEPLOYMENT_VERSION ${CFLAGS_DEPLOYMENT_VERSION_TVOS})
     elseif("${CFLAGS_SDK}" STREQUAL "WATCHOS" OR "${CFLAGS_SDK}" STREQUAL "WATCHOS_SIMULATOR")
       set(DEPLOYMENT_VERSION ${CFLAGS_DEPLOYMENT_VERSION_WATCHOS})
+    elseif("${CFLAGS_SDK}" STREQUAL "XROS" OR "${CFLAGS_SDK}" STREQUAL "XROS_SIMULATOR")
+      set(DEPLOYMENT_VERSION ${CFLAGS_DEPLOYMENT_VERSION_XROS})
     endif()
 
     if("${DEPLOYMENT_VERSION}" STREQUAL "")
@@ -154,6 +158,7 @@ endfunction()
 function(_add_target_variant_c_compile_flags)
   set(oneValueArgs SDK ARCH BUILD_TYPE ENABLE_ASSERTIONS ANALYZE_CODE_COVERAGE
     DEPLOYMENT_VERSION_OSX DEPLOYMENT_VERSION_MACCATALYST DEPLOYMENT_VERSION_IOS DEPLOYMENT_VERSION_TVOS DEPLOYMENT_VERSION_WATCHOS
+    DEPLOYMENT_VERSION_XROS
     RESULT_VAR_NAME ENABLE_LTO
     MACCATALYST_BUILD_FLAVOR)
   cmake_parse_arguments(CFLAGS
@@ -189,6 +194,7 @@ function(_add_target_variant_c_compile_flags)
     DEPLOYMENT_VERSION_IOS "${CFLAGS_DEPLOYMENT_VERSION_IOS}"
     DEPLOYMENT_VERSION_TVOS "${CFLAGS_DEPLOYMENT_VERSION_TVOS}"
     DEPLOYMENT_VERSION_WATCHOS "${CFLAGS_DEPLOYMENT_VERSION_WATCHOS}"
+    DEPLOYMENT_VERSION_XROS "${CFLAGS_DEPLOYMENT_VERSION_XROS}"
     RESULT_VAR_NAME result
     MACCATALYST_BUILD_FLAVOR "${CFLAGS_MACCATALYST_BUILD_FLAVOR}")
 
@@ -469,6 +475,7 @@ endfunction()
 function(_add_target_variant_link_flags)
   set(oneValueArgs SDK ARCH BUILD_TYPE ENABLE_ASSERTIONS ANALYZE_CODE_COVERAGE
   DEPLOYMENT_VERSION_OSX DEPLOYMENT_VERSION_MACCATALYST DEPLOYMENT_VERSION_IOS DEPLOYMENT_VERSION_TVOS DEPLOYMENT_VERSION_WATCHOS
+  DEPLOYMENT_VERSION_XROS
   RESULT_VAR_NAME ENABLE_LTO LTO_OBJECT_NAME LINK_LIBRARIES_VAR_NAME LIBRARY_SEARCH_DIRECTORIES_VAR_NAME
   MACCATALYST_BUILD_FLAVOR
   )
@@ -497,6 +504,7 @@ function(_add_target_variant_link_flags)
     DEPLOYMENT_VERSION_IOS "${LFLAGS_DEPLOYMENT_VERSION_IOS}"
     DEPLOYMENT_VERSION_TVOS "${LFLAGS_DEPLOYMENT_VERSION_TVOS}"
     DEPLOYMENT_VERSION_WATCHOS "${LFLAGS_DEPLOYMENT_VERSION_WATCHOS}"
+    DEPLOYMENT_VERSION_XROS "${LFLAGS_DEPLOYMENT_VERSION_XROS}"
     RESULT_VAR_NAME result
     MACCATALYST_BUILD_FLAVOR  "${LFLAGS_MACCATALYST_BUILD_FLAVOR}")
   if("${LFLAGS_SDK}" STREQUAL "LINUX")
@@ -783,6 +791,7 @@ function(add_swift_target_library_single target name)
         DEPLOYMENT_VERSION_OSX
         DEPLOYMENT_VERSION_TVOS
         DEPLOYMENT_VERSION_WATCHOS
+        DEPLOYMENT_VERSION_XROS
         INSTALL_IN_COMPONENT
         DARWIN_INSTALL_NAME_DIR
         SDK
@@ -881,6 +890,7 @@ function(add_swift_target_library_single target name)
   if(SWIFT_EMBED_BITCODE_SECTION AND NOT SWIFTLIB_SINGLE_DONT_EMBED_BITCODE)
     if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "IOS" OR
        "${SWIFTLIB_SINGLE_SDK}" STREQUAL "TVOS" OR
+       "${SWIFTLIB_SINGLE_SDK}" STREQUAL "XROS" OR
        "${SWIFTLIB_SINGLE_SDK}" STREQUAL "WATCHOS")
       list(APPEND SWIFTLIB_SINGLE_C_COMPILE_FLAGS "-fembed-bitcode")
       set(embed_bitcode_arg EMBED_BITCODE)
@@ -1403,6 +1413,7 @@ function(add_swift_target_library_single target name)
     DEPLOYMENT_VERSION_IOS "${SWIFTLIB_DEPLOYMENT_VERSION_IOS}"
     DEPLOYMENT_VERSION_TVOS "${SWIFTLIB_DEPLOYMENT_VERSION_TVOS}"
     DEPLOYMENT_VERSION_WATCHOS "${SWIFTLIB_DEPLOYMENT_VERSION_WATCHOS}"
+    DEPLOYMENT_VERSION_XROS "${SWIFTLIB_DEPLOYMENT_VERSION_XROS}"
     RESULT_VAR_NAME c_compile_flags
     MACCATALYST_BUILD_FLAVOR "${SWIFTLIB_SINGLE_MACCATALYST_BUILD_FLAVOR}"
     )
@@ -1425,6 +1436,7 @@ function(add_swift_target_library_single target name)
     DEPLOYMENT_VERSION_IOS "${SWIFTLIB_DEPLOYMENT_VERSION_IOS}"
     DEPLOYMENT_VERSION_TVOS "${SWIFTLIB_DEPLOYMENT_VERSION_TVOS}"
     DEPLOYMENT_VERSION_WATCHOS "${SWIFTLIB_DEPLOYMENT_VERSION_WATCHOS}"
+    DEPLOYMENT_VERSION_XROS "${SWIFTLIB_DEPLOYMENT_VERSION_XROS}"
     RESULT_VAR_NAME link_flags
     LINK_LIBRARIES_VAR_NAME link_libraries
     LIBRARY_SEARCH_DIRECTORIES_VAR_NAME library_search_directories
@@ -1503,6 +1515,7 @@ function(add_swift_target_library_single target name)
     if(SWIFT_EMBED_BITCODE_SECTION AND NOT SWIFTLIB_SINGLE_DONT_EMBED_BITCODE)
       if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "IOS" OR
          "${SWIFTLIB_SINGLE_SDK}" STREQUAL "TVOS" OR
+         "${SWIFTLIB_SINGLE_SDK}" STREQUAL "XROS" OR
          "${SWIFTLIB_SINGLE_SDK}" STREQUAL "WATCHOS")
         # Please note that using a generator expression to fit
         # this in a single target_link_options does not work
@@ -1659,6 +1672,7 @@ endfunction()
 #     DEPLOYMENT_VERSION_IOS version
 #     DEPLOYMENT_VERSION_TVOS version
 #     DEPLOYMENT_VERSION_WATCHOS version
+#     DEPLOYMENT_VERSION_XROS version
 #     MACCATALYST_BUILD_FLAVOR flavor
 #     BACK_DEPLOYMENT_LIBRARY version
 #     source1 [source2 source3 ...])
@@ -1701,6 +1715,9 @@ endfunction()
 # SWIFT_MODULE_DEPENDS_WATCHOS
 #   Swift modules this library depends on when built for watchOS.
 #
+# SWIFT_MODULE_DEPENDS_XROS
+#   Swift modules this library depends on when built for xrOS.
+#
 # SWIFT_MODULE_DEPENDS_FREESTANDING
 #   Swift modules this library depends on when built for Freestanding.
 #
@@ -1777,6 +1794,9 @@ endfunction()
 # DEPLOYMENT_VERSION_WATCHOS
 #   The minimum deployment version to build for if this is an WATCHOS library.
 #
+# DEPLOYMENT_VERSION_XROS
+#   The minimum deployment version to build for if this is an XROS library.
+#
 # INSTALL_WITH_SHARED
 #   Install a static library target alongside shared libraries
 #
@@ -1806,6 +1826,7 @@ function(add_swift_target_library name)
         DEPLOYMENT_VERSION_OSX
         DEPLOYMENT_VERSION_TVOS
         DEPLOYMENT_VERSION_WATCHOS
+        DEPLOYMENT_VERSION_XROS
         INSTALL_IN_COMPONENT
         INSTALL_BINARY_SWIFTMODULE
         DARWIN_INSTALL_NAME_DIR
@@ -1838,6 +1859,7 @@ function(add_swift_target_library name)
         SWIFT_COMPILE_FLAGS_OSX
         SWIFT_COMPILE_FLAGS_TVOS
         SWIFT_COMPILE_FLAGS_WATCHOS
+        SWIFT_COMPILE_FLAGS_XROS
         SWIFT_COMPILE_FLAGS_LINUX
         SWIFT_MODULE_DEPENDS
         SWIFT_MODULE_DEPENDS_CYGWIN
@@ -1851,6 +1873,7 @@ function(add_swift_target_library name)
         SWIFT_MODULE_DEPENDS_TVOS
         SWIFT_MODULE_DEPENDS_WASI
         SWIFT_MODULE_DEPENDS_WATCHOS
+        SWIFT_MODULE_DEPENDS_XROS
         SWIFT_MODULE_DEPENDS_WINDOWS
         SWIFT_MODULE_DEPENDS_FROM_SDK
         TARGET_SDKS
@@ -2026,6 +2049,9 @@ function(add_swift_target_library name)
     elseif(sdk STREQUAL "WATCHOS" OR sdk STREQUAL "WATCHOS_SIMULATOR")
       list(APPEND swiftlib_module_depends_flattened
            ${SWIFTLIB_SWIFT_MODULE_DEPENDS_WATCHOS})
+    elseif("${sdk}" STREQUAL "XROS" OR "${sdk}" STREQUAL "XROS_SIMULATOR")
+        list(APPEND swiftlib_module_depends_flattened
+            ${SWIFTLIB_SWIFT_MODULE_DEPENDS_XROS})
     elseif(sdk STREQUAL "FREESTANDING")
       list(APPEND swiftlib_module_depends_flattened
            ${SWIFTLIB_SWIFT_MODULE_DEPENDS_FREESTANDING})
@@ -2077,6 +2103,9 @@ function(add_swift_target_library name)
     elseif(sdk STREQUAL "WATCHOS" OR sdk STREQUAL "WATCHOS_SIMULATOR")
       list(APPEND swiftlib_swift_compile_flags_all
            ${SWIFTLIB_SWIFT_COMPILE_FLAGS_WATCHOS})
+    elseif("${sdk}" STREQUAL "XROS" OR "${sdk}" STREQUAL "XROS_SIMULATOR")
+        list(APPEND swiftlib_swift_compile_flags_all
+            ${SWIFTLIB_SWIFT_COMPILE_FLAGS_XROS})
     elseif(sdk STREQUAL "LINUX")
       list(APPEND swiftlib_swift_compile_flags_all
            ${SWIFTLIB_SWIFT_COMPILE_FLAGS_LINUX})
@@ -2326,6 +2355,7 @@ function(add_swift_target_library name)
         DEPLOYMENT_VERSION_IOS "${SWIFTLIB_DEPLOYMENT_VERSION_IOS}"
         DEPLOYMENT_VERSION_TVOS "${SWIFTLIB_DEPLOYMENT_VERSION_TVOS}"
         DEPLOYMENT_VERSION_WATCHOS "${SWIFTLIB_DEPLOYMENT_VERSION_WATCHOS}"
+        DEPLOYMENT_VERSION_XROS "${SWIFTLIB_DEPLOYMENT_VERSION_XROS}"
         MACCATALYST_BUILD_FLAVOR "${maccatalyst_build_flavor}"
         ${back_deployment_library_option}
         ENABLE_LTO "${SWIFT_STDLIB_ENABLE_LTO}"
diff --git a/stdlib/private/OSLog/CMakeLists.txt b/stdlib/private/OSLog/CMakeLists.txt
index 8dce747672109..befc43e172b7c 100644
--- a/stdlib/private/OSLog/CMakeLists.txt
+++ b/stdlib/private/OSLog/CMakeLists.txt
@@ -29,6 +29,7 @@ add_swift_target_library(swiftOSLogTestHelper
   SWIFT_MODULE_DEPENDS_OSX ${swift_oslog_darwin_dependencies}
   SWIFT_MODULE_DEPENDS_TVOS ${swift_oslog_darwin_dependencies}
   SWIFT_MODULE_DEPENDS_WATCHOS ${swift_oslog_darwin_dependencies}
+  SWIFT_MODULE_DEPENDS_XROS ${swift_oslog_darwin_dependencies}
   SWIFT_MODULE_DEPENDS_MACCATALYST ${swift_oslog_darwin_dependencies}
   TARGET_SDKS ALL_APPLE_PLATFORMS
   SWIFT_COMPILE_FLAGS ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
diff --git a/stdlib/private/StdlibUnittest/CMakeLists.txt b/stdlib/private/StdlibUnittest/CMakeLists.txt
index 71e1a480fd869..711ee520376c0 100644
--- a/stdlib/private/StdlibUnittest/CMakeLists.txt
+++ b/stdlib/private/StdlibUnittest/CMakeLists.txt
@@ -59,6 +59,7 @@ add_swift_target_library(swiftStdlibUnittest ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES}
   SWIFT_MODULE_DEPENDS_OSX ${swift_stdlib_unittest_darwin_dependencies}
   SWIFT_MODULE_DEPENDS_TVOS ${swift_stdlib_unittest_darwin_dependencies}
   SWIFT_MODULE_DEPENDS_WATCHOS ${swift_stdlib_unittest_darwin_dependencies}
+  SWIFT_MODULE_DEPENDS_XROS ${swift_stdlib_unittest_darwin_dependencies}
   SWIFT_MODULE_DEPENDS_MACCATALYST ${swift_stdlib_unittest_darwin_dependencies}
   SWIFT_MODULE_DEPENDS_FREESTANDING "${SWIFT_FREESTANDING_TEST_DEPENDENCIES}"
   SWIFT_MODULE_DEPENDS_LINUX Glibc
diff --git a/stdlib/private/StdlibUnittest/StdlibUnittest.swift b/stdlib/private/StdlibUnittest/StdlibUnittest.swift
index d73f63feda0e5..11e60e1dbad41 100644
--- a/stdlib/private/StdlibUnittest/StdlibUnittest.swift
+++ b/stdlib/private/StdlibUnittest/StdlibUnittest.swift
@@ -2205,9 +2205,11 @@ public enum OSVersion : CustomStringConvertible {
   case iOS(major: Int, minor: Int, bugFix: Int)
   case tvOS(major: Int, minor: Int, bugFix: Int)
   case watchOS(major: Int, minor: Int, bugFix: Int)
+  case visionOS(major: Int, minor: Int, bugFix: Int)
   case iOSSimulator
   case tvOSSimulator
   case watchOSSimulator
+  case visionOSSimulator
   case linux
   case freeBSD
   case openBSD
@@ -2228,12 +2230,16 @@ public enum OSVersion : CustomStringConvertible {
       return "TVOS \(major).\(minor).\(bugFix)"
     case .watchOS(let major, let minor, let bugFix):
       return "watchOS \(major).\(minor).\(bugFix)"
+    case .visionOS(let major, let minor, let bugFix):
+      return "visionOS \(major).\(minor).\(bugFix)"
     case .iOSSimulator:
       return "iOSSimulator"
     case .tvOSSimulator:
       return "TVOSSimulator"
     case .watchOSSimulator:
       return "watchOSSimulator"
+    case .visionOSSimulator:
+      return "visionOSSimulator"
     case .linux:
       return "Linux"
     case .freeBSD:
@@ -2282,6 +2288,8 @@ func _getOSVersion() -> OSVersion {
   return .tvOSSimulator
 #elseif os(watchOS) && targetEnvironment(simulator)
   return .watchOSSimulator
+#elseif os(visionOS) && targetEnvironment(simulator)
+  return .visionOSSimulator
 #elseif os(Linux)
   return .linux
 #elseif os(FreeBSD)
@@ -2311,6 +2319,8 @@ func _getOSVersion() -> OSVersion {
   return .tvOS(major: major, minor: minor, bugFix: bugFix)
   #elseif os(watchOS)
   return .watchOS(major: major, minor: minor, bugFix: bugFix)
+  #elseif os(visionOS)
+  return .visionOS(major: major, minor: minor, bugFix: bugFix)
   #else
   fatalError("could not determine OS version")
   #endif
@@ -2373,6 +2383,16 @@ public enum TestRunPredicate : CustomStringConvertible {
 
   case watchOSSimulatorAny(/*reason:*/ String)
 
+  case visionOSAny(/*reason:*/ String)
+  case visionOSMajor(Int, reason: String)
+  case visionOSMajorRange(ClosedRange<Int>, reason: String)
+  case visionOSMinor(Int, Int, reason: String)
+  case visionOSMinorRange(Int, ClosedRange<Int>, reason: String)
+  case visionOSBugFix(Int, Int, Int, reason: String)
+  case visionOSBugFixRange(Int, Int, ClosedRange<Int>, reason: String)
+
+  case visionOSSimulatorAny(/*reason:*/ String)
+
   case linuxAny(reason: String)
 
   case freeBSDAny(reason: String)
@@ -2467,6 +2487,24 @@ public enum TestRunPredicate : CustomStringConvertible {
     case .watchOSSimulatorAny(let reason):
       return "watchOSSimulatorAny(*, reason: \(reason))"
 
+    case .visionOSAny(let reason):
+      return "visionOS(*, reason: \(reason))"
+    case .visionOSMajor(let major, let reason):
+      return "visionOS(\(major).*, reason: \(reason))"
+    case .visionOSMajorRange(let range, let reason):
+      return "visionOS([\(range)], reason: \(reason))"
+    case .visionOSMinor(let major, let minor, let reason):
+      return "visionOS(\(major).\(minor), reason: \(reason))"
+    case .visionOSMinorRange(let major, let minorRange, let reason):
+      return "visionOS(\(major).[\(minorRange)], reason: \(reason))"
+    case .visionOSBugFix(let major, let minor, let bugFix, let reason):
+      return "visionOS(\(major).\(minor).\(bugFix), reason: \(reason))"
+    case .visionOSBugFixRange(let major, let minor, let bugFixRange, let reason):
+      return "visionOS(\(major).\(minor).[\(bugFixRange)], reason: \(reason))"
+
+    case .visionOSSimulatorAny(let reason):
+      return "visionOSSimulatorAny(*, reason: \(reason))"
+
     case .linuxAny(reason: let reason):
       return "linuxAny(*, reason: \(reason))"
 
@@ -2745,6 +2783,70 @@ public enum TestRunPredicate : CustomStringConvertible {
         return false
       }
 
+    case .visionOSAny:
+      switch _getRunningOSVersion() {
+      case .visionOS:
+        return true
+      default:
+        return false
+      }
+
+    case .visionOSMajor(let major, _):
+      switch _getRunningOSVersion() {
+      case .visionOS(major, _, _):
+        return true
+      default:
+        return false
+      }
+
+    case .visionOSMajorRange(let range, _):
+      switch _getRunningOSVersion() {
+      case .visionOS(let major, _, _):
+        return range.contains(major)
+      default:
+        return false
+      }
+
+    case .visionOSMinor(let major, let minor, _):
+      switch _getRunningOSVersion() {
+      case .visionOS(major, minor, _):
+        return true
+      default:
+        return false
+      }
+
+    case .visionOSMinorRange(let major, let minorRange, _):
+      switch _getRunningOSVersion() {
+      case .visionOS(major, let runningMinor, _):
+        return minorRange.contains(runningMinor)
+      default:
+        return false
+      }
+
+    case .visionOSBugFix(let major, let minor, let bugFix, _):
+      switch _getRunningOSVersion() {
+      case .visionOS(major, minor, bugFix):
+        return true
+      default:
+        return false
+      }
+
+    case .visionOSBugFixRange(let major, let minor, let bugFixRange, _):
+      switch _getRunningOSVersion() {
+      case .visionOS(major, minor, let runningBugFix):
+        return bugFixRange.contains(runningBugFix)
+      default:
+        return false
+      }
+
+    case .visionOSSimulatorAny:
+      switch _getRunningOSVersion() {
+      case .visionOSSimulator:
+        return true
+      default:
+        return false
+      }
+
     case .linuxAny:
       switch _getRunningOSVersion() {
       case .linux:
diff --git a/stdlib/private/StdlibUnittestFoundationExtras/StdlibUnittestFoundationExtras.swift b/stdlib/private/StdlibUnittestFoundationExtras/StdlibUnittestFoundationExtras.swift
index f6f97598786dd..c90f6c8508a77 100644
--- a/stdlib/private/StdlibUnittestFoundationExtras/StdlibUnittestFoundationExtras.swift
+++ b/stdlib/private/StdlibUnittestFoundationExtras/StdlibUnittestFoundationExtras.swift
@@ -23,7 +23,7 @@ import StdlibUnittest
 public func autoreleasepoolIfUnoptimizedReturnAutoreleased(
   invoking body: () -> Void
 ) {
-#if targetEnvironment(simulator) && arch(i386) && (os(iOS) || os(watchOS))
+#if targetEnvironment(simulator) && arch(i386) && (os(iOS) || os(watchOS) || os(visionOS))
   autoreleasepool(invoking: body)
 #else
   body()
diff --git a/stdlib/private/SwiftPrivateLibcExtras/CMakeLists.txt b/stdlib/private/SwiftPrivateLibcExtras/CMakeLists.txt
index 5a1d12abe8eed..0e921de472932 100644
--- a/stdlib/private/SwiftPrivateLibcExtras/CMakeLists.txt
+++ b/stdlib/private/SwiftPrivateLibcExtras/CMakeLists.txt
@@ -35,6 +35,7 @@ add_swift_target_library(swiftSwiftPrivateLibcExtras ${SWIFT_STDLIB_LIBRARY_BUIL
   SWIFT_MODULE_DEPENDS_IOS ${swift_private_libc_extras_darwin_depencencies}
   SWIFT_MODULE_DEPENDS_TVOS ${swift_private_libc_extras_darwin_depencencies}
   SWIFT_MODULE_DEPENDS_WATCHOS ${swift_private_libc_extras_darwin_depencencies}
+  SWIFT_MODULE_DEPENDS_XROS ${swift_private_libc_extras_darwin_depencencies}
   SWIFT_MODULE_DEPENDS_MACCATALYST ${swift_private_libc_extras_darwin_depencencies}
   SWIFT_MODULE_DEPENDS_FREESTANDING "${SWIFT_FREESTANDING_TEST_DEPENDENCIES}"
   SWIFT_MODULE_DEPENDS_LINUX Glibc
diff --git a/stdlib/private/SwiftPrivateThreadExtras/CMakeLists.txt b/stdlib/private/SwiftPrivateThreadExtras/CMakeLists.txt
index ced3246859d38..dd60a70551f02 100644
--- a/stdlib/private/SwiftPrivateThreadExtras/CMakeLists.txt
+++ b/stdlib/private/SwiftPrivateThreadExtras/CMakeLists.txt
@@ -16,6 +16,7 @@ add_swift_target_library(swiftSwiftPrivateThreadExtras ${SWIFT_STDLIB_LIBRARY_BU
   SWIFT_MODULE_DEPENDS_OSX ${swift_private_thread_extras_darwin_depencencies}
   SWIFT_MODULE_DEPENDS_TVOS ${swift_private_thread_extras_darwin_depencencies}
   SWIFT_MODULE_DEPENDS_WATCHOS ${swift_private_thread_extras_darwin_depencencies}
+  SWIFT_MODULE_DEPENDS_XROS ${swift_private_thread_extras_darwin_depencencies}
   SWIFT_MODULE_DEPENDS_MACCATALYST ${swift_private_thread_extras_darwin_depencencies}
   SWIFT_MODULE_DEPENDS_FREESTANDING "${SWIFT_FREESTANDING_TEST_DEPENDENCIES}"
   SWIFT_MODULE_DEPENDS_LINUX Glibc
diff --git a/stdlib/private/SwiftReflectionTest/CMakeLists.txt b/stdlib/private/SwiftReflectionTest/CMakeLists.txt
index d751d84aeb10d..357b08b77b352 100644
--- a/stdlib/private/SwiftReflectionTest/CMakeLists.txt
+++ b/stdlib/private/SwiftReflectionTest/CMakeLists.txt
@@ -13,6 +13,7 @@ if (SWIFT_INCLUDE_TESTS AND SWIFT_BUILD_DYNAMIC_STDLIB)
     SWIFT_MODULE_DEPENDS_IOS ${swift_reflection_test_darwin_depencencies}
     SWIFT_MODULE_DEPENDS_TVOS ${swift_reflection_test_darwin_depencencies}
     SWIFT_MODULE_DEPENDS_WATCHOS ${swift_reflection_test_darwin_depencencies}
+    SWIFT_MODULE_DEPENDS_XROS ${swift_reflection_test_darwin_depencencies}
     SWIFT_MODULE_DEPENDS_LINUX Glibc
     SWIFT_MODULE_DEPENDS_FREEBSD Glibc
     SWIFT_MODULE_DEPENDS_OPENBSD Glibc
diff --git a/stdlib/private/SwiftReflectionTest/SwiftReflectionTest.swift b/stdlib/private/SwiftReflectionTest/SwiftReflectionTest.swift
index 3fc54debe1d49..44175a187da1b 100644
--- a/stdlib/private/SwiftReflectionTest/SwiftReflectionTest.swift
+++ b/stdlib/private/SwiftReflectionTest/SwiftReflectionTest.swift
@@ -28,7 +28,7 @@ let RequestDone = "d"
 let RequestPointerSize = "p"
 
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
 import MachO
 import Darwin
 
diff --git a/stdlib/public/Cxx/std/CMakeLists.txt b/stdlib/public/Cxx/std/CMakeLists.txt
index 4da89471a1dce..85087204882ae 100644
--- a/stdlib/public/Cxx/std/CMakeLists.txt
+++ b/stdlib/public/Cxx/std/CMakeLists.txt
@@ -43,6 +43,7 @@ add_swift_target_library(swiftCxxStdlib STATIC NO_LINK_NAME IS_STDLIB IS_SWIFT_O
     SWIFT_MODULE_DEPENDS_OSX ${swift_cxxstdlib_darwin_dependencies}
     SWIFT_MODULE_DEPENDS_TVOS ${swift_cxxstdlib_darwin_dependencies}
     SWIFT_MODULE_DEPENDS_WATCHOS ${swift_cxxstdlib_darwin_dependencies}
+    SWIFT_MODULE_DEPENDS_XROS ${swift_cxxstdlib_darwin_dependencies}
     SWIFT_MODULE_DEPENDS_MACCATALYST ${swift_cxxstdlib_darwin_dependencies}
 
     SWIFT_COMPILE_FLAGS ${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS} ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
diff --git a/stdlib/public/Differentiation/CMakeLists.txt b/stdlib/public/Differentiation/CMakeLists.txt
index f9c1199da9c11..1bb1c2c3e22f5 100644
--- a/stdlib/public/Differentiation/CMakeLists.txt
+++ b/stdlib/public/Differentiation/CMakeLists.txt
@@ -41,6 +41,7 @@ add_swift_target_library(swift_Differentiation ${SWIFT_STDLIB_LIBRARY_BUILD_TYPE
   SWIFT_MODULE_DEPENDS_IOS ${swiftDifferentiationDarwinDependencies}
   SWIFT_MODULE_DEPENDS_TVOS ${swiftDifferentiationDarwinDependencies}
   SWIFT_MODULE_DEPENDS_WATCHOS ${swiftDifferentiationDarwinDependencies}
+  SWIFT_MODULE_DEPENDS_XROS ${swiftDifferentiationDarwinDependencies}
   SWIFT_MODULE_DEPENDS_LINUX Glibc
   SWIFT_MODULE_DEPENDS_FREEBSD Glibc
   SWIFT_MODULE_DEPENDS_OPENBSD Glibc
diff --git a/stdlib/public/Differentiation/TgmathDerivatives.swift.gyb b/stdlib/public/Differentiation/TgmathDerivatives.swift.gyb
index 9428393c2b401..a517dade14502 100644
--- a/stdlib/public/Differentiation/TgmathDerivatives.swift.gyb
+++ b/stdlib/public/Differentiation/TgmathDerivatives.swift.gyb
@@ -14,7 +14,7 @@
 
 import Swift
 
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
   import Darwin.C.tgmath
 #elseif canImport(Musl)
   import Musl
diff --git a/stdlib/public/Platform/MachError.swift b/stdlib/public/Platform/MachError.swift
index d79fb7382a456..1dfecd66a5f1c 100644
--- a/stdlib/public/Platform/MachError.swift
+++ b/stdlib/public/Platform/MachError.swift
@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS)) && _runtime(_ObjC)
+#if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)) && _runtime(_ObjC)
 /// Enumeration describing Mach error codes.
 @objc
 public enum MachErrorCode : Int32 {
@@ -202,4 +202,4 @@ public enum MachErrorCode : Int32 {
   /// The requested property cannot be changed at this time.
   case policyStatic             = 51
 }
-#endif // (os(macOS) || os(iOS) || os(tvOS) || os(watchOS)) && _runtime(_ObjC)
+#endif // (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)) && _runtime(_ObjC)
diff --git a/stdlib/public/Platform/POSIXError.swift b/stdlib/public/Platform/POSIXError.swift
index 84777cb380436..8f1b488089bc0 100644
--- a/stdlib/public/Platform/POSIXError.swift
+++ b/stdlib/public/Platform/POSIXError.swift
@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS)) && _runtime(_ObjC)
+#if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)) && _runtime(_ObjC)
 
 /// Enumeration describing POSIX error codes.
 @objc
diff --git a/stdlib/public/Platform/Platform.swift b/stdlib/public/Platform/Platform.swift
index 272b8e2c84850..a3e8f439fe44c 100644
--- a/stdlib/public/Platform/Platform.swift
+++ b/stdlib/public/Platform/Platform.swift
@@ -13,7 +13,7 @@
 import SwiftShims
 import SwiftOverlayShims
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
 //===----------------------------------------------------------------------===//
 // MacTypes.h
 //===----------------------------------------------------------------------===//
@@ -102,7 +102,7 @@ public var errno : Int32 {
 // stdio.h
 //===----------------------------------------------------------------------===//
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(FreeBSD) || os(PS4)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS) || os(FreeBSD) || os(PS4)
 public var stdin : UnsafeMutablePointer<FILE> {
   get {
     return __stdinp
@@ -250,7 +250,7 @@ public var S_IFBLK: mode_t  { return mode_t(0o060000) }
 public var S_IFREG: mode_t  { return mode_t(0o100000) }
 public var S_IFLNK: mode_t  { return mode_t(0o120000) }
 public var S_IFSOCK: mode_t { return mode_t(0o140000) }
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
 public var S_IFWHT: mode_t  { return mode_t(0o160000) }
 #endif
 
@@ -317,7 +317,7 @@ public func ioctl(
 // unistd.h
 //===----------------------------------------------------------------------===//
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
 @available(*, unavailable, message: "Please use threads or posix_spawn*()")
 public func fork() -> Int32 {
   fatalError("unavailable function can't be called")
@@ -333,7 +333,7 @@ public func vfork() -> Int32 {
 // signal.h
 //===----------------------------------------------------------------------===//
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
 public var SIG_DFL: sig_t? { return nil }
 public var SIG_IGN: sig_t { return unsafeBitCast(1, to: sig_t.self) }
 public var SIG_ERR: sig_t { return unsafeBitCast(-1, to: sig_t.self) }
@@ -397,7 +397,7 @@ public typealias Semaphore = UnsafeMutablePointer<sem_t>
 
 /// The value returned by `sem_open()` in the case of failure.
 public var SEM_FAILED: Semaphore? {
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
   // The value is ABI.  Value verified to be correct for OS X, iOS, watchOS, tvOS.
   return Semaphore(bitPattern: -1)
 #elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(PS4) || os(Android) || os(Cygwin) || os(Haiku) || os(WASI)
@@ -430,7 +430,7 @@ public func sem_open(
 // time.h
 //===----------------------------------------------------------------------===//
 
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(Linux)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS) || os(Linux)
 
 @available(SwiftStdlib 5.7, *)
 extension timespec {
@@ -483,7 +483,7 @@ extension Duration {
 
 // Some platforms don't have `extern char** environ` imported from C.
 #if SWIFT_STDLIB_HAS_ENVIRON
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(FreeBSD) || os(OpenBSD) || os(PS4)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS) || os(FreeBSD) || os(OpenBSD) || os(PS4)
 public var environ: UnsafeMutablePointer<UnsafeMutablePointer<CChar>?> {
   return _swift_stdlib_getEnviron()
 }
diff --git a/stdlib/public/Platform/TiocConstants.swift b/stdlib/public/Platform/TiocConstants.swift
index 272f7e242e64d..9510315d19908 100644
--- a/stdlib/public/Platform/TiocConstants.swift
+++ b/stdlib/public/Platform/TiocConstants.swift
@@ -13,7 +13,7 @@
 // Tty ioctl request constants, needed only on Darwin and FreeBSD.
 
 // Constants available on all platforms, also available on Linux.
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(FreeBSD) || os(Haiku)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS) || os(FreeBSD) || os(Haiku)
 
 /// Set exclusive use of tty.
 public var TIOCEXCL: UInt { return 0x2000740d }
@@ -115,7 +115,7 @@ public var TIOCGLTC: UInt { return 0x40067474 }
 
 
 // Darwin only constants, also available on Linux.
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
 
 /// Get termios struct.
 public var TIOCGETA: UInt { return 0x40487413 }
diff --git a/stdlib/public/Platform/tgmath.swift.gyb b/stdlib/public/Platform/tgmath.swift.gyb
index 29b011a4c51da..1680044d4d59f 100644
--- a/stdlib/public/Platform/tgmath.swift.gyb
+++ b/stdlib/public/Platform/tgmath.swift.gyb
@@ -234,7 +234,7 @@ public func ${ufunc}(_ x: ${T}) -> ${T} {
 
 % end
 
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
 // Unary intrinsic functions
 // Note these have a corresponding LLVM intrinsic
 % for T, ufunc in TypedUnaryIntrinsicFunctions():
diff --git a/stdlib/public/core/AssertCommon.swift b/stdlib/public/core/AssertCommon.swift
index e2f217b46e532..001756e78858b 100644
--- a/stdlib/public/core/AssertCommon.swift
+++ b/stdlib/public/core/AssertCommon.swift
@@ -74,7 +74,7 @@ func _isStdlibDebugChecksEnabled() -> Bool {
 internal func _fatalErrorFlags() -> UInt32 {
   // The current flags are:
   // (1 << 0): Report backtrace on fatal error
-#if os(iOS) || os(tvOS) || os(watchOS)
+#if os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
   return 0
 #else
   return _isDebugAssertConfiguration() ? 1 : 0
diff --git a/stdlib/public/core/Availability.swift b/stdlib/public/core/Availability.swift
index eef9ec5cd2deb..43da1ff6dfff6 100644
--- a/stdlib/public/core/Availability.swift
+++ b/stdlib/public/core/Availability.swift
@@ -25,7 +25,7 @@ public func _stdlib_isOSVersionAtLeast(
   _ minor: Builtin.Word,
   _ patch: Builtin.Word
 ) -> Builtin.Int1 {
-#if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS)) && SWIFT_RUNTIME_OS_VERSIONING
+#if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)) && SWIFT_RUNTIME_OS_VERSIONING
   if Int(major) == 9999 {
     return true._value
   }
diff --git a/stdlib/public/core/CTypes.swift b/stdlib/public/core/CTypes.swift
index f7e0592be83fe..b5c1cff68767e 100644
--- a/stdlib/public/core/CTypes.swift
+++ b/stdlib/public/core/CTypes.swift
@@ -69,7 +69,7 @@ public typealias CFloat = Float
 public typealias CDouble = Double
 
 /// The C 'long double' type.
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
 // On Darwin, long double is Float80 on x86, and Double otherwise.
 #if arch(x86_64) || arch(i386)
 public typealias CLongDouble = Float80
@@ -273,7 +273,7 @@ extension UInt {
 }
 
 /// A wrapper around a C `va_list` pointer.
-#if arch(arm64) && !(os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(Windows))
+#if arch(arm64) && !(os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS) ||  os(Windows))
 @frozen
 public struct CVaListPointer {
   @usableFromInline // unsafe-performance
diff --git a/stdlib/public/core/ErrorType.swift b/stdlib/public/core/ErrorType.swift
index d48b87a2ad6ec..632e9da1b400c 100644
--- a/stdlib/public/core/ErrorType.swift
+++ b/stdlib/public/core/ErrorType.swift
@@ -195,7 +195,7 @@ func _willThrowTypedImpl<E: Error>(_ error: E)
 @_alwaysEmitIntoClient
 @_silgen_name("swift_willThrowTyped")
 public func _willThrowTyped<E: Error>(_ error: E) {
-  if #available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, *) {
+  if #available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, visionOS 9999, *) {
     _willThrowTypedImpl(error)
   }
 }
diff --git a/stdlib/public/core/VarArgs.swift b/stdlib/public/core/VarArgs.swift
index 7dc05b341aa0c..c7b514c126599 100644
--- a/stdlib/public/core/VarArgs.swift
+++ b/stdlib/public/core/VarArgs.swift
@@ -102,7 +102,7 @@ internal let _countGPRegisters = 16
 @usableFromInline
 internal let _registerSaveWords = _countGPRegisters
 
-#elseif arch(arm64) && !(os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(Windows))
+#elseif arch(arm64) && !(os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS) || os(Windows))
 // ARM Procedure Call Standard for aarch64. (IHI0055B)
 // The va_list type may refer to any parameter in a parameter list may be in one
 // of three memory locations depending on its type and position in the argument
@@ -444,7 +444,7 @@ extension Float80: CVarArg, _CVarArgAligned {
 }
 #endif
 
-#if (arch(x86_64) && !os(Windows)) || arch(s390x) || (arch(arm64) && !(os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(Windows)))
+#if (arch(x86_64) && !os(Windows)) || arch(s390x) || (arch(arm64) && !(os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS) || os(Windows)))
 
 /// An object that can manage the lifetime of storage backing a
 /// `CVaListPointer`.
diff --git a/stdlib/toolchain/Compatibility50/CMakeLists.txt b/stdlib/toolchain/Compatibility50/CMakeLists.txt
index 7cc357cb03232..af8b8f2c686dd 100644
--- a/stdlib/toolchain/Compatibility50/CMakeLists.txt
+++ b/stdlib/toolchain/Compatibility50/CMakeLists.txt
@@ -20,6 +20,7 @@ add_swift_target_library("${library_name}" STATIC
   DEPLOYMENT_VERSION_IOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_IOS}
   DEPLOYMENT_VERSION_TVOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_TVOS}
   DEPLOYMENT_VERSION_WATCHOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_WATCHOS}
+  DEPLOYMENT_VERSION_XROS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_XROS}
 
   INSTALL_IN_COMPONENT compiler
   INSTALL_WITH_SHARED)
diff --git a/stdlib/toolchain/Compatibility51/CMakeLists.txt b/stdlib/toolchain/Compatibility51/CMakeLists.txt
index ce88f26470894..bca90850dc8da 100644
--- a/stdlib/toolchain/Compatibility51/CMakeLists.txt
+++ b/stdlib/toolchain/Compatibility51/CMakeLists.txt
@@ -20,6 +20,7 @@ add_swift_target_library("${library_name}" STATIC
   DEPLOYMENT_VERSION_IOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_IOS}
   DEPLOYMENT_VERSION_TVOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_TVOS}
   DEPLOYMENT_VERSION_WATCHOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_WATCHOS}
+  DEPLOYMENT_VERSION_XROS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_XROS}
 
   MACCATALYST_BUILD_FLAVOR "zippered"
 
diff --git a/stdlib/toolchain/Compatibility56/CMakeLists.txt b/stdlib/toolchain/Compatibility56/CMakeLists.txt
index 977d5f684d7e7..a1a55abd56c5d 100644
--- a/stdlib/toolchain/Compatibility56/CMakeLists.txt
+++ b/stdlib/toolchain/Compatibility56/CMakeLists.txt
@@ -29,6 +29,7 @@ add_swift_target_library("${library_name}" STATIC
   DEPLOYMENT_VERSION_IOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_IOS}
   DEPLOYMENT_VERSION_TVOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_TVOS}
   DEPLOYMENT_VERSION_WATCHOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_WATCHOS}
+  DEPLOYMENT_VERSION_XROS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_XROS}
 
   MACCATALYST_BUILD_FLAVOR "zippered"
 
diff --git a/stdlib/toolchain/CompatibilityDynamicReplacements/CMakeLists.txt b/stdlib/toolchain/CompatibilityDynamicReplacements/CMakeLists.txt
index 13aa1d744bc3c..ef1df81a9ab92 100644
--- a/stdlib/toolchain/CompatibilityDynamicReplacements/CMakeLists.txt
+++ b/stdlib/toolchain/CompatibilityDynamicReplacements/CMakeLists.txt
@@ -15,6 +15,7 @@ add_swift_target_library("${library_name}" STATIC
   DEPLOYMENT_VERSION_IOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_IOS}
   DEPLOYMENT_VERSION_TVOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_TVOS}
   DEPLOYMENT_VERSION_WATCHOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_WATCHOS}
+  DEPLOYMENT_VERSION_XROS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_XROS}
 
   INSTALL_IN_COMPONENT compiler
   INSTALL_WITH_SHARED)
diff --git a/stdlib/toolchain/CompatibilityPacks/CMakeLists.txt b/stdlib/toolchain/CompatibilityPacks/CMakeLists.txt
index 8e52618c59179..4b2657b7a5511 100644
--- a/stdlib/toolchain/CompatibilityPacks/CMakeLists.txt
+++ b/stdlib/toolchain/CompatibilityPacks/CMakeLists.txt
@@ -18,6 +18,7 @@ add_swift_target_library("${library_name}" STATIC
   DEPLOYMENT_VERSION_IOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_IOS}
   DEPLOYMENT_VERSION_TVOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_TVOS}
   DEPLOYMENT_VERSION_WATCHOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_WATCHOS}
+  DEPLOYMENT_VERSION_XROS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_XROS}
 
   MACCATALYST_BUILD_FLAVOR "zippered"
 
diff --git a/stdlib/toolchain/CompatibilityThreading/CMakeLists.txt b/stdlib/toolchain/CompatibilityThreading/CMakeLists.txt
index f2c94243cf41e..7bfd2ae1b130f 100644
--- a/stdlib/toolchain/CompatibilityThreading/CMakeLists.txt
+++ b/stdlib/toolchain/CompatibilityThreading/CMakeLists.txt
@@ -16,5 +16,6 @@ add_swift_target_library(swiftCompatibilityThreading OBJECT_LIBRARY
   DEPLOYMENT_VERSION_IOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_IOS}
   DEPLOYMENT_VERSION_TVOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_TVOS}
   DEPLOYMENT_VERSION_WATCHOS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_WATCHOS}
+  DEPLOYMENT_VERSION_XROS ${COMPATIBILITY_MINIMUM_DEPLOYMENT_VERSION_XROS}
 
   MACCATALYST_BUILD_FLAVOR "zippered")
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index e1bce074e518e..cf7886047cf4e 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -101,10 +101,12 @@ function(get_test_dependencies SDK result_var_name)
   if(("${SDK}" STREQUAL "IOS") OR
      ("${SDK}" STREQUAL "TVOS") OR
      ("${SDK}" STREQUAL "WATCHOS") OR
+     ("${SDK}" STREQUAL "XROS") OR
      ("${SDK}" STREQUAL "OSX") OR
      ("${SDK}" STREQUAL "IOS_SIMULATOR") OR
      ("${SDK}" STREQUAL "TVOS_SIMULATOR") OR
      ("${SDK}" STREQUAL "WATCHOS_SIMULATOR") OR
+     ("${SDK}" STREQUAL "XROS_SIMULATOR") OR
      ("${SDK}" STREQUAL "FREESTANDING") OR
      ("${SDK}" STREQUAL "LINUX") OR
      ("${SDK}" STREQUAL "CYGWIN") OR
@@ -335,7 +337,7 @@ foreach(SDK ${SWIFT_SDKS})
 
       set(command_upload_stdlib)
       set(command_upload_swift_reflection_test)
-      if("${SDK}" STREQUAL "IOS" OR "${SDK}" STREQUAL "TVOS" OR "${SDK}" STREQUAL "WATCHOS")
+      if("${SDK}" STREQUAL "IOS" OR "${SDK}" STREQUAL "TVOS" OR "${SDK}" STREQUAL "WATCHOS" OR "${SDK}" STREQUAL "XROS")
         # These are supported testing SDKs, but their implementation of
         # `command_upload_stdlib` is hidden.
       elseif("${SDK}" STREQUAL "ANDROID" AND NOT "${SWIFT_HOST_VARIANT}" STREQUAL "android")
diff --git a/test/ClangImporter/availability_open_enums.swift b/test/ClangImporter/availability_open_enums.swift
index 686e8a9c4b1d3..913dc033d1038 100644
--- a/test/ClangImporter/availability_open_enums.swift
+++ b/test/ClangImporter/availability_open_enums.swift
@@ -1,6 +1,7 @@
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify -I %S/Inputs/custom-modules -enable-nonfrozen-enum-exhaustivity-diagnostics %s
 
 // REQUIRES: objc_interop
+// UNSUPPORTED: OS=xros
 
 import Foundation
 import AvailabilityExtras
@@ -16,4 +17,4 @@ func exhaustiveSwitch(e: NSEnumAddedCasesIn2017) {
   case .existingCaseThree:
     return    
   }
-}
\ No newline at end of file
+}
diff --git a/test/DebugInfo/mandatory-inlining-ownership.swift b/test/DebugInfo/mandatory-inlining-ownership.swift
index 1b377fa4cd74d..5a99d9f0da7b1 100644
--- a/test/DebugInfo/mandatory-inlining-ownership.swift
+++ b/test/DebugInfo/mandatory-inlining-ownership.swift
@@ -6,7 +6,7 @@
 
 // CHECK: sil_scope [[S0:[0-9]+]] { {{.*}} parent @$s4null3baryyF
 // CHECK: sil_scope [[S1:[0-9]+]] { loc "{{.*}}":18:3 parent [[S0]] }
-// CHECK: sil_scope [[S2:[0-9]+]] { loc "{{.*}}":18:67 parent [[S1]] }
+// CHECK: sil_scope [[S2:[0-9]+]] { loc "{{.*}}":18:82 parent [[S1]] }
 
 // CHECK: begin_borrow {{.*}} : $OSLog, loc {{.*}}, scope [[S2]]
 // CHECK: tuple (), loc {{.*}}, scope [[S2]]
@@ -15,7 +15,7 @@
 import os
 
 func bar() {
-  if #available(macOS 10.14, iOS 12.0, watchOS 5.0, tvOS 12.0, *) {
+  if #available(macOS 10.14, iOS 12.0, watchOS 5.0, tvOS 12.0, visionOS 9999, *) {
     foo(OSLog.default)
   }
 }
diff --git a/test/IDE/complete_decl_attribute.swift b/test/IDE/complete_decl_attribute.swift
index f6fb95a483d4e..5d656c4e4d5d0 100644
--- a/test/IDE/complete_decl_attribute.swift
+++ b/test/IDE/complete_decl_attribute.swift
@@ -69,10 +69,12 @@ actor MyGenericGlobalActor<T> {
 // AVAILABILITY1-NEXT: Keyword/None:                       iOS[#Platform#]; name=iOS{{$}}
 // AVAILABILITY1-NEXT: Keyword/None:                       tvOS[#Platform#]; name=tvOS{{$}}
 // AVAILABILITY1-NEXT: Keyword/None:                       watchOS[#Platform#]; name=watchOS{{$}}
+// AVAILABILITY1-NEXT: Keyword/None:                       visionOS[#Platform#]; name=visionOS{{$}}
 // AVAILABILITY1-NEXT: Keyword/None:                       macOS[#Platform#]; name=macOS{{$}}
 // AVAILABILITY1-NEXT: Keyword/None:                       iOSApplicationExtension[#Platform#]; name=iOSApplicationExtension{{$}}
 // AVAILABILITY1-NEXT: Keyword/None:                       tvOSApplicationExtension[#Platform#]; name=tvOSApplicationExtension{{$}}
 // AVAILABILITY1-NEXT: Keyword/None:                       watchOSApplicationExtension[#Platform#]; name=watchOSApplicationExtension{{$}}
+// AVAILABILITY1-NEXT: Keyword/None:                       visionOSApplicationExtension[#Platform#]; name=visionOSApplicationExtension{{$}}
 // AVAILABILITY1-NEXT: Keyword/None:                       macOSApplicationExtension[#Platform#]; name=macOSApplicationExtension{{$}}
 // AVAILABILITY1-NEXT: Keyword/None:                       macCatalyst[#Platform#]; name=macCatalyst
 // AVAILABILITY1-NEXT: Keyword/None:                       macCatalystApplicationExtension[#Platform#]; name=macCatalystApplicationExtension
diff --git a/test/IRGen/abitypes_objc.swift b/test/IRGen/abitypes_objc.swift
index c626728a81513..3bf060dd3a650 100644
--- a/test/IRGen/abitypes_objc.swift
+++ b/test/IRGen/abitypes_objc.swift
@@ -20,6 +20,7 @@ import Foundation
 // arm64_32-watchos: [[ARM64_MYRECT:%.*]] = type { float, float, float, float }
 // arm64-watchos: [[ARM64_MYRECT:%.*]] = type { float, float, float, float }
 // arm64-macosx: [[ARM64_MYRECT:%.*]] = type { float, float, float, float }
+// arm64-xros: [[ARM64_MYRECT:%.*]] = type { float, float, float, float }
 
 class Foo {
   // x86_64-macosx: define hidden swiftcc { float, float, float, float } @"$s8abitypes3FooC3bar{{[_0-9a-zA-Z]*}}F"(ptr swiftself %0) {{.*}} {
@@ -48,6 +49,8 @@ class Foo {
   // arm64-watchos: define internal [[ARM64_MYRECT]] @"$s8abitypes3FooC3bar{{[_0-9a-zA-Z]*}}FTo"(ptr %0, ptr %1) {{[#0-9]*}} {
   // x86_64-watchos: define hidden swiftcc { float, float, float, float } @"$s8abitypes3FooC3bar{{[_0-9a-zA-Z]*}}F"(ptr swiftself %0) {{.*}} {
   // x86_64-watchos: define internal { <2 x float>, <2 x float> } @"$s8abitypes3FooC3bar{{[_0-9a-zA-Z]*}}FTo"(ptr %0, ptr %1) {{[#0-9]*}} {
+  // arm64-xros: define hidden swiftcc { float, float, float, float } @"$s8abitypes3FooC3bar{{[_0-9a-zA-Z]*}}F"(ptr swiftself %0) {{.*}} {
+  // arm64-xros: define internal [[ARM64_MYRECT]] @"$s8abitypes3FooC3bar{{[_0-9a-zA-Z]*}}FTo"(ptr %0, ptr %1) {{[#0-9]*}} {
   @objc dynamic func bar() -> MyRect {
     return MyRect(x: 1, y: 2, width: 3, height: 4)
   }
diff --git a/test/IRGen/availability.swift b/test/IRGen/availability.swift
index 029f8a3403137..49afdf00514b2 100644
--- a/test/IRGen/availability.swift
+++ b/test/IRGen/availability.swift
@@ -19,7 +19,7 @@ import Foundation
 // OPT: s10Foundation11MeasurementVySo17NSUnitTemperature
 
 public func dontHoist() {
-  if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) {
+  if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, visionOS 1.1, *) {
       let measurement = Measurement<UnitTemperature>(value: Double(42), unit: .celsius)
       print("\(measurement)")
   } else {
@@ -49,13 +49,13 @@ public func dontHoist() {
 // OPT-NOT: call {{.*}} @"$ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF"
 // OPT: ret void
 public func multipleAvailabilityChecks() {
-  if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) {
+  if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, visionOS 1.1, *) {
     print("test one")
   }
-  if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) {
+  if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, visionOS 1.1, *) {
     print("test two")
   }
-  if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) {
+  if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, visionOS 1.1, *) {
     print("test three")
   }
 }
diff --git a/test/IRGen/extended_existential_metadata_weak.swift b/test/IRGen/extended_existential_metadata_weak.swift
index d293d98009916..7847c8e34911f 100644
--- a/test/IRGen/extended_existential_metadata_weak.swift
+++ b/test/IRGen/extended_existential_metadata_weak.swift
@@ -1,5 +1,6 @@
 // RUN: %target-swift-frontend -emit-ir %s -target %target-swift-abi-5.5-triple | %FileCheck %s
 // REQUIRES: VENDOR=apple
+// UNSUPPORTED: OS=xros
 
 public protocol P<A> {
   associatedtype A
@@ -10,4 +11,4 @@ public func f<T>(_: T.Type) {}
 @available(SwiftStdlib 5.7, *)
 public func g<T>(_: T.Type) { f((any P<T>).self) }
 
-// CHECK-LABEL: declare extern_weak ptr @swift_getExtendedExistentialTypeMetadata(ptr, ptr)
\ No newline at end of file
+// CHECK-LABEL: declare extern_weak ptr @swift_getExtendedExistentialTypeMetadata(ptr, ptr)
diff --git a/test/IRGen/objc_globals.swift b/test/IRGen/objc_globals.swift
index 39491efa715bc..8d0cbe921ae01 100644
--- a/test/IRGen/objc_globals.swift
+++ b/test/IRGen/objc_globals.swift
@@ -2,6 +2,7 @@
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -I %S/Inputs/abi %s -emit-ir | %FileCheck %s
 //
 // REQUIRES: objc_interop
+// UNSUPPORTED: OS=xros
 
 import gadget
 import Foundation
diff --git a/test/IRGen/objc_methods.swift b/test/IRGen/objc_methods.swift
index fb7390eca901b..6b87f188ce1f0 100644
--- a/test/IRGen/objc_methods.swift
+++ b/test/IRGen/objc_methods.swift
@@ -54,6 +54,7 @@ class ObjcDestructible: NSObject {
 // CHECK-ios: [[FAIL_SIGNATURE:@.*]] = private unnamed_addr constant [12 x i8] c"B24@0:8^@16\00"
 // CHECK-tvos: [[FAIL_SIGNATURE:@.*]] = private unnamed_addr constant [12 x i8] c"B24@0:8^@16\00"
 // CHECK-watchos: [[FAIL_SIGNATURE:@.*]] = private unnamed_addr constant [12 x i8] c"B24@0:8^@16\00"
+// CHECK-xros: [[FAIL_SIGNATURE:@.*]] = private unnamed_addr constant [12 x i8] c"B24@0:8^@16\00"
 // CHECK: @_INSTANCE_METHODS__TtC12objc_methods3Foo = internal constant { {{.*}}] } {
 // CHECK:   i32 24,
 // CHECK:   i32 10,
@@ -82,6 +83,7 @@ class ObjcDestructible: NSObject {
 // CHECK:     ptr [[FAIL_SIGNATURE]],
 // CHECK-macosx:     ptr @"$s12objc_methods3FooC4failyyKFTo"
 // CHECK-ios:     ptr @"$s12objc_methods3FooC4failyyKFTo"
+// CHECK-xros:     ptr @"$s12objc_methods3FooC4failyyKFTo"
 // CHECK:   }]
 // CHECK: }, section "__DATA, {{.*}}", align 8
 // CHECK: @_INSTANCE_METHODS__TtC12objc_methods16ObjcDestructible = internal constant { {{.*}}] } {
diff --git a/test/IRGen/objc_type_encoding.swift b/test/IRGen/objc_type_encoding.swift
index dcbc1dbc22a6a..5d7366c64b008 100644
--- a/test/IRGen/objc_type_encoding.swift
+++ b/test/IRGen/objc_type_encoding.swift
@@ -20,6 +20,7 @@ import gizmo
 // CHECK-ios: private unnamed_addr constant [8 x i8] c"#16@0:8\00"
 // CHECK-tvos: private unnamed_addr constant [8 x i8] c"#16@0:8\00"
 // CHECK-watchos: private unnamed_addr constant [8 x i8] c"#16@0:8\00"
+// CHECK-xros: private unnamed_addr constant [8 x i8] c"#16@0:8\00"
 
 @objc class Methods {
   @objc func testSizedUnsignedTypes(_ a: UInt8, b: UInt16, c: UInt32, d: UInt64) {}
@@ -27,18 +28,21 @@ import gizmo
 // CHECK-ios: private unnamed_addr constant [20 x i8] c"v36@0:8C16S20I24Q28\00"
 // CHECK-tvos: private unnamed_addr constant [20 x i8] c"v36@0:8C16S20I24Q28\00"
 // CHECK-watchos: private unnamed_addr constant [20 x i8] c"v36@0:8C16S20I24Q28\00"
+// CHECK-xros: private unnamed_addr constant [20 x i8] c"v36@0:8C16S20I24Q28\00"
 
   @objc func testSizedFloats(_ a: Float32, b: Float64) {}
 // CHECK-macosx: private unnamed_addr constant [14 x i8] c"v28@0:8f16d20\00"
 // CHECK-ios: private unnamed_addr constant [14 x i8] c"v28@0:8f16d20\00"
 // CHECK-tvos: private unnamed_addr constant [14 x i8] c"v28@0:8f16d20\00"
 // CHECK-watchos: private unnamed_addr constant [14 x i8] c"v28@0:8f16d20\00"
+// CHECK-xros: private unnamed_addr constant [14 x i8] c"v28@0:8f16d20\00"
 
   @objc func testParens(_ a: ((Int))) {}
 // CHECK-macosx: private unnamed_addr constant [11 x i8] c"v24@0:8q16\00"
 // CHECK-ios: private unnamed_addr constant [11 x i8] c"v24@0:8q16\00"
 // CHECK-tvos: private unnamed_addr constant [11 x i8] c"v24@0:8q16\00"
 // CHECK-watchos: private unnamed_addr constant [11 x i8] c"v24@0:8q16\00"
+// CHECK-xros: private unnamed_addr constant [11 x i8] c"v24@0:8q16\00"
 
   @objc func testPrimitives(_ b: CBool, i: Int, f: Float, d: Double)
     -> OpaquePointer { fatalError() }
@@ -46,6 +50,7 @@ import gizmo
 // CHECK-ios: private unnamed_addr constant [21 x i8] c"^v40@0:8B16q20f28d32\00"
 // CHECK-tvos: private unnamed_addr constant [21 x i8] c"^v40@0:8B16q20f28d32\00"
 // CHECK-watchos: private unnamed_addr constant [21 x i8] c"^v40@0:8B16q20f28d32\00"
+// CHECK-xros: private unnamed_addr constant [21 x i8] c"^v40@0:8B16q20f28d32\00"
 
   @objc func testOptionalPrimitives()
     -> OpaquePointer? { return nil }
@@ -53,36 +58,42 @@ import gizmo
 // CHECK-ios: private unnamed_addr constant [9 x i8] c"^v16@0:8\00"
 // CHECK-tvos: private unnamed_addr constant [9 x i8] c"^v16@0:8\00"
 // CHECK-watchos: private unnamed_addr constant [9 x i8] c"^v16@0:8\00"
+// CHECK-xros: private unnamed_addr constant [9 x i8] c"^v16@0:8\00"
 
   @objc func testCSignedTypes(_ a: CSignedChar, b: CShort, c: CInt, d: CLong, e: CLongLong) {}
 // CHECK-macosx: private unnamed_addr constant [23 x i8] c"v44@0:8c16s20i24q28q36\00"
 // CHECK-ios: private unnamed_addr constant [23 x i8] c"v44@0:8c16s20i24q28q36\00"
 // CHECK-tvos: private unnamed_addr constant [23 x i8] c"v44@0:8c16s20i24q28q36\00"
 // CHECK-watchos: private unnamed_addr constant [23 x i8] c"v44@0:8c16s20i24q28q36\00"
+// CHECK-xros: private unnamed_addr constant [23 x i8] c"v44@0:8c16s20i24q28q36\00"
 
   @objc func testCUnsignedTypes(_ a: CUnsignedChar, b: CUnsignedShort, c: CUnsignedInt, d: CUnsignedLong, e: CUnsignedLongLong) {}
 // CHECK-macosx: private unnamed_addr constant [23 x i8] c"v44@0:8C16S20I24Q28Q36\00"
 // CHECK-ios: private unnamed_addr constant [23 x i8] c"v44@0:8C16S20I24Q28Q36\00"
 // CHECK-tvos: private unnamed_addr constant [23 x i8] c"v44@0:8C16S20I24Q28Q36\00"
 // CHECK-watchos: private unnamed_addr constant [23 x i8] c"v44@0:8C16S20I24Q28Q36\00"
+// CHECK-xros: private unnamed_addr constant [23 x i8] c"v44@0:8C16S20I24Q28Q36\00"
 
   @objc func testCChars(_ basic: CChar, wchar wide: CWideChar, char16: CChar16, char32: CChar32) {}
 // CHECK-macosx: private unnamed_addr constant [20 x i8] c"v32@0:8c16i20S24i28\00"
 // CHECK-ios: private unnamed_addr constant [20 x i8] c"v32@0:8c16i20S24i28\00"
 // CHECK-tvos: private unnamed_addr constant [20 x i8] c"v32@0:8c16i20S24i28\00"
 // CHECK-watchos: private unnamed_addr constant [20 x i8] c"v32@0:8c16i20S24i28\00"
+// CHECK-xros: private unnamed_addr constant [20 x i8] c"v32@0:8c16i20S24i28\00"
 
   @objc func testCBool(_ a: CBool) {}
 // CHECK-macosx: private unnamed_addr constant [11 x i8] c"v20@0:8c16\00"
 // CHECK-ios: private unnamed_addr constant [11 x i8] c"v20@0:8B16\00"
 // CHECK-tvos: private unnamed_addr constant [11 x i8] c"v20@0:8B16\00"
 // CHECK-watchos: private unnamed_addr constant [11 x i8] c"v20@0:8B16\00"
+// CHECK-xros: private unnamed_addr constant [11 x i8] c"v20@0:8B16\00"
 
   @objc func testSizedSignedTypes(_ a: Int8, b: Int16, c: Int32, d: Int64) {}
 // CHECK-macosx: private unnamed_addr constant [20 x i8] c"v36@0:8c16s20i24q28\00"
 // CHECK-ios: private unnamed_addr constant [20 x i8] c"v36@0:8c16s20i24q28\00"
 // CHECK-tvos: private unnamed_addr constant [20 x i8] c"v36@0:8c16s20i24q28\00"
 // CHECK-watchos: private unnamed_addr constant [20 x i8] c"v36@0:8c16s20i24q28\00"
+// CHECK-xros: private unnamed_addr constant [20 x i8] c"v36@0:8c16s20i24q28\00"
 
   @objc class func getSelf() -> Methods.Type { return self }
 // These strings are required for another purpose and so are tested above.
@@ -92,48 +103,56 @@ import gizmo
 // CHECK-ios: private unnamed_addr constant [8 x i8] c"@16@0:8\00"
 // CHECK-tvos: private unnamed_addr constant [8 x i8] c"@16@0:8\00"
 // CHECK-watchos: private unnamed_addr constant [8 x i8] c"@16@0:8\00"
+// CHECK-xros: private unnamed_addr constant [8 x i8] c"@16@0:8\00"
 
   @objc func testId(_ s: AnyObject) -> AnyObject { return self }
 // CHECK-macosx: private unnamed_addr constant [11 x i8] c"@24@0:8@16\00"
 // CHECK-ios: private unnamed_addr constant [11 x i8] c"@24@0:8@16\00"
 // CHECK-tvos: private unnamed_addr constant [11 x i8] c"@24@0:8@16\00"
 // CHECK-watchos: private unnamed_addr constant [11 x i8] c"@24@0:8@16\00"
+// CHECK-xros: private unnamed_addr constant [11 x i8] c"@24@0:8@16\00"
 
   @objc func comp1(_ a: P1 & P2, b: P1 & P2 & P3) -> P1 & P2 { return a }
 // CHECK-macosx: private unnamed_addr constant [14 x i8] c"@32@0:8@16@24\00"
 // CHECK-ios: private unnamed_addr constant [14 x i8] c"@32@0:8@16@24\00"
 // CHECK-tvos: private unnamed_addr constant [14 x i8] c"@32@0:8@16@24\00"
 // CHECK-watchos: private unnamed_addr constant [14 x i8] c"@32@0:8@16@24\00"
+// CHECK-xros: private unnamed_addr constant [14 x i8] c"@32@0:8@16@24\00"
 
   @objc func returnsBool(_ b : Bool) -> Bool { return b }
 // CHECK-macosx: private unnamed_addr constant [11 x i8] c"c20@0:8c16\00"
 // CHECK-ios: private unnamed_addr constant [11 x i8] c"B20@0:8B16\00"
 // CHECK-tvos: private unnamed_addr constant [11 x i8] c"B20@0:8B16\00"
 // CHECK-watchos: private unnamed_addr constant [11 x i8] c"B20@0:8B16\00"
+// CHECK-xros: private unnamed_addr constant [11 x i8] c"B20@0:8B16\00"
 
   @objc func comp1(_ a: Methods, b: Methods, c: Methods) -> Methods { return a }
 // CHECK-macosx: private unnamed_addr constant [17 x i8] c"@40@0:8@16@24@32\00"
 // CHECK-ios: private unnamed_addr constant [17 x i8] c"@40@0:8@16@24@32\00"
 // CHECK-tvos: private unnamed_addr constant [17 x i8] c"@40@0:8@16@24@32\00"
 // CHECK-watchos: private unnamed_addr constant [17 x i8] c"@40@0:8@16@24@32\00"
+// CHECK-xros: private unnamed_addr constant [17 x i8] c"@40@0:8@16@24@32\00"
 
   @objc func passSelector(_ aSelector : Selector) {}
 // CHECK-macosx: private unnamed_addr constant [11 x i8] c"v24@0:8:16\00"
 // CHECK-ios: private unnamed_addr constant [11 x i8] c"v24@0:8:16\00"
 // CHECK-tvos: private unnamed_addr constant [11 x i8] c"v24@0:8:16\00"
 // CHECK-watchos: private unnamed_addr constant [11 x i8] c"v24@0:8:16\00"
+// CHECK-xros: private unnamed_addr constant [11 x i8] c"v24@0:8:16\00"
 
   @objc func copyUnsafeMutablePointer(_ p: UnsafeMutablePointer<Int32>) -> UnsafeMutablePointer<Int32> { return p }
 // CHECK-macosx: private unnamed_addr constant [13 x i8] c"^i24@0:8^i16\00"
 // CHECK-ios: private unnamed_addr constant [13 x i8] c"^i24@0:8^i16\00"
 // CHECK-tvos: private unnamed_addr constant [13 x i8] c"^i24@0:8^i16\00"
 // CHECK-watchos: private unnamed_addr constant [13 x i8] c"^i24@0:8^i16\00"
+// CHECK-xros: private unnamed_addr constant [13 x i8] c"^i24@0:8^i16\00"
 
   @objc func copyUnsafeMutablePointerInt(_ p: UnsafeMutablePointer<Int>) -> UnsafeMutablePointer<Int> { return p }
 // CHECK-macosx: private unnamed_addr constant [13 x i8] c"^q24@0:8^q16\00"
 // CHECK-ios: private unnamed_addr constant [13 x i8] c"^q24@0:8^q16\00"
 // CHECK-tvos: private unnamed_addr constant [13 x i8] c"^q24@0:8^q16\00"
 // CHECK-watchos: private unnamed_addr constant [13 x i8] c"^q24@0:8^q16\00"
+// CHECK-xros: private unnamed_addr constant [13 x i8] c"^q24@0:8^q16\00"
 
   @objc func testArchetype(_ work: P3) {
   }
@@ -141,6 +160,7 @@ import gizmo
 // CHECK-ios: private unnamed_addr constant [11 x i8] c"v24@0:8@16\00"
 // CHECK-tvos: private unnamed_addr constant [11 x i8] c"v24@0:8@16\00"
 // CHECK-watchos: private unnamed_addr constant [11 x i8] c"v24@0:8@16\00"
+// CHECK-xros: private unnamed_addr constant [11 x i8] c"v24@0:8@16\00"
 
   @objc func foo(_ x: (Int) -> Int) -> Int {
     return 1
@@ -149,6 +169,7 @@ import gizmo
 // CHECK-ios: private unnamed_addr constant [12 x i8] c"q24@0:8@?16\00"
 // CHECK-tvos: private unnamed_addr constant [12 x i8] c"q24@0:8@?16\00"
 // CHECK-watchos: private unnamed_addr constant [12 x i8] c"q24@0:8@?16\00"
+// CHECK-xros: private unnamed_addr constant [12 x i8] c"q24@0:8@?16\00"
 
   @objc func returnNSRadixedOptions() -> NSRadixedOptions {
     return .octal
@@ -157,6 +178,7 @@ import gizmo
 // CHECK-ios: [[ENUMENCODING:@.*]] = private unnamed_addr constant [8 x i8] c"i16@0:8\00"
 // CHECK-tvos: [[ENUMENCODING:@.*]] = private unnamed_addr constant [8 x i8] c"i16@0:8\00"
 // CHECK-watchos: [[ENUMENCODING:@.*]] = private unnamed_addr constant [8 x i8] c"i16@0:8\00"
+// CHECK-xros: [[ENUMENCODING:@.*]] = private unnamed_addr constant [8 x i8] c"i16@0:8\00"
 
   @objc func returnChoseNSRadixedOptions(_ choice: NSRadixedOptions) -> NSRadixedOptions {
     switch choice {
@@ -168,10 +190,12 @@ import gizmo
 // CHECK-ios: private unnamed_addr constant [11 x i8] c"i20@0:8i16\00"
 // CHECK-tvos: private unnamed_addr constant [11 x i8] c"i20@0:8i16\00"
 // CHECK-watchos: private unnamed_addr constant [11 x i8] c"i20@0:8i16\00"
+// CHECK-xros: private unnamed_addr constant [11 x i8] c"i20@0:8i16\00"
 
   @objc func getRawEnumInGizmo() -> RawEnumInGizmo {
     return InGizmoTwo
   }
+
 // CHECK-macosx: { ptr @"\01L_selector_data(getRawEnumInGizmo)",
 // CHECK-macosx: ptr [[ENUMENCODING]]
 // CHECK-ios: { ptr @"\01L_selector_data(getRawEnumInGizmo)",
@@ -180,6 +204,8 @@ import gizmo
 // CHECK-tvos: ptr [[ENUMENCODING]]
 // CHECK-watchos: { ptr @"\01L_selector_data(getRawEnumInGizmo)",
 // CHECK-watchos: ptr [[ENUMENCODING]]
+// CHECK-xros: { ptr @"\01L_selector_data(getRawEnumInGizmo)",
+// CHECK-xros: ptr [[ENUMENCODING]]
 
 }
 
diff --git a/test/IRGen/temporary_allocation/codegen_very_large_allocation.swift b/test/IRGen/temporary_allocation/codegen_very_large_allocation.swift
index 8a24a9952fe53..335355724ecce 100644
--- a/test/IRGen/temporary_allocation/codegen_very_large_allocation.swift
+++ b/test/IRGen/temporary_allocation/codegen_very_large_allocation.swift
@@ -2,6 +2,11 @@
 // RUN: %target-swift-frontend -primary-file %s -O -emit-ir | %FileCheck %s --check-prefix=CHECK-LARGE-STACK-ALLOC -DWORD=i%target-ptrsize
 // RUN: %target-swift-frontend -primary-file %s -O -emit-ir | %FileCheck %s --check-prefix=CHECK-LARGE-HEAP-ALLOC -DWORD=i%target-ptrsize
 
+// This test for conditionally checking the version with ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF
+// xrOS is always succeeds the availability check so there is no need to call
+// this function.
+// UNSUPPORTED: OS=xros
+
 @_silgen_name("blackHole")
 func blackHole(_ value: UnsafeMutableRawPointer?) -> Void
 
diff --git a/test/Inputs/MockPlatformRemapSDKConfig/SDKSettings.json b/test/Inputs/MockPlatformRemapSDKConfig/SDKSettings.json
new file mode 100644
index 0000000000000..acd8af4ae68c0
--- /dev/null
+++ b/test/Inputs/MockPlatformRemapSDKConfig/SDKSettings.json
@@ -0,0 +1,25 @@
+{
+  "DisplayName": "visionOS 1.1",
+  "Version": "1.1",
+  "VersionMap": {
+    "xrOS_iOS": {
+      "1.0": "17.1",
+      "1.1": "17.4"
+    },
+    "iOS_visionOS": {
+      "17.1": "1.0",
+      "17.4": "1.1"
+    },
+    "iOS_xrOS": {
+      "17.1": "1.0",
+      "17.4": "1.1"
+    },
+    "visionOS_iOS": {
+      "1.0": "17.1",
+      "1.1": "17.4"
+    }
+  },
+  "DefaultDeploymentTarget": "1.1",
+  "MaximumDeploymentTarget": "1.1.99",
+  "CanonicalName": "xros1.1"
+}
diff --git a/test/Inputs/clang-importer-sdk/usr/include/Foundation.h b/test/Inputs/clang-importer-sdk/usr/include/Foundation.h
index 25a405472946e..53499fd42cb1d 100644
--- a/test/Inputs/clang-importer-sdk/usr/include/Foundation.h
+++ b/test/Inputs/clang-importer-sdk/usr/include/Foundation.h
@@ -29,7 +29,8 @@ typedef struct _NSRange {
 extern NSUInteger NSRealMemoryAvailable(void) __attribute__((availability(macosx,introduced=10.0 ,deprecated=10.8,message="" ))) __attribute__((availability(ios,introduced=2.0 ,deprecated=6.0,message="" )));
 extern NSUInteger SomeCrazyAppExtensionForbiddenAPI(void)
   __attribute__((availability(macosx_app_extension,unavailable,message="Not available in App Extensions")))
-  __attribute__((availability(ios_app_extension,unavailable,message="Not available in App Extensions")));
+  __attribute__((availability(ios_app_extension,unavailable,message="Not available in App Extensions")))
+  __attribute__((availability(xros_app_extension,unavailable,message="Not available in App Extensions")));
 
 extern NSString *const globalStringAvailableOn10_51 __attribute__((availability(macosx,introduced=10.51)));
 extern NSString *const globalStringAvailableOn10_52 __attribute__((availability(macosx,introduced=10.52)));
diff --git a/test/Interpreter/Inputs/FakeUnavailableObjCFramework.framework/Headers/FakeUnavailableObjCFramework.h b/test/Interpreter/Inputs/FakeUnavailableObjCFramework.framework/Headers/FakeUnavailableObjCFramework.h
index 44676ddfe756c..d373b8ba75a56 100644
--- a/test/Interpreter/Inputs/FakeUnavailableObjCFramework.framework/Headers/FakeUnavailableObjCFramework.h
+++ b/test/Interpreter/Inputs/FakeUnavailableObjCFramework.framework/Headers/FakeUnavailableObjCFramework.h
@@ -1,8 +1,8 @@
 #include <Foundation/NSObject.h>
 
-extern int UnavailableObjCGlobalVariable __attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availability(ios,introduced=1066.0)));
+extern int UnavailableObjCGlobalVariable __attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availability(ios,introduced=1066.0)))  __attribute__((availability(visionos,introduced=1066.0)));
 
-__attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availability(ios,introduced=1066.0)))
+__attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availability(ios,introduced=1066.0)))  __attribute__((availability(visionos,introduced=1066.0)))
 @protocol UnavailableObjCProtocol
 - (void)someMethod;
 @end
@@ -12,10 +12,10 @@ __attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availabi
 - (void)someMethod;
 @end
 
-__attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availability(ios,introduced=1066.0)))
+__attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availability(ios,introduced=1066.0)))  __attribute__((availability(visionos,introduced=1066.0)))
 @interface UnavailableObjCClass : NSObject
 - (void)someMethod;
 @end
 
-__attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availability(ios,introduced=1066.0)))
+__attribute__((availability(macosx,introduced=1066.0)))  __attribute__((availability(ios,introduced=1066.0)))__attribute__((availability(visionos,introduced=1066.0)))
 void someFunction();
diff --git a/test/Interpreter/Inputs/FakeUnavailableSwiftDylib.swift b/test/Interpreter/Inputs/FakeUnavailableSwiftDylib.swift
index a5214503f8033..e2efee662576f 100644
--- a/test/Interpreter/Inputs/FakeUnavailableSwiftDylib.swift
+++ b/test/Interpreter/Inputs/FakeUnavailableSwiftDylib.swift
@@ -1,9 +1,9 @@
-@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *)
+@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *)
 public protocol UnavailableSwiftProtocol {
   func someMethod()
 }
 
-@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *)
+@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *)
 public class UnavailableSwiftClass {
   func someMethod() {}
 }
diff --git a/test/Interpreter/SDK/GLKit.swift b/test/Interpreter/SDK/GLKit.swift
index 3e967e3bdf917..a689625fbbdb5 100644
--- a/test/Interpreter/SDK/GLKit.swift
+++ b/test/Interpreter/SDK/GLKit.swift
@@ -10,6 +10,7 @@
 
 // GLKit is not available on watchOS.
 // UNSUPPORTED: OS=watchos
+// UNSUPPORTED: OS=xros
 
 import GLKit
 
diff --git a/test/Interpreter/SDK/GLKit_parse.swift b/test/Interpreter/SDK/GLKit_parse.swift
index fa17b81abeaf1..d081ca600d361 100644
--- a/test/Interpreter/SDK/GLKit_parse.swift
+++ b/test/Interpreter/SDK/GLKit_parse.swift
@@ -4,6 +4,7 @@
 // REQUIRES: objc_interop
 // UNSUPPORTED: OS=watchos
 // UNSUPPORTED: OS=tvos
+// UNSUPPORTED: OS=xros
 
 import GLKit
 
diff --git a/test/Interpreter/availability_weak_linking.swift b/test/Interpreter/availability_weak_linking.swift
index d4b65d7e76389..edb1d14e081fd 100644
--- a/test/Interpreter/availability_weak_linking.swift
+++ b/test/Interpreter/availability_weak_linking.swift
@@ -34,7 +34,7 @@ import Foundation
 print("Running...")
 
 func useUnavailableObjCGlobal() {
-  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
     let g = UnavailableObjCGlobalVariable
     _blackHole(g)
   }
@@ -53,7 +53,7 @@ func useClassConformingToUnavailableObjCProtocol() {
   let o = ClassConformingToUnavailableObjCProtocol()
   o.someMethod()
 
-  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
     let oAsUP: UnavailableObjCProtocol = o as UnavailableObjCProtocol
     oAsUP.someMethod()
   }
@@ -76,7 +76,7 @@ func useClassThatWillBeExtendedToConformToUnavailableObjCProtocol() {
   let o = ClassThatWillBeExtendedToConformToUnavailableObjCProtocol()
   o.someMethod()
 
-  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
     let oAsUP: UnavailableObjCProtocol = o as UnavailableObjCProtocol
     oAsUP.someMethod()
   }
@@ -116,13 +116,13 @@ func printClassMetadataViaGeneric<T>() -> T {
 }
 
 func useUnavailableObjCClass() {
-  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
     let o = UnavailableObjCClass()
     o.someMethod()
   }
 
   for i in 0 ..< getInt(5) {
-    if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+    if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
       let o: UnavailableObjCClass = printClassMetadataViaGeneric()
       _blackHole(o)
     }
@@ -132,14 +132,14 @@ func useUnavailableObjCClass() {
   let someObject: AnyObject = _opaqueIdentity(SomeClass() as AnyObject)
 
   for i in 0 ..< getInt(5) {
-    if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+    if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
       let isUnavailable = someObject is UnavailableObjCClass
       _blackHole(isUnavailable)
     }
   }
 
   for i in 0 ..< getInt(5) {
-    if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+    if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
       let asUnavailable = someObject as? UnavailableObjCClass
       _blackHole(asUnavailable)
     }
@@ -155,10 +155,10 @@ useUnavailableObjCClass()
 
 // Allow extending a weakly-linked class to conform to a protocol.
 protocol SomeSwiftProtocol { }
-@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *)
+@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *)
 extension UnavailableObjCClass : SomeSwiftProtocol {
 }
-@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *)
+@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *)
 extension UnavailableSwiftClass : SomeSwiftProtocol {
 }
 
@@ -181,7 +181,7 @@ func useClassConformingToUnavailableSwiftProtocol() {
   let o = ClassConformingToUnavailableSwiftProtocol()
   o.someMethod()
 
-  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
     let oAsUP: UnavailableSwiftProtocol = o as UnavailableSwiftProtocol
     oAsUP.someMethod()
   }
@@ -203,7 +203,7 @@ func useClassThatWillBeExtendedToConformToUnavailableSwiftProtocol() {
   let o = ClassThatWillBeExtendedToConformToUnavailableSwiftProtocol()
   o.someMethod()
 
-  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, visionOS 1066.0, *) {
     let oAsUP: UnavailableSwiftProtocol = o as UnavailableSwiftProtocol
     oAsUP.someMethod()
   }
diff --git a/test/Interpreter/builtin_bridge_object.swift b/test/Interpreter/builtin_bridge_object.swift
index da7aac1cf1ca2..7756d5b7c3d54 100644
--- a/test/Interpreter/builtin_bridge_object.swift
+++ b/test/Interpreter/builtin_bridge_object.swift
@@ -3,6 +3,8 @@
 
 // REQUIRES: executable_test
 // REQUIRES: objc_interop
+// rdar://124700033
+// UNSUPPORTED: OS=xros
 
 // FIXME: rdar://problem/19648117 Needs splitting objc parts out
 
diff --git a/test/Interpreter/llvm_link_time_opt.swift b/test/Interpreter/llvm_link_time_opt.swift
index 389644db66e4f..7f60f66770109 100644
--- a/test/Interpreter/llvm_link_time_opt.swift
+++ b/test/Interpreter/llvm_link_time_opt.swift
@@ -3,6 +3,8 @@
 
 // XFAIL: OS=linux-android, OS=linux-androideabi
 
+// UNSUPPORTED: OS=xros
+
 // For LTO, the linker dlopen()'s the libLTO library, which is a scenario that
 // ASan cannot work in ("Interceptors are not working, AddressSanitizer is
 // loaded too late").
diff --git a/test/Migrator/api-diff-data-dir.swift b/test/Migrator/api-diff-data-dir.swift
index 3b2a259915025..ec2434c2d5ecc 100644
--- a/test/Migrator/api-diff-data-dir.swift
+++ b/test/Migrator/api-diff-data-dir.swift
@@ -1,4 +1,5 @@
 // REQUIRES: objc_interop
+// UNSUPPORTED: OS=xros
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s -F %S/mock-sdk -api-diff-data-dir %S/Inputs/api-diff-data-dir -emit-migrated-file-path %t/api-diff-data-dir.swift.result -emit-remap-file-path %t/api-diff-data-dir.swift.remap -o /dev/null
 // RUN: %FileCheck %s -input-file %t/api-diff-data-dir.swift.result -match-full-lines -check-prefix=SWIFT4
 
diff --git a/test/Migrator/fixit_flatMap.swift b/test/Migrator/fixit_flatMap.swift
index 8bb4fc8eb87b6..c4f4de58163b5 100644
--- a/test/Migrator/fixit_flatMap.swift
+++ b/test/Migrator/fixit_flatMap.swift
@@ -3,6 +3,7 @@
 // RUN: diff -u %s.expected %t.result
 
 // REQUIRES: VENDOR=apple
+// UNSUPPORTED: OS=xros
 
 func migrate<T, U: Sequence, V: Collection>(lseq: LazySequence<T>, lcol: LazyCollection<T>, seq: U, col: V, test: Bool) {
   _ = lseq.flatMap { test ? nil : $0 }
diff --git a/test/Migrator/fixit_flatMap.swift.expected b/test/Migrator/fixit_flatMap.swift.expected
index 40ad11d3e7389..ee69ce010467f 100644
--- a/test/Migrator/fixit_flatMap.swift.expected
+++ b/test/Migrator/fixit_flatMap.swift.expected
@@ -3,6 +3,7 @@
 // RUN: diff -u %s.expected %t.result
 
 // REQUIRES: VENDOR=apple
+// UNSUPPORTED: OS=xros
 
 func migrate<T, U: Sequence, V: Collection>(lseq: LazySequence<T>, lcol: LazyCollection<T>, seq: U, col: V, test: Bool) {
   _ = lseq.compactMap { test ? nil : $0 }
diff --git a/test/Migrator/stdlib_rename.swift b/test/Migrator/stdlib_rename.swift
index 6a39bb2b5ae45..e4d72b611fbcf 100644
--- a/test/Migrator/stdlib_rename.swift
+++ b/test/Migrator/stdlib_rename.swift
@@ -1,4 +1,5 @@
 // REQUIRES: objc_interop
+// UNSUPPORTED: OS=xros
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s -F %S/mock-sdk -emit-migrated-file-path %t/stdlib_rename.swift.result -emit-remap-file-path %t/stdlib_rename.swift.remap -o /dev/null %api_diff_data_dir
 // RUN: diff -u %S/stdlib_rename.swift.expected %t/stdlib_rename.swift.result
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s -F %S/mock-sdk -emit-migrated-file-path %t/stdlib_rename.swift.result -emit-remap-file-path %t/stdlib_rename.swift.remap -o /dev/null -swift-version 4.2 %api_diff_data_dir
diff --git a/test/Migrator/stdlib_rename.swift.expected b/test/Migrator/stdlib_rename.swift.expected
index 5174e069f1cff..e0f60e7f988b6 100644
--- a/test/Migrator/stdlib_rename.swift.expected
+++ b/test/Migrator/stdlib_rename.swift.expected
@@ -1,4 +1,5 @@
 // REQUIRES: objc_interop
+// UNSUPPORTED: OS=xros
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s -F %S/mock-sdk -emit-migrated-file-path %t/stdlib_rename.swift.result -emit-remap-file-path %t/stdlib_rename.swift.remap -o /dev/null %api_diff_data_dir
 // RUN: diff -u %S/stdlib_rename.swift.expected %t/stdlib_rename.swift.result
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s -F %S/mock-sdk -emit-migrated-file-path %t/stdlib_rename.swift.result -emit-remap-file-path %t/stdlib_rename.swift.remap -o /dev/null -swift-version 4.2 %api_diff_data_dir
diff --git a/test/ModuleInterface/actor_availability.swift b/test/ModuleInterface/actor_availability.swift
index fccb5a376eaaa..c605ef71f6dca 100644
--- a/test/ModuleInterface/actor_availability.swift
+++ b/test/ModuleInterface/actor_availability.swift
@@ -80,7 +80,7 @@ extension Enum {
 // CHECK-PUBLIC:      @available(macOS, unavailable)
 // CHECK-PUBLIC-NEXT: @available(iOS, unavailable)
 // CHECK-PUBLIC-NEXT: @available(watchOS, unavailable)
-// CHECK-PUBLIC-NEXT: @available(tvOS, unavailable)
+// CHECK-PUBLIC-NEXT: @available(tvOS, unavailable
 // CHECK-PUBLIC-NEXT: public struct SPIAvailableStruct
 // CHECK-PRIVATE: @_spi_available(macOS, introduced: 10.15.4)
 // CHECK-PRIVATE-NEXT: @_spi_available(iOS, introduced: 13.4)
diff --git a/test/ModuleInterface/distributed-actor.swift b/test/ModuleInterface/distributed-actor.swift
index 1af26faf298b9..7aef5a6f1ced0 100644
--- a/test/ModuleInterface/distributed-actor.swift
+++ b/test/ModuleInterface/distributed-actor.swift
@@ -67,7 +67,7 @@ public distributed actor DAG<ActorSystem> where ActorSystem: DistributedActorSys
 // CHECK:   get
 // CHECK: }
 // CHECK: public init(actorSystem system: ActorSystem)
-// CHECK: @available(iOS 9999, tvOS 9999, watchOS 9999, macOS 9999, *)
+// CHECK: @available(iOS 9999, tvOS 9999, watchOS 9999, visionOS 9999, macOS 9999, *)
 // CHECK: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor {
 // CHECK:   get
 // CHECK: }
@@ -84,7 +84,7 @@ public distributed actor DAG<ActorSystem> where ActorSystem: DistributedActorSys
 // CHECK-NEXT:extension Library.DA : Swift.Decodable {}
 
 // CHECK-NOT: #if compiler(>=5.3) && $Actors
-// CHECK: @available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, *)
+// CHECK: @available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, visionOS 9999, *)
 // CHECK-NEXT: extension Library.DAG : Distributed.DistributedActor {}
 
 //--- Client.swift
diff --git a/test/Parse/ConditionalCompilation/basicParseErrors.swift b/test/Parse/ConditionalCompilation/basicParseErrors.swift
index b1fd6e0237788..e5fe7972f514c 100644
--- a/test/Parse/ConditionalCompilation/basicParseErrors.swift
+++ b/test/Parse/ConditionalCompilation/basicParseErrors.swift
@@ -79,6 +79,12 @@ struct S {
 // expected-note@-3{{did you mean 'Android'?}} {{8-15=Android}}
 // expected-note@-4{{did you mean 'OSX'?}} {{8-15=OSX}}
 // expected-note@-5{{did you mean 'OpenBSD'?}} {{8-15=OpenBSD}}
+// expected-note@-6{{did you mean 'xrOS'?}} {{8-15=xrOS}}
+#endif
+
+#if os(bisionos) // expected-warning {{unknown operating system for build configuration 'os'}}
+// expected-note@-1{{did you mean 'visionOS'?}} {{8-16=visionOS}}
+
 #endif
 
 #if arch(leg) // expected-warning {{unknown architecture for build configuration 'arch'}} expected-note{{did you mean 'arm'?}} {{10-13=arm}}
@@ -137,6 +143,7 @@ fn_k()
 // expected-warning@-4 {{unknown architecture for build configuration 'arch'}}
 // expected-note@-5 {{did you mean 'arm'?}} {{26-29=arm}}
 // expected-note@-6 {{did you mean 'i386'?}} {{26-29=i386}}
+// expected-note@-7 {{did you mean 'visionOS'?}} {{8-16=visionOS}}
 func undefinedFunc() // ignored.
 #endif
 undefinedFunc() // expected-error {{cannot find 'undefinedFunc' in scope}}
diff --git a/test/PrintAsObjC/resilient-ancestry.swift b/test/PrintAsObjC/resilient-ancestry.swift
index ca877beeff5e8..2025177bdd6b3 100644
--- a/test/PrintAsObjC/resilient-ancestry.swift
+++ b/test/PrintAsObjC/resilient-ancestry.swift
@@ -12,6 +12,7 @@
 
 // REQUIRES: objc_interop
 // UNSUPPORTED: OS=iosmac
+// UNSUPPORTED: OS=xros
 
 // See also resilient-ancestry.swift, for the stable ABI deployment target test.
 
diff --git a/test/Reflection/conformance_descriptors.swift b/test/Reflection/conformance_descriptors.swift
index 02d601c9f7164..b2d6901522aa9 100644
--- a/test/Reflection/conformance_descriptors.swift
+++ b/test/Reflection/conformance_descriptors.swift
@@ -1,5 +1,8 @@
 // UNSUPPORTED: OS=windows-msvc
-
+//
+// LC_DYLD_CHAINED_FIXUPS decode not currently supported (default on visionOS)
+// UNSUPPORTED: OS=xros
+//
 // Temporarily disable on AArch64 Linux (rdar://88451721)
 // UNSUPPORTED: OS=linux-gnu && CPU=aarch64
 
diff --git a/test/Reflection/typeref_decoding.swift b/test/Reflection/typeref_decoding.swift
index 1b8fa31b87635..b1bc12da5ec82 100644
--- a/test/Reflection/typeref_decoding.swift
+++ b/test/Reflection/typeref_decoding.swift
@@ -1,5 +1,8 @@
 // REQUIRES: no_asan
-
+//
+// LC_DYLD_CHAINED_FIXUPS decode not currently supported (default on visionOS)
+// UNSUPPORTED: OS=xros
+//
 // rdar://100805115
 // UNSUPPORTED: CPU=arm64e
 
diff --git a/test/Reflection/typeref_decoding_imported.swift b/test/Reflection/typeref_decoding_imported.swift
index fd0b2527dc8a1..d877e3015d70d 100644
--- a/test/Reflection/typeref_decoding_imported.swift
+++ b/test/Reflection/typeref_decoding_imported.swift
@@ -1,5 +1,8 @@
 // XFAIL: OS=windows-msvc
-
+//
+// LC_DYLD_CHAINED_FIXUPS decode not currently supported (default on visionOS)
+// UNSUPPORTED: OS=xros
+//
 // https://github.com/apple/swift/issues/55339
 // XFAIL: OS=openbsd
 
diff --git a/test/Reflection/typeref_lowering.swift b/test/Reflection/typeref_lowering.swift
index 03df741b3d8e3..4d53be234c945 100644
--- a/test/Reflection/typeref_lowering.swift
+++ b/test/Reflection/typeref_lowering.swift
@@ -1,4 +1,8 @@
 // REQUIRES: no_asan
+//
+// LC_DYLD_CHAINED_FIXUPS decode not currently supported (default on visionOS)
+// UNSUPPORTED: OS=xros
+//
 // XFAIL: OS=windows-msvc
 // RUN: %empty-directory(%t)
 
diff --git a/test/Runtime/protocol_conformance_collision.swift b/test/Runtime/protocol_conformance_collision.swift
index 391cc9669b83c..b74c8a804f206 100644
--- a/test/Runtime/protocol_conformance_collision.swift
+++ b/test/Runtime/protocol_conformance_collision.swift
@@ -13,6 +13,7 @@
 // UNSUPPORTED: DARWIN_SIMULATOR=ios
 // UNSUPPORTED: DARWIN_SIMULATOR=tvos
 // UNSUPPORTED: DARWIN_SIMULATOR=watchos
+// UNSUPPORTED: DARWIN_SIMULATOR=xros
 
 // UNSUPPORTED: use_os_stdlib
 // UNSUPPORTED: back_deployment_runtime
diff --git a/test/SILGen/Inputs/mock-visionos-sdk/SDKSettings.json b/test/SILGen/Inputs/mock-visionos-sdk/SDKSettings.json
new file mode 100644
index 0000000000000..92ce99f0fd99e
--- /dev/null
+++ b/test/SILGen/Inputs/mock-visionos-sdk/SDKSettings.json
@@ -0,0 +1,56 @@
+{
+    "CanonicalName": "xros1.0",
+    "DefaultDeploymentTarget": "1.0",
+    "DefaultProperties": {},
+    "DisplayName": "visionOS 1.0",
+    "IsBaseSDK": "YES",
+    "MaximumDeploymentTarget": "1.0.99",
+    "MinimalDisplayName": "1.0",
+    "SupportedTargets": {
+        "xros": {
+            "Archs": [
+                "arm64e",
+                "arm64"
+            ],
+            "BuildVersionPlatformID": "11",
+            "ClangRuntimeLibraryPlatformName": "xros",
+            "DefaultDeploymentTarget": "1.0",
+            "DeploymentTargetSettingName": "XROS_DEPLOYMENT_TARGET",
+            "DeviceFamilies": [
+                {
+                    "DisplayName": "Apple Vision",
+                    "Identifier": "7"
+                }
+            ],
+            "LLVMTargetTripleEnvironment": "",
+            "LLVMTargetTripleSys": "xros",
+            "LLVMTargetTripleVendor": "apple",
+            "MaximumDeploymentTarget": "1.0.99",
+            "MinimumDeploymentTarget": "1.0",
+            "PlatformFamilyDisplayName": "visionOS",
+            "PlatformFamilyName": "xrOS",
+            "RecommendedDeploymentTarget": "1.0",
+            "SwiftConcurrencyMinimumDeploymentTarget": "1.0",
+            "SwiftOSRuntimeMinimumDeploymentTarget": "1.0",
+            "SystemPrefix": "",
+            "ValidDeploymentTargets": [
+                "1.0"
+            ]
+        }
+    },
+    "Version": "1.0",
+    "VersionMap": {
+        "iOS_visionOS": {
+            "17.0": "1.0"
+        },
+        "iOS_xrOS": {
+            "17.0": "1.0"
+        },
+        "visionOS_iOS": {
+            "1.0": "17.0"
+        },
+        "xrOS_iOS": {
+            "1.0": "17.0"
+        }
+    }
+}
diff --git a/test/SILGen/unavailable_decl_optimization_visionos.swift b/test/SILGen/unavailable_decl_optimization_visionos.swift
new file mode 100644
index 0000000000000..68a6b201d1a45
--- /dev/null
+++ b/test/SILGen/unavailable_decl_optimization_visionos.swift
@@ -0,0 +1,68 @@
+// RUN: %target-swift-emit-silgen -module-name Test -parse-as-library %s -verify -target arm64-apple-xros1.0 | %FileCheck %s --check-prefixes=CHECK
+// RUN: %target-swift-emit-silgen -module-name Test -parse-as-library %s -verify -unavailable-decl-optimization=none -target arm64-apple-xros1.0 | %FileCheck %s --check-prefixes=CHECK
+
+// REQUIRES: OS=xros
+
+public struct S {}
+
+// CHECK-LABEL: sil{{.*}}@$s4Test19visionOSUnavailableAA1SVyF
+// CHECK-NOT:     ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+// CHECK:       } // end sil function '$s4Test19visionOSUnavailableAA1SVyF'
+@available(visionOS, unavailable)
+public func visionOSUnavailable() -> S {
+  return S()
+}
+
+// CHECK-LABEL: sil{{.*}}@$s4Test14iOSUnavailableAA1SVyF
+// CHECK-NOT:     ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+// CHECK:       } // end sil function '$s4Test14iOSUnavailableAA1SVyF'
+@available(iOS, unavailable)
+public func iOSUnavailable() -> S {
+  return S()
+}
+
+// CHECK-LABEL: sil{{.*}}@$s4Test16macOSUnavailableAA1SVyF
+// CHECK-NOT:     ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+// CHECK:       } // end sil function '$s4Test16macOSUnavailableAA1SVyF'
+@available(macOS, unavailable)
+public func macOSUnavailable() -> S {
+  return S()
+}
+
+// CHECK-LABEL: sil{{.*}}@$s4Test31iOSUnavailableVisionOSAvailableAA1SVyF
+// CHECK-NOT:     ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+// CHECK:       } // end sil function '$s4Test31iOSUnavailableVisionOSAvailableAA1SVyF'
+@available(iOS, unavailable)
+@available(visionOS, introduced: 1.0)
+public func iOSUnavailableVisionOSAvailable() -> S {
+  return S()
+}
+
+// CHECK-LABEL: sil{{.*}}@$s4Test25iOSAndVisionOSUnavailableAA1SVyF
+// CHECK-NOT:     ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+// CHECK:       } // end sil function '$s4Test25iOSAndVisionOSUnavailableAA1SVyF'
+@available(iOS, unavailable)
+@available(visionOS, unavailable)
+public func iOSAndVisionOSUnavailable() -> S {
+  // FIXME: This function should be optimized (rdar://116742214)
+  return S()
+}
+
+@available(visionOS, unavailable)
+public struct UnavailableOnVisionOS {
+  // CHECK-LABEL: sil{{.*}}@$s4Test21UnavailableOnVisionOSV14noAvailabilityAA1SVyF
+  // CHECK-NOT:     ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+  // CHECK:       } // end sil function '$s4Test21UnavailableOnVisionOSV14noAvailabilityAA1SVyF'
+  public func noAvailability() -> S {
+    return S()
+  }
+
+  // CHECK-LABEL: sil{{.*}}@$s4Test21UnavailableOnVisionOSV022iOSUnavailableInheritsdF0AA1SVyF
+  // CHECK-NOT:     ss31_diagnoseUnavailableCodeReacheds5NeverOyF
+  // CHECK:       } // end sil function '$s4Test21UnavailableOnVisionOSV022iOSUnavailableInheritsdF0AA1SVyF'
+  @available(iOS, unavailable)
+  public func iOSUnavailableInheritsVisionOSUnavailable() -> S {
+    // FIXME: This function should be optimized (rdar://116742214)
+    return S()
+  }
+}
diff --git a/test/SILGen/visionos_available_rawvalue_enum.swift b/test/SILGen/visionos_available_rawvalue_enum.swift
new file mode 100644
index 0000000000000..8cb9c16b49ec0
--- /dev/null
+++ b/test/SILGen/visionos_available_rawvalue_enum.swift
@@ -0,0 +1,19 @@
+// Mock SDK will contain an appropriate SDKSettings and a loadable stdlib
+// RUN: %empty-directory(%t/mock-sdk)
+// RUN: %empty-directory(%t/mock-sdk/usr/lib/swift)
+// RUN: cp -r %test-resource-dir/xros/Swift.swiftmodule %t/mock-sdk/usr/lib/swift/Swift.swiftmodule
+// RUN: cp %S/Inputs/mock-visionos-sdk/SDKSettings.json %t/mock-sdk/SDKSettings.json
+// RUN: %swift -emit-sil -parse-as-library %s -target arm64-apple-xros1.0 -sdk %t/mock-sdk -I %t/mock-sdk/usr/lib/swift/ -verify
+// RUN: %swift -emit-silgen -parse-as-library %s -target arm64-apple-xros1.0 -sdk %t/mock-sdk -I %t/mock-sdk/usr/lib/swift/ -o %t/ios_available_rawvalue_enum_on_visionos.sil
+// RUN: %FileCheck %s < %t/ios_available_rawvalue_enum_on_visionos.sil
+
+// REQUIRES: OS=xros
+
+// CHECK-LABEL: // Metasyntactics.init(rawValue:)
+// Ensure that OS version check is generated for the current platform
+// CHECK: function_ref @$ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF
+public enum Metasyntactics: String, RawRepresentable {
+    case foo
+    @available(visionOS 1.1, *)
+    case bar
+}
diff --git a/test/Sema/availability_refinement_contexts_target_min_inlining.swift b/test/Sema/availability_refinement_contexts_target_min_inlining.swift
index 4674f0bb65144..61a990b949c9e 100644
--- a/test/Sema/availability_refinement_contexts_target_min_inlining.swift
+++ b/test/Sema/availability_refinement_contexts_target_min_inlining.swift
@@ -10,9 +10,11 @@
 // CHECK-ios: {{^}}(root versions=[8.0,+Inf)
 // CHECK-tvos: {{^}}(root versions=[9.0,+Inf)
 // CHECK-watchos: {{^}}(root versions=[2.0,+Inf)
+// CHECK-xros: {{^}}(root versions=[1.0,+Inf)
 
 // CHECK-macosx-NEXT: {{^}}  (decl_implicit versions=[10.15,+Inf) decl=foo()
 // CHECK-ios-NEXT: {{^}}  (decl_implicit versions=[13,+Inf) decl=foo()
 // CHECK-tvos-NEXT: {{^}}  (decl_implicit versions=[13,+Inf) decl=foo()
 // CHECK-watchos-NEXT: {{^}}  (decl_implicit versions=[6,+Inf) decl=foo()
+
 func foo() {}
diff --git a/test/SourceKit/InterfaceGen/gen_vision_availability.swift b/test/SourceKit/InterfaceGen/gen_vision_availability.swift
new file mode 100644
index 0000000000000..fc994f96265e1
--- /dev/null
+++ b/test/SourceKit/InterfaceGen/gen_vision_availability.swift
@@ -0,0 +1,39 @@
+// REQUIRES: concurrency
+
+// RUN: %empty-directory(%t)
+
+// RUN: %sourcekitd-test -req=interface-gen %s -- %s -target %target-triple -module-name MyModule | %FileCheck %s --check-prefix=SWIFTSOURCE
+
+// RUN: %target-swift-frontend -emit-module -module-name MyModule -o %t/MyModule.swiftmodule %s
+// RUN: %sourcekitd-test -req=interface-gen -module MyModule -- -target %target-triple -I %t | %FileCheck %s --check-prefix=SWIFTMODULE
+// RUN: %sourcekitd-test -req=doc-info -module MyModule -- -target %target-triple -I %t | %FileCheck %s --check-prefix=DOCINFO
+
+@available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, visionOS 1.0, *)
+public struct SomeStruct {}
+
+public struct TestStruct {
+  @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, visionOS 1.0, *)
+  public func availableMethod() {}
+}
+
+// SWIFTSOURCE: @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, visionOS 1.0, *)
+// SWIFTSOURCE: public struct SomeStruct {
+// SWIFTSOURCE: }
+// SWIFTSOURCE: public struct TestStruct {
+// SWIFTSOURCE:     @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, visionOS 1.0, *)
+// SWIFTSOURCE:     public func availableMethod()
+// SWIFTSOURCE: }
+
+// SWIFTMODULE: @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, visionOS 1.0, *)
+// SWIFTMODULE: public struct SomeStruct {
+// SWIFTMODULE: }
+// SWIFTMODULE: public struct TestStruct {
+// SWIFTMODULE:         @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, visionOS 1.0, *)
+// SWIFTMODULE:         public func availableMethod()
+// SWIFTMODULE: }
+
+// DOCINFO: struct SomeStruct {
+// DOCINFO: }
+// DOCINFO: struct TestStruct {
+// DOCINFO:      func availableMethod()
+// DOCINFO: }
diff --git a/test/TBD/multimodule-implied-objc.swift b/test/TBD/multimodule-implied-objc.swift
index 55404539acab8..6e2321cd94b74 100644
--- a/test/TBD/multimodule-implied-objc.swift
+++ b/test/TBD/multimodule-implied-objc.swift
@@ -1,4 +1,5 @@
 // REQUIRES: VENDOR=apple
+// XFAIL: OS=xros
 // RUN: %empty-directory(%t)
 // RUN: %empty-directory(%t/cache)
 // RUN: split-file %s %t
diff --git a/test/attr/attr_ibaction_ios.swift b/test/attr/attr_ibaction_ios.swift
index 47546317e5655..392b502730e4c 100644
--- a/test/attr/attr_ibaction_ios.swift
+++ b/test/attr/attr_ibaction_ios.swift
@@ -8,22 +8,25 @@ class IBActionWrapperTy {
   // CHECK-macosx: attr_ibaction_ios.swift:[[@LINE-2]]:18: error: @IBAction methods must have 1 argument
   // CHECK-tvos-NOT: attr_ibaction_ios.swift:[[@LINE-3]]
   // CHECK-watchos-NOT: attr_ibaction_ios.swift:[[@LINE-4]]
+  // CHECK-xros-NOT: attr_ibaction_ios.swift:[[@LINE-5]]
 
   @IBAction func unary(_: AnyObject) {}
   // CHECK-ios-NOT: attr_ibaction_ios.swift:[[@LINE-1]]
   // CHECK-macosx-NOT: attr_ibaction_ios.swift:[[@LINE-2]]
   // CHECK-tvos-NOT: attr_ibaction_ios.swift:[[@LINE-3]]
   // CHECK-watchos-NOT: attr_ibaction_ios.swift:[[@LINE-4]]
+  // CHECK-xros-NOT: attr_ibaction_ios.swift:[[@LINE-5]]
 
   @IBAction func binary(_: AnyObject, _: AnyObject) {}
   // CHECK-ios-NOT: attr_ibaction_ios.swift:[[@LINE-1]]
   // CHECK-macosx: attr_ibaction_ios.swift:[[@LINE-2]]:18: error: @IBAction methods must have 1 argument
   // CHECK-tvos-NOT: attr_ibaction_ios.swift:[[@LINE-3]]
   // CHECK-watchos-NOT: attr_ibaction_ios.swift:[[@LINE-4]]
+  // CHECK-xros-NOT: attr_ibaction_ios.swift:[[@LINE-5]]
 
   @IBAction func ternary(_: AnyObject, _: AnyObject, _: AnyObject) {}
   // CHECK-ios: attr_ibaction_ios.swift:[[@LINE-1]]:18: error: @IBAction methods must have at most 2 arguments
   // CHECK-macosx: attr_ibaction_ios.swift:[[@LINE-2]]:18: error: @IBAction methods must have 1 argument
   // CHECK-tvos: attr_ibaction_ios.swift:[[@LINE-3]]:18: error: @IBAction methods must have at most 2 arguments
   // CHECK-watchos: attr_ibaction_ios.swift:[[@LINE-4]]:18: error: @IBAction methods must have at most 2 arguments
-}
+  // CHECK-xros: attr_ibaction_ios.swift:[[@LINE-5]]:18: error: @IBAction methods must have at most 2 arguments
diff --git a/test/attr/attr_objc_resilience.swift b/test/attr/attr_objc_resilience.swift
index 0afd4cefa6acd..e69b0322b9a81 100644
--- a/test/attr/attr_objc_resilience.swift
+++ b/test/attr/attr_objc_resilience.swift
@@ -4,6 +4,7 @@
 // RUN: %target-swift-frontend -typecheck -verify %s -I %t
 
 // REQUIRES: objc_interop
+// UNSUPPORTED: OS=xros
 
 import Foundation
 import resilient_objc_class
diff --git a/test/lit.cfg b/test/lit.cfg
index 59781fc96d28c..f2f2f391f40be 100644
--- a/test/lit.cfg
+++ b/test/lit.cfg
@@ -111,6 +111,9 @@ def get_simulator_command(run_os, run_cpu):
               return "simctl spawn --standalone 'Apple Watch Series 2 - 42mm'"
         else:
            return "simctl spawn --standalone 'Apple Watch Series 9 (45mm)'"
+    elif run_os == 'xros':
+        lit_config.note("xrOS Simulator Is Not Supported Yet - Tests Will Fail")
+        return "simctl spawn --standalone 'Apple Vision Pro'"
     else:
         lit_config.fatal("Unknown simulator OS %r" % run_os)
 
@@ -542,6 +545,7 @@ config.sil_test_options = os.environ.get('SIL_TEST_OPTIONS', '')
 config.clang_module_cache_path = make_path(config.swift_test_results_dir, "clang-module-cache")
 shutil.rmtree(config.clang_module_cache_path, ignore_errors=True)
 mcp_opt = "-module-cache-path %s" % shell_quote(config.clang_module_cache_path)
+platform_remap_mock_sdk_config = "%s" % make_path(config.test_source_root, 'Inputs', 'MockPlatformRemapSDKConfig/')
 clang_mcp_opt = "-fmodules-cache-path=%r" % config.clang_module_cache_path
 lit_config.note("Using Clang module cache: " + config.clang_module_cache_path)
 lit_config.note("Using test results dir: " + config.swift_test_results_dir)
@@ -925,7 +929,8 @@ if run_vendor == 'apple':
                 'ios': '12.1',
                 'maccatalyst': '12.1',
                 'tvos': '12.1',
-                'watchos': '5.1'
+                'watchos': '5.1',
+                'xros': '1.0'
             }
             pre_stable_version = PRE_STABLE_VERSION.get(run_os, '')
 
@@ -936,7 +941,8 @@ if run_vendor == 'apple':
             'ios': '12.2',
             'maccatalyst': '12.2',
             'tvos': '12.2',
-            'watchos': '5.2'
+            'watchos': '5.2',
+            'xros': '1.0'
         }
         stable_version = STABLE_VERSION.get(run_os, '')
         config.stable_abi_triple = '%s-%s-%s%s%s' % (run_cpu, run_vendor, run_os,
@@ -947,7 +953,8 @@ if run_vendor == 'apple':
             'ios': '13',
             'maccatalyst': '13',
             'tvos': '13',
-            'watchos': '6'
+            'watchos': '6',
+            'xros': '1.0'
         }
         next_stable_version = NEXT_STABLE_VERSION.get(run_os, '')
         config.next_stable_abi_triple = '%s-%s-%s%s%s' % (run_cpu, run_vendor, run_os,
@@ -993,7 +1000,8 @@ target_os_abi = run_os
 target_os_is_maccatalyst = "FALSE"
 target_mandates_stable_abi = "FALSE"
 if (run_cpu in ('arm64e',) or \
-    (run_os == 'watchos' and run_cpu == 'x86_64')):
+    (run_os == 'watchos' and run_cpu == 'x86_64') or \
+    (run_os == 'xros')):
   target_mandates_stable_abi = "TRUE"
   config.available_features.add('swift_only_stable_abi')
 if run_os in ('maccatalyst',):
@@ -1300,6 +1308,11 @@ if run_vendor == 'apple':
             lit_config.note("Testing watchOS simulator " + config.variant_triple)
             xcrun_sdk_name = "watchsimulator"
             target_future_version = "99.99.0"
+        elif run_os == 'xros':
+            config.available_features.add('DARWIN_SIMULATOR=xros')
+            lit_config.note("Testing xrOS simulator " + config.variant_triple)
+            xcrun_sdk_name = "xrsimulator"
+            target_future_version = "99.99.0"
         else:
             config.available_features.add('DARWIN_SIMULATOR=tvos')
             lit_config.note("Testing AppleTV simulator " + config.variant_triple)
@@ -1415,14 +1428,23 @@ if run_vendor == 'apple':
     maccatalyst_extra_frameworks = ""
     if run_os == 'maccatalyst':
         maccatalyst_extra_frameworks = "-F {}/System/iOSSupport/System/Library/Frameworks".format(config.variant_sdk)
+
+    swift_frontend_platform_remap_config = ""
+    swiftc_platform_remap_config = ""
+    if run_os == 'xros':
+        swift_frontend_platform_remap_config = "-platform-availability-inheritance-map-path %s" % platform_remap_mock_sdk_config
+        swiftc_platform_remap_config = "-Xfrontend -platform-availability-inheritance-map-path -Xfrontend %s" % platform_remap_mock_sdk_config
+
     config.target_swift_frontend = (
-        "%s %s -sdk %r %s %s %s" %
+        "%s %s -sdk %r %s %s %s %s" %
         (config.swift_frontend, target_options, config.variant_sdk, maccatalyst_extra_frameworks,
-         config.swift_test_options, config.swift_frontend_test_options))
+         config.swift_test_options, config.swift_frontend_test_options,
+         swift_frontend_platform_remap_config))
     subst_target_swift_frontend_mock_sdk = (
-        "%s %s -sdk %r %s %s" %
+        "%s %s -sdk %r %s %s %s" %
         (config.swift_frontend, target_options_for_mock_sdk, config.variant_sdk,
-         config.swift_test_options, config.swift_frontend_test_options))
+         config.swift_test_options, config.swift_frontend_test_options,
+         swift_frontend_platform_remap_config))
     config.target_swift_modulewrap = (
         '%s -modulewrap -target %s' %
         (config.swiftc, config.variant_triple))
@@ -1459,8 +1481,8 @@ if run_vendor == 'apple':
         ("%s %s -toolchain-stdlib-rpath %s " +
          # This ensures LC_LOAD_DYLIB rewrite will succeed in %target-codesign (rdar://7885126):
          "-Xlinker -headerpad_max_install_names " +  
-         "-Xlinker -rpath -Xlinker /usr/lib/swift %s ")%
-        (xcrun_prefix, config.swiftc, target_options, config.swift_driver_test_options))
+         "-Xlinker -rpath -Xlinker /usr/lib/swift %s %s ")%
+        (xcrun_prefix, config.swiftc, target_options, config.swift_driver_test_options, swiftc_platform_remap_config))
     config.target_stdlib_swiftc_driver = config.target_swiftc_driver
     config.target_clang = (
         "%s %s %s" %
@@ -1481,7 +1503,8 @@ if run_vendor == 'apple':
         'ios': '14.0',
         'maccatalyst': '14.0',
         'tvos': '14.0',
-        'watchos': '7.0'
+        'watchos': '7.0',
+        'xros': '1.0'
     }
     sdk_2020_version = SDK_2020_VERSION.get(run_os, '')
     SDK_2021_VERSION = {
@@ -1489,17 +1512,20 @@ if run_vendor == 'apple':
         'ios': '15.0',
         'maccatalyst': '15.0',
         'tvos': '15.0',
-        'watchos': '8.0'
+        'watchos': '8.0',
+        'xros': '1.0'
     }
     sdk_2021_version = SDK_2021_VERSION.get(run_os, '')
     linker_os = {
         'iphoneos': 'ios',
         'appletvos': 'tvos',
         'watchos': 'watchos',
+        'xros': 'xros',
         'iphonesimulator': 'ios-simulator',
         'watchsimulator': 'watchos-simulator',
         'appletvsimulator': 'tvos-simulator',
-        'macosx': 'macos'
+        'macosx': 'macos',
+        'xrsimulator': 'xros-simulator'
     }.get(config.target_sdk_name, run_os)
 
     config.target_link_sdk_2020_version = (
@@ -2168,9 +2194,11 @@ config.compiler_rt_platform = {
     'iphoneos': 'ios',
     'appletvos': 'tvos',
     'watchos': 'watchos',
+    'xros': 'xros',
     'iphonesimulator': 'iossim',
     'watchsimulator': 'watchossim',
     'appletvsimulator': 'tvossim',
+    'xrsimulator': 'xrossim',
     'macosx': 'osx'
 }.get(config.target_sdk_name, run_cpu)
 
diff --git a/test/stdlib/BridgeEquatableToObjC.swift b/test/stdlib/BridgeEquatableToObjC.swift
index 6fafbed6c5059..02b1f5088b4d0 100644
--- a/test/stdlib/BridgeEquatableToObjC.swift
+++ b/test/stdlib/BridgeEquatableToObjC.swift
@@ -32,7 +32,7 @@ BridgeEquatableToObjC.test("Bridge equatable struct") {
   let objcResult = objcA.isEqual(objcB)
 
   expectEqual(swiftResult, true)
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
   // Apple platforms use old semantics for now...
   expectEqual(objcResult, false)
 #else
diff --git a/test/stdlib/Runtime.swift.gyb b/test/stdlib/Runtime.swift.gyb
index 330119f9b642f..c4f872f1961e7 100644
--- a/test/stdlib/Runtime.swift.gyb
+++ b/test/stdlib/Runtime.swift.gyb
@@ -377,7 +377,7 @@ Runtime.test("demangleName") {
   expectEqual("Foobar", _stdlib_demangleName("$s13__lldb_expr_46FoobarCD"))
 }
 
-if #available(macOS 11.0, iOS 14.0, tvOS 14.0, watchOS 7.0, *) {
+if #available(macOS 11.0, iOS 14.0, tvOS 14.0, watchOS 7.0, visionOS 1.0, *) {
   Runtime.test("demangleTruncate") {
     // Swift.Int requires 10 bytes to be fully demangled.
     let buffer = UnsafeMutableBufferPointer<Int8>.allocate(capacity: 10)
diff --git a/test/stdlib/SwiftObjectNSObject.swift b/test/stdlib/SwiftObjectNSObject.swift
index 8f7c65f570541..841160d3eeaa5 100644
--- a/test/stdlib/SwiftObjectNSObject.swift
+++ b/test/stdlib/SwiftObjectNSObject.swift
@@ -91,7 +91,7 @@ func TestSwiftObjectNSObjectAssertNoErrors()
 // Verify that Obj-C isEqual: provides same answer as Swift ==
 func TestEquatableEquals<T: Equatable & AnyObject>(_ e1: T, _ e2: T) {
   if e1 == e2 {
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
     // Legacy behavior: Equatable Swift does not imply == in ObjC
     TestSwiftObjectNSObjectNotEquals(e1, e2)
 #else
@@ -109,7 +109,7 @@ func TestNonEquatableEquals(_ e1: AnyObject, _ e2: AnyObject) {
 // Verify that Obj-C hashValue matches Swift hashValue for Hashable types
 func TestHashable(_ h: H)
 {
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
   // Legacy behavior: Hash value is identity in ObjC
   TestSwiftObjectNSObjectDefaultHashValue(h)
 #else
@@ -121,7 +121,7 @@ func TestHashable(_ h: H)
 // Test Obj-C hashValue for Swift types that are Equatable but not Hashable
 func TestEquatableHash(_ e: AnyObject)
 {
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
   // Legacy behavior: Equatable in Swift => ObjC hashes with identity
   TestSwiftObjectNSObjectDefaultHashValue(e)
   fakeEquatableWarning(e)
diff --git a/test/stdlib/SwiftValueNSObject.swift b/test/stdlib/SwiftValueNSObject.swift
index 6fd50b198eaa9..8d04961756dca 100644
--- a/test/stdlib/SwiftValueNSObject.swift
+++ b/test/stdlib/SwiftValueNSObject.swift
@@ -90,7 +90,7 @@ func TestHashableEquals<T: Equatable>(_ e1: T, _ e2: T) {
 // This has not always been true for Equatable value types
 func TestEquatableEquals<T: Equatable>(_ e1: T, _ e2: T) {
   if e1 == e2 {
-#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
+#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
     // Legacy: Swift Equatable is not used in ObjC
     TestSwiftValueNSObjectNotEquals(e1 as AnyObject, e2 as AnyObject)
 #else
@@ -114,7 +114,7 @@ func TestHashable<T: Hashable>(_ h: T)
 // Test Obj-C hashValue for Swift types that are Equatable but not Hashable
 func TestEquatableHash<T: Equatable>(_ e: T)
 {
-#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS)
+#if os(macOS) || os(iOS) || os(watchOS) || os(tvOS) || os(visionOS)
   // Legacy behavior used the pointer value, which is
   // incompatible with user-defined equality.
   TestSwiftValueNSObjectDefaultHashValue(e as AnyObject)
diff --git a/tools/SourceKit/lib/SwiftLang/SwiftDocSupport.cpp b/tools/SourceKit/lib/SwiftLang/SwiftDocSupport.cpp
index a90b4439b3d8f..6d342fe3e5fdd 100644
--- a/tools/SourceKit/lib/SwiftLang/SwiftDocSupport.cpp
+++ b/tools/SourceKit/lib/SwiftLang/SwiftDocSupport.cpp
@@ -715,6 +715,9 @@ static void reportAttributes(ASTContext &Ctx,
         PlatformUID = PlatformWatchOS; break;
       case PlatformKind::iOSApplicationExtension:
         PlatformUID = PlatformIOSAppExt; break;
+      case PlatformKind::visionOS:
+        // FIXME: Formal platform support in SourceKit is needed.
+        PlatformUID = UIdent(); break;
       case PlatformKind::macCatalystApplicationExtension:
         PlatformUID = PlatformMacCatalystAppExt; break;
       case PlatformKind::macOSApplicationExtension:
@@ -723,6 +726,9 @@ static void reportAttributes(ASTContext &Ctx,
         PlatformUID = PlatformtvOSAppExt; break;
       case PlatformKind::watchOSApplicationExtension:
         PlatformUID = PlatformWatchOSAppExt; break;
+      case PlatformKind::visionOSApplicationExtension:
+        // FIXME: Formal platform support in SourceKit is needed.
+        PlatformUID = UIdent(); break;
       case PlatformKind::OpenBSD:
         PlatformUID = PlatformOpenBSD; break;
       case PlatformKind::Windows:
diff --git a/utils/availability-macros.def b/utils/availability-macros.def
index 4754b750ca03d..828314c02ed01 100644
--- a/utils/availability-macros.def
+++ b/utils/availability-macros.def
@@ -34,8 +34,8 @@ SwiftStdlib 5.6:macOS 12.3, iOS 15.4, watchOS 8.5, tvOS 15.4
 SwiftStdlib 5.7:macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0
 SwiftStdlib 5.8:macOS 13.3, iOS 16.4, watchOS 9.4, tvOS 16.4
 SwiftStdlib 5.9:macOS 14.0, iOS 17.0, watchOS 10.0, tvOS 17.0
-SwiftStdlib 5.10:macOS 14.4, iOS 17.4, watchOS 10.4, tvOS 17.4
-SwiftStdlib 6.0:macOS 9999, iOS 9999, watchOS 9999, tvOS 9999
+SwiftStdlib 5.10:macOS 14.4, iOS 17.4, watchOS 10.4, tvOS 17.4, visionOS 1.1
+SwiftStdlib 6.0:macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, visionOS 9999
 # TODO: Also update ASTContext::getSwift510Availability when needed
 # TODO: Also update ASTContext::getSwift60Availability when needed
 
diff --git a/utils/build-presets.ini b/utils/build-presets.ini
index 808404c02f12b..e522ce98990f6 100644
--- a/utils/build-presets.ini
+++ b/utils/build-presets.ini
@@ -73,6 +73,8 @@ skip-build-tvos
 skip-test-tvos
 skip-build-watchos
 skip-test-watchos
+skip-build-xros
+skip-test-xros
 stdlib-deployment-targets=macosx-x86_64
 swift-primary-variant-sdk=OSX
 swift-primary-variant-arch=x86_64
@@ -167,6 +169,7 @@ mixin-preset=
 skip-test-ios-host
 skip-test-tvos-host
 skip-test-watchos-host
+skip-test-xros-host
 
 
 [preset: buildbot,tools=RA,stdlib=DA,test=non_executable]
@@ -179,6 +182,7 @@ skip-test-osx
 skip-test-ios-simulator
 skip-test-tvos-simulator
 skip-test-watchos-simulator
+skip-test-xros-simulator
 
 [preset: buildbot,tools=RA,stdlib=RD]
 mixin-preset=
@@ -189,6 +193,7 @@ mixin-preset=
 skip-test-ios-host
 skip-test-tvos-host
 skip-test-watchos-host
+skip-test-xros-host
 
 [preset: buildbot,tools=RA,stdlib=RD,test=non_executable]
 mixin-preset=
@@ -200,6 +205,7 @@ skip-test-osx
 skip-test-ios-simulator
 skip-test-tvos-simulator
 skip-test-watchos-simulator
+skip-test-xros-simulator
 
 [preset: buildbot,tools=R,stdlib=RD]
 mixin-preset=
@@ -210,6 +216,7 @@ mixin-preset=
 skip-test-ios-host
 skip-test-tvos-host
 skip-test-watchos-host
+skip-test-xros-host
 check-incremental-compilation
 
 [preset: buildbot,tools=R,stdlib=RD,test=non_executable]
@@ -222,6 +229,7 @@ skip-test-osx
 skip-test-ios-simulator
 skip-test-tvos-simulator
 skip-test-watchos-simulator
+skip-test-xros-simulator
 
 [preset: buildbot,tools=RA,stdlib=RDA]
 mixin-preset=
@@ -232,6 +240,7 @@ mixin-preset=
 skip-test-ios-host
 skip-test-tvos-host
 skip-test-watchos-host
+skip-test-xros-host
 
 [preset: buildbot,tools=RA,stdlib=RDA,test=non_executable]
 mixin-preset=
@@ -243,6 +252,7 @@ skip-test-osx
 skip-test-ios-simulator
 skip-test-tvos-simulator
 skip-test-watchos-simulator
+skip-test-xros-simulator
 
 [preset: buildbot,tools=RA,stdlib=RDA,long_test]
 mixin-preset=
@@ -266,6 +276,7 @@ lto
 skip-test-ios-host
 skip-test-tvos-host
 skip-test-watchos-host
+skip-test-xros-host
 
 [preset: buildbot,tools=RDA-flto,stdlib=RDA]
 mixin-preset=
@@ -278,6 +289,7 @@ lto
 skip-test-ios-host
 skip-test-tvos-host
 skip-test-watchos-host
+skip-test-xros-host
 
 # This is a mixin preset which builds and smoke-tests lldb.
 [preset: lldb-smoketest,tools=RA]
@@ -379,6 +391,7 @@ skip-test-playgroundsupport
 skip-test-ios
 skip-test-tvos
 skip-test-watchos
+skip-test-xros
 
 install-llvm
 install-swift
@@ -448,6 +461,10 @@ skip-test-tvos
 skip-build-watchos
 skip-test-watchos
 
+# FIXME: Swift/ASan does not support xros yet.
+skip-build-xros
+skip-test-xros
+
 enable-asan
 
 [preset: buildbot_incremental_tsan,tools=RDA,stdlib=RDA]
@@ -468,6 +485,8 @@ skip-build-tvos
 skip-test-tvos
 skip-build-watchos
 skip-test-watchos
+skip-build-xros
+skip-test-xros
 
 [preset: buildbot_incremental_asan_ubsan,tools=RDA,stdlib=RDA]
 mixin-preset=buildbot_incremental_base_all_platforms
@@ -496,6 +515,10 @@ skip-test-tvos
 skip-build-watchos
 skip-test-watchos
 
+# FIXME: Swift/ASan does not support xros yet.
+skip-build-xros
+skip-test-xros
+
 enable-asan
 enable-ubsan
 
@@ -522,6 +545,8 @@ skip-build-tvos
 skip-test-tvos
 skip-build-watchos
 skip-test-watchos
+skip-build-xros
+skip-test-xros
 stdlib-deployment-targets=macosx-x86_64
 swift-primary-variant-sdk=OSX
 swift-primary-variant-arch=x86_64
@@ -557,6 +582,10 @@ skip-test-tvos
 skip-build-watchos
 skip-test-watchos
 
+# FIXME: Swift/ASan does not support xros yet.
+skip-build-xros
+skip-test-xros
+
 enable-asan
 
 swift-stdlib-build-type=RelWithDebInfo
@@ -610,6 +639,8 @@ skip-build-tvos
 skip-test-tvos
 skip-build-watchos
 skip-test-watchos
+skip-build-xros
+skip-test-xros
 stdlib-deployment-targets=macosx-x86_64
 swift-primary-variant-sdk=OSX
 swift-primary-variant-arch=x86_64
@@ -1261,6 +1292,7 @@ mixin-preset=mixin_buildbot_install_components_with_clang
 ios
 tvos
 watchos
+xros
 
 lldb
 llbuild
@@ -1557,6 +1589,7 @@ build-subdir=buildbot_incremental
 # Skip watchOS and tvOS
 skip-build-watchos
 skip-build-tvos
+skip-build-xros
 
 # Build Release without debug info, because it is faster to build.
 release
@@ -1651,6 +1684,7 @@ sil-verify-all-macos-only
 # faster.
 skip-test-ios-host
 skip-test-watchos-host
+skip-test-xros-host
 
 # Skip LLBuild test until GitHub issue is fixed:
 # https://github.com/apple/swift-llbuild/issues/894
@@ -1663,6 +1697,7 @@ llvm-include-tests
 
 # Skip downstream project tests
 skip-test-watchos
+skip-test-xros
 skip-test-swiftsyntax
 skip-test-indexstore-db
 skip-test-sourcekit-lsp
@@ -2078,6 +2113,8 @@ skip-build-tvos
 skip-test-tvos
 skip-build-watchos
 skip-test-watchos
+skip-build-xros
+skip-test-xros
 swift-sdks=IOS
 swift-primary-variant-sdk=IOS
 swift-primary-variant-arch=arm64
@@ -2116,6 +2153,8 @@ skip-build-osx
 skip-test-osx
 skip-build-watchos
 skip-test-watchos
+skip-build-xros
+skip-test-xros
 skip-build-ios
 skip-test-ios
 swift-sdks=TVOS
@@ -2167,6 +2206,7 @@ lit-args=-v
 skip-test-ios
 skip-test-tvos
 skip-test-watchos
+skip-test-xros
 skip-reconfigure
 
 [preset: mixin_buildbot_incremental,test=iOS,type=simulator]
@@ -2178,6 +2218,7 @@ lit-args=-v
 skip-test-osx
 skip-test-tvos
 skip-test-watchos
+skip-test-xros
 skip-reconfigure
 
 [preset: mixin_buildbot_incremental,test=tvOS,type=simulator]
@@ -2187,6 +2228,7 @@ lit-args=-v
 
 skip-test-osx
 skip-test-watchos
+skip-test-xros
 skip-test-ios
 skip-reconfigure
 
@@ -2418,6 +2460,7 @@ validation-test
 skip-test-ios
 skip-test-tvos
 skip-test-watchos
+skip-test-xros
 skip-build-benchmark
 verbose-build
 lit-args=-v
diff --git a/utils/build-script b/utils/build-script
index e4cbfb5594de8..529865512f780 100755
--- a/utils/build-script
+++ b/utils/build-script
@@ -96,7 +96,8 @@ def initialize_runtime_environment():
             'MACOSX_DEPLOYMENT_TARGET',
             'IPHONEOS_DEPLOYMENT_TARGET',
             'TVOS_DEPLOYMENT_TARGET',
-            'WATCHOS_DEPLOYMENT_TARGET']:
+            'WATCHOS_DEPLOYMENT_TARGET',
+            'XROS_DEPLOYMENT_TARGET']:
         os.environ.pop(v, None)
 
     # Provide a default NINJA_STATUS to format ninja output.
@@ -296,6 +297,12 @@ def default_stdlib_deployment_targets(args):
                            .AppleWatchSimulator.targets)
         if args.build_watchos and args.build_watchos_device:
             targets.extend(StdlibDeploymentTarget.AppleWatch.targets)
+        if StdlibDeploymentTarget.XROSSimulator and \
+           args.build_xros and args.build_xros_simulator:
+            targets.extend(StdlibDeploymentTarget.XROSSimulator.targets)
+        if StdlibDeploymentTarget.XROS and \
+           args.build_xros and args.build_xros_device:
+            targets.extend(StdlibDeploymentTarget.XROS.targets)
         return targets
     else:
         # All other machines only configure their host stdlib by default.
diff --git a/utils/build-script-impl b/utils/build-script-impl
index f4dbb8391c850..55954d26ab32d 100755
--- a/utils/build-script-impl
+++ b/utils/build-script-impl
@@ -99,6 +99,7 @@ KNOWN_SETTINGS=(
     darwin-deployment-version-osx                 "10.13"           "minimum deployment target version for OS X"
     darwin-deployment-version-tvos                "11.0"            "minimum deployment target version for tvOS"
     darwin-deployment-version-watchos             "4.0"             "minimum deployment target version for watchOS"
+    darwin-deployment-version-xros                "1.0"             "minimum deployment target version for xrOS"
     darwin-install-extract-symbols                ""                "whether to extract symbols with dsymutil during installations"
     darwin-install-extract-symbols-use-just-built-dsymutil "1"       "whether we should extract symbols using the just built dsymutil"
     darwin-symroot-path-filters                   ""                "space-separated list of path patterns to consider for symbol generation"
@@ -500,6 +501,9 @@ function verify_host_is_supported() {
       | watchsimulator-arm64    \
       | watchos-armv7k          \
       | watchos-arm64_32        \
+      | xrsimulator-arm64  \
+      | xros-arm64         \
+      | xros-arm64e        \
       | wasi-wasm32             \
       | android-armv7           \
       | android-aarch64         \
@@ -587,7 +591,9 @@ function set_build_options_for_host() {
         appletvos-*         | \
         appletvsimulator-*  | \
         watchos-*           | \
-        watchsimulator-*)
+        watchsimulator-*    | \
+        xros-*              | \
+        xrsimulator-*)
             swift_cmake_options+=(
               -DPython3_EXECUTABLE="$(xcrun -f python3)"
             )
@@ -710,6 +716,27 @@ function set_build_options_for_host() {
                     SWIFT_HOST_VARIANT_SDK="WATCHOS"
                     cmake_osx_deployment_target=""
                     ;;
+                xrsimulator-arm64)
+                    SWIFT_HOST_TRIPLE="arm64-apple-xros${DARWIN_DEPLOYMENT_VERSION_XROS}-simulator"
+                    llvm_target_arch="AArch64"
+
+                    SWIFT_HOST_VARIANT_SDK="XROS_SIMULATOR"
+                    cmake_osx_deployment_target=""
+                    ;;
+                xros-arm64)
+                    SWIFT_HOST_TRIPLE="arm64-apple-xros${DARWIN_DEPLOYMENT_VERSION_XROS}"
+                    llvm_target_arch="AArch64"
+
+                    SWIFT_HOST_VARIANT_SDK="XROS"
+                    cmake_osx_deployment_target=""
+                    ;;
+                xros-arm64e)
+                    SWIFT_HOST_TRIPLE="arm64e-apple-xros${DARWIN_DEPLOYMENT_VERSION_XROS}"
+                    llvm_target_arch="AArch64"
+
+                    SWIFT_HOST_VARIANT_SDK="XROS"
+                    cmake_osx_deployment_target=""
+                    ;;
             esac
 
             if [[ "${DARWIN_SDK_DEPLOYMENT_TARGETS}" != "" ]]; then
@@ -735,6 +762,7 @@ function set_build_options_for_host() {
                 -DCMAKE_OSX_SYSROOT:PATH="${cmake_os_sysroot}"
                 -DCOMPILER_RT_ENABLE_IOS:BOOL=FALSE
                 -DCOMPILER_RT_ENABLE_WATCHOS:BOOL=FALSE
+                -DCOMPILER_RT_ENABLE_XROS:BOOL=FALSE
                 -DCOMPILER_RT_ENABLE_TVOS:BOOL=FALSE
                 -DLLVM_ENABLE_MODULES:BOOL="$(true_false ${LLVM_ENABLE_MODULES})"
                 -DCMAKE_OSX_ARCHITECTURES="${architecture}"
@@ -767,6 +795,7 @@ function set_build_options_for_host() {
                 -DSWIFT_DARWIN_DEPLOYMENT_VERSION_IOS="${DARWIN_DEPLOYMENT_VERSION_IOS}"
                 -DSWIFT_DARWIN_DEPLOYMENT_VERSION_TVOS="${DARWIN_DEPLOYMENT_VERSION_TVOS}"
                 -DSWIFT_DARWIN_DEPLOYMENT_VERSION_WATCHOS="${DARWIN_DEPLOYMENT_VERSION_WATCHOS}"
+                -DSWIFT_DARWIN_DEPLOYMENT_VERSION_XROS="${DARWIN_DEPLOYMENT_VERSION_XROS}"
                 -DCMAKE_OSX_SYSROOT:PATH="${cmake_os_sysroot}"
                 # This is needed to make sure to avoid using the wrong architecture
                 # in the compiler checks CMake performs
@@ -1366,6 +1395,12 @@ function common_cross_c_flags() {
         watchos-*)
             echo -n " -arch ${arch} -target ${arch}-apple-watchos${DARWIN_DEPLOYMENT_VERSION_WATCHOS}"
             ;;
+        xrsimulator-*)
+            echo -n " -arch ${arch}  -target ${arch}-apple-xros${DARWIN_DEPLOYMENT_VERSION_XROS}-simulator"
+            ;;
+        xros-*)
+            echo -n " -arch ${arch}  -target ${arch}-apple-xros${DARWIN_DEPLOYMENT_VERSION_XROS}"
+            ;;
     esac
 
     local build_type=$2
diff --git a/utils/build-tooling-libs b/utils/build-tooling-libs
index 0163d76830859..b2cd7453cd165 100755
--- a/utils/build-tooling-libs
+++ b/utils/build-tooling-libs
@@ -156,6 +156,29 @@ class Builder(object):
             ]
             llvm_c_flags += " -target " + host_triple
 
+        elif self.host == "xrsimulator":
+            deployment_version = "1.0"
+            host_triple = "%s-apple-xros%s-simulator" % (
+                self.arch,
+                deployment_version,
+            )
+            host_sdk = "XROS_SIMULATOR"
+            cmake_args += [
+                "-DCMAKE_OSX_DEPLOYMENT_TARGET=" + deployment_version,
+                "-DSWIFT_DARWIN_DEPLOYMENT_VERSION_XROS=" + deployment_version,
+            ]
+            llvm_c_flags += " -target " + host_triple
+
+        elif self.host == "xros":
+            deployment_version = "1.0"
+            host_triple = "%s-apple-xros%s" % (self.arch, deployment_version)
+            host_sdk = "XROS"
+            cmake_args += [
+                "-DCMAKE_OSX_DEPLOYMENT_TARGET=" + deployment_version,
+                "-DSWIFT_DARWIN_DEPLOYMENT_VERSION_XROS=" + deployment_version,
+            ]
+            llvm_c_flags += " -target " + host_triple
+
         assert host_triple
         assert host_sdk
         cmake_args += [
diff --git a/utils/build_swift/build_swift/defaults.py b/utils/build_swift/build_swift/defaults.py
index 0fc8cd90873ab..41ed3725e3db8 100644
--- a/utils/build_swift/build_swift/defaults.py
+++ b/utils/build_swift/build_swift/defaults.py
@@ -31,6 +31,7 @@
     'DARWIN_DEPLOYMENT_VERSION_IOS',
     'DARWIN_DEPLOYMENT_VERSION_TVOS',
     'DARWIN_DEPLOYMENT_VERSION_WATCHOS',
+    'DARWIN_DEPLOYMENT_VERSION_XROS',
     'UNIX_INSTALL_PREFIX',
     'DARWIN_INSTALL_PREFIX',
     'LLVM_MAX_PARALLEL_LTO_LINK_JOBS',
@@ -55,6 +56,7 @@
 DARWIN_DEPLOYMENT_VERSION_IOS = '11.0'
 DARWIN_DEPLOYMENT_VERSION_TVOS = '11.0'
 DARWIN_DEPLOYMENT_VERSION_WATCHOS = '4.0'
+DARWIN_DEPLOYMENT_VERSION_XROS = '1.0'
 
 UNIX_INSTALL_PREFIX = '/usr'
 DARWIN_INSTALL_PREFIX = ('/Applications/Xcode.app/Contents/Developer/'
diff --git a/utils/build_swift/build_swift/driver_arguments.py b/utils/build_swift/build_swift/driver_arguments.py
index 68774fb159f25..37d82d8a48a6d 100644
--- a/utils/build_swift/build_swift/driver_arguments.py
+++ b/utils/build_swift/build_swift/driver_arguments.py
@@ -143,6 +143,10 @@ def _apply_default_arguments(args):
         raise ValueError('error: --watchos-all is unavailable in open-source '
                          'Swift.\nUse --watchos to skip watchOS device tests.')
 
+    if args.xros_all:
+        raise ValueError('error: --xros-all is unavailable in open-source '
+                         'Swift.\nUse --xros to skip xrOS device tests.')
+
     # --skip-{ios,tvos,watchos} or --skip-build-{ios,tvos,watchos} are
     # merely shorthands for --skip-build-{**os}-{device,simulator}
     if not args.ios or not args.build_ios:
@@ -157,6 +161,10 @@ def _apply_default_arguments(args):
         args.build_watchos_device = False
         args.build_watchos_simulator = False
 
+    if not args.xros or not args.build_xros:
+        args.build_xros_device = False
+        args.build_xros_simulator = False
+
     if not args.android or not args.build_android:
         args.build_android = False
 
@@ -199,6 +207,7 @@ def _apply_default_arguments(args):
         args.test_ios = False
         args.test_tvos = False
         args.test_watchos = False
+        args.test_xros = False
         args.test_android = False
         args.test_cmark = False
         args.test_swiftpm = False
@@ -230,6 +239,11 @@ def _apply_default_arguments(args):
     if not args.test_watchos:
         args.test_watchos_host = False
         args.test_watchos_simulator = False
+    # --skip-test-xros is merely a shorthand for host and simulator
+    # --tests.
+    if not args.test_xros:
+        args.test_xros_host = False
+        args.test_xros_simulator = False
 
     # --skip-build-{ios,tvos,watchos}-{device,simulator} implies
     # --skip-test-{ios,tvos,watchos}-{host,simulator}
@@ -248,6 +262,11 @@ def _apply_default_arguments(args):
     if not args.build_watchos_simulator:
         args.test_watchos_simulator = False
 
+    if not args.build_xros_device:
+        args.test_xros_host = False
+    if not args.build_xros_simulator:
+        args.test_xros_simulator = False
+
     if not args.build_android:
         # If building natively on an Android host, allow running the test suite
         # without the NDK config.
@@ -263,6 +282,7 @@ def _apply_default_arguments(args):
         args.test_ios_host = False
         args.test_tvos_host = False
         args.test_watchos_host = False
+        args.test_xros_host = False
         args.test_android_host = False
 
 
@@ -345,6 +365,15 @@ def create_argument_parser():
     option('--skip-watchos', store_false('watchos'),
            help='set to skip everything watchOS-related')
 
+    option('--xros', toggle_true,
+           help='also build for xrOS, but disallow tests that require an '
+                'xrOS device')
+    option('--xros-all', toggle_true('xros_all'),
+           help='also build for Apple xrOS, and allow all Apple xrOS '
+                'tests')
+    option('--skip-xros', store_false('xros'),
+           help='set to skip everything xrOS-related')
+
     option('--maccatalyst', toggle_true,
            help='Enable building Swift with macCatalyst support')
 
@@ -497,6 +526,10 @@ def create_argument_parser():
            default=defaults.DARWIN_DEPLOYMENT_VERSION_WATCHOS,
            metavar='MAJOR.MINOR',
            help='minimum deployment target version for watchOS')
+    option('--darwin-deployment-version-xros', store,
+           default=defaults.DARWIN_DEPLOYMENT_VERSION_XROS,
+           metavar='MAJOR.MINOR',
+           help='minimum deployment target version for xrOS')
 
     option('--extra-cmake-options', append,
            type=argparse.ShellSplitType(),
@@ -1155,6 +1188,16 @@ def create_argument_parser():
            help='skip building Swift stdlibs for watchOS simulator '
                 '(i.e. build devices only)')
 
+    option('--skip-build-xros', toggle_false('build_xros'),
+           help='skip building Swift stdlibs for xrOS')
+    option('--skip-build-xros-device', toggle_false('build_xros_device'),
+           help='skip building Swift stdlibs for xrOS devices '
+                '(i.e. build simulators only)')
+    option('--skip-build-xros-simulator',
+           toggle_false('build_xros_simulator'),
+           help='skip building Swift stdlibs for xrOS simulator '
+                '(i.e. build devices only)')
+
     option('--skip-build-android', toggle_false('build_android'),
            help='skip building Swift stdlibs for Android')
 
@@ -1216,6 +1259,17 @@ def create_argument_parser():
            help='skip testing watchOS device targets on the host machine (the '
                 'watch itself)')
 
+    option('--skip-test-xros',
+           toggle_false('test_xros'),
+           help='skip testing all xrOS targets. Equivalent to specifying both '
+                '--skip-test-xros-simulator and --skip-test-xros-host')
+    option('--skip-test-xros-simulator',
+           toggle_false('test_xros_simulator'),
+           help='skip testing xrOS simulator targets')
+    option('--skip-test-xros-host',
+           toggle_false('test_xros_host'),
+           help='skip testing xrOS device targets on the host machine')
+
     option('--skip-test-android',
            toggle_false('test_android'),
            help='skip testing all Android targets.')
diff --git a/utils/build_swift/tests/expected_options.py b/utils/build_swift/tests/expected_options.py
index 24236d6eea6b2..b29f52c2b77e0 100644
--- a/utils/build_swift/tests/expected_options.py
+++ b/utils/build_swift/tests/expected_options.py
@@ -128,6 +128,9 @@
     'build_watchos': True,
     'build_watchos_device': False,
     'build_watchos_simulator': False,
+    'build_xros': True,
+    'build_xros_device': False,
+    'build_xros_simulator': False,
     'build_xctest': False,
     'build_wasmstdlib': False,
     'build_wasmkit': False,
@@ -156,6 +159,8 @@
         defaults.DARWIN_DEPLOYMENT_VERSION_TVOS,
     'darwin_deployment_version_watchos':
         defaults.DARWIN_DEPLOYMENT_VERSION_WATCHOS,
+    'darwin_deployment_version_xros':
+        defaults.DARWIN_DEPLOYMENT_VERSION_XROS,
     'darwin_symroot_path_filters': [],
     'darwin_xcrun_toolchain': None,
     'distcc': False,
@@ -289,6 +294,9 @@
     'test_watchos': False,
     'test_watchos_host': False,
     'test_watchos_simulator': False,
+    'test_xros': False,
+    'test_xros_host': False,
+    'test_xros_simulator': False,
     'test_playgroundsupport': True,
     'test_cmark': False,
     'test_swiftpm': False,
@@ -307,6 +315,8 @@
     'verbose_build': False,
     'watchos': False,
     'watchos_all': False,
+    'xros': False,
+    'xros_all': False,
     'llvm_install_components': defaults.llvm_install_components(),
     'clean_install_destdir': False,
 }
@@ -519,6 +529,7 @@ class BuildScriptImplOption(_BaseOption):
     SetOption('--skip-ios', dest='ios', value=False),
     SetOption('--skip-tvos', dest='tvos', value=False),
     SetOption('--skip-watchos', dest='watchos', value=False),
+    SetOption('--skip-xros', dest='xros', value=False),
     SetOption('--skip-test-early-swift-driver',
               dest='test_early_swift_driver', value=False),
 
@@ -654,6 +665,7 @@ class BuildScriptImplOption(_BaseOption):
     EnableOption('--validation-test'),
     EnableOption('--verbose-build'),
     EnableOption('--watchos'),
+    EnableOption('--xros'),
     EnableOption('--xctest', dest='build_xctest'),
     EnableOption('--swift-disable-dead-stripping'),
     EnableOption('--clean-early-swift-driver', dest='clean_early_swift_driver'),
@@ -683,6 +695,9 @@ class BuildScriptImplOption(_BaseOption):
                   dest='build_watchos_device'),
     DisableOption('--skip-build-watchos-simulator',
                   dest='build_watchos_simulator'),
+    DisableOption('--skip-build-xros', dest='build_xros'),
+    DisableOption('--skip-build-xros-device', dest='build_xros_device'),
+    DisableOption('--skip-build-xros-simulator', dest='build_xros_simulator'),
     DisableOption('--skip-clean-libdispatch', dest='clean_libdispatch'),
     DisableOption('--skip-clean-foundation', dest='clean_foundation'),
     DisableOption('--skip-clean-xctest', dest='clean_xctest'),
@@ -748,6 +763,10 @@ class BuildScriptImplOption(_BaseOption):
     StrOption('--darwin-deployment-version-osx'),
     StrOption('--darwin-deployment-version-tvos'),
     StrOption('--darwin-deployment-version-watchos'),
+    StrOption('--darwin-deployment-version-xros'),
+    DisableOption('--skip-test-xros-host', dest='test_xros_host'),
+    DisableOption('--skip-test-xros', dest='test_xros'),
+    DisableOption('--skip-test-xros-simulator', dest='test_xros_simulator'),
     StrOption('--darwin-xcrun-toolchain'),
     StrOption('--host-target'),
     StrOption('--lit-args'),
@@ -836,6 +855,7 @@ class BuildScriptImplOption(_BaseOption):
     IgnoreOption('--ios-all'),
     IgnoreOption('--tvos-all'),
     IgnoreOption('--watchos-all'),
+    IgnoreOption('--xros-all'),
 
     StrOption('--llvm-install-components'),
 ]
diff --git a/utils/swift_build_support/swift_build_support/build_script_invocation.py b/utils/swift_build_support/swift_build_support/build_script_invocation.py
index dc86c97f7dc0c..d61731aa4a281 100644
--- a/utils/swift_build_support/swift_build_support/build_script_invocation.py
+++ b/utils/swift_build_support/swift_build_support/build_script_invocation.py
@@ -103,6 +103,8 @@ def convert_to_impl_arguments(self):
                 args.darwin_deployment_version_tvos),
             "--darwin-deployment-version-watchos=%s" % (
                 args.darwin_deployment_version_watchos),
+            "--darwin-deployment-version-xros=%s" % (
+                args.darwin_deployment_version_xros),
             "--cmake", toolchain.cmake,
             "--llvm-build-type", args.llvm_build_variant,
             "--swift-build-type", args.swift_build_variant,
diff --git a/utils/swift_build_support/swift_build_support/host_specific_configuration.py b/utils/swift_build_support/swift_build_support/host_specific_configuration.py
index 55f742cb95e89..cbb5b22e52b0c 100644
--- a/utils/swift_build_support/swift_build_support/host_specific_configuration.py
+++ b/utils/swift_build_support/swift_build_support/host_specific_configuration.py
@@ -250,6 +250,13 @@ def __platforms_to_skip_build(self, args, stage_dependent_args):
         if not stage_dependent_args.build_watchos_simulator:
             platforms_to_skip_build.add(
                 StdlibDeploymentTarget.AppleWatchSimulator)
+        if StdlibDeploymentTarget.XROS and \
+           not stage_dependent_args.build_xros_device:
+            platforms_to_skip_build.add(StdlibDeploymentTarget.XROS)
+        if StdlibDeploymentTarget.XROSSimulator and \
+           not stage_dependent_args.build_xros_simulator:
+            platforms_to_skip_build.add(
+                StdlibDeploymentTarget.XROSSimulator)
         if not stage_dependent_args.build_android:
             platforms_to_skip_build.add(StdlibDeploymentTarget.Android)
         if not args.build_wasm:
@@ -293,6 +300,18 @@ def __platforms_to_skip_test(self, args, stage_dependent_args):
         if not stage_dependent_args.test_watchos_simulator:
             platforms_to_skip_test.add(
                 StdlibDeploymentTarget.AppleWatchSimulator)
+        if StdlibDeploymentTarget.XROS and \
+           not stage_dependent_args.test_xros_host and \
+           not args.only_non_executable_test:
+            platforms_to_skip_test.add(StdlibDeploymentTarget.XROS)
+        elif StdlibDeploymentTarget.XROS and not args.only_non_executable_test:
+            raise ArgumentError(None,
+                                "error: xrOS device tests are not " +
+                                "supported in open-source Swift.")
+        if StdlibDeploymentTarget.XROSSimulator and \
+           not stage_dependent_args.test_xros_simulator:
+            platforms_to_skip_test.add(
+                StdlibDeploymentTarget.XROSSimulator)
         if not stage_dependent_args.test_android:
             platforms_to_skip_test.add(StdlibDeploymentTarget.Android)
 
@@ -310,6 +329,9 @@ def __platforms_archs_to_skip_test(self, args, stage_dependent_args, host_target
                 StdlibDeploymentTarget.AppleTVSimulator.arm64)
             platforms_archs_to_skip_test.add(
                 StdlibDeploymentTarget.AppleWatchSimulator.arm64)
+            if StdlibDeploymentTarget.XROSSimulator is not None:
+                platforms_archs_to_skip_test.add(
+                    StdlibDeploymentTarget.XROSSimulator.arm64)
         if host_target == StdlibDeploymentTarget.OSX.arm64.name:
             platforms_archs_to_skip_test.add(
                 StdlibDeploymentTarget.iOSSimulator.x86_64)
@@ -335,4 +357,8 @@ def __platforms_to_skip_test_host(self, args, stage_dependent_args):
         if not stage_dependent_args.test_watchos_host and \
            not args.only_non_executable_test:
             platforms_to_skip_test_host.add(StdlibDeploymentTarget.AppleWatch)
+        if StdlibDeploymentTarget.XROS and \
+           not stage_dependent_args.test_xros_host and \
+           not args.only_non_executable_test:
+            platforms_to_skip_test_host.add(StdlibDeploymentTarget.XROS)
         return platforms_to_skip_test_host
diff --git a/utils/swift_build_support/swift_build_support/products/cmake_product.py b/utils/swift_build_support/swift_build_support/products/cmake_product.py
index 568e9069a8056..de148ec8c76e6 100644
--- a/utils/swift_build_support/swift_build_support/products/cmake_product.py
+++ b/utils/swift_build_support/swift_build_support/products/cmake_product.py
@@ -201,7 +201,9 @@ def host_cmake_options(self, host_target):
         elif host_target.startswith('macosx') or \
                 host_target.startswith('iphone') or \
                 host_target.startswith('appletv') or \
-                host_target.startswith('watch'):
+                host_target.startswith('watch') or \
+                host_target.startswith('xros-') or \
+                host_target.startswith('xrsimulator-'):
 
             swift_cmake_options.define('Python3_EXECUTABLE',
                                        self.toolchain.find_tool('python3'))
@@ -329,6 +331,27 @@ def host_cmake_options(self, host_target):
                 swift_host_variant_sdk = 'WATCHOS'
                 cmake_osx_deployment_target = None
 
+            elif host_target == 'xrsimulator-arm64':
+                swift_host_triple = 'arm64-apple-xros{}-simulator'.format(
+                    self.args.darwin_deployment_version_xros)
+                llvm_target_arch = 'AARCH64'
+                swift_host_variant_sdk = 'XROS_SIMULATOR'
+                cmake_osx_deployment_target = None
+
+            elif host_target == 'xros-arm64':
+                swift_host_triple = 'arm64-apple-xros{}'.format(
+                    self.args.darwin_deployment_version_xros)
+                llvm_target_arch = 'AARCH64'
+                swift_host_variant_sdk = 'XROS'
+                cmake_osx_deployment_target = None
+
+            elif host_target == 'xros-arm64e':
+                swift_host_triple = 'arm64e-apple-xros{}'.format(
+                    self.args.darwin_deployment_version_xros)
+                llvm_target_arch = 'AARCH64'
+                swift_host_variant_sdk = 'XROS'
+                cmake_osx_deployment_target = None
+
             darwin_sdk_deployment_targets = os.environ.get(
                 'DARWIN_SDK_DEPLOYMENT_TARGETS')
             if darwin_sdk_deployment_targets:
diff --git a/utils/swift_build_support/swift_build_support/products/product.py b/utils/swift_build_support/swift_build_support/products/product.py
index 927263f52d9a6..ababc351f95ee 100644
--- a/utils/swift_build_support/swift_build_support/products/product.py
+++ b/utils/swift_build_support/swift_build_support/products/product.py
@@ -288,6 +288,9 @@ def target_for_platform(self, platform, arch, include_version=True):
             target = '{}-apple-watchos{}'.format(
                 arch,
                 self.args.darwin_deployment_version_watchos if include_version else "")
+        elif platform in ['xrsimulator', 'xros']:
+            target = '{}-apple-xros{}'.format(
+                arch, self.args.darwin_deployment_version_xros)
         return target
 
     def generate_darwin_toolchain_file(self, platform, arch):
diff --git a/utils/swift_build_support/swift_build_support/targets.py b/utils/swift_build_support/swift_build_support/targets.py
index 588ba88161d84..4124989e9bc48 100644
--- a/utils/swift_build_support/swift_build_support/targets.py
+++ b/utils/swift_build_support/swift_build_support/targets.py
@@ -258,6 +258,14 @@ class StdlibDeploymentTarget(object):
                                          sdk_name="WATCHOS_SIMULATOR",
                                          is_simulator=True)
 
+    XROS = DarwinPlatform("xros", archs=["arm64", "arm64e"],
+                          sdk_name="XROS")
+
+    XROSSimulator = DarwinPlatform("xrsimulator",
+                                   archs=["arm64"],
+                                   sdk_name="XROS_SIMULATOR",
+                                   is_simulator=True)
+
     # A platform that's not tied to any particular OS, and it meant to be used
     # to build the stdlib as standalone and/or statically linked.
     Freestanding = Platform("freestanding", archs=[
@@ -298,6 +306,7 @@ class StdlibDeploymentTarget(object):
         iOS, iOSSimulator,
         AppleTV, AppleTVSimulator,
         AppleWatch, AppleWatchSimulator,
+        XROS, XROSSimulator,
         Freestanding,
         Linux,
         FreeBSD,
@@ -321,6 +330,8 @@ class StdlibDeploymentTarget(object):
         'TVOS_SIMULATOR': AppleTVSimulator.targets,
         'WATCHOS': AppleWatch.targets,
         'WATCHOS_SIMULATOR': AppleWatchSimulator.targets,
+        'XROS': XROS.targets,
+        'XROS_SIMULATOR': XROSSimulator.targets,
     }
 
     @staticmethod
diff --git a/validation-test/BuildSystem/skip_clean_corelibs.test b/validation-test/BuildSystem/skip_clean_corelibs.test
index 173f3f829f944..8814648cd3628 100644
--- a/validation-test/BuildSystem/skip_clean_corelibs.test
+++ b/validation-test/BuildSystem/skip_clean_corelibs.test
@@ -3,7 +3,8 @@
 # UNSUPPORTED: OS=ios
 # UNSUPPORTED: OS=tvos
 # UNSUPPORTED: OS=watchos
-
+# UNSUPPORTED: OS=xros
+#
 # RUN: %empty-directory(%t)
 # RUN: mkdir -p %t
 # RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --xctest --cmake %cmake  2>&1 | %FileCheck --check-prefix=CLEAN-CORELIBS-CHECK %s
diff --git a/validation-test/stdlib/ArrayTrapsObjC.swift b/validation-test/stdlib/ArrayTrapsObjC.swift
index 0bbf644ffe019..8b1f28c440761 100644
--- a/validation-test/stdlib/ArrayTrapsObjC.swift
+++ b/validation-test/stdlib/ArrayTrapsObjC.swift
@@ -7,6 +7,9 @@
 // Temporarily disable for backdeployment (rdar://89821303)
 // UNSUPPORTED: use_os_stdlib
 
+// rdar://121343746
+// UNSUPPORTED: OS=xros
+
 import StdlibUnittest
 import Foundation