swiftlang · ahatanaka · Oct 17, 2025
diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
@@ -376,6 +376,8 @@ if (APPLE AND NOT CMAKE_LINKER MATCHES ".*lld.*")
 endif()
 
 include(AddClang)
+include(AddDarwinPlatform)
+clang_add_additional_platform()
 
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 

diff --git a/clang/cmake/modules/AddDarwinPlatform.cmake b/clang/cmake/modules/AddDarwinPlatform.cmake
@@ -0,0 +1,23 @@
+# FIXME: How to generalize this to be driven by discovered SDKs?
+function(clang_add_additional_platform)
+  # Add a platform.
+  set(name "xros")
+  set(CLANG_PLATFORM_${name}_PLATFORM_AVAILABILITY_NAME "xros" PARENT_SCOPE)
+  set(platformFallBack "iphoneos")
+
+  if (NOT "${platformFallBack}" STREQUAL "")
+    set(fallbackTripleName "${platformFallBack}")
+    # FIXME: we need a generic platform -> triple mapping.
+    if ("${fallbackTripleName}" STREQUAL "iphoneos")
+      set(fallbackTripleName "ios")
+    endif()
+
+    message(STATUS "Platform ${name} has fallback platform - ${fallbackTripleName}")
+    set(CLANG_PLATFORM_${name}_FALLBACK_PLATFORM_AVAILABILITY_NAME "${fallbackTripleName}" PARENT_SCOPE)
+
+    # FIXME: This is a hack for xrOS, but should be in the SDKSettings too.
+    set(CLANG_PLATFORM_${name}_INFER_UNAVAILABLE 1 PARENT_SCOPE)
+    set(CLANG_PLATFORM_${name}_PLATFORM_TRIPLE_OS_VALUE "XROS" PARENT_SCOPE)
+    set(CLANG_PLATFORM_${name}_FALLBACK_PLATFORM_TRIPLE_OS_VALUE "IOS" PARENT_SCOPE)
+  endif()
+endfunction()
diff --git a/clang/lib/Sema/CMakeLists.txt b/clang/lib/Sema/CMakeLists.txt
@@ -13,6 +13,38 @@ clang_tablegen(OpenCLBuiltins.inc -gen-clang-opencl-builtins
   TARGET ClangOpenCLBuiltinsImpl
   )
 
+# Configure additional platform-specific code that controls things like
+# availability attributes.
+set(TEMPLATE_INCLUDES_INFER_AVAILABILITY_ATTRIBUTE "")
+
+foreach(supported_platform ${LLVM_SUPPORTED_PLATFORMS})
+  if (${CLANG_PLATFORM_${supported_platform}_INFER_UNAVAILABLE})
+    # Generate code that infers availability(unavailable) attribute if a platform
+    # requires that.
+    set(output_file_name "InferUnavailableAvailabilityFromFallbackPlatform_${supported_platform}.def")
+    message(STATUS "Adding platform specific availability attribute code - ${output_file_name}")
+
+    set(PLATFORM_TRIPLE_OS_VALUE
+        "${CLANG_PLATFORM_${supported_platform}_PLATFORM_TRIPLE_OS_VALUE}")
+    set(FALLBACK_PLATFORM_TRIPLE_OS_VALUE
+        "${CLANG_PLATFORM_${supported_platform}_FALLBACK_PLATFORM_TRIPLE_OS_VALUE}")
+    set(PLATFORM_AVAILABILITY_NAME
+        "${CLANG_PLATFORM_${supported_platform}_PLATFORM_AVAILABILITY_NAME}")
+    set(FALLBACK_PLATFORM_AVAILABILITY_NAME
+        "${CLANG_PLATFORM_${supported_platform}_FALLBACK_PLATFORM_AVAILABILITY_NAME}")
+    configure_file(
+      ${CMAKE_CURRENT_SOURCE_DIR}/PlatformTemplates/InferUnavailableAvailabilityFromFallbackPlatform.def.in
+      ${CMAKE_CURRENT_BINARY_DIR}/PlatformTemplates/${output_file_name}
+    )
+    set(TEMPLATE_INCLUDES_INFER_AVAILABILITY_ATTRIBUTE "${TEMPLATE_INCLUDES_INFER_AVAILABILITY_ATTRIBUTE}\n#include \"PlatformTemplates/${output_file_name}\"")
+  endif()
+endforeach()
+
+configure_file(
+  ${CMAKE_CURRENT_SOURCE_DIR}/InferAvailabilityAttribute.cpp.in
+  ${CMAKE_CURRENT_BINARY_DIR}/InferAvailabilityAttribute.cpp
+)
+
 add_clang_library(clangSema
   AnalysisBasedWarnings.cpp
   # TO_UPSTREAM(BoundsSafety) ON
@@ -108,6 +140,7 @@ add_clang_library(clangSema
   SemaWasm.cpp
   SemaX86.cpp
   TypeLocBuilder.cpp
+  ${CMAKE_CURRENT_BINARY_DIR}/InferAvailabilityAttribute.cpp
 
   DEPENDS
   ClangOpenCLBuiltinsImpl

diff --git a/clang/lib/Sema/InferAvailabilityAttribute.cpp.in b/clang/lib/Sema/InferAvailabilityAttribute.cpp.in
@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/ASTContext.h"
+#include "clang/Basic/DarwinSDKInfo.h"
+#include "clang/Basic/IdentifierTable.h"
+#include "clang/Basic/LLVM.h"
+#include "llvm/Support/VersionTuple.h"
+#include "llvm/TargetParser/Triple.h"
+
+namespace clang {
+
+/// Returns true if the given availability attribute should be inferred, and
+/// adjusts the value of the attribute as necessary to facilitate that.
+bool shouldInferAvailabilityAttribute(const llvm::Triple &TT,
+                                      const DarwinSDKInfo *SDKInfo,
+                                      const ASTContext &Context,
+                                      IdentifierInfo *&II,
+                                      bool &IsUnavailable,
+                                      VersionTuple &Introduced,
+                                      VersionTuple &Deprecated,
+                                      VersionTuple &Obsolete) {
+  for (const auto &f : {
+    // function ptr promotion
+    +([] (const llvm::Triple &TT,
+    const DarwinSDKInfo *SDKInfo,
+    const ASTContext &Context,
+    IdentifierInfo *&II,
+    bool &IsUnavailable,
+    VersionTuple &Introduced,
+    VersionTuple &Deprecated,
+    VersionTuple &Obsolete) -> bool { return false; }),
+    @TEMPLATE_INCLUDES_INFER_AVAILABILITY_ATTRIBUTE@
+  }) {
+    if (f(TT, SDKInfo, Context, II, IsUnavailable, Introduced, Deprecated,
+          Obsolete))
+      return true;
+  }
+  return false;
+}
+
+} // end namespace clang
diff --git a/clang/lib/Sema/PlatformTemplates/InferUnavailableAvailabilityFromFallbackPlatform.def.in b/clang/lib/Sema/PlatformTemplates/InferUnavailableAvailabilityFromFallbackPlatform.def.in
@@ -0,0 +1,108 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This platform-specific template implements inferral of
+//  __attribute__((availability(platform, unavailable))) from a base platform
+//  attribute __attribute__((availability(fallback platform, unavailable))).
+//
+// INPUTS:
+//    PLATFORM_TRIPLE_OS_VALUE - the name of the target OS enum in the Triple.
+//    FALLBACK_PLATFORM_TRIPLE_OS_VALUE - the name of the fallback target OS
+//                                        enum in the Triple.
+//    PLATFORM_AVAILABILITY_NAME - the name of availability platform.
+//    FALLBACK_PLATFORM_AVAILABILITY_NAME - the name of availability for the
+//                                          fallback platform.
+//
+//===----------------------------------------------------------------------===//
+
+// FIXME: This is now doing more than 'unavailable', the docs have to be updated.
+
+// x introduced := map(ios introduced, 1.0, None)
+//                     None           -> x unavailable
+//                     <version>      -> x introduced <version>
+
+// x deprecated := map(ios deprecated, 1.0, MaximumDeploymentVersion)
+//                        None -> None
+//                        <version> -> x deprecated <version>
+
+// x obsoleted := map(ios obsoleted, 1.0, MaximumDeploymentVersion)
+//                    None -> x unavailable
+//                    <version> -> x obsoleted <version>
+
+/// Returns true if the given availability attribute should be inferred.
++([] (const llvm::Triple &TT,
+    const DarwinSDKInfo *SDKInfo,
+    const ASTContext &Context,
+    IdentifierInfo *&II,
+    bool &IsUnavailable,
+    VersionTuple &Introduced,
+    VersionTuple &Deprecated,
+    VersionTuple &Obsolete) -> bool {
+  if (TT.getOS() != llvm::Triple::@PLATFORM_TRIPLE_OS_VALUE@)
+    return false;
+  IdentifierInfo *NewII = nullptr;
+  if (II->getName() == "@FALLBACK_PLATFORM_AVAILABILITY_NAME@")
+    NewII = &Context.Idents.get("@PLATFORM_AVAILABILITY_NAME@");
+  else if (II->getName() == "@FALLBACK_PLATFORM_AVAILABILITY_NAME@_app_extension")
+    NewII = &Context.Idents.get("@PLATFORM_AVAILABILITY_NAME@_app_extension");
+  if (!NewII)
+    return false;
+  II = NewII;
+
+  auto MakeUnavailable = [&]() {
+    IsUnavailable = true;
+    // Reset introduced, deprecated, obsoleted.
+    Introduced = VersionTuple();
+    Deprecated = VersionTuple();
+    Obsolete = VersionTuple();
+  };
+
+  if (!SDKInfo) {
+    MakeUnavailable();
+    return true;
+  }
+  // Map from the fallback platform availability to the current platform
+  // availability.
+  const auto *Mapping = SDKInfo->getVersionMapping(
+                           DarwinSDKInfo::OSEnvPair(
+                             llvm::Triple::@FALLBACK_PLATFORM_TRIPLE_OS_VALUE@,
+                             llvm::Triple::UnknownEnvironment,
+                             llvm::Triple::@PLATFORM_TRIPLE_OS_VALUE@,
+                             llvm::Triple::UnknownEnvironment));
+  if (!Mapping) {
+    MakeUnavailable();
+    return true;
+  }
+
+  if (Introduced) {
+    auto NewIntroduced = Mapping->mapIntroducedAvailabilityVersion(Introduced);
+    if (!NewIntroduced) {
+      MakeUnavailable();
+      return true;
+    }
+    Introduced = *NewIntroduced;
+  }
+
+  if (Obsolete) {
+    auto NewObsolete =
+        Mapping->mapDeprecatedObsoletedAvailabilityVersion(Obsolete);
+    if (!NewObsolete) {
+      MakeUnavailable();
+      return true;
+    }
+    Obsolete = *NewObsolete;
+  }
+
+  if (Deprecated) {
+    auto NewDeprecated =
+        Mapping->mapDeprecatedObsoletedAvailabilityVersion(Deprecated);
+    Deprecated = NewDeprecated ? *NewDeprecated : VersionTuple();
+  }
+
+  return true;
+}),
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -2453,6 +2453,17 @@ AvailabilityAttr *Sema::mergeAvailabilityAttr(
   return nullptr;
 }
 
+namespace clang {
+
+/// Returns true if the given availability attribute should be inferred, and
+/// adjusts the value of the attribute as necessary to facilitate that.
+bool shouldInferAvailabilityAttribute(
+    const llvm::Triple &TT, const DarwinSDKInfo *SDKInfo,
+    const ASTContext &Context, IdentifierInfo *&II, bool &IsUnavailable,
+    VersionTuple &Introduced, VersionTuple &Deprecated, VersionTuple &Obsolete);
+
+} // end namespace clang
+
 static void handleFeatureAvailabilityAttr(Sema &S, Decl *D,
                                           const ParsedAttr &AL) {
   if (S.getLangOpts().CPlusPlus) {
@@ -2634,6 +2645,32 @@ static void handleAvailabilityAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   if (NewAttr)
     D->addAttr(NewAttr);
 
+  /* TO_UPSTREAM(XROS) ON */
+  if (S.Context.getTargetInfo().getTriple().getOS() == llvm::Triple::XROS) {
+    // Infer availability attributes using platform-specific logic, driven by
+    // the SDKSettings if necessary.
+    IdentifierInfo *NewII = II;
+    bool NewIsUnavailable = IsUnavailable;
+    VersionTuple NewIntroduced = Introduced.Version;
+    VersionTuple NewDeprecated = Deprecated.Version;
+    VersionTuple NewObsoleted = Obsoleted.Version;
+    if (shouldInferAvailabilityAttribute(S.Context.getTargetInfo().getTriple(),
+                                         S.getDarwinSDKInfoForAvailabilityChecking(AL.getRange().getBegin(), "ios"),
+                                         S.Context, NewII,
+                                         NewIsUnavailable, NewIntroduced,
+                                         NewDeprecated, NewObsoleted)) {
+      AvailabilityAttr *NewAttr = S.mergeAvailabilityAttr(
+          ND, AL, NewII, true /*Implicit*/, NewIntroduced, NewDeprecated,
+          NewObsoleted, NewIsUnavailable, Str, IsStrict, Replacement,
+          AvailabilityMergeKind::None, PriorityModifier + Sema::AP_InferredFromOtherPlatform,
+          IIEnvironment);
+      if (NewAttr)
+        D->addAttr(NewAttr);
+    }
+  }
+
+  /* TO_UPSTREAM(XROS) OFF */
+
   // Transcribe "ios" to "watchos" (and add a new attribute) if the versioning
   // matches before the start of the watchOS platform.
   if (S.Context.getTargetInfo().getTriple().isWatchOS()) {

diff --git a/clang/test/PlatformSpecific/xrOS/Sema/Inputs/XROS.sdk/SDKSettings.json b/clang/test/PlatformSpecific/xrOS/Sema/Inputs/XROS.sdk/SDKSettings.json
@@ -0,0 +1,9 @@
+{
+  "DefaultVariant": "xrOS", "DisplayName": "xrOS",
+  "Version": "1.0",
+  "CanonicalName": "xros1.0",
+  "MaximumDeploymentTarget": "1.0.99",
+  "VersionMap": {
+    "iOS_xrOS":{"15.0":"1.0"}
+  }
+}