[Clang][Sema] clang generates incorrect fix-its for API_AVAILABLE

clang/include/clang/Basic/Attr.td

@@ -1073,6 +1073,36 @@ static llvm::StringRef canonicalizePlatformName(llvm::StringRef Platform) {
              .Case("ShaderModel", "shadermodel")
              .Default(Platform);
 }
+static std::vector<llvm::StringRef> equivalentPlatformNames(llvm::StringRef Platform) {
+    return llvm::StringSwitch<std::vector<llvm::StringRef>>(Platform)
+             .Case("ios", {"ios", "iOS"})
+             .Case("iOS", {"ios", "iOS"})
+             .Case("macos", {"macos", "macOS"})
+             .Case("macOS", {"macos", "macOS"})
+             .Case("tvos", {"tvos", "tvOS"})
+             .Case("tvOS", {"tvos", "tvOS"})
+             .Case("watchos", {"watchos", "watchOS"})
+             .Case("watchOS", {"watchos", "watchOS"})
+             .Case("ios_app_extension", {"iOSApplicationExtension", "ios_app_extension"})
+             .Case("iOSApplicationExtension", {"iOSApplicationExtension", "ios_app_extension"})
+             .Case("macos_app_extension", {"macOSApplicationExtension", "macos_app_extension"})
+             .Case("macOSApplicationExtension", {"macOSApplicationExtension", "macos_app_extension"})
+             .Case("tvos_app_extension", {"tvOSApplicationExtension", "tvos_app_extension"})
+             .Case("tvOSApplicationExtension", {"tvOSApplicationExtension", "tvos_app_extension"})
+             .Case("watchos_app_extension", {"watchOSApplicationExtension", "watchos_app_extension"})
+             .Case("watchOSApplicationExtension", {"watchOSApplicationExtension", "watchos_app_extension"})
+             .Case("maccatalyst", {"macCatalyst", "maccatalyst"})
+             .Case("macCatalyst", {"macCatalyst", "maccatalyst"})
+             .Case("maccatalyst_app_extension", {"macCatalystApplicationExtension", "maccatalyst_app_extension"})
+             .Case("macCatalystApplicationExtension", {"macCatalystApplicationExtension", "maccatalyst_app_extension"})
+             .Case("xros", {"visionos", "visionOS", "xros"})
+             .Case("visionOS", {"visionos", "visionOS", "xros"})
+             .Case("visionos", {"visionos", "visionOS", "xros"})
+             .Case("xros_app_extension", {"visionOSApplicationExtension", "visionos_app_extension", "xros_app_extension"})
+             .Case("visionOSApplicationExtension", {"visionOSApplicationExtension", "visionos_app_extension", "xros_app_extension"})
+             .Case("visionos_app_extension", {"visionOSApplicationExtension", "visionos_app_extension", "xros_app_extension"})
+             .Default({Platform});
+}
 static llvm::Triple::EnvironmentType getEnvironmentType(llvm::StringRef Environment) {
     return llvm::StringSwitch<llvm::Triple::EnvironmentType>(Environment)
              .Case("pixel", llvm::Triple::Pixel)

clang/lib/Sema/SemaAvailability.cpp

@@ -488,22 +488,41 @@ static void DoEmitAvailabilityWarning(Sema &S, AvailabilityResult K,
       // Don't offer a fixit for declarations with availability attributes.
       if (Enclosing->hasAttr<AvailabilityAttr>())
         return;
-      if (!S.getPreprocessor().isMacroDefined("API_AVAILABLE"))
+      Preprocessor &PP = S.getPreprocessor();
+      if (!PP.isMacroDefined("API_AVAILABLE"))
         return;
       std::optional<AttributeInsertion> Insertion = createAttributeInsertion(
           Enclosing, S.getSourceManager(), S.getLangOpts());
       if (!Insertion)
         return;
-      std::string PlatformName =
-          AvailabilityAttr::getPlatformNameSourceSpelling(
-              S.getASTContext().getTargetInfo().getPlatformName())
-              .lower();
+      StringRef PlatformName =
+          S.getASTContext().getTargetInfo().getPlatformName();
+
+      // Apple's API_AVAILABLE macro expands roughly like this.
+      // API_AVAILABLE(ios(17.0))
+      // __attribute__((availability(__API_AVAILABLE_PLATFORM_ios(17.0)))
+      // __attribute__((availability(ios,introduced=17.0)))
+      // In order to figure out which platform name to use in the API_AVAILABLE
+      // macro, the associated __API_AVAILABLE_PLATFORM_ macro needs to be
+      // found. The __API_AVAILABLE_PLATFORM_ macros aren't consistent about
+      // using the canonical platform name, source spelling name, or one of the
+      // other supported names (i.e. one of the keys in canonicalizePlatformName
+      // that's neither). Check all of the supported names for a match.
+      std::vector<StringRef> EquivalentPlatforms =
+          AvailabilityAttr::equivalentPlatformNames(PlatformName);
+      llvm::Twine MacroPrefix = "__API_AVAILABLE_PLATFORM_";
+      auto AvailablePlatform =
+          llvm::find_if(EquivalentPlatforms, [&](StringRef EquivalentPlatform) {
+            return PP.isMacroDefined((MacroPrefix + EquivalentPlatform).str());
+          });
+      if (AvailablePlatform == EquivalentPlatforms.end())
+        return;
       std::string Introduced =
           OffendingDecl->getVersionIntroduced().getAsString();
       FixitNoteDiag << FixItHint::CreateInsertion(
           Insertion->Loc,
-          (llvm::Twine(Insertion->Prefix) + "API_AVAILABLE(" + PlatformName +
-           "(" + Introduced + "))" + Insertion->Suffix)
+          (llvm::Twine(Insertion->Prefix) + "API_AVAILABLE(" +
+           *AvailablePlatform + "(" + Introduced + "))" + Insertion->Suffix)
               .str());
     }
     return;

clang/test/FixIt/fixit-availability-maccatalyst.m

@@ -11,14 +11,15 @@ int use(void) {
 // CHECK-NEXT: fix-it:{{.*}}:{[[@LINE-2]]:14-[[@LINE-2]]:14}:"\n  } else {\n      // Fallback on earlier versions\n  }"
 }
 
-#define API_AVAILABLE(X) __attribute__((availability(macCatalyst, introduced=13.2))) __attribute__((availability(ios, introduced=13.1))) // dummy macro
+#define API_AVAILABLE(x) __attribute__((availability(__API_AVAILABLE_PLATFORM_##x)))
+#define __API_AVAILABLE_PLATFORM_macCatalyst(x) macCatalyst,introduced=x
 
-API_AVAILABLE(macos(10.12))
+API_AVAILABLE(macCatalyst(13.2))
 @interface NewClass
 @end
 
 @interface OldButOfferFixit
 @property(copy) NewClass *prop;
-// CHECK: fix-it:{{.*}}:{[[@LINE-2]]:1-[[@LINE-2]]:1}:"API_AVAILABLE(maccatalyst(13.2))\n"
+// CHECK: fix-it:{{.*}}:{[[@LINE-2]]:1-[[@LINE-2]]:1}:"API_AVAILABLE(macCatalyst(13.2))\n"
 
 @end

clang/test/FixIt/fixit-availability.mm

@@ -118,7 +118,8 @@ void wrapDeclStmtUses() {
   }
 }
 
-#define API_AVAILABLE(X) __attribute__((availability(macos, introduced=10.12))) // dummy macro
+#define API_AVAILABLE(x) __attribute__((availability(__API_AVAILABLE_PLATFORM_##x)))
+#define __API_AVAILABLE_PLATFORM_macos(x) macos,introduced=x
 
 API_AVAILABLE(macos(10.12))
 @interface NewClass