AST: Introduce Decl::getActiveAvailableAttrForCurrentPlatform().

Author: tshortli

include/swift/AST/Attr.h

@@ -2925,12 +2925,6 @@ class DeclAttributes {
     return UnaryOperatorKind::None;
   }
 
-  /// Finds the most-specific platform-specific attribute that is
-  /// active for the current platform.
-  const AvailableAttr *
-  findMostSpecificActivePlatform(const ASTContext &ctx,
-                                 bool ignoreAppExtensions = false) const;
-
   /// Returns the `@backDeployed` attribute that is active for the current
   /// platform.
   const BackDeployedAttr *getBackDeployed(const ASTContext &ctx,

include/swift/AST/Decl.h

@@ -1390,6 +1390,12 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl>, public Swi
   /// and its DeclContext does not.
   bool isOutermostPrivateOrFilePrivateScope() const;
 
+  /// Returns the active platform-specific `@available` attribute for this decl.
+  /// There may be multiple `@available` attributes that are relevant to the
+  /// current platform, but the returned one has the highest priority.
+  const AvailableAttr *getActiveAvailableAttrForCurrentPlatform(
+      bool ignoreAppExtensions = false) const;
+
   /// Returns true if the declaration is deprecated at the current deployment
   /// target.
   bool isDeprecated() const { return getDeprecatedAttr() != nullptr; }

lib/AST/Attr.cpp

@@ -370,40 +370,6 @@ DeclAttribute *DeclAttribute::clone(ASTContext &ctx) const {
   }
 }
 
-const AvailableAttr *
-DeclAttributes::findMostSpecificActivePlatform(const ASTContext &ctx,
-                                               bool ignoreAppExtensions) const {
-  const AvailableAttr *bestAttr = nullptr;
-
-  for (auto attr : *this) {
-    auto *avAttr = dyn_cast<AvailableAttr>(attr);
-    if (!avAttr)
-      continue;
-
-    if (avAttr->isInvalid())
-      continue;
-
-    if (!avAttr->hasPlatform())
-      continue;
-
-    if (!avAttr->isActivePlatform(ctx))
-      continue;
-
-    if (ignoreAppExtensions &&
-        isApplicationExtensionPlatform(avAttr->getPlatform()))
-      continue;
-
-    // We have an attribute that is active for the platform, but
-    // is it more specific than our current best?
-    if (!bestAttr || inheritsAvailabilityFromPlatform(
-                         avAttr->getPlatform(), bestAttr->getPlatform())) {
-      bestAttr = avAttr;
-    }
-  }
-
-  return bestAttr;
-}
-
 const BackDeployedAttr *
 DeclAttributes::getBackDeployed(const ASTContext &ctx,
                                 bool forTargetVariant) const {

lib/AST/Availability.cpp

@@ -486,11 +486,36 @@ bool Decl::isAvailableAsSPI() const {
   return AvailabilityInference::isAvailableAsSPI(this);
 }
 
+const AvailableAttr *
+Decl::getActiveAvailableAttrForCurrentPlatform(bool ignoreAppExtensions) const {
+  auto &ctx = getASTContext();
+  const AvailableAttr *bestAttr = nullptr;
+
+  for (auto attr :
+       getAttrs().getAttributes<AvailableAttr, /*AllowInvalid=*/false>()) {
+    if (!attr->hasPlatform() || !attr->isActivePlatform(ctx))
+      continue;
+
+    if (ignoreAppExtensions &&
+        isApplicationExtensionPlatform(attr->getPlatform()))
+      continue;
+
+    // We have an attribute that is active for the platform, but is it more
+    // specific than our current best?
+    if (!bestAttr || inheritsAvailabilityFromPlatform(
+                         attr->getPlatform(), bestAttr->getPlatform())) {
+      bestAttr = attr;
+    }
+  }
+
+  return bestAttr;
+}
+
 const AvailableAttr *Decl::getDeprecatedAttr() const {
   auto &ctx = getASTContext();
   auto attrs = getAttrs();
   const AvailableAttr *result = nullptr;
-  const AvailableAttr *bestActive = attrs.findMostSpecificActivePlatform(ctx);
+  const AvailableAttr *bestActive = getActiveAvailableAttrForCurrentPlatform();
 
   for (auto attr :
        attrs.getAttributes<AvailableAttr, /*AllowInvalid=*/false>()) {
@@ -531,7 +556,7 @@ const AvailableAttr *Decl::getSoftDeprecatedAttr() const {
   auto &ctx = getASTContext();
   auto attrs = getAttrs();
   const AvailableAttr *result = nullptr;
-  const AvailableAttr *bestActive = attrs.findMostSpecificActivePlatform(ctx);
+  const AvailableAttr *bestActive = getActiveAvailableAttrForCurrentPlatform();
 
   for (auto attr :
        attrs.getAttributes<AvailableAttr, /*AllowInvalid=*/false>()) {
@@ -608,10 +633,9 @@ bool Decl::isUnavailableInCurrentSwiftVersion() const {
 static const AvailableAttr *
 getDeclUnavailableAttr(const Decl *D, bool ignoreAppExtensions) {
   auto &ctx = D->getASTContext();
-  auto attrs = D->getAttrs();
   const AvailableAttr *result = nullptr;
   const AvailableAttr *bestActive =
-      attrs.findMostSpecificActivePlatform(ctx, ignoreAppExtensions);
+      D->getActiveAvailableAttrForCurrentPlatform(ignoreAppExtensions);
 
   for (auto attr :
        D->getAttrs().getAttributes<AvailableAttr, /*AllowInvalid=*/false>()) {

lib/Sema/TypeCheckAttr.cpp

@@ -2162,18 +2162,18 @@ void AttributeChecker::visitAvailableAttr(AvailableAttr *attr) {
     return;
 
   // Make sure there isn't a more specific attribute we should be using instead.
-  // findMostSpecificActivePlatform() is O(N), so only do this if we're checking
-  // an iOS attribute while building for macCatalyst.
+  // getActiveAvailableAttrForCurrentPlatform() is O(N), so only do this if
+  // we're checking an iOS attribute while building for macCatalyst.
   if (attr->getPlatform() == PlatformKind::iOS &&
       isPlatformActive(PlatformKind::macCatalyst, Ctx.LangOpts)) {
-    if (attr != D->getAttrs().findMostSpecificActivePlatform(Ctx)) {
+    if (attr != D->getActiveAvailableAttrForCurrentPlatform()) {
       return;
     }
   }
 
   if (attr->getPlatform() == PlatformKind::iOS &&
       isPlatformActive(PlatformKind::visionOS, Ctx.LangOpts)) {
-    if (attr != D->getAttrs().findMostSpecificActivePlatform(Ctx)) {
+    if (attr != D->getActiveAvailableAttrForCurrentPlatform()) {
       return;
     }
   }