AST: Fix macCatalyst availability for synthesized declarations.

The macCatalyst platform availability of a declaration may be inferred from the
iOS platform availability of that declaration in the absence of an explicit
macCatalyst availability attribute. This means that when inheriting macCatalyst
platform availability, the explict iOS availability of an inner ancestor should
take precedence over explicit macCatalyst availability of an outer ancestor.
The algorithm that computes inferred availability attributes for synthesized
declarations was treating macCatalyst and iOS as independent platforms, though,
sometimes yielding inapproparite macCatalyst availability.

Resolves rdar://107766644

Author: tshortli

lib/AST/Availability.cpp

@@ -136,13 +136,28 @@ void AvailabilityInference::applyInferredAvailableAttrs(
   // a per-platform basis.
   std::map<PlatformKind, InferredAvailability> Inferred;
   for (const Decl *D : InferredFromDecls) {
+    llvm::SmallVector<const AvailableAttr *, 8> MergedAttrs;
+
     do {
+      llvm::SmallVector<const AvailableAttr *, 8> PendingAttrs;
+
       for (const DeclAttribute *Attr : D->getAttrs()) {
         auto *AvAttr = dyn_cast<AvailableAttr>(Attr);
         if (!AvAttr || AvAttr->isInvalid())
           continue;
 
+        // Skip an attribute from an outer declaration if it is for a platform
+        // that was already handled implicitly by an attribute from an inner
+        // declaration.
+        if (llvm::any_of(MergedAttrs,
+                         [&AvAttr](const AvailableAttr *MergedAttr) {
+                           return inheritsAvailabilityFromPlatform(
+                               AvAttr->Platform, MergedAttr->Platform);
+                         }))
+          continue;
+
         mergeWithInferredAvailability(AvAttr, Inferred[AvAttr->Platform]);
+        PendingAttrs.push_back(AvAttr);
 
         if (Message.empty() && !AvAttr->Message.empty())
           Message = AvAttr->Message;
@@ -153,6 +168,8 @@ void AvailabilityInference::applyInferredAvailableAttrs(
         }
       }
 
+      MergedAttrs.append(PendingAttrs);
+
       // Walk up the enclosing declaration hierarchy to make sure we aren't
       // missing any inherited attributes.
       D = AvailabilityInference::parentDeclForInferredAvailability(D);

test/ModuleInterface/actor_availability.swift

@@ -110,3 +110,43 @@ public struct SPIAvailableStruct {
     // CHECK-PRIVATE-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor
   }
 }
+
+// CHECK: @_hasMissingDesignatedInitializers @available(macCatalyst 13.1, *)
+// CHECK-NEXT: public class MacCatalystAvailableClass
+@available(macCatalyst 13.1, *)
+public class MacCatalystAvailableClass {
+  // CHECK: #if compiler(>=5.3) && $Actors
+  // CHECK-NEXT: @_hasMissingDesignatedInitializers public actor NestedActor
+  public actor NestedActor {
+    // CHECK: @available(iOS 13.0, tvOS 13.0, watchOS 6.0, macOS 10.15, macCatalyst 13.1, *)
+    // CHECK-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor
+  }
+
+  // CHECK: #if compiler(>=5.3) && $Actors
+  // CHECK-NEXT: @_hasMissingDesignatedInitializers @available(macCatalyst 14, *)
+  // CHECK-NEXT: public actor LessAvailableMacCatalystActor
+  @available(macCatalyst 14, *)
+  public actor LessAvailableMacCatalystActor {
+    // CHECK: @available(iOS 13.0, tvOS 13.0, watchOS 6.0, macOS 10.15, macCatalyst 14, *)
+    // CHECK-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor
+  }
+
+  // CHECK: #if compiler(>=5.3) && $Actors
+  // CHECK-NEXT: @_hasMissingDesignatedInitializers @available(iOS 15.0, macOS 12.0, *)
+  // CHECK-NEXT: public actor AvailableiOSAndMacOSNestedActor {
+  @available(iOS 15.0, macOS 12.0, *)
+  public actor AvailableiOSAndMacOSNestedActor {
+    // CHECK: @available(iOS 15.0, tvOS 13.0, watchOS 6.0, macOS 12.0, *)
+    // CHECK-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor
+  }
+
+  // CHECK: #if compiler(>=5.3) && $Actors
+  // CHECK-NEXT: @_hasMissingDesignatedInitializers @available(iOS, unavailable)
+  // CHECK-NEXT: public actor UnavailableiOSNestedActor
+  @available(iOS, unavailable)
+  public actor UnavailableiOSNestedActor {
+    // CHECK: @available(tvOS 13.0, watchOS 6.0, macOS 10.15, *)
+    // CHECK-NEXT: @available(iOS, unavailable, introduced: 13.0)
+    // CHECK-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor
+  }
+}