Sema: Don't diagnose declarations more available than unavailable container.

It turns out that we must allow declarations with `introduced:` availability
nested inside of other declarations that are `unavailable` in order to
influence weak linking. Stop diagnosing declarations as being more available
than their unavailable containers and revert some changes to availability
inference that were designed to avoid creating these nestings but caused
regressions for declarations marked `@_spi_available.`

Reverts parts of #64310,
#64015, and
#62900.

Author: tshortli

include/swift/AST/DiagnosticsSema.def

@@ -5990,10 +5990,6 @@ ERROR(availability_decl_more_than_enclosing, none,
       "%0 cannot be more available than enclosing scope",
       (DescriptiveDeclKind))
 
-WARNING(availability_decl_more_than_unavailable_enclosing, none,
-        "%0 cannot be more available than unavailable enclosing scope",
-        (DescriptiveDeclKind))
-
 NOTE(availability_implicit_decl_here, none,
      "%0 implicitly declared here with availability of %1 %2 or newer",
      (DescriptiveDeclKind, StringRef, llvm::VersionTuple))

lib/AST/Availability.cpp

@@ -109,15 +109,6 @@ static AvailableAttr *createAvailableAttr(PlatformKind Platform,
   llvm::VersionTuple Obsoleted =
       Inferred.Obsoleted.value_or(llvm::VersionTuple());
 
-  // If a decl is unavailable then it cannot have any introduced, deprecated, or
-  // obsoleted version.
-  if (Inferred.PlatformAgnostic ==
-      PlatformAgnosticAvailabilityKind::Unavailable) {
-    Introduced = llvm::VersionTuple();
-    Deprecated = llvm::VersionTuple();
-    Obsoleted = llvm::VersionTuple();
-  }
-
   return new (Context)
       AvailableAttr(SourceLoc(), SourceRange(), Platform,
                     Message, Rename, RenameDecl,
@@ -168,27 +159,6 @@ void AvailabilityInference::applyInferredAvailableAttrs(
 
   DeclAttributes &Attrs = ToDecl->getAttrs();
 
-  // Some kinds of platform agnostic availability supersede any platform
-  // specific availability.
-  auto InferredAgnostic = Inferred.find(PlatformKind::none);
-  if (InferredAgnostic != Inferred.end()) {
-    switch (InferredAgnostic->second.PlatformAgnostic) {
-    case PlatformAgnosticAvailabilityKind::Deprecated:
-    case PlatformAgnosticAvailabilityKind::UnavailableInSwift:
-    case PlatformAgnosticAvailabilityKind::Unavailable:
-      Attrs.add(createAvailableAttr(PlatformKind::none,
-                                    InferredAgnostic->second, Message, Rename,
-                                    RenameDecl, Context));
-      return;
-
-    case PlatformAgnosticAvailabilityKind::None:
-    case PlatformAgnosticAvailabilityKind::SwiftVersionSpecific:
-    case PlatformAgnosticAvailabilityKind::PackageDescriptionVersionSpecific:
-    case PlatformAgnosticAvailabilityKind::NoAsync:
-      break;
-    }
-  }
-
   // Create an availability attribute for each observed platform and add
   // to ToDecl.
   for (auto &Pair : Inferred) {

lib/Sema/TypeCheckAttr.cpp

@@ -1945,17 +1945,7 @@ void AttributeChecker::visitAvailableAttr(AvailableAttr *attr) {
       AvailabilityInference::availableRange(attr, Ctx);
 
   if (auto *parent = getEnclosingDeclForDecl(D)) {
-    if (auto enclosingUnavailable = parent->getSemanticUnavailableAttr()) {
-      if (!AttrRange.isKnownUnreachable()) {
-        const Decl *enclosingDecl = enclosingUnavailable.value().second;
-        diagnose(D->isImplicit() ? enclosingDecl->getLoc()
-                                 : attr->getLocation(),
-                 diag::availability_decl_more_than_unavailable_enclosing,
-                 D->getDescriptiveKind());
-        diagnose(parent->getLoc(),
-                 diag::availability_decl_more_than_unavailable_enclosing_here);
-      }
-    } else if (auto enclosingAvailable =
+    if (auto enclosingAvailable =
                    parent->getSemanticAvailableRangeAttr()) {
       const AvailableAttr *enclosingAttr = enclosingAvailable.value().first;
       const Decl *enclosingDecl = enclosingAvailable.value().second;

test/ModuleInterface/actor_availability.swift

@@ -1,7 +1,9 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-emit-module-interface(%t/Library.swiftinterface) %s -module-name Library -target %target-swift-abi-5.3-triple
+// RUN: %target-swift-emit-module-interfaces(%t/Library.swiftinterface, %t/Library.private.swiftinterface) %s -module-name Library -target %target-swift-abi-5.3-triple
 // RUN: %target-swift-typecheck-module-from-interface(%t/Library.swiftinterface) -module-name Library
-// RUN: %FileCheck %s < %t/Library.swiftinterface
+// RUN: %target-swift-typecheck-module-from-interface(%t/Library.private.swiftinterface) -module-name Library
+// RUN: %FileCheck %s --check-prefixes=CHECK,CHECK-PUBLIC < %t/Library.swiftinterface
+// RUN: %FileCheck %s --check-prefixes=CHECK,CHECK-PRIVATE < %t/Library.private.swiftinterface
 
 // REQUIRES: VENDOR=apple
 
@@ -33,7 +35,7 @@ public actor ActorWithExplicitAvailability {
 @available(macOS, unavailable)
 public actor UnavailableActor {
   // CHECK: @available(iOS 13.0, tvOS 13.0, watchOS 6.0, *)
-  // CHECK-NEXT: @available(macOS, unavailable)
+  // CHECK-NEXT: @available(macOS, unavailable, introduced: 10.15)
   // CHECK-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor {
   // CHECK-NEXT:   get
   // CHECK-NEXT: }
@@ -72,9 +74,39 @@ extension Enum {
   @available(macOS, unavailable)
   public actor UnavailableExtensionNestedActor {
     // CHECK: @available(iOS 13.4, tvOS 13.4, watchOS 6.2, *)
-    // CHECK-NEXT: @available(macOS, unavailable)
+    // CHECK-NEXT: @available(macOS, unavailable, introduced: 10.15.4)
     // CHECK-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor {
     // CHECK-NEXT:   get
     // CHECK-NEXT: }
   }
 }
+
+// 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: public struct SPIAvailableStruct
+// CHECK-PRIVATE: @_spi_available(macOS, introduced: 10.15.4)
+// CHECK-PRIVATE-NEXT: @_spi_available(iOS, introduced: 13.4)
+// CHECK-PRIVATE-NEXT: @_spi_available(watchOS, introduced: 6.2)
+// CHECK-PRIVATE-NEXT: @_spi_available(tvOS, introduced: 13.4)
+// CHECK-PRIVATE-NEXT: public struct SPIAvailableStruct
+@_spi_available(SwiftStdlib 5.2, *)
+public struct SPIAvailableStruct {
+  // CHECK: #if compiler(>=5.3) && $Actors
+  // CHECK-NEXT: @_hasMissingDesignatedInitializers @available(macOS, unavailable)
+  // CHECK-NEXT: public actor UnavailableNestedActor
+  @available(macOS, unavailable)
+  public actor UnavailableNestedActor {
+    // CHECK-PUBLIC: @available(iOS, unavailable)
+    // CHECK-PUBLIC-NEXT: @available(tvOS, unavailable)
+    // CHECK-PUBLIC-NEXT: @available(watchOS, unavailable)
+    // CHECK-PUBLIC-NEXT: @available(macOS, unavailable)
+    // CHECK-PUBLIC-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor
+    // CHECK-PRIVATE: @_spi_available(iOS, introduced: 13.4)
+    // CHECK-PRIVATE-NEXT: @_spi_available(tvOS, introduced: 13.4)
+    // CHECK-PRIVATE-NEXT: @_spi_available(watchOS, introduced: 6.2)
+    // CHECK-PRIVATE-NEXT: @_spi_available(macOS, unavailable, introduced: 10.15.4)
+    // CHECK-PRIVATE-NEXT: @_semantics("defaultActor") nonisolated final public var unownedExecutor: _Concurrency.UnownedSerialExecutor
+  }
+}

test/Sema/availability_versions.swift

@@ -1731,12 +1731,11 @@ struct HasUnavailableExtension {
 
 @available(OSX, unavailable)
 extension HasUnavailableExtension {
-    // expected-note@-1 {{enclosing scope has been explicitly marked unavailable here}}
 
   public func inheritsUnavailable() { }
       // expected-note@-1 {{'inheritsUnavailable()' has been explicitly marked unavailable here}}
 
-  @available(OSX 10.9, *) // expected-warning {{instance method cannot be more available than unavailable enclosing scope}}
+  @available(OSX 10.9, *)
   public func moreAvailableButStillUnavailable() { }
       // expected-note@-1 {{'moreAvailableButStillUnavailable()' has been explicitly marked unavailable here}}
 }

test/Sema/generalized_accessors_availability.swift

@@ -131,6 +131,20 @@ func testButtNested(x: inout Butt.Nested) { // expected-error {{'Nested' is unav
   x.$wrapped_modify_more_available = 0 // expected-error {{is unavailable in macOS}}
 }
 
+@available(iOS, unavailable)
+@_spi_available(macOS, introduced: 10.51)
+extension Butt {
+  struct NestedInSPIAvailableExtension {
+    @available(macOS, unavailable)
+    public var unavailable: Int // expected-note {{'unavailable' has been explicitly marked unavailable here}}
+  }
+}
+
+@available(macOS, introduced: 10.51)
+func testButtNested(x: inout Butt.NestedInSPIAvailableExtension) {
+  x.unavailable = 0 // expected-error {{is unavailable in macOS}}
+}
+
 @available(macOS 11.0, *)
 struct LessAvailable {
   @SetterConditionallyAvailable

test/attr/attr_availability_transitive_osx.swift

@@ -105,7 +105,6 @@ extension Outer {
 }
 
 @available(OSX, unavailable)
-// expected-note@+1 {{enclosing scope has been explicitly marked unavailable here}}
 extension Outer {
   // expected-note@+1 {{'outer_osx_init_osx' has been explicitly marked unavailable here}}
   static var outer_osx_init_osx = osx() // OK
@@ -124,7 +123,7 @@ extension Outer {
   }
 
   // This @available should be ignored; inherited unavailability takes precedence
-  @available(OSX 999, *) // expected-warning {{instance method cannot be more available than unavailable enclosing scope}}
+  @available(OSX 999, *)
   // expected-note@+1 {{'osx_more_available_but_still_unavailable_call_osx()' has been explicitly marked unavailable here}}
   func osx_more_available_but_still_unavailable_call_osx() {
     osx() // OK