[AST] Add a missing check for Sendable in single protocol existential case

`any Sendable` should be considered Objective-C capable just like
it's protocol composition with other Objective-C capable types.

Resolves: rdar://102728938
(cherry picked from commit b399479)

Author: xedin

include/swift/AST/ExistentialLayout.h

@@ -105,6 +105,10 @@ struct ExistentialLayout {
   /// Zero or more primary associated type requirements from a
   /// ParameterizedProtocolType
   ArrayRef<Type> sameTypeRequirements;
+
+  /// Existentials allow a relaxed notion of \c ValueDecl::isObjC
+  /// that includes `Sendable` protocol.
+  static bool isObjCProtocol(ProtocolDecl *P);
 };
 
 }

lib/AST/Type.cpp

@@ -299,7 +299,7 @@ ExistentialLayout::ExistentialLayout(CanProtocolType type) {
   auto *protoDecl = type->getDecl();
 
   hasExplicitAnyObject = false;
-  containsNonObjCProtocol = !protoDecl->isObjC();
+  containsNonObjCProtocol = !isObjCProtocol(protoDecl);
   containsParameterized = false;
 
   protocols.push_back(protoDecl);
@@ -327,9 +327,7 @@ ExistentialLayout::ExistentialLayout(CanProtocolCompositionType type) {
       protoDecl = parameterized->getProtocol();
       containsParameterized = true;
     }
-    containsNonObjCProtocol |=
-        !protoDecl->isObjC() &&
-        !protoDecl->isSpecificProtocol(KnownProtocolKind::Sendable);
+    containsNonObjCProtocol |= !isObjCProtocol(protoDecl);
     protocols.push_back(protoDecl);
   }
 }
@@ -340,6 +338,10 @@ ExistentialLayout::ExistentialLayout(CanParameterizedProtocolType type)
   containsParameterized = true;
 }
 
+bool ExistentialLayout::isObjCProtocol(ProtocolDecl *P) {
+  return P->isObjC() || P->isSpecificProtocol(KnownProtocolKind::Sendable);
+}
+
 ExistentialLayout TypeBase::getExistentialLayout() {
   return getCanonicalType().getExistentialLayout();
 }

test/Concurrency/emit_objc_header_with_Sendable.swift

@@ -0,0 +1,29 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck %s -parse-as-library -emit-objc-header-path %t/swift.h
+// RUN: %FileCheck %s < %t/swift.h
+
+// REQUIRES: concurrency
+// REQUIRES: asserts
+// REQUIRES: objc_interop
+
+import Foundation
+
+@objc public protocol P {}
+
+@objc public class Klass : NSObject {
+  // CHECK: - (void)test1:(NSDictionary<NSString *, id> * _Nonnull)_;
+  @objc public func test1(_: [String: any Sendable]) {}
+  // CHECK: - (void)test2:(NSDictionary<NSString *, id <P>> * _Nonnull)_;
+  @objc public func test2(_: [String: any P & Sendable]) {}
+}
+
+@objc public protocol Q {
+  // CHECK: - (NSArray<NSDictionary<NSString *, id> *> * _Nonnull)data1 SWIFT_WARN_UNUSED_RESULT;
+  func data1() -> [[String: any Sendable]]
+  // CHECK: - (NSArray<id> * _Nullable)data2 SWIFT_WARN_UNUSED_RESULT;
+  func data2() -> [any Sendable]?
+  // CHECK: - (void)data3:(id _Nonnull)_;
+  func data3(_: any Sendable)
+  // CHECK: - (void)data4:(id _Nullable)_;
+  func data4(_: (any Sendable)?)
+}