[ConstraintSystem] Strip Sendable while processing AnyObject lookup results

All of the declarations returned by dynamic `AnyObject` lookup
are `@objc` and hence `@preconcurrency` which means that it should
be possible to introduce `@Sendable` and `any Sendable` annotations
without affecting lookup and shadowing behavior.

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -331,9 +331,14 @@ void ConstraintSystem::recordAppliedDisjunction(
 /// Retrieve a dynamic result signature for the given declaration.
 static std::tuple<char, ObjCSelector, CanType>
 getDynamicResultSignature(ValueDecl *decl) {
+  // Handle functions.
   if (auto func = dyn_cast<AbstractFunctionDecl>(decl)) {
-    // Handle functions.
-    auto type = func->getMethodInterfaceType();
+    // Strip `@Sendable` and `any Sendable` because it should be
+    // possible to add them without affecting lookup results and
+    // shadowing. All of the declarations that are processed here
+    // are `@objc` and hence `@preconcurrency`.
+    auto type = func->getMethodInterfaceType()->stripConcurrency(
+        /*recursive=*/true, /*dropGlobalActor=*/false);
     return std::make_tuple(func->isStatic(), func->getObjCSelector(),
                            type->getCanonicalType());
   }

test/Concurrency/sendable_objc_attr_in_type_context_swift5.swift

@@ -74,6 +74,10 @@ void doSomethingConcurrently(__attribute__((noescape)) void SWIFT_SENDABLE (^blo
 -(void)updateWithCompletionHandler: (void (^_Nullable)(void)) handler;
 @end
 
+@protocol TestWitnesses
+-(void)willSendDataWithCompletion: (void (^)(void)) completion;
+@end
+
 #pragma clang assume_nonnull end
 
 //--- main.swift
@@ -176,3 +180,12 @@ class TestConformanceWithoutStripping : InnerSendableTypes {
     self.update { }  // Ok - no ambiguity
   }
 }
+
+@objc
+class ImplicitShadowing : NSObject, TestWitnesses {
+  func willSendData(completion: @escaping () -> Void) {}
+
+  func test() {
+    (self as AnyObject).willSendData { } // Ok
+  }
+}

test/Concurrency/sendable_objc_attr_in_type_context_swift6.swift

@@ -74,6 +74,10 @@ void doSomethingConcurrently(__attribute__((noescape)) void SWIFT_SENDABLE (^blo
 -(void)updateWithCompletionHandler: (void (^_Nullable)(void)) handler;
 @end
 
+@protocol TestWitnesses
+-(void)willSendDataWithCompletion: (void (^)(void)) completion;
+@end
+
 #pragma clang assume_nonnull end
 
 //--- main.swift
@@ -178,8 +182,17 @@ class TestConformanceWithoutStripping : InnerSendableTypes {
 
   @objc func update(completionHandler: (() -> Void)? = nil) {}
 
-  func testCompute() {
+  func test() {
     self.compute { } // Ok - no ambiguity
     self.update { }  // Ok - no ambiguity
   }
 }
+
+@objc
+class ImplicitShadowing : NSObject, TestWitnesses {
+  func willSendData(completion: @escaping () -> Void) {}
+
+  func test() {
+    (self as AnyObject).willSendData { } // Ok
+  }
+}