[TypeChecker/NameLookup] SE-0463: A few fixes for SendableCompletionHandlers feature

include/swift/AST/DiagnosticsSema.def

@@ -1898,6 +1898,11 @@ ERROR(objc_implementation_type_mismatch,none,
       "%kind0 of type %1 does not match type %2 declared by the header",
       (ValueDecl *, Type, Type))
 
+ERROR(objc_implementation_sendability_mismatch,none,
+      "sendability of function types in %kind0 of type %1 does not match "
+      "type %2 declared by the header",
+      (ValueDecl *, Type, Type))
+
 ERROR(objc_implementation_required_attr_mismatch,none,
       "%kind0 %select{should not|should}2 be 'required' to match %1 declared "
       "by the header",

include/swift/AST/TypeMatcher.h

@@ -375,7 +375,8 @@ class TypeMatcher {
         if (firstFunc->isNoEscape() != secondFunc->isNoEscape())
           return mismatch(firstFunc.getPointer(), secondFunc, sugaredFirstType);
 
-        if (firstFunc->isSendable() != secondFunc->isSendable())
+        if (!Matcher.asDerived().allowSendableFunctionMismatch() &&
+            firstFunc->isSendable() != secondFunc->isSendable())
           return mismatch(firstFunc.getPointer(), secondFunc, sugaredFirstType);
 
         auto sugaredFirstFunc = sugaredFirstType->castTo<AnyFunctionType>();
@@ -554,6 +555,8 @@ class TypeMatcher {
 
   bool alwaysMismatchTypeParameters() const { return false; }
 
+  bool allowSendableFunctionMismatch() const { return false; }
+
   void pushPosition(Position pos) {}
   void popPosition(Position pos) {}
 

lib/AST/NameLookup.cpp

@@ -826,6 +826,20 @@ static void recordShadowedDeclsAfterSignatureMatch(
     else
       type = removeThrownError(decl->getInterfaceType()->getCanonicalType());
 
+    // Strip `@Sendable` annotations for declarations that come from
+    // or are exposed to Objective-C to make it possible to introduce
+    // new annotations without breaking shadowing rules.
+    //
+    // This is a narrow fix for specific backwards-incompatible cases
+    // we know about, it could be extended to use `isObjC()` in the
+    // future if we find problematic cases were a more general change
+    // is required.
+    if (decl->hasClangNode() || decl->getAttrs().hasAttribute<ObjCAttr>()) {
+      type =
+          type->stripConcurrency(/*recursive=*/true, /*dropGlobalActor=*/false)
+              ->getCanonicalType();
+    }
+
     // Record this declaration based on its signature.
     auto &known = collisions[type];
     if (known.size() == 1) {

lib/Sema/AssociatedTypeInference.cpp

@@ -2269,6 +2269,25 @@ AssociatedTypeInference::getPotentialTypeWitnessesByMatchingTypes(ValueDecl *req
       return true;
     }
 
+    bool allowSendableFunctionMismatch() const {
+      // Allow mismatches on `@Sendable` only if the witness comes
+      // from ObjC as a very narrow fix to avoid introducing new
+      // ambiguities like this:
+      //
+      // protocol P {
+      //   associatedtype T
+      //   func test(_: (T) -> Void)
+      // }
+      //
+      // struct S : P {
+      //   func test(_: @Sendable (Int) -> Void) {}
+      //   func test(_: (Int) -> Void) {}
+      // }
+      //
+      // Currently, there is only one binding for `T` - `Int`.
+      return Inferred.Witness && Inferred.Witness->hasClangNode();
+    }
+
     bool mismatch(GenericTypeParamType *selfParamType,
                   TypeBase *secondType, Type sugaredFirstType) {
       if (selfParamType->isEqual(Conformance->getProtocol()->getSelfInterfaceType())) {

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());
   }

lib/Sema/TypeCheckAttr.cpp

@@ -3873,62 +3873,106 @@ findSimilarFunction(DeclNameRef replacedFunctionName,
   // Note: we might pass a constant attribute when typechecker is nullptr.
   // Any modification to attr must be guarded by a null check on TC.
   //
-  SmallVector<ValueDecl *, 4> results;
-  lookupReplacedDecl(replacedFunctionName, attr, base, results);
+  SmallVector<ValueDecl *, 4> lookupResults;
+  lookupReplacedDecl(replacedFunctionName, attr, base, lookupResults);
 
-  for (auto *result : results) {
+  SmallVector<AbstractFunctionDecl *, 4> candidates;
+  for (auto *result : lookupResults) {
     // Protocol requirements are not replaceable.
     if (isa<ProtocolDecl>(result->getDeclContext()))
       continue;
     // Check for static/instance mismatch.
     if (result->isStatic() != base->isStatic())
       continue;
 
-    auto resultTy = result->getInterfaceType();
-    auto replaceTy = base->getInterfaceType();
-    TypeMatchOptions matchMode = TypeMatchFlags::AllowABICompatible;
-    matchMode |= TypeMatchFlags::AllowCompatibleOpaqueTypeArchetypes;
-    if (resultTy->matches(replaceTy, matchMode)) {
-      if (forDynamicReplacement && !result->isDynamic()) {
-        if (Diags) {
-          Diags->diagnose(attr->getLocation(),
-                          diag::dynamic_replacement_function_not_dynamic,
-                          result->getName());
-          attr->setInvalid();
-        }
-        return nullptr;
+    if (auto *AFD = dyn_cast<AbstractFunctionDecl>(result))
+      candidates.push_back(AFD);
+  }
+
+  if (candidates.empty()) {
+    if (Diags) {
+      Diags->diagnose(attr->getLocation(),
+                      forDynamicReplacement
+                          ? diag::dynamic_replacement_function_not_found
+                          : diag::specialize_target_function_not_found,
+                      replacedFunctionName);
+    }
+
+    attr->setInvalid();
+    return nullptr;
+  }
+
+  auto replaceTy = base->getInterfaceType();
+
+  // Filter based on the exact type match first.
+  SmallVector<AbstractFunctionDecl *> matches;
+  llvm::copy_if(candidates, std::back_inserter(matches),
+                [&replaceTy](AbstractFunctionDecl *F) {
+                  auto resultTy = F->getInterfaceType();
+                  TypeMatchOptions matchMode =
+                      TypeMatchFlags::AllowABICompatible;
+                  matchMode |=
+                      TypeMatchFlags::AllowCompatibleOpaqueTypeArchetypes;
+                  return resultTy->matches(replaceTy, matchMode);
+                });
+
+  // If there are no exact matches, strip sendability annotations
+  // from functions imported from Objective-C. This is a narrow
+  // fix for now but it could be extended to cover all `@preconcurrency`
+  // declarations.
+  if (matches.empty()) {
+    llvm::copy_if(candidates, std::back_inserter(matches),
+                  [&replaceTy](AbstractFunctionDecl *F) {
+                    if (!F->hasClangNode())
+                      return false;
+
+                    auto resultTy = F->getInterfaceType();
+                    TypeMatchOptions matchMode =
+                        TypeMatchFlags::AllowABICompatible;
+                    matchMode |=
+                        TypeMatchFlags::AllowCompatibleOpaqueTypeArchetypes;
+                    matchMode |= TypeMatchFlags::IgnoreFunctionSendability;
+                    matchMode |= TypeMatchFlags::IgnoreSendability;
+                    return resultTy->matches(replaceTy, matchMode);
+                  });
+  }
+
+  if (matches.size() == 1) {
+    auto result = matches.front();
+    if (forDynamicReplacement && !result->isDynamic()) {
+      if (Diags) {
+        Diags->diagnose(attr->getLocation(),
+                        diag::dynamic_replacement_function_not_dynamic,
+                        result->getName());
+        attr->setInvalid();
       }
-      return cast<AbstractFunctionDecl>(result);
+      return nullptr;
     }
+
+    return result;
   }
 
+  attr->setInvalid();
+
   if (!Diags)
     return nullptr;
 
-  if (results.empty()) {
-    Diags->diagnose(attr->getLocation(),
-                    forDynamicReplacement
-                        ? diag::dynamic_replacement_function_not_found
-                        : diag::specialize_target_function_not_found,
-                    replacedFunctionName);
-  } else {
-    Diags->diagnose(attr->getLocation(),
-                    forDynamicReplacement
-                        ? diag::dynamic_replacement_function_of_type_not_found
-                        : diag::specialize_target_function_of_type_not_found,
-                    replacedFunctionName,
-                    base->getInterfaceType()->getCanonicalType());
+  Diags->diagnose(attr->getLocation(),
+                  forDynamicReplacement
+                      ? diag::dynamic_replacement_function_of_type_not_found
+                      : diag::specialize_target_function_of_type_not_found,
+                  replacedFunctionName,
+                  base->getInterfaceType()->getCanonicalType());
 
-    for (auto *result : results) {
-      Diags->diagnose(SourceLoc(),
-                      forDynamicReplacement
-                          ? diag::dynamic_replacement_found_function_of_type
-                          : diag::specialize_found_function_of_type,
-                      result->getName(),
-                      result->getInterfaceType()->getCanonicalType());
-    }
+  for (auto *result : matches) {
+    Diags->diagnose(SourceLoc(),
+                    forDynamicReplacement
+                        ? diag::dynamic_replacement_found_function_of_type
+                        : diag::specialize_found_function_of_type,
+                    result->getName(),
+                    result->getInterfaceType()->getCanonicalType());
   }
-  attr->setInvalid();
+
   return nullptr;
 }