[Concurrency] Distributed actor's unownedExecutor should be optional

include/swift/AST/Decl.h

@@ -4533,6 +4533,7 @@ class ClassDecl final : public NominalTypeDecl {
 
   /// Fetch this class's unownedExecutor property, if it has one.
   const VarDecl *getUnownedExecutorProperty() const;
+  const VarDecl *getLocalUnownedExecutorProperty() const;
 
   /// Is this the NSObject class type?
   bool isNSObject() const;

include/swift/AST/KnownIdentifiers.def

@@ -231,6 +231,8 @@ IDENTIFIER(className)
 IDENTIFIER(_defaultActorInitialize)
 IDENTIFIER(_defaultActorDestroy)
 IDENTIFIER(unownedExecutor)
+IDENTIFIER(localUnownedExecutor)
+IDENTIFIER(_unwrapLocalUnownedExecutor)
 
 IDENTIFIER_(ErrorType)
 IDENTIFIER(Code)

include/swift/AST/KnownSDKDecls.def

@@ -20,6 +20,7 @@
 #endif
 
 KNOWN_SDK_FUNC_DECL(Distributed, IsRemoteDistributedActor, "__isRemoteActor")
+KNOWN_SDK_FUNC_DECL(Distributed, IsLocalDistributedActor, "__isLocalActor")
 
 #undef KNOWN_SDK_FUNC_DECL
 

include/swift/SIL/SILFunction.h

@@ -1273,6 +1273,7 @@ class SILFunction
   const SILBasicBlock *getEntryBlock() const { return &front(); }
 
   SILBasicBlock *createBasicBlock();
+  SILBasicBlock *createBasicBlock(llvm::StringRef debugName);
   SILBasicBlock *createBasicBlockAfter(SILBasicBlock *afterBB);
   SILBasicBlock *createBasicBlockBefore(SILBasicBlock *beforeBB);
 

lib/AST/Decl.cpp

@@ -9625,6 +9625,29 @@ const VarDecl *ClassDecl::getUnownedExecutorProperty() const {
   return nullptr;
 }
 
+const VarDecl *ClassDecl::getLocalUnownedExecutorProperty() const {
+  auto &C = getASTContext();
+
+  if (!isDistributedActor())
+    return nullptr;
+
+  llvm::SmallVector<ValueDecl *, 2> results;
+  this->lookupQualified(getSelfNominalTypeDecl(),
+                        DeclNameRef(C.Id_localUnownedExecutor),
+                        NL_ProtocolMembers,
+                        results);
+
+  for (auto candidate: results) {
+    if (isa<ProtocolDecl>(candidate->getDeclContext()))
+      continue;
+
+    if (VarDecl *var = dyn_cast<VarDecl>(candidate))
+      return var;
+  }
+
+  return nullptr;
+}
+
 bool ClassDecl::isRootDefaultActor() const {
   return isRootDefaultActor(getModuleContext(), ResilienceExpansion::Maximal);
 }

lib/SIL/IR/SILFunction.cpp

@@ -533,6 +533,13 @@ SILBasicBlock *SILFunction::createBasicBlock() {
   return newBlock;
 }
 
+SILBasicBlock *SILFunction::createBasicBlock(llvm::StringRef debugName) {
+  SILBasicBlock *newBlock = new (getModule()) SILBasicBlock(this);
+  newBlock->setDebugName(debugName);
+  BlockList.push_back(newBlock);
+  return newBlock;
+}
+
 SILBasicBlock *SILFunction::createBasicBlockAfter(SILBasicBlock *afterBB) {
   SILBasicBlock *newBlock = new (getModule()) SILBasicBlock(this);
   BlockList.insertAfter(afterBB->getIterator(), newBlock);

lib/SILOptimizer/Mandatory/LowerHopToActor.cpp

@@ -154,6 +154,28 @@ static AccessorDecl *getUnownedExecutorGetter(ASTContext &ctx,
   return nullptr;
 }
 
+static AccessorDecl *getUnwrapLocalUnownedExecutorGetter(ASTContext &ctx,
+                                              ProtocolDecl *actorProtocol) {
+  for (auto member: actorProtocol->getAllMembers()) { // FIXME: remove this, just go to the extension
+    if (auto var = dyn_cast<VarDecl>(member)) {
+      if (var->getName() == ctx.Id__unwrapLocalUnownedExecutor)
+        return var->getAccessor(AccessorKind::Get);
+    }
+  }
+
+  for (auto extension: actorProtocol->getExtensions()) {
+    for (auto member: extension->getAllMembers()) {
+      if (auto var = dyn_cast<VarDecl>(member)) {
+        if (var->getName() == ctx.Id__unwrapLocalUnownedExecutor) {
+          return var->getAccessor(AccessorKind::Get);
+        }
+      }
+    }
+  }
+
+  return nullptr;
+}
+
 SILValue LowerHopToActor::emitGetExecutor(SILBuilderWithScope &B,
                                           SILLocation loc, SILValue actor,
                                           bool makeOptional) {
@@ -186,11 +208,36 @@ SILValue LowerHopToActor::emitGetExecutor(SILBuilderWithScope &B,
     unmarkedExecutor =
       B.createBuiltin(loc, builtinName, resultType, subs, {actor});
 
-  // Otherwise, go through Actor.unownedExecutor.
+    // Otherwise, go through Actor.unownedExecutor.
+  } else if (actorType->isDistributedActor()) {
+    auto actorKind = KnownProtocolKind::DistributedActor;
+    auto actorProtocol = ctx.getProtocol(actorKind);
+    auto req = getUnwrapLocalUnownedExecutorGetter(ctx, actorProtocol);
+    assert(req && "Distributed library broken");
+    SILDeclRef fn(req, SILDeclRef::Kind::Func);
+
+    auto actorConf = module->lookupConformance(actorType, actorProtocol);
+    assert(actorConf &&
+           "hop_to_executor with distributed actor that doesn't conform to DistributedActor");
+
+    auto subs = SubstitutionMap::get(req->getGenericSignature(),
+                                     {actorType}, {actorConf});
+    auto fnType = F->getModule().Types.getConstantFunctionType(*F, fn);
+
+    auto witness =
+      B.createWitnessMethod(loc, actorType, actorConf, fn,
+                            SILType::getPrimitiveObjectType(fnType));
+    auto witnessCall = B.createApply(loc, witness, subs, {actor});
+
+    // The protocol requirement returns an Optional<UnownedSerialExecutor>;
+    // extract the Builtin.Executor from it.
+    auto executorDecl = ctx.getUnownedSerialExecutorDecl();
+    auto executorProps = executorDecl->getStoredProperties();
+    assert(executorProps.size() == 1);
+    unmarkedExecutor =
+      B.createStructExtract(loc, witnessCall, executorProps[0]);
   } else {
-    auto actorKind = actorType->isDistributedActor() ?
-                     KnownProtocolKind::DistributedActor :
-                     KnownProtocolKind::Actor;
+    auto actorKind = KnownProtocolKind::Actor;
     auto actorProtocol = ctx.getProtocol(actorKind);
     auto req = getUnownedExecutorGetter(ctx, actorProtocol);
     assert(req && "Concurrency library broken");

lib/Sema/DerivedConformanceDistributedActor.cpp

@@ -621,10 +621,13 @@ static Expr *constructDistributedUnownedSerialExecutor(ASTContext &ctx,
 }
 
 static std::pair<BraceStmt *, bool>
-deriveBodyDistributedActor_unownedExecutor(AbstractFunctionDecl *getter, void *) {
-  // var unownedExecutor: UnownedSerialExecutor {
+deriveBodyDistributedActor_localUnownedExecutor(AbstractFunctionDecl *getter, void *) {
+  // var localUnownedExecutor: UnownedSerialExecutor? {
   //   get {
-  //     return Builtin.buildDefaultActorExecutorRef(self)
+  //     guard __isLocalActor(self) else {
+  //       return nil
+  //     }
+  //     return Optional(Builtin.buildDefaultActorExecutorRef(self))
   //   }
   // }
   ASTContext &ctx = getter->getASTContext();
@@ -641,33 +644,53 @@ deriveBodyDistributedActor_unownedExecutor(AbstractFunctionDecl *getter, void *)
   Expr *selfArg = DerivedConformance::createSelfDeclRef(getter);
   selfArg->setType(selfType);
 
+  // Prepare the builtin call, we'll use it after the guard, but want to take the type
+  // of its return type earlier, so we prepare it here.
+
   // The builtin call gives us a Builtin.Executor.
   auto builtinCall =
       DerivedConformance::createBuiltinCall(ctx,
                                             BuiltinValueKind::BuildDefaultActorExecutorRef,
                                             {selfType}, {}, {selfArg});
-
   // Turn that into an UnownedSerialExecutor.
   auto initCall = constructDistributedUnownedSerialExecutor(ctx, builtinCall);
   if (!initCall) return failure();
 
-  auto ret = new (ctx) ReturnStmt(SourceLoc(), initCall, /*implicit*/ true);
+  // guard __isLocalActor(self) else {
+  //   return nil
+  // }
+  auto isLocalActorDecl = ctx.getIsLocalDistributedActor();
+  DeclRefExpr *isLocalActorExpr =
+      new (ctx) DeclRefExpr(ConcreteDeclRef(isLocalActorDecl), DeclNameLoc(), /*implicit=*/true,
+                            AccessSemantics::Ordinary,
+                            FunctionType::get({AnyFunctionType::Param(ctx.getAnyObjectType())},
+                                              ctx.getBoolType()));
+  Expr *selfForIsLocalArg = DerivedConformance::createSelfDeclRef(getter);
+  selfForIsLocalArg->setType(selfType);
+  auto *argListForIsLocal =
+      ArgumentList::forImplicitSingle(ctx, Identifier(),
+                                      ErasureExpr::create(ctx, selfForIsLocalArg, ctx.getAnyObjectType(), {}, {}));
+  CallExpr *isLocalActorCall = CallExpr::createImplicit(ctx, isLocalActorExpr, argListForIsLocal);
+  isLocalActorCall->setType(ctx.getBoolType());
+  isLocalActorCall->setThrows(false);
+  auto returnNilIfRemoteStmt = DerivedConformance::returnNilIfFalseGuardTypeChecked(
+      ctx, isLocalActorCall, /*optionalWrappedType=*/initCall->getType());
+
+
+  // Finalize preparing the unowned executor for returning.
+  auto wrappedCall = new (ctx) InjectIntoOptionalExpr(initCall, initCall->getType()->wrapInOptionalType());
+
+  auto ret = new (ctx) ReturnStmt(SourceLoc(), wrappedCall, /*implicit*/ true);
 
   auto body = BraceStmt::create(
-      ctx, SourceLoc(), { ret }, SourceLoc(), /*implicit=*/true);
+      ctx, SourceLoc(), { returnNilIfRemoteStmt, ret }, SourceLoc(), /*implicit=*/true);
   return { body, /*isTypeChecked=*/true };
 }
 
-/// Derive the declaration of DistributedActor's unownedExecutor property.
-static ValueDecl *deriveDistributedActor_unownedExecutor(DerivedConformance &derived) {
+/// Derive the declaration of DistributedActor's localUnownedExecutor property.
+static ValueDecl *deriveDistributedActor_localUnownedExecutor(DerivedConformance &derived) {
   ASTContext &ctx = derived.Context;
 
-  if (auto classDecl = dyn_cast<ClassDecl>(derived.Nominal)) {
-    if (auto existing = classDecl->getUnownedExecutorProperty()) {
-      return const_cast<VarDecl*>(existing);
-    }
-  }
-
   // Retrieve the types and declarations we'll need to form this operation.
   auto executorDecl = ctx.getUnownedSerialExecutorDecl();
   if (!executorDecl) {
@@ -676,16 +699,28 @@ static ValueDecl *deriveDistributedActor_unownedExecutor(DerivedConformance &der
     return nullptr;
   }
   Type executorType = executorDecl->getDeclaredInterfaceType();
+  Type optionalExecutorType = executorType->wrapInOptionalType();
+
+  if (auto classDecl = dyn_cast<ClassDecl>(derived.Nominal)) {
+    if (auto existing = classDecl->getLocalUnownedExecutorProperty()) {
+      if (existing->getInterfaceType()->isEqual(optionalExecutorType)) {
+        return const_cast<VarDecl *>(existing);
+      } else {
+        // bad type, should be diagnosed elsewhere
+        return nullptr;
+      }
+    }
+  }
 
   auto propertyPair = derived.declareDerivedProperty(
-      DerivedConformance::SynthesizedIntroducer::Var, ctx.Id_unownedExecutor,
-      executorType, executorType,
+      DerivedConformance::SynthesizedIntroducer::Var, ctx.Id_localUnownedExecutor,
+      optionalExecutorType, optionalExecutorType,
       /*static*/ false, /*final*/ false);
   auto property = propertyPair.first;
   property->setSynthesized(true);
   property->getAttrs().add(new (ctx) SemanticsAttr(SEMANTICS_DEFAULT_ACTOR,
                                                    SourceLoc(), SourceRange(),
-      /*implicit*/ true));
+                                                   /*implicit*/ true));
   property->getAttrs().add(new (ctx) NonisolatedAttr(/*IsImplicit=*/true));
 
   // Make the property implicitly final.
@@ -703,8 +738,8 @@ static ValueDecl *deriveDistributedActor_unownedExecutor(DerivedConformance &der
       property, asAvailableAs, ctx);
 
   auto getter =
-      derived.addGetterToReadOnlyDerivedProperty(property, executorType);
-  getter->setBodySynthesizer(deriveBodyDistributedActor_unownedExecutor);
+      derived.addGetterToReadOnlyDerivedProperty(property, optionalExecutorType);
+  getter->setBodySynthesizer(deriveBodyDistributedActor_localUnownedExecutor);
 
   // IMPORTANT: MUST BE AFTER [id, actorSystem].
   if (auto id = derived.Nominal->getDistributedActorIDProperty()) {
@@ -747,24 +782,24 @@ static void assertRequiredSynthesizedPropertyOrder(DerivedConformance &derived,
     if (auto id = Nominal->getDistributedActorIDProperty()) {
       if (auto system = Nominal->getDistributedActorSystemProperty()) {
         if (auto classDecl = dyn_cast<ClassDecl>(derived.Nominal)) {
-          if (auto unownedExecutor = classDecl->getUnownedExecutorProperty()) {
-            int idIdx, actorSystemIdx, unownedExecutorIdx = 0;
+          if (auto localUnownedExecutor = classDecl->getLocalUnownedExecutorProperty()) {
+            int idIdx, actorSystemIdx, localUnownedExecutorIdx = 0;
             int idx = 0;
             for (auto member: Nominal->getMembers()) {
               if (auto binding = dyn_cast<PatternBindingDecl>(member)) {
                 if (binding->getSingleVar()->getName() == Context.Id_id) {
                   idIdx = idx;
                 } else if (binding->getSingleVar()->getName() == Context.Id_actorSystem) {
                   actorSystemIdx = idx;
-                } else if (binding->getSingleVar()->getName() == Context.Id_unownedExecutor) {
-                  unownedExecutorIdx = idx;
+                } else if (binding->getSingleVar()->getName() == Context.Id_localUnownedExecutor) {
+                  localUnownedExecutorIdx = idx;
                 }
                 idx += 1;
               }
             }
-            if (idIdx + actorSystemIdx + unownedExecutorIdx >= 0 + 1 + 2) {
+            if (idIdx + actorSystemIdx + localUnownedExecutorIdx >= 0 + 1 + 2) {
               // we have found all the necessary fields, let's assert their order
-              assert(idIdx < actorSystemIdx < unownedExecutorIdx && "order of fields MUST be exact.");
+              assert(idIdx < actorSystemIdx < localUnownedExecutorIdx && "order of fields MUST be exact.");
             }
           }
         }
@@ -786,8 +821,8 @@ ValueDecl *DerivedConformance::deriveDistributedActor(ValueDecl *requirement) {
       derivedValue = deriveDistributedActor_id(*this);
     } else if (var->getName() == Context.Id_actorSystem) {
       derivedValue = deriveDistributedActor_actorSystem(*this);
-    } else if (var->getName() == Context.Id_unownedExecutor) {
-      derivedValue = deriveDistributedActor_unownedExecutor(*this);
+    } else if (var->getName() == Context.Id_localUnownedExecutor) {
+      derivedValue = deriveDistributedActor_localUnownedExecutor(*this);
     }
 
     assertRequiredSynthesizedPropertyOrder(*this, derivedValue);

lib/Sema/DerivedConformances.cpp

@@ -335,11 +335,7 @@ ValueDecl *DerivedConformance::getDerivableRequirement(NominalTypeDecl *nominal,
 
     // Actor.unownedExecutor
     if (name.isSimpleName(ctx.Id_unownedExecutor)) {
-      if (nominal->isDistributedActor()) {
-        return getRequirement(KnownProtocolKind::DistributedActor);
-      } else {
-        return getRequirement(KnownProtocolKind::Actor);
-      }
+      return getRequirement(KnownProtocolKind::Actor);
     }
 
     // DistributedActor.id
@@ -350,6 +346,11 @@ ValueDecl *DerivedConformance::getDerivableRequirement(NominalTypeDecl *nominal,
     if (name.isSimpleName(ctx.Id_actorSystem))
       return getRequirement(KnownProtocolKind::DistributedActor);
 
+    // DistributedActor.localUnownedExecutor
+    if (name.isSimpleName(ctx.Id_localUnownedExecutor)) {
+      return getRequirement(KnownProtocolKind::DistributedActor);
+    }
+
     return nullptr;
   }
 
@@ -674,6 +675,36 @@ GuardStmt *DerivedConformance::returnFalseIfNotEqualGuard(ASTContext &C,
   auto falseExpr = new (C) BooleanLiteralExpr(false, SourceLoc(), true);
   return returnIfNotEqualGuard(C, lhsExpr, rhsExpr, falseExpr);
 }
+/// Returns a generated guard statement that checks whether the given expr is true.
+/// If it is false, the else block for the guard returns `nil`.
+/// \p C The AST context.
+/// \p testExpr The expression that should be tested.
+/// \p baseType The wrapped type of the to-be-returned Optional<Wrapped>.
+GuardStmt *DerivedConformance::returnNilIfFalseGuardTypeChecked(ASTContext &C,
+                                        Expr *testExpr,
+                                        Type optionalWrappedType) {
+  auto nilExpr = new (C) NilLiteralExpr(SourceLoc(), /*implicit=*/true);
+  nilExpr->setType(optionalWrappedType->wrapInOptionalType());
+
+  SmallVector<StmtConditionElement, 1> conditions;
+  SmallVector<ASTNode, 1> statements;
+
+  auto returnStmt = new (C) ReturnStmt(SourceLoc(), nilExpr);
+  statements.push_back(returnStmt);
+
+  // Next, generate the condition being checked.
+//  auto cmpFuncExpr = new (C) UnresolvedDeclRefExpr(
+//      DeclNameRef(C.Id_EqualsOperator), DeclRefKind::BinaryOperator,
+//      DeclNameLoc());
+//  auto *cmpExpr = BinaryExpr::create(C, lhsExpr, cmpFuncExpr, rhsExpr,
+//      /*implicit*/ true);
+  conditions.emplace_back(testExpr);
+
+  // Build and return the complete guard statement.
+  // guard lhs == rhs else { return lhs < rhs }
+  auto body = BraceStmt::create(C, SourceLoc(), statements, SourceLoc());
+  return new (C) GuardStmt(SourceLoc(), C.AllocateCopy(conditions), body);
+}
 /// Returns a generated guard statement that checks whether the given lhs and
 /// rhs expressions are equal. If not equal, the else block for the guard
 /// returns lhs < rhs.

lib/Sema/DerivedConformances.h

@@ -409,6 +409,12 @@ class DerivedConformance {
   // return false
   static GuardStmt *returnFalseIfNotEqualGuard(ASTContext &C, Expr *lhsExpr,
                                                Expr *rhsExpr);
+
+  // Return `nil` is the `testExp` is `false`.
+  static GuardStmt *returnNilIfFalseGuardTypeChecked(ASTContext &C,
+                                                     Expr *testExpr,
+                                                     Type optionalWrappedType);
+
   // return lhs < rhs
   static GuardStmt *
   returnComparisonIfNotEqualGuard(ASTContext &C, Expr *lhsExpr, Expr *rhsExpr);