swift-mirror/lib/Sema/CodeSynthesisDistributedActor.cpp

//===--- CodeSynthesis.cpp - Type Checking for Declarations ---------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#include "CodeSynthesis.h"

#include "TypeChecker.h"
#include "TypeCheckDecl.h"
#include "TypeCheckObjC.h"
#include "TypeCheckType.h"
#include "swift/AST/ASTPrinter.h"
#include "swift/AST/Availability.h"
#include "swift/AST/Expr.h"
#include "swift/AST/GenericEnvironment.h"
#include "swift/AST/Initializer.h"
#include "swift/AST/ParameterList.h"
#include "swift/AST/PrettyStackTrace.h"
#include "swift/AST/ProtocolConformance.h"
#include "swift/AST/SourceFile.h"
#include "swift/AST/TypeCheckRequests.h"
#include "swift/Basic/Defer.h"
#include "swift/ClangImporter/ClangModule.h"
#include "swift/Sema/ConstraintSystem.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
#include "DerivedConformances.h"
using namespace swift;

/******************************************************************************/
/******************************* INITIALIZERS *********************************/
/******************************************************************************/

// ==== Distributed Actor: Local Initializer -----------------------------------

/// Creates a new \c CallExpr representing
///
///     transport.assignAddress(Self.self)
///
/// \param C The AST context to create the expression in.
/// \param DC The \c DeclContext to create any decls in.
/// \param base The base expression to make the call on.
/// \param returnType The return type of the call.
/// \param param The parameter to the call.
static CallExpr *
createCall_DistributedActor_transport_assignAddress(ASTContext &C,
                                                    DeclContext *DC,
                                                    Expr *base, Type returnType,
                                                    Type param) {
  // (_ actorType:)
  auto *paramDecl = new (C) ParamDecl(SourceLoc(),
                                      SourceLoc(), Identifier(),
                                      SourceLoc(), C.Id_actorType, DC);
  paramDecl->setImplicit();
  paramDecl->setSpecifier(ParamSpecifier::Default);
  paramDecl->setInterfaceType(returnType);

  // transport.assignAddress(_:) expr
  auto *paramList = ParameterList::createWithoutLoc(paramDecl);
  auto *unboundCall = UnresolvedDotExpr::createImplicit(C, base,
                                                        C.Id_assignAddress,
                                                        paramList);

  // DC->mapTypeIntoContext(param->getInterfaceType());
  auto *selfTypeExpr = TypeExpr::createImplicit(param, C);
  auto *dotSelfTypeExpr = new (C) DotSelfExpr(selfTypeExpr, SourceLoc(),
                                              SourceLoc(), param);

  // Full bound self.assignAddress(Self.self) call
  Expr *args[1] = {dotSelfTypeExpr};
  Identifier argLabels[1] = {Identifier()};
  return CallExpr::createImplicit(C, unboundCall, C.AllocateCopy(args),
                                  C.AllocateCopy(argLabels));
}


/// Creates a new \c CallExpr representing
///
///     transport.actorReady(self)
static CallExpr *
createCall_DistributedActor_transport_actorReady(ASTContext &C,
                                                 DeclContext *DC,
                                                 Expr *base, Type actorType,
                                                 Expr *initalizedSelf) {
  // (_ actor:)
  auto *paramDecl = new (C) ParamDecl(SourceLoc(),
                                      SourceLoc(), Identifier(),
                                      SourceLoc(), C.Id_actor, DC);
  paramDecl->setImplicit();
  paramDecl->setSpecifier(ParamSpecifier::Default);
  paramDecl->setInterfaceType(actorType);

  // transport.actorReady(_:) expr
  auto *paramList = ParameterList::createWithoutLoc(paramDecl);
  auto *unboundCall = UnresolvedDotExpr::createImplicit(C, base,
                                                        C.Id_actorReady,
                                                        paramList);

  // Full bound transport.actorReady(self) call
  Expr *args[1] = {initalizedSelf};
  Identifier argLabels[1] = {Identifier()};
  return CallExpr::createImplicit(C, unboundCall, C.AllocateCopy(args),
                                  C.AllocateCopy(argLabels));
}

/// Synthesizes the body of the `init(transport:)` initializer as:
///
/// ```
/// init(transport: ActorTransport)
///   self.actorTransport = transport
///   self.actorAddress = try transport.assignAddress(Self.self)
/// }
/// ```
///
/// \param initDecl The function decl whose body to synthesize.
static std::pair<BraceStmt *, bool>
createBody_DistributedActor_init_transport(AbstractFunctionDecl *initDecl, void *) {

  auto *funcDC = cast<DeclContext>(initDecl);
  ASTContext &C = funcDC->getASTContext();

  SmallVector<ASTNode, 2> statements;

  auto transportParam = initDecl->getParameters()->get(0);
  auto *transportExpr = new (C) DeclRefExpr(ConcreteDeclRef(transportParam),
                                            DeclNameLoc(), /*Implicit=*/true);

  auto *selfRef = DerivedConformance::createSelfDeclRef(initDecl);

  // ==== `self.actorTransport = transport`
  {
    // self.actorTransport
    auto *varTransportExpr = UnresolvedDotExpr::createImplicit(C, selfRef,
                                                               C.Id_actorTransport);
    auto *assignTransportExpr = new (C) AssignExpr(
        varTransportExpr, SourceLoc(), transportExpr, /*Implicit=*/true);
    statements.push_back(assignTransportExpr);
  }

  auto selfType = funcDC->getInnermostTypeContext()->getSelfTypeInContext();

  // ==== `self.actorAddress = transport.assignAddress<Self>(Self.self)`
  {
    // self.actorAddress
    auto *varAddressExpr = UnresolvedDotExpr::createImplicit(C, selfRef,
                                                             C.Id_actorAddress);
    // Bound transport.assignAddress(Self.self) call
    auto addressType = C.getActorAddressDecl()->getDeclaredInterfaceType();
    auto *callExpr = createCall_DistributedActor_transport_assignAddress(C, funcDC,
                                                                         /*base=*/transportExpr,
                                                                         /*returnType=*/addressType,
                                                                         /*param=*/selfType);
    auto *assignAddressExpr = new (C) AssignExpr(
        varAddressExpr, SourceLoc(), callExpr, /*Implicit=*/true);
    statements.push_back(assignAddressExpr);
  }

  // ---=== Done initializing ===---
  // === `transport.actorReady(self)`
  {
    // Bound transport.actorReady(self) call
    auto selfType = funcDC->getInnermostTypeContext()->getSelfTypeInContext();
    auto *callExpr = createCall_DistributedActor_transport_actorReady(C, funcDC,
                                                                      /*base=*/transportExpr,
                                                                      /*actorType=*/selfType,
                                                                      /*param=*/selfRef);
    statements.push_back(callExpr);
  }

  auto *body = BraceStmt::create(C, SourceLoc(), statements, SourceLoc(),
                                 /*implicit=*/true);
  return { body, /*isTypeChecked=*/false };
}

/// Synthesizes the
///
/// ```
/// init(transport: ActorTransport)
/// ```
///
/// local initializer.
static ConstructorDecl *
createDistributedActor_init_local(ClassDecl *classDecl,
                                  ASTContext &ctx) {
  auto &C = ctx;

  //  auto conformanceDC = derived.getConformanceContext();
  auto conformanceDC = classDecl;

  // Expected type: (Self) -> (ActorTransport) -> (Self)
  //
  // Params: (transport transport: ActorTransport)
  auto transportType = C.getActorTransportDecl()->getDeclaredInterfaceType();
  auto *transportParamDecl = new (C) ParamDecl(
      SourceLoc(), SourceLoc(), C.Id_transport,
      SourceLoc(), C.Id_transport, conformanceDC);
  transportParamDecl->setImplicit();
  transportParamDecl->setSpecifier(ParamSpecifier::Default);
  transportParamDecl->setInterfaceType(transportType);

  auto *paramList = ParameterList::createWithoutLoc(transportParamDecl);

  // Func name: init(transport:)
  DeclName name(C, DeclBaseName::createConstructor(), paramList);

  auto *initDecl =
      new (C) ConstructorDecl(name, SourceLoc(),
                              /*Failable=*/false, SourceLoc(),
                              /*Async=*/false, SourceLoc(),
                              /*Throws=*/false, SourceLoc(),
                              paramList,
                              /*GenericParams=*/nullptr, conformanceDC);
  initDecl->setImplicit();
  initDecl->setSynthesized();
  initDecl->setBodySynthesizer(&createBody_DistributedActor_init_transport);

  // This constructor is 'required', all distributed actors MUST invoke it.
  auto *reqAttr = new (C) RequiredAttr(/*IsImplicit*/true);
  initDecl->getAttrs().add(reqAttr);

  auto *nonIsoAttr = new (C) NonisolatedAttr(/*IsImplicit*/true);
  initDecl->getAttrs().add(nonIsoAttr);

  initDecl->copyFormalAccessFrom(classDecl, /*sourceIsParentContext=*/true);

  return initDecl;
}

// ==== Distributed Actor: Resolve Initializer ---------------------------------

/// Synthesizes the body for
///
/// ```
/// init(resolve address: ActorAddress, using transport: ActorTransport) throws {
///   // TODO: implement calling the transport
///   switch try transport.resolve(address: address, as: Self.self) {
///   case .instance(let instance):
///     self = instance
///   case .makeProxy:
///   // TODO: use RebindSelfInConstructorExpr here?
///     self = <<MAGIC MAKE PROXY>>(address, transport) // TODO: implement this
///   }
/// }
/// ```
///
/// \param initDecl The function decl whose body to synthesize.
static std::pair<BraceStmt *, bool>
createDistributedActor_init_resolve_body(AbstractFunctionDecl *initDecl, void *) {

  auto *funcDC = cast<DeclContext>(initDecl);
  auto &C = funcDC->getASTContext();

  SmallVector<ASTNode, 2> statements; // TODO: how many?

  auto addressParam = initDecl->getParameters()->get(0);
  auto *addressExpr = new (C) DeclRefExpr(ConcreteDeclRef(addressParam),
                                          DeclNameLoc(), /*Implicit=*/true);

  auto transportParam = initDecl->getParameters()->get(1);
  auto *transportExpr = new (C) DeclRefExpr(ConcreteDeclRef(transportParam),
                                            DeclNameLoc(), /*Implicit=*/true);

  auto *selfRef = DerivedConformance::createSelfDeclRef(initDecl);

  // ==== `self.actorTransport = transport`
  auto *varTransportExpr = UnresolvedDotExpr::createImplicit(C, selfRef,
                                                             C.Id_actorTransport);
  auto *assignTransportExpr = new (C) AssignExpr(
      varTransportExpr, SourceLoc(), transportExpr, /*Implicit=*/true);
  statements.push_back(assignTransportExpr);

  // ==== `self.actorAddress = transport.assignAddress<Self>(Self.self)`
  // self.actorAddress
  auto *varAddressExpr = UnresolvedDotExpr::createImplicit(C, selfRef,
                                                           C.Id_actorAddress);
  // TODO implement calling the transport with the address and Self.self
  // FIXME: this must be checking with the transport instead
  auto *assignAddressExpr = new (C) AssignExpr(
      varAddressExpr, SourceLoc(), addressExpr, /*Implicit=*/true);
  statements.push_back(assignAddressExpr);
  // end-of-FIXME: this must be checking with the transport instead

  auto *body = BraceStmt::create(C, SourceLoc(), statements, SourceLoc(),
                                 /*implicit=*/true);

  return { body, /*isTypeChecked=*/false };
}

/// Synthesizes the
///
/// ```
/// init(resolve address: ActorAddress, using transport: ActorTransport) throws
/// ```
///
/// resolve initializer.
static ConstructorDecl *
createDistributedActor_init_resolve(ClassDecl *classDecl,
                                    ASTContext &ctx) {
  auto &C = ctx;

  auto conformanceDC = classDecl;

  // Expected type: (Self) -> (ActorAddress, ActorTransport) -> (Self)
  //
  // Param: (resolve address: ActorAddress)
  auto addressType = C.getActorAddressDecl()->getDeclaredInterfaceType();
  auto *addressParamDecl = new (C) ParamDecl(
      SourceLoc(), SourceLoc(), C.Id_resolve,
      SourceLoc(), C.Id_address, conformanceDC);
  addressParamDecl->setImplicit();
  addressParamDecl->setSpecifier(ParamSpecifier::Default);
  addressParamDecl->setInterfaceType(addressType);

  // Param: (using transport: ActorTransport)
  auto transportType = C.getActorTransportDecl()->getDeclaredInterfaceType();
  auto *transportParamDecl = new (C) ParamDecl(
      SourceLoc(), SourceLoc(), C.Id_using,
      SourceLoc(), C.Id_transport, conformanceDC);
  transportParamDecl->setImplicit();
  transportParamDecl->setSpecifier(ParamSpecifier::Default);
  transportParamDecl->setInterfaceType(transportType);

  auto *paramList = ParameterList::create(
      C,
      /*LParenLoc=*/SourceLoc(),
      /*params=*/{addressParamDecl, transportParamDecl},
      /*RParenLoc=*/SourceLoc()
      );

  // Func name: init(resolve:using:)
  DeclName name(C, DeclBaseName::createConstructor(), paramList);

  auto *initDecl =
      new (C) ConstructorDecl(name, SourceLoc(),
                              /*Failable=*/false, SourceLoc(),
                              /*Async=*/false, SourceLoc(),
                              /*Throws=*/true, SourceLoc(),
                              paramList,
                              /*GenericParams=*/nullptr, conformanceDC);
  initDecl->setImplicit();
  initDecl->setSynthesized();
  initDecl->setBodySynthesizer(&createDistributedActor_init_resolve_body);

  // This constructor is 'required', all distributed actors MUST have it.
  initDecl->getAttrs().add(new (C) RequiredAttr(/*IsImplicit*/true));

  auto *nonIsoAttr = new (C) NonisolatedAttr(/*IsImplicit*/true);
  initDecl->getAttrs().add(nonIsoAttr);

  initDecl->copyFormalAccessFrom(classDecl, /*sourceIsParentContext=*/true);

  return initDecl;
}

/// Detects which initializer to create, and does so.
static ConstructorDecl *
createDistributedActorInit(ClassDecl *classDecl,
                           ConstructorDecl *requirement,
                           ASTContext &ctx) {
  assert(classDecl->isDistributedActor());

  const auto name = requirement->getName();
  auto argumentNames = name.getArgumentNames();

  switch (argumentNames.size()) {
  case 1: {
    if (requirement->isDistributedActorLocalInit()) {
      return createDistributedActor_init_local(classDecl, ctx);
    }

    break;
  }
  case 2: {
    if (requirement->isDistributedActorResolveInit()) {
      return createDistributedActor_init_resolve(classDecl, ctx);
    }

    break;
  }
  }

  return nullptr;
}

static void collectNonOveriddenDistributedActorInits(
    ASTContext& Context,
    ClassDecl *actorDecl,
    SmallVectorImpl<ConstructorDecl *> &results) {
  assert(actorDecl->isDistributedActor());
  auto protoDecl = Context.getProtocol(KnownProtocolKind::DistributedActor);

  //  // Record all of the initializers the actorDecl has implemented.
  //  llvm::SmallPtrSet<ConstructorDecl *, 4> overriddenInits;
  //  for (auto member : actorDecl->getMembers())
  //    if (auto ctor = dyn_cast<ConstructorDecl>(member))
  //      if (!ctor->hasStubImplementation())
  //         // if (auto overridden = ctor->getOverriddenDecl())
  //          overriddenInits.insert(ctor);
  //
  //  actorDecl->synthesizeSemanticMembersIfNeeded(
  //    DeclBaseName::createConstructor());

  NLOptions subOptions = (NL_QualifiedDefault | NL_IgnoreAccessControl);
  SmallVector<ValueDecl *, 4> lookupResults;
  actorDecl->lookupQualified(
      protoDecl, DeclNameRef::createConstructor(),
      subOptions, lookupResults);

  for (auto decl : lookupResults) {
    // Distributed Actor Constructor
    auto daCtor = cast<ConstructorDecl>(decl);

    // TODO: Don't require it if overriden
    //    if (!overriddenInits.count(daCtor))
    results.push_back(daCtor);
  }
}


/// For a distributed actor, automatically define initializers
/// that match the DistributedActor requirements.
// TODO: inheritance is tricky here?
static void addImplicitDistributedActorConstructors(ClassDecl *decl) {
  // Bail out if not a distributed actor definition.
  if (!decl->isDistributedActor())
    return;

  for (auto member : decl->getMembers()) {
    if (auto ctor = dyn_cast<ConstructorDecl>(member)) {
      if (ctor->isRecursiveValidation())
        return;
    }
  }

  decl->setAddedImplicitInitializers();

  // Check whether the user has defined a designated initializer for this class,
  // and whether all of its stored properties have initial values.
  auto &ctx = decl->getASTContext();
  //  bool foundDesignatedInit = hasUserDefinedDesignatedInit(ctx.evaluator, decl);
  //  bool defaultInitable =
  //      areAllStoredPropertiesDefaultInitializable(ctx.evaluator, decl);
  //
  //  // We can't define these overrides if we have any uninitialized
  //  // stored properties.
  //  if (!defaultInitable && !foundDesignatedInit)
  //    return;

  SmallVector<ConstructorDecl *, 4> nonOverridenCtors;
  collectNonOveriddenDistributedActorInits(
      ctx, decl, nonOverridenCtors);

  for (auto *daCtor : nonOverridenCtors) {
    if (auto ctor = createDistributedActorInit(decl, daCtor, ctx)) {
      decl->addMember(ctor);
    }
  }
}

/******************************************************************************/
/******************************** PROPERTIES **********************************/
/******************************************************************************/

// TODO: deduplicate with 'declareDerivedProperty' from DerivedConformance...
std::pair<VarDecl *, PatternBindingDecl *>
createStoredProperty(ClassDecl *classDecl, ASTContext &ctx,
                     VarDecl::Introducer introducer, Identifier name,
                     Type propertyInterfaceType, Type propertyContextType,
                     bool isStatic, bool isFinal) {
  auto parentDC = classDecl;

  VarDecl *propDecl = new (ctx)
      VarDecl(/*IsStatic*/ isStatic, introducer,
                           SourceLoc(), name, parentDC);
  propDecl->setImplicit();
  propDecl->setSynthesized();
  propDecl->copyFormalAccessFrom(classDecl, /*sourceIsParentContext*/ true);
  propDecl->setInterfaceType(propertyInterfaceType);

  Pattern *propPat = NamedPattern::createImplicit(ctx, propDecl);
  propPat->setType(propertyContextType);

  propPat = TypedPattern::createImplicit(ctx, propPat, propertyContextType);
  propPat->setType(propertyContextType);

  auto *pbDecl = PatternBindingDecl::createImplicit(
      ctx, StaticSpellingKind::None, propPat, /*InitExpr*/ nullptr,
      parentDC);
  return {propDecl, pbDecl};
}

/// Adds the following, fairly special, properties to each distributed actor:
/// - actorTransport
/// - actorAddress
static void addImplicitDistributedActorStoredProperties(ClassDecl *decl) {
  assert(decl->isDistributedActor());

  auto &C = decl->getASTContext();

  // ```
  // @_distributedActorIndependent
  // let actorAddress: ActorAddress
  // ```
  // (no need for @actorIndependent because it is an immutable let)
  {
    auto propertyType = C.getActorAddressDecl()->getDeclaredInterfaceType();

    VarDecl *propDecl;
    PatternBindingDecl *pbDecl;
    std::tie(propDecl, pbDecl) = createStoredProperty(
        decl, C,
        VarDecl::Introducer::Let, C.Id_actorAddress,
        propertyType, propertyType,
        /*isStatic=*/false, /*isFinal=*/true);

    // mark as @_distributedActorIndependent, allowing access to it from everywhere
    propDecl->getAttrs().add(
        new (C) DistributedActorIndependentAttr(/*IsImplicit=*/true));

    decl->addMember(propDecl);
    decl->addMember(pbDecl);
  }

  // ```
  // @_distributedActorIndependent
  // let actorTransport: ActorTransport
  // ```
  // (no need for @actorIndependent because it is an immutable let)
  {
    auto propertyType = C.getActorTransportDecl()->getDeclaredInterfaceType();

    VarDecl *propDecl;
    PatternBindingDecl *pbDecl;
    std::tie(propDecl, pbDecl) = createStoredProperty(
        decl, C,
        VarDecl::Introducer::Let, C.Id_actorTransport,
        propertyType, propertyType,
        /*isStatic=*/false, /*isFinal=*/true);

    // mark as @_distributedActorIndependent, allowing access to it from everywhere
    propDecl->getAttrs().add(
        new (C) DistributedActorIndependentAttr(/*IsImplicit=*/true));

    decl->addMember(propDecl);
    decl->addMember(pbDecl);
  }
}

/******************************************************************************/
/*************************** _REMOTE_ FUNCTIONS *******************************/
/******************************************************************************/

/// Synthesizes the for `_remote_xxx` functions.
///
/// Create a stub body that emits a fatal error message.
static std::pair<BraceStmt *, bool>
synthesizeRemoteFuncStubBody(AbstractFunctionDecl *func, void *) {
  auto classDecl = func->getDeclContext()->getSelfClassDecl();
  auto &ctx = func->getASTContext();

  auto *staticStringDecl = ctx.getStaticStringDecl();
  auto staticStringType = staticStringDecl->getDeclaredInterfaceType();
  auto staticStringInit = ctx.getStringBuiltinInitDecl(staticStringDecl);

  auto *uintDecl = ctx.getUIntDecl();
  auto uintType = uintDecl->getDeclaredInterfaceType();
  auto uintInit = ctx.getIntBuiltinInitDecl(uintDecl);

  auto missingTransportDecl = ctx.getMissingDistributedActorTransport();

  // Create a call to Swift._missingDistributedActorTransport // TODO: move to `Distributed` module
  auto loc = func->getLoc();
  Expr *ref = new (ctx) DeclRefExpr(missingTransportDecl,
                                    DeclNameLoc(loc), /*Implicit=*/true);
  ref->setType(missingTransportDecl->getInterfaceType()
  ->removeArgumentLabels(1));

  llvm::SmallString<64> buffer;
  StringRef fullClassName = ctx.AllocateCopy(
      (classDecl->getModuleContext()->getName().str() +
      "." +
      classDecl->getName().str()).toStringRef(buffer));

  auto *className = new (ctx) StringLiteralExpr(fullClassName, loc,
                                                /*Implicit=*/true);
  className->setBuiltinInitializer(staticStringInit);
  assert(isa<ConstructorDecl>(className->getBuiltinInitializer().getDecl()));
  className->setType(staticStringType);

  auto *funcName = new (ctx) MagicIdentifierLiteralExpr(
      MagicIdentifierLiteralExpr::Function, loc, /*Implicit=*/true);
  funcName->setType(staticStringType);
  funcName->setBuiltinInitializer(staticStringInit);

  auto *file = new (ctx) MagicIdentifierLiteralExpr(
      MagicIdentifierLiteralExpr::FileID, loc, /*Implicit=*/true);
  file->setType(staticStringType);
  file->setBuiltinInitializer(staticStringInit);

  auto *line = new (ctx) MagicIdentifierLiteralExpr(
      MagicIdentifierLiteralExpr::Line, loc, /*Implicit=*/true);
  line->setType(uintType);
  line->setBuiltinInitializer(uintInit);

  auto *column = new (ctx) MagicIdentifierLiteralExpr(
      MagicIdentifierLiteralExpr::Column, loc, /*Implicit=*/true);
  column->setType(uintType);
  column->setBuiltinInitializer(uintInit);

  auto *call = CallExpr::createImplicit(
      ctx, ref, { className, funcName, file, line, column }, {});
  call->setType(ctx.getNeverType());
  call->setThrows(false);

  SmallVector<ASTNode, 2> stmts;
  stmts.push_back(call); // something() -> Never
  // stmts.push_back(new (ctx) ReturnStmt(SourceLoc(), /*Result=*/nullptr)); // FIXME: this causes 'different types for return type: String vs. ()'
  auto body = BraceStmt::create(ctx, SourceLoc(), stmts, SourceLoc(),
                                /*implicit=*/true);



  return { body, /*isTypeChecked=*/true };
}

static Identifier makeRemoteFuncIdentifier(FuncDecl* func) {
  auto &C = func->getASTContext();
  auto localFuncName = func->getBaseIdentifier().str().str();
  auto remoteFuncIdent = C.getIdentifier("_remote_" + localFuncName);
  return remoteFuncIdent;
}

/// Create a remote stub for the passed in \c func.
/// The remote stub function is not user accessible and mirrors the API of
/// the local function. It is always throwing, async, and user-inaccessible.
///
/// ```
/// // func greet(name: String) { ... }
/// dynamic <access> func _remote_greet(name: String) async throws {
///     fatalError(...)
/// }
/// ```
///
/// and is intended to be replaced by a transport library by providing an
/// appropriate @_dynamicReplacement function.
static void addImplicitRemoteActorFunction(ClassDecl *decl, FuncDecl *func) {
  auto &C = decl->getASTContext();
  auto parentDC = decl;

  auto remoteFuncIdent = makeRemoteFuncIdentifier(func);

  auto params = ParameterList::clone(C, func->getParameters());
  auto genericParams = func->getGenericParams(); // TODO: also clone those
  Type resultTy = func->getResultInterfaceType();

  DeclName name(C, remoteFuncIdent, params);
  auto *const remoteFuncDecl = FuncDecl::createImplicit(
      C, StaticSpellingKind::None, name, /*NameLoc=*/SourceLoc(),
      /*Async=*/true, /*Throws=*/true,
      /*GenericParams=*/genericParams, params,
      resultTy, parentDC);

  // *dynamic* because we'll be replacing it with specific transports
  remoteFuncDecl->getAttrs().add(
      new (C) DynamicAttr(/*implicit=*/true));

  // @_distributedActorIndependent
  remoteFuncDecl->getAttrs().add(
      new (C) DistributedActorIndependentAttr(/*IsImplicit=*/true));

  // users should never have to access this function directly;
  // it is only invoked from our distributed function thunk if the actor is remote.
  remoteFuncDecl->setUserAccessible(false);
  remoteFuncDecl->setSynthesized();

  remoteFuncDecl->setBodySynthesizer(&synthesizeRemoteFuncStubBody);

  // same access control as the original function is fine
  remoteFuncDecl->copyFormalAccessFrom(func, /*sourceIsParentContext=*/false);

  decl->addMember(remoteFuncDecl);
}

/// Synthesize dynamic _remote stub functions for each encountered distributed function.
static void addImplicitRemoteActorFunctions(ClassDecl *decl) {
  assert(decl->isDistributedActor());

  for (auto member : decl->getMembers()) {
    auto func = dyn_cast<FuncDecl>(member);
    if (func && func->isDistributed()) {
      addImplicitRemoteActorFunction(decl, func);
    }
  }
}

/******************************************************************************/
/************************ SYNTHESIS ENTRY POINT *******************************/
/******************************************************************************/

/// Entry point for adding all computed members to a distributed actor decl.
static void addImplicitDistributedActorMembersToClass(ClassDecl *decl) {
  // Bail out if not a distributed actor definition.
  if (!decl->isDistributedActor())
    return;

  auto &C = decl->getASTContext();

  if (!C.getLoadedModule(C.Id_Distributed)) {
    // seems we're missing the _Distributed module, ask to import it explicitly
    decl->diagnose(diag::distributed_actor_needs_explicit_distributed_import);
    return;
  }

  addImplicitDistributedActorConstructors(decl);
  addImplicitDistributedActorStoredProperties(decl);
  addImplicitRemoteActorFunctions(decl);
}