swift-mirror/lib/Sema/CodeSynthesis.cpp

//===--- CodeSynthesis.cpp - Type Checking for Declarations ---------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file implements semantic analysis for declarations.
//
//===----------------------------------------------------------------------===//

#include "CodeSynthesis.h"

#include "ConstraintSystem.h"
#include "TypeChecker.h"
#include "swift/AST/ASTWalker.h"
#include "swift/AST/Attr.h"
#include "swift/AST/Availability.h"
#include "swift/AST/Expr.h"
#include "swift/AST/ParameterList.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
using namespace swift;

const bool IsImplicit = true;

/// Insert the specified decl into the DeclContext's member list.  If the hint
/// decl is specified, the new decl is inserted next to the hint.
static void addMemberToContextIfNeeded(Decl *D, DeclContext *DC,
                                       Decl *Hint = nullptr) {
  if (auto *ntd = dyn_cast<NominalTypeDecl>(DC)) {
    ntd->addMember(D, Hint);
  } else if (auto *ed = dyn_cast<ExtensionDecl>(DC)) {
    ed->addMember(D, Hint);
  } else if (isa<SourceFile>(DC)) {
    auto *mod = DC->getParentModule();
    mod->getDerivedFileUnit().addDerivedDecl(cast<FuncDecl>(D));
  } else {
    assert((isa<AbstractFunctionDecl>(DC) || isa<FileUnit>(DC)) &&
           "Unknown declcontext");
  }
}

static ParamDecl *getParamDeclAtIndex(FuncDecl *fn, unsigned index) {
  return fn->getParameterLists().back()->get(index);
}

static VarDecl *getFirstParamDecl(FuncDecl *fn) {
  return getParamDeclAtIndex(fn, 0);
};


static ParamDecl *buildArgument(SourceLoc loc, DeclContext *DC,
                               StringRef name, Type type, bool isLet) {
  auto &context = DC->getASTContext();
  auto *param = new (context) ParamDecl(isLet, SourceLoc(), Identifier(),
                                        loc, context.getIdentifier(name),
                                        Type(), DC);
  param->setImplicit();
  param->getTypeLoc().setType(type);
  return param;
}

static ParamDecl *buildLetArgument(SourceLoc loc, DeclContext *DC,
                                  StringRef name, Type type) {
  return buildArgument(loc, DC, name, type, /*isLet*/ true);
}

static ParamDecl *buildInOutArgument(SourceLoc loc, DeclContext *DC,
                                     StringRef name, Type type) {
  return buildArgument(loc, DC, name, InOutType::get(type), /*isLet*/ false);
}

static Type getTypeOfStorage(AbstractStorageDecl *storage,
                             TypeChecker &TC) {
  if (auto var = dyn_cast<VarDecl>(storage)) {
    return TC.getTypeOfRValue(var, /*want interface type*/ false);
  } else {
    // None of the transformations done by getTypeOfRValue are
    // necessary for subscripts.
    auto subscript = cast<SubscriptDecl>(storage);
    return subscript->getElementType();
  }
}

/// Build a parameter list which can forward the formal index parameters of a
/// declaration.
///
/// \param prefix optional arguments to be prefixed onto the index
///   forwarding pattern.
static ParameterList *
buildIndexForwardingParamList(AbstractStorageDecl *storage,
                              ArrayRef<ParamDecl*> prefix) {
  auto &context = storage->getASTContext();
  auto subscript = dyn_cast<SubscriptDecl>(storage);

  // Fast path: if this isn't a subscript, just use whatever we have.
  if (!subscript)
    return ParameterList::create(context, prefix);

  // Clone the parameter list over for a new decl, so we get new ParamDecls.
  auto indices = subscript->getIndices()->clone(context,
                                                ParameterList::Implicit);
  if (prefix.empty())
    return indices;
  
  
  // Otherwise, we need to build up a new parameter list.
  SmallVector<ParamDecl*, 4> elements;

  // Start with the fields we were given, if there are any.
  elements.append(prefix.begin(), prefix.end());
  elements.append(indices->begin(), indices->end());
  return ParameterList::create(context, elements);
}

static FuncDecl *createGetterPrototype(AbstractStorageDecl *storage,
                                       TypeChecker &TC) {
  SourceLoc loc = storage->getLoc();

  // Create the parameter list for the getter.
  SmallVector<ParameterList*, 2> getterParams;

  // The implicit 'self' argument if in a type context.
  if (storage->getDeclContext()->isTypeContext())
    getterParams.push_back(ParameterList::createSelf(loc,
                                                     storage->getDeclContext(),
                                                     /*isStatic*/false));
    
  // Add an index-forwarding clause.
  getterParams.push_back(buildIndexForwardingParamList(storage, {}));

  SourceLoc staticLoc;
  if (auto var = dyn_cast<VarDecl>(storage)) {
    if (var->isStatic())
      staticLoc = var->getLoc();
  }

  auto storageType = getTypeOfStorage(storage, TC);

  auto getter = FuncDecl::create(
      TC.Context, staticLoc, StaticSpellingKind::None, loc, Identifier(), loc,
      SourceLoc(), SourceLoc(), /*GenericParams=*/nullptr, Type(), getterParams,
      TypeLoc::withoutLoc(storageType), storage->getDeclContext());
  getter->setImplicit();

  if (storage->isGetterMutating())
    getter->setMutating();

  // If the var is marked final, then so is the getter.
  if (storage->isFinal())
    makeFinal(TC.Context, getter);

  if (storage->isStatic())
    getter->setStatic();

  return getter;
}

static FuncDecl *createSetterPrototype(AbstractStorageDecl *storage,
                                       ParamDecl *&valueDecl,
                                       TypeChecker &TC) {
  SourceLoc loc = storage->getLoc();

  // Create the parameter list for the setter.
  SmallVector<ParameterList*, 2> params;

  // The implicit 'self' argument if in a type context.
  if (storage->getDeclContext()->isTypeContext()) {
    params.push_back(ParameterList::createSelf(loc,
                                               storage->getDeclContext(),
                                               /*isStatic*/false));
  }
  
  // Add a "(value : T, indices...)" argument list.
  auto storageType = getTypeOfStorage(storage, TC);
  valueDecl = buildLetArgument(storage->getLoc(),
                                     storage->getDeclContext(), "value",
                                     storageType);
  params.push_back(buildIndexForwardingParamList(storage, valueDecl));

  Type setterRetTy = TupleType::getEmpty(TC.Context);
  FuncDecl *setter = FuncDecl::create(
      TC.Context, /*StaticLoc=*/SourceLoc(), StaticSpellingKind::None, loc,
      Identifier(), loc, SourceLoc(), SourceLoc(), /*generic=*/nullptr, Type(),
      params, TypeLoc::withoutLoc(setterRetTy), storage->getDeclContext());
  setter->setImplicit();

  if (!storage->isSetterNonMutating())
    setter->setMutating();

  // If the var is marked final, then so is the getter.
  if (storage->isFinal())
    makeFinal(TC.Context, setter);

  if (storage->isStatic())
    setter->setStatic();

  return setter;
}

/// Returns the type of the self argument of a materializeForSet
/// callback.  If we don't have a meaningful direct self type, just
/// use something meaningless and hope it doesn't matter.
static Type getSelfTypeForMaterializeForSetCallback(ASTContext &ctx,
                                                    DeclContext *DC,
                                                    bool isStatic) {
  Type selfType = DC->getDeclaredTypeInContext();
  if (!selfType) {
    // This restriction is theoretically liftable by writing the necessary
    // contextual information into the callback storage.
    assert(!DC->isGenericContext() &&
           "no enclosing type for generic materializeForSet; callback "
           "will not be able to bind type arguments!");
    return TupleType::getEmpty(ctx);
  }

  // If we're in a protocol, we want to actually use the Self type.
  if (selfType->is<ProtocolType>()) {
    selfType = DC->getProtocolSelf()->getArchetype();
  }

  // Use the metatype if this is a static member.
  if (isStatic) {
    return MetatypeType::get(selfType, ctx);
  } else {
    return selfType;
  }
}

// True if the storage is dynamic or imported from Objective-C. In these cases,
// we need to emit a static materializeForSet thunk that dynamically dispatches
// to 'get' and 'set', rather than the normal dynamically dispatched
// materializeForSet that peer dispatches to 'get' and 'set'.
static bool needsDynamicMaterializeForSet(AbstractStorageDecl *storage) {
  return storage->isDynamic() || storage->hasClangNode();
}

// True if a generated accessor needs to be registered as an external decl.
bool needsToBeRegisteredAsExternalDecl(AbstractStorageDecl *storage) {
  // Either the storage itself was imported from Clang...
  if (storage->hasClangNode())
    return true;

  // ...or it was synthesized into an imported type.
  auto nominal = dyn_cast<NominalTypeDecl>(storage->getDeclContext());
  if (!nominal)
    return false;
  return nominal->hasClangNode();
}

static Type createMaterializeForSetReturnType(AbstractStorageDecl *storage,
                                              TypeChecker &TC) {
  auto &ctx = storage->getASTContext();
  SourceLoc loc = storage->getLoc();

  auto DC = storage->getDeclContext();

  if (DC->getDeclaredTypeInContext() &&
      DC->getDeclaredTypeInContext()->is<ErrorType>()) {
    return ErrorType::get(ctx);
  }

  Type callbackSelfType =
    getSelfTypeForMaterializeForSetCallback(ctx, DC, storage->isStatic());
  TupleTypeElt callbackArgs[] = {
    ctx.TheRawPointerType,
    InOutType::get(ctx.TheUnsafeValueBufferType),
    InOutType::get(callbackSelfType),
    MetatypeType::get(callbackSelfType, MetatypeRepresentation::Thick),
  };
  auto callbackExtInfo = FunctionType::ExtInfo()
    .withRepresentation(FunctionType::Representation::Thin);
  auto callbackType = FunctionType::get(TupleType::get(callbackArgs, ctx),
                                        TupleType::getEmpty(ctx),
                                        callbackExtInfo);

  // Try to make the callback type optional.  Don't crash if it doesn't
  // work, though.
  auto optCallbackType = TC.getOptionalType(loc, callbackType);
  if (!optCallbackType) optCallbackType = callbackType;

  TupleTypeElt retElts[] = {
    { ctx.TheRawPointerType },
    { optCallbackType },
  };
  return TupleType::get(retElts, ctx);
}

static FuncDecl *createMaterializeForSetPrototype(AbstractStorageDecl *storage,
                                                  TypeChecker &TC) {
  auto &ctx = storage->getASTContext();
  SourceLoc loc = storage->getLoc();

  // Create the parameter list:
  SmallVector<ParameterList*, 2> params;

  //  - The implicit 'self' argument if in a type context.
  auto DC = storage->getDeclContext();
  if (DC->isTypeContext())
    params.push_back(ParameterList::createSelf(loc, DC, /*isStatic*/false));

  //  - The buffer parameter, (buffer: Builtin.RawPointer,
  //                           inout storage: Builtin.UnsafeValueBuffer,
  //                           indices...).
  ParamDecl *bufferElements[] = {
    buildLetArgument(loc, DC, "buffer", ctx.TheRawPointerType),
    buildInOutArgument(loc, DC, "callbackStorage", ctx.TheUnsafeValueBufferType)
  };
  params.push_back(buildIndexForwardingParamList(storage, bufferElements));

  // The accessor returns (Builtin.RawPointer, (@convention(thin) (...) -> ())?),
  // where the first pointer is the materialized address and the
  // second is an optional callback.
  Type retTy = createMaterializeForSetReturnType(storage, TC);

  auto *materializeForSet = FuncDecl::create(
      ctx, /*StaticLoc=*/SourceLoc(), StaticSpellingKind::None, loc,
      Identifier(), loc, SourceLoc(), SourceLoc(), /*generic=*/nullptr, Type(),
      params, TypeLoc::withoutLoc(retTy), DC);
  materializeForSet->setImplicit();
  
  // materializeForSet is mutating and static if the setter is.
  auto setter = storage->getSetter();

  // Open-code the setMutating() calculation since we might run before
  // the setter has been type checked. Also as a hack, always mark the
  // setter mutating if we're inside a protocol, because it seems some
  // things break otherwise -- the root cause should be fixed eventually.
  materializeForSet->setMutating(
      setter->getDeclContext()->isProtocolOrProtocolExtensionContext() ||
      (!setter->getAttrs().hasAttribute<NonMutatingAttr>() &&
       !storage->isSetterNonMutating()));

  materializeForSet->setStatic(setter->isStatic());

  // materializeForSet is final if the storage is.
  if (storage->isFinal())
    makeFinal(ctx, materializeForSet);
  
  // If the storage is dynamic or ObjC-native, we can't add a dynamically-
  // dispatched method entry for materializeForSet, so force it to be
  // statically dispatched. ("final" would be inappropriate because the
  // property can still be overridden.)
  if (needsDynamicMaterializeForSet(storage))
    materializeForSet->setForcedStaticDispatch(true);

  // Make sure materializeForSet is available enough to access
  // the storage (and its getters/setters if it has them).
  SmallVector<const Decl *, 2> asAvailableAs;
  asAvailableAs.push_back(storage);
  if (FuncDecl *getter = storage->getGetter()) {
    asAvailableAs.push_back(getter);
  }
  if (FuncDecl *setter = storage->getSetter()) {
    asAvailableAs.push_back(setter);
  }

  AvailabilityInference::applyInferredAvailableAttrs(materializeForSet,
                                                        asAvailableAs, ctx);

  // If the property came from ObjC, we need to register this as an external
  // definition to be compiled.
  if (needsToBeRegisteredAsExternalDecl(storage))
    TC.Context.addExternalDecl(materializeForSet);
  
  return materializeForSet;
}

void swift::convertStoredVarInProtocolToComputed(VarDecl *VD, TypeChecker &TC) {
  auto *Get = createGetterPrototype(VD, TC);
  
  // Okay, we have both the getter and setter.  Set them in VD.
  VD->makeComputed(VD->getLoc(), Get, nullptr, nullptr, VD->getLoc());
  
  // We've added some members to our containing class, add them to the members
  // list.
  addMemberToContextIfNeeded(Get, VD->getDeclContext());

  // Type check the getter declaration.
  TC.typeCheckDecl(VD->getGetter(), true);
  TC.typeCheckDecl(VD->getGetter(), false);
}


/// Build an expression that evaluates the specified parameter list as a tuple
/// or paren expr, suitable for use in an applyexpr.
///
/// NOTE: This returns null if a varargs parameter exists in the list, as it
/// cannot be forwarded correctly yet.
///
static Expr *buildArgumentForwardingExpr(ArrayRef<ParamDecl*> params,
                                         ASTContext &ctx) {
  SmallVector<Identifier, 4> labels;
  SmallVector<SourceLoc, 4> labelLocs;
  SmallVector<Expr *, 4> args;
  
  for (auto param : params) {
    // We cannot express how to forward variadic parameters yet.
    if (param->isVariadic())
      return nullptr;
    
    Expr *ref = new (ctx) DeclRefExpr(param, SourceLoc(), /*implicit*/ true);
    if (param->getType()->is<InOutType>())
      ref = new (ctx) InOutExpr(SourceLoc(), ref, Type(), /*implicit=*/true);
    args.push_back(ref);
    
    labels.push_back(param->getArgumentName());
    labelLocs.push_back(SourceLoc());
  }
  
  // A single unlabelled value is not a tuple.
  if (args.size() == 1 && labels[0].empty())
    return args[0];
  
  return TupleExpr::create(ctx, SourceLoc(), args, labels, labelLocs,
                           SourceLoc(), false, IsImplicit);
}





/// Build a reference to the subscript index variables for this subscript
/// accessor.
static Expr *buildSubscriptIndexReference(ASTContext &ctx, FuncDecl *accessor) {
  // Pull out the body parameters, which we should have cloned
  // previously to be forwardable.  Drop the initial buffer/value
  // parameter in accessors that have one.
  auto params = accessor->getParameterLists().back()->getArray();
  auto accessorKind = accessor->getAccessorKind();

  // Ignore the value/buffer parameter.
  if (accessorKind != AccessorKind::IsGetter)
    params = params.slice(1);

  // Ignore the materializeForSet callback storage parameter.
  if (accessorKind == AccessorKind::IsMaterializeForSet)
    params = params.slice(1);
  
  // Okay, everything else should be forwarded, build the expression.
  auto result = buildArgumentForwardingExpr(params, ctx);
  assert(result && "FIXME: Cannot forward varargs");
  return result;
}

enum class SelfAccessKind {
  /// We're building a derived accessor on top of whatever this
  /// class provides.
  Peer,

  /// We're building a setter or something around an underlying
  /// implementation, which might be storage or inherited from a
  /// superclass.
  Super,
};

static Expr *buildSelfReference(VarDecl *selfDecl,
                                SelfAccessKind selfAccessKind,
                                TypeChecker &TC) {
  switch (selfAccessKind) {
  case SelfAccessKind::Peer:
    return new (TC.Context) DeclRefExpr(selfDecl, SourceLoc(), IsImplicit);

  case SelfAccessKind::Super:
    return new (TC.Context) SuperRefExpr(selfDecl, SourceLoc(), IsImplicit);
  }
  llvm_unreachable("bad self access kind");
}

namespace {
  /// A simple helper interface for buildStorageReference.
  class StorageReferenceContext {
    StorageReferenceContext(const StorageReferenceContext &) = delete;
  public:
    StorageReferenceContext() = default;
    virtual ~StorageReferenceContext() = default;

    /// Returns the declaration of the entity to use as the base of
    /// the access, or nil if no base is required.
    virtual VarDecl *getSelfDecl() const = 0;

    /// Returns an expression producing the index value, assuming that
    /// the storage is a subscript declaration.
    virtual Expr *getIndexRefExpr(ASTContext &ctx,
                                  SubscriptDecl *subscript) const = 0;
  };

  /// A reference to storage from within an accessor.
  class AccessorStorageReferenceContext : public StorageReferenceContext {
    FuncDecl *Accessor;
  public:
    AccessorStorageReferenceContext(FuncDecl *accessor) : Accessor(accessor) {}
    virtual ~AccessorStorageReferenceContext() = default;

    VarDecl *getSelfDecl() const override {
      return Accessor->getImplicitSelfDecl();
    }
    Expr *getIndexRefExpr(ASTContext &ctx,
                          SubscriptDecl *subscript) const override {
      return buildSubscriptIndexReference(ctx, Accessor);
    }
  };
}

/// Build an l-value for the storage of a declaration.
static Expr *buildStorageReference(
                             const StorageReferenceContext &referenceContext,
                                   AbstractStorageDecl *storage,
                                   AccessSemantics semantics,
                                   SelfAccessKind selfAccessKind,
                                   TypeChecker &TC) {
  ASTContext &ctx = TC.Context;

  VarDecl *selfDecl = referenceContext.getSelfDecl();
  if (!selfDecl) {
    return new (ctx) DeclRefExpr(storage, SourceLoc(), IsImplicit, semantics);
  }

  // If we should use a super access if applicable, and we have an
  // overridden decl, then use ordinary access to it.
  if (selfAccessKind == SelfAccessKind::Super) {
    if (auto overridden = storage->getOverriddenDecl()) {
      storage = overridden;
      semantics = AccessSemantics::Ordinary;
    } else {
      selfAccessKind = SelfAccessKind::Peer;
    }
  }

  Expr *selfDRE = buildSelfReference(selfDecl, selfAccessKind, TC);

  if (auto subscript = dyn_cast<SubscriptDecl>(storage)) {
    Expr *indices = referenceContext.getIndexRefExpr(ctx, subscript);
    return new (ctx) SubscriptExpr(selfDRE, indices, storage,
                                   IsImplicit, semantics);
  }

  // This is a potentially polymorphic access, which is unnecessary;
  // however, it shouldn't be problematic because any overrides
  // should also redefine materializeForSet.
  return new (ctx) MemberRefExpr(selfDRE, SourceLoc(), storage,
                                 SourceLoc(), IsImplicit, semantics);
}

static Expr *buildStorageReference(FuncDecl *accessor,
                                   AbstractStorageDecl *storage,
                                   AccessSemantics semantics,
                                   SelfAccessKind selfAccessKind,
                                   TypeChecker &TC) {
  return buildStorageReference(AccessorStorageReferenceContext(accessor),
                               storage, semantics, selfAccessKind, TC);
}

/// Load the value of VD.  If VD is an @override of another value, we call the
/// superclass getter.  Otherwise, we do a direct load of the value.
static Expr *createPropertyLoadOrCallSuperclassGetter(FuncDecl *accessor,
                                              AbstractStorageDecl *storage,
                                                      TypeChecker &TC) {
  return buildStorageReference(accessor, storage,
                               AccessSemantics::DirectToStorage,
                               SelfAccessKind::Super, TC);
}

/// Look up the NSCopying protocol from the Foundation module, if present.
/// Otherwise return null.
static ProtocolDecl *getNSCopyingProtocol(TypeChecker &TC,
                                          DeclContext *DC) {
  ASTContext &ctx = TC.Context;
  auto foundation = ctx.getLoadedModule(ctx.Id_Foundation);
  if (!foundation)
    return nullptr;

  SmallVector<ValueDecl *, 2> results;
  DC->lookupQualified(ModuleType::get(foundation),
                      ctx.getSwiftId(KnownFoundationEntity::NSCopying),
                      NL_QualifiedDefault | NL_KnownNonCascadingDependency,
                      /*resolver=*/nullptr,
                      results);

  if (results.size() != 1)
    return nullptr;

  return dyn_cast<ProtocolDecl>(results.front());
}



/// Synthesize the code to store 'Val' to 'VD', given that VD has an @NSCopying
/// attribute on it.  We know that VD is a stored property in a class, so we
/// just need to generate something like "self.property = val.copyWithZone(nil)"
/// here.  This does some type checking to validate that the call will succeed.
static Expr *synthesizeCopyWithZoneCall(Expr *Val, VarDecl *VD,
                                        TypeChecker &TC) {
  auto &Ctx = TC.Context;

  // We support @NSCopying on class types (which conform to NSCopying),
  // protocols which conform, and option types thereof.
  Type UnderlyingType = TC.getTypeOfRValue(VD, /*want interface type*/false);

  bool isOptional = false;
  if (Type optionalEltTy = UnderlyingType->getAnyOptionalObjectType()) {
    UnderlyingType = optionalEltTy;
    isOptional = true;
  }

  // The element type must conform to NSCopying.  If not, emit an error and just
  // recovery by synthesizing without the copy call.
  auto *CopyingProto = getNSCopyingProtocol(TC, VD->getDeclContext());
  if (!CopyingProto || !TC.conformsToProtocol(UnderlyingType, CopyingProto,
                                              VD->getDeclContext(), None)) {
    TC.diagnose(VD->getLoc(), diag::nscopying_doesnt_conform);
    return Val;
  }

  // If we have an optional type, we have to "?" the incoming value to only
  // evaluate the subexpression if the incoming value is non-null.
  if (isOptional)
    Val = new (Ctx) BindOptionalExpr(Val, SourceLoc(), 0);

  // Generate:
  // (force_value_expr type='<null>'
  //   (call_expr type='<null>'
  //     (unresolved_dot_expr type='<null>' field 'copyWithZone'
  //       "Val")
  //     (paren_expr type='<null>'
  //       (nil_literal_expr type='<null>'))))
  auto UDE = new (Ctx) UnresolvedDotExpr(Val, SourceLoc(),
                                         Ctx.getIdentifier("copyWithZone"),
                                         SourceLoc(), /*implicit*/true);
  Expr *Nil = new (Ctx) NilLiteralExpr(SourceLoc(), /*implicit*/true);
  Nil = new (Ctx) ParenExpr(SourceLoc(), Nil, SourceLoc(), false);

  //- (id)copyWithZone:(NSZone *)zone;
  Expr *Call = new (Ctx) CallExpr(UDE, Nil, /*implicit*/true);

  TypeLoc ResultTy;
  ResultTy.setType(VD->getType(), true);

  // If we're working with non-optional types, we're forcing the cast.
  if (!isOptional) {
    Call = new (Ctx) ForcedCheckedCastExpr(Call, SourceLoc(), SourceLoc(),
                                           TypeLoc::withoutLoc(UnderlyingType));
    Call->setImplicit();
    return Call;
  }

  // We're working with optional types, so perform a conditional checked
  // downcast.
  Call = new (Ctx) ConditionalCheckedCastExpr(Call, SourceLoc(), SourceLoc(),
                                           TypeLoc::withoutLoc(UnderlyingType));
  Call->setImplicit();

  // Use OptionalEvaluationExpr to evaluate the "?".
  return new (Ctx) OptionalEvaluationExpr(Call);
}

/// In a synthesized accessor body, store 'value' to the appropriate element.
///
/// If the property is an override, we call the superclass setter.
/// Otherwise, we do a direct store of the value.
static void createPropertyStoreOrCallSuperclassSetter(FuncDecl *accessor,
                                                      Expr *value,
                                               AbstractStorageDecl *storage,
                                               SmallVectorImpl<ASTNode> &body,
                                                      TypeChecker &TC) {
  // If the storage is an @NSCopying property, then we store the
  // result of a copyWithZone call on the value, not the value itself.
  if (auto property = dyn_cast<VarDecl>(storage)) {
    if (property->getAttrs().hasAttribute<NSCopyingAttr>())
      value = synthesizeCopyWithZoneCall(value, property, TC);
  }

  // Create:
  //   (assign (decl_ref_expr(VD)), decl_ref_expr(value))
  // or:
  //   (assign (member_ref_expr(decl_ref_expr(self), VD)), decl_ref_expr(value))
  Expr *dest = buildStorageReference(accessor, storage,
                                     AccessSemantics::DirectToStorage,
                                     SelfAccessKind::Super, TC);

  body.push_back(new (TC.Context) AssignExpr(dest, SourceLoc(), value,
                                             IsImplicit));
}

/// Mark the accessor as transparent if we can.
///
/// If the storage is inside a fixed-layout nominal type, we can mark the
/// accessor as transparent, since in this case we just want it for abstraction
/// purposes (i.e., to make access to the variable uniform and to be able to
/// put the getter in a vtable).
///
/// If the storage is for a global stored property or a stored property of a
/// resilient type, we are synthesizing accessors to present a resilient
/// interface to the storage and they should not be transparent.
static void maybeMarkTransparent(FuncDecl *accessor,
                                 AbstractStorageDecl *storage,
                                 TypeChecker &TC) {
  auto *nominal = storage->getDeclContext()
      ->isNominalTypeOrNominalTypeExtensionContext();
  if (nominal && nominal->hasFixedLayout())
    accessor->getAttrs().add(new (TC.Context) TransparentAttr(IsImplicit));
}

/// Synthesize the body of a trivial getter.  For a non-member vardecl or one
/// which is not an override of a base class property, it performs a direct
/// storage load.  For an override of a base member property, it chains up to
/// super.
static void synthesizeTrivialGetter(FuncDecl *getter,
                                    AbstractStorageDecl *storage,
                                    TypeChecker &TC) {
  auto &ctx = TC.Context;
  
  Expr *result = createPropertyLoadOrCallSuperclassGetter(getter, storage, TC);
  ASTNode returnStmt = new (ctx) ReturnStmt(SourceLoc(), result, IsImplicit);

  SourceLoc loc = storage->getLoc();
  getter->setBody(BraceStmt::create(ctx, loc, returnStmt, loc, true));

  maybeMarkTransparent(getter, storage, TC);
 
  // Register the accessor as an external decl if the storage was imported.
  if (needsToBeRegisteredAsExternalDecl(storage))
    TC.Context.addExternalDecl(getter);
}

/// Synthesize the body of a trivial setter.
static void synthesizeTrivialSetter(FuncDecl *setter,
                                    AbstractStorageDecl *storage,
                                    VarDecl *valueVar,
                                    TypeChecker &TC) {
  if (storage->isInvalid()) return;

  auto &ctx = TC.Context;
  SourceLoc loc = storage->getLoc();

  auto *valueDRE = new (ctx) DeclRefExpr(valueVar, SourceLoc(), IsImplicit);
  SmallVector<ASTNode, 1> setterBody;
  createPropertyStoreOrCallSuperclassSetter(setter, valueDRE, storage,
                                            setterBody, TC);
  setter->setBody(BraceStmt::create(ctx, loc, setterBody, loc, true));

  maybeMarkTransparent(setter, storage, TC);

  // Register the accessor as an external decl if the storage was imported.
  if (needsToBeRegisteredAsExternalDecl(storage))
    TC.Context.addExternalDecl(setter);
}

/// Does a storage decl currently lacking accessor functions require a
/// setter to be synthesized?
static bool doesStorageNeedSetter(AbstractStorageDecl *storage) {
  assert(!storage->hasAccessorFunctions());
  switch (storage->getStorageKind()) {
  // Add a setter to a stored variable unless it's a let.
  case AbstractStorageDecl::Stored:
    return !cast<VarDecl>(storage)->isLet();

  // Addressed storage gets a setter if it has a mutable addressor.
  case AbstractStorageDecl::Addressed:
    return storage->getMutableAddressor() != nullptr;

  // These should already have accessor functions.
  case AbstractStorageDecl::StoredWithTrivialAccessors:
  case AbstractStorageDecl::StoredWithObservers:
  case AbstractStorageDecl::InheritedWithObservers:
  case AbstractStorageDecl::AddressedWithTrivialAccessors:
  case AbstractStorageDecl::AddressedWithObservers:
  case AbstractStorageDecl::ComputedWithMutableAddress:
    llvm_unreachable("already has accessor functions");

  case AbstractStorageDecl::Computed:
    llvm_unreachable("not stored");
  }
  llvm_unreachable("bad storage kind");
}

/// Add a materializeForSet accessor to the given declaration.
static FuncDecl *addMaterializeForSet(AbstractStorageDecl *storage,
                                      TypeChecker &TC) {
  auto materializeForSet = createMaterializeForSetPrototype(storage, TC);
  addMemberToContextIfNeeded(materializeForSet, storage->getDeclContext(),
                             storage->getSetter());
  storage->setMaterializeForSetFunc(materializeForSet);

  TC.computeAccessibility(materializeForSet);

  TC.validateDecl(materializeForSet);

  return materializeForSet;
}

/// Add trivial accessors to a Stored or Addressed property.
void swift::addTrivialAccessorsToStorage(AbstractStorageDecl *storage,
                                         TypeChecker &TC) {
  assert(!storage->hasAccessorFunctions() && "already has accessors?");

  // Create the getter.
  auto *getter = createGetterPrototype(storage, TC);

  // Create the setter.
  FuncDecl *setter = nullptr;
  ParamDecl *setterValueParam = nullptr;
  if (doesStorageNeedSetter(storage)) {
    setter = createSetterPrototype(storage, setterValueParam, TC);
  }
  
  // Okay, we have both the getter and setter.  Set them in VD.
  storage->addTrivialAccessors(getter, setter, nullptr);

  bool isDynamic = (storage->isDynamic() && storage->isObjC());
  if (isDynamic)
    getter->getAttrs().add(new (TC.Context) DynamicAttr(IsImplicit));

  // Synthesize and type-check the body of the getter.
  synthesizeTrivialGetter(getter, storage, TC);
  TC.typeCheckDecl(getter, true);
  TC.typeCheckDecl(getter, false);

  if (setter) {
    if (isDynamic)
      setter->getAttrs().add(new (TC.Context) DynamicAttr(IsImplicit));

    // Synthesize and type-check the body of the setter.
    synthesizeTrivialSetter(setter, storage, setterValueParam, TC);
    TC.typeCheckDecl(setter, true);
    TC.typeCheckDecl(setter, false);
  }

  auto *DC = storage->getDeclContext();

  // We've added some members to our containing context, add them to
  // the right list.
  addMemberToContextIfNeeded(getter, DC);
  if (setter)
    addMemberToContextIfNeeded(setter, DC);

  // If we're creating trivial accessors for a stored property of a
  // nominal type, the stored property is either witnessing a
  // protocol requirement or the nominal type is resilient. In both
  // cases, we need to expose a materializeForSet.
  //
  // Global stored properties don't get a materializeForSet.
  if (setter && DC->isNominalTypeOrNominalTypeExtensionContext()) {
    FuncDecl *materializeForSet = addMaterializeForSet(storage, TC);
    synthesizeMaterializeForSet(materializeForSet, storage, TC);
    TC.typeCheckDecl(materializeForSet, false);
  }
}

/// Add a trivial setter and materializeForSet to a
/// ComputedWithMutableAddress storage decl.
void swift::
synthesizeSetterForMutableAddressedStorage(AbstractStorageDecl *storage,
                                           TypeChecker &TC) {
  auto setter = storage->getSetter();
  assert(setter);
  assert(!storage->getSetter()->getBody());
  assert(storage->getStorageKind() ==
           AbstractStorageDecl::ComputedWithMutableAddress);

  // Synthesize and type-check the body of the setter.
  VarDecl *valueParamDecl = getFirstParamDecl(setter);
  synthesizeTrivialSetter(setter, storage, valueParamDecl, TC);
  TC.typeCheckDecl(setter, true);
  TC.typeCheckDecl(setter, false);
}

/// The specified AbstractStorageDecl was just found to satisfy a
/// protocol property requirement.  Ensure that it has the full
/// complement of accessors.
void TypeChecker::synthesizeWitnessAccessorsForStorage(
                                             AbstractStorageDecl *requirement,
                                             AbstractStorageDecl *storage) {
  // If the decl is stored, convert it to StoredWithTrivialAccessors
  // by synthesizing the full set of accessors.
  if (!storage->hasAccessorFunctions()) {
    addTrivialAccessorsToStorage(storage, *this);
    return;
  }
  
  // Otherwise, if the requirement is settable, ensure that there's a
  // materializeForSet function.
  //
  // @objc protocols don't need a materializeForSet since ObjC doesn't have
  // that concept.
  if (!requirement->isObjC() &&
      requirement->getSetter() && !storage->getMaterializeForSetFunc()) {
    FuncDecl *materializeForSet = addMaterializeForSet(storage, *this);
    synthesizeMaterializeForSet(materializeForSet, storage, *this);
    typeCheckDecl(materializeForSet, false);
  }
  return;
}

void swift::synthesizeMaterializeForSet(FuncDecl *materializeForSet,
                                        AbstractStorageDecl *storage,
                                        TypeChecker &TC) {
  // The body is actually emitted by SILGen

  maybeMarkTransparent(materializeForSet, storage, TC);

  TC.typeCheckDecl(materializeForSet, true);
  
  // Register the accessor as an external decl if the storage was imported.
  if (needsToBeRegisteredAsExternalDecl(storage))
    TC.Context.addExternalDecl(materializeForSet);
}

/// Given a VarDecl with a willSet: and/or didSet: specifier, synthesize the
/// (trivial) getter and the setter, which calls these.
void swift::synthesizeObservingAccessors(VarDecl *VD, TypeChecker &TC) {
  assert(VD->hasObservers());
  assert(VD->getGetter() && VD->getSetter() &&
         !VD->getGetter()->hasBody() && !VD->getSetter()->hasBody() &&
         "willSet/didSet var already has a getter or setter");
  
  auto &Ctx = VD->getASTContext();
  SourceLoc Loc = VD->getLoc();
  
  // The getter is always trivial: just perform a (direct!) load of storage, or
  // a call of a superclass getter if this is an override.
  auto *Get = VD->getGetter();
  synthesizeTrivialGetter(Get, VD, TC);

  // Okay, the getter is done, create the setter now.  Start by finding the
  // decls for 'self' and 'value'.
  auto *Set = VD->getSetter();
  auto *SelfDecl = Set->getImplicitSelfDecl();
  VarDecl *ValueDecl = Set->getParameterLists().back()->get(0);

  // The setter loads the oldValue, invokes willSet with the incoming value,
  // does a direct store, then invokes didSet with the oldValue.
  SmallVector<ASTNode, 6> SetterBody;

  // If there is a didSet, it will take the old value.  Load it into a temporary
  // 'let' so we have it for later.
  // TODO: check the body of didSet to only do this load (which may call the
  // superclass getter) if didSet takes an argument.
  VarDecl *OldValue = nullptr;
  if (VD->getDidSetFunc()) {
    Expr *OldValueExpr
      = createPropertyLoadOrCallSuperclassGetter(Set, VD, TC);
    
    OldValue = new (Ctx) VarDecl(/*isStatic*/false, /*isLet*/ true,
                                 SourceLoc(), Ctx.getIdentifier("tmp"),
                                 Type(), Set);
    OldValue->setImplicit();
    auto *tmpPattern = new (Ctx) NamedPattern(OldValue, /*implicit*/ true);
    auto tmpPBD = PatternBindingDecl::create(Ctx, SourceLoc(),
                                             StaticSpellingKind::None,
                                             SourceLoc(),
                                             tmpPattern, OldValueExpr, Set);
    tmpPBD->setImplicit();
    SetterBody.push_back(tmpPBD);
    SetterBody.push_back(OldValue);
  }
  
  // Create:
  //   (call_expr (dot_syntax_call_expr (decl_ref_expr(willSet)),
  //                                    (decl_ref_expr(self))),
  //              (declrefexpr(value)))
  // or:
  //   (call_expr (decl_ref_expr(willSet)), (declrefexpr(value)))
  if (auto willSet = VD->getWillSetFunc()) {
    Expr *Callee = new (Ctx) DeclRefExpr(willSet, SourceLoc(), /*imp*/true);
    auto *ValueDRE = new (Ctx) DeclRefExpr(ValueDecl, SourceLoc(), /*imp*/true);
    if (SelfDecl) {
      auto *SelfDRE = new (Ctx) DeclRefExpr(SelfDecl, SourceLoc(), /*imp*/true);
      Callee = new (Ctx) DotSyntaxCallExpr(Callee, SourceLoc(), SelfDRE);
    }
    SetterBody.push_back(new (Ctx) CallExpr(Callee, ValueDRE, true));

    // Make sure the didSet/willSet accessors are marked final if in a class.
    if (!willSet->isFinal() &&
        VD->getDeclContext()->isClassOrClassExtensionContext())
      makeFinal(Ctx, willSet);
  }
  
  // Create an assignment into the storage or call to superclass setter.
  auto *ValueDRE = new (Ctx) DeclRefExpr(ValueDecl, SourceLoc(), true);
  createPropertyStoreOrCallSuperclassSetter(Set, ValueDRE, VD, SetterBody, TC);

  // Create:
  //   (call_expr (dot_syntax_call_expr (decl_ref_expr(didSet)),
  //                                    (decl_ref_expr(self))),
  //              (decl_ref_expr(tmp)))
  // or:
  //   (call_expr (decl_ref_expr(didSet)), (decl_ref_expr(tmp)))
  if (auto didSet = VD->getDidSetFunc()) {
    auto *OldValueExpr = new (Ctx) DeclRefExpr(OldValue, SourceLoc(),
                                               /*impl*/true);
    Expr *Callee = new (Ctx) DeclRefExpr(didSet, SourceLoc(), /*imp*/true);
    if (SelfDecl) {
      auto *SelfDRE = new (Ctx) DeclRefExpr(SelfDecl, SourceLoc(), /*imp*/true);
      Callee = new (Ctx) DotSyntaxCallExpr(Callee, SourceLoc(), SelfDRE);
    }
    SetterBody.push_back(new (Ctx) CallExpr(Callee, OldValueExpr, true));

    // Make sure the didSet/willSet accessors are marked final if in a class.
    if (!didSet->isFinal() &&
        VD->getDeclContext()->isClassOrClassExtensionContext())
      makeFinal(Ctx, didSet);
  }

  Set->setBody(BraceStmt::create(Ctx, Loc, SetterBody, Loc, true));

  // Type check the body of the getter and setter.
  TC.typeCheckDecl(Get, true);
  TC.typeCheckDecl(Get, false);
  TC.typeCheckDecl(Set, true);
  TC.typeCheckDecl(Set, false);
}

static void convertNSManagedStoredVarToComputed(VarDecl *VD, TypeChecker &TC) {
  assert(VD->getStorageKind() == AbstractStorageDecl::Stored);

  // Create the getter.
  auto *Get = createGetterPrototype(VD, TC);

  // Create the setter.
  ParamDecl *SetValueDecl = nullptr;
  auto *Set = createSetterPrototype(VD, SetValueDecl, TC);

  // Okay, we have both the getter and setter.  Set them in VD.
  VD->makeComputed(VD->getLoc(), Get, Set, nullptr, VD->getLoc());

  TC.validateDecl(Get);
  TC.validateDecl(Set);

  // We've added some members to our containing class/extension, add them to
  // the members list.
  addMemberToContextIfNeeded(Get, VD->getDeclContext());
  addMemberToContextIfNeeded(Set, VD->getDeclContext());
}

namespace {
  /// This ASTWalker explores an expression tree looking for expressions (which
  /// are DeclContext's) and changes their parent DeclContext to NewDC.
  class RecontextualizeClosures : public ASTWalker {
    DeclContext *NewDC;
  public:
    RecontextualizeClosures(DeclContext *NewDC) : NewDC(NewDC) {}

    std::pair<bool, Expr *> walkToExprPre(Expr *E) override {
      // If we find a closure, update its declcontext and do *not* walk into it.
      if (auto CE = dyn_cast<AbstractClosureExpr>(E)) {
        CE->setParent(NewDC);
        return { false, E };
      }
      
      if (auto CLE = dyn_cast<CaptureListExpr>(E)) {
        // Make sure to recontextualize any decls in the capture list as well.
        for (auto &CLE : CLE->getCaptureList()) {
          CLE.Var->setDeclContext(NewDC);
          CLE.Init->setDeclContext(NewDC);
        }
      }

      return { true, E };
    }

    /// We don't want to recurse into declarations or statements.
    bool walkToDeclPre(Decl *) override { return false; }
    std::pair<bool, Stmt*> walkToStmtPre(Stmt *S) override { return {false,S}; }
  };
}

/// Synthesize the getter for a lazy property with the specified storage
/// vardecl.
static FuncDecl *completeLazyPropertyGetter(VarDecl *VD, VarDecl *Storage,
                                            TypeChecker &TC) {
  auto &Ctx = VD->getASTContext();

  // The getter checks the optional, storing the initial value in if nil.  The
  // specific pattern we generate is:
  //   get {
  //     let tmp1 = storage
  //     if tmp1 {
  //       return tmp1!
  //     }
  //     let tmp2 : Ty = <<initializer expression>>
  //     storage = tmp2
  //     return tmp2
  //   }
  auto *Get = VD->getGetter();
  TC.validateDecl(Get);

  SmallVector<ASTNode, 6> Body;

  // Load the existing storage and store it into the 'tmp1' temporary.
  auto *Tmp1VD = new (Ctx) VarDecl(/*isStatic*/false, /*isLet*/true,SourceLoc(),
                                   Ctx.getIdentifier("tmp1"), Type(), Get);
  Tmp1VD->setImplicit();

  auto *Tmp1PBDPattern = new (Ctx) NamedPattern(Tmp1VD, /*implicit*/true);
  auto *Tmp1Init = createPropertyLoadOrCallSuperclassGetter(Get, Storage, TC);
  auto *Tmp1PBD = PatternBindingDecl::create(Ctx, /*StaticLoc*/SourceLoc(),
                                             StaticSpellingKind::None,
                                             /*VarLoc*/SourceLoc(),
                                             Tmp1PBDPattern, Tmp1Init, Get);
  Body.push_back(Tmp1PBD);
  Body.push_back(Tmp1VD);

  // Build the early return inside the if.
  auto *Tmp1DRE = new (Ctx) DeclRefExpr(Tmp1VD, SourceLoc(), /*Implicit*/true,
                                        AccessSemantics::DirectToStorage);
  auto *EarlyReturnVal = new (Ctx) ForceValueExpr(Tmp1DRE, SourceLoc());
  auto *Return = new (Ctx) ReturnStmt(SourceLoc(), EarlyReturnVal,
                                      /*implicit*/true);

  // Build the "if" around the early return.
  Tmp1DRE = new (Ctx) DeclRefExpr(Tmp1VD, SourceLoc(), /*Implicit*/true,
                                  AccessSemantics::DirectToStorage);
  
  // Call through "hasValue" on the decl ref.
  Tmp1DRE->setType(OptionalType::get(VD->getType()));
  constraints::ConstraintSystem cs(TC,
                                   VD->getDeclContext(),
                                   constraints::ConstraintSystemOptions());
  constraints::Solution solution(cs, constraints::Score());
  auto HasValueExpr = solution.convertOptionalToBool(Tmp1DRE, nullptr);
  
  Body.push_back(new (Ctx) IfStmt(SourceLoc(), HasValueExpr, Return,
                                  /*elseloc*/SourceLoc(), /*else*/nullptr,
                                  /*implicit*/ true, Ctx));


  auto *Tmp2VD = new (Ctx) VarDecl(/*isStatic*/false, /*isLet*/true,
                                   SourceLoc(), Ctx.getIdentifier("tmp2"),
                                   VD->getType(), Get);
  Tmp2VD->setImplicit();


  // Take the initializer from the PatternBindingDecl for VD.
  // TODO: This doesn't work with complicated patterns like:
  //   lazy var (a,b) = foo()
  auto *InitValue = VD->getParentInitializer();
  auto PBD = VD->getParentPatternBinding();
  unsigned entryIndex = PBD->getPatternEntryIndexForVarDecl(VD);
  PBD->setInit(entryIndex, nullptr);
  PBD->setInitializerChecked(entryIndex);

  // Recontextualize any closure declcontexts nested in the initializer to
  // realize that they are in the getter function.
  InitValue->walk(RecontextualizeClosures(Get));


  Pattern *Tmp2PBDPattern = new (Ctx) NamedPattern(Tmp2VD, /*implicit*/true);
  Tmp2PBDPattern = new (Ctx) TypedPattern(Tmp2PBDPattern,
                                          TypeLoc::withoutLoc(VD->getType()),
                                          /*implicit*/true);

  auto *Tmp2PBD = PatternBindingDecl::create(Ctx, /*StaticLoc*/SourceLoc(),
                                             StaticSpellingKind::None,
                                             InitValue->getStartLoc(),
                                             Tmp2PBDPattern, InitValue, Get);
  Body.push_back(Tmp2PBD);
  Body.push_back(Tmp2VD);

  // Assign tmp2 into storage.
  auto Tmp2DRE = new (Ctx) DeclRefExpr(Tmp2VD, SourceLoc(), /*Implicit*/true,
                                       AccessSemantics::DirectToStorage);
  createPropertyStoreOrCallSuperclassSetter(Get, Tmp2DRE, Storage, Body, TC);

  // Return tmp2.
  Tmp2DRE = new (Ctx) DeclRefExpr(Tmp2VD, SourceLoc(), /*Implicit*/true,
                                  AccessSemantics::DirectToStorage);

  Body.push_back(new (Ctx) ReturnStmt(SourceLoc(), Tmp2DRE, /*implicit*/true));

  Get->setBody(BraceStmt::create(Ctx, VD->getLoc(), Body, VD->getLoc(),
                                 /*implicit*/true));

  return Get;
}


void TypeChecker::completeLazyVarImplementation(VarDecl *VD) {
  assert(VD->getAttrs().hasAttribute<LazyAttr>());
  assert(VD->getStorageKind() == AbstractStorageDecl::Computed &&
         "variable not validated yet");
  assert(!VD->isStatic() && "Static vars are already lazy on their own");

  // Create the storage property as an optional of VD's type.
  SmallString<64> NameBuf = VD->getName().str();
  NameBuf += ".storage";
  auto StorageName = Context.getIdentifier(NameBuf);
  auto StorageTy = OptionalType::get(VD->getType());

  auto *Storage = new (Context) VarDecl(/*isStatic*/false, /*isLet*/false,
                                        VD->getLoc(), StorageName, StorageTy,
                                        VD->getDeclContext());
  Storage->setUserAccessible(false);
  addMemberToContextIfNeeded(Storage, VD->getDeclContext(), VD);

  // Create the pattern binding decl for the storage decl.  This will get
  // default initialized to nil.
  Pattern *PBDPattern = new (Context) NamedPattern(Storage, /*implicit*/true);
  PBDPattern = new (Context) TypedPattern(PBDPattern,
                                          TypeLoc::withoutLoc(StorageTy),
                                          /*implicit*/true);
  auto *PBD = PatternBindingDecl::create(Context, /*staticloc*/SourceLoc(),
                                         StaticSpellingKind::None,
                                         /*varloc*/VD->getLoc(),
                                         PBDPattern, /*init*/nullptr,
                                         VD->getDeclContext());
  PBD->setImplicit();
  addMemberToContextIfNeeded(PBD, VD->getDeclContext());


  // Now that we've got the storage squared away, synthesize the getter.
  auto *Get = completeLazyPropertyGetter(VD, Storage, *this);

  // The setter just forwards on to storage without materializing the initial
  // value.
  auto *Set = VD->getSetter();
  validateDecl(Set);
  VarDecl *SetValueDecl = getFirstParamDecl(Set);
  // FIXME: This is wrong for observed properties.
  synthesizeTrivialSetter(Set, Storage, SetValueDecl, *this);

  // Mark the vardecl to be final, implicit, and private.  In a class, this
  // prevents it from being dynamically dispatched.  Note that we do this after
  // the accessors are set up, because we don't want the setter for the lazy
  // property to inherit these properties from the storage.
  if (VD->getDeclContext()->isClassOrClassExtensionContext())
    makeFinal(Context, Storage);
  Storage->setImplicit();
  Storage->setAccessibility(Accessibility::Private);
  Storage->setSetterAccessibility(Accessibility::Private);

  typeCheckDecl(Get, true);
  typeCheckDecl(Get, false);

  typeCheckDecl(Set, true);
  typeCheckDecl(Set, false);
}


/// Consider add a materializeForSet accessor to the given storage
/// decl (which has accessors).
void swift::maybeAddMaterializeForSet(AbstractStorageDecl *storage,
                                      TypeChecker &TC) {
  assert(storage->hasAccessorFunctions());

  // Be idempotent.  There are a bunch of places where we want to
  // ensure that there's a materializeForSet accessor.
  if (storage->getMaterializeForSetFunc()) return;

  // Never add materializeForSet to readonly declarations.
  if (!storage->getSetter()) return;

  // Don't bother if the declaration is invalid.
  if (storage->isInvalid()) return;

  // We only need materializeForSet in polymorphic contexts:
  auto containerTy =
    storage->getDeclContext()->getDeclaredTypeOfContext();
  if (!containerTy) return;

  NominalTypeDecl *container = containerTy->getAnyNominal();
  assert(container && "extension of non-nominal type?");

  //   - in non-ObjC protocols, but not protocol extensions.
  if (auto protocol = dyn_cast<ProtocolDecl>(container)) {
    if (protocol->isObjC()) return;
    if (storage->getDeclContext()->isProtocolExtensionContext()) return;

  //   - in classes when the storage decl is not final and does
  //     not override a decl that requires a materializeForSet
  } else if (isa<ClassDecl>(container)) {
    if (storage->isFinal()) {
      auto overridden = storage->getOverriddenDecl();
      if (!overridden || !overridden->getMaterializeForSetFunc())
        return;
    }

  // Enums don't need this.
  } else if (isa<EnumDecl>(container)) {
    return;

  // Structs imported by Clang don't need this, because we can
  // synthesize it later.
  } else {
    assert(isa<StructDecl>(container));
    if (container->hasClangNode())
      return;
  }

  addMaterializeForSet(storage, TC);
}

void swift::maybeAddAccessorsToVariable(VarDecl *var, TypeChecker &TC) {
  // If we've already synthesized accessors or are currently in the process
  // of doing so, don't proceed.
  if (var->getGetter() || var->isBeingTypeChecked())
    return;

  // Local variables don't get accessors.
  if (var->getDeclContext()->isLocalContext())
    return;

  assert(!var->hasAccessorFunctions());

  // Lazy properties require special handling.
  if (var->getAttrs().hasAttribute<LazyAttr>()) {
    var->setIsBeingTypeChecked();

    auto *getter = createGetterPrototype(var, TC);
    // lazy getters are mutating on an enclosing value type.
    if (!var->getDeclContext()->isClassOrClassExtensionContext())
      getter->setMutating();
    getter->setAccessibility(var->getFormalAccess());

    ParamDecl *newValueParam = nullptr;
    auto *setter = createSetterPrototype(var, newValueParam, TC);
    var->makeComputed(var->getLoc(), getter, setter, nullptr,
                      var->getLoc());
    var->setIsBeingTypeChecked(false);

    TC.validateDecl(getter);
    TC.validateDecl(setter);

    addMemberToContextIfNeeded(getter, var->getDeclContext());
    addMemberToContextIfNeeded(setter, var->getDeclContext());
    return;
  }

  // Implicit properties don't get accessors.
  if (var->isImplicit())
    return;

  auto nominal = var->getDeclContext()->isNominalTypeOrNominalTypeExtensionContext();
  if (!nominal) {
    // Fixed-layout global variables don't get accessors.
    if (var->hasFixedLayout())
      return;

  // Stored properties in protocols are converted to computed
  // elsewhere.
  } else if (isa<ProtocolDecl>(nominal)) {
    return;

  // NSManaged properties on classes require special handling.
  } else if (isa<ClassDecl>(nominal)) {
    if (var->getAttrs().hasAttribute<NSManagedAttr>()) {
      var->setIsBeingTypeChecked();
      convertNSManagedStoredVarToComputed(var, TC);
      var->setIsBeingTypeChecked(false);
      return;
    }

  // Stored properties imported from Clang don't get accessors.
  } else if (isa<StructDecl>(nominal)) {
    if (nominal->hasClangNode())
      return;
  }

  // Stored properties in SIL mode don't get accessors.
  if (auto sourceFile = var->getDeclContext()->getParentSourceFile())
    if (sourceFile->Kind == SourceFileKind::SIL)
      return;

  // Everything else gets accessors.
  var->setIsBeingTypeChecked();
  addTrivialAccessorsToStorage(var, TC);
  var->setIsBeingTypeChecked(false);
}

/// \brief Create an implicit struct or class constructor.
///
/// \param decl The struct or class for which a constructor will be created.
/// \param ICK The kind of implicit constructor to create.
///
/// \returns The newly-created constructor, which has already been type-checked
/// (but has not been added to the containing struct or class).
ConstructorDecl *swift::createImplicitConstructor(TypeChecker &tc,
                                                  NominalTypeDecl *decl,
                                                  ImplicitConstructorKind ICK) {
  ASTContext &context = tc.Context;
  SourceLoc Loc = decl->getLoc();
  Accessibility accessLevel = decl->getFormalAccess();
  if (!decl->hasClangNode())
    accessLevel = std::min(accessLevel, Accessibility::Internal);

  // Determine the parameter type of the implicit constructor.
  SmallVector<ParamDecl*, 8> params;
  if (ICK == ImplicitConstructorKind::Memberwise) {
    assert(isa<StructDecl>(decl) && "Only struct have memberwise constructor");

    // Computed and static properties are not initialized.
    for (auto var : decl->getStoredProperties()) {
      if (var->isImplicit())
        continue;
      tc.validateDecl(var);
      
      // Initialized 'let' properties have storage, but don't get an argument
      // to the memberwise initializer since they already have an initial
      // value that cannot be overridden.
      if (var->isLet() && var->getParentInitializer())
        continue;
      
      accessLevel = std::min(accessLevel, var->getFormalAccess());

      auto varType = tc.getTypeOfRValue(var);

      // If var is a lazy property, its value is provided for the underlying
      // storage.  We thus take an optional of the properties type.  We only
      // need to do this because the implicit constructor is added before all
      // the properties are type checked.  Perhaps init() synth should be moved
      // later.
      if (var->getAttrs().hasAttribute<LazyAttr>())
        varType = OptionalType::get(varType);

      // Create the parameter.
      auto *arg = new (context) ParamDecl(/*IsLet*/true, Loc, var->getName(),
                                          Loc, var->getName(), varType, decl);
      arg->setImplicit();
      params.push_back(arg);
    }
  }

  auto paramList = ParameterList::create(context, params);
  
  // Create the constructor.
  DeclName name(context, context.Id_init, paramList);
  auto *selfParam = ParamDecl::createSelf(Loc, decl,
                                          /*static*/false, /*inout*/true);
  auto *ctor = new (context) ConstructorDecl(name, Loc, OTK_None, SourceLoc(),
                                             selfParam, paramList,
                                             nullptr, SourceLoc(), decl);

  // Mark implicit.
  ctor->setImplicit();
  ctor->setAccessibility(accessLevel);

  if (ICK == ImplicitConstructorKind::Memberwise)
    ctor->setIsMemberwiseInitializer();

  // If we are defining a default initializer for a class that has a superclass,
  // it overrides the default initializer of its superclass. Add an implicit
  // 'override' attribute.
  if (auto classDecl = dyn_cast<ClassDecl>(decl)) {
    if (classDecl->getSuperclass())
      ctor->getAttrs().add(new (tc.Context) OverrideAttr(/*implicit=*/true));
  }

  // Type-check the constructor declaration.
  tc.typeCheckDecl(ctor, /*isFirstPass=*/true);

  // If the struct in which this constructor is being added was imported,
  // add it as an external definition.
  if (decl->hasClangNode()) {
    tc.Context.addExternalDecl(ctor);
  }

  return ctor;
}

/// Create a stub body that emits a fatal error message.
static void createStubBody(TypeChecker &tc, ConstructorDecl *ctor) {
  auto unimplementedInitDecl = tc.Context.getUnimplementedInitializerDecl(&tc);
  auto classDecl = ctor->getExtensionType()->getClassOrBoundGenericClass();
  if (!unimplementedInitDecl) {
    tc.diagnose(classDecl->getLoc(), diag::missing_unimplemented_init_runtime);
    return;
  }

  // Create a call to Swift._unimplemented_initializer
  auto loc = classDecl->getLoc();
  Expr *fn = new (tc.Context) DeclRefExpr(unimplementedInitDecl, loc,
                                          /*Implicit=*/true);

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

  Expr *className = new (tc.Context) StringLiteralExpr(fullClassName, loc);
  className = new (tc.Context) ParenExpr(loc, className, loc, false);
  Expr *call = new (tc.Context) CallExpr(fn, className, /*Implicit=*/true);
  ctor->setBody(BraceStmt::create(tc.Context, SourceLoc(),
                                  ASTNode(call),
                                  SourceLoc(),
                                  /*Implicit=*/true));

  // Note that this is a stub implementation.
  ctor->setStubImplementation(true);
}

ConstructorDecl *
swift::createDesignatedInitOverride(TypeChecker &tc,
                                    ClassDecl *classDecl,
                                    ConstructorDecl *superclassCtor,
                                    DesignatedInitKind kind) {
  // Determine the initializer parameters.
  Type superInitType = superclassCtor->getInitializerInterfaceType();
  if (superInitType->is<GenericFunctionType>() ||
      classDecl->getGenericParamsOfContext()) {
    // FIXME: Handle generic initializers as well.
    return nullptr;
  }

  auto &ctx = tc.Context;

  // Create the 'self' declaration and patterns.
  auto *selfDecl = ParamDecl::createSelf(SourceLoc(), classDecl);

  // Create the initializer parameter patterns.
  OptionSet<ParameterList::CloneFlags> options = ParameterList::Implicit;
  options |= ParameterList::Inherited;
  auto *bodyParams = superclassCtor->getParameterList(1)->clone(ctx,options);
  
  // Create the initializer declaration.
  auto ctor = new (ctx) ConstructorDecl(superclassCtor->getFullName(), 
                                        classDecl->getBraces().Start,
                                        superclassCtor->getFailability(),
                                        SourceLoc(), selfDecl, bodyParams,
                                        nullptr, SourceLoc(), classDecl);
  ctor->setImplicit();
  ctor->setAccessibility(std::min(classDecl->getFormalAccess(),
                                  superclassCtor->getFormalAccess()));

  // Make sure the constructor is only as available as its superclass's
  // constructor.
  AvailabilityInference::applyInferredAvailableAttrs(ctor, superclassCtor,
                                                        ctx);

  // Configure 'self'.
  auto selfType = configureImplicitSelf(tc, ctor);

  // Set the type of the initializer.
  configureConstructorType(ctor, selfType, bodyParams->getType(ctx),
                           superclassCtor->isBodyThrowing());
  if (superclassCtor->isObjC()) {
    auto errorConvention = superclassCtor->getForeignErrorConvention();
    markAsObjC(tc, ctor, ObjCReason::ImplicitlyObjC, errorConvention);

    // Inherit the @objc name from the superclass initializer, if it
    // has one.
    if (auto objcAttr = superclassCtor->getAttrs().getAttribute<ObjCAttr>()) {
      if (objcAttr->hasName()) {
        auto *clonedAttr = objcAttr->clone(ctx);
        // Set it to implicit to disable printing it for SIL.
        clonedAttr->setImplicit(true);
        ctor->getAttrs().add(clonedAttr);
      }
    }
  }
  if (superclassCtor->isRequired())
    ctor->getAttrs().add(new (tc.Context) RequiredAttr(/*implicit=*/true));

  // Wire up the overrides.
  ctor->getAttrs().add(new (tc.Context) OverrideAttr(/*Implicit=*/true));
  checkOverrides(tc, ctor);

  if (kind == DesignatedInitKind::Stub) {
    // Make this a stub implementation.
    createStubBody(tc, ctor);
    return ctor;
  }

  // Form the body of a chaining designated initializer.
  assert(kind == DesignatedInitKind::Chaining);

  // Reference to super.init.
  Expr *superRef = new (ctx) SuperRefExpr(selfDecl, SourceLoc(),
                                          /*Implicit=*/true);
  Expr *ctorRef  = new (ctx) UnresolvedConstructorExpr(superRef,
                                                       SourceLoc(),
                                                       SourceLoc(),
                                                       /*Implicit=*/true);

  auto ctorArgs = buildArgumentForwardingExpr(bodyParams->getArray(), ctx);

  // If buildArgumentForwardingExpr failed, then it was because we tried to
  // forward varargs, which cannot be done yet.
  // TODO: We should be able to forward varargs!
  if (!ctorArgs) {
    tc.diagnose(classDecl->getLoc(),
                diag::unsupported_synthesize_init_variadic,
                classDecl->getDeclaredType());
    tc.diagnose(superclassCtor, diag::variadic_superclass_init_here);
    createStubBody(tc, ctor);
    return ctor;
  }

  Expr *superCall = new (ctx) CallExpr(ctorRef, ctorArgs, /*Implicit=*/true);
  if (superclassCtor->isBodyThrowing()) {
    superCall = new (ctx) TryExpr(SourceLoc(), superCall, Type(),
                                  /*Implicit=*/true);
  }
  ctor->setBody(BraceStmt::create(tc.Context, SourceLoc(),
                                  ASTNode(superCall),
                                  SourceLoc(),
                                  /*Implicit=*/true));

  return ctor;
}

void TypeChecker::addImplicitDestructor(ClassDecl *CD) {
  if (CD->hasDestructor() || CD->isInvalid())
    return;

  auto *selfDecl = ParamDecl::createSelf(CD->getLoc(), CD);

  auto *DD = new (Context) DestructorDecl(Context.Id_deinit, CD->getLoc(),
                                          selfDecl, CD);

  DD->setImplicit();

  // Type-check the destructor declaration.
  typeCheckDecl(DD, /*isFirstPass=*/true);

  // Create an empty body for the destructor.
  DD->setBody(BraceStmt::create(Context, CD->getLoc(), { }, CD->getLoc(),true));
  CD->addMember(DD);
  CD->setHasDestructor();
}