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 - 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
//
//===----------------------------------------------------------------------===//
//
// This file implements semantic analysis for declarations.
//
//===----------------------------------------------------------------------===//

#include "CodeSynthesis.h"

#include "ConstraintSystem.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 "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
using namespace swift;

const bool IsImplicit = true;

Expr *swift::buildSelfReference(VarDecl *selfDecl,
                                SelfAccessorKind selfAccessorKind,
                                bool isLValue,
                                ASTContext &ctx) {
  switch (selfAccessorKind) {
  case SelfAccessorKind::Peer:
    return new (ctx) DeclRefExpr(selfDecl, DeclNameLoc(), IsImplicit,
                                 AccessSemantics::Ordinary,
                                 isLValue
                                  ? LValueType::get(selfDecl->getType())
                                  : selfDecl->getType());

  case SelfAccessorKind::Super:
    assert(!isLValue);
    return new (ctx) SuperRefExpr(selfDecl, SourceLoc(), IsImplicit,
                                  selfDecl->getType()->getSuperclass());
  }
  llvm_unreachable("bad self access kind");
}

/// Build an expression that evaluates the specified parameter list as a tuple
/// or paren expr, suitable for use in an apply expr.
Expr *swift::buildArgumentForwardingExpr(ArrayRef<ParamDecl*> params,
                                         ASTContext &ctx) {
  SmallVector<Identifier, 4> labels;
  SmallVector<SourceLoc, 4> labelLocs;
  SmallVector<Expr *, 4> args;
  SmallVector<AnyFunctionType::Param, 4> elts;

  for (auto param : params) {
    auto type = param->getType();
    elts.push_back(param->toFunctionParam(type));

    Expr *ref = new (ctx) DeclRefExpr(param, DeclNameLoc(), /*implicit*/ true);
    ref->setType(param->isInOut() ? LValueType::get(type) : type);

    if (param->isInOut()) {
      ref = new (ctx) InOutExpr(SourceLoc(), ref, type, /*isImplicit=*/true);
    } else if (param->isVariadic()) {
      ref = new (ctx) VarargExpansionExpr(ref, /*implicit*/ true);
      ref->setType(type);
    }

    args.push_back(ref);
    
    labels.push_back(param->getArgumentName());
    labelLocs.push_back(SourceLoc());
  }

  Expr *argExpr;
  if (args.size() == 1 &&
      labels[0].empty() &&
      !isa<VarargExpansionExpr>(args[0])) {
    argExpr = new (ctx) ParenExpr(SourceLoc(), args[0], SourceLoc(),
                                  /*hasTrailingClosure=*/false);
    argExpr->setImplicit();
  } else {
    argExpr = TupleExpr::create(ctx, SourceLoc(), args, labels, labelLocs,
                                SourceLoc(), false, IsImplicit);
  }

  auto argTy = AnyFunctionType::composeInput(ctx, elts, /*canonical*/false);
  argExpr->setType(argTy);

  return argExpr;
}

static void maybeAddMemberwiseDefaultArg(ParamDecl *arg, VarDecl *var,
                    SmallVectorImpl<DefaultArgumentInitializer *> &defaultInits,
                                         unsigned paramSize, ASTContext &ctx) {
  // First and foremost, if this is a constant don't bother.
  if (var->isLet())
    return;

  // We can only provide default values for patterns binding a single variable.
  // i.e. var (a, b) = getSomeTuple() is not allowed.
  if (!var->getParentPattern()->getSingleVar())
    return;

  // Whether we have explicit initialization.
  bool isExplicitlyInitialized = false;
  if (auto pbd = var->getParentPatternBinding()) {
    auto &entry = pbd->getPatternEntryForVarDecl(var);
    isExplicitlyInitialized =
      entry.isInitialized() && entry.getEqualLoc().isValid();
  }

  // Whether we can default-initialize this property.
  auto binding = var->getParentPatternBinding();
  bool isDefaultInitializable =
      var->getAttrs().hasAttribute<LazyAttr>() ||
      (binding && binding->isDefaultInitializable());

  // If this is neither explicitly initialized nor
  // default-initializable, don't add anything.
  if (!isExplicitlyInitialized && !isDefaultInitializable)
    return;

  // We can add a default value now.

  // Give this some bogus context right now, we'll fix it after making
  // the constructor.
  auto *initDC = new (ctx) DefaultArgumentInitializer(
    arg->getDeclContext(), paramSize);

  defaultInits.push_back(initDC);

  // If the variable has a type T? and no initial value, return a nil literal
  // default arg. All lazy variables return a nil literal as well. *Note* that
  // the type will always be a sugared T? because we don't default init an
  // explicit Optional<T>.
  bool isNilInitialized =
    var->getAttrs().hasAttribute<LazyAttr>() ||
    (!isExplicitlyInitialized && isDefaultInitializable &&
     var->getValueInterfaceType()->getAnyNominal() == ctx.getOptionalDecl() &&
     !var->getAttachedPropertyWrapperTypeInfo(0).defaultInit);
  if (isNilInitialized) {
    arg->setDefaultArgumentKind(DefaultArgumentKind::NilLiteral);
    return;
  }

  // If there's a backing storage property, the memberwise initializer
  // will be in terms of that.
  VarDecl *backingStorageVar = var->getPropertyWrapperBackingProperty();

  // Set the default value to the variable. When we emit this in silgen
  // we're going to call the variable's initializer expression.
  arg->setStoredProperty(backingStorageVar ? backingStorageVar : var);
  arg->setDefaultArgumentKind(DefaultArgumentKind::StoredProperty);
}

/// Describes the kind of implicit constructor that will be
/// generated.
enum class ImplicitConstructorKind {
  /// The default constructor, which default-initializes each
  /// of the instance variables.
  Default,
  /// The memberwise constructor, which initializes each of
  /// the instance variables from a parameter of the same type and
  /// name.
  Memberwise
};

/// 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).
static ConstructorDecl *createImplicitConstructor(NominalTypeDecl *decl,
                                                  ImplicitConstructorKind ICK,
                                                  ASTContext &ctx) {
  assert(!decl->hasClangNode());

  SourceLoc Loc = decl->getLoc();
  auto accessLevel = AccessLevel::Internal;

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

    for (auto member : decl->getMembers()) {
      auto var = dyn_cast<VarDecl>(member);
      if (!var)
        continue;

      if (!var->isMemberwiseInitialized(/*preferDeclaredProperties=*/true))
        continue;

      accessLevel = std::min(accessLevel, var->getFormalAccess());

      auto varInterfaceType = var->getValueInterfaceType();

      if (var->getAttrs().hasAttribute<LazyAttr>()) {
        // If var is a lazy property, its value is provided for the underlying
        // storage.  We thus take an optional of the property's type.  We only
        // need to do this because the implicit initializer is added before all
        // the properties are type checked.  Perhaps init() synth should be
        // moved later.
        varInterfaceType = OptionalType::get(varInterfaceType);
      } else if (Type backingPropertyType =
                     var->getPropertyWrapperBackingPropertyType()) {
        // For a property that has a wrapper, writing the initializer
        // with an '=' implies that the memberwise initializer should also
        // accept a value of the original property type. Otherwise, the
        // memberwise initializer will be in terms of the backing storage
        // type.
        if (!var->isPropertyMemberwiseInitializedWithWrappedType()) {
          varInterfaceType = backingPropertyType;
        }
      }

      // Create the parameter.
      auto *arg = new (ctx)
          ParamDecl(ParamDecl::Specifier::Default, SourceLoc(), Loc,
                    var->getName(), Loc, var->getName(), decl);
      arg->setInterfaceType(varInterfaceType);
      arg->setImplicit();
      
      maybeAddMemberwiseDefaultArg(arg, var, defaultInits, params.size(), ctx);
      
      params.push_back(arg);
    }
  }

  auto paramList = ParameterList::create(ctx, params);
  
  // Create the constructor.
  DeclName name(ctx, DeclBaseName::createConstructor(), paramList);
  auto *ctor =
    new (ctx) ConstructorDecl(name, Loc,
                              /*Failable=*/false, /*FailabilityLoc=*/SourceLoc(),
                              /*Throws=*/false, /*ThrowsLoc=*/SourceLoc(),
                              paramList, /*GenericParams=*/nullptr, decl);

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

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

    // Fix default argument init contexts now that we have a constructor.
    for (auto initDC : defaultInits) {
      initDC->changeFunction(ctor, paramList);
    }
  }

  // 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 (ctx) OverrideAttr(/*IsImplicit=*/true));
  }

  return ctor;
}

ConstructorDecl *swift::createMemberwiseImplicitConstructor(
    TypeChecker &tc, NominalTypeDecl *decl) {
  return createImplicitConstructor(decl, ImplicitConstructorKind::Memberwise,
                                   tc.Context);
}

/// Create a stub body that emits a fatal error message.
static std::pair<BraceStmt *, bool>
synthesizeStubBody(AbstractFunctionDecl *fn, void *) {
  auto *ctor = cast<ConstructorDecl>(fn);
  auto &ctx = ctor->getASTContext();

  auto unimplementedInitDecl = ctx.getUnimplementedInitializer();
  auto classDecl = ctor->getDeclContext()->getSelfClassDecl();
  if (!unimplementedInitDecl) {
    ctx.Diags.diagnose(classDecl->getLoc(),
                       diag::missing_unimplemented_init_runtime);
    return { nullptr, true };
  }

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

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

  // Create a call to Swift._unimplementedInitializer
  auto loc = classDecl->getLoc();
  Expr *ref = new (ctx) DeclRefExpr(unimplementedInitDecl,
                                   DeclNameLoc(loc),
                                   /*Implicit=*/true);
  ref->setType(unimplementedInitDecl->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 *initName = new (ctx) MagicIdentifierLiteralExpr(
    MagicIdentifierLiteralExpr::Function, loc, /*Implicit=*/true);
  initName->setType(staticStringType);
  initName->setBuiltinInitializer(staticStringInit);

  auto *file = new (ctx) MagicIdentifierLiteralExpr(
    MagicIdentifierLiteralExpr::File, 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, initName, file, line, column }, {});
  call->setType(ctx.getNeverType());
  call->setThrows(false);

  SmallVector<ASTNode, 2> stmts;
  stmts.push_back(call);
  stmts.push_back(new (ctx) ReturnStmt(SourceLoc(), /*Result=*/nullptr));
  return { BraceStmt::create(ctx, SourceLoc(), stmts, SourceLoc(),
                             /*implicit=*/true),
           /*isTypeChecked=*/true };
}

static std::tuple<GenericSignature, GenericParamList *, SubstitutionMap>
configureGenericDesignatedInitOverride(ASTContext &ctx,
                                       ClassDecl *classDecl,
                                       Type superclassTy,
                                       ConstructorDecl *superclassCtor) {
  auto *superclassDecl = superclassTy->getAnyNominal();

  auto *moduleDecl = classDecl->getParentModule();
  auto subMap = superclassTy->getContextSubstitutionMap(
      moduleDecl, superclassDecl);

  GenericSignature genericSig;

  // Inheriting initializers that have their own generic parameters
  auto *genericParams = superclassCtor->getGenericParams();
  if (genericParams) {
    SmallVector<GenericTypeParamDecl *, 4> newParams;

    // First, clone the superclass constructor's generic parameter list,
    // but change the depth of the generic parameters to be one greater
    // than the depth of the subclass.
    unsigned depth = 0;
    if (auto genericSig = classDecl->getGenericSignature())
      depth = genericSig->getGenericParams().back()->getDepth() + 1;

    for (auto *param : genericParams->getParams()) {
      auto *newParam = new (ctx) GenericTypeParamDecl(classDecl,
                                                      param->getName(),
                                                      SourceLoc(),
                                                      depth,
                                                      param->getIndex());
      newParams.push_back(newParam);
    }

    // We don't have to clone the requirements, because they're not
    // used for anything.
    genericParams = GenericParamList::create(ctx,
                                             SourceLoc(),
                                             newParams,
                                             SourceLoc(),
                                             ArrayRef<RequirementRepr>(),
                                             SourceLoc());

    // Build a generic signature for the derived class initializer.

    // Add the generic parameters.
    SmallVector<GenericTypeParamType *, 1> newParamTypes;
    for (auto *newParam : newParams) {
      newParamTypes.push_back(
          newParam->getDeclaredInterfaceType()->castTo<GenericTypeParamType>());
    }

    auto superclassSig = superclassCtor->getGenericSignature();

    unsigned superclassDepth = 0;
    if (auto genericSig = superclassDecl->getGenericSignature())
      superclassDepth = genericSig->getGenericParams().back()->getDepth() + 1;

    // We're going to be substituting the requirements of the base class
    // initializer to form the requirements of the derived class initializer.
    auto substFn = [&](SubstitutableType *type) -> Type {
      auto *gp = cast<GenericTypeParamType>(type);
      if (gp->getDepth() < superclassDepth)
        return Type(gp).subst(subMap);
      return CanGenericTypeParamType::get(
        gp->getDepth() - superclassDepth + depth,
          gp->getIndex(),
          ctx);
    };

    auto lookupConformanceFn =
      [&](CanType depTy, Type substTy, ProtocolDecl *proto)
        -> Optional<ProtocolConformanceRef> {
      if (auto conf = subMap.lookupConformance(depTy, proto))
        return conf;

      return ProtocolConformanceRef(proto);
    };

    SmallVector<Requirement, 2> requirements;
    for (auto reqt : superclassSig->getRequirements())
      if (auto substReqt = reqt.subst(substFn, lookupConformanceFn))
        requirements.push_back(*substReqt);

    // Now form the substitution map that will be used to remap parameter
    // types.
    subMap = SubstitutionMap::get(superclassSig,
                                  substFn, lookupConformanceFn);

    genericSig = evaluateOrDefault(
        ctx.evaluator,
        AbstractGenericSignatureRequest{
          classDecl->getGenericSignature().getPointer(),
          std::move(newParamTypes),
          std::move(requirements)
        },
        GenericSignature());
  } else {
    genericSig = classDecl->getGenericSignature();
  }

  return std::make_tuple(genericSig, genericParams, subMap);
}

static void
configureInheritedDesignatedInitAttributes(ClassDecl *classDecl,
                                           ConstructorDecl *ctor,
                                           ConstructorDecl *superclassCtor,
                                           ASTContext &ctx) {
  assert(ctor->getDeclContext() == classDecl);

  AccessLevel access = classDecl->getFormalAccess();
  access = std::max(access, AccessLevel::Internal);
  access = std::min(access, superclassCtor->getFormalAccess());

  ctor->setAccess(access);

  AccessScope superclassInliningAccessScope =
      superclassCtor->getFormalAccessScope(/*useDC*/nullptr,
                                           /*usableFromInlineAsPublic=*/true);

  if (superclassInliningAccessScope.isPublic()) {
    if (superclassCtor->getAttrs().hasAttribute<InlinableAttr>()) {
      // Inherit the @inlinable attribute.
      auto *clonedAttr = new (ctx) InlinableAttr(/*implicit=*/true);
      ctor->getAttrs().add(clonedAttr);

    } else if (access == AccessLevel::Internal && !superclassCtor->isDynamic()){
      // Inherit the @usableFromInline attribute.
      auto *clonedAttr = new (ctx) UsableFromInlineAttr(/*implicit=*/true);
      ctor->getAttrs().add(clonedAttr);
    }
  }

  // Inherit the @discardableResult attribute.
  if (superclassCtor->getAttrs().hasAttribute<DiscardableResultAttr>()) {
    auto *clonedAttr = new (ctx) DiscardableResultAttr(/*implicit=*/true);
    ctor->getAttrs().add(clonedAttr);
  }

  // If the superclass has its own availability, make sure the synthesized
  // constructor is only as available as its superclass's constructor.
  if (superclassCtor->getAttrs().hasAttribute<AvailableAttr>()) {
    SmallVector<Decl *, 2> asAvailableAs;

    // We don't have to look at enclosing contexts of the superclass constructor,
    // because designated initializers must always be defined in the superclass
    // body, and we already enforce that a superclass is at least as available as
    // a subclass.
    asAvailableAs.push_back(superclassCtor);
    Decl *parentDecl = classDecl;
    while (parentDecl != nullptr) {
      asAvailableAs.push_back(parentDecl);
      parentDecl = parentDecl->getDeclContext()->getAsDecl();
    }
    AvailabilityInference::applyInferredAvailableAttrs(
        ctor, asAvailableAs, ctx);
  }

  // Wire up the overrides.
  ctor->setOverriddenDecl(superclassCtor);

  if (superclassCtor->isRequired())
    ctor->getAttrs().add(new (ctx) RequiredAttr(/*IsImplicit=*/false));
  else
    ctor->getAttrs().add(new (ctx) OverrideAttr(/*IsImplicit=*/false));

  // If the superclass constructor is @objc but the subclass constructor is
  // not representable in Objective-C, add @nonobjc implicitly.
  Optional<ForeignErrorConvention> errorConvention;
  if (superclassCtor->isObjC() &&
      !isRepresentableInObjC(ctor, ObjCReason::MemberOfObjCSubclass,
                             errorConvention))
    ctor->getAttrs().add(new (ctx) NonObjCAttr(/*isImplicit=*/true));
}

static std::pair<BraceStmt *, bool>
synthesizeDesignatedInitOverride(AbstractFunctionDecl *fn, void *context) {
  auto *ctor = cast<ConstructorDecl>(fn);
  auto &ctx = ctor->getASTContext();

  auto *superclassCtor = (ConstructorDecl *) context;

  // Reference to super.init.
  auto *selfDecl = ctor->getImplicitSelfDecl();
  auto *superRef = buildSelfReference(selfDecl, SelfAccessorKind::Super,
                                      /*isLValue=*/false, ctx);

  SubstitutionMap subs;
  if (auto *genericEnv = fn->getGenericEnvironment())
    subs = genericEnv->getForwardingSubstitutionMap();
  subs = SubstitutionMap::getOverrideSubstitutions(superclassCtor, fn, subs);
  ConcreteDeclRef ctorRef(superclassCtor, subs);

  auto type = superclassCtor->getInitializerInterfaceType().subst(subs);
  auto *ctorRefExpr =
      new (ctx) OtherConstructorDeclRefExpr(ctorRef, DeclNameLoc(),
                                            IsImplicit, type);

  if (auto *funcTy = type->getAs<FunctionType>())
    type = funcTy->getResult();
  auto *superclassCtorRefExpr =
      new (ctx) DotSyntaxCallExpr(ctorRefExpr, SourceLoc(), superRef, type);
  superclassCtorRefExpr->setIsSuper(true);
  superclassCtorRefExpr->setThrows(false);

  auto *bodyParams = ctor->getParameters();
  auto ctorArgs = buildArgumentForwardingExpr(bodyParams->getArray(), ctx);
  auto *superclassCallExpr =
    CallExpr::create(ctx, superclassCtorRefExpr, ctorArgs,
                     superclassCtor->getFullName().getArgumentNames(), { },
                     /*hasTrailingClosure=*/false, /*implicit=*/true);

  if (auto *funcTy = type->getAs<FunctionType>())
    type = funcTy->getResult();
  superclassCallExpr->setType(type);
  superclassCallExpr->setThrows(superclassCtor->hasThrows());

  Expr *expr = superclassCallExpr;

  if (superclassCtor->hasThrows()) {
    expr = new (ctx) TryExpr(SourceLoc(), expr, type, /*implicit=*/true);
  }

  auto *rebindSelfExpr =
    new (ctx) RebindSelfInConstructorExpr(expr, selfDecl);

  SmallVector<ASTNode, 2> stmts;
  stmts.push_back(rebindSelfExpr);
  stmts.push_back(new (ctx) ReturnStmt(SourceLoc(), /*Result=*/nullptr));
  return { BraceStmt::create(ctx, SourceLoc(), stmts, SourceLoc(),
                            /*implicit=*/true),
           /*isTypeChecked=*/true };
}

/// The kind of designated initializer to synthesize.
enum class DesignatedInitKind {
  /// A stub initializer, which is not visible to name lookup and
  /// merely aborts at runtime.
  Stub,

  /// An initializer that simply chains to the corresponding
  /// superclass initializer.
  Chaining
};

/// Create a new initializer that overrides the given designated
/// initializer.
///
/// \param classDecl The subclass in which the new initializer will
/// be declared.
///
/// \param superclassCtor The superclass initializer for which this
/// routine will create an override.
///
/// \param kind The kind of initializer to synthesize.
///
/// \returns the newly-created initializer that overrides \p
/// superclassCtor.
static ConstructorDecl *
createDesignatedInitOverride(ClassDecl *classDecl,
                             ConstructorDecl *superclassCtor,
                             DesignatedInitKind kind,
                             ASTContext &ctx) {
  // Lookup will sometimes give us initializers that are from the ancestors of
  // our immediate superclass.  So, from the superclass constructor, we look
  // one level up to the enclosing type context which will either be a class
  // or an extension.  We can use the type declared in that context to check
  // if it's our immediate superclass and give up if we didn't.
  //
  // FIXME: Remove this when lookup of initializers becomes restricted to our
  // immediate superclass.
  auto *superclassCtorDecl =
      superclassCtor->getDeclContext()->getSelfNominalTypeDecl();
  Type superclassTy = classDecl->getSuperclass();
  NominalTypeDecl *superclassDecl = superclassTy->getAnyNominal();
  if (superclassCtorDecl != superclassDecl) {
    return nullptr;
  }

  GenericSignature genericSig;
  GenericParamList *genericParams;
  SubstitutionMap subMap;

  std::tie(genericSig, genericParams, subMap) =
      configureGenericDesignatedInitOverride(ctx,
                                             classDecl,
                                             superclassTy,
                                             superclassCtor);

  // Determine the initializer parameters.

  // Create the initializer parameter patterns.
  OptionSet<ParameterList::CloneFlags> options
    = (ParameterList::Implicit |
       ParameterList::Inherited |
       ParameterList::WithoutTypes);
  auto *superclassParams = superclassCtor->getParameters();
  auto *bodyParams = superclassParams->clone(ctx, options);

  // If the superclass is generic, we need to map the superclass constructor's
  // parameter types into the generic context of our class.
  //
  // We might have to apply substitutions, if for example we have a declaration
  // like 'class A : B<Int>'.
  for (unsigned idx : range(superclassParams->size())) {
    auto *superclassParam = superclassParams->get(idx);
    auto *bodyParam = bodyParams->get(idx);

    auto paramTy = superclassParam->getInterfaceType();
    auto substTy = paramTy.subst(subMap);

    bodyParam->setInterfaceType(substTy);
    bodyParam->getTypeLoc() = TypeLoc::withoutLoc(substTy);
  }

  // Create the initializer declaration, inheriting the name,
  // failability, and throws from the superclass initializer.
  auto ctor =
    new (ctx) ConstructorDecl(superclassCtor->getFullName(),
                              classDecl->getBraces().Start,
                              superclassCtor->isFailable(),
                              /*FailabilityLoc=*/SourceLoc(),
                              /*Throws=*/superclassCtor->hasThrows(),
                              /*ThrowsLoc=*/SourceLoc(),
                              bodyParams, genericParams, classDecl);

  ctor->setImplicit();

  // Set the interface type of the initializer.
  ctor->setGenericSignature(genericSig);
  ctor->computeType();

  ctor->setImplicitlyUnwrappedOptional(
    superclassCtor->isImplicitlyUnwrappedOptional());

  configureInheritedDesignatedInitAttributes(classDecl, ctor,
                                             superclassCtor, ctx);

  if (kind == DesignatedInitKind::Stub) {
    // Make this a stub implementation.
    ctor->setBodySynthesizer(synthesizeStubBody);

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

    return ctor;
  }

  // Form the body of a chaining designated initializer.
  assert(kind == DesignatedInitKind::Chaining);
  ctor->setBodySynthesizer(synthesizeDesignatedInitOverride, superclassCtor);

  return ctor;
}

/// Diagnose a missing required initializer.
static void diagnoseMissingRequiredInitializer(
              ClassDecl *classDecl,
              ConstructorDecl *superInitializer,
              ASTContext &ctx) {
  // Find the location at which we should insert the new initializer.
  SourceLoc insertionLoc;
  SourceLoc indentationLoc;
  for (auto member : classDecl->getMembers()) {
    // If we don't have an indentation location yet, grab one from this
    // member.
    if (indentationLoc.isInvalid()) {
      indentationLoc = member->getLoc();
    }

    // We only want to look at explicit constructors.
    auto ctor = dyn_cast<ConstructorDecl>(member);
    if (!ctor)
      continue;

    if (ctor->isImplicit())
      continue;

    insertionLoc = ctor->getEndLoc();
    indentationLoc = ctor->getLoc();
  }

  // If no initializers were listed, start at the opening '{' for the class.
  if (insertionLoc.isInvalid()) {
    insertionLoc = classDecl->getBraces().Start;
  }
  if (indentationLoc.isInvalid()) {
    indentationLoc = classDecl->getBraces().End;
  }

  // Adjust the insertion location to point at the end of this line (i.e.,
  // the start of the next line).
  insertionLoc = Lexer::getLocForEndOfLine(ctx.SourceMgr,
                                           insertionLoc);

  // Find the indentation used on the indentation line.
  StringRef extraIndentation;
  StringRef indentation = Lexer::getIndentationForLine(
      ctx.SourceMgr, indentationLoc, &extraIndentation);

  // Pretty-print the superclass initializer into a string.
  // FIXME: Form a new initializer by performing the appropriate
  // substitutions of subclass types into the superclass types, so that
  // we get the right generic parameters.
  std::string initializerText;
  {
    PrintOptions options;
    options.PrintImplicitAttrs = false;

    // Render the text.
    llvm::raw_string_ostream out(initializerText);
    {
      ExtraIndentStreamPrinter printer(out, indentation);
      printer.printNewline();

      // If there is no explicit 'required', print one.
      bool hasExplicitRequiredAttr = false;
      if (auto requiredAttr
            = superInitializer->getAttrs().getAttribute<RequiredAttr>())
          hasExplicitRequiredAttr = !requiredAttr->isImplicit();

      if (!hasExplicitRequiredAttr)
        printer << "required ";

      superInitializer->print(printer, options);
    }

    // Add a dummy body.
    out << " {\n";
    out << indentation << extraIndentation << "fatalError(\"";
    superInitializer->getFullName().printPretty(out);
    out << " has not been implemented\")\n";
    out << indentation << "}\n";
  }

  // Complain.
  ctx.Diags.diagnose(insertionLoc, diag::required_initializer_missing,
                     superInitializer->getFullName(),
                     superInitializer->getDeclContext()->getDeclaredInterfaceType())
    .fixItInsert(insertionLoc, initializerText);

  ctx.Diags.diagnose(findNonImplicitRequiredInit(superInitializer),
                     diag::required_initializer_here);
}

static bool areAllStoredPropertiesDefaultInitializable(NominalTypeDecl *decl) {
  if (decl->hasClangNode())
    return true;

  for (auto member : decl->getMembers()) {
    // If a stored property lacks an initial value and if there is no way to
    // synthesize an initial value (e.g. for an optional) then we suppress
    // generation of the default initializer.
    if (auto pbd = dyn_cast<PatternBindingDecl>(member)) {
      if (pbd->hasStorage() && !pbd->isStatic()) {
        for (auto entry : pbd->getPatternList()) {
          if (entry.isInitialized()) continue;

          // If one of the bound variables is @NSManaged, go ahead no matter
          // what.
          bool CheckDefaultInitializer = true;
          entry.getPattern()->forEachVariable([&](VarDecl *vd) {
            if (vd->getAttrs().hasAttribute<NSManagedAttr>())
              CheckDefaultInitializer = false;
          });
        
          // If we cannot default initialize the property, we cannot
          // synthesize a default initializer for the class.
          if (CheckDefaultInitializer && !pbd->isDefaultInitializable())
            return false;
        }
      }
    }
  }

  return true;
}

static void addImplicitConstructorsToStruct(StructDecl *decl, ASTContext &ctx) {
  assert(!decl->hasClangNode() &&
         "ClangImporter is responsible for adding implicit constructors");
  assert(!decl->hasUnreferenceableStorage() &&
         "User-defined structs cannot have unreferenceable storage");

  decl->setAddedImplicitInitializers();

  // Check whether there is a user-declared constructor or an instance
  // variable.
  bool FoundMemberwiseInitializedProperty = false;

  for (auto member : decl->getMembers()) {
    if (auto ctor = dyn_cast<ConstructorDecl>(member)) {
      // Initializers that were synthesized to fulfill derived conformances
      // should not prevent default initializer synthesis.
      if (ctor->isDesignatedInit() && !ctor->isSynthesized())
        return;
    }

    if (auto var = dyn_cast<VarDecl>(member)) {
      // If this is a backing storage property for a property wrapper,
      // skip it.
      if (var->getOriginalWrappedProperty())
        continue;

      if (var->isMemberwiseInitialized(/*preferDeclaredProperties=*/true)) {
        // 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->isParentInitialized()) {
          // We cannot handle properties like:
          //   let (a,b) = (1,2)
          // for now, just disable implicit init synthesization in structs in
          // this case.
          auto SP = var->getParentPattern();
          if (auto *TP = dyn_cast<TypedPattern>(SP))
            SP = TP->getSubPattern();
          if (!isa<NamedPattern>(SP))
            return;

          continue;
        }

        FoundMemberwiseInitializedProperty = true;
      }
    }
  }

  if (FoundMemberwiseInitializedProperty) {
    // Create the implicit memberwise constructor.
    auto ctor = createImplicitConstructor(
        decl, ImplicitConstructorKind::Memberwise, ctx);
    decl->addMember(ctor);
  }

  if (areAllStoredPropertiesDefaultInitializable(decl))
    TypeChecker::defineDefaultConstructor(decl);
}

static void addImplicitConstructorsToClass(ClassDecl *decl, ASTContext &ctx) {
  // Bail out if we're validating one of our constructors already;
  // we'll revisit the issue later.
  if (!decl->hasClangNode()) {
    for (auto member : decl->getMembers()) {
      if (auto ctor = dyn_cast<ConstructorDecl>(member)) {
        if (ctor->isRecursiveValidation())
          return;
      }
    }
  }

  decl->setAddedImplicitInitializers();

  // Check whether there is a user-declared constructor or an instance
  // variable.
  bool FoundDesignatedInit = false;

  SmallVector<std::pair<ValueDecl *, Type>, 4> declaredInitializers;
  llvm::SmallPtrSet<ConstructorDecl *, 4> overriddenInits;
  if (decl->hasClangNode()) {
    // Objective-C classes may have interesting initializers in extensions.
    for (auto member : decl->lookupDirect(DeclBaseName::createConstructor())) {
      auto ctor = dyn_cast<ConstructorDecl>(member);
      if (!ctor)
        continue;

      // Swift initializers added in extensions of Objective-C classes can never
      // be overrides.
      if (!ctor->hasClangNode())
        continue;

      if (auto overridden = ctor->getOverriddenDecl())
        overriddenInits.insert(overridden);
    }

  } else {
    for (auto member : decl->getMembers()) {
      if (auto ctor = dyn_cast<ConstructorDecl>(member)) {
        // Initializers that were synthesized to fulfill derived conformances
        // should not prevent default initializer synthesis.
        if (ctor->isDesignatedInit() && !ctor->isSynthesized())
          FoundDesignatedInit = true;

        if (!ctor->isInvalid()) {
          auto type = getMemberTypeForComparison(ctx, ctor, nullptr);
          declaredInitializers.push_back({ctor, type});
        }

        if (auto overridden = ctor->getOverriddenDecl())
          overriddenInits.insert(overridden);

        continue;
      }
    }
  }

  bool SuppressDefaultInitializer =
    !areAllStoredPropertiesDefaultInitializable(decl);

  // For a class with a superclass, automatically define overrides
  // for all of the superclass's designated initializers.
  if (Type superclassTy = decl->getSuperclass()) {
    bool canInheritInitializers = (!SuppressDefaultInitializer &&
                                   !FoundDesignatedInit);

    // We can't define these overrides if we have any uninitialized
    // stored properties.
    if (SuppressDefaultInitializer && !FoundDesignatedInit &&
        !decl->hasClangNode()) {
      return;
    }

    auto *superclassDecl = superclassTy->getClassOrBoundGenericClass();
    assert(superclassDecl && "Superclass of class is not a class?");
    if (!superclassDecl->addedImplicitInitializers())
      ctx.getLazyResolver()->resolveImplicitConstructors(superclassDecl);

    auto ctors = TypeChecker::lookupConstructors(
        decl, superclassTy,
        NameLookupFlags::IgnoreAccessControl);

    bool canInheritConvenienceInitalizers =
        !superclassDecl->hasMissingDesignatedInitializers();
    SmallVector<ConstructorDecl *, 4> requiredConvenienceInitializers;
    for (auto memberResult : ctors) {
      auto member = memberResult.getValueDecl();

      // Skip unavailable superclass initializers.
      if (AvailableAttr::isUnavailable(member))
        continue;

      // Skip invalid superclass initializers.
      auto superclassCtor = dyn_cast<ConstructorDecl>(member);
      if (superclassCtor->isInvalid())
        continue;

      // If we have an override for this constructor, it's okay.
      if (overriddenInits.count(superclassCtor) > 0)
        continue;

      // We only care about required or designated initializers.
      if (!superclassCtor->isDesignatedInit()) {
        if (superclassCtor->isRequired()) {
          assert(superclassCtor->isInheritable() &&
                 "factory initializers cannot be 'required'");
          requiredConvenienceInitializers.push_back(superclassCtor);
        }
        continue;
      }

      // Otherwise, it may no longer be safe to inherit convenience
      // initializers.
      canInheritConvenienceInitalizers &= canInheritInitializers;

      // Everything after this is only relevant for Swift classes being defined.
      if (decl->hasClangNode())
        continue;

      // If the superclass initializer is not accessible from the derived
      // class, don't synthesize an override, since we cannot reference the
      // superclass initializer's method descriptor at all.
      //
      // FIXME: This should be checked earlier as part of calculating
      // canInheritInitializers.
      if (!superclassCtor->isAccessibleFrom(decl))
        continue;

      // Diagnose a missing override of a required initializer.
      if (superclassCtor->isRequired() && !canInheritInitializers) {
        diagnoseMissingRequiredInitializer(decl, superclassCtor, ctx);
        continue;
      }

      // A designated or required initializer has not been overridden.

      bool alreadyDeclared = false;
      for (const auto &ctorAndType : declaredInitializers) {
        auto *ctor = ctorAndType.first;
        auto type = ctorAndType.second;
        auto parentType = getMemberTypeForComparison(
            ctx, superclassCtor, ctor);

        if (isOverrideBasedOnType(ctor, type, superclassCtor, parentType)) {
          alreadyDeclared = true;
          break;
        }
      }

      // If we have already introduced an initializer with this parameter type,
      // don't add one now.
      if (alreadyDeclared)
        continue;

      // If we're inheriting initializers, create an override delegating
      // to 'super.init'. Otherwise, create a stub which traps at runtime.
      auto kind = canInheritInitializers
                    ? DesignatedInitKind::Chaining
                    : DesignatedInitKind::Stub;

      if (auto ctor = createDesignatedInitOverride(
                        decl, superclassCtor, kind, ctx)) {
        decl->addMember(ctor);
      }
    }

    if (canInheritConvenienceInitalizers) {
      decl->setInheritsSuperclassInitializers();
    } else {
      for (ConstructorDecl *requiredCtor : requiredConvenienceInitializers)
        diagnoseMissingRequiredInitializer(decl, requiredCtor, ctx);
    }

    return;
  }

  if (!FoundDesignatedInit) {
    // For a class with no superclass, automatically define a default
    // constructor.

    // ... unless there are uninitialized stored properties.
    if (SuppressDefaultInitializer)
      return;

    // Clang-imported types should never get a default constructor, just a
    // memberwise one.
    if (decl->hasClangNode())
      return;

    TypeChecker::defineDefaultConstructor(decl);
  }
}

void TypeChecker::addImplicitConstructors(NominalTypeDecl *decl) {
  // If we already added implicit initializers, we're done.
  if (decl->addedImplicitInitializers())
    return;
  
  // Don't add implicit constructors for an invalid declaration
  if (decl->isInvalid())
    return;

  // Don't add implicit constructors in module interfaces.
  if (auto *SF = decl->getParentSourceFile()) {
    if (SF->Kind == SourceFileKind::Interface) {
      decl->setAddedImplicitInitializers();
      return;
    }
  }

  if (auto *structDecl = dyn_cast<StructDecl>(decl))
    addImplicitConstructorsToStruct(structDecl, Context);
  if (auto *classDecl = dyn_cast<ClassDecl>(decl))
    addImplicitConstructorsToClass(classDecl, Context);
}

void TypeChecker::synthesizeMemberForLookup(NominalTypeDecl *target,
                                            DeclName member) {
  auto baseName = member.getBaseName();

  // Checks whether the target conforms to the given protocol. If the
  // conformance is incomplete, force the conformance.
  //
  // Returns whether the target conforms to the protocol.
  auto evaluateTargetConformanceTo = [&](ProtocolDecl *protocol) {
    if (!protocol)
      return false;

    auto targetType = target->getDeclaredInterfaceType();
    if (auto ref = conformsToProtocol(
                        targetType, protocol, target,
                        ConformanceCheckFlags::SkipConditionalRequirements)) {
      if (auto *conformance = dyn_cast<NormalProtocolConformance>(
            ref->getConcrete()->getRootConformance())) {
        if (conformance->getState() == ProtocolConformanceState::Incomplete) {
          checkConformance(conformance);
        }
      }

      return true;
    }

    return false;
  };

  if (member.isSimpleName() && !baseName.isSpecial()) {
    if (baseName.getIdentifier() == Context.Id_CodingKeys) {
      // CodingKeys is a special type which may be synthesized as part of
      // Encodable/Decodable conformance. If the target conforms to either
      // protocol and would derive conformance to either, the type may be
      // synthesized.
      // If the target conforms to either and the conformance has not yet been
      // evaluated, then we should do that here.
      //
      // Try to synthesize Decodable first. If that fails, try to synthesize
      // Encodable. If either succeeds and CodingKeys should have been
      // synthesized, it will be synthesized.
      auto *decodableProto = Context.getProtocol(KnownProtocolKind::Decodable);
      auto *encodableProto = Context.getProtocol(KnownProtocolKind::Encodable);
      if (!evaluateTargetConformanceTo(decodableProto))
        (void)evaluateTargetConformanceTo(encodableProto);
    }

    if ((baseName.getIdentifier().str().startswith("$") ||
         baseName.getIdentifier().str().startswith("_")) &&
        baseName.getIdentifier().str().size() > 1) {
      // $- and _-prefixed variables can be generated by properties that have
      // attached property wrappers.
      auto originalPropertyName =
        Context.getIdentifier(baseName.getIdentifier().str().substr(1));
      for (auto member : target->lookupDirect(originalPropertyName)) {
        if (auto var = dyn_cast<VarDecl>(member)) {
          if (var->hasAttachedPropertyWrapper()) {
            auto sourceFile = var->getDeclContext()->getParentSourceFile();
            if (sourceFile && sourceFile->Kind != SourceFileKind::Interface)
              (void)var->getPropertyWrapperBackingPropertyInfo();
          }
        }
      }
    }

  } else {
    auto argumentNames = member.getArgumentNames();
    if (member.isCompoundName() && argumentNames.size() != 1)
      return;

    if (baseName == DeclBaseName::createConstructor() &&
        (member.isSimpleName() || argumentNames.front() == Context.Id_from)) {
      // init(from:) may be synthesized as part of derived conformance to the
      // Decodable protocol.
      // If the target should conform to the Decodable protocol, check the
      // conformance here to attempt synthesis.
      auto *decodableProto = Context.getProtocol(KnownProtocolKind::Decodable);
      (void)evaluateTargetConformanceTo(decodableProto);
    } else if (!baseName.isSpecial() &&
               baseName.getIdentifier() == Context.Id_encode &&
               (member.isSimpleName() ||
                argumentNames.front() == Context.Id_to)) {
      // encode(to:) may be synthesized as part of derived conformance to the
      // Encodable protocol.
      // If the target should conform to the Encodable protocol, check the
      // conformance here to attempt synthesis.
      auto *encodableProto = Context.getProtocol(KnownProtocolKind::Encodable);
      (void)evaluateTargetConformanceTo(encodableProto);
    }
  }
}

/// Synthesizer callback for a function body consisting of "return".
static std::pair<BraceStmt *, bool>
synthesizeSingleReturnFunctionBody(AbstractFunctionDecl *afd, void *) {
  ASTContext &ctx = afd->getASTContext();
  SmallVector<ASTNode, 1> stmts;
  stmts.push_back(new (ctx) ReturnStmt(afd->getLoc(), nullptr));
  return { BraceStmt::create(ctx, afd->getLoc(), stmts, afd->getLoc(), true),
           /*isTypeChecked=*/true };
}

void TypeChecker::defineDefaultConstructor(NominalTypeDecl *decl) {
  auto &ctx = decl->getASTContext();

  FrontendStatsTracer StatsTracer(ctx.Stats, "define-default-ctor", decl);
  PrettyStackTraceDecl stackTrace("defining default constructor for",
                                  decl);

  // Create the default constructor.
  auto ctor = createImplicitConstructor(decl,
                                        ImplicitConstructorKind::Default,
                                        ctx);

  // Add the constructor.
  decl->addMember(ctor);

  // Lazily synthesize an empty body for the default constructor.
  ctor->setBodySynthesizer(synthesizeSingleReturnFunctionBody);
}