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 - 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 "TypeCheckObjC.h"
#include "TypeCheckType.h"
#include "swift/AST/ASTWalker.h"
#include "swift/AST/Availability.h"
#include "swift/AST/Expr.h"
#include "swift/AST/GenericEnvironment.h"
#include "swift/AST/GenericSignatureBuilder.h"
#include "swift/AST/Initializer.h"
#include "swift/AST/ParameterList.h"
#include "swift/AST/PropertyWrappers.h"
#include "swift/AST/ProtocolConformance.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);
}

/// 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) {
  assert(!decl->hasClangNode());

  ASTContext &ctx = tc.Context;
  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());

      tc.validateDecl(var);
      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,
                              OTK_None, /*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;
}

/// 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<GenericEnvironment *, 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);

  GenericEnvironment *genericEnv;

  // 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.
    GenericSignatureBuilder builder(ctx);
    builder.addGenericSignature(classDecl->getGenericSignature());

    // Add the generic parameters.
    for (auto *newParam : newParams)
      builder.addGenericParameter(newParam);

    auto source =
      GenericSignatureBuilder::FloatingRequirementSource::forAbstract();
    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);
    };

    for (auto reqt : superclassSig->getRequirements())
      if (auto substReqt = reqt.subst(substFn, lookupConformanceFn))
        builder.addRequirement(*substReqt, source, nullptr);

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

    auto *genericSig = std::move(builder).computeGenericSignature(SourceLoc());
    genericEnv = genericSig->createGenericEnvironment();
  } else {
    genericEnv = classDecl->getGenericEnvironment();
  }

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

static void
configureInheritedDesignatedInitAttributes(TypeChecker &tc,
                                           ClassDecl *classDecl,
                                           ConstructorDecl *ctor,
                                           ConstructorDecl *superclassCtor) {
  assert(ctor->getDeclContext() == classDecl);
  auto &ctx = tc.Context;

  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;

  if (!superclassCtor->hasValidSignature())
    ctx.getLazyResolver()->resolveDeclSignature(superclassCtor);

  // 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, SubstFlags::UseErrorType);
  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 };
}

ConstructorDecl *
swift::createDesignatedInitOverride(TypeChecker &tc,
                                    ClassDecl *classDecl,
                                    ConstructorDecl *superclassCtor,
                                    DesignatedInitKind kind) {
  auto &ctx = tc.Context;

  // 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;
  }

  GenericEnvironment *genericEnv;
  GenericParamList *genericParams;
  SubstitutionMap subMap;

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

  // Determine the initializer parameters.

  // Create the initializer parameter patterns.
  OptionSet<ParameterList::CloneFlags> options = ParameterList::Implicit;
  options |= ParameterList::Inherited;
  auto *bodyParams = superclassCtor->getParameters()->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 (auto *decl : *bodyParams) {
    auto paramTy = decl->getInterfaceType();
    auto substTy = paramTy.subst(subMap, SubstFlags::UseErrorType);
    decl->setInterfaceType(substTy);
    decl->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->getFailability(),
                              /*FailabilityLoc=*/SourceLoc(),
                              /*Throws=*/superclassCtor->hasThrows(),
                              /*ThrowsLoc=*/SourceLoc(),
                              bodyParams, genericParams, classDecl);

  ctor->setImplicit();

  // Set the interface type of the initializer.
  ctor->setGenericEnvironment(genericEnv);
  ctor->computeType();

  if (ctor->getFailability() == OTK_ImplicitlyUnwrappedOptional) {
    ctor->getAttrs().add(
      new (ctx) ImplicitlyUnwrappedOptionalAttr(/*implicit=*/true));
  }

  ctor->setValidationToChecked();

  configureInheritedDesignatedInitAttributes(tc, classDecl, ctor,
                                             superclassCtor);

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

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

    // Stub constructors don't appear in the vtable.
    ctor->setNeedsNewVTableEntry(false);
    return ctor;
  }

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

  return ctor;
}