SemaDeclCXX.cpp

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//===------ SemaDeclCXX.cpp - Semantic Analysis for C++ Declarations ------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This file implements semantic analysis for C++ declarations.
//
//===----------------------------------------------------------------------===//
 
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTLambda.h"
#include "clang/AST/ASTMutationListener.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/CharUnits.h"
#include "clang/AST/ComparisonCategories.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/EvaluatedExprVisitor.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/TypeLoc.h"
#include "clang/AST/TypeOrdering.h"
#include "clang/Basic/AttributeCommonInfo.h"
#include "clang/Basic/PartialDiagnostic.h"
#include "clang/Basic/Specifiers.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Lex/LiteralSupport.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Sema/CXXFieldCollector.h"
#include "clang/Sema/DeclSpec.h"
#include "clang/Sema/EnterExpressionEvaluationContext.h"
#include "clang/Sema/Initialization.h"
#include "clang/Sema/Lookup.h"
#include "clang/Sema/Ownership.h"
#include "clang/Sema/ParsedTemplate.h"
#include "clang/Sema/Scope.h"
#include "clang/Sema/ScopeInfo.h"
#include "clang/Sema/SemaInternal.h"
#include "clang/Sema/Template.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/SaveAndRestore.h"
#include <map>
#include <optional>
#include <set>
 
using namespace clang;
 
//===----------------------------------------------------------------------===//
// CheckDefaultArgumentVisitor
//===----------------------------------------------------------------------===//
 
namespace {
/// CheckDefaultArgumentVisitor - C++ [dcl.fct.default] Traverses
/// the default argument of a parameter to determine whether it
/// contains any ill-formed subexpressions. For example, this will
/// diagnose the use of local variables or parameters within the
/// default argument expression.
class CheckDefaultArgumentVisitor
    : public ConstStmtVisitor<CheckDefaultArgumentVisitor, bool> {
  Sema &S;
  const Expr *DefaultArg;
 
public:
  CheckDefaultArgumentVisitor(Sema &S, const Expr *DefaultArg)
      : S(S), DefaultArg(DefaultArg) {}
 
  bool VisitExpr(const Expr *Node);
  bool VisitDeclRefExpr(const DeclRefExpr *DRE);
  bool VisitCXXThisExpr(const CXXThisExpr *ThisE);
  bool VisitLambdaExpr(const LambdaExpr *Lambda);
  bool VisitPseudoObjectExpr(const PseudoObjectExpr *POE);
};
 
/// VisitExpr - Visit all of the children of this expression.
bool CheckDefaultArgumentVisitor::VisitExpr(const Expr *Node) {
  bool IsInvalid = false;
  for (const Stmt *SubStmt : Node->children())
    if (SubStmt)
      IsInvalid |= Visit(SubStmt);
  return IsInvalid;
}
 
/// VisitDeclRefExpr - Visit a reference to a declaration, to
/// determine whether this declaration can be used in the default
/// argument expression.
bool CheckDefaultArgumentVisitor::VisitDeclRefExpr(const DeclRefExpr *DRE) {
  const ValueDecl *Decl = dyn_cast<ValueDecl>(DRE->getDecl());
 
  if (!isa<VarDecl, BindingDecl>(Decl))
    return false;
 
  if (const auto *Param = dyn_cast<ParmVarDecl>(Decl)) {
    // C++ [dcl.fct.default]p9:
    //   [...] parameters of a function shall not be used in default
    //   argument expressions, even if they are not evaluated. [...]
    //
    // C++17 [dcl.fct.default]p9 (by CWG 2082):
    //   [...] A parameter shall not appear as a potentially-evaluated
    //   expression in a default argument. [...]
    //
    if (DRE->isNonOdrUse() != NOUR_Unevaluated)
      return S.Diag(DRE->getBeginLoc(),
                    diag::err_param_default_argument_references_param)
             << Param->getDeclName() << DefaultArg->getSourceRange();
  } else if (auto *VD = Decl->getPotentiallyDecomposedVarDecl()) {
    // C++ [dcl.fct.default]p7:
    //   Local variables shall not be used in default argument
    //   expressions.
    //
    // C++17 [dcl.fct.default]p7 (by CWG 2082):
    //   A local variable shall not appear as a potentially-evaluated
    //   expression in a default argument.
    //
    // C++20 [dcl.fct.default]p7 (DR as part of P0588R1, see also CWG 2346):
    //   Note: A local variable cannot be odr-used (6.3) in a default
    //   argument.
    //
    if (VD->isLocalVarDecl() && !DRE->isNonOdrUse())
      return S.Diag(DRE->getBeginLoc(),
                    diag::err_param_default_argument_references_local)
             << Decl << DefaultArg->getSourceRange();
  }
  return false;
}
 
/// VisitCXXThisExpr - Visit a C++ "this" expression.
bool CheckDefaultArgumentVisitor::VisitCXXThisExpr(const CXXThisExpr *ThisE) {
  // C++ [dcl.fct.default]p8:
  //   The keyword this shall not be used in a default argument of a
  //   member function.
  return S.Diag(ThisE->getBeginLoc(),
                diag::err_param_default_argument_references_this)
         << ThisE->getSourceRange();
}
 
bool CheckDefaultArgumentVisitor::VisitPseudoObjectExpr(
    const PseudoObjectExpr *POE) {
  bool Invalid = false;
  for (const Expr *E : POE->semantics()) {
    // Look through bindings.
    if (const auto *OVE = dyn_cast<OpaqueValueExpr>(E)) {
      E = OVE->getSourceExpr();
      assert(E && "pseudo-object binding without source expression?");
    }
 
    Invalid |= Visit(E);
  }
  return Invalid;
}
 
bool CheckDefaultArgumentVisitor::VisitLambdaExpr(const LambdaExpr *Lambda) {
  // [expr.prim.lambda.capture]p9
  // a lambda-expression appearing in a default argument cannot implicitly or
  // explicitly capture any local entity. Such a lambda-expression can still
  // have an init-capture if any full-expression in its initializer satisfies
  // the constraints of an expression appearing in a default argument.
  bool Invalid = false;
  for (const LambdaCapture &LC : Lambda->captures()) {
    if (!Lambda->isInitCapture(&LC))
      return S.Diag(LC.getLocation(), diag::err_lambda_capture_default_arg);
    // Init captures are always VarDecl.
    auto *D = cast<VarDecl>(LC.getCapturedVar());
    Invalid |= Visit(D->getInit());
  }
  return Invalid;
}
} // namespace
 
void
Sema::ImplicitExceptionSpecification::CalledDecl(SourceLocation CallLoc,
                                                 const CXXMethodDecl *Method) {
  // If we have an MSAny spec already, don't bother.
  if (!Method || ComputedEST == EST_MSAny)
    return;
 
  const FunctionProtoType *Proto
    = Method->getType()->getAs<FunctionProtoType>();
  Proto = Self->ResolveExceptionSpec(CallLoc, Proto);
  if (!Proto)
    return;
 
  ExceptionSpecificationType EST = Proto->getExceptionSpecType();
 
  // If we have a throw-all spec at this point, ignore the function.
  if (ComputedEST == EST_None)
    return;
 
  if (EST == EST_None && Method->hasAttr<NoThrowAttr>())
    EST = EST_BasicNoexcept;
 
  switch (EST) {
  case EST_Unparsed:
  case EST_Uninstantiated:
  case EST_Unevaluated:
    llvm_unreachable("should not see unresolved exception specs here");
 
  // If this function can throw any exceptions, make a note of that.
  case EST_MSAny:
  case EST_None:
    // FIXME: Whichever we see last of MSAny and None determines our result.
    // We should make a consistent, order-independent choice here.
    ClearExceptions();
    ComputedEST = EST;
    return;
  case EST_NoexceptFalse:
    ClearExceptions();
    ComputedEST = EST_None;
    return;
  // FIXME: If the call to this decl is using any of its default arguments, we
  // need to search them for potentially-throwing calls.
  // If this function has a basic noexcept, it doesn't affect the outcome.
  case EST_BasicNoexcept:
  case EST_NoexceptTrue:
  case EST_NoThrow:
    return;
  // If we're still at noexcept(true) and there's a throw() callee,
  // change to that specification.
  case EST_DynamicNone:
    if (ComputedEST == EST_BasicNoexcept)
      ComputedEST = EST_DynamicNone;
    return;
  case EST_DependentNoexcept:
    llvm_unreachable(
        "should not generate implicit declarations for dependent cases");
  case EST_Dynamic:
    break;
  }
  assert(EST == EST_Dynamic && "EST case not considered earlier.");
  assert(ComputedEST != EST_None &&
         "Shouldn't collect exceptions when throw-all is guaranteed.");
  ComputedEST = EST_Dynamic;
  // Record the exceptions in this function's exception specification.
  for (const auto &E : Proto->exceptions())
    if (ExceptionsSeen.insert(Self->Context.getCanonicalType(E)).second)
      Exceptions.push_back(E);
}
 
void Sema::ImplicitExceptionSpecification::CalledStmt(Stmt *S) {
  if (!S || ComputedEST == EST_MSAny)
    return;
 
  // FIXME:
  //
  // C++0x [except.spec]p14:
  //   [An] implicit exception-specification specifies the type-id T if and
  // only if T is allowed by the exception-specification of a function directly
  // invoked by f's implicit definition; f shall allow all exceptions if any
  // function it directly invokes allows all exceptions, and f shall allow no
  // exceptions if every function it directly invokes allows no exceptions.
  //
  // Note in particular that if an implicit exception-specification is generated
  // for a function containing a throw-expression, that specification can still
  // be noexcept(true).
  //
  // Note also that 'directly invoked' is not defined in the standard, and there
  // is no indication that we should only consider potentially-evaluated calls.
  //
  // Ultimately we should implement the intent of the standard: the exception
  // specification should be the set of exceptions which can be thrown by the
  // implicit definition. For now, we assume that any non-nothrow expression can
  // throw any exception.
 
  if (Self->canThrow(S))
    ComputedEST = EST_None;
}
 
ExprResult Sema::ConvertParamDefaultArgument(ParmVarDecl *Param, Expr *Arg,
                                             SourceLocation EqualLoc) {
  if (RequireCompleteType(Param->getLocation(), Param->getType(),
                          diag::err_typecheck_decl_incomplete_type))
    return true;
 
  // C++ [dcl.fct.default]p5
  //   A default argument expression is implicitly converted (clause
  //   4) to the parameter type. The default argument expression has
  //   the same semantic constraints as the initializer expression in
  //   a declaration of a variable of the parameter type, using the
  //   copy-initialization semantics (8.5).
  InitializedEntity Entity = InitializedEntity::InitializeParameter(Context,
                                                                    Param);
  InitializationKind Kind = InitializationKind::CreateCopy(Param->getLocation(),
                                                           EqualLoc);
  InitializationSequence InitSeq(*this, Entity, Kind, Arg);
  ExprResult Result = InitSeq.Perform(*this, Entity, Kind, Arg);
  if (Result.isInvalid())
    return true;
  Arg = Result.getAs<Expr>();
 
  CheckCompletedExpr(Arg, EqualLoc);
  Arg = MaybeCreateExprWithCleanups(Arg);
 
  return Arg;
}
 
void Sema::SetParamDefaultArgument(ParmVarDecl *Param, Expr *Arg,
                                   SourceLocation EqualLoc) {
  // Add the default argument to the parameter
  Param->setDefaultArg(Arg);
 
  // We have already instantiated this parameter; provide each of the
  // instantiations with the uninstantiated default argument.
  UnparsedDefaultArgInstantiationsMap::iterator InstPos
    = UnparsedDefaultArgInstantiations.find(Param);
  if (InstPos != UnparsedDefaultArgInstantiations.end()) {
    for (unsigned I = 0, N = InstPos->second.size(); I != N; ++I)
      InstPos->second[I]->setUninstantiatedDefaultArg(Arg);
 
    // We're done tracking this parameter's instantiations.
    UnparsedDefaultArgInstantiations.erase(InstPos);
  }
}
 
/// ActOnParamDefaultArgument - Check whether the default argument
/// provided for a function parameter is well-formed. If so, attach it
/// to the parameter declaration.
void
Sema::ActOnParamDefaultArgument(Decl *param, SourceLocation EqualLoc,
                                Expr *DefaultArg) {
  if (!param || !DefaultArg)
    return;
 
  ParmVarDecl *Param = cast<ParmVarDecl>(param);
  UnparsedDefaultArgLocs.erase(Param);
 
  // Default arguments are only permitted in C++
  if (!getLangOpts().CPlusPlus) {
    Diag(EqualLoc, diag::err_param_default_argument)
      << DefaultArg->getSourceRange();
    return ActOnParamDefaultArgumentError(param, EqualLoc, DefaultArg);
  }
 
  // Check for unexpanded parameter packs.
  if (DiagnoseUnexpandedParameterPack(DefaultArg, UPPC_DefaultArgument))
    return ActOnParamDefaultArgumentError(param, EqualLoc, DefaultArg);
 
  // C++11 [dcl.fct.default]p3
  //   A default argument expression [...] shall not be specified for a
  //   parameter pack.
  if (Param->isParameterPack()) {
    Diag(EqualLoc, diag::err_param_default_argument_on_parameter_pack)
        << DefaultArg->getSourceRange();
    // Recover by discarding the default argument.
    Param->setDefaultArg(nullptr);
    return;
  }
 
  ExprResult Result = ConvertParamDefaultArgument(Param, DefaultArg, EqualLoc);
  if (Result.isInvalid())
    return ActOnParamDefaultArgumentError(param, EqualLoc, DefaultArg);
 
  DefaultArg = Result.getAs<Expr>();
 
  // Check that the default argument is well-formed
  CheckDefaultArgumentVisitor DefaultArgChecker(*this, DefaultArg);
  if (DefaultArgChecker.Visit(DefaultArg))
    return ActOnParamDefaultArgumentError(param, EqualLoc, DefaultArg);
 
  SetParamDefaultArgument(Param, DefaultArg, EqualLoc);
}
 
/// ActOnParamUnparsedDefaultArgument - We've seen a default
/// argument for a function parameter, but we can't parse it yet
/// because we're inside a class definition. Note that this default
/// argument will be parsed later.
void Sema::ActOnParamUnparsedDefaultArgument(Decl *param,
                                             SourceLocation EqualLoc,
                                             SourceLocation ArgLoc) {
  if (!param)
    return;
 
  ParmVarDecl *Param = cast<ParmVarDecl>(param);
  Param->setUnparsedDefaultArg();
  UnparsedDefaultArgLocs[Param] = ArgLoc;
}
 
/// ActOnParamDefaultArgumentError - Parsing or semantic analysis of
/// the default argument for the parameter param failed.
void Sema::ActOnParamDefaultArgumentError(Decl *param, SourceLocation EqualLoc,
                                          Expr *DefaultArg) {
  if (!param)
    return;
 
  ParmVarDecl *Param = cast<ParmVarDecl>(param);
  Param->setInvalidDecl();
  UnparsedDefaultArgLocs.erase(Param);
  ExprResult RE;
  if (DefaultArg) {
    RE = CreateRecoveryExpr(EqualLoc, DefaultArg->getEndLoc(), {DefaultArg},
                            Param->getType().getNonReferenceType());
  } else {
    RE = CreateRecoveryExpr(EqualLoc, EqualLoc, {},
                            Param->getType().getNonReferenceType());
  }
  Param->setDefaultArg(RE.get());
}
 
/// CheckExtraCXXDefaultArguments - Check for any extra default
/// arguments in the declarator, which is not a function declaration
/// or definition and therefore is not permitted to have default
/// arguments. This routine should be invoked for every declarator
/// that is not a function declaration or definition.
void Sema::CheckExtraCXXDefaultArguments(Declarator &D) {
  // C++ [dcl.fct.default]p3
  //   A default argument expression shall be specified only in the
  //   parameter-declaration-clause of a function declaration or in a
  //   template-parameter (14.1). It shall not be specified for a
  //   parameter pack. If it is specified in a
  //   parameter-declaration-clause, it shall not occur within a
  //   declarator or abstract-declarator of a parameter-declaration.
  bool MightBeFunction = D.isFunctionDeclarationContext();
  for (unsigned i = 0, e = D.getNumTypeObjects(); i != e; ++i) {
    DeclaratorChunk &chunk = D.getTypeObject(i);
    if (chunk.Kind == DeclaratorChunk::Function) {
      if (MightBeFunction) {
        // This is a function declaration. It can have default arguments, but
        // keep looking in case its return type is a function type with default
        // arguments.
        MightBeFunction = false;
        continue;
      }
      for (unsigned argIdx = 0, e = chunk.Fun.NumParams; argIdx != e;
           ++argIdx) {
        ParmVarDecl *Param = cast<ParmVarDecl>(chunk.Fun.Params[argIdx].Param);
        if (Param->hasUnparsedDefaultArg()) {
          std::unique_ptr<CachedTokens> Toks =
              std::move(chunk.Fun.Params[argIdx].DefaultArgTokens);
          SourceRange SR;
          if (Toks->size() > 1)
            SR = SourceRange((*Toks)[1].getLocation(),
                             Toks->back().getLocation());
          else
            SR = UnparsedDefaultArgLocs[Param];
          Diag(Param->getLocation(), diag::err_param_default_argument_nonfunc)
            << SR;
        } else if (Param->getDefaultArg()) {
          Diag(Param->getLocation(), diag::err_param_default_argument_nonfunc)
            << Param->getDefaultArg()->getSourceRange();
          Param->setDefaultArg(nullptr);
        }
      }
    } else if (chunk.Kind != DeclaratorChunk::Paren) {
      MightBeFunction = false;
    }
  }
}
 
static bool functionDeclHasDefaultArgument(const FunctionDecl *FD) {
  return llvm::any_of(FD->parameters(), [](ParmVarDecl *P) {
    return P->hasDefaultArg() && !P->hasInheritedDefaultArg();
  });
}
 
/// MergeCXXFunctionDecl - Merge two declarations of the same C++
/// function, once we already know that they have the same
/// type. Subroutine of MergeFunctionDecl. Returns true if there was an
/// error, false otherwise.
bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old,
                                Scope *S) {
  bool Invalid = false;
 
  // The declaration context corresponding to the scope is the semantic
  // parent, unless this is a local function declaration, in which case
  // it is that surrounding function.
  DeclContext *ScopeDC = New->isLocalExternDecl()
                             ? New->getLexicalDeclContext()
                             : New->getDeclContext();
 
  // Find the previous declaration for the purpose of default arguments.
  FunctionDecl *PrevForDefaultArgs = Old;
  for (/**/; PrevForDefaultArgs;
       // Don't bother looking back past the latest decl if this is a local
       // extern declaration; nothing else could work.
       PrevForDefaultArgs = New->isLocalExternDecl()
                                ? nullptr
                                : PrevForDefaultArgs->getPreviousDecl()) {
    // Ignore hidden declarations.
    if (!LookupResult::isVisible(*this, PrevForDefaultArgs))
      continue;
 
    if (S && !isDeclInScope(PrevForDefaultArgs, ScopeDC, S) &&
        !New->isCXXClassMember()) {
      // Ignore default arguments of old decl if they are not in
      // the same scope and this is not an out-of-line definition of
      // a member function.
      continue;
    }
 
    if (PrevForDefaultArgs->isLocalExternDecl() != New->isLocalExternDecl()) {
      // If only one of these is a local function declaration, then they are
      // declared in different scopes, even though isDeclInScope may think
      // they're in the same scope. (If both are local, the scope check is
      // sufficient, and if neither is local, then they are in the same scope.)
      continue;
    }
 
    // We found the right previous declaration.
    break;
  }
 
  // C++ [dcl.fct.default]p4:
  //   For non-template functions, default arguments can be added in
  //   later declarations of a function in the same
  //   scope. Declarations in different scopes have completely
  //   distinct sets of default arguments. That is, declarations in
  //   inner scopes do not acquire default arguments from
  //   declarations in outer scopes, and vice versa. In a given
  //   function declaration, all parameters subsequent to a
  //   parameter with a default argument shall have default
  //   arguments supplied in this or previous declarations. A
  //   default argument shall not be redefined by a later
  //   declaration (not even to the same value).
  //
  // C++ [dcl.fct.default]p6:
  //   Except for member functions of class templates, the default arguments
  //   in a member function definition that appears outside of the class
  //   definition are added to the set of default arguments provided by the
  //   member function declaration in the class definition.
  for (unsigned p = 0, NumParams = PrevForDefaultArgs
                                       ? PrevForDefaultArgs->getNumParams()
                                       : 0;
       p < NumParams; ++p) {
    ParmVarDecl *OldParam = PrevForDefaultArgs->getParamDecl(p);
    ParmVarDecl *NewParam = New->getParamDecl(p);
 
    bool OldParamHasDfl = OldParam ? OldParam->hasDefaultArg() : false;
    bool NewParamHasDfl = NewParam->hasDefaultArg();
 
    if (OldParamHasDfl && NewParamHasDfl) {
      unsigned DiagDefaultParamID =
        diag::err_param_default_argument_redefinition;
 
      // MSVC accepts that default parameters be redefined for member functions
      // of template class. The new default parameter's value is ignored.
      Invalid = true;
      if (getLangOpts().MicrosoftExt) {
        CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(New);
        if (MD && MD->getParent()->getDescribedClassTemplate()) {
          // Merge the old default argument into the new parameter.
          NewParam->setHasInheritedDefaultArg();
          if (OldParam->hasUninstantiatedDefaultArg())
            NewParam->setUninstantiatedDefaultArg(
                                      OldParam->getUninstantiatedDefaultArg());
          else
            NewParam->setDefaultArg(OldParam->getInit());
          DiagDefaultParamID = diag::ext_param_default_argument_redefinition;
          Invalid = false;
        }
      }
 
      // FIXME: If we knew where the '=' was, we could easily provide a fix-it
      // hint here. Alternatively, we could walk the type-source information
      // for NewParam to find the last source location in the type... but it
      // isn't worth the effort right now. This is the kind of test case that
      // is hard to get right:
      //   int f(int);
      //   void g(int (*fp)(int) = f);
      //   void g(int (*fp)(int) = &f);
      Diag(NewParam->getLocation(), DiagDefaultParamID)
        << NewParam->getDefaultArgRange();
 
      // Look for the function declaration where the default argument was
      // actually written, which may be a declaration prior to Old.
      for (auto Older = PrevForDefaultArgs;
           OldParam->hasInheritedDefaultArg(); /**/) {
        Older = Older->getPreviousDecl();
        OldParam = Older->getParamDecl(p);
      }
 
      Diag(OldParam->getLocation(), diag::note_previous_definition)
        << OldParam->getDefaultArgRange();
    } else if (OldParamHasDfl) {
      // Merge the old default argument into the new parameter unless the new
      // function is a friend declaration in a template class. In the latter
      // case the default arguments will be inherited when the friend
      // declaration will be instantiated.
      if (New->getFriendObjectKind() == Decl::FOK_None ||
          !New->getLexicalDeclContext()->isDependentContext()) {
        // It's important to use getInit() here;  getDefaultArg()
        // strips off any top-level ExprWithCleanups.
        NewParam->setHasInheritedDefaultArg();
        if (OldParam->hasUnparsedDefaultArg())
          NewParam->setUnparsedDefaultArg();
        else if (OldParam->hasUninstantiatedDefaultArg())
          NewParam->setUninstantiatedDefaultArg(
                                       OldParam->getUninstantiatedDefaultArg());
        else
          NewParam->setDefaultArg(OldParam->getInit());
      }
    } else if (NewParamHasDfl) {
      if (New->getDescribedFunctionTemplate()) {
        // Paragraph 4, quoted above, only applies to non-template functions.
        Diag(NewParam->getLocation(),
             diag::err_param_default_argument_template_redecl)
          << NewParam->getDefaultArgRange();
        Diag(PrevForDefaultArgs->getLocation(),
             diag::note_template_prev_declaration)
            << false;
      } else if (New->getTemplateSpecializationKind()
                   != TSK_ImplicitInstantiation &&
                 New->getTemplateSpecializationKind() != TSK_Undeclared) {
        // C++ [temp.expr.spec]p21:
        //   Default function arguments shall not be specified in a declaration
        //   or a definition for one of the following explicit specializations:
        //     - the explicit specialization of a function template;
        //     - the explicit specialization of a member function template;
        //     - the explicit specialization of a member function of a class
        //       template where the class template specialization to which the
        //       member function specialization belongs is implicitly
        //       instantiated.
        Diag(NewParam->getLocation(), diag::err_template_spec_default_arg)
          << (New->getTemplateSpecializationKind() ==TSK_ExplicitSpecialization)
          << New->getDeclName()
          << NewParam->getDefaultArgRange();
      } else if (New->getDeclContext()->isDependentContext()) {
        // C++ [dcl.fct.default]p6 (DR217):
        //   Default arguments for a member function of a class template shall
        //   be specified on the initial declaration of the member function
        //   within the class template.
        //
        // Reading the tea leaves a bit in DR217 and its reference to DR205
        // leads me to the conclusion that one cannot add default function
        // arguments for an out-of-line definition of a member function of a
        // dependent type.
        int WhichKind = 2;
        if (CXXRecordDecl *Record
              = dyn_cast<CXXRecordDecl>(New->getDeclContext())) {
          if (Record->getDescribedClassTemplate())
            WhichKind = 0;
          else if (isa<ClassTemplatePartialSpecializationDecl>(Record))
            WhichKind = 1;
          else
            WhichKind = 2;
        }
 
        Diag(NewParam->getLocation(),
             diag::err_param_default_argument_member_template_redecl)
          << WhichKind
          << NewParam->getDefaultArgRange();
      }
    }
  }
 
  // DR1344: If a default argument is added outside a class definition and that
  // default argument makes the function a special member function, the program
  // is ill-formed. This can only happen for constructors.
  if (isa<CXXConstructorDecl>(New) &&
      New->getMinRequiredArguments() < Old->getMinRequiredArguments()) {
    CXXSpecialMember NewSM = getSpecialMember(cast<CXXMethodDecl>(New)),
                     OldSM = getSpecialMember(cast<CXXMethodDecl>(Old));
    if (NewSM != OldSM) {
      ParmVarDecl *NewParam = New->getParamDecl(New->getMinRequiredArguments());
      assert(NewParam->hasDefaultArg());
      Diag(NewParam->getLocation(), diag::err_default_arg_makes_ctor_special)
        << NewParam->getDefaultArgRange() << NewSM;
      Diag(Old->getLocation(), diag::note_previous_declaration);
    }
  }
 
  const FunctionDecl *Def;
  // C++11 [dcl.constexpr]p1: If any declaration of a function or function
  // template has a constexpr specifier then all its declarations shall
  // contain the constexpr specifier.
  if (New->getConstexprKind() != Old->getConstexprKind()) {
    Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
        << New << static_cast<int>(New->getConstexprKind())
        << static_cast<int>(Old->getConstexprKind());
    Diag(Old->getLocation(), diag::note_previous_declaration);
    Invalid = true;
  } else if (!Old->getMostRecentDecl()->isInlined() && New->isInlined() &&
             Old->isDefined(Def) &&
             // If a friend function is inlined but does not have 'inline'
             // specifier, it is a definition. Do not report attribute conflict
             // in this case, redefinition will be diagnosed later.
             (New->isInlineSpecified() ||
              New->getFriendObjectKind() == Decl::FOK_None)) {
    // C++11 [dcl.fcn.spec]p4:
    //   If the definition of a function appears in a translation unit before its
    //   first declaration as inline, the program is ill-formed.
    Diag(New->getLocation(), diag::err_inline_decl_follows_def) << New;
    Diag(Def->getLocation(), diag::note_previous_definition);
    Invalid = true;
  }
 
  // C++17 [temp.deduct.guide]p3:
  //   Two deduction guide declarations in the same translation unit
  //   for the same class template shall not have equivalent
  //   parameter-declaration-clauses.
  if (isa<CXXDeductionGuideDecl>(New) &&
      !New->isFunctionTemplateSpecialization() && isVisible(Old)) {
    Diag(New->getLocation(), diag::err_deduction_guide_redeclared);
    Diag(Old->getLocation(), diag::note_previous_declaration);
  }
 
  // C++11 [dcl.fct.default]p4: If a friend declaration specifies a default
  // argument expression, that declaration shall be a definition and shall be
  // the only declaration of the function or function template in the
  // translation unit.
  if (Old->getFriendObjectKind() == Decl::FOK_Undeclared &&
      functionDeclHasDefaultArgument(Old)) {
    Diag(New->getLocation(), diag::err_friend_decl_with_def_arg_redeclared);
    Diag(Old->getLocation(), diag::note_previous_declaration);
    Invalid = true;
  }
 
  // C++11 [temp.friend]p4 (DR329):
  //   When a function is defined in a friend function declaration in a class
  //   template, the function is instantiated when the function is odr-used.
  //   The same restrictions on multiple declarations and definitions that
  //   apply to non-template function declarations and definitions also apply
  //   to these implicit definitions.
  const FunctionDecl *OldDefinition = nullptr;
  if (New->isThisDeclarationInstantiatedFromAFriendDefinition() &&
      Old->isDefined(OldDefinition, true))
    CheckForFunctionRedefinition(New, OldDefinition);
 
  return Invalid;
}
 
void Sema::DiagPlaceholderVariableDefinition(SourceLocation Loc) {
  Diag(Loc, getLangOpts().CPlusPlus26
                ? diag::warn_cxx23_placeholder_var_definition
                : diag::ext_placeholder_var_definition);
}
 
NamedDecl *
Sema::ActOnDecompositionDeclarator(Scope *S, Declarator &D,
                                   MultiTemplateParamsArg TemplateParamLists) {
  assert(D.isDecompositionDeclarator());
  const DecompositionDeclarator &Decomp = D.getDecompositionDeclarator();
 
  // The syntax only allows a decomposition declarator as a simple-declaration,
  // a for-range-declaration, or a condition in Clang, but we parse it in more
  // cases than that.
  if (!D.mayHaveDecompositionDeclarator()) {
    Diag(Decomp.getLSquareLoc(), diag::err_decomp_decl_context)
      << Decomp.getSourceRange();
    return nullptr;
  }
 
  if (!TemplateParamLists.empty()) {
    // FIXME: There's no rule against this, but there are also no rules that
    // would actually make it usable, so we reject it for now.
    Diag(TemplateParamLists.front()->getTemplateLoc(),
         diag::err_decomp_decl_template);
    return nullptr;
  }
 
  Diag(Decomp.getLSquareLoc(),
       !getLangOpts().CPlusPlus17
           ? diag::ext_decomp_decl
           : D.getContext() == DeclaratorContext::Condition
                 ? diag::ext_decomp_decl_cond
                 : diag::warn_cxx14_compat_decomp_decl)
      << Decomp.getSourceRange();
 
  // The semantic context is always just the current context.
  DeclContext *const DC = CurContext;
 
  // C++17 [dcl.dcl]/8:
  //   The decl-specifier-seq shall contain only the type-specifier auto
  //   and cv-qualifiers.
  // C++20 [dcl.dcl]/8:
  //   If decl-specifier-seq contains any decl-specifier other than static,
  //   thread_local, auto, or cv-qualifiers, the program is ill-formed.
  // C++23 [dcl.pre]/6:
  //   Each decl-specifier in the decl-specifier-seq shall be static,
  //   thread_local, auto (9.2.9.6 [dcl.spec.auto]), or a cv-qualifier.
  auto &DS = D.getDeclSpec();
  {
    // Note: While constrained-auto needs to be checked, we do so separately so
    // we can emit a better diagnostic.
    SmallVector<StringRef, 8> BadSpecifiers;
    SmallVector<SourceLocation, 8> BadSpecifierLocs;
    SmallVector<StringRef, 8> CPlusPlus20Specifiers;
    SmallVector<SourceLocation, 8> CPlusPlus20SpecifierLocs;
    if (auto SCS = DS.getStorageClassSpec()) {
      if (SCS == DeclSpec::SCS_static) {
        CPlusPlus20Specifiers.push_back(DeclSpec::getSpecifierName(SCS));
        CPlusPlus20SpecifierLocs.push_back(DS.getStorageClassSpecLoc());
      } else {
        BadSpecifiers.push_back(DeclSpec::getSpecifierName(SCS));
        BadSpecifierLocs.push_back(DS.getStorageClassSpecLoc());
      }
    }
    if (auto TSCS = DS.getThreadStorageClassSpec()) {
      CPlusPlus20Specifiers.push_back(DeclSpec::getSpecifierName(TSCS));
      CPlusPlus20SpecifierLocs.push_back(DS.getThreadStorageClassSpecLoc());
    }
    if (DS.hasConstexprSpecifier()) {
      BadSpecifiers.push_back(
          DeclSpec::getSpecifierName(DS.getConstexprSpecifier()));
      BadSpecifierLocs.push_back(DS.getConstexprSpecLoc());
    }
    if (DS.isInlineSpecified()) {
      BadSpecifiers.push_back("inline");
      BadSpecifierLocs.push_back(DS.getInlineSpecLoc());
    }
 
    if (!BadSpecifiers.empty()) {
      auto &&Err = Diag(BadSpecifierLocs.front(), diag::err_decomp_decl_spec);
      Err << (int)BadSpecifiers.size()
          << llvm::join(BadSpecifiers.begin(), BadSpecifiers.end(), " ");
      // Don't add FixItHints to remove the specifiers; we do still respect
      // them when building the underlying variable.
      for (auto Loc : BadSpecifierLocs)
        Err << SourceRange(Loc, Loc);
    } else if (!CPlusPlus20Specifiers.empty()) {
      auto &&Warn = Diag(CPlusPlus20SpecifierLocs.front(),
                         getLangOpts().CPlusPlus20
                             ? diag::warn_cxx17_compat_decomp_decl_spec
                             : diag::ext_decomp_decl_spec);
      Warn << (int)CPlusPlus20Specifiers.size()
           << llvm::join(CPlusPlus20Specifiers.begin(),
                         CPlusPlus20Specifiers.end(), " ");
      for (auto Loc : CPlusPlus20SpecifierLocs)
        Warn << SourceRange(Loc, Loc);
    }
    // We can't recover from it being declared as a typedef.
    if (DS.getStorageClassSpec() == DeclSpec::SCS_typedef)
      return nullptr;
  }
 
  // C++2a [dcl.struct.bind]p1:
  //   A cv that includes volatile is deprecated
  if ((DS.getTypeQualifiers() & DeclSpec::TQ_volatile) &&
      getLangOpts().CPlusPlus20)
    Diag(DS.getVolatileSpecLoc(),
         diag::warn_deprecated_volatile_structured_binding);
 
  TypeSourceInfo *TInfo = GetTypeForDeclarator(D, S);
  QualType R = TInfo->getType();
 
  if (DiagnoseUnexpandedParameterPack(D.getIdentifierLoc(), TInfo,
                                      UPPC_DeclarationType))
    D.setInvalidType();
 
  // The syntax only allows a single ref-qualifier prior to the decomposition
  // declarator. No other declarator chunks are permitted. Also check the type
  // specifier here.
  if (DS.getTypeSpecType() != DeclSpec::TST_auto ||
      D.hasGroupingParens() || D.getNumTypeObjects() > 1 ||
      (D.getNumTypeObjects() == 1 &&
       D.getTypeObject(0).Kind != DeclaratorChunk::Reference)) {
    Diag(Decomp.getLSquareLoc(),
         (D.hasGroupingParens() ||
          (D.getNumTypeObjects() &&
           D.getTypeObject(0).Kind == DeclaratorChunk::Paren))
             ? diag::err_decomp_decl_parens
             : diag::err_decomp_decl_type)
        << R;
 
    // In most cases, there's no actual problem with an explicitly-specified
    // type, but a function type won't work here, and ActOnVariableDeclarator
    // shouldn't be called for such a type.
    if (R->isFunctionType())
      D.setInvalidType();
  }
 
  // Constrained auto is prohibited by [decl.pre]p6, so check that here.
  if (DS.isConstrainedAuto()) {
    TemplateIdAnnotation *TemplRep = DS.getRepAsTemplateId();
    assert(TemplRep->Kind == TNK_Concept_template &&
           "No other template kind should be possible for a constrained auto");
 
    SourceRange TemplRange{TemplRep->TemplateNameLoc,
                           TemplRep->RAngleLoc.isValid()
                               ? TemplRep->RAngleLoc
                               : TemplRep->TemplateNameLoc};
    Diag(TemplRep->TemplateNameLoc, diag::err_decomp_decl_constraint)
        << TemplRange << FixItHint::CreateRemoval(TemplRange);
  }
 
  // Build the BindingDecls.
  SmallVector<BindingDecl*, 8> Bindings;
 
  // Build the BindingDecls.
  for (auto &B : D.getDecompositionDeclarator().bindings()) {
    // Check for name conflicts.
    DeclarationNameInfo NameInfo(B.Name, B.NameLoc);
    IdentifierInfo *VarName = B.Name;
    assert(VarName && "Cannot have an unnamed binding declaration");
 
    LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
                          ForVisibleRedeclaration);
    LookupName(Previous, S,
               /*CreateBuiltins*/DC->getRedeclContext()->isTranslationUnit());
 
    // It's not permitted to shadow a template parameter name.
    if (Previous.isSingleResult() &&
        Previous.getFoundDecl()->isTemplateParameter()) {
      DiagnoseTemplateParameterShadow(D.getIdentifierLoc(),
                                      Previous.getFoundDecl());
      Previous.clear();
    }
 
    auto *BD = BindingDecl::Create(Context, DC, B.NameLoc, VarName);
 
    // Find the shadowed declaration before filtering for scope.
    NamedDecl *ShadowedDecl = D.getCXXScopeSpec().isEmpty()
                                  ? getShadowedDeclaration(BD, Previous)
                                  : nullptr;
 
    bool ConsiderLinkage = DC->isFunctionOrMethod() &&
                           DS.getStorageClassSpec() == DeclSpec::SCS_extern;
    FilterLookupForScope(Previous, DC, S, ConsiderLinkage,
                         /*AllowInlineNamespace*/false);
 
    bool IsPlaceholder = DS.getStorageClassSpec() != DeclSpec::SCS_static &&
                         DC->isFunctionOrMethod() && VarName->isPlaceholder();
    if (!Previous.empty()) {
      if (IsPlaceholder) {
        bool sameDC = (Previous.end() - 1)
                          ->getDeclContext()
                          ->getRedeclContext()
                          ->Equals(DC->getRedeclContext());
        if (sameDC &&
            isDeclInScope(*(Previous.end() - 1), CurContext, S, false)) {
          Previous.clear();
          DiagPlaceholderVariableDefinition(B.NameLoc);
        }
      } else {
        auto *Old = Previous.getRepresentativeDecl();
        Diag(B.NameLoc, diag::err_redefinition) << B.Name;
        Diag(Old->getLocation(), diag::note_previous_definition);
      }
    } else if (ShadowedDecl && !D.isRedeclaration()) {
      CheckShadow(BD, ShadowedDecl, Previous);
    }
    PushOnScopeChains(BD, S, true);
    Bindings.push_back(BD);
    ParsingInitForAutoVars.insert(BD);
  }
 
  // There are no prior lookup results for the variable itself, because it
  // is unnamed.
  DeclarationNameInfo NameInfo((IdentifierInfo *)nullptr,
                               Decomp.getLSquareLoc());
  LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
                        ForVisibleRedeclaration);
 
  // Build the variable that holds the non-decomposed object.
  bool AddToScope = true;
  NamedDecl *New =
      ActOnVariableDeclarator(S, D, DC, TInfo, Previous,
                              MultiTemplateParamsArg(), AddToScope, Bindings);
  if (AddToScope) {
    S->AddDecl(New);
    CurContext->addHiddenDecl(New);
  }
 
  if (isInOpenMPDeclareTargetContext())
    checkDeclIsAllowedInOpenMPTarget(nullptr, New);
 
  return New;
}
 
static bool checkSimpleDecomposition(
    Sema &S, ArrayRef<BindingDecl *> Bindings, ValueDecl *Src,
    QualType DecompType, const llvm::APSInt &NumElems, QualType ElemType,
    llvm::function_ref<ExprResult(SourceLocation, Expr *, unsigned)> GetInit) {
  if ((int64_t)Bindings.size() != NumElems) {
    S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
        << DecompType << (unsigned)Bindings.size()
        << (unsigned)NumElems.getLimitedValue(UINT_MAX)
        << toString(NumElems, 10) << (NumElems < Bindings.size());
    return true;
  }
 
  unsigned I = 0;
  for (auto *B : Bindings) {
    SourceLocation Loc = B->getLocation();
    ExprResult E = S.BuildDeclRefExpr(Src, DecompType, VK_LValue, Loc);
    if (E.isInvalid())
      return true;
    E = GetInit(Loc, E.get(), I++);
    if (E.isInvalid())
      return true;
    B->setBinding(ElemType, E.get());
  }
 
  return false;
}
 
static bool checkArrayLikeDecomposition(Sema &S,
                                        ArrayRef<BindingDecl *> Bindings,
                                        ValueDecl *Src, QualType DecompType,
                                        const llvm::APSInt &NumElems,
                                        QualType ElemType) {
  return checkSimpleDecomposition(
      S, Bindings, Src, DecompType, NumElems, ElemType,
      [&](SourceLocation Loc, Expr *Base, unsigned I) -> ExprResult {
        ExprResult E = S.ActOnIntegerConstant(Loc, I);
        if (E.isInvalid())
          return ExprError();
        return S.CreateBuiltinArraySubscriptExpr(Base, Loc, E.get(), Loc);
      });
}
 
static bool checkArrayDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
                                    ValueDecl *Src, QualType DecompType,
                                    const ConstantArrayType *CAT) {
  return checkArrayLikeDecomposition(S, Bindings, Src, DecompType,
                                     llvm::APSInt(CAT->getSize()),
                                     CAT->getElementType());
}
 
static bool checkVectorDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
                                     ValueDecl *Src, QualType DecompType,
                                     const VectorType *VT) {
  return checkArrayLikeDecomposition(
      S, Bindings, Src, DecompType, llvm::APSInt::get(VT->getNumElements()),
      S.Context.getQualifiedType(VT->getElementType(),
                                 DecompType.getQualifiers()));
}
 
static bool checkComplexDecomposition(Sema &S,
                                      ArrayRef<BindingDecl *> Bindings,
                                      ValueDecl *Src, QualType DecompType,
                                      const ComplexType *CT) {
  return checkSimpleDecomposition(
      S, Bindings, Src, DecompType, llvm::APSInt::get(2),
      S.Context.getQualifiedType(CT->getElementType(),
                                 DecompType.getQualifiers()),
      [&](SourceLocation Loc, Expr *Base, unsigned I) -> ExprResult {
        return S.CreateBuiltinUnaryOp(Loc, I ? UO_Imag : UO_Real, Base);
      });
}
 
static std::string printTemplateArgs(const PrintingPolicy &PrintingPolicy,
                                     TemplateArgumentListInfo &Args,
                                     const TemplateParameterList *Params) {
  SmallString<128> SS;
  llvm::raw_svector_ostream OS(SS);
  bool First = true;
  unsigned I = 0;
  for (auto &Arg : Args.arguments()) {
    if (!First)
      OS << ", ";
    Arg.getArgument().print(PrintingPolicy, OS,
                            TemplateParameterList::shouldIncludeTypeForArgument(
                                PrintingPolicy, Params, I));
    First = false;
    I++;
  }
  return std::string(OS.str());
}
 
static bool lookupStdTypeTraitMember(Sema &S, LookupResult &TraitMemberLookup,
                                     SourceLocation Loc, StringRef Trait,
                                     TemplateArgumentListInfo &Args,
                                     unsigned DiagID) {
  auto DiagnoseMissing = [&] {
    if (DiagID)
      S.Diag(Loc, DiagID) << printTemplateArgs(S.Context.getPrintingPolicy(),
                                               Args, /*Params*/ nullptr);
    return true;
  };
 
  // FIXME: Factor out duplication with lookupPromiseType in SemaCoroutine.
  NamespaceDecl *Std = S.getStdNamespace();
  if (!Std)
    return DiagnoseMissing();
 
  // Look up the trait itself, within namespace std. We can diagnose various
  // problems with this lookup even if we've been asked to not diagnose a
  // missing specialization, because this can only fail if the user has been
  // declaring their own names in namespace std or we don't support the
  // standard library implementation in use.
  LookupResult Result(S, &S.PP.getIdentifierTable().get(Trait),
                      Loc, Sema::LookupOrdinaryName);
  if (!S.LookupQualifiedName(Result, Std))
    return DiagnoseMissing();
  if (Result.isAmbiguous())
    return true;
 
  ClassTemplateDecl *TraitTD = Result.getAsSingle<ClassTemplateDecl>();
  if (!TraitTD) {
    Result.suppressDiagnostics();
    NamedDecl *Found = *Result.begin();
    S.Diag(Loc, diag::err_std_type_trait_not_class_template) << Trait;
    S.Diag(Found->getLocation(), diag::note_declared_at);
    return true;
  }
 
  // Build the template-id.
  QualType TraitTy = S.CheckTemplateIdType(TemplateName(TraitTD), Loc, Args);
  if (TraitTy.isNull())
    return true;
  if (!S.isCompleteType(Loc, TraitTy)) {
    if (DiagID)
      S.RequireCompleteType(
          Loc, TraitTy, DiagID,
          printTemplateArgs(S.Context.getPrintingPolicy(), Args,
                            TraitTD->getTemplateParameters()));
    return true;
  }
 
  CXXRecordDecl *RD = TraitTy->getAsCXXRecordDecl();
  assert(RD && "specialization of class template is not a class?");
 
  // Look up the member of the trait type.
  S.LookupQualifiedName(TraitMemberLookup, RD);
  return TraitMemberLookup.isAmbiguous();
}
 
static TemplateArgumentLoc
getTrivialIntegralTemplateArgument(Sema &S, SourceLocation Loc, QualType T,
                                   uint64_t I) {
  TemplateArgument Arg(S.Context, S.Context.MakeIntValue(I, T), T);
  return S.getTrivialTemplateArgumentLoc(Arg, T, Loc);
}
 
static TemplateArgumentLoc
getTrivialTypeTemplateArgument(Sema &S, SourceLocation Loc, QualType T) {
  return S.getTrivialTemplateArgumentLoc(TemplateArgument(T), QualType(), Loc);
}
 
namespace { enum class IsTupleLike { TupleLike, NotTupleLike, Error }; }
 
static IsTupleLike isTupleLike(Sema &S, SourceLocation Loc, QualType T,
                               llvm::APSInt &Size) {
  EnterExpressionEvaluationContext ContextRAII(
      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
  DeclarationName Value = S.PP.getIdentifierInfo("value");
  LookupResult R(S, Value, Loc, Sema::LookupOrdinaryName);
 
  // Form template argument list for tuple_size<T>.
  TemplateArgumentListInfo Args(Loc, Loc);
  Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T));
 
  // If there's no tuple_size specialization or the lookup of 'value' is empty,
  // it's not tuple-like.
  if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/ 0) ||
      R.empty())
    return IsTupleLike::NotTupleLike;
 
  // If we get this far, we've committed to the tuple interpretation, but
  // we can still fail if there actually isn't a usable ::value.
 
  struct ICEDiagnoser : Sema::VerifyICEDiagnoser {
    LookupResult &R;
    TemplateArgumentListInfo &Args;
    ICEDiagnoser(LookupResult &R, TemplateArgumentListInfo &Args)
        : R(R), Args(Args) {}
    Sema::SemaDiagnosticBuilder diagnoseNotICE(Sema &S,
                                               SourceLocation Loc) override {
      return S.Diag(Loc, diag::err_decomp_decl_std_tuple_size_not_constant)
             << printTemplateArgs(S.Context.getPrintingPolicy(), Args,
                                  /*Params*/ nullptr);
    }
  } Diagnoser(R, Args);
 
  ExprResult E =
      S.BuildDeclarationNameExpr(CXXScopeSpec(), R, /*NeedsADL*/false);
  if (E.isInvalid())
    return IsTupleLike::Error;
 
  E = S.VerifyIntegerConstantExpression(E.get(), &Size, Diagnoser);
  if (E.isInvalid())
    return IsTupleLike::Error;
 
  return IsTupleLike::TupleLike;
}
 
/// \return std::tuple_element<I, T>::type.
static QualType getTupleLikeElementType(Sema &S, SourceLocation Loc,
                                        unsigned I, QualType T) {
  // Form template argument list for tuple_element<I, T>.
  TemplateArgumentListInfo Args(Loc, Loc);
  Args.addArgument(
      getTrivialIntegralTemplateArgument(S, Loc, S.Context.getSizeType(), I));
  Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T));
 
  DeclarationName TypeDN = S.PP.getIdentifierInfo("type");
  LookupResult R(S, TypeDN, Loc, Sema::LookupOrdinaryName);
  if (lookupStdTypeTraitMember(
          S, R, Loc, "tuple_element", Args,
          diag::err_decomp_decl_std_tuple_element_not_specialized))
    return QualType();
 
  auto *TD = R.getAsSingle<TypeDecl>();
  if (!TD) {
    R.suppressDiagnostics();
    S.Diag(Loc, diag::err_decomp_decl_std_tuple_element_not_specialized)
        << printTemplateArgs(S.Context.getPrintingPolicy(), Args,
                             /*Params*/ nullptr);
    if (!R.empty())
      S.Diag(R.getRepresentativeDecl()->getLocation(), diag::note_declared_at);
    return QualType();
  }
 
  return S.Context.getTypeDeclType(TD);
}
 
namespace {
struct InitializingBinding {
  Sema &S;
  InitializingBinding(Sema &S, BindingDecl *BD) : S(S) {
    Sema::CodeSynthesisContext Ctx;
    Ctx.Kind = Sema::CodeSynthesisContext::InitializingStructuredBinding;
    Ctx.PointOfInstantiation = BD->getLocation();
    Ctx.Entity = BD;
    S.pushCodeSynthesisContext(Ctx);
  }
  ~InitializingBinding() {
    S.popCodeSynthesisContext();
  }
};
}
 
static bool checkTupleLikeDecomposition(Sema &S,
                                        ArrayRef<BindingDecl *> Bindings,
                                        VarDecl *Src, QualType DecompType,
                                        const llvm::APSInt &TupleSize) {
  if ((int64_t)Bindings.size() != TupleSize) {
    S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
        << DecompType << (unsigned)Bindings.size()
        << (unsigned)TupleSize.getLimitedValue(UINT_MAX)
        << toString(TupleSize, 10) << (TupleSize < Bindings.size());
    return true;
  }
 
  if (Bindings.empty())
    return false;
 
  DeclarationName GetDN = S.PP.getIdentifierInfo("get");
 
  // [dcl.decomp]p3:
  //   The unqualified-id get is looked up in the scope of E by class member
  //   access lookup ...
  LookupResult MemberGet(S, GetDN, Src->getLocation(), Sema::LookupMemberName);
  bool UseMemberGet = false;
  if (S.isCompleteType(Src->getLocation(), DecompType)) {
    if (auto *RD = DecompType->getAsCXXRecordDecl())
      S.LookupQualifiedName(MemberGet, RD);
    if (MemberGet.isAmbiguous())
      return true;
    //   ... and if that finds at least one declaration that is a function
    //   template whose first template parameter is a non-type parameter ...
    for (NamedDecl *D : MemberGet) {
      if (FunctionTemplateDecl *FTD =
              dyn_cast<FunctionTemplateDecl>(D->getUnderlyingDecl())) {
        TemplateParameterList *TPL = FTD->getTemplateParameters();
        if (TPL->size() != 0 &&
            isa<NonTypeTemplateParmDecl>(TPL->getParam(0))) {
          //   ... the initializer is e.get<i>().
          UseMemberGet = true;
          break;
        }
      }
    }
  }
 
  unsigned I = 0;
  for (auto *B : Bindings) {
    InitializingBinding InitContext(S, B);
    SourceLocation Loc = B->getLocation();
 
    ExprResult E = S.BuildDeclRefExpr(Src, DecompType, VK_LValue, Loc);
    if (E.isInvalid())
      return true;
 
    //   e is an lvalue if the type of the entity is an lvalue reference and
    //   an xvalue otherwise
    if (!Src->getType()->isLValueReferenceType())
      E = ImplicitCastExpr::Create(S.Context, E.get()->getType(), CK_NoOp,
                                   E.get(), nullptr, VK_XValue,
                                   FPOptionsOverride());
 
    TemplateArgumentListInfo Args(Loc, Loc);
    Args.addArgument(
        getTrivialIntegralTemplateArgument(S, Loc, S.Context.getSizeType(), I));
 
    if (UseMemberGet) {
      //   if [lookup of member get] finds at least one declaration, the
      //   initializer is e.get<i-1>().
      E = S.BuildMemberReferenceExpr(E.get(), DecompType, Loc, false,
                                     CXXScopeSpec(), SourceLocation(), nullptr,
                                     MemberGet, &Args, nullptr);
      if (E.isInvalid())
        return true;
 
      E = S.BuildCallExpr(nullptr, E.get(), Loc, std::nullopt, Loc);
    } else {
      //   Otherwise, the initializer is get<i-1>(e), where get is looked up
      //   in the associated namespaces.
      Expr *Get = UnresolvedLookupExpr::Create(
          S.Context, nullptr, NestedNameSpecifierLoc(), SourceLocation(),
          DeclarationNameInfo(GetDN, Loc), /*RequiresADL*/true, &Args,
          UnresolvedSetIterator(), UnresolvedSetIterator());
 
      Expr *Arg = E.get();
      E = S.BuildCallExpr(nullptr, Get, Loc, Arg, Loc);
    }
    if (E.isInvalid())
      return true;
    Expr *Init = E.get();
 
    //   Given the type T designated by std::tuple_element<i - 1, E>::type,
    QualType T = getTupleLikeElementType(S, Loc, I, DecompType);
    if (T.isNull())
      return true;
 
    //   each vi is a variable of type "reference to T" initialized with the
    //   initializer, where the reference is an lvalue reference if the
    //   initializer is an lvalue and an rvalue reference otherwise
    QualType RefType =
        S.BuildReferenceType(T, E.get()->isLValue(), Loc, B->getDeclName());
    if (RefType.isNull())
      return true;
    auto *RefVD = VarDecl::Create(
        S.Context, Src->getDeclContext(), Loc, Loc,
        B->getDeclName().getAsIdentifierInfo(), RefType,
        S.Context.getTrivialTypeSourceInfo(T, Loc), Src->getStorageClass());
    RefVD->setLexicalDeclContext(Src->getLexicalDeclContext());
    RefVD->setTSCSpec(Src->getTSCSpec());
    RefVD->setImplicit();
    if (Src->isInlineSpecified())
      RefVD->setInlineSpecified();
    RefVD->getLexicalDeclContext()->addHiddenDecl(RefVD);
 
    InitializedEntity Entity = InitializedEntity::InitializeBinding(RefVD);
    InitializationKind Kind = InitializationKind::CreateCopy(Loc, Loc);
    InitializationSequence Seq(S, Entity, Kind, Init);
    E = Seq.Perform(S, Entity, Kind, Init);
    if (E.isInvalid())
      return true;
    E = S.ActOnFinishFullExpr(E.get(), Loc, /*DiscardedValue*/ false);
    if (E.isInvalid())
      return true;
    RefVD->setInit(E.get());
    S.CheckCompleteVariableDeclaration(RefVD);
 
    E = S.BuildDeclarationNameExpr(CXXScopeSpec(),
                                   DeclarationNameInfo(B->getDeclName(), Loc),
                                   RefVD);
    if (E.isInvalid())
      return true;
 
    B->setBinding(T, E.get());
    I++;
  }
 
  return false;
}
 
/// Find the base class to decompose in a built-in decomposition of a class type.
/// This base class search is, unfortunately, not quite like any other that we
/// perform anywhere else in C++.
static DeclAccessPair findDecomposableBaseClass(Sema &S, SourceLocation Loc,
                                                const CXXRecordDecl *RD,
                                                CXXCastPath &BasePath) {
  auto BaseHasFields = [](const CXXBaseSpecifier *Specifier,
                          CXXBasePath &Path) {
    return Specifier->getType()->getAsCXXRecordDecl()->hasDirectFields();
  };
 
  const CXXRecordDecl *ClassWithFields = nullptr;
  AccessSpecifier AS = AS_public;
  if (RD->hasDirectFields())
    // [dcl.decomp]p4:
    //   Otherwise, all of E's non-static data members shall be public direct
    //   members of E ...
    ClassWithFields = RD;
  else {
    //   ... or of ...
    CXXBasePaths Paths;
    Paths.setOrigin(const_cast<CXXRecordDecl*>(RD));
    if (!RD->lookupInBases(BaseHasFields, Paths)) {
      // If no classes have fields, just decompose RD itself. (This will work
      // if and only if zero bindings were provided.)
      return DeclAccessPair::make(const_cast<CXXRecordDecl*>(RD), AS_public);
    }
 
    CXXBasePath *BestPath = nullptr;
    for (auto &P : Paths) {
      if (!BestPath)
        BestPath = &P;
      else if (!S.Context.hasSameType(P.back().Base->getType(),
                                      BestPath->back().Base->getType())) {
        //   ... the same ...
        S.Diag(Loc, diag::err_decomp_decl_multiple_bases_with_members)
          << false << RD << BestPath->back().Base->getType()
          << P.back().Base->getType();
        return DeclAccessPair();
      } else if (P.Access < BestPath->Access) {
        BestPath = &P;
      }
    }
 
    //   ... unambiguous ...
    QualType BaseType = BestPath->back().Base->getType();
    if (Paths.isAmbiguous(S.Context.getCanonicalType(BaseType))) {
      S.Diag(Loc, diag::err_decomp_decl_ambiguous_base)
        << RD << BaseType << S.getAmbiguousPathsDisplayString(Paths);
      return DeclAccessPair();
    }
 
    //   ... [accessible, implied by other rules] base class of E.
    S.CheckBaseClassAccess(Loc, BaseType, S.Context.getRecordType(RD),
                           *BestPath, diag::err_decomp_decl_inaccessible_base);
    AS = BestPath->Access;
 
    ClassWithFields = BaseType->getAsCXXRecordDecl();
    S.BuildBasePathArray(Paths, BasePath);
  }
 
  // The above search did not check whether the selected class itself has base
  // classes with fields, so check that now.
  CXXBasePaths Paths;
  if (ClassWithFields->lookupInBases(BaseHasFields, Paths)) {
    S.Diag(Loc, diag::err_decomp_decl_multiple_bases_with_members)
      << (ClassWithFields == RD) << RD << ClassWithFields
      << Paths.front().back().Base->getType();
    return DeclAccessPair();
  }
 
  return DeclAccessPair::make(const_cast<CXXRecordDecl*>(ClassWithFields), AS);
}
 
static bool checkMemberDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
                                     ValueDecl *Src, QualType DecompType,
                                     const CXXRecordDecl *OrigRD) {
  if (S.RequireCompleteType(Src->getLocation(), DecompType,
                            diag::err_incomplete_type))
    return true;
 
  CXXCastPath BasePath;
  DeclAccessPair BasePair =
      findDecomposableBaseClass(S, Src->getLocation(), OrigRD, BasePath);
  const CXXRecordDecl *RD = cast_or_null<CXXRecordDecl>(BasePair.getDecl());
  if (!RD)
    return true;
  QualType BaseType = S.Context.getQualifiedType(S.Context.getRecordType(RD),
                                                 DecompType.getQualifiers());
 
  auto DiagnoseBadNumberOfBindings = [&]() -> bool {
    unsigned NumFields = llvm::count_if(
        RD->fields(), [](FieldDecl *FD) { return !FD->isUnnamedBitfield(); });
    assert(Bindings.size() != NumFields);
    S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
        << DecompType << (unsigned)Bindings.size() << NumFields << NumFields
        << (NumFields < Bindings.size());
    return true;
  };
 
  //   all of E's non-static data members shall be [...] well-formed
  //   when named as e.name in the context of the structured binding,
  //   E shall not have an anonymous union member, ...
  unsigned I = 0;
  for (auto *FD : RD->fields()) {
    if (FD->isUnnamedBitfield())
      continue;
 
    // All the non-static data members are required to be nameable, so they
    // must all have names.
    if (!FD->getDeclName()) {
      if (RD->isLambda()) {
        S.Diag(Src->getLocation(), diag::err_decomp_decl_lambda);
        S.Diag(RD->getLocation(), diag::note_lambda_decl);
        return true;
      }
 
      if (FD->isAnonymousStructOrUnion()) {
        S.Diag(Src->getLocation(), diag::err_decomp_decl_anon_union_member)
          << DecompType << FD->getType()->isUnionType();
        S.Diag(FD->getLocation(), diag::note_declared_at);
        return true;
      }
 
      // FIXME: Are there any other ways we could have an anonymous member?
    }
 
    // We have a real field to bind.
    if (I >= Bindings.size())
      return DiagnoseBadNumberOfBindings();
    auto *B = Bindings[I++];
    SourceLocation Loc = B->getLocation();
 
    // The field must be accessible in the context of the structured binding.
    // We already checked that the base class is accessible.
    // FIXME: Add 'const' to AccessedEntity's classes so we can remove the
    // const_cast here.
    S.CheckStructuredBindingMemberAccess(
        Loc, const_cast<CXXRecordDecl *>(OrigRD),
        DeclAccessPair::make(FD, CXXRecordDecl::MergeAccess(
                                     BasePair.getAccess(), FD->getAccess())));
 
    // Initialize the binding to Src.FD.
    ExprResult E = S.BuildDeclRefExpr(Src, DecompType, VK_LValue, Loc);
    if (E.isInvalid())
      return true;
    E = S.ImpCastExprToType(E.get(), BaseType, CK_UncheckedDerivedToBase,
                            VK_LValue, &BasePath);
    if (E.isInvalid())
      return true;
    E = S.BuildFieldReferenceExpr(E.get(), /*IsArrow*/ false, Loc,
                                  CXXScopeSpec(), FD,
                                  DeclAccessPair::make(FD, FD->getAccess()),
                                  DeclarationNameInfo(FD->getDeclName(), Loc));
    if (E.isInvalid())
      return true;
 
    // If the type of the member is T, the referenced type is cv T, where cv is
    // the cv-qualification of the decomposition expression.
    //
    // FIXME: We resolve a defect here: if the field is mutable, we do not add
    // 'const' to the type of the field.
    Qualifiers Q = DecompType.getQualifiers();
    if (FD->isMutable())
      Q.removeConst();
    B->setBinding(S.BuildQualifiedType(FD->getType(), Loc, Q), E.get());
  }
 
  if (I != Bindings.size())
    return DiagnoseBadNumberOfBindings();
 
  return false;
}
 
void Sema::CheckCompleteDecompositionDeclaration(DecompositionDecl *DD) {
  QualType DecompType = DD->getType();
 
  // If the type of the decomposition is dependent, then so is the type of
  // each binding.
  if (DecompType->isDependentType()) {
    for (auto *B : DD->bindings())
      B->setType(Context.DependentTy);
    return;
  }
 
  DecompType = DecompType.getNonReferenceType();
  ArrayRef<BindingDecl*> Bindings = DD->bindings();
 
  // C++1z [dcl.decomp]/2:
  //   If E is an array type [...]
  // As an extension, we also support decomposition of built-in complex and
  // vector types.
  if (auto *CAT = Context.getAsConstantArrayType(DecompType)) {
    if (checkArrayDecomposition(*this, Bindings, DD, DecompType, CAT))
      DD->setInvalidDecl();
    return;
  }
  if (auto *VT = DecompType->getAs<VectorType>()) {
    if (checkVectorDecomposition(*this, Bindings, DD, DecompType, VT))
      DD->setInvalidDecl();
    return;
  }
  if (auto *CT = DecompType->getAs<ComplexType>()) {
    if (checkComplexDecomposition(*this, Bindings, DD, DecompType, CT))
      DD->setInvalidDecl();
    return;
  }
 
  // C++1z [dcl.decomp]/3:
  //   if the expression std::tuple_size<E>::value is a well-formed integral
  //   constant expression, [...]
  llvm::APSInt TupleSize(32);
  switch (isTupleLike(*this, DD->getLocation(), DecompType, TupleSize)) {
  case IsTupleLike::Error:
    DD->setInvalidDecl();
    return;
 
  case IsTupleLike::TupleLike:
    if (checkTupleLikeDecomposition(*this, Bindings, DD, DecompType, TupleSize))
      DD->setInvalidDecl();
    return;
 
  case IsTupleLike::NotTupleLike:
    break;
  }
 
  // C++1z [dcl.dcl]/8:
  //   [E shall be of array or non-union class type]
  CXXRecordDecl *RD = DecompType->getAsCXXRecordDecl();
  if (!RD || RD->isUnion()) {
    Diag(DD->getLocation(), diag::err_decomp_decl_unbindable_type)
        << DD << !RD << DecompType;
    DD->setInvalidDecl();
    return;
  }
 
  // C++1z [dcl.decomp]/4:
  //   all of E's non-static data members shall be [...] direct members of
  //   E or of the same unambiguous public base class of E, ...
  if (checkMemberDecomposition(*this, Bindings, DD, DecompType, RD))
    DD->setInvalidDecl();
}
 
/// Merge the exception specifications of two variable declarations.
///
/// This is called when there's a redeclaration of a VarDecl. The function
/// checks if the redeclaration might have an exception specification and
/// validates compatibility and merges the specs if necessary.
void Sema::MergeVarDeclExceptionSpecs(VarDecl *New, VarDecl *Old) {
  // Shortcut if exceptions are disabled.
  if (!getLangOpts().CXXExceptions)
    return;
 
  assert(Context.hasSameType(New->getType(), Old->getType()) &&
         "Should only be called if types are otherwise the same.");
 
  QualType NewType = New->getType();
  QualType OldType = Old->getType();
 
  // We're only interested in pointers and references to functions, as well
  // as pointers to member functions.
  if (const ReferenceType *R = NewType->getAs<ReferenceType>()) {
    NewType = R->getPointeeType();
    OldType = OldType->castAs<ReferenceType>()->getPointeeType();
  } else if (const PointerType *P = NewType->getAs<PointerType>()) {
    NewType = P->getPointeeType();
    OldType = OldType->castAs<PointerType>()->getPointeeType();
  } else if (const MemberPointerType *M = NewType->getAs<MemberPointerType>()) {
    NewType = M->getPointeeType();
    OldType = OldType->castAs<MemberPointerType>()->getPointeeType();
  }
 
  if (!NewType->isFunctionProtoType())
    return;
 
  // There's lots of special cases for functions. For function pointers, system
  // libraries are hopefully not as broken so that we don't need these
  // workarounds.
  if (CheckEquivalentExceptionSpec(
        OldType->getAs<FunctionProtoType>(), Old->getLocation(),
        NewType->getAs<FunctionProtoType>(), New->getLocation())) {
    New->setInvalidDecl();
  }
}
 
/// CheckCXXDefaultArguments - Verify that the default arguments for a
/// function declaration are well-formed according to C++
/// [dcl.fct.default].
void Sema::CheckCXXDefaultArguments(FunctionDecl *FD) {
  unsigned NumParams = FD->getNumParams();
  unsigned ParamIdx = 0;
 
  // This checking doesn't make sense for explicit specializations; their
  // default arguments are determined by the declaration we're specializing,
  // not by FD.
  if (FD->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
    return;
  if (auto *FTD = FD->getDescribedFunctionTemplate())
    if (FTD->isMemberSpecialization())
      return;
 
  // Find first parameter with a default argument
  for (; ParamIdx < NumParams; ++ParamIdx) {
    ParmVarDecl *Param = FD->getParamDecl(ParamIdx);
    if (Param->hasDefaultArg())
      break;
  }
 
  // C++20 [dcl.fct.default]p4:
  //   In a given function declaration, each parameter subsequent to a parameter
  //   with a default argument shall have a default argument supplied in this or
  //   a previous declaration, unless the parameter was expanded from a
  //   parameter pack, or shall be a function parameter pack.
  for (; ParamIdx < NumParams; ++ParamIdx) {
    ParmVarDecl *Param = FD->getParamDecl(ParamIdx);
    if (!Param->hasDefaultArg() && !Param->isParameterPack() &&
        !(CurrentInstantiationScope &&
          CurrentInstantiationScope->isLocalPackExpansion(Param))) {
      if (Param->isInvalidDecl())
        /* We already complained about this parameter. */;
      else if (Param->getIdentifier())
        Diag(Param->getLocation(),
             diag::err_param_default_argument_missing_name)
          << Param->getIdentifier();
      else
        Diag(Param->getLocation(),
             diag::err_param_default_argument_missing);
    }
  }
}
 
/// Check that the given type is a literal type. Issue a diagnostic if not,
/// if Kind is Diagnose.
/// \return \c true if a problem has been found (and optionally diagnosed).
template <typename... Ts>
static bool CheckLiteralType(Sema &SemaRef, Sema::CheckConstexprKind Kind,
                             SourceLocation Loc, QualType T, unsigned DiagID,
                             Ts &&...DiagArgs) {
  if (T->isDependentType())
    return false;
 
  switch (Kind) {
  case Sema::CheckConstexprKind::Diagnose:
    return SemaRef.RequireLiteralType(Loc, T, DiagID,
                                      std::forward<Ts>(DiagArgs)...);
 
  case Sema::CheckConstexprKind::CheckValid:
    return !T->isLiteralType(SemaRef.Context);
  }
 
  llvm_unreachable("unknown CheckConstexprKind");
}
 
/// Determine whether a destructor cannot be constexpr due to
static bool CheckConstexprDestructorSubobjects(Sema &SemaRef,
                                               const CXXDestructorDecl *DD,
                                               Sema::CheckConstexprKind Kind) {
  auto Check = [&](SourceLocation Loc, QualType T, const FieldDecl *FD) {
    const CXXRecordDecl *RD =
        T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
    if (!RD || RD->hasConstexprDestructor())
      return true;
 
    if (Kind == Sema::CheckConstexprKind::Diagnose) {
      SemaRef.Diag(DD->getLocation(), diag::err_constexpr_dtor_subobject)
          << static_cast<int>(DD->getConstexprKind()) << !FD
          << (FD ? FD->getDeclName() : DeclarationName()) << T;
      SemaRef.Diag(Loc, diag::note_constexpr_dtor_subobject)
          << !FD << (FD ? FD->getDeclName() : DeclarationName()) << T;
    }
    return false;
  };
 
  const CXXRecordDecl *RD = DD->getParent();
  for (const CXXBaseSpecifier &B : RD->bases())
    if (!Check(B.getBaseTypeLoc(), B.getType(), nullptr))
      return false;
  for (const FieldDecl *FD : RD->fields())
    if (!Check(FD->getLocation(), FD->getType(), FD))
      return false;
  return true;
}
 
/// Check whether a function's parameter types are all literal types. If so,
/// return true. If not, produce a suitable diagnostic and return false.
static bool CheckConstexprParameterTypes(Sema &SemaRef,
                                         const FunctionDecl *FD,
                                         Sema::CheckConstexprKind Kind) {
  unsigned ArgIndex = 0;
  const auto *FT = FD->getType()->castAs<FunctionProtoType>();
  for (FunctionProtoType::param_type_iterator i = FT->param_type_begin(),
                                              e = FT->param_type_end();
       i != e; ++i, ++ArgIndex) {
    const ParmVarDecl *PD = FD->getParamDecl(ArgIndex);
    assert(PD && "null in a parameter list");
    SourceLocation ParamLoc = PD->getLocation();
    if (CheckLiteralType(SemaRef, Kind, ParamLoc, *i,
                         diag::err_constexpr_non_literal_param, ArgIndex + 1,
                         PD->getSourceRange(), isa<CXXConstructorDecl>(FD),
                         FD->isConsteval()))
      return false;
  }
  return true;
}
 
/// Check whether a function's return type is a literal type. If so, return
/// true. If not, produce a suitable diagnostic and return false.
static bool CheckConstexprReturnType(Sema &SemaRef, const FunctionDecl *FD,
                                     Sema::CheckConstexprKind Kind) {
  if (CheckLiteralType(SemaRef, Kind, FD->getLocation(), FD->getReturnType(),
                       diag::err_constexpr_non_literal_return,
                       FD->isConsteval()))
    return false;
  return true;
}
 
/// Get diagnostic %select index for tag kind for
/// record diagnostic message.
/// WARNING: Indexes apply to particular diagnostics only!
///
/// \returns diagnostic %select index.
static unsigned getRecordDiagFromTagKind(TagTypeKind Tag) {
  switch (Tag) {
  case TTK_Struct: return 0;
  case TTK_Interface: return 1;
  case TTK_Class:  return 2;
  default: llvm_unreachable("Invalid tag kind for record diagnostic!");
  }
}
 
static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
                                       Stmt *Body,
                                       Sema::CheckConstexprKind Kind);
 
// Check whether a function declaration satisfies the requirements of a
// constexpr function definition or a constexpr constructor definition. If so,
// return true. If not, produce appropriate diagnostics (unless asked not to by
// Kind) and return false.
//
// This implements C++11 [dcl.constexpr]p3,4, as amended by DR1360.
bool Sema::CheckConstexprFunctionDefinition(const FunctionDecl *NewFD,
                                            CheckConstexprKind Kind) {
  const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(NewFD);
  if (MD && MD->isInstance()) {
    // C++11 [dcl.constexpr]p4:
    //  The definition of a constexpr constructor shall satisfy the following
    //  constraints:
    //  - the class shall not have any virtual base classes;
    //
    // FIXME: This only applies to constructors and destructors, not arbitrary
    // member functions.
    const CXXRecordDecl *RD = MD->getParent();
    if (RD->getNumVBases()) {
      if (Kind == CheckConstexprKind::CheckValid)
        return false;
 
      Diag(NewFD->getLocation(), diag::err_constexpr_virtual_base)
        << isa<CXXConstructorDecl>(NewFD)
        << getRecordDiagFromTagKind(RD->getTagKind()) << RD->getNumVBases();
      for (const auto &I : RD->vbases())
        Diag(I.getBeginLoc(), diag::note_constexpr_virtual_base_here)
            << I.getSourceRange();
      return false;
    }
  }
 
  if (!isa<CXXConstructorDecl>(NewFD)) {
    // C++11 [dcl.constexpr]p3:
    //  The definition of a constexpr function shall satisfy the following
    //  constraints:
    // - it shall not be virtual; (removed in C++20)
    const CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(NewFD);
    if (Method && Method->isVirtual()) {
      if (getLangOpts().CPlusPlus20) {
        if (Kind == CheckConstexprKind::Diagnose)
          Diag(Method->getLocation(), diag::warn_cxx17_compat_constexpr_virtual);
      } else {
        if (Kind == CheckConstexprKind::CheckValid)
          return false;
 
        Method = Method->getCanonicalDecl();
        Diag(Method->getLocation(), diag::err_constexpr_virtual);
 
        // If it's not obvious why this function is virtual, find an overridden
        // function which uses the 'virtual' keyword.
        const CXXMethodDecl *WrittenVirtual = Method;
        while (!WrittenVirtual->isVirtualAsWritten())
          WrittenVirtual = *WrittenVirtual->begin_overridden_methods();
        if (WrittenVirtual != Method)
          Diag(WrittenVirtual->getLocation(),
               diag::note_overridden_virtual_function);
        return false;
      }
    }
 
    // - its return type shall be a literal type;
    if (!CheckConstexprReturnType(*this, NewFD, Kind))
      return false;
  }
 
  if (auto *Dtor = dyn_cast<CXXDestructorDecl>(NewFD)) {
    // A destructor can be constexpr only if the defaulted destructor could be;
    // we don't need to check the members and bases if we already know they all
    // have constexpr destructors.
    if (!Dtor->getParent()->defaultedDestructorIsConstexpr()) {
      if (Kind == CheckConstexprKind::CheckValid)
        return false;
      if (!CheckConstexprDestructorSubobjects(*this, Dtor, Kind))
        return false;
    }
  }
 
  // - each of its parameter types shall be a literal type;
  if (!CheckConstexprParameterTypes(*this, NewFD, Kind))
    return false;
 
  Stmt *Body = NewFD->getBody();
  assert(Body &&
         "CheckConstexprFunctionDefinition called on function with no body");
  return CheckConstexprFunctionBody(*this, NewFD, Body, Kind);
}
 
/// Check the given declaration statement is legal within a constexpr function
/// body. C++11 [dcl.constexpr]p3,p4, and C++1y [dcl.constexpr]p3.
///
/// \return true if the body is OK (maybe only as an extension), false if we
///         have diagnosed a problem.
static bool CheckConstexprDeclStmt(Sema &SemaRef, const FunctionDecl *Dcl,
                                   DeclStmt *DS, SourceLocation &Cxx1yLoc,
                                   Sema::CheckConstexprKind Kind) {
  // C++11 [dcl.constexpr]p3 and p4:
  //  The definition of a constexpr function(p3) or constructor(p4) [...] shall
  //  contain only
  for (const auto *DclIt : DS->decls()) {
    switch (DclIt->getKind()) {
    case Decl::StaticAssert:
    case Decl::Using:
    case Decl::UsingShadow:
    case Decl::UsingDirective:
    case Decl::UnresolvedUsingTypename:
    case Decl::UnresolvedUsingValue:
    case Decl::UsingEnum:
      //   - static_assert-declarations
      //   - using-declarations,
      //   - using-directives,
      //   - using-enum-declaration
      continue;
 
    case Decl::Typedef:
    case Decl::TypeAlias: {
      //   - typedef declarations and alias-declarations that do not define
      //     classes or enumerations,
      const auto *TN = cast<TypedefNameDecl>(DclIt);
      if (TN->getUnderlyingType()->isVariablyModifiedType()) {
        // Don't allow variably-modified types in constexpr functions.
        if (Kind == Sema::CheckConstexprKind::Diagnose) {
          TypeLoc TL = TN->getTypeSourceInfo()->getTypeLoc();
          SemaRef.Diag(TL.getBeginLoc(), diag::err_constexpr_vla)
            << TL.getSourceRange() << TL.getType()
            << isa<CXXConstructorDecl>(Dcl);
        }
        return false;
      }
      continue;
    }
 
    case Decl::Enum:
    case Decl::CXXRecord:
      // C++1y allows types to be defined, not just declared.
      if (cast<TagDecl>(DclIt)->isThisDeclarationADefinition()) {
        if (Kind == Sema::CheckConstexprKind::Diagnose) {
          SemaRef.Diag(DS->getBeginLoc(),
                       SemaRef.getLangOpts().CPlusPlus14
                           ? diag::warn_cxx11_compat_constexpr_type_definition
                           : diag::ext_constexpr_type_definition)
              << isa<CXXConstructorDecl>(Dcl);
        } else if (!SemaRef.getLangOpts().CPlusPlus14) {
          return false;
        }
      }
      continue;
 
    case Decl::EnumConstant:
    case Decl::IndirectField:
    case Decl::ParmVar:
      // These can only appear with other declarations which are banned in
      // C++11 and permitted in C++1y, so ignore them.
      continue;
 
    case Decl::Var:
    case Decl::Decomposition: {
      // C++1y [dcl.constexpr]p3 allows anything except:
      //   a definition of a variable of non-literal type or of static or
      //   thread storage duration or [before C++2a] for which no
      //   initialization is performed.
      const auto *VD = cast<VarDecl>(DclIt);
      if (VD->isThisDeclarationADefinition()) {
        if (VD->isStaticLocal()) {
          if (Kind == Sema::CheckConstexprKind::Diagnose) {
            SemaRef.Diag(VD->getLocation(),
                         SemaRef.getLangOpts().CPlusPlus23
                             ? diag::warn_cxx20_compat_constexpr_var
                             : diag::ext_constexpr_static_var)
                << isa<CXXConstructorDecl>(Dcl)
                << (VD->getTLSKind() == VarDecl::TLS_Dynamic);
          } else if (!SemaRef.getLangOpts().CPlusPlus23) {
            return false;
          }
        }
        if (SemaRef.LangOpts.CPlusPlus23) {
          CheckLiteralType(SemaRef, Kind, VD->getLocation(), VD->getType(),
                           diag::warn_cxx20_compat_constexpr_var,
                           isa<CXXConstructorDecl>(Dcl),
                           /*variable of non-literal type*/ 2);
        } else if (CheckLiteralType(
                       SemaRef, Kind, VD->getLocation(), VD->getType(),
                       diag::err_constexpr_local_var_non_literal_type,
                       isa<CXXConstructorDecl>(Dcl))) {
          return false;
        }
        if (!VD->getType()->isDependentType() &&
            !VD->hasInit() && !VD->isCXXForRangeDecl()) {
          if (Kind == Sema::CheckConstexprKind::Diagnose) {
            SemaRef.Diag(
                VD->getLocation(),
                SemaRef.getLangOpts().CPlusPlus20
                    ? diag::warn_cxx17_compat_constexpr_local_var_no_init
                    : diag::ext_constexpr_local_var_no_init)
                << isa<CXXConstructorDecl>(Dcl);
          } else if (!SemaRef.getLangOpts().CPlusPlus20) {
            return false;
          }
          continue;
        }
      }
      if (Kind == Sema::CheckConstexprKind::Diagnose) {
        SemaRef.Diag(VD->getLocation(),
                     SemaRef.getLangOpts().CPlusPlus14
                      ? diag::warn_cxx11_compat_constexpr_local_var
                      : diag::ext_constexpr_local_var)
          << isa<CXXConstructorDecl>(Dcl);
      } else if (!SemaRef.getLangOpts().CPlusPlus14) {
        return false;
      }
      continue;
    }
 
    case Decl::NamespaceAlias:
    case Decl::Function:
      // These are disallowed in C++11 and permitted in C++1y. Allow them
      // everywhere as an extension.
      if (!Cxx1yLoc.isValid())
        Cxx1yLoc = DS->getBeginLoc();
      continue;
 
    default:
      if (Kind == Sema::CheckConstexprKind::Diagnose) {
        SemaRef.Diag(DS->getBeginLoc(), diag::err_constexpr_body_invalid_stmt)
            << isa<CXXConstructorDecl>(Dcl) << Dcl->isConsteval();
      }
      return false;
    }
  }
 
  return true;
}
 
/// Check that the given field is initialized within a constexpr constructor.
///
/// \param Dcl The constexpr constructor being checked.
/// \param Field The field being checked. This may be a member of an anonymous
///        struct or union nested within the class being checked.
/// \param Inits All declarations, including anonymous struct/union members and
///        indirect members, for which any initialization was provided.
/// \param Diagnosed Whether we've emitted the error message yet. Used to attach
///        multiple notes for different members to the same error.
/// \param Kind Whether we're diagnosing a constructor as written or determining
///        whether the formal requirements are satisfied.
/// \return \c false if we're checking for validity and the constructor does
///         not satisfy the requirements on a constexpr constructor.
static bool CheckConstexprCtorInitializer(Sema &SemaRef,
                                          const FunctionDecl *Dcl,
                                          FieldDecl *Field,
                                          llvm::SmallSet<Decl*, 16> &Inits,
                                          bool &Diagnosed,
                                          Sema::CheckConstexprKind Kind) {
  // In C++20 onwards, there's nothing to check for validity.
  if (Kind == Sema::CheckConstexprKind::CheckValid &&
      SemaRef.getLangOpts().CPlusPlus20)
    return true;
 
  if (Field->isInvalidDecl())
    return true;
 
  if (Field->isUnnamedBitfield())
    return true;
 
  // Anonymous unions with no variant members and empty anonymous structs do not
  // need to be explicitly initialized. FIXME: Anonymous structs that contain no
  // indirect fields don't need initializing.
  if (Field->isAnonymousStructOrUnion() &&
      (Field->getType()->isUnionType()
           ? !Field->getType()->getAsCXXRecordDecl()->hasVariantMembers()
           : Field->getType()->getAsCXXRecordDecl()->isEmpty()))
    return true;
 
  if (!Inits.count(Field)) {
    if (Kind == Sema::CheckConstexprKind::Diagnose) {
      if (!Diagnosed) {
        SemaRef.Diag(Dcl->getLocation(),
                     SemaRef.getLangOpts().CPlusPlus20
                         ? diag::warn_cxx17_compat_constexpr_ctor_missing_init
                         : diag::ext_constexpr_ctor_missing_init);
        Diagnosed = true;
      }
      SemaRef.Diag(Field->getLocation(),
                   diag::note_constexpr_ctor_missing_init);
    } else if (!SemaRef.getLangOpts().CPlusPlus20) {
      return false;
    }
  } else if (Field->isAnonymousStructOrUnion()) {
    const RecordDecl *RD = Field->getType()->castAs<RecordType>()->getDecl();
    for (auto *I : RD->fields())
      // If an anonymous union contains an anonymous struct of which any member
      // is initialized, all members must be initialized.
      if (!RD->isUnion() || Inits.count(I))
        if (!CheckConstexprCtorInitializer(SemaRef, Dcl, I, Inits, Diagnosed,
                                           Kind))
          return false;
  }
  return true;
}
 
/// Check the provided statement is allowed in a constexpr function
/// definition.
static bool
CheckConstexprFunctionStmt(Sema &SemaRef, const FunctionDecl *Dcl, Stmt *S,
                           SmallVectorImpl<SourceLocation> &ReturnStmts,
                           SourceLocation &Cxx1yLoc, SourceLocation &Cxx2aLoc,
                           SourceLocation &Cxx2bLoc,
                           Sema::CheckConstexprKind Kind) {
  // - its function-body shall be [...] a compound-statement that contains only
  switch (S->getStmtClass()) {
  case Stmt::NullStmtClass:
    //   - null statements,
    return true;
 
  case Stmt::DeclStmtClass:
    //   - static_assert-declarations
    //   - using-declarations,
    //   - using-directives,
    //   - typedef declarations and alias-declarations that do not define
    //     classes or enumerations,
    if (!CheckConstexprDeclStmt(SemaRef, Dcl, cast<DeclStmt>(S), Cxx1yLoc, Kind))
      return false;
    return true;
 
  case Stmt::ReturnStmtClass:
    //   - and exactly one return statement;
    if (isa<CXXConstructorDecl>(Dcl)) {
      // C++1y allows return statements in constexpr constructors.
      if (!Cxx1yLoc.isValid())
        Cxx1yLoc = S->getBeginLoc();
      return true;
    }
 
    ReturnStmts.push_back(S->getBeginLoc());
    return true;
 
  case Stmt::AttributedStmtClass:
    // Attributes on a statement don't affect its formal kind and hence don't
    // affect its validity in a constexpr function.
    return CheckConstexprFunctionStmt(
        SemaRef, Dcl, cast<AttributedStmt>(S)->getSubStmt(), ReturnStmts,
        Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind);
 
  case Stmt::CompoundStmtClass: {
    // C++1y allows compound-statements.
    if (!Cxx1yLoc.isValid())
      Cxx1yLoc = S->getBeginLoc();
 
    CompoundStmt *CompStmt = cast<CompoundStmt>(S);
    for (auto *BodyIt : CompStmt->body()) {
      if (!CheckConstexprFunctionStmt(SemaRef, Dcl, BodyIt, ReturnStmts,
                                      Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
        return false;
    }
    return true;
  }
 
  case Stmt::IfStmtClass: {
    // C++1y allows if-statements.
    if (!Cxx1yLoc.isValid())
      Cxx1yLoc = S->getBeginLoc();
 
    IfStmt *If = cast<IfStmt>(S);
    if (!CheckConstexprFunctionStmt(SemaRef, Dcl, If->getThen(), ReturnStmts,
                                    Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
      return false;
    if (If->getElse() &&
        !CheckConstexprFunctionStmt(SemaRef, Dcl, If->getElse(), ReturnStmts,
                                    Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
      return false;
    return true;
  }
 
  case Stmt::WhileStmtClass:
  case Stmt::DoStmtClass:
  case Stmt::ForStmtClass:
  case Stmt::CXXForRangeStmtClass:
  case Stmt::ContinueStmtClass:
    // C++1y allows all of these. We don't allow them as extensions in C++11,
    // because they don't make sense without variable mutation.
    if (!SemaRef.getLangOpts().CPlusPlus14)
      break;
    if (!Cxx1yLoc.isValid())
      Cxx1yLoc = S->getBeginLoc();
    for (Stmt *SubStmt : S->children()) {
      if (SubStmt &&
          !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
                                      Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
        return false;
    }
    return true;
 
  case Stmt::SwitchStmtClass:
  case Stmt::CaseStmtClass:
  case Stmt::DefaultStmtClass:
  case Stmt::BreakStmtClass:
    // C++1y allows switch-statements, and since they don't need variable
    // mutation, we can reasonably allow them in C++11 as an extension.
    if (!Cxx1yLoc.isValid())
      Cxx1yLoc = S->getBeginLoc();
    for (Stmt *SubStmt : S->children()) {
      if (SubStmt &&
          !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
                                      Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
        return false;
    }
    return true;
 
  case Stmt::LabelStmtClass:
  case Stmt::GotoStmtClass:
    if (Cxx2bLoc.isInvalid())
      Cxx2bLoc = S->getBeginLoc();
    for (Stmt *SubStmt : S->children()) {
      if (SubStmt &&
          !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
                                      Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
        return false;
    }
    return true;
 
  case Stmt::GCCAsmStmtClass:
  case Stmt::MSAsmStmtClass:
    // C++2a allows inline assembly statements.
  case Stmt::CXXTryStmtClass:
    if (Cxx2aLoc.isInvalid())
      Cxx2aLoc = S->getBeginLoc();
    for (Stmt *SubStmt : S->children()) {
      if (SubStmt &&
          !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
                                      Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
        return false;
    }
    return true;
 
  case Stmt::CXXCatchStmtClass:
    // Do not bother checking the language mode (already covered by the
    // try block check).
    if (!CheckConstexprFunctionStmt(
            SemaRef, Dcl, cast<CXXCatchStmt>(S)->getHandlerBlock(), ReturnStmts,
            Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
      return false;
    return true;
 
  default:
    if (!isa<Expr>(S))
      break;
 
    // C++1y allows expression-statements.
    if (!Cxx1yLoc.isValid())
      Cxx1yLoc = S->getBeginLoc();
    return true;
  }
 
  if (Kind == Sema::CheckConstexprKind::Diagnose) {
    SemaRef.Diag(S->getBeginLoc(), diag::err_constexpr_body_invalid_stmt)
        << isa<CXXConstructorDecl>(Dcl) << Dcl->isConsteval();
  }
  return false;
}
 
/// Check the body for the given constexpr function declaration only contains
/// the permitted types of statement. C++11 [dcl.constexpr]p3,p4.
///
/// \return true if the body is OK, false if we have found or diagnosed a
/// problem.
static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
                                       Stmt *Body,
                                       Sema::CheckConstexprKind Kind) {
  SmallVector<SourceLocation, 4> ReturnStmts;
 
  if (isa<CXXTryStmt>(Body)) {
    // C++11 [dcl.constexpr]p3:
    //  The definition of a constexpr function shall satisfy the following
    //  constraints: [...]
    // - its function-body shall be = delete, = default, or a
    //   compound-statement
    //
    // C++11 [dcl.constexpr]p4:
    //  In the definition of a constexpr constructor, [...]
    // - its function-body shall not be a function-try-block;
    //
    // This restriction is lifted in C++2a, as long as inner statements also
    // apply the general constexpr rules.
    switch (Kind) {
    case Sema::CheckConstexprKind::CheckValid:
      if (!SemaRef.getLangOpts().CPlusPlus20)
        return false;
      break;
 
    case Sema::CheckConstexprKind::Diagnose:
      SemaRef.Diag(Body->getBeginLoc(),
           !SemaRef.getLangOpts().CPlusPlus20
               ? diag::ext_constexpr_function_try_block_cxx20
               : diag::warn_cxx17_compat_constexpr_function_try_block)
          << isa<CXXConstructorDecl>(Dcl);
      break;
    }
  }
 
  // - its function-body shall be [...] a compound-statement that contains only
  //   [... list of cases ...]
  //
  // Note that walking the children here is enough to properly check for
  // CompoundStmt and CXXTryStmt body.
  SourceLocation Cxx1yLoc, Cxx2aLoc, Cxx2bLoc;
  for (Stmt *SubStmt : Body->children()) {
    if (SubStmt &&
        !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
                                    Cxx1yLoc, Cxx2aLoc, Cxx2bLoc, Kind))
      return false;
  }
 
  if (Kind == Sema::CheckConstexprKind::CheckValid) {
    // If this is only valid as an extension, report that we don't satisfy the
    // constraints of the current language.
    if ((Cxx2bLoc.isValid() && !SemaRef.getLangOpts().CPlusPlus23) ||
        (Cxx2aLoc.isValid() && !SemaRef.getLangOpts().CPlusPlus20) ||
        (Cxx1yLoc.isValid() && !SemaRef.getLangOpts().CPlusPlus17))
      return false;
  } else if (Cxx2bLoc.isValid()) {
    SemaRef.Diag(Cxx2bLoc,
                 SemaRef.getLangOpts().CPlusPlus23
                     ? diag::warn_cxx20_compat_constexpr_body_invalid_stmt
                     : diag::ext_constexpr_body_invalid_stmt_cxx23)
        << isa<CXXConstructorDecl>(Dcl);
  } else if (Cxx2aLoc.isValid()) {
    SemaRef.Diag(Cxx2aLoc,
         SemaRef.getLangOpts().CPlusPlus20
           ? diag::warn_cxx17_compat_constexpr_body_invalid_stmt
           : diag::ext_constexpr_body_invalid_stmt_cxx20)
      << isa<CXXConstructorDecl>(Dcl);
  } else if (Cxx1yLoc.isValid()) {
    SemaRef.Diag(Cxx1yLoc,
         SemaRef.getLangOpts().CPlusPlus14
           ? diag::warn_cxx11_compat_constexpr_body_invalid_stmt
           : diag::ext_constexpr_body_invalid_stmt)
      << isa<CXXConstructorDecl>(Dcl);
  }
 
  if (const CXXConstructorDecl *Constructor
        = dyn_cast<CXXConstructorDecl>(Dcl)) {
    const CXXRecordDecl *RD = Constructor->getParent();
    // DR1359:
    // - every non-variant non-static data member and base class sub-object
    //   shall be initialized;
    // DR1460:
    // - if the class is a union having variant members, exactly one of them
    //   shall be initialized;
    if (RD->isUnion()) {
      if (Constructor->getNumCtorInitializers() == 0 &&
          RD->hasVariantMembers()) {
        if (Kind == Sema::CheckConstexprKind::Diagnose) {
          SemaRef.Diag(
              Dcl->getLocation(),
              SemaRef.getLangOpts().CPlusPlus20
                  ? diag::warn_cxx17_compat_constexpr_union_ctor_no_init
                  : diag::ext_constexpr_union_ctor_no_init);
        } else if (!SemaRef.getLangOpts().CPlusPlus20) {
          return false;
        }
      }
    } else if (!Constructor->isDependentContext() &&
               !Constructor->isDelegatingConstructor()) {
      assert(RD->getNumVBases() == 0 && "constexpr ctor with virtual bases");
 
      // Skip detailed checking if we have enough initializers, and we would
      // allow at most one initializer per member.
      bool AnyAnonStructUnionMembers = false;
      unsigned Fields = 0;
      for (CXXRecordDecl::field_iterator I = RD->field_begin(),
           E = RD->field_end(); I != E; ++I, ++Fields) {
        if (I->isAnonymousStructOrUnion()) {
          AnyAnonStructUnionMembers = true;
          break;
        }
      }
      // DR1460:
      // - if the class is a union-like class, but is not a union, for each of
      //   its anonymous union members having variant members, exactly one of
      //   them shall be initialized;
      if (AnyAnonStructUnionMembers ||
          Constructor->getNumCtorInitializers() != RD->getNumBases() + Fields) {
        // Check initialization of non-static data members. Base classes are
        // always initialized so do not need to be checked. Dependent bases
        // might not have initializers in the member initializer list.
        llvm::SmallSet<Decl*, 16> Inits;
        for (const auto *I: Constructor->inits()) {
          if (FieldDecl *FD = I->getMember())
            Inits.insert(FD);
          else if (IndirectFieldDecl *ID = I->getIndirectMember())
            Inits.insert(ID->chain_begin(), ID->chain_end());
        }
 
        bool Diagnosed = false;
        for (auto *I : RD->fields())
          if (!CheckConstexprCtorInitializer(SemaRef, Dcl, I, Inits, Diagnosed,
                                             Kind))
            return false;
      }
    }
  } else {
    if (ReturnStmts.empty()) {
      // C++1y doesn't require constexpr functions to contain a 'return'
      // statement. We still do, unless the return type might be void, because
      // otherwise if there's no return statement, the function cannot
      // be used in a core constant expression.
      bool OK = SemaRef.getLangOpts().CPlusPlus14 &&
                (Dcl->getReturnType()->isVoidType() ||
                 Dcl->getReturnType()->isDependentType());
      switch (Kind) {
      case Sema::CheckConstexprKind::Diagnose:
        SemaRef.Diag(Dcl->getLocation(),
                     OK ? diag::warn_cxx11_compat_constexpr_body_no_return
                        : diag::err_constexpr_body_no_return)
            << Dcl->isConsteval();
        if (!OK)
          return false;
        break;
 
      case Sema::CheckConstexprKind::CheckValid:
        // The formal requirements don't include this rule in C++14, even
        // though the "must be able to produce a constant expression" rules
        // still imply it in some cases.
        if (!SemaRef.getLangOpts().CPlusPlus14)
          return false;
        break;
      }
    } else if (ReturnStmts.size() > 1) {
      switch (Kind) {
      case Sema::CheckConstexprKind::Diagnose:
        SemaRef.Diag(
            ReturnStmts.back(),
            SemaRef.getLangOpts().CPlusPlus14
                ? diag::warn_cxx11_compat_constexpr_body_multiple_return
                : diag::ext_constexpr_body_multiple_return);
        for (unsigned I = 0; I < ReturnStmts.size() - 1; ++I)
          SemaRef.Diag(ReturnStmts[I],
                       diag::note_constexpr_body_previous_return);
        break;
 
      case Sema::CheckConstexprKind::CheckValid:
        if (!SemaRef.getLangOpts().CPlusPlus14)
          return false;
        break;
      }
    }
  }
 
  // C++11 [dcl.constexpr]p5:
  //   if no function argument values exist such that the function invocation
  //   substitution would produce a constant expression, the program is
  //   ill-formed; no diagnostic required.
  // C++11 [dcl.constexpr]p3:
  //   - every constructor call and implicit conversion used in initializing the
  //     return value shall be one of those allowed in a constant expression.
  // C++11 [dcl.constexpr]p4:
  //   - every constructor involved in initializing non-static data members and
  //     base class sub-objects shall be a constexpr constructor.
  //
  // Note that this rule is distinct from the "requirements for a constexpr
  // function", so is not checked in CheckValid mode.
  SmallVector<PartialDiagnosticAt, 8> Diags;
  if (Kind == Sema::CheckConstexprKind::Diagnose &&
      !Expr::isPotentialConstantExpr(Dcl, Diags)) {
    SemaRef.Diag(Dcl->getLocation(),
                 diag::ext_constexpr_function_never_constant_expr)
        << isa<CXXConstructorDecl>(Dcl) << Dcl->isConsteval();
    for (size_t I = 0, N = Diags.size(); I != N; ++I)
      SemaRef.Diag(Diags[I].first, Diags[I].second);
    // Don't return false here: we allow this for compatibility in
    // system headers.
  }
 
  return true;
}
 
bool Sema::CheckImmediateEscalatingFunctionDefinition(
    FunctionDecl *FD, const sema::FunctionScopeInfo *FSI) {
  if (!getLangOpts().CPlusPlus20 || !FD->isImmediateEscalating())
    return true;
  FD->setBodyContainsImmediateEscalatingExpressions(
      FSI->FoundImmediateEscalatingExpression);
  if (FSI->FoundImmediateEscalatingExpression) {
    auto it = UndefinedButUsed.find(FD->getCanonicalDecl());
    if (it != UndefinedButUsed.end()) {
      Diag(it->second, diag::err_immediate_function_used_before_definition)
          << it->first;
      Diag(FD->getLocation(), diag::note_defined_here) << FD;
      if (FD->isImmediateFunction() && !FD->isConsteval())
        DiagnoseImmediateEscalatingReason(FD);
      return false;
    }
  }
  return true;
}
 
void Sema::DiagnoseImmediateEscalatingReason(FunctionDecl *FD) {
  assert(FD->isImmediateEscalating() && !FD->isConsteval() &&
         "expected an immediate function");
  assert(FD->hasBody() && "expected the function to have a body");
  struct ImmediateEscalatingExpressionsVisitor
      : public RecursiveASTVisitor<ImmediateEscalatingExpressionsVisitor> {
 
    using Base = RecursiveASTVisitor<ImmediateEscalatingExpressionsVisitor>;
    Sema &SemaRef;
 
    const FunctionDecl *ImmediateFn;
    bool ImmediateFnIsConstructor;
    CXXConstructorDecl *CurrentConstructor = nullptr;
    CXXCtorInitializer *CurrentInit = nullptr;
 
    ImmediateEscalatingExpressionsVisitor(Sema &SemaRef, FunctionDecl *FD)
        : SemaRef(SemaRef), ImmediateFn(FD),
          ImmediateFnIsConstructor(isa<CXXConstructorDecl>(FD)) {}
 
    bool shouldVisitImplicitCode() const { return true; }
    bool shouldVisitLambdaBody() const { return false; }
 
    void Diag(const Expr *E, const FunctionDecl *Fn, bool IsCall) {
      SourceLocation Loc = E->getBeginLoc();
      SourceRange Range = E->getSourceRange();
      if (CurrentConstructor && CurrentInit) {
        Loc = CurrentConstructor->getLocation();
        Range = CurrentInit->isWritten() ? CurrentInit->getSourceRange()
                                         : SourceRange();
      }
 
      FieldDecl* InitializedField = CurrentInit ? CurrentInit->getAnyMember() : nullptr;
 
      SemaRef.Diag(Loc, diag::note_immediate_function_reason)
          << ImmediateFn << Fn << Fn->isConsteval() << IsCall
          << isa<CXXConstructorDecl>(Fn) << ImmediateFnIsConstructor
          << (InitializedField != nullptr)
          << (CurrentInit && !CurrentInit->isWritten())
          << InitializedField << Range;
    }
    bool TraverseCallExpr(CallExpr *E) {
      if (const auto *DR =
              dyn_cast<DeclRefExpr>(E->getCallee()->IgnoreImplicit());
          DR && DR->isImmediateEscalating()) {
        Diag(E, E->getDirectCallee(), /*IsCall=*/true);
        return false;
      }
 
      for (Expr *A : E->arguments())
        if (!getDerived().TraverseStmt(A))
          return false;
 
      return true;
    }
 
    bool VisitDeclRefExpr(DeclRefExpr *E) {
      if (const auto *ReferencedFn = dyn_cast<FunctionDecl>(E->getDecl());
          ReferencedFn && E->isImmediateEscalating()) {
        Diag(E, ReferencedFn, /*IsCall=*/false);
        return false;
      }
 
      return true;
    }
 
    bool VisitCXXConstructExpr(CXXConstructExpr *E) {
      CXXConstructorDecl *D = E->getConstructor();
      if (E->isImmediateEscalating()) {
        Diag(E, D, /*IsCall=*/true);
        return false;
      }
      return true;
    }
 
    bool TraverseConstructorInitializer(CXXCtorInitializer *Init) {
      llvm::SaveAndRestore RAII(CurrentInit, Init);
      return Base::TraverseConstructorInitializer(Init);
    }
 
    bool TraverseCXXConstructorDecl(CXXConstructorDecl *Ctr) {
      llvm::SaveAndRestore RAII(CurrentConstructor, Ctr);
      return Base::TraverseCXXConstructorDecl(Ctr);
    }
 
    bool TraverseType(QualType T) { return true; }
    bool VisitBlockExpr(BlockExpr *T) { return true; }
 
  } Visitor(*this, FD);
  Visitor.TraverseDecl(FD);
}
 
/// Get the class that is directly named by the current context. This is the
/// class for which an unqualified-id in this scope could name a constructor
/// or destructor.
///
/// If the scope specifier denotes a class, this will be that class.
/// If the scope specifier is empty, this will be the class whose
/// member-specification we are currently within. Otherwise, there
/// is no such class.
CXXRecordDecl *Sema::getCurrentClass(Scope *, const CXXScopeSpec *SS) {
  assert(getLangOpts().CPlusPlus && "No class names in C!");
 
  if (SS && SS->isInvalid())
    return nullptr;
 
  if (SS && SS->isNotEmpty()) {
    DeclContext *DC = computeDeclContext(*SS, true);
    return dyn_cast_or_null<CXXRecordDecl>(DC);
  }
 
  return dyn_cast_or_null<CXXRecordDecl>(CurContext);
}
 
/// isCurrentClassName - Determine whether the identifier II is the
/// name of the class type currently being defined. In the case of
/// nested classes, this will only return true if II is the name of
/// the innermost class.
bool Sema::isCurrentClassName(const IdentifierInfo &II, Scope *S,
                              const CXXScopeSpec *SS) {
  CXXRecordDecl *CurDecl = getCurrentClass(S, SS);
  return CurDecl && &II == CurDecl->getIdentifier();
}
 
/// Determine whether the identifier II is a typo for the name of
/// the class type currently being defined. If so, update it to the identifier
/// that should have been used.
bool Sema::isCurrentClassNameTypo(IdentifierInfo *&II, const CXXScopeSpec *SS) {
  assert(getLangOpts().CPlusPlus && "No class names in C!");
 
  if (!getLangOpts().SpellChecking)
    return false;
 
  CXXRecordDecl *CurDecl;
  if (SS && SS->isSet() && !SS->isInvalid()) {
    DeclContext *DC = computeDeclContext(*SS, true);
    CurDecl = dyn_cast_or_null<CXXRecordDecl>(DC);
  } else
    CurDecl = dyn_cast_or_null<CXXRecordDecl>(CurContext);
 
  if (CurDecl && CurDecl->getIdentifier() && II != CurDecl->getIdentifier() &&
      3 * II->getName().edit_distance(CurDecl->getIdentifier()->getName())
          < II->getLength()) {
    II = CurDecl->getIdentifier();
    return true;
  }
 
  return false;
}
 
/// Determine whether the given class is a base class of the given
/// class, including looking at dependent bases.
static bool findCircularInheritance(const CXXRecordDecl *Class,
                                    const CXXRecordDecl *Current) {
  SmallVector<const CXXRecordDecl*, 8> Queue;
 
  Class = Class->getCanonicalDecl();
  while (true) {
    for (const auto &I : Current->bases()) {
      CXXRecordDecl *Base = I.getType()->getAsCXXRecordDecl();
      if (!Base)
        continue;
 
      Base = Base->getDefinition();
      if (!Base)
        continue;
 
      if (Base->getCanonicalDecl() == Class)
        return true;
 
      Queue.push_back(Base);
    }
 
    if (Queue.empty())
      return false;
 
    Current = Queue.pop_back_val();
  }
 
  return false;
}
 
/// Check the validity of a C++ base class specifier.
///
/// \returns a new CXXBaseSpecifier if well-formed, emits diagnostics
/// and returns NULL otherwise.
CXXBaseSpecifier *
Sema::CheckBaseSpecifier(CXXRecordDecl *Class,
                         SourceRange SpecifierRange,
                         bool Virtual, AccessSpecifier Access,
                         TypeSourceInfo *TInfo,
                         SourceLocation EllipsisLoc) {
  // In HLSL, unspecified class access is public rather than private.
  if (getLangOpts().HLSL && Class->getTagKind() == TTK_Class &&
      Access == AS_none)
    Access = AS_public;
 
  QualType BaseType = TInfo->getType();
  if (BaseType->containsErrors()) {
    // Already emitted a diagnostic when parsing the error type.
    return nullptr;
  }
  // C++ [class.union]p1:
  //   A union shall not have base classes.
  if (Class->isUnion()) {
    Diag(Class->getLocation(), diag::err_base_clause_on_union)
      << SpecifierRange;
    return nullptr;
  }
 
  if (EllipsisLoc.isValid() &&
      !TInfo->getType()->containsUnexpandedParameterPack()) {
    Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
      << TInfo->getTypeLoc().getSourceRange();
    EllipsisLoc = SourceLocation();
  }
 
  SourceLocation BaseLoc = TInfo->getTypeLoc().getBeginLoc();
 
  if (BaseType->isDependentType()) {
    // Make sure that we don't have circular inheritance among our dependent
    // bases. For non-dependent bases, the check for completeness below handles
    // this.
    if (CXXRecordDecl *BaseDecl = BaseType->getAsCXXRecordDecl()) {
      if (BaseDecl->getCanonicalDecl() == Class->getCanonicalDecl() ||
          ((BaseDecl = BaseDecl->getDefinition()) &&
           findCircularInheritance(Class, BaseDecl))) {
        Diag(BaseLoc, diag::err_circular_inheritance)
          << BaseType << Context.getTypeDeclType(Class);
 
        if (BaseDecl->getCanonicalDecl() != Class->getCanonicalDecl())
          Diag(BaseDecl->getLocation(), diag::note_previous_decl)
            << BaseType;
 
        return nullptr;
      }
    }
 
    // Make sure that we don't make an ill-formed AST where the type of the
    // Class is non-dependent and its attached base class specifier is an
    // dependent type, which violates invariants in many clang code paths (e.g.
    // constexpr evaluator). If this case happens (in errory-recovery mode), we
    // explicitly mark the Class decl invalid. The diagnostic was already
    // emitted.
    if (!Class->getTypeForDecl()->isDependentType())
      Class->setInvalidDecl();
    return new (Context) CXXBaseSpecifier(SpecifierRange, Virtual,
                                          Class->getTagKind() == TTK_Class,
                                          Access, TInfo, EllipsisLoc);
  }
 
  // Base specifiers must be record types.
  if (!BaseType->isRecordType()) {
    Diag(BaseLoc, diag::err_base_must_be_class) << SpecifierRange;
    return nullptr;
  }
 
  // C++ [class.union]p1:
  //   A union shall not be used as a base class.
  if (BaseType->isUnionType()) {
    Diag(BaseLoc, diag::err_union_as_base_class) << SpecifierRange;
    return nullptr;
  }
 
  // For the MS ABI, propagate DLL attributes to base class templates.
  if (Context.getTargetInfo().getCXXABI().isMicrosoft() ||
      Context.getTargetInfo().getTriple().isPS()) {
    if (Attr *ClassAttr = getDLLAttr(Class)) {
      if (auto *BaseTemplate = dyn_cast_or_null<ClassTemplateSpecializationDecl>(
              BaseType->getAsCXXRecordDecl())) {
        propagateDLLAttrToBaseClassTemplate(Class, ClassAttr, BaseTemplate,
                                            BaseLoc);
      }
    }
  }
 
  // C++ [class.derived]p2:
  //   The class-name in a base-specifier shall not be an incompletely
  //   defined class.
  if (RequireCompleteType(BaseLoc, BaseType,
                          diag::err_incomplete_base_class, SpecifierRange)) {
    Class->setInvalidDecl();
    return nullptr;
  }
 
  // If the base class is polymorphic or isn't empty, the new one is/isn't, too.
  RecordDecl *BaseDecl = BaseType->castAs<RecordType>()->getDecl();
  assert(BaseDecl && "Record type has no declaration");
  BaseDecl = BaseDecl->getDefinition();
  assert(BaseDecl && "Base type is not incomplete, but has no definition");
  CXXRecordDecl *CXXBaseDecl = cast<CXXRecordDecl>(BaseDecl);
  assert(CXXBaseDecl && "Base type is not a C++ type");
 
  // Microsoft docs say:
  // "If a base-class has a code_seg attribute, derived classes must have the
  // same attribute."
  const auto *BaseCSA = CXXBaseDecl->getAttr<CodeSegAttr>();
  const auto *DerivedCSA = Class->getAttr<CodeSegAttr>();
  if ((DerivedCSA || BaseCSA) &&
      (!BaseCSA || !DerivedCSA || BaseCSA->getName() != DerivedCSA->getName())) {
    Diag(Class->getLocation(), diag::err_mismatched_code_seg_base);
    Diag(CXXBaseDecl->getLocation(), diag::note_base_class_specified_here)
      << CXXBaseDecl;
    return nullptr;
  }
 
  // A class which contains a flexible array member is not suitable for use as a
  // base class:
  //   - If the layout determines that a base comes before another base,
  //     the flexible array member would index into the subsequent base.
  //   - If the layout determines that base comes before the derived class,
  //     the flexible array member would index into the derived class.
  if (CXXBaseDecl->hasFlexibleArrayMember()) {
    Diag(BaseLoc, diag::err_base_class_has_flexible_array_member)
      << CXXBaseDecl->getDeclName();
    return nullptr;
  }
 
  // C++ [class]p3:
  //   If a class is marked final and it appears as a base-type-specifier in
  //   base-clause, the program is ill-formed.
  if (FinalAttr *FA = CXXBaseDecl->getAttr<FinalAttr>()) {
    Diag(BaseLoc, diag::err_class_marked_final_used_as_base)
      << CXXBaseDecl->getDeclName()
      << FA->isSpelledAsSealed();
    Diag(CXXBaseDecl->getLocation(), diag::note_entity_declared_at)
        << CXXBaseDecl->getDeclName() << FA->getRange();
    return nullptr;
  }
 
  if (BaseDecl->isInvalidDecl())
    Class->setInvalidDecl();
 
  // Create the base specifier.
  return new (Context) CXXBaseSpecifier(SpecifierRange, Virtual,
                                        Class->getTagKind() == TTK_Class,
                                        Access, TInfo, EllipsisLoc);
}
 
/// ActOnBaseSpecifier - Parsed a base specifier. A base specifier is
/// one entry in the base class list of a class specifier, for
/// example:
///    class foo : public bar, virtual private baz {
/// 'public bar' and 'virtual private baz' are each base-specifiers.
BaseResult Sema::ActOnBaseSpecifier(Decl *classdecl, SourceRange SpecifierRange,
                                    const ParsedAttributesView &Attributes,
                                    bool Virtual, AccessSpecifier Access,
                                    ParsedType basetype, SourceLocation BaseLoc,
                                    SourceLocation EllipsisLoc) {
  if (!classdecl)
    return true;
 
  AdjustDeclIfTemplate(classdecl);
  CXXRecordDecl *Class = dyn_cast<CXXRecordDecl>(classdecl);
  if (!Class)
    return true;
 
  // We haven't yet attached the base specifiers.
  Class->setIsParsingBaseSpecifiers();
 
  // We do not support any C++11 attributes on base-specifiers yet.
  // Diagnose any attributes we see.
  for (const ParsedAttr &AL : Attributes) {
    if (AL.isInvalid() || AL.getKind() == ParsedAttr::IgnoredAttribute)
      continue;
    if (AL.getKind() == ParsedAttr::UnknownAttribute)
      Diag(AL.getLoc(), diag::warn_unknown_attribute_ignored)
          << AL << AL.getRange();
    else
      Diag(AL.getLoc(), diag::err_base_specifier_attribute)
          << AL << AL.isRegularKeywordAttribute() << AL.getRange();
  }
 
  TypeSourceInfo *TInfo = nullptr;
  GetTypeFromParser(basetype, &TInfo);
 
  if (EllipsisLoc.isInvalid() &&
      DiagnoseUnexpandedParameterPack(SpecifierRange.getBegin(), TInfo,
                                      UPPC_BaseType))
    return true;
 
  if (CXXBaseSpecifier *BaseSpec = CheckBaseSpecifier(Class, SpecifierRange,
                                                      Virtual, Access, TInfo,
                                                      EllipsisLoc))
    return BaseSpec;
  else
    Class->setInvalidDecl();
 
  return true;
}
 
/// Use small set to collect indirect bases.  As this is only used
/// locally, there's no need to abstract the small size parameter.
typedef llvm::SmallPtrSet<QualType, 4> IndirectBaseSet;
 
/// Recursively add the bases of Type.  Don't add Type itself.
static void
NoteIndirectBases(ASTContext &Context, IndirectBaseSet &Set,
                  const QualType &Type)
{
  // Even though the incoming type is a base, it might not be
  // a class -- it could be a template parm, for instance.
  if (auto Rec = Type->getAs<RecordType>()) {
    auto Decl = Rec->getAsCXXRecordDecl();
 
    // Iterate over its bases.
    for (const auto &BaseSpec : Decl->bases()) {
      QualType Base = Context.getCanonicalType(BaseSpec.getType())
        .getUnqualifiedType();
      if (Set.insert(Base).second)
        // If we've not already seen it, recurse.
        NoteIndirectBases(Context, Set, Base);
    }
  }
}
 
/// Performs the actual work of attaching the given base class
/// specifiers to a C++ class.
bool Sema::AttachBaseSpecifiers(CXXRecordDecl *Class,
                                MutableArrayRef<CXXBaseSpecifier *> Bases) {
 if (Bases.empty())
    return false;
 
  // Used to keep track of which base types we have already seen, so
  // that we can properly diagnose redundant direct base types. Note
  // that the key is always the unqualified canonical type of the base
  // class.
  std::map<QualType, CXXBaseSpecifier*, QualTypeOrdering> KnownBaseTypes;
 
  // Used to track indirect bases so we can see if a direct base is
  // ambiguous.
  IndirectBaseSet IndirectBaseTypes;
 
  // Copy non-redundant base specifiers into permanent storage.
  unsigned NumGoodBases = 0;
  bool Invalid = false;
  for (unsigned idx = 0; idx < Bases.size(); ++idx) {
    QualType NewBaseType
      = Context.getCanonicalType(Bases[idx]->getType());
    NewBaseType = NewBaseType.getLocalUnqualifiedType();
 
    CXXBaseSpecifier *&KnownBase = KnownBaseTypes[NewBaseType];
    if (KnownBase) {
      // C++ [class.mi]p3:
      //   A class shall not be specified as a direct base class of a
      //   derived class more than once.
      Diag(Bases[idx]->getBeginLoc(), diag::err_duplicate_base_class)
          << KnownBase->getType() << Bases[idx]->getSourceRange();
 
      // Delete the duplicate base class specifier; we're going to
      // overwrite its pointer later.
      Context.Deallocate(Bases[idx]);
 
      Invalid = true;
    } else {
      // Okay, add this new base class.
      KnownBase = Bases[idx];
      Bases[NumGoodBases++] = Bases[idx];
 
      if (NewBaseType->isDependentType())
        continue;
      // Note this base's direct & indirect bases, if there could be ambiguity.
      if (Bases.size() > 1)
        NoteIndirectBases(Context, IndirectBaseTypes, NewBaseType);
 
      if (const RecordType *Record = NewBaseType->getAs<RecordType>()) {
        const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl());
        if (Class->isInterface() &&
              (!RD->isInterfaceLike() ||
               KnownBase->getAccessSpecifier() != AS_public)) {
          // The Microsoft extension __interface does not permit bases that
          // are not themselves public interfaces.
          Diag(KnownBase->getBeginLoc(), diag::err_invalid_base_in_interface)
              << getRecordDiagFromTagKind(RD->getTagKind()) << RD
              << RD->getSourceRange();
          Invalid = true;
        }
        if (RD->hasAttr<WeakAttr>())
          Class->addAttr(WeakAttr::CreateImplicit(Context));
      }
    }
  }
 
  // Attach the remaining base class specifiers to the derived class.
  Class->setBases(Bases.data(), NumGoodBases);
 
  // Check that the only base classes that are duplicate are virtual.
  for (unsigned idx = 0; idx < NumGoodBases; ++idx) {
    // Check whether this direct base is inaccessible due to ambiguity.
    QualType BaseType = Bases[idx]->getType();
 
    // Skip all dependent types in templates being used as base specifiers.
    // Checks below assume that the base specifier is a CXXRecord.
    if (BaseType->isDependentType())
      continue;
 
    CanQualType CanonicalBase = Context.getCanonicalType(BaseType)
      .getUnqualifiedType();
 
    if (IndirectBaseTypes.count(CanonicalBase)) {
      CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
                         /*DetectVirtual=*/true);
      bool found
        = Class->isDerivedFrom(CanonicalBase->getAsCXXRecordDecl(), Paths);
      assert(found);
      (void)found;
 
      if (Paths.isAmbiguous(CanonicalBase))
        Diag(Bases[idx]->getBeginLoc(), diag::warn_inaccessible_base_class)
            << BaseType << getAmbiguousPathsDisplayString(Paths)
            << Bases[idx]->getSourceRange();
      else
        assert(Bases[idx]->isVirtual());
    }
 
    // Delete the base class specifier, since its data has been copied
    // into the CXXRecordDecl.
    Context.Deallocate(Bases[idx]);
  }
 
  return Invalid;
}
 
/// ActOnBaseSpecifiers - Attach the given base specifiers to the
/// class, after checking whether there are any duplicate base
/// classes.
void Sema::ActOnBaseSpecifiers(Decl *ClassDecl,
                               MutableArrayRef<CXXBaseSpecifier *> Bases) {
  if (!ClassDecl || Bases.empty())
    return;
 
  AdjustDeclIfTemplate(ClassDecl);
  AttachBaseSpecifiers(cast<CXXRecordDecl>(ClassDecl), Bases);
}
 
/// Determine whether the type \p Derived is a C++ class that is
/// derived from the type \p Base.
bool Sema::IsDerivedFrom(SourceLocation Loc, QualType Derived, QualType Base) {
  if (!getLangOpts().CPlusPlus)
    return false;
 
  CXXRecordDecl *DerivedRD = Derived->getAsCXXRecordDecl();
  if (!DerivedRD)
    return false;
 
  CXXRecordDecl *BaseRD = Base->getAsCXXRecordDecl();
  if (!BaseRD)
    return false;
 
  // If either the base or the derived type is invalid, don't try to
  // check whether one is derived from the other.
  if (BaseRD->isInvalidDecl() || DerivedRD->isInvalidDecl())
    return false;
 
  // FIXME: In a modules build, do we need the entire path to be visible for us
  // to be able to use the inheritance relationship?
  if (!isCompleteType(Loc, Derived) && !DerivedRD->isBeingDefined())
    return false;
 
  return DerivedRD->isDerivedFrom(BaseRD);
}
 
/// Determine whether the type \p Derived is a C++ class that is
/// derived from the type \p Base.
bool Sema::IsDerivedFrom(SourceLocation Loc, QualType Derived, QualType Base,
                         CXXBasePaths &Paths) {
  if (!getLangOpts().CPlusPlus)
    return false;
 
  CXXRecordDecl *DerivedRD = Derived->getAsCXXRecordDecl();
  if (!DerivedRD)
    return false;
 
  CXXRecordDecl *BaseRD = Base->getAsCXXRecordDecl();
  if (!BaseRD)
    return false;
 
  if (!isCompleteType(Loc, Derived) && !DerivedRD->isBeingDefined())
    return false;
 
  return DerivedRD->isDerivedFrom(BaseRD, Paths);
}
 
static void BuildBasePathArray(const CXXBasePath &Path,
                               CXXCastPath &BasePathArray) {
  // We first go backward and check if we have a virtual base.
  // FIXME: It would be better if CXXBasePath had the base specifier for
  // the nearest virtual base.
  unsigned Start = 0;
  for (unsigned I = Path.size(); I != 0; --I) {
    if (Path[I - 1].Base->isVirtual()) {
      Start = I - 1;
      break;
    }
  }
 
  // Now add all bases.
  for (unsigned I = Start, E = Path.size(); I != E; ++I)
    BasePathArray.push_back(const_cast<CXXBaseSpecifier*>(Path[I].Base));
}
 
 
void Sema::BuildBasePathArray(const CXXBasePaths &Paths,
                              CXXCastPath &BasePathArray) {
  assert(BasePathArray.empty() && "Base path array must be empty!");
  assert(Paths.isRecordingPaths() && "Must record paths!");
  return ::BuildBasePathArray(Paths.front(), BasePathArray);
}
/// CheckDerivedToBaseConversion - Check whether the Derived-to-Base
/// conversion (where Derived and Base are class types) is
/// well-formed, meaning that the conversion is unambiguous (and
/// that all of the base classes are accessible). Returns true
/// and emits a diagnostic if the code is ill-formed, returns false
/// otherwise. Loc is the location where this routine should point to
/// if there is an error, and Range is the source range to highlight
/// if there is an error.
///
/// If either InaccessibleBaseID or AmbiguousBaseConvID are 0, then the
/// diagnostic for the respective type of error will be suppressed, but the
/// check for ill-formed code will still be performed.
bool
Sema::CheckDerivedToBaseConversion(QualType Derived, QualType Base,
                                   unsigned InaccessibleBaseID,
                                   unsigned AmbiguousBaseConvID,
                                   SourceLocation Loc, SourceRange Range,
                                   DeclarationName Name,
                                   CXXCastPath *BasePath,
                                   bool IgnoreAccess) {
  // First, determine whether the path from Derived to Base is
  // ambiguous. This is slightly more expensive than checking whether
  // the Derived to Base conversion exists, because here we need to
  // explore multiple paths to determine if there is an ambiguity.
  CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
                     /*DetectVirtual=*/false);
  bool DerivationOkay = IsDerivedFrom(Loc, Derived, Base, Paths);
  if (!DerivationOkay)
    return true;
 
  const CXXBasePath *Path = nullptr;
  if (!Paths.isAmbiguous(Context.getCanonicalType(Base).getUnqualifiedType()))
    Path = &Paths.front();
 
  // For MSVC compatibility, check if Derived directly inherits from Base. Clang
  // warns about this hierarchy under -Winaccessible-base, but MSVC allows the
  // user to access such bases.
  if (!Path && getLangOpts().MSVCCompat) {
    for (const CXXBasePath &PossiblePath : Paths) {
      if (PossiblePath.size() == 1) {
        Path = &PossiblePath;
        if (AmbiguousBaseConvID)
          Diag(Loc, diag::ext_ms_ambiguous_direct_base)
              << Base << Derived << Range;
        break;
      }
    }
  }
 
  if (Path) {
    if (!IgnoreAccess) {
      // Check that the base class can be accessed.
      switch (
          CheckBaseClassAccess(Loc, Base, Derived, *Path, InaccessibleBaseID)) {
      case AR_inaccessible:
        return true;
      case AR_accessible:
      case AR_dependent:
      case AR_delayed:
        break;
      }
    }
 
    // Build a base path if necessary.
    if (BasePath)
      ::BuildBasePathArray(*Path, *BasePath);
    return false;
  }
 
  if (AmbiguousBaseConvID) {
    // We know that the derived-to-base conversion is ambiguous, and
    // we're going to produce a diagnostic. Perform the derived-to-base
    // search just one more time to compute all of the possible paths so
    // that we can print them out. This is more expensive than any of
    // the previous derived-to-base checks we've done, but at this point
    // performance isn't as much of an issue.
    Paths.clear();
    Paths.setRecordingPaths(true);
    bool StillOkay = IsDerivedFrom(Loc, Derived, Base, Paths);
    assert(StillOkay && "Can only be used with a derived-to-base conversion");
    (void)StillOkay;
 
    // Build up a textual representation of the ambiguous paths, e.g.,
    // D -> B -> A, that will be used to illustrate the ambiguous
    // conversions in the diagnostic. We only print one of the paths
    // to each base class subobject.
    std::string PathDisplayStr = getAmbiguousPathsDisplayString(Paths);
 
    Diag(Loc, AmbiguousBaseConvID)
    << Derived << Base << PathDisplayStr << Range << Name;
  }
  return true;
}
 
bool
Sema::CheckDerivedToBaseConversion(QualType Derived, QualType Base,
                                   SourceLocation Loc, SourceRange Range,
                                   CXXCastPath *BasePath,
                                   bool IgnoreAccess) {
  return CheckDerivedToBaseConversion(
      Derived, Base, diag::err_upcast_to_inaccessible_base,
      diag::err_ambiguous_derived_to_base_conv, Loc, Range, DeclarationName(),
      BasePath, IgnoreAccess);
}
 
 
/// Builds a string representing ambiguous paths from a
/// specific derived class to different subobjects of the same base
/// class.
///
/// This function builds a string that can be used in error messages
/// to show the different paths that one can take through the
/// inheritance hierarchy to go from the derived class to different
/// subobjects of a base class. The result looks something like this:
/// @code
/// struct D -> struct B -> struct A
/// struct D -> struct C -> struct A
/// @endcode
std::string Sema::getAmbiguousPathsDisplayString(CXXBasePaths &Paths) {
  std::string PathDisplayStr;
  std::set<unsigned> DisplayedPaths;
  for (CXXBasePaths::paths_iterator Path = Paths.begin();
       Path != Paths.end(); ++Path) {
    if (DisplayedPaths.insert(Path->back().SubobjectNumber).second) {
      // We haven't displayed a path to this particular base
      // class subobject yet.
      PathDisplayStr += "\n    ";
      PathDisplayStr += Context.getTypeDeclType(Paths.getOrigin()).getAsString();
      for (CXXBasePath::const_iterator Element = Path->begin();
           Element != Path->end(); ++Element)
        PathDisplayStr += " -> " + Element->Base->getType().getAsString();
    }
  }
 
  return PathDisplayStr;
}
 
//===----------------------------------------------------------------------===//
// C++ class member Handling
//===----------------------------------------------------------------------===//
 
/// ActOnAccessSpecifier - Parsed an access specifier followed by a colon.
bool Sema::ActOnAccessSpecifier(AccessSpecifier Access, SourceLocation ASLoc,
                                SourceLocation ColonLoc,
                                const ParsedAttributesView &Attrs) {
  assert(Access != AS_none && "Invalid kind for syntactic access specifier!");
  AccessSpecDecl *ASDecl = AccessSpecDecl::Create(Context, Access, CurContext,
                                                  ASLoc, ColonLoc);
  CurContext->addHiddenDecl(ASDecl);
  return ProcessAccessDeclAttributeList(ASDecl, Attrs);
}
 
/// CheckOverrideControl - Check C++11 override control semantics.
void Sema::CheckOverrideControl(NamedDecl *D) {
  if (D->isInvalidDecl())
    return;
 
  // We only care about "override" and "final" declarations.
  if (!D->hasAttr<OverrideAttr>() && !D->hasAttr<FinalAttr>())
    return;
 
  CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(D);
 
  // We can't check dependent instance methods.
  if (MD && MD->isInstance() &&
      (MD->getParent()->hasAnyDependentBases() ||
       MD->getType()->isDependentType()))
    return;
 
  if (MD && !MD->isVirtual()) {
    // If we have a non-virtual method, check if it hides a virtual method.
    // (In that case, it's most likely the method has the wrong type.)
    SmallVector<CXXMethodDecl *, 8> OverloadedMethods;
    FindHiddenVirtualMethods(MD, OverloadedMethods);
 
    if (!OverloadedMethods.empty()) {
      if (OverrideAttr *OA = D->getAttr<OverrideAttr>()) {
        Diag(OA->getLocation(),
             diag::override_keyword_hides_virtual_member_function)
          << "override" << (OverloadedMethods.size() > 1);
      } else if (FinalAttr *FA = D->getAttr<FinalAttr>()) {
        Diag(FA->getLocation(),
             diag::override_keyword_hides_virtual_member_function)
          << (FA->isSpelledAsSealed() ? "sealed" : "final")
          << (OverloadedMethods.size() > 1);
      }
      NoteHiddenVirtualMethods(MD, OverloadedMethods);
      MD->setInvalidDecl();
      return;
    }
    // Fall through into the general case diagnostic.
    // FIXME: We might want to attempt typo correction here.
  }
 
  if (!MD || !MD->isVirtual()) {
    if (OverrideAttr *OA = D->getAttr<OverrideAttr>()) {
      Diag(OA->getLocation(),
           diag::override_keyword_only_allowed_on_virtual_member_functions)
        << "override" << FixItHint::CreateRemoval(OA->getLocation());
      D->dropAttr<OverrideAttr>();
    }
    if (FinalAttr *FA = D->getAttr<FinalAttr>()) {
      Diag(FA->getLocation(),
           diag::override_keyword_only_allowed_on_virtual_member_functions)
        << (FA->isSpelledAsSealed() ? "sealed" : "final")
        << FixItHint::CreateRemoval(FA->getLocation());
      D->dropAttr<FinalAttr>();
    }
    return;
  }
 
  // C++11 [class.virtual]p5:
  //   If a function is marked with the virt-specifier override and
  //   does not override a member function of a base class, the program is
  //   ill-formed.
  bool HasOverriddenMethods = MD->size_overridden_methods() != 0;
  if (MD->hasAttr<OverrideAttr>() && !HasOverriddenMethods)
    Diag(MD->getLocation(), diag::err_function_marked_override_not_overriding)
      << MD->getDeclName();
}
 
void Sema::DiagnoseAbsenceOfOverrideControl(NamedDecl *D, bool Inconsistent) {
  if (D->isInvalidDecl() || D->hasAttr<OverrideAttr>())
    return;
  CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(D);
  if (!MD || MD->isImplicit() || MD->hasAttr<FinalAttr>())
    return;
 
  SourceLocation Loc = MD->getLocation();
  SourceLocation SpellingLoc = Loc;
  if (getSourceManager().isMacroArgExpansion(Loc))
    SpellingLoc = getSourceManager().getImmediateExpansionRange(Loc).getBegin();
  SpellingLoc = getSourceManager().getSpellingLoc(SpellingLoc);
  if (SpellingLoc.isValid() && getSourceManager().isInSystemHeader(SpellingLoc))
      return;
 
  if (MD->size_overridden_methods() > 0) {
    auto EmitDiag = [&](unsigned DiagInconsistent, unsigned DiagSuggest) {
      unsigned DiagID =
          Inconsistent && !Diags.isIgnored(DiagInconsistent, MD->getLocation())
              ? DiagInconsistent
              : DiagSuggest;
      Diag(MD->getLocation(), DiagID) << MD->getDeclName();
      const CXXMethodDecl *OMD = *MD->begin_overridden_methods();
      Diag(OMD->getLocation(), diag::note_overridden_virtual_function);
    };
    if (isa<CXXDestructorDecl>(MD))
      EmitDiag(
          diag::warn_inconsistent_destructor_marked_not_override_overriding,
          diag::warn_suggest_destructor_marked_not_override_overriding);
    else
      EmitDiag(diag::warn_inconsistent_function_marked_not_override_overriding,
               diag::warn_suggest_function_marked_not_override_overriding);
  }
}
 
/// CheckIfOverriddenFunctionIsMarkedFinal - Checks whether a virtual member
/// function overrides a virtual member function marked 'final', according to
/// C++11 [class.virtual]p4.
bool Sema::CheckIfOverriddenFunctionIsMarkedFinal(const CXXMethodDecl *New,
                                                  const CXXMethodDecl *Old) {
  FinalAttr *FA = Old->getAttr<FinalAttr>();
  if (!FA)
    return false;
 
  Diag(New->getLocation(), diag::err_final_function_overridden)
    << New->getDeclName()
    << FA->isSpelledAsSealed();
  Diag(Old->getLocation(), diag::note_overridden_virtual_function);
  return true;
}
 
static bool InitializationHasSideEffects(const FieldDecl &FD) {
  const Type *T = FD.getType()->getBaseElementTypeUnsafe();
  // FIXME: Destruction of ObjC lifetime types has side-effects.
  if (const CXXRecordDecl *RD = T->getAsCXXRecordDecl())
    return !RD->isCompleteDefinition() ||
           !RD->hasTrivialDefaultConstructor() ||
           !RD->hasTrivialDestructor();
  return false;
}
 
// Check if there is a field shadowing.
void Sema::CheckShadowInheritedFields(const SourceLocation &Loc,
                                      DeclarationName FieldName,
                                      const CXXRecordDecl *RD,
                                      bool DeclIsField) {
  if (Diags.isIgnored(diag::warn_shadow_field, Loc))
    return;
 
  // To record a shadowed field in a base
  std::map<CXXRecordDecl*, NamedDecl*> Bases;
  auto FieldShadowed = [&](const CXXBaseSpecifier *Specifier,
                           CXXBasePath &Path) {
    const auto Base = Specifier->getType()->getAsCXXRecordDecl();
    // Record an ambiguous path directly
    if (Bases.find(Base) != Bases.end())
      return true;
    for (const auto Field : Base->lookup(FieldName)) {
      if ((isa<FieldDecl>(Field) || isa<IndirectFieldDecl>(Field)) &&
          Field->getAccess() != AS_private) {
        assert(Field->getAccess() != AS_none);
        assert(Bases.find(Base) == Bases.end());
        Bases[Base] = Field;
        return true;
      }
    }
    return false;
  };
 
  CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
                     /*DetectVirtual=*/true);
  if (!RD->lookupInBases(FieldShadowed, Paths))
    return;
 
  for (const auto &P : Paths) {
    auto Base = P.back().Base->getType()->getAsCXXRecordDecl();
    auto It = Bases.find(Base);
    // Skip duplicated bases
    if (It == Bases.end())
      continue;
    auto BaseField = It->second;
    assert(BaseField->getAccess() != AS_private);
    if (AS_none !=
        CXXRecordDecl::MergeAccess(P.Access, BaseField->getAccess())) {
      Diag(Loc, diag::warn_shadow_field)
        << FieldName << RD << Base << DeclIsField;
      Diag(BaseField->getLocation(), diag::note_shadow_field);
      Bases.erase(It);
    }
  }
}
 
/// ActOnCXXMemberDeclarator - This is invoked when a C++ class member
/// declarator is parsed. 'AS' is the access specifier, 'BW' specifies the
/// bitfield width if there is one, 'InitExpr' specifies the initializer if
/// one has been parsed, and 'InitStyle' is set if an in-class initializer is
/// present (but parsing it has been deferred).
NamedDecl *
Sema::ActOnCXXMemberDeclarator(Scope *S, AccessSpecifier AS, Declarator &D,
                               MultiTemplateParamsArg TemplateParameterLists,
                               Expr *BW, const VirtSpecifiers &VS,
                               InClassInitStyle InitStyle) {
  const DeclSpec &DS = D.getDeclSpec();
  DeclarationNameInfo NameInfo = GetNameForDeclarator(D);
  DeclarationName Name = NameInfo.getName();
  SourceLocation Loc = NameInfo.getLoc();
 
  // For anonymous bitfields, the location should point to the type.
  if (Loc.isInvalid())
    Loc = D.getBeginLoc();
 
  Expr *BitWidth = static_cast<Expr*>(BW);
 
  assert(isa<CXXRecordDecl>(CurContext));
  assert(!DS.isFriendSpecified());
 
  bool isFunc = D.isDeclarationOfFunction();
  const ParsedAttr *MSPropertyAttr =
      D.getDeclSpec().getAttributes().getMSPropertyAttr();
 
  if (cast<CXXRecordDecl>(CurContext)->isInterface()) {
    // The Microsoft extension __interface only permits public member functions
    // and prohibits constructors, destructors, operators, non-public member
    // functions, static methods and data members.
    unsigned InvalidDecl;
    bool ShowDeclName = true;
    if (!isFunc &&
        (DS.getStorageClassSpec() == DeclSpec::SCS_typedef || MSPropertyAttr))
      InvalidDecl = 0;
    else if (!isFunc)
      InvalidDecl = 1;
    else if (AS != AS_public)
      InvalidDecl = 2;
    else if (DS.getStorageClassSpec() == DeclSpec::SCS_static)
      InvalidDecl = 3;
    else switch (Name.getNameKind()) {
      case DeclarationName::CXXConstructorName:
        InvalidDecl = 4;
        ShowDeclName = false;
        break;
 
      case DeclarationName::CXXDestructorName:
        InvalidDecl = 5;
        ShowDeclName = false;
        break;
 
      case DeclarationName::CXXOperatorName:
      case DeclarationName::CXXConversionFunctionName:
        InvalidDecl = 6;
        break;
 
      default:
        InvalidDecl = 0;
        break;
    }
 
    if (InvalidDecl) {
      if (ShowDeclName)
        Diag(Loc, diag::err_invalid_member_in_interface)
          << (InvalidDecl-1) << Name;
      else
        Diag(Loc, diag::err_invalid_member_in_interface)
          << (InvalidDecl-1) << "";
      return nullptr;
    }
  }
 
  // C++ 9.2p6: A member shall not be declared to have automatic storage
  // duration (auto, register) or with the extern storage-class-specifier.
  // C++ 7.1.1p8: The mutable specifier can be applied only to names of class
  // data members and cannot be applied to names declared const or static,
  // and cannot be applied to reference members.
  switch (DS.getStorageClassSpec()) {
  case DeclSpec::SCS_unspecified:
  case DeclSpec::SCS_typedef:
  case DeclSpec::SCS_static:
    break;
  case DeclSpec::SCS_mutable:
    if (isFunc) {
      Diag(DS.getStorageClassSpecLoc(), diag::err_mutable_function);
 
      // FIXME: It would be nicer if the keyword was ignored only for this
      // declarator. Otherwise we could get follow-up errors.
      D.getMutableDeclSpec().ClearStorageClassSpecs();
    }
    break;
  default:
    Diag(DS.getStorageClassSpecLoc(),
         diag::err_storageclass_invalid_for_member);
    D.getMutableDeclSpec().ClearStorageClassSpecs();
    break;
  }
 
  bool isInstField = ((DS.getStorageClassSpec() == DeclSpec::SCS_unspecified ||
                       DS.getStorageClassSpec() == DeclSpec::SCS_mutable) &&
                      !isFunc);
 
  if (DS.hasConstexprSpecifier() && isInstField) {
    SemaDiagnosticBuilder B =
        Diag(DS.getConstexprSpecLoc(), diag::err_invalid_constexpr_member);
    SourceLocation ConstexprLoc = DS.getConstexprSpecLoc();
    if (InitStyle == ICIS_NoInit) {
      B << 0 << 0;
      if (D.getDeclSpec().getTypeQualifiers() & DeclSpec::TQ_const)
        B << FixItHint::CreateRemoval(ConstexprLoc);
      else {
        B << FixItHint::CreateReplacement(ConstexprLoc, "const");
        D.getMutableDeclSpec().ClearConstexprSpec();
        const char *PrevSpec;
        unsigned DiagID;
        bool Failed = D.getMutableDeclSpec().SetTypeQual(
            DeclSpec::TQ_const, ConstexprLoc, PrevSpec, DiagID, getLangOpts());
        (void)Failed;
        assert(!Failed && "Making a constexpr member const shouldn't fail");
      }
    } else {
      B << 1;
      const char *PrevSpec;
      unsigned DiagID;
      if (D.getMutableDeclSpec().SetStorageClassSpec(
          *this, DeclSpec::SCS_static, ConstexprLoc, PrevSpec, DiagID,
          Context.getPrintingPolicy())) {
        assert(DS.getStorageClassSpec() == DeclSpec::SCS_mutable &&
               "This is the only DeclSpec that should fail to be applied");
        B << 1;
      } else {
        B << 0 << FixItHint::CreateInsertion(ConstexprLoc, "static ");
        isInstField = false;
      }
    }
  }
 
  NamedDecl *Member;
  if (isInstField) {
    CXXScopeSpec &SS = D.getCXXScopeSpec();
 
    // Data members must have identifiers for names.
    if (!Name.isIdentifier()) {
      Diag(Loc, diag::err_bad_variable_name)
        << Name;
      return nullptr;
    }
 
    IdentifierInfo *II = Name.getAsIdentifierInfo();
 
    // Member field could not be with "template" keyword.
    // So TemplateParameterLists should be empty in this case.
    if (TemplateParameterLists.size()) {
      TemplateParameterList* TemplateParams = TemplateParameterLists[0];
      if (TemplateParams->size()) {
        // There is no such thing as a member field template.
        Diag(D.getIdentifierLoc(), diag::err_template_member)
            << II
            << SourceRange(TemplateParams->getTemplateLoc(),
                TemplateParams->getRAngleLoc());
      } else {
        // There is an extraneous 'template<>' for this member.
        Diag(TemplateParams->getTemplateLoc(),
            diag::err_template_member_noparams)
            << II
            << SourceRange(TemplateParams->getTemplateLoc(),
                TemplateParams->getRAngleLoc());
      }
      return nullptr;
    }
 
    if (D.getName().getKind() == UnqualifiedIdKind::IK_TemplateId) {
      Diag(D.getIdentifierLoc(), diag::err_member_with_template_arguments)
          << II
          << SourceRange(D.getName().TemplateId->LAngleLoc,
                         D.getName().TemplateId->RAngleLoc)
          << D.getName().TemplateId->LAngleLoc;
      D.SetIdentifier(II, Loc);
    }
 
    if (SS.isSet() && !SS.isInvalid()) {
      // The user provided a superfluous scope specifier inside a class
      // definition:
      //
      // class X {
      //   int X::member;
      // };
      if (DeclContext *DC = computeDeclContext(SS, false))
        diagnoseQualifiedDeclaration(SS, DC, Name, D.getIdentifierLoc(),
                                     D.getName().getKind() ==
                                         UnqualifiedIdKind::IK_TemplateId);
      else
        Diag(D.getIdentifierLoc(), diag::err_member_qualification)
          << Name << SS.getRange();
 
      SS.clear();
    }
 
    if (MSPropertyAttr) {
      Member = HandleMSProperty(S, cast<CXXRecordDecl>(CurContext), Loc, D,
                                BitWidth, InitStyle, AS, *MSPropertyAttr);
      if (!Member)
        return nullptr;
      isInstField = false;
    } else {
      Member = HandleField(S, cast<CXXRecordDecl>(CurContext), Loc, D,
                                BitWidth, InitStyle, AS);
      if (!Member)
        return nullptr;
    }
 
    CheckShadowInheritedFields(Loc, Name, cast<CXXRecordDecl>(CurContext));
  } else {
    Member = HandleDeclarator(S, D, TemplateParameterLists);
    if (!Member)
      return nullptr;
 
    // Non-instance-fields can't have a bitfield.
    if (BitWidth) {
      if (Member->isInvalidDecl()) {
        // don't emit another diagnostic.
      } else if (isa<VarDecl>(Member) || isa<VarTemplateDecl>(Member)) {
        // C++ 9.6p3: A bit-field shall not be a static member.
        // "static member 'A' cannot be a bit-field"
        Diag(Loc, diag::err_static_not_bitfield)
          << Name << BitWidth->getSourceRange();
      } else if (isa<TypedefDecl>(Member)) {
        // "typedef member 'x' cannot be a bit-field"
        Diag(Loc, diag::err_typedef_not_bitfield)
          << Name << BitWidth->getSourceRange();
      } else {
        // A function typedef ("typedef int f(); f a;").
        // C++ 9.6p3: A bit-field shall have integral or enumeration type.
        Diag(Loc, diag::err_not_integral_type_bitfield)
          << Name << cast<ValueDecl>(Member)->getType()
          << BitWidth->getSourceRange();
      }
 
      BitWidth = nullptr;
      Member->setInvalidDecl();
    }
 
    NamedDecl *NonTemplateMember = Member;
    if (FunctionTemplateDecl *FunTmpl = dyn_cast<FunctionTemplateDecl>(Member))
      NonTemplateMember = FunTmpl->getTemplatedDecl();
    else if (VarTemplateDecl *VarTmpl = dyn_cast<VarTemplateDecl>(Member))
      NonTemplateMember = VarTmpl->getTemplatedDecl();
 
    Member->setAccess(AS);
 
    // If we have declared a member function template or static data member
    // template, set the access of the templated declaration as well.
    if (NonTemplateMember != Member)
      NonTemplateMember->setAccess(AS);
 
    // C++ [temp.deduct.guide]p3:
    //   A deduction guide [...] for a member class template [shall be
    //   declared] with the same access [as the template].
    if (auto *DG = dyn_cast<CXXDeductionGuideDecl>(NonTemplateMember)) {
      auto *TD = DG->getDeducedTemplate();
      // Access specifiers are only meaningful if both the template and the
      // deduction guide are from the same scope.
      if (AS != TD->getAccess() &&
          TD->getDeclContext()->getRedeclContext()->Equals(
              DG->getDeclContext()->getRedeclContext())) {
        Diag(DG->getBeginLoc(), diag::err_deduction_guide_wrong_access);
        Diag(TD->getBeginLoc(), diag::note_deduction_guide_template_access)
            << TD->getAccess();
        const AccessSpecDecl *LastAccessSpec = nullptr;
        for (const auto *D : cast<CXXRecordDecl>(CurContext)->decls()) {
          if (const auto *AccessSpec = dyn_cast<AccessSpecDecl>(D))
            LastAccessSpec = AccessSpec;
        }
        assert(LastAccessSpec && "differing access with no access specifier");
        Diag(LastAccessSpec->getBeginLoc(), diag::note_deduction_guide_access)
            << AS;
      }
    }
  }
 
  if (VS.isOverrideSpecified())
    Member->addAttr(OverrideAttr::Create(Context, VS.getOverrideLoc()));
  if (VS.isFinalSpecified())
    Member->addAttr(FinalAttr::Create(Context, VS.getFinalLoc(),
                                      VS.isFinalSpelledSealed()
                                          ? FinalAttr::Keyword_sealed
                                          : FinalAttr::Keyword_final));
 
  if (VS.getLastLocation().isValid()) {
    // Update the end location of a method that has a virt-specifiers.
    if (CXXMethodDecl *MD = dyn_cast_or_null<CXXMethodDecl>(Member))
      MD->setRangeEnd(VS.getLastLocation());
  }
 
  CheckOverrideControl(Member);
 
  assert((Name || isInstField) && "No identifier for non-field ?");
 
  if (isInstField) {
    FieldDecl *FD = cast<FieldDecl>(Member);
    FieldCollector->Add(FD);
 
    if (!Diags.isIgnored(diag::warn_unused_private_field, FD->getLocation())) {
      // Remember all explicit private FieldDecls that have a name, no side
      // effects and are not part of a dependent type declaration.
 
      auto DeclHasUnusedAttr = [](const QualType &T) {
        if (const TagDecl *TD = T->getAsTagDecl())
          return TD->hasAttr<UnusedAttr>();
        if (const TypedefType *TDT = T->getAs<TypedefType>())
          return TDT->getDecl()->hasAttr<UnusedAttr>();
        return false;
      };
 
      if (!FD->isImplicit() && FD->getDeclName() &&
          FD->getAccess() == AS_private &&
          !FD->hasAttr<UnusedAttr>() &&
          !FD->getParent()->isDependentContext() &&
          !DeclHasUnusedAttr(FD->getType()) &&
          !InitializationHasSideEffects(*FD))
        UnusedPrivateFields.insert(FD);
    }
  }
 
  return Member;
}
 
namespace {
  class UninitializedFieldVisitor
      : public EvaluatedExprVisitor<UninitializedFieldVisitor> {
    Sema &S;
    // List of Decls to generate a warning on.  Also remove Decls that become
    // initialized.
    llvm::SmallPtrSetImpl<ValueDecl*> &Decls;
    // List of base classes of the record.  Classes are removed after their
    // initializers.
    llvm::SmallPtrSetImpl<QualType> &BaseClasses;
    // Vector of decls to be removed from the Decl set prior to visiting the
    // nodes.  These Decls may have been initialized in the prior initializer.
    llvm::SmallVector<ValueDecl*, 4> DeclsToRemove;
    // If non-null, add a note to the warning pointing back to the constructor.
    const CXXConstructorDecl *Constructor;
    // Variables to hold state when processing an initializer list.  When
    // InitList is true, special case initialization of FieldDecls matching
    // InitListFieldDecl.
    bool InitList;
    FieldDecl *InitListFieldDecl;
    llvm::SmallVector<unsigned, 4> InitFieldIndex;
 
  public:
    typedef EvaluatedExprVisitor<UninitializedFieldVisitor> Inherited;
    UninitializedFieldVisitor(Sema &S,
                              llvm::SmallPtrSetImpl<ValueDecl*> &Decls,
                              llvm::SmallPtrSetImpl<QualType> &BaseClasses)
      : Inherited(S.Context), S(S), Decls(Decls), BaseClasses(BaseClasses),
        Constructor(nullptr), InitList(false), InitListFieldDecl(nullptr) {}
 
    // Returns true if the use of ME is not an uninitialized use.
    bool IsInitListMemberExprInitialized(MemberExpr *ME,
                                         bool CheckReferenceOnly) {
      llvm::SmallVector<FieldDecl*, 4> Fields;
      bool ReferenceField = false;
      while (ME) {
        FieldDecl *FD = dyn_cast<FieldDecl>(ME->getMemberDecl());
        if (!FD)
          return false;
        Fields.push_back(FD);
        if (FD->getType()->isReferenceType())
          ReferenceField = true;
        ME = dyn_cast<MemberExpr>(ME->getBase()->IgnoreParenImpCasts());
      }
 
      // Binding a reference to an uninitialized field is not an
      // uninitialized use.
      if (CheckReferenceOnly && !ReferenceField)
        return true;
 
      llvm::SmallVector<unsigned, 4> UsedFieldIndex;
      // Discard the first field since it is the field decl that is being
      // initialized.
      for (const FieldDecl *FD : llvm::drop_begin(llvm::reverse(Fields)))
        UsedFieldIndex.push_back(FD->getFieldIndex());
 
      for (auto UsedIter = UsedFieldIndex.begin(),
                UsedEnd = UsedFieldIndex.end(),
                OrigIter = InitFieldIndex.begin(),
                OrigEnd = InitFieldIndex.end();
           UsedIter != UsedEnd && OrigIter != OrigEnd; ++UsedIter, ++OrigIter) {
        if (*UsedIter < *OrigIter)
          return true;
        if (*UsedIter > *OrigIter)
          break;
      }
 
      return false;
    }
 
    void HandleMemberExpr(MemberExpr *ME, bool CheckReferenceOnly,
                          bool AddressOf) {
      if (isa<EnumConstantDecl>(ME->getMemberDecl()))
        return;
 
      // FieldME is the inner-most MemberExpr that is not an anonymous struct
      // or union.
      MemberExpr *FieldME = ME;
 
      bool AllPODFields = FieldME->getType().isPODType(S.Context);
 
      Expr *Base = ME;
      while (MemberExpr *SubME =
                 dyn_cast<MemberExpr>(Base->IgnoreParenImpCasts())) {
 
        if (isa<VarDecl>(SubME->getMemberDecl()))
          return;
 
        if (FieldDecl *FD = dyn_cast<FieldDecl>(SubME->getMemberDecl()))
          if (!FD->isAnonymousStructOrUnion())
            FieldME = SubME;
 
        if (!FieldME->getType().isPODType(S.Context))
          AllPODFields = false;
 
        Base = SubME->getBase();
      }
 
      if (!isa<CXXThisExpr>(Base->IgnoreParenImpCasts())) {
        Visit(Base);
        return;
      }
 
      if (AddressOf && AllPODFields)
        return;
 
      ValueDecl* FoundVD = FieldME->getMemberDecl();
 
      if (ImplicitCastExpr *BaseCast = dyn_cast<ImplicitCastExpr>(Base)) {
        while (isa<ImplicitCastExpr>(BaseCast->getSubExpr())) {
          BaseCast = cast<ImplicitCastExpr>(BaseCast->getSubExpr());
        }
 
        if (BaseCast->getCastKind() == CK_UncheckedDerivedToBase) {
          QualType T = BaseCast->getType();
          if (T->isPointerType() &&
              BaseClasses.count(T->getPointeeType())) {
            S.Diag(FieldME->getExprLoc(), diag::warn_base_class_is_uninit)
                << T->getPointeeType() << FoundVD;
          }
        }
      }
 
      if (!Decls.count(FoundVD))
        return;
 
      const bool IsReference = FoundVD->getType()->isReferenceType();
 
      if (InitList && !AddressOf && FoundVD == InitListFieldDecl) {
        // Special checking for initializer lists.
        if (IsInitListMemberExprInitialized(ME, CheckReferenceOnly)) {
          return;
        }
      } else {
        // Prevent double warnings on use of unbounded references.
        if (CheckReferenceOnly && !IsReference)
          return;
      }
 
      unsigned diag = IsReference
          ? diag::warn_reference_field_is_uninit
          : diag::warn_field_is_uninit;
      S.Diag(FieldME->getExprLoc(), diag) << FoundVD;
      if (Constructor)
        S.Diag(Constructor->getLocation(),
               diag::note_uninit_in_this_constructor)
          << (Constructor->isDefaultConstructor() && Constructor->isImplicit());
 
    }
 
    void HandleValue(Expr *E, bool AddressOf) {
      E = E->IgnoreParens();
 
      if (MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
        HandleMemberExpr(ME, false /*CheckReferenceOnly*/,
                         AddressOf /*AddressOf*/);
        return;
      }
 
      if (ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) {
        Visit(CO->getCond());
        HandleValue(CO->getTrueExpr(), AddressOf);
        HandleValue(CO->getFalseExpr(), AddressOf);
        return;
      }
 
      if (BinaryConditionalOperator *BCO =
              dyn_cast<BinaryConditionalOperator>(E)) {
        Visit(BCO->getCond());
        HandleValue(BCO->getFalseExpr(), AddressOf);
        return;
      }
 
      if (OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(E)) {
        HandleValue(OVE->getSourceExpr(), AddressOf);
        return;
      }
 
      if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
        switch (BO->getOpcode()) {
        default:
          break;
        case(BO_PtrMemD):
        case(BO_PtrMemI):
          HandleValue(BO->getLHS(), AddressOf);
          Visit(BO->getRHS());
          return;
        case(BO_Comma):
          Visit(BO->getLHS());
          HandleValue(BO->getRHS(), AddressOf);
          return;
        }
      }
 
      Visit(E);
    }
 
    void CheckInitListExpr(InitListExpr *ILE) {
      InitFieldIndex.push_back(0);
      for (auto *Child : ILE->children()) {
        if (InitListExpr *SubList = dyn_cast<InitListExpr>(Child)) {
          CheckInitListExpr(SubList);
        } else {
          Visit(Child);
        }
        ++InitFieldIndex.back();
      }
      InitFieldIndex.pop_back();
    }
 
    void CheckInitializer(Expr *E, const CXXConstructorDecl *FieldConstructor,
                          FieldDecl *Field, const Type *BaseClass) {
      // Remove Decls that may have been initialized in the previous
      // initializer.
      for (ValueDecl* VD : DeclsToRemove)
        Decls.erase(VD);
      DeclsToRemove.clear();
 
      Constructor = FieldConstructor;
      InitListExpr *ILE = dyn_cast<InitListExpr>(E);
 
      if (ILE && Field) {
        InitList = true;
        InitListFieldDecl = Field;
        InitFieldIndex.clear();
        CheckInitListExpr(ILE);
      } else {
        InitList = false;
        Visit(E);
      }
 
      if (Field)
        Decls.erase(Field);
      if (BaseClass)
        BaseClasses.erase(BaseClass->getCanonicalTypeInternal());
    }
 
    void VisitMemberExpr(MemberExpr *ME) {
      // All uses of unbounded reference fields will warn.
      HandleMemberExpr(ME, true /*CheckReferenceOnly*/, false /*AddressOf*/);
    }
 
    void VisitImplicitCastExpr(ImplicitCastExpr *E) {
      if (E->getCastKind() == CK_LValueToRValue) {
        HandleValue(E->getSubExpr(), false /*AddressOf*/);
        return;
      }
 
      Inherited::VisitImplicitCastExpr(E);
    }
 
    void VisitCXXConstructExpr(CXXConstructExpr *E) {
      if (E->getConstructor()->isCopyConstructor()) {
        Expr *ArgExpr = E->getArg(0);
        if (InitListExpr *ILE = dyn_cast<InitListExpr>(ArgExpr))
          if (ILE->getNumInits() == 1)
            ArgExpr = ILE->getInit(0);
        if (ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(ArgExpr))
          if (ICE->getCastKind() == CK_NoOp)
            ArgExpr = ICE->getSubExpr();
        HandleValue(ArgExpr, false /*AddressOf*/);
        return;
      }
      Inherited::VisitCXXConstructExpr(E);
    }
 
    void VisitCXXMemberCallExpr(CXXMemberCallExpr *E) {
      Expr *Callee = E->getCallee();
      if (isa<MemberExpr>(Callee)) {
        HandleValue(Callee, false /*AddressOf*/);
        for (auto *Arg : E->arguments())
          Visit(Arg);
        return;
      }
 
      Inherited::VisitCXXMemberCallExpr(E);
    }
 
    void VisitCallExpr(CallExpr *E) {
      // Treat std::move as a use.
      if (E->isCallToStdMove()) {
        HandleValue(E->getArg(0), /*AddressOf=*/false);
        return;
      }
 
      Inherited::VisitCallExpr(E);
    }
 
    void VisitCXXOperatorCallExpr(CXXOperatorCallExpr *E) {
      Expr *Callee = E->getCallee();
 
      if (isa<UnresolvedLookupExpr>(Callee))
        return Inherited::VisitCXXOperatorCallExpr(E);
 
      Visit(Callee);
      for (auto *Arg : E->arguments())
        HandleValue(Arg->IgnoreParenImpCasts(), false /*AddressOf*/);
    }
 
    void VisitBinaryOperator(BinaryOperator *E) {
      // If a field assignment is detected, remove the field from the
      // uninitiailized field set.
      if (E->getOpcode() == BO_Assign)
        if (MemberExpr *ME = dyn_cast<MemberExpr>(E->getLHS()))
          if (FieldDecl *FD = dyn_cast<FieldDecl>(ME->getMemberDecl()))
            if (!FD->getType()->isReferenceType())
              DeclsToRemove.push_back(FD);
 
      if (E->isCompoundAssignmentOp()) {
        HandleValue(E->getLHS(), false /*AddressOf*/);
        Visit(E->getRHS());
        return;
      }
 
      Inherited::VisitBinaryOperator(E);
    }
 
    void VisitUnaryOperator(UnaryOperator *E) {
      if (E->isIncrementDecrementOp()) {
        HandleValue(E->getSubExpr(), false /*AddressOf*/);
        return;
      }
      if (E->getOpcode() == UO_AddrOf) {
        if (MemberExpr *ME = dyn_cast<MemberExpr>(E->getSubExpr())) {
          HandleValue(ME->getBase(), true /*AddressOf*/);
          return;
        }
      }
 
      Inherited::VisitUnaryOperator(E);
    }
  };
 
  // Diagnose value-uses of fields to initialize themselves, e.g.
  //   foo(foo)
  // where foo is not also a parameter to the constructor.
  // Also diagnose across field uninitialized use such as
  //   x(y), y(x)
  // TODO: implement -Wuninitialized and fold this into that framework.
  static void DiagnoseUninitializedFields(
      Sema &SemaRef, const CXXConstructorDecl *Constructor) {
 
    if (SemaRef.getDiagnostics().isIgnored(diag::warn_field_is_uninit,
                                           Constructor->getLocation())) {
      return;
    }
 
    if (Constructor->isInvalidDecl())
      return;
 
    const CXXRecordDecl *RD = Constructor->getParent();
 
    if (RD->isDependentContext())
      return;
 
    // Holds fields that are uninitialized.
    llvm::SmallPtrSet<ValueDecl*, 4> UninitializedFields;
 
    // At the beginning, all fields are uninitialized.
    for (auto *I : RD->decls()) {
      if (auto *FD = dyn_cast<FieldDecl>(I)) {
        UninitializedFields.insert(FD);
      } else if (auto *IFD = dyn_cast<IndirectFieldDecl>(I)) {
        UninitializedFields.insert(IFD->getAnonField());
      }
    }
 
    llvm::SmallPtrSet<QualType, 4> UninitializedBaseClasses;
    for (const auto &I : RD->bases())
      UninitializedBaseClasses.insert(I.getType().getCanonicalType());
 
    if (UninitializedFields.empty() && UninitializedBaseClasses.empty())
      return;
 
    UninitializedFieldVisitor UninitializedChecker(SemaRef,
                                                   UninitializedFields,
                                                   UninitializedBaseClasses);
 
    for (const auto *FieldInit : Constructor->inits()) {
      if (UninitializedFields.empty() && UninitializedBaseClasses.empty())
        break;
 
      Expr *InitExpr = FieldInit->getInit();
      if (!InitExpr)
        continue;
 
      if (CXXDefaultInitExpr *Default =
              dyn_cast<CXXDefaultInitExpr>(InitExpr)) {
        InitExpr = Default->getExpr();
        if (!InitExpr)
          continue;
        // In class initializers will point to the constructor.
        UninitializedChecker.CheckInitializer(InitExpr, Constructor,
                                              FieldInit->getAnyMember(),
                                              FieldInit->getBaseClass());
      } else {
        UninitializedChecker.CheckInitializer(InitExpr, nullptr,
                                              FieldInit->getAnyMember(),
                                              FieldInit->getBaseClass());
      }
    }
  }
} // namespace
 
/// Enter a new C++ default initializer scope. After calling this, the
/// caller must call \ref ActOnFinishCXXInClassMemberInitializer, even if
/// parsing or instantiating the initializer failed.
void Sema::ActOnStartCXXInClassMemberInitializer() {
  // Create a synthetic function scope to represent the call to the constructor
  // that notionally surrounds a use of this initializer.
  PushFunctionScope();
}
 
void Sema::ActOnStartTrailingRequiresClause(Scope *S, Declarator &D) {
  if (!D.isFunctionDeclarator())
    return;
  auto &FTI = D.getFunctionTypeInfo();
  if (!FTI.Params)
    return;
  for (auto &Param : ArrayRef<DeclaratorChunk::ParamInfo>(FTI.Params,
                                                          FTI.NumParams)) {
    auto *ParamDecl = cast<NamedDecl>(Param.Param);
    if (ParamDecl->getDeclName())
      PushOnScopeChains(ParamDecl, S, /*AddToContext=*/false);
  }
}
 
ExprResult Sema::ActOnFinishTrailingRequiresClause(ExprResult ConstraintExpr) {
  return ActOnRequiresClause(ConstraintExpr);
}
 
ExprResult Sema::ActOnRequiresClause(ExprResult ConstraintExpr) {
  if (ConstraintExpr.isInvalid())
    return ExprError();
 
  ConstraintExpr = CorrectDelayedTyposInExpr(ConstraintExpr);
  if (ConstraintExpr.isInvalid())
    return ExprError();
 
  if (DiagnoseUnexpandedParameterPack(ConstraintExpr.get(),
                                      UPPC_RequiresClause))
    return ExprError();
 
  return ConstraintExpr;
}
 
ExprResult Sema::ConvertMemberDefaultInitExpression(FieldDecl *FD,
                                                    Expr *InitExpr,
                                                    SourceLocation InitLoc) {
  InitializedEntity Entity =
      InitializedEntity::InitializeMemberFromDefaultMemberInitializer(FD);
  InitializationKind Kind =
      FD->getInClassInitStyle() == ICIS_ListInit
          ? InitializationKind::CreateDirectList(InitExpr->getBeginLoc(),
                                                 InitExpr->getBeginLoc(),
                                                 InitExpr->getEndLoc())
          : InitializationKind::CreateCopy(InitExpr->getBeginLoc(), InitLoc);
  InitializationSequence Seq(*this, Entity, Kind, InitExpr);
  return Seq.Perform(*this, Entity, Kind, InitExpr);
}
 
/// This is invoked after parsing an in-class initializer for a
/// non-static C++ class member, and after instantiating an in-class initializer
/// in a class template. Such actions are deferred until the class is complete.
void Sema::ActOnFinishCXXInClassMemberInitializer(Decl *D,
                                                  SourceLocation InitLoc,
                                                  Expr *InitExpr) {
  // Pop the notional constructor scope we created earlier.
  PopFunctionScopeInfo(nullptr, D);
 
  FieldDecl *FD = dyn_cast<FieldDecl>(D);
  assert((isa<MSPropertyDecl>(D) || FD->getInClassInitStyle() != ICIS_NoInit) &&
         "must set init style when field is created");
 
  if (!InitExpr) {
    D->setInvalidDecl();
    if (FD)
      FD->removeInClassInitializer();
    return;
  }
 
  if (DiagnoseUnexpandedParameterPack(InitExpr, UPPC_Initializer)) {
    FD->setInvalidDecl();
    FD->removeInClassInitializer();
    return;
  }
 
  ExprResult Init = CorrectDelayedTyposInExpr(InitExpr, /*InitDecl=*/nullptr,
                                              /*RecoverUncorrectedTypos=*/true);
  assert(Init.isUsable() && "Init should at least have a RecoveryExpr");
  if (!FD->getType()->isDependentType() && !Init.get()->isTypeDependent()) {
    Init = ConvertMemberDefaultInitExpression(FD, Init.get(), InitLoc);
    // C++11 [class.base.init]p7:
    //   The initialization of each base and member constitutes a
    //   full-expression.
    if (!Init.isInvalid())
      Init = ActOnFinishFullExpr(Init.get(), /*DiscarededValue=*/false);
    if (Init.isInvalid()) {
      FD->setInvalidDecl();
      return;
    }
  }
 
  FD->setInClassInitializer(Init.get());
}
 
/// Find the direct and/or virtual base specifiers that
/// correspond to the given base type, for use in base initialization
/// within a constructor.
static bool FindBaseInitializer(Sema &SemaRef,
                                CXXRecordDecl *ClassDecl,
                                QualType BaseType,
                                const CXXBaseSpecifier *&DirectBaseSpec,
                                const CXXBaseSpecifier *&VirtualBaseSpec) {
  // First, check for a direct base class.
  DirectBaseSpec = nullptr;
  for (const auto &Base : ClassDecl->bases()) {
    if (SemaRef.Context.hasSameUnqualifiedType(BaseType, Base.getType())) {
      // We found a direct base of this type. That's what we're
      // initializing.
      DirectBaseSpec = &Base;
      break;
    }
  }
 
  // Check for a virtual base class.
  // FIXME: We might be able to short-circuit this if we know in advance that
  // there are no virtual bases.
  VirtualBaseSpec = nullptr;
  if (!DirectBaseSpec || !DirectBaseSpec->isVirtual()) {
    // We haven't found a base yet; search the class hierarchy for a
    // virtual base class.
    CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
                       /*DetectVirtual=*/false);
    if (SemaRef.IsDerivedFrom(ClassDecl->getLocation(),
                              SemaRef.Context.getTypeDeclType(ClassDecl),
                              BaseType, Paths)) {
      for (CXXBasePaths::paths_iterator Path = Paths.begin();
           Path != Paths.end(); ++Path) {
        if (Path->back().Base->isVirtual()) {
          VirtualBaseSpec = Path->back().Base;
          break;
        }
      }
    }
  }
 
  return DirectBaseSpec || VirtualBaseSpec;
}
 
/// Handle a C++ member initializer using braced-init-list syntax.
MemInitResult
Sema::ActOnMemInitializer(Decl *ConstructorD,
                          Scope *S,
                          CXXScopeSpec &SS,
                          IdentifierInfo *MemberOrBase,
                          ParsedType TemplateTypeTy,
                          const DeclSpec &DS,
                          SourceLocation IdLoc,
                          Expr *InitList,
                          SourceLocation EllipsisLoc) {
  return BuildMemInitializer(ConstructorD, S, SS, MemberOrBase, TemplateTypeTy,
                             DS, IdLoc, InitList,
                             EllipsisLoc);
}
 
/// Handle a C++ member initializer using parentheses syntax.
MemInitResult
Sema::ActOnMemInitializer(Decl *ConstructorD,
                          Scope *S,
                          CXXScopeSpec &SS,
                          IdentifierInfo *MemberOrBase,
                          ParsedType TemplateTypeTy,
                          const DeclSpec &DS,
                          SourceLocation IdLoc,
                          SourceLocation LParenLoc,
                          ArrayRef<Expr *> Args,
                          SourceLocation RParenLoc,
                          SourceLocation EllipsisLoc) {
  Expr *List = ParenListExpr::Create(Context, LParenLoc, Args, RParenLoc);
  return BuildMemInitializer(ConstructorD, S, SS, MemberOrBase, TemplateTypeTy,
                             DS, IdLoc, List, EllipsisLoc);
}
 
namespace {
 
// Callback to only accept typo corrections that can be a valid C++ member
// initializer: either a non-static field member or a base class.
class MemInitializerValidatorCCC final : public CorrectionCandidateCallback {
public:
  explicit MemInitializerValidatorCCC(CXXRecordDecl *ClassDecl)
      : ClassDecl(ClassDecl) {}
 
  bool ValidateCandidate(const TypoCorrection &candidate) override {
    if (NamedDecl *ND = candidate.getCorrectionDecl()) {
      if (FieldDecl *Member = dyn_cast<FieldDecl>(ND))
        return Member->getDeclContext()->getRedeclContext()->Equals(ClassDecl);
      return isa<TypeDecl>(ND);
    }
    return false;
  }
 
  std::unique_ptr<CorrectionCandidateCallback> clone() override {
    return std::make_unique<MemInitializerValidatorCCC>(*this);
  }
 
private:
  CXXRecordDecl *ClassDecl;
};
 
}
 
bool Sema::DiagRedefinedPlaceholderFieldDecl(SourceLocation Loc,
                                             RecordDecl *ClassDecl,
                                             const IdentifierInfo *Name) {
  DeclContextLookupResult Result = ClassDecl->lookup(Name);
  DeclContextLookupResult::iterator Found =
      llvm::find_if(Result, [this](const NamedDecl *Elem) {
        return isa<FieldDecl, IndirectFieldDecl>(Elem) &&
               Elem->isPlaceholderVar(getLangOpts());
      });
  // We did not find a placeholder variable
  if (Found == Result.end())
    return false;
  Diag(Loc, diag::err_using_placeholder_variable) << Name;
  for (DeclContextLookupResult::iterator It = Found; It != Result.end(); It++) {
    const NamedDecl *ND = *It;
    if (ND->getDeclContext() != ND->getDeclContext())
      break;
    if (isa<FieldDecl, IndirectFieldDecl>(ND) &&
        ND->isPlaceholderVar(getLangOpts()))
      Diag(ND->getLocation(), diag::note_reference_placeholder) << ND;
  }
  return true;
}
 
ValueDecl *
Sema::tryLookupUnambiguousFieldDecl(RecordDecl *ClassDecl,
                                    const IdentifierInfo *MemberOrBase) {
  ValueDecl *ND = nullptr;
  for (auto *D : ClassDecl->lookup(MemberOrBase)) {
    if (isa<FieldDecl, IndirectFieldDecl>(D)) {
      bool IsPlaceholder = D->isPlaceholderVar(getLangOpts());
      if (ND) {
        if (IsPlaceholder && D->getDeclContext() == ND->getDeclContext())
          return nullptr;
        break;
      }
      if (!IsPlaceholder)
        return cast<ValueDecl>(D);
      ND = cast<ValueDecl>(D);
    }
  }
  return ND;
}
 
ValueDecl *Sema::tryLookupCtorInitMemberDecl(CXXRecordDecl *ClassDecl,
                                             CXXScopeSpec &SS,
                                             ParsedType TemplateTypeTy,
                                             IdentifierInfo *MemberOrBase) {
  if (SS.getScopeRep() || TemplateTypeTy)
    return nullptr;
  return tryLookupUnambiguousFieldDecl(ClassDecl, MemberOrBase);
}
 
/// Handle a C++ member initializer.
MemInitResult
Sema::BuildMemInitializer(Decl *ConstructorD,
                          Scope *S,
                          CXXScopeSpec &SS,
                          IdentifierInfo *MemberOrBase,
                          ParsedType TemplateTypeTy,
                          const DeclSpec &DS,
                          SourceLocation IdLoc,
                          Expr *Init,
                          SourceLocation EllipsisLoc) {
  ExprResult Res = CorrectDelayedTyposInExpr(Init, /*InitDecl=*/nullptr,
                                             /*RecoverUncorrectedTypos=*/true);
  if (!Res.isUsable())
    return true;
  Init = Res.get();
 
  if (!ConstructorD)
    return true;
 
  AdjustDeclIfTemplate(ConstructorD);
 
  CXXConstructorDecl *Constructor
    = dyn_cast<CXXConstructorDecl>(ConstructorD);
  if (!Constructor) {
    // The user wrote a constructor initializer on a function that is
    // not a C++ constructor. Ignore the error for now, because we may
    // have more member initializers coming; we'll diagnose it just
    // once in ActOnMemInitializers.
    return true;
  }
 
  CXXRecordDecl *ClassDecl = Constructor->getParent();
 
  // C++ [class.base.init]p2:
  //   Names in a mem-initializer-id are looked up in the scope of the
  //   constructor's class and, if not found in that scope, are looked
  //   up in the scope containing the constructor's definition.
  //   [Note: if the constructor's class contains a member with the
  //   same name as a direct or virtual base class of the class, a
  //   mem-initializer-id naming the member or base class and composed
  //   of a single identifier refers to the class member. A
  //   mem-initializer-id for the hidden base class may be specified
  //   using a qualified name. ]
 
  // Look for a member, first.
  if (ValueDecl *Member = tryLookupCtorInitMemberDecl(
          ClassDecl, SS, TemplateTypeTy, MemberOrBase)) {
    if (EllipsisLoc.isValid())
      Diag(EllipsisLoc, diag::err_pack_expansion_member_init)
          << MemberOrBase
          << SourceRange(IdLoc, Init->getSourceRange().getEnd());
 
    return BuildMemberInitializer(Member, Init, IdLoc);
  }
  // It didn't name a member, so see if it names a class.
  QualType BaseType;
  TypeSourceInfo *TInfo = nullptr;
 
  if (TemplateTypeTy) {
    BaseType = GetTypeFromParser(TemplateTypeTy, &TInfo);
    if (BaseType.isNull())
      return true;
  } else if (DS.getTypeSpecType() == TST_decltype) {
    BaseType = BuildDecltypeType(DS.getRepAsExpr());
  } else if (DS.getTypeSpecType() == TST_decltype_auto) {
    Diag(DS.getTypeSpecTypeLoc(), diag::err_decltype_auto_invalid);
    return true;
  } else {
    LookupResult R(*this, MemberOrBase, IdLoc, LookupOrdinaryName);
    LookupParsedName(R, S, &SS);
 
    TypeDecl *TyD = R.getAsSingle<TypeDecl>();
    if (!TyD) {
      if (R.isAmbiguous()) return true;
 
      // We don't want access-control diagnostics here.
      R.suppressDiagnostics();
 
      if (SS.isSet() && isDependentScopeSpecifier(SS)) {
        bool NotUnknownSpecialization = false;
        DeclContext *DC = computeDeclContext(SS, false);
        if (CXXRecordDecl *Record = dyn_cast_or_null<CXXRecordDecl>(DC))
          NotUnknownSpecialization = !Record->hasAnyDependentBases();
 
        if (!NotUnknownSpecialization) {
          // When the scope specifier can refer to a member of an unknown
          // specialization, we take it as a type name.
          BaseType = CheckTypenameType(ETK_None, SourceLocation(),
                                       SS.getWithLocInContext(Context),
                                       *MemberOrBase, IdLoc);
          if (BaseType.isNull())
            return true;
 
          TInfo = Context.CreateTypeSourceInfo(BaseType);
          DependentNameTypeLoc TL =
              TInfo->getTypeLoc().castAs<DependentNameTypeLoc>();
          if (!TL.isNull()) {
            TL.setNameLoc(IdLoc);
            TL.setElaboratedKeywordLoc(SourceLocation());
            TL.setQualifierLoc(SS.getWithLocInContext(Context));
          }
 
          R.clear();
          R.setLookupName(MemberOrBase);
        }
      }
 
      if (getLangOpts().MSVCCompat && !getLangOpts().CPlusPlus20) {
        if (auto UnqualifiedBase = R.getAsSingle<ClassTemplateDecl>()) {
          auto *TempSpec = cast<TemplateSpecializationType>(
              UnqualifiedBase->getInjectedClassNameSpecialization());
          TemplateName TN = TempSpec->getTemplateName();
          for (auto const &Base : ClassDecl->bases()) {
            auto BaseTemplate =
                Base.getType()->getAs<TemplateSpecializationType>();
            if (BaseTemplate && Context.hasSameTemplateName(
                                    BaseTemplate->getTemplateName(), TN)) {
              Diag(IdLoc, diag::ext_unqualified_base_class)
                  << SourceRange(IdLoc, Init->getSourceRange().getEnd());
              BaseType = Base.getType();
              break;
            }
          }
        }
      }
 
      // If no results were found, try to correct typos.
      TypoCorrection Corr;
      MemInitializerValidatorCCC CCC(ClassDecl);
      if (R.empty() && BaseType.isNull() &&
          (Corr = CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), S, &SS,
                              CCC, CTK_ErrorRecovery, ClassDecl))) {
        if (FieldDecl *Member = Corr.getCorrectionDeclAs<FieldDecl>()) {
          // We have found a non-static data member with a similar
          // name to what was typed; complain and initialize that
          // member.
          diagnoseTypo(Corr,
                       PDiag(diag::err_mem_init_not_member_or_class_suggest)
                         << MemberOrBase << true);
          return BuildMemberInitializer(Member, Init, IdLoc);
        } else if (TypeDecl *Type = Corr.getCorrectionDeclAs<TypeDecl>()) {
          const CXXBaseSpecifier *DirectBaseSpec;
          const CXXBaseSpecifier *VirtualBaseSpec;
          if (FindBaseInitializer(*this, ClassDecl,
                                  Context.getTypeDeclType(Type),
                                  DirectBaseSpec, VirtualBaseSpec)) {
            // We have found a direct or virtual base class with a
            // similar name to what was typed; complain and initialize
            // that base class.
            diagnoseTypo(Corr,
                         PDiag(diag::err_mem_init_not_member_or_class_suggest)
                           << MemberOrBase << false,
                         PDiag() /*Suppress note, we provide our own.*/);
 
            const CXXBaseSpecifier *BaseSpec = DirectBaseSpec ? DirectBaseSpec
                                                              : VirtualBaseSpec;
            Diag(BaseSpec->getBeginLoc(), diag::note_base_class_specified_here)
                << BaseSpec->getType() << BaseSpec->getSourceRange();
 
            TyD = Type;
          }
        }
      }
 
      if (!TyD && BaseType.isNull()) {
        Diag(IdLoc, diag::err_mem_init_not_member_or_class)
          << MemberOrBase << SourceRange(IdLoc,Init->getSourceRange().getEnd());
        return true;
      }
    }
 
    if (BaseType.isNull()) {
      BaseType = getElaboratedType(ETK_None, SS, Context.getTypeDeclType(TyD));
      MarkAnyDeclReferenced(TyD->getLocation(), TyD, /*OdrUse=*/false);
      TInfo = Context.CreateTypeSourceInfo(BaseType);
      ElaboratedTypeLoc TL = TInfo->getTypeLoc().castAs<ElaboratedTypeLoc>();
      TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(IdLoc);
      TL.setElaboratedKeywordLoc(SourceLocation());
      TL.setQualifierLoc(SS.getWithLocInContext(Context));
    }
  }
 
  if (!TInfo)
    TInfo = Context.getTrivialTypeSourceInfo(BaseType, IdLoc);
 
  return BuildBaseInitializer(BaseType, TInfo, Init, ClassDecl, EllipsisLoc);
}
 
MemInitResult
Sema::BuildMemberInitializer(ValueDecl *Member, Expr *Init,
                             SourceLocation IdLoc) {
  FieldDecl *DirectMember = dyn_cast<FieldDecl>(Member);
  IndirectFieldDecl *IndirectMember = dyn_cast<IndirectFieldDecl>(Member);
  assert((DirectMember || IndirectMember) &&
         "Member must be a FieldDecl or IndirectFieldDecl");
 
  if (DiagnoseUnexpandedParameterPack(Init, UPPC_Initializer))
    return true;
 
  if (Member->isInvalidDecl())
    return true;
 
  MultiExprArg Args;
  if (ParenListExpr *ParenList = dyn_cast<ParenListExpr>(Init)) {
    Args = MultiExprArg(ParenList->getExprs(), ParenList->getNumExprs());
  } else if (InitListExpr *InitList = dyn_cast<InitListExpr>(Init)) {
    Args = MultiExprArg(InitList->getInits(), InitList->getNumInits());
  } else {
    // Template instantiation doesn't reconstruct ParenListExprs for us.
    Args = Init;
  }
 
  SourceRange InitRange = Init->getSourceRange();
 
  if (Member->getType()->isDependentType() || Init->isTypeDependent()) {
    // Can't check initialization for a member of dependent type or when
    // any of the arguments are type-dependent expressions.
    DiscardCleanupsInEvaluationContext();
  } else {
    bool InitList = false;
    if (isa<InitListExpr>(Init)) {
      InitList = true;
      Args = Init;
    }
 
    // Initialize the member.
    InitializedEntity MemberEntity =
      DirectMember ? InitializedEntity::InitializeMember(DirectMember, nullptr)
                   : InitializedEntity::InitializeMember(IndirectMember,
                                                         nullptr);
    InitializationKind Kind =
        InitList ? InitializationKind::CreateDirectList(
                       IdLoc, Init->getBeginLoc(), Init->getEndLoc())
                 : InitializationKind::CreateDirect(IdLoc, InitRange.getBegin(),
                                                    InitRange.getEnd());
 
    InitializationSequence InitSeq(*this, MemberEntity, Kind, Args);
    ExprResult MemberInit = InitSeq.Perform(*this, MemberEntity, Kind, Args,
                                            nullptr);
    if (!MemberInit.isInvalid()) {
      // C++11 [class.base.init]p7:
      //   The initialization of each base and member constitutes a
      //   full-expression.
      MemberInit = ActOnFinishFullExpr(MemberInit.get(), InitRange.getBegin(),
                                       /*DiscardedValue*/ false);
    }
 
    if (MemberInit.isInvalid()) {
      // Args were sensible expressions but we couldn't initialize the member
      // from them. Preserve them in a RecoveryExpr instead.
      Init = CreateRecoveryExpr(InitRange.getBegin(), InitRange.getEnd(), Args,
                                Member->getType())
                 .get();
      if (!Init)
        return true;
    } else {
      Init = MemberInit.get();
    }
  }
 
  if (DirectMember) {
    return new (Context) CXXCtorInitializer(Context, DirectMember, IdLoc,
                                            InitRange.getBegin(), Init,
                                            InitRange.getEnd());
  } else {
    return new (Context) CXXCtorInitializer(Context, IndirectMember, IdLoc,
                                            InitRange.getBegin(), Init,
                                            InitRange.getEnd());
  }
}
 
MemInitResult
Sema::BuildDelegatingInitializer(TypeSourceInfo *TInfo, Expr *Init,
                                 CXXRecordDecl *ClassDecl) {
  SourceLocation NameLoc = TInfo->getTypeLoc().getSourceRange().getBegin();
  if (!LangOpts.CPlusPlus11)
    return Diag(NameLoc, diag::err_delegating_ctor)
           << TInfo->getTypeLoc().getSourceRange();
  Diag(NameLoc, diag::warn_cxx98_compat_delegating_ctor);
 
  bool InitList = true;
  MultiExprArg Args = Init;
  if (ParenListExpr *ParenList = dyn_cast<ParenListExpr>(Init)) {
    InitList = false;
    Args = MultiExprArg(ParenList->getExprs(), ParenList->getNumExprs());
  }
 
  SourceRange InitRange = Init->getSourceRange();
  // Initialize the object.
  InitializedEntity DelegationEntity = InitializedEntity::InitializeDelegation(
                                     QualType(ClassDecl->getTypeForDecl(), 0));
  InitializationKind Kind =
      InitList ? InitializationKind::CreateDirectList(
                     NameLoc, Init->getBeginLoc(), Init->getEndLoc())
               : InitializationKind::CreateDirect(NameLoc, InitRange.getBegin(),
                                                  InitRange.getEnd());
  InitializationSequence InitSeq(*this, DelegationEntity, Kind, Args);
  ExprResult DelegationInit = InitSeq.Perform(*this, DelegationEntity, Kind,
                                              Args, nullptr);
  if (!DelegationInit.isInvalid()) {
    assert((DelegationInit.get()->containsErrors() ||
            cast<CXXConstructExpr>(DelegationInit.get())->getConstructor()) &&
           "Delegating constructor with no target?");
 
    // C++11 [class.base.init]p7:
    //   The initialization of each base and member constitutes a
    //   full-expression.
    DelegationInit = ActOnFinishFullExpr(
        DelegationInit.get(), InitRange.getBegin(), /*DiscardedValue*/ false);
  }
 
  if (DelegationInit.isInvalid()) {
    DelegationInit =
        CreateRecoveryExpr(InitRange.getBegin(), InitRange.getEnd(), Args,
                           QualType(ClassDecl->getTypeForDecl(), 0));
    if (DelegationInit.isInvalid())
      return true;
  } else {
    // If we are in a dependent context, template instantiation will
    // perform this type-checking again. Just save the arguments that we
    // received in a ParenListExpr.
    // FIXME: This isn't quite ideal, since our ASTs don't capture all
    // of the information that we have about the base
    // initializer. However, deconstructing the ASTs is a dicey process,
    // and this approach is far more likely to get the corner cases right.
    if (CurContext->isDependentContext())
      DelegationInit = Init;
  }
 
  return new (Context) CXXCtorInitializer(Context, TInfo, InitRange.getBegin(),
                                          DelegationInit.getAs<Expr>(),
                                          InitRange.getEnd());
}
 
MemInitResult
Sema::BuildBaseInitializer(QualType BaseType, TypeSourceInfo *BaseTInfo,
                           Expr *Init, CXXRecordDecl *ClassDecl,
                           SourceLocation EllipsisLoc) {
  SourceLocation BaseLoc = BaseTInfo->getTypeLoc().getBeginLoc();
 
  if (!BaseType->isDependentType() && !BaseType->isRecordType())
    return Diag(BaseLoc, diag::err_base_init_does_not_name_class)
           << BaseType << BaseTInfo->getTypeLoc().getSourceRange();
 
  // C++ [class.base.init]p2:
  //   [...] Unless the mem-initializer-id names a nonstatic data
  //   member of the constructor's class or a direct or virtual base
  //   of that class, the mem-initializer is ill-formed. A
  //   mem-initializer-list can initialize a base class using any
  //   name that denotes that base class type.
 
  // We can store the initializers in "as-written" form and delay analysis until
  // instantiation if the constructor is dependent. But not for dependent
  // (broken) code in a non-template! SetCtorInitializers does not expect this.
  bool Dependent = CurContext->isDependentContext() &&
                   (BaseType->isDependentType() || Init->isTypeDependent());
 
  SourceRange InitRange = Init->getSourceRange();
  if (EllipsisLoc.isValid()) {
    // This is a pack expansion.
    if (!BaseType->containsUnexpandedParameterPack())  {
      Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
        << SourceRange(BaseLoc, InitRange.getEnd());
 
      EllipsisLoc = SourceLocation();
    }
  } else {
    // Check for any unexpanded parameter packs.
    if (DiagnoseUnexpandedParameterPack(BaseLoc, BaseTInfo, UPPC_Initializer))
      return true;
 
    if (DiagnoseUnexpandedParameterPack(Init, UPPC_Initializer))
      return true;
  }
 
  // Check for direct and virtual base classes.
  const CXXBaseSpecifier *DirectBaseSpec = nullptr;
  const CXXBaseSpecifier *VirtualBaseSpec = nullptr;
  if (!Dependent) {
    if (Context.hasSameUnqualifiedType(QualType(ClassDecl->getTypeForDecl(),0),
                                       BaseType))
      return BuildDelegatingInitializer(BaseTInfo, Init, ClassDecl);
 
    FindBaseInitializer(*this, ClassDecl, BaseType, DirectBaseSpec,
                        VirtualBaseSpec);
 
    // C++ [base.class.init]p2:
    // Unless the mem-initializer-id names a nonstatic data member of the
    // constructor's class or a direct or virtual base of that class, the
    // mem-initializer is ill-formed.
    if (!DirectBaseSpec && !VirtualBaseSpec) {
      // If the class has any dependent bases, then it's possible that
      // one of those types will resolve to the same type as
      // BaseType. Therefore, just treat this as a dependent base
      // class initialization.  FIXME: Should we try to check the
      // initialization anyway? It seems odd.
      if (ClassDecl->hasAnyDependentBases())
        Dependent = true;
      else
        return Diag(BaseLoc, diag::err_not_direct_base_or_virtual)
               << BaseType << Context.getTypeDeclType(ClassDecl)
               << BaseTInfo->getTypeLoc().getSourceRange();
    }
  }
 
  if (Dependent) {
    DiscardCleanupsInEvaluationContext();
 
    return new (Context) CXXCtorInitializer(Context, BaseTInfo,
                                            /*IsVirtual=*/false,
                                            InitRange.getBegin(), Init,
                                            InitRange.getEnd(), EllipsisLoc);
  }
 
  // C++ [base.class.init]p2:
  //   If a mem-initializer-id is ambiguous because it designates both
  //   a direct non-virtual base class and an inherited virtual base
  //   class, the mem-initializer is ill-formed.
  if (DirectBaseSpec && VirtualBaseSpec)
    return Diag(BaseLoc, diag::err_base_init_direct_and_virtual)
      << BaseType << BaseTInfo->getTypeLoc().getLocalSourceRange();
 
  const CXXBaseSpecifier *BaseSpec = DirectBaseSpec;
  if (!BaseSpec)
    BaseSpec = VirtualBaseSpec;
 
  // Initialize the base.
  bool InitList = true;
  MultiExprArg Args = Init;
  if (ParenListExpr *ParenList = dyn_cast<ParenListExpr>(Init)) {
    InitList = false;
    Args = MultiExprArg(ParenList->getExprs(), ParenList->getNumExprs());
  }
 
  InitializedEntity BaseEntity =
    InitializedEntity::InitializeBase(Context, BaseSpec, VirtualBaseSpec);
  InitializationKind Kind =
      InitList ? InitializationKind::CreateDirectList(BaseLoc)
               : InitializationKind::CreateDirect(BaseLoc, InitRange.getBegin(),
                                                  InitRange.getEnd());
  InitializationSequence InitSeq(*this, BaseEntity, Kind, Args);
  ExprResult BaseInit = InitSeq.Perform(*this, BaseEntity, Kind, Args, nullptr);
  if (!BaseInit.isInvalid()) {
    // C++11 [class.base.init]p7:
    //   The initialization of each base and member constitutes a
    //   full-expression.
    BaseInit = ActOnFinishFullExpr(BaseInit.get(), InitRange.getBegin(),
                                   /*DiscardedValue*/ false);
  }
 
  if (BaseInit.isInvalid()) {
    BaseInit = CreateRecoveryExpr(InitRange.getBegin(), InitRange.getEnd(),
                                  Args, BaseType);
    if (BaseInit.isInvalid())
      return true;
  } else {
    // If we are in a dependent context, template instantiation will
    // perform this type-checking again. Just save the arguments that we
    // received in a ParenListExpr.
    // FIXME: This isn't quite ideal, since our ASTs don't capture all
    // of the information that we have about the base
    // initializer. However, deconstructing the ASTs is a dicey process,
    // and this approach is far more likely to get the corner cases right.
    if (CurContext->isDependentContext())
      BaseInit = Init;
  }
 
  return new (Context) CXXCtorInitializer(Context, BaseTInfo,
                                          BaseSpec->isVirtual(),
                                          InitRange.getBegin(),
                                          BaseInit.getAs<Expr>(),
                                          InitRange.getEnd(), EllipsisLoc);
}
 
// Create a static_cast<T&&>(expr).
static Expr *CastForMoving(Sema &SemaRef, Expr *E) {
  QualType TargetType =
      SemaRef.BuildReferenceType(E->getType(), /*SpelledAsLValue*/ false,
                                 SourceLocation(), DeclarationName());
  SourceLocation ExprLoc = E->getBeginLoc();
  TypeSourceInfo *TargetLoc = SemaRef.Context.getTrivialTypeSourceInfo(
      TargetType, ExprLoc);
 
  return SemaRef.BuildCXXNamedCast(ExprLoc, tok::kw_static_cast, TargetLoc, E,
                                   SourceRange(ExprLoc, ExprLoc),
                                   E->getSourceRange()).get();
}
 
/// ImplicitInitializerKind - How an implicit base or member initializer should
/// initialize its base or member.
enum ImplicitInitializerKind {
  IIK_Default,
  IIK_Copy,
  IIK_Move,
  IIK_Inherit
};
 
static bool
BuildImplicitBaseInitializer(Sema &SemaRef, CXXConstructorDecl *Constructor,
                             ImplicitInitializerKind ImplicitInitKind,
                             CXXBaseSpecifier *BaseSpec,
                             bool IsInheritedVirtualBase,
                             CXXCtorInitializer *&CXXBaseInit) {
  InitializedEntity InitEntity
    = InitializedEntity::InitializeBase(SemaRef.Context, BaseSpec,
                                        IsInheritedVirtualBase);
 
  ExprResult BaseInit;
 
  switch (ImplicitInitKind) {
  case IIK_Inherit:
  case IIK_Default: {
    InitializationKind InitKind
      = InitializationKind::CreateDefault(Constructor->getLocation());
    InitializationSequence InitSeq(SemaRef, InitEntity, InitKind, std::nullopt);
    BaseInit = InitSeq.Perform(SemaRef, InitEntity, InitKind, std::nullopt);
    break;
  }
 
  case IIK_Move:
  case IIK_Copy: {
    bool Moving = ImplicitInitKind == IIK_Move;
    ParmVarDecl *Param = Constructor->getParamDecl(0);
    QualType ParamType = Param->getType().getNonReferenceType();
 
    Expr *CopyCtorArg =
      DeclRefExpr::Create(SemaRef.Context, NestedNameSpecifierLoc(),
                          SourceLocation(), Param, false,
                          Constructor->getLocation(), ParamType,
                          VK_LValue, nullptr);
 
    SemaRef.MarkDeclRefReferenced(cast<DeclRefExpr>(CopyCtorArg));
 
    // Cast to the base class to avoid ambiguities.
    QualType ArgTy =
      SemaRef.Context.getQualifiedType(BaseSpec->getType().getUnqualifiedType(),
                                       ParamType.getQualifiers());
 
    if (Moving) {
      CopyCtorArg = CastForMoving(SemaRef, CopyCtorArg);
    }
 
    CXXCastPath BasePath;
    BasePath.push_back(BaseSpec);
    CopyCtorArg = SemaRef.ImpCastExprToType(CopyCtorArg, ArgTy,
                                            CK_UncheckedDerivedToBase,
                                            Moving ? VK_XValue : VK_LValue,
                                            &BasePath).get();
 
    InitializationKind InitKind
      = InitializationKind::CreateDirect(Constructor->getLocation(),
                                         SourceLocation(), SourceLocation());
    InitializationSequence InitSeq(SemaRef, InitEntity, InitKind, CopyCtorArg);
    BaseInit = InitSeq.Perform(SemaRef, InitEntity, InitKind, CopyCtorArg);
    break;
  }
  }
 
  BaseInit = SemaRef.MaybeCreateExprWithCleanups(BaseInit);
  if (BaseInit.isInvalid())
    return true;
 
  CXXBaseInit =
    new (SemaRef.Context) CXXCtorInitializer(SemaRef.Context,
               SemaRef.Context.getTrivialTypeSourceInfo(BaseSpec->getType(),
                                                        SourceLocation()),
                                             BaseSpec->isVirtual(),
                                             SourceLocation(),
                                             BaseInit.getAs<Expr>(),
                                             SourceLocation(),
                                             SourceLocation());
 
  return false;
}
 
static bool RefersToRValueRef(Expr *MemRef) {
  ValueDecl *Referenced = cast<MemberExpr>(MemRef)->getMemberDecl();
  return Referenced->getType()->isRValueReferenceType();
}
 
static bool
BuildImplicitMemberInitializer(Sema &SemaRef, CXXConstructorDecl *Constructor,
                               ImplicitInitializerKind ImplicitInitKind,
                               FieldDecl *Field, IndirectFieldDecl *Indirect,
                               CXXCtorInitializer *&CXXMemberInit) {
  if (Field->isInvalidDecl())
    return true;
 
  SourceLocation Loc = Constructor->getLocation();
 
  if (ImplicitInitKind == IIK_Copy || ImplicitInitKind == IIK_Move) {
    bool Moving = ImplicitInitKind == IIK_Move;
    ParmVarDecl *Param = Constructor->getParamDecl(0);
    QualType ParamType = Param->getType().getNonReferenceType();
 
    // Suppress copying zero-width bitfields.
    if (Field->isZeroLengthBitField(SemaRef.Context))
      return false;
 
    Expr *MemberExprBase =
      DeclRefExpr::Create(SemaRef.Context, NestedNameSpecifierLoc(),
                          SourceLocation(), Param, false,
                          Loc, ParamType, VK_LValue, nullptr);
 
    SemaRef.MarkDeclRefReferenced(cast<DeclRefExpr>(MemberExprBase));
 
    if (Moving) {
      MemberExprBase = CastForMoving(SemaRef, MemberExprBase);
    }
 
    // Build a reference to this field within the parameter.
    CXXScopeSpec SS;
    LookupResult MemberLookup(SemaRef, Field->getDeclName(), Loc,
                              Sema::LookupMemberName);
    MemberLookup.addDecl(Indirect ? cast<ValueDecl>(Indirect)
                                  : cast<ValueDecl>(Field), AS_public);
    MemberLookup.resolveKind();
    ExprResult CtorArg
      = SemaRef.BuildMemberReferenceExpr(MemberExprBase,
                                         ParamType, Loc,
                                         /*IsArrow=*/false,
                                         SS,
                                         /*TemplateKWLoc=*/SourceLocation(),
                                         /*FirstQualifierInScope=*/nullptr,
                                         MemberLookup,
                                         /*TemplateArgs=*/nullptr,
                                         /*S*/nullptr);
    if (CtorArg.isInvalid())
      return true;
 
    // C++11 [class.copy]p15:
    //   - if a member m has rvalue reference type T&&, it is direct-initialized
    //     with static_cast<T&&>(x.m);
    if (RefersToRValueRef(CtorArg.get())) {
      CtorArg = CastForMoving(SemaRef, CtorArg.get());
    }
 
    InitializedEntity Entity =
        Indirect ? InitializedEntity::InitializeMember(Indirect, nullptr,
                                                       /*Implicit*/ true)
                 : InitializedEntity::InitializeMember(Field, nullptr,
                                                       /*Implicit*/ true);
 
    // Direct-initialize to use the copy constructor.
    InitializationKind InitKind =
      InitializationKind::CreateDirect(Loc, SourceLocation(), SourceLocation());
 
    Expr *CtorArgE = CtorArg.getAs<Expr>();
    InitializationSequence InitSeq(SemaRef, Entity, InitKind, CtorArgE);
    ExprResult MemberInit =
        InitSeq.Perform(SemaRef, Entity, InitKind, MultiExprArg(&CtorArgE, 1));
    MemberInit = SemaRef.MaybeCreateExprWithCleanups(MemberInit);
    if (MemberInit.isInvalid())
      return true;
 
    if (Indirect)
      CXXMemberInit = new (SemaRef.Context) CXXCtorInitializer(
          SemaRef.Context, Indirect, Loc, Loc, MemberInit.getAs<Expr>(), Loc);
    else
      CXXMemberInit = new (SemaRef.Context) CXXCtorInitializer(
          SemaRef.Context, Field, Loc, Loc, MemberInit.getAs<Expr>(), Loc);
    return false;
  }
 
  assert((ImplicitInitKind == IIK_Default || ImplicitInitKind == IIK_Inherit) &&
         "Unhandled implicit init kind!");
 
  QualType FieldBaseElementType =
    SemaRef.Context.getBaseElementType(Field->getType());
 
  if (FieldBaseElementType->isRecordType()) {
    InitializedEntity InitEntity =
        Indirect ? InitializedEntity::InitializeMember(Indirect, nullptr,
                                                       /*Implicit*/ true)
                 : InitializedEntity::InitializeMember(Field, nullptr,
                                                       /*Implicit*/ true);
    InitializationKind InitKind =
      InitializationKind::CreateDefault(Loc);
 
    InitializationSequence InitSeq(SemaRef, InitEntity, InitKind, std::nullopt);
    ExprResult MemberInit =
        InitSeq.Perform(SemaRef, InitEntity, InitKind, std::nullopt);
 
    MemberInit = SemaRef.MaybeCreateExprWithCleanups(MemberInit);
    if (MemberInit.