Sema.h

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//===--- Sema.h - Semantic Analysis & AST Building --------------*- C++ -*-===//
//
// 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 defines the Sema class, which performs semantic analysis and
// builds ASTs.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CLANG_SEMA_SEMA_H
#define LLVM_CLANG_SEMA_SEMA_H
 
#include "clang/APINotes/APINotesManager.h"
#include "clang/AST/ASTConcept.h"
#include "clang/AST/ASTFwd.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Availability.h"
#include "clang/AST/ComparisonCategories.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclarationName.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/ExprConcepts.h"
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ExprOpenMP.h"
#include "clang/AST/ExternalASTSource.h"
#include "clang/AST/LocInfoType.h"
#include "clang/AST/MangleNumberingContext.h"
#include "clang/AST/NSAPI.h"
#include "clang/AST/PrettyPrinter.h"
#include "clang/AST/StmtCXX.h"
#include "clang/AST/StmtOpenMP.h"
#include "clang/AST/TypeLoc.h"
#include "clang/AST/TypeOrdering.h"
#include "clang/Basic/BitmaskEnum.h"
#include "clang/Basic/Builtins.h"
#include "clang/Basic/DarwinSDKInfo.h"
#include "clang/Basic/ExpressionTraits.h"
#include "clang/Basic/Module.h"
#include "clang/Basic/OpenCLOptions.h"
#include "clang/Basic/OpenMPKinds.h"
#include "clang/Basic/PragmaKinds.h"
#include "clang/Basic/Specifiers.h"
#include "clang/Basic/TemplateKinds.h"
#include "clang/Basic/TypeTraits.h"
#include "clang/Sema/AnalysisBasedWarnings.h"
#include "clang/Sema/CleanupInfo.h"
#include "clang/Sema/DeclSpec.h"
#include "clang/Sema/ExternalSemaSource.h"
#include "clang/Sema/IdentifierResolver.h"
#include "clang/Sema/ObjCMethodList.h"
#include "clang/Sema/Ownership.h"
#include "clang/Sema/Scope.h"
#include "clang/Sema/SemaConcept.h"
#include "clang/Sema/TypoCorrection.h"
#include "clang/Sema/Weak.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Frontend/OpenMP/OMPConstants.h"
#include <deque>
#include <memory>
#include <optional>
#include <string>
#include <tuple>
#include <vector>
 
namespace llvm {
  class APSInt;
  template <typename ValueT, typename ValueInfoT> class DenseSet;
  class SmallBitVector;
  struct InlineAsmIdentifierInfo;
}
 
namespace clang {
  class ADLResult;
  class ASTConsumer;
  class ASTContext;
  class ASTMutationListener;
  class ASTReader;
  class ASTWriter;
  class ArrayType;
  class ParsedAttr;
  class BindingDecl;
  class BlockDecl;
  class CapturedDecl;
  class CXXBasePath;
  class CXXBasePaths;
  class CXXBindTemporaryExpr;
  typedef SmallVector<CXXBaseSpecifier*, 4> CXXCastPath;
  class CXXConstructorDecl;
  class CXXConversionDecl;
  class CXXDeleteExpr;
  class CXXDestructorDecl;
  class CXXFieldCollector;
  class CXXMemberCallExpr;
  class CXXMethodDecl;
  class CXXScopeSpec;
  class CXXTemporary;
  class CXXTryStmt;
  class CallExpr;
  class ClassTemplateDecl;
  class ClassTemplatePartialSpecializationDecl;
  class ClassTemplateSpecializationDecl;
  class VarTemplatePartialSpecializationDecl;
  class CodeCompleteConsumer;
  class CodeCompletionAllocator;
  class CodeCompletionTUInfo;
  class CodeCompletionResult;
  class CoroutineBodyStmt;
  class Decl;
  class DeclAccessPair;
  class DeclContext;
  class DeclRefExpr;
  class DeclaratorDecl;
  class DeducedTemplateArgument;
  class DependentDiagnostic;
  class DesignatedInitExpr;
  class Designation;
  class EnableIfAttr;
  class EnumConstantDecl;
  class Expr;
  class ExtVectorType;
  class FormatAttr;
  class FriendDecl;
  class FunctionDecl;
  class FunctionProtoType;
  class FunctionTemplateDecl;
  class ImplicitConversionSequence;
  typedef MutableArrayRef<ImplicitConversionSequence> ConversionSequenceList;
  class InitListExpr;
  class InitializationKind;
  class InitializationSequence;
  class InitializedEntity;
  class IntegerLiteral;
  class LabelStmt;
  class LambdaExpr;
  class LangOptions;
  class LocalInstantiationScope;
  class LookupResult;
  class MacroInfo;
  typedef ArrayRef<std::pair<IdentifierInfo *, SourceLocation>> ModuleIdPath;
  class ModuleLoader;
  class MultiLevelTemplateArgumentList;
  class NamedDecl;
  class ObjCCategoryDecl;
  class ObjCCategoryImplDecl;
  class ObjCCompatibleAliasDecl;
  class ObjCContainerDecl;
  class ObjCImplDecl;
  class ObjCImplementationDecl;
  class ObjCInterfaceDecl;
  class ObjCIvarDecl;
  template <class T> class ObjCList;
  class ObjCMessageExpr;
  class ObjCMethodDecl;
  class ObjCPropertyDecl;
  class ObjCProtocolDecl;
  class OMPThreadPrivateDecl;
  class OMPRequiresDecl;
  class OMPDeclareReductionDecl;
  class OMPDeclareSimdDecl;
  class OMPClause;
  struct OMPVarListLocTy;
  struct OverloadCandidate;
  enum class OverloadCandidateParamOrder : char;
  enum OverloadCandidateRewriteKind : unsigned;
  class OverloadCandidateSet;
  class OverloadExpr;
  class ParenListExpr;
  class ParmVarDecl;
  class Preprocessor;
  class PseudoDestructorTypeStorage;
  class PseudoObjectExpr;
  class QualType;
  class StandardConversionSequence;
  class Stmt;
  class StringLiteral;
  class SwitchStmt;
  class TemplateArgument;
  class TemplateArgumentList;
  class TemplateArgumentLoc;
  class TemplateDecl;
  class TemplateInstantiationCallback;
  class TemplateParameterList;
  class TemplatePartialOrderingContext;
  class TemplateTemplateParmDecl;
  class Token;
  class TypeAliasDecl;
  class TypedefDecl;
  class TypedefNameDecl;
  class TypeLoc;
  class TypoCorrectionConsumer;
  class UnqualifiedId;
  class UnresolvedLookupExpr;
  class UnresolvedMemberExpr;
  class UnresolvedSetImpl;
  class UnresolvedSetIterator;
  class UsingDecl;
  class UsingShadowDecl;
  class ValueDecl;
  class VarDecl;
  class VarTemplateSpecializationDecl;
  class VisibilityAttr;
  class VisibleDeclConsumer;
  class IndirectFieldDecl;
  struct DeductionFailureInfo;
  class TemplateSpecCandidateSet;
 
namespace sema {
  class AccessedEntity;
  class BlockScopeInfo;
  class Capture;
  class CapturedRegionScopeInfo;
  class CapturingScopeInfo;
  class CompoundScopeInfo;
  class DelayedDiagnostic;
  class DelayedDiagnosticPool;
  class FunctionScopeInfo;
  class LambdaScopeInfo;
  class PossiblyUnreachableDiag;
  class RISCVIntrinsicManager;
  class SemaPPCallbacks;
  class TemplateDeductionInfo;
}
 
namespace threadSafety {
  class BeforeSet;
  void threadSafetyCleanup(BeforeSet* Cache);
}
 
// FIXME: No way to easily map from TemplateTypeParmTypes to
// TemplateTypeParmDecls, so we have this horrible PointerUnion.
typedef std::pair<llvm::PointerUnion<const TemplateTypeParmType *, NamedDecl *>,
                  SourceLocation>
    UnexpandedParameterPack;
 
/// Describes whether we've seen any nullability information for the given
/// file.
struct FileNullability {
  /// The first pointer declarator (of any pointer kind) in the file that does
  /// not have a corresponding nullability annotation.
  SourceLocation PointerLoc;
 
  /// The end location for the first pointer declarator in the file. Used for
  /// placing fix-its.
  SourceLocation PointerEndLoc;
 
  /// Which kind of pointer declarator we saw.
  uint8_t PointerKind;
 
  /// Whether we saw any type nullability annotations in the given file.
  bool SawTypeNullability = false;
};
 
/// A mapping from file IDs to a record of whether we've seen nullability
/// information in that file.
class FileNullabilityMap {
  /// A mapping from file IDs to the nullability information for each file ID.
  llvm::DenseMap<FileID, FileNullability> Map;
 
  /// A single-element cache based on the file ID.
  struct {
    FileID File;
    FileNullability Nullability;
  } Cache;
 
public:
  FileNullability &operator[](FileID file) {
    // Check the single-element cache.
    if (file == Cache.File)
      return Cache.Nullability;
 
    // It's not in the single-element cache; flush the cache if we have one.
    if (!Cache.File.isInvalid()) {
      Map[Cache.File] = Cache.Nullability;
    }
 
    // Pull this entry into the cache.
    Cache.File = file;
    Cache.Nullability = Map[file];
    return Cache.Nullability;
  }
};
 
/// Tracks expected type during expression parsing, for use in code completion.
/// The type is tied to a particular token, all functions that update or consume
/// the type take a start location of the token they are looking at as a
/// parameter. This avoids updating the type on hot paths in the parser.
class PreferredTypeBuilder {
public:
  PreferredTypeBuilder(bool Enabled) : Enabled(Enabled) {}
 
  void enterCondition(Sema &S, SourceLocation Tok);
  void enterReturn(Sema &S, SourceLocation Tok);
  void enterVariableInit(SourceLocation Tok, Decl *D);
  /// Handles e.g. BaseType{ .D = Tok...
  void enterDesignatedInitializer(SourceLocation Tok, QualType BaseType,
                                  const Designation &D);
  /// Computing a type for the function argument may require running
  /// overloading, so we postpone its computation until it is actually needed.
  ///
  /// Clients should be very careful when using this function, as it stores a
  /// function_ref, clients should make sure all calls to get() with the same
  /// location happen while function_ref is alive.
  ///
  /// The callback should also emit signature help as a side-effect, but only
  /// if the completion point has been reached.
  void enterFunctionArgument(SourceLocation Tok,
                             llvm::function_ref<QualType()> ComputeType);
 
  void enterParenExpr(SourceLocation Tok, SourceLocation LParLoc);
  void enterUnary(Sema &S, SourceLocation Tok, tok::TokenKind OpKind,
                  SourceLocation OpLoc);
  void enterBinary(Sema &S, SourceLocation Tok, Expr *LHS, tok::TokenKind Op);
  void enterMemAccess(Sema &S, SourceLocation Tok, Expr *Base);
  void enterSubscript(Sema &S, SourceLocation Tok, Expr *LHS);
  /// Handles all type casts, including C-style cast, C++ casts, etc.
  void enterTypeCast(SourceLocation Tok, QualType CastType);
 
  /// Get the expected type associated with this location, if any.
  ///
  /// If the location is a function argument, determining the expected type
  /// involves considering all function overloads and the arguments so far.
  /// In this case, signature help for these function overloads will be reported
  /// as a side-effect (only if the completion point has been reached).
  QualType get(SourceLocation Tok) const {
    if (!Enabled || Tok != ExpectedLoc)
      return QualType();
    if (!Type.isNull())
      return Type;
    if (ComputeType)
      return ComputeType();
    return QualType();
  }
 
private:
  bool Enabled;
  /// Start position of a token for which we store expected type.
  SourceLocation ExpectedLoc;
  /// Expected type for a token starting at ExpectedLoc.
  QualType Type;
  /// A function to compute expected type at ExpectedLoc. It is only considered
  /// if Type is null.
  llvm::function_ref<QualType()> ComputeType;
};
 
/// Sema - This implements semantic analysis and AST building for C.
class Sema final {
  Sema(const Sema &) = delete;
  void operator=(const Sema &) = delete;
 
  ///Source of additional semantic information.
  IntrusiveRefCntPtr<ExternalSemaSource> ExternalSource;
 
  static bool mightHaveNonExternalLinkage(const DeclaratorDecl *FD);
 
  /// Determine whether two declarations should be linked together, given that
  /// the old declaration might not be visible and the new declaration might
  /// not have external linkage.
  bool shouldLinkPossiblyHiddenDecl(const NamedDecl *Old,
                                    const NamedDecl *New) {
    if (isVisible(Old))
     return true;
    // See comment in below overload for why it's safe to compute the linkage
    // of the new declaration here.
    if (New->isExternallyDeclarable()) {
      assert(Old->isExternallyDeclarable() &&
             "should not have found a non-externally-declarable previous decl");
      return true;
    }
    return false;
  }
  bool shouldLinkPossiblyHiddenDecl(LookupResult &Old, const NamedDecl *New);
 
  void setupImplicitSpecialMemberType(CXXMethodDecl *SpecialMem,
                                      QualType ResultTy,
                                      ArrayRef<QualType> Args);
 
public:
  /// The maximum alignment, same as in llvm::Value. We duplicate them here
  /// because that allows us not to duplicate the constants in clang code,
  /// which we must to since we can't directly use the llvm constants.
  /// The value is verified against llvm here: lib/CodeGen/CGDecl.cpp
  ///
  /// This is the greatest alignment value supported by load, store, and alloca
  /// instructions, and global values.
  static const unsigned MaxAlignmentExponent = 32;
  static const uint64_t MaximumAlignment = 1ull << MaxAlignmentExponent;
 
  typedef OpaquePtr<DeclGroupRef> DeclGroupPtrTy;
  typedef OpaquePtr<TemplateName> TemplateTy;
  typedef OpaquePtr<QualType> TypeTy;
 
  OpenCLOptions OpenCLFeatures;
  FPOptions CurFPFeatures;
 
  const LangOptions &LangOpts;
  Preprocessor &PP;
  ASTContext &Context;
  ASTConsumer &Consumer;
  DiagnosticsEngine &Diags;
  SourceManager &SourceMgr;
  api_notes::APINotesManager APINotes;
 
  /// Flag indicating whether or not to collect detailed statistics.
  bool CollectStats;
 
  /// Code-completion consumer.
  CodeCompleteConsumer *CodeCompleter;
 
  /// CurContext - This is the current declaration context of parsing.
  DeclContext *CurContext;
 
  /// Generally null except when we temporarily switch decl contexts,
  /// like in \see ActOnObjCTemporaryExitContainerContext.
  DeclContext *OriginalLexicalContext;
 
  /// VAListTagName - The declaration name corresponding to __va_list_tag.
  /// This is used as part of a hack to omit that class from ADL results.
  DeclarationName VAListTagName;
 
  bool MSStructPragmaOn; // True when \#pragma ms_struct on
 
  /// Controls member pointer representation format under the MS ABI.
  LangOptions::PragmaMSPointersToMembersKind
      MSPointerToMemberRepresentationMethod;
 
  /// Stack of active SEH __finally scopes.  Can be empty.
  SmallVector<Scope*, 2> CurrentSEHFinally;
 
  /// Source location for newly created implicit MSInheritanceAttrs
  SourceLocation ImplicitMSInheritanceAttrLoc;
 
  /// Holds TypoExprs that are created from `createDelayedTypo`. This is used by
  /// `TransformTypos` in order to keep track of any TypoExprs that are created
  /// recursively during typo correction and wipe them away if the correction
  /// fails.
  llvm::SmallVector<TypoExpr *, 2> TypoExprs;
 
  /// pragma clang section kind
  enum PragmaClangSectionKind {
    PCSK_Invalid      = 0,
    PCSK_BSS          = 1,
    PCSK_Data         = 2,
    PCSK_Rodata       = 3,
    PCSK_Text         = 4,
    PCSK_Relro        = 5
   };
 
  enum PragmaClangSectionAction {
    PCSA_Set     = 0,
    PCSA_Clear   = 1
  };
 
  struct PragmaClangSection {
    std::string SectionName;
    bool Valid = false;
    SourceLocation PragmaLocation;
  };
 
   PragmaClangSection PragmaClangBSSSection;
   PragmaClangSection PragmaClangDataSection;
   PragmaClangSection PragmaClangRodataSection;
   PragmaClangSection PragmaClangRelroSection;
   PragmaClangSection PragmaClangTextSection;
 
  enum PragmaMsStackAction {
    PSK_Reset     = 0x0,                // #pragma ()
    PSK_Set       = 0x1,                // #pragma (value)
    PSK_Push      = 0x2,                // #pragma (push[, id])
    PSK_Pop       = 0x4,                // #pragma (pop[, id])
    PSK_Show      = 0x8,                // #pragma (show) -- only for "pack"!
    PSK_Push_Set  = PSK_Push | PSK_Set, // #pragma (push[, id], value)
    PSK_Pop_Set   = PSK_Pop | PSK_Set,  // #pragma (pop[, id], value)
  };
 
  struct PragmaPackInfo {
    PragmaMsStackAction Action;
    StringRef SlotLabel;
    Token Alignment;
  };
 
  // #pragma pack and align.
  class AlignPackInfo {
  public:
    // `Native` represents default align mode, which may vary based on the
    // platform.
    enum Mode : unsigned char { Native, Natural, Packed, Mac68k };
 
    // #pragma pack info constructor
    AlignPackInfo(AlignPackInfo::Mode M, unsigned Num, bool IsXL)
        : PackAttr(true), AlignMode(M), PackNumber(Num), XLStack(IsXL) {
      assert(Num == PackNumber && "The pack number has been truncated.");
    }
 
    // #pragma align info constructor
    AlignPackInfo(AlignPackInfo::Mode M, bool IsXL)
        : PackAttr(false), AlignMode(M),
          PackNumber(M == Packed ? 1 : UninitPackVal), XLStack(IsXL) {}
 
    explicit AlignPackInfo(bool IsXL) : AlignPackInfo(Native, IsXL) {}
 
    AlignPackInfo() : AlignPackInfo(Native, false) {}
 
    // When a AlignPackInfo itself cannot be used, this returns an 32-bit
    // integer encoding for it. This should only be passed to
    // AlignPackInfo::getFromRawEncoding, it should not be inspected directly.
    static uint32_t getRawEncoding(const AlignPackInfo &Info) {
      std::uint32_t Encoding{};
      if (Info.IsXLStack())
        Encoding |= IsXLMask;
 
      Encoding |= static_cast<uint32_t>(Info.getAlignMode()) << 1;
 
      if (Info.IsPackAttr())
        Encoding |= PackAttrMask;
 
      Encoding |= static_cast<uint32_t>(Info.getPackNumber()) << 4;
 
      return Encoding;
    }
 
    static AlignPackInfo getFromRawEncoding(unsigned Encoding) {
      bool IsXL = static_cast<bool>(Encoding & IsXLMask);
      AlignPackInfo::Mode M =
          static_cast<AlignPackInfo::Mode>((Encoding & AlignModeMask) >> 1);
      int PackNumber = (Encoding & PackNumMask) >> 4;
 
      if (Encoding & PackAttrMask)
        return AlignPackInfo(M, PackNumber, IsXL);
 
      return AlignPackInfo(M, IsXL);
    }
 
    bool IsPackAttr() const { return PackAttr; }
 
    bool IsAlignAttr() const { return !PackAttr; }
 
    Mode getAlignMode() const { return AlignMode; }
 
    unsigned getPackNumber() const { return PackNumber; }
 
    bool IsPackSet() const {
      // #pragma align, #pragma pack(), and #pragma pack(0) do not set the pack
      // attriute on a decl.
      return PackNumber != UninitPackVal && PackNumber != 0;
    }
 
    bool IsXLStack() const { return XLStack; }
 
    bool operator==(const AlignPackInfo &Info) const {
      return std::tie(AlignMode, PackNumber, PackAttr, XLStack) ==
             std::tie(Info.AlignMode, Info.PackNumber, Info.PackAttr,
                      Info.XLStack);
    }
 
    bool operator!=(const AlignPackInfo &Info) const {
      return !(*this == Info);
    }
 
  private:
    /// \brief True if this is a pragma pack attribute,
    ///         not a pragma align attribute.
    bool PackAttr;
 
    /// \brief The alignment mode that is in effect.
    Mode AlignMode;
 
    /// \brief The pack number of the stack.
    unsigned char PackNumber;
 
    /// \brief True if it is a XL #pragma align/pack stack.
    bool XLStack;
 
    /// \brief Uninitialized pack value.
    static constexpr unsigned char UninitPackVal = -1;
 
    // Masks to encode and decode an AlignPackInfo.
    static constexpr uint32_t IsXLMask{0x0000'0001};
    static constexpr uint32_t AlignModeMask{0x0000'0006};
    static constexpr uint32_t PackAttrMask{0x00000'0008};
    static constexpr uint32_t PackNumMask{0x0000'01F0};
  };
 
  template<typename ValueType>
  struct PragmaStack {
    struct Slot {
      llvm::StringRef StackSlotLabel;
      ValueType Value;
      SourceLocation PragmaLocation;
      SourceLocation PragmaPushLocation;
      Slot(llvm::StringRef StackSlotLabel, ValueType Value,
           SourceLocation PragmaLocation, SourceLocation PragmaPushLocation)
          : StackSlotLabel(StackSlotLabel), Value(Value),
            PragmaLocation(PragmaLocation),
            PragmaPushLocation(PragmaPushLocation) {}
    };
 
    void Act(SourceLocation PragmaLocation, PragmaMsStackAction Action,
             llvm::StringRef StackSlotLabel, ValueType Value) {
      if (Action == PSK_Reset) {
        CurrentValue = DefaultValue;
        CurrentPragmaLocation = PragmaLocation;
        return;
      }
      if (Action & PSK_Push)
        Stack.emplace_back(StackSlotLabel, CurrentValue, CurrentPragmaLocation,
                           PragmaLocation);
      else if (Action & PSK_Pop) {
        if (!StackSlotLabel.empty()) {
          // If we've got a label, try to find it and jump there.
          auto I = llvm::find_if(llvm::reverse(Stack), [&](const Slot &x) {
            return x.StackSlotLabel == StackSlotLabel;
          });
          // If we found the label so pop from there.
          if (I != Stack.rend()) {
            CurrentValue = I->Value;
            CurrentPragmaLocation = I->PragmaLocation;
            Stack.erase(std::prev(I.base()), Stack.end());
          }
        } else if (!Stack.empty()) {
          // We do not have a label, just pop the last entry.
          CurrentValue = Stack.back().Value;
          CurrentPragmaLocation = Stack.back().PragmaLocation;
          Stack.pop_back();
        }
      }
      if (Action & PSK_Set) {
        CurrentValue = Value;
        CurrentPragmaLocation = PragmaLocation;
      }
    }
 
    // MSVC seems to add artificial slots to #pragma stacks on entering a C++
    // method body to restore the stacks on exit, so it works like this:
    //
    //   struct S {
    //     #pragma <name>(push, InternalPragmaSlot, <current_pragma_value>)
    //     void Method {}
    //     #pragma <name>(pop, InternalPragmaSlot)
    //   };
    //
    // It works even with #pragma vtordisp, although MSVC doesn't support
    //   #pragma vtordisp(push [, id], n)
    // syntax.
    //
    // Push / pop a named sentinel slot.
    void SentinelAction(PragmaMsStackAction Action, StringRef Label) {
      assert((Action == PSK_Push || Action == PSK_Pop) &&
             "Can only push / pop #pragma stack sentinels!");
      Act(CurrentPragmaLocation, Action, Label, CurrentValue);
    }
 
    // Constructors.
    explicit PragmaStack(const ValueType &Default)
        : DefaultValue(Default), CurrentValue(Default) {}
 
    bool hasValue() const { return CurrentValue != DefaultValue; }
 
    SmallVector<Slot, 2> Stack;
    ValueType DefaultValue; // Value used for PSK_Reset action.
    ValueType CurrentValue;
    SourceLocation CurrentPragmaLocation;
  };
  // FIXME: We should serialize / deserialize these if they occur in a PCH (but
  // we shouldn't do so if they're in a module).
 
  /// Whether to insert vtordisps prior to virtual bases in the Microsoft
  /// C++ ABI.  Possible values are 0, 1, and 2, which mean:
  ///
  /// 0: Suppress all vtordisps
  /// 1: Insert vtordisps in the presence of vbase overrides and non-trivial
  ///    structors
  /// 2: Always insert vtordisps to support RTTI on partially constructed
  ///    objects
  PragmaStack<MSVtorDispMode> VtorDispStack;
  PragmaStack<AlignPackInfo> AlignPackStack;
  // The current #pragma align/pack values and locations at each #include.
  struct AlignPackIncludeState {
    AlignPackInfo CurrentValue;
    SourceLocation CurrentPragmaLocation;
    bool HasNonDefaultValue, ShouldWarnOnInclude;
  };
  SmallVector<AlignPackIncludeState, 8> AlignPackIncludeStack;
  // Segment #pragmas.
  PragmaStack<StringLiteral *> DataSegStack;
  PragmaStack<StringLiteral *> BSSSegStack;
  PragmaStack<StringLiteral *> ConstSegStack;
  PragmaStack<StringLiteral *> CodeSegStack;
 
  // #pragma strict_gs_check.
  PragmaStack<bool> StrictGuardStackCheckStack;
 
  // This stack tracks the current state of Sema.CurFPFeatures.
  PragmaStack<FPOptionsOverride> FpPragmaStack;
  FPOptionsOverride CurFPFeatureOverrides() {
    FPOptionsOverride result;
    if (!FpPragmaStack.hasValue()) {
      result = FPOptionsOverride();
    } else {
      result = FpPragmaStack.CurrentValue;
    }
    return result;
  }
 
  // Saves the current floating-point pragma stack and clear it in this Sema.
  class FpPragmaStackSaveRAII {
  public:
    FpPragmaStackSaveRAII(Sema &S)
        : S(S), SavedStack(std::move(S.FpPragmaStack)) {
      S.FpPragmaStack.Stack.clear();
    }
    ~FpPragmaStackSaveRAII() { S.FpPragmaStack = std::move(SavedStack); }
 
  private:
    Sema &S;
    PragmaStack<FPOptionsOverride> SavedStack;
  };
 
  void resetFPOptions(FPOptions FPO) {
    CurFPFeatures = FPO;
    FpPragmaStack.CurrentValue = FPO.getChangesFrom(FPOptions(LangOpts));
  }
 
  // RAII object to push / pop sentinel slots for all MS #pragma stacks.
  // Actions should be performed only if we enter / exit a C++ method body.
  class PragmaStackSentinelRAII {
  public:
    PragmaStackSentinelRAII(Sema &S, StringRef SlotLabel, bool ShouldAct);
    ~PragmaStackSentinelRAII();
 
  private:
    Sema &S;
    StringRef SlotLabel;
    bool ShouldAct;
  };
 
  /// A mapping that describes the nullability we've seen in each header file.
  FileNullabilityMap NullabilityMap;
 
  /// Last section used with #pragma init_seg.
  StringLiteral *CurInitSeg;
  SourceLocation CurInitSegLoc;
 
  /// Sections used with #pragma alloc_text.
  llvm::StringMap<std::tuple<StringRef, SourceLocation>> FunctionToSectionMap;
 
  /// VisContext - Manages the stack for \#pragma GCC visibility.
  void *VisContext; // Really a "PragmaVisStack*"
 
  /// This an attribute introduced by \#pragma clang attribute.
  struct PragmaAttributeEntry {
    SourceLocation Loc;
    ParsedAttr *Attribute;
    SmallVector<attr::SubjectMatchRule, 4> MatchRules;
    bool IsUsed;
  };
 
  /// A push'd group of PragmaAttributeEntries.
  struct PragmaAttributeGroup {
    /// The location of the push attribute.
    SourceLocation Loc;
    /// The namespace of this push group.
    const IdentifierInfo *Namespace;
    SmallVector<PragmaAttributeEntry, 2> Entries;
  };
 
  SmallVector<PragmaAttributeGroup, 2> PragmaAttributeStack;
 
  /// The declaration that is currently receiving an attribute from the
  /// #pragma attribute stack.
  const Decl *PragmaAttributeCurrentTargetDecl;
 
  /// This represents the last location of a "#pragma clang optimize off"
  /// directive if such a directive has not been closed by an "on" yet. If
  /// optimizations are currently "on", this is set to an invalid location.
  SourceLocation OptimizeOffPragmaLocation;
 
  /// The "on" or "off" argument passed by \#pragma optimize, that denotes
  /// whether the optimizations in the list passed to the pragma should be
  /// turned off or on. This boolean is true by default because command line
  /// options are honored when `#pragma optimize("", on)`.
  /// (i.e. `ModifyFnAttributeMSPragmaOptimze()` does nothing)
  bool MSPragmaOptimizeIsOn = true;
 
  /// Set of no-builtin functions listed by \#pragma function.
  llvm::SmallSetVector<StringRef, 4> MSFunctionNoBuiltins;
 
  /// Flag indicating if Sema is building a recovery call expression.
  ///
  /// This flag is used to avoid building recovery call expressions
  /// if Sema is already doing so, which would cause infinite recursions.
  bool IsBuildingRecoveryCallExpr;
 
  /// Used to control the generation of ExprWithCleanups.
  CleanupInfo Cleanup;
 
  /// ExprCleanupObjects - This is the stack of objects requiring
  /// cleanup that are created by the current full expression.
  SmallVector<ExprWithCleanups::CleanupObject, 8> ExprCleanupObjects;
 
  /// Store a set of either DeclRefExprs or MemberExprs that contain a reference
  /// to a variable (constant) that may or may not be odr-used in this Expr, and
  /// we won't know until all lvalue-to-rvalue and discarded value conversions
  /// have been applied to all subexpressions of the enclosing full expression.
  /// This is cleared at the end of each full expression.
  using MaybeODRUseExprSet = llvm::SmallSetVector<Expr *, 4>;
  MaybeODRUseExprSet MaybeODRUseExprs;
 
  std::unique_ptr<sema::FunctionScopeInfo> CachedFunctionScope;
 
  /// Stack containing information about each of the nested
  /// function, block, and method scopes that are currently active.
  SmallVector<sema::FunctionScopeInfo *, 4> FunctionScopes;
 
  /// The index of the first FunctionScope that corresponds to the current
  /// context.
  unsigned FunctionScopesStart = 0;
 
  /// Track the number of currently active capturing scopes.
  unsigned CapturingFunctionScopes = 0;
 
  ArrayRef<sema::FunctionScopeInfo*> getFunctionScopes() const {
    return llvm::ArrayRef(FunctionScopes.begin() + FunctionScopesStart,
                          FunctionScopes.end());
  }
 
  /// Stack containing information needed when in C++2a an 'auto' is encountered
  /// in a function declaration parameter type specifier in order to invent a
  /// corresponding template parameter in the enclosing abbreviated function
  /// template. This information is also present in LambdaScopeInfo, stored in
  /// the FunctionScopes stack.
  SmallVector<InventedTemplateParameterInfo, 4> InventedParameterInfos;
 
  /// The index of the first InventedParameterInfo that refers to the current
  /// context.
  unsigned InventedParameterInfosStart = 0;
 
  ArrayRef<InventedTemplateParameterInfo> getInventedParameterInfos() const {
    return llvm::ArrayRef(InventedParameterInfos.begin() +
                              InventedParameterInfosStart,
                          InventedParameterInfos.end());
  }
 
  typedef LazyVector<TypedefNameDecl *, ExternalSemaSource,
                     &ExternalSemaSource::ReadExtVectorDecls, 2, 2>
    ExtVectorDeclsType;
 
  /// ExtVectorDecls - This is a list all the extended vector types. This allows
  /// us to associate a raw vector type with one of the ext_vector type names.
  /// This is only necessary for issuing pretty diagnostics.
  ExtVectorDeclsType ExtVectorDecls;
 
  /// FieldCollector - Collects CXXFieldDecls during parsing of C++ classes.
  std::unique_ptr<CXXFieldCollector> FieldCollector;
 
  typedef llvm::SmallSetVector<const NamedDecl *, 16> NamedDeclSetType;
 
  /// Set containing all declared private fields that are not used.
  NamedDeclSetType UnusedPrivateFields;
 
  /// Set containing all typedefs that are likely unused.
  llvm::SmallSetVector<const TypedefNameDecl *, 4>
      UnusedLocalTypedefNameCandidates;
 
  /// Delete-expressions to be analyzed at the end of translation unit
  ///
  /// This list contains class members, and locations of delete-expressions
  /// that could not be proven as to whether they mismatch with new-expression
  /// used in initializer of the field.
  typedef std::pair<SourceLocation, bool> DeleteExprLoc;
  typedef llvm::SmallVector<DeleteExprLoc, 4> DeleteLocs;
  llvm::MapVector<FieldDecl *, DeleteLocs> DeleteExprs;
 
  typedef llvm::SmallPtrSet<const CXXRecordDecl*, 8> RecordDeclSetTy;
 
  /// PureVirtualClassDiagSet - a set of class declarations which we have
  /// emitted a list of pure virtual functions. Used to prevent emitting the
  /// same list more than once.
  std::unique_ptr<RecordDeclSetTy> PureVirtualClassDiagSet;
 
  /// ParsingInitForAutoVars - a set of declarations with auto types for which
  /// we are currently parsing the initializer.
  llvm::SmallPtrSet<const Decl*, 4> ParsingInitForAutoVars;
 
  /// Look for a locally scoped extern "C" declaration by the given name.
  NamedDecl *findLocallyScopedExternCDecl(DeclarationName Name);
 
  typedef LazyVector<VarDecl *, ExternalSemaSource,
                     &ExternalSemaSource::ReadTentativeDefinitions, 2, 2>
    TentativeDefinitionsType;
 
  /// All the tentative definitions encountered in the TU.
  TentativeDefinitionsType TentativeDefinitions;
 
  /// All the external declarations encoutered and used in the TU.
  SmallVector<VarDecl *, 4> ExternalDeclarations;
 
  typedef LazyVector<const DeclaratorDecl *, ExternalSemaSource,
                     &ExternalSemaSource::ReadUnusedFileScopedDecls, 2, 2>
    UnusedFileScopedDeclsType;
 
  /// The set of file scoped decls seen so far that have not been used
  /// and must warn if not used. Only contains the first declaration.
  UnusedFileScopedDeclsType UnusedFileScopedDecls;
 
  typedef LazyVector<CXXConstructorDecl *, ExternalSemaSource,
                     &ExternalSemaSource::ReadDelegatingConstructors, 2, 2>
    DelegatingCtorDeclsType;
 
  /// All the delegating constructors seen so far in the file, used for
  /// cycle detection at the end of the TU.
  DelegatingCtorDeclsType DelegatingCtorDecls;
 
  /// All the overriding functions seen during a class definition
  /// that had their exception spec checks delayed, plus the overridden
  /// function.
  SmallVector<std::pair<const CXXMethodDecl*, const CXXMethodDecl*>, 2>
    DelayedOverridingExceptionSpecChecks;
 
  /// All the function redeclarations seen during a class definition that had
  /// their exception spec checks delayed, plus the prior declaration they
  /// should be checked against. Except during error recovery, the new decl
  /// should always be a friend declaration, as that's the only valid way to
  /// redeclare a special member before its class is complete.
  SmallVector<std::pair<FunctionDecl*, FunctionDecl*>, 2>
    DelayedEquivalentExceptionSpecChecks;
 
  typedef llvm::MapVector<const FunctionDecl *,
                          std::unique_ptr<LateParsedTemplate>>
      LateParsedTemplateMapT;
  LateParsedTemplateMapT LateParsedTemplateMap;
 
  /// Callback to the parser to parse templated functions when needed.
  typedef void LateTemplateParserCB(void *P, LateParsedTemplate &LPT);
  typedef void LateTemplateParserCleanupCB(void *P);
  LateTemplateParserCB *LateTemplateParser;
  LateTemplateParserCleanupCB *LateTemplateParserCleanup;
  void *OpaqueParser;
 
  void SetLateTemplateParser(LateTemplateParserCB *LTP,
                             LateTemplateParserCleanupCB *LTPCleanup,
                             void *P) {
    LateTemplateParser = LTP;
    LateTemplateParserCleanup = LTPCleanup;
    OpaqueParser = P;
  }
 
  class DelayedDiagnostics;
 
  class DelayedDiagnosticsState {
    sema::DelayedDiagnosticPool *SavedPool = nullptr;
    friend class Sema::DelayedDiagnostics;
  };
  typedef DelayedDiagnosticsState ParsingDeclState;
  typedef DelayedDiagnosticsState ProcessingContextState;
 
  /// A class which encapsulates the logic for delaying diagnostics
  /// during parsing and other processing.
  class DelayedDiagnostics {
    /// The current pool of diagnostics into which delayed
    /// diagnostics should go.
    sema::DelayedDiagnosticPool *CurPool = nullptr;
 
  public:
    DelayedDiagnostics() = default;
 
    /// Adds a delayed diagnostic.
    void add(const sema::DelayedDiagnostic &diag); // in DelayedDiagnostic.h
 
    /// Determines whether diagnostics should be delayed.
    bool shouldDelayDiagnostics() { return CurPool != nullptr; }
 
    /// Returns the current delayed-diagnostics pool.
    sema::DelayedDiagnosticPool *getCurrentPool() const {
      return CurPool;
    }
 
    /// Enter a new scope.  Access and deprecation diagnostics will be
    /// collected in this pool.
    DelayedDiagnosticsState push(sema::DelayedDiagnosticPool &pool) {
      DelayedDiagnosticsState state;
      state.SavedPool = CurPool;
      CurPool = &pool;
      return state;
    }
 
    /// Leave a delayed-diagnostic state that was previously pushed.
    /// Do not emit any of the diagnostics.  This is performed as part
    /// of the bookkeeping of popping a pool "properly".
    void popWithoutEmitting(DelayedDiagnosticsState state) {
      CurPool = state.SavedPool;
    }
 
    /// Enter a new scope where access and deprecation diagnostics are
    /// not delayed.
    DelayedDiagnosticsState pushUndelayed() {
      DelayedDiagnosticsState state;
      state.SavedPool = CurPool;
      CurPool = nullptr;
      return state;
    }
 
    /// Undo a previous pushUndelayed().
    void popUndelayed(DelayedDiagnosticsState state) {
      assert(CurPool == nullptr);
      CurPool = state.SavedPool;
    }
  } DelayedDiagnostics;
 
  enum CUDAFunctionTarget {
    CFT_Device,
    CFT_Global,
    CFT_Host,
    CFT_HostDevice,
    CFT_InvalidTarget
  };
 
  /// A RAII object to temporarily push a declaration context.
  class ContextRAII {
  private:
    Sema &S;
    DeclContext *SavedContext;
    ProcessingContextState SavedContextState;
    QualType SavedCXXThisTypeOverride;
    unsigned SavedFunctionScopesStart;
    unsigned SavedInventedParameterInfosStart;
 
  public:
    ContextRAII(Sema &S, DeclContext *ContextToPush, bool NewThisContext = true)
      : S(S), SavedContext(S.CurContext),
        SavedContextState(S.DelayedDiagnostics.pushUndelayed()),
        SavedCXXThisTypeOverride(S.CXXThisTypeOverride),
        SavedFunctionScopesStart(S.FunctionScopesStart),
        SavedInventedParameterInfosStart(S.InventedParameterInfosStart)
    {
      assert(ContextToPush && "pushing null context");
      S.CurContext = ContextToPush;
      if (NewThisContext)
        S.CXXThisTypeOverride = QualType();
      // Any saved FunctionScopes do not refer to this context.
      S.FunctionScopesStart = S.FunctionScopes.size();
      S.InventedParameterInfosStart = S.InventedParameterInfos.size();
    }
 
    void pop() {
      if (!SavedContext) return;
      S.CurContext = SavedContext;
      S.DelayedDiagnostics.popUndelayed(SavedContextState);
      S.CXXThisTypeOverride = SavedCXXThisTypeOverride;
      S.FunctionScopesStart = SavedFunctionScopesStart;
      S.InventedParameterInfosStart = SavedInventedParameterInfosStart;
      SavedContext = nullptr;
    }
 
    ~ContextRAII() {
      pop();
    }
  };
 
  /// RAII object to handle the state changes required to synthesize
  /// a function body.
  class SynthesizedFunctionScope {
    Sema &S;
    Sema::ContextRAII SavedContext;
    bool PushedCodeSynthesisContext = false;
 
  public:
    SynthesizedFunctionScope(Sema &S, DeclContext *DC)
        : S(S), SavedContext(S, DC) {
      auto *FD = dyn_cast<FunctionDecl>(DC);
      S.PushFunctionScope();
      S.PushExpressionEvaluationContext(
          (FD && FD->isConsteval())
              ? ExpressionEvaluationContext::ImmediateFunctionContext
              : ExpressionEvaluationContext::PotentiallyEvaluated);
      if (FD) {
        FD->setWillHaveBody(true);
        S.ExprEvalContexts.back().InImmediateFunctionContext =
            FD->isImmediateFunction();
        S.ExprEvalContexts.back().InImmediateEscalatingFunctionContext =
            S.getLangOpts().CPlusPlus20 && FD->isImmediateEscalating();
      } else
        assert(isa<ObjCMethodDecl>(DC));
    }
 
    void addContextNote(SourceLocation UseLoc) {
      assert(!PushedCodeSynthesisContext);
 
      Sema::CodeSynthesisContext Ctx;
      Ctx.Kind = Sema::CodeSynthesisContext::DefiningSynthesizedFunction;
      Ctx.PointOfInstantiation = UseLoc;
      Ctx.Entity = cast<Decl>(S.CurContext);
      S.pushCodeSynthesisContext(Ctx);
 
      PushedCodeSynthesisContext = true;
    }
 
    ~SynthesizedFunctionScope() {
      if (PushedCodeSynthesisContext)
        S.popCodeSynthesisContext();
      if (auto *FD = dyn_cast<FunctionDecl>(S.CurContext)) {
        FD->setWillHaveBody(false);
        S.CheckImmediateEscalatingFunctionDefinition(FD, S.getCurFunction());
      }
      S.PopExpressionEvaluationContext();
      S.PopFunctionScopeInfo();
    }
  };
 
  /// WeakUndeclaredIdentifiers - Identifiers contained in \#pragma weak before
  /// declared. Rare. May alias another identifier, declared or undeclared.
  ///
  /// For aliases, the target identifier is used as a key for eventual
  /// processing when the target is declared. For the single-identifier form,
  /// the sole identifier is used as the key. Each entry is a `SetVector`
  /// (ordered by parse order) of aliases (identified by the alias name) in case
  /// of multiple aliases to the same undeclared identifier.
  llvm::MapVector<
      IdentifierInfo *,
      llvm::SetVector<
          WeakInfo, llvm::SmallVector<WeakInfo, 1u>,
          llvm::SmallDenseSet<WeakInfo, 2u, WeakInfo::DenseMapInfoByAliasOnly>>>
      WeakUndeclaredIdentifiers;
 
  /// ExtnameUndeclaredIdentifiers - Identifiers contained in
  /// \#pragma redefine_extname before declared.  Used in Solaris system headers
  /// to define functions that occur in multiple standards to call the version
  /// in the currently selected standard.
  llvm::DenseMap<IdentifierInfo*,AsmLabelAttr*> ExtnameUndeclaredIdentifiers;
 
 
  /// Load weak undeclared identifiers from the external source.
  void LoadExternalWeakUndeclaredIdentifiers();
 
  /// WeakTopLevelDecl - Translation-unit scoped declarations generated by
  /// \#pragma weak during processing of other Decls.
  /// I couldn't figure out a clean way to generate these in-line, so
  /// we store them here and handle separately -- which is a hack.
  /// It would be best to refactor this.
  SmallVector<Decl*,2> WeakTopLevelDecl;
 
  IdentifierResolver IdResolver;
 
  /// Translation Unit Scope - useful to Objective-C actions that need
  /// to lookup file scope declarations in the "ordinary" C decl namespace.
  /// For example, user-defined classes, built-in "id" type, etc.
  Scope *TUScope;
 
  /// The C++ "std" namespace, where the standard library resides.
  LazyDeclPtr StdNamespace;
 
  /// The C++ "std::bad_alloc" class, which is defined by the C++
  /// standard library.
  LazyDeclPtr StdBadAlloc;
 
  /// The C++ "std::align_val_t" enum class, which is defined by the C++
  /// standard library.
  LazyDeclPtr StdAlignValT;
 
  /// The C++ "std::initializer_list" template, which is defined in
  /// <initializer_list>.
  ClassTemplateDecl *StdInitializerList;
 
  /// The C++ "std::coroutine_traits" template, which is defined in
  /// <coroutine_traits>
  ClassTemplateDecl *StdCoroutineTraitsCache;
 
  /// The C++ "type_info" declaration, which is defined in <typeinfo>.
  RecordDecl *CXXTypeInfoDecl;
 
  /// The C++ "std::source_location::__impl" struct, defined in
  /// <source_location>.
  RecordDecl *StdSourceLocationImplDecl;
 
  /// Caches identifiers/selectors for NSFoundation APIs.
  std::unique_ptr<NSAPI> NSAPIObj;
 
  /// The declaration of the Objective-C NSNumber class.
  ObjCInterfaceDecl *NSNumberDecl;
 
  /// The declaration of the Objective-C NSValue class.
  ObjCInterfaceDecl *NSValueDecl;
 
  /// Pointer to NSNumber type (NSNumber *).
  QualType NSNumberPointer;
 
  /// Pointer to NSValue type (NSValue *).
  QualType NSValuePointer;
 
  /// The Objective-C NSNumber methods used to create NSNumber literals.
  ObjCMethodDecl *NSNumberLiteralMethods[NSAPI::NumNSNumberLiteralMethods];
 
  /// The declaration of the Objective-C NSString class.
  ObjCInterfaceDecl *NSStringDecl;
 
  /// Pointer to NSString type (NSString *).
  QualType NSStringPointer;
 
  /// The declaration of the stringWithUTF8String: method.
  ObjCMethodDecl *StringWithUTF8StringMethod;
 
  /// The declaration of the valueWithBytes:objCType: method.
  ObjCMethodDecl *ValueWithBytesObjCTypeMethod;
 
  /// The declaration of the Objective-C NSArray class.
  ObjCInterfaceDecl *NSArrayDecl;
 
  /// The declaration of the arrayWithObjects:count: method.
  ObjCMethodDecl *ArrayWithObjectsMethod;
 
  /// The declaration of the Objective-C NSDictionary class.
  ObjCInterfaceDecl *NSDictionaryDecl;
 
  /// The declaration of the dictionaryWithObjects:forKeys:count: method.
  ObjCMethodDecl *DictionaryWithObjectsMethod;
 
  /// id<NSCopying> type.
  QualType QIDNSCopying;
 
  /// will hold 'respondsToSelector:'
  Selector RespondsToSelectorSel;
 
  /// A flag to remember whether the implicit forms of operator new and delete
  /// have been declared.
  bool GlobalNewDeleteDeclared;
 
  /// Describes how the expressions currently being parsed are
  /// evaluated at run-time, if at all.
  enum class ExpressionEvaluationContext {
    /// The current expression and its subexpressions occur within an
    /// unevaluated operand (C++11 [expr]p7), such as the subexpression of
    /// \c sizeof, where the type of the expression may be significant but
    /// no code will be generated to evaluate the value of the expression at
    /// run time.
    Unevaluated,
 
    /// The current expression occurs within a braced-init-list within
    /// an unevaluated operand. This is mostly like a regular unevaluated
    /// context, except that we still instantiate constexpr functions that are
    /// referenced here so that we can perform narrowing checks correctly.
    UnevaluatedList,
 
    /// The current expression occurs within a discarded statement.
    /// This behaves largely similarly to an unevaluated operand in preventing
    /// definitions from being required, but not in other ways.
    DiscardedStatement,
 
    /// The current expression occurs within an unevaluated
    /// operand that unconditionally permits abstract references to
    /// fields, such as a SIZE operator in MS-style inline assembly.
    UnevaluatedAbstract,
 
    /// The current context is "potentially evaluated" in C++11 terms,
    /// but the expression is evaluated at compile-time (like the values of
    /// cases in a switch statement).
    ConstantEvaluated,
 
    /// In addition of being constant evaluated, the current expression
    /// occurs in an immediate function context - either a consteval function
    /// or a consteval if statement.
    ImmediateFunctionContext,
 
    /// The current expression is potentially evaluated at run time,
    /// which means that code may be generated to evaluate the value of the
    /// expression at run time.
    PotentiallyEvaluated,
 
    /// The current expression is potentially evaluated, but any
    /// declarations referenced inside that expression are only used if
    /// in fact the current expression is used.
    ///
    /// This value is used when parsing default function arguments, for which
    /// we would like to provide diagnostics (e.g., passing non-POD arguments
    /// through varargs) but do not want to mark declarations as "referenced"
    /// until the default argument is used.
    PotentiallyEvaluatedIfUsed
  };
 
  using ImmediateInvocationCandidate = llvm::PointerIntPair<ConstantExpr *, 1>;
 
  /// Data structure used to record current or nested
  /// expression evaluation contexts.
  struct ExpressionEvaluationContextRecord {
    /// The expression evaluation context.
    ExpressionEvaluationContext Context;
 
    /// Whether the enclosing context needed a cleanup.
    CleanupInfo ParentCleanup;
 
    /// The number of active cleanup objects when we entered
    /// this expression evaluation context.
    unsigned NumCleanupObjects;
 
    /// The number of typos encountered during this expression evaluation
    /// context (i.e. the number of TypoExprs created).
    unsigned NumTypos;
 
    MaybeODRUseExprSet SavedMaybeODRUseExprs;
 
    /// The lambdas that are present within this context, if it
    /// is indeed an unevaluated context.
    SmallVector<LambdaExpr *, 2> Lambdas;
 
    /// The declaration that provides context for lambda expressions
    /// and block literals if the normal declaration context does not
    /// suffice, e.g., in a default function argument.
    Decl *ManglingContextDecl;
 
    /// If we are processing a decltype type, a set of call expressions
    /// for which we have deferred checking the completeness of the return type.
    SmallVector<CallExpr *, 8> DelayedDecltypeCalls;
 
    /// If we are processing a decltype type, a set of temporary binding
    /// expressions for which we have deferred checking the destructor.
    SmallVector<CXXBindTemporaryExpr *, 8> DelayedDecltypeBinds;
 
    llvm::SmallPtrSet<const Expr *, 8> PossibleDerefs;
 
    /// Expressions appearing as the LHS of a volatile assignment in this
    /// context. We produce a warning for these when popping the context if
    /// they are not discarded-value expressions nor unevaluated operands.
    SmallVector<Expr*, 2> VolatileAssignmentLHSs;
 
    /// Set of candidates for starting an immediate invocation.
    llvm::SmallVector<ImmediateInvocationCandidate, 4> ImmediateInvocationCandidates;
 
    /// Set of DeclRefExprs referencing a consteval function when used in a
    /// context not already known to be immediately invoked.
    llvm::SmallPtrSet<DeclRefExpr *, 4> ReferenceToConsteval;
 
    /// \brief Describes whether we are in an expression constext which we have
    /// to handle differently.
    enum ExpressionKind {
      EK_Decltype, EK_TemplateArgument, EK_Other
    } ExprContext;
 
    // A context can be nested in both a discarded statement context and
    // an immediate function context, so they need to be tracked independently.
    bool InDiscardedStatement;
    bool InImmediateFunctionContext;
    bool InImmediateEscalatingFunctionContext;
 
    bool IsCurrentlyCheckingDefaultArgumentOrInitializer = false;
 
    // We are in a constant context, but we also allow
    // non constant expressions, for example for array bounds (which may be
    // VLAs).
    bool InConditionallyConstantEvaluateContext = false;
 
    // When evaluating immediate functions in the initializer of a default
    // argument or default member initializer, this is the declaration whose
    // default initializer is being evaluated and the location of the call
    // or constructor definition.
    struct InitializationContext {
      InitializationContext(SourceLocation Loc, ValueDecl *Decl,
                            DeclContext *Context)
          : Loc(Loc), Decl(Decl), Context(Context) {
        assert(Decl && Context && "invalid initialization context");
      }
 
      SourceLocation Loc;
      ValueDecl *Decl = nullptr;
      DeclContext *Context = nullptr;
    };
    std::optional<InitializationContext> DelayedDefaultInitializationContext;
 
    ExpressionEvaluationContextRecord(ExpressionEvaluationContext Context,
                                      unsigned NumCleanupObjects,
                                      CleanupInfo ParentCleanup,
                                      Decl *ManglingContextDecl,
                                      ExpressionKind ExprContext)
        : Context(Context), ParentCleanup(ParentCleanup),
          NumCleanupObjects(NumCleanupObjects), NumTypos(0),
          ManglingContextDecl(ManglingContextDecl), ExprContext(ExprContext),
          InDiscardedStatement(false), InImmediateFunctionContext(false),
          InImmediateEscalatingFunctionContext(false) {}
 
    bool isUnevaluated() const {
      return Context == ExpressionEvaluationContext::Unevaluated ||
             Context == ExpressionEvaluationContext::UnevaluatedAbstract ||
             Context == ExpressionEvaluationContext::UnevaluatedList;
    }
 
    bool isConstantEvaluated() const {
      return Context == ExpressionEvaluationContext::ConstantEvaluated ||
             Context == ExpressionEvaluationContext::ImmediateFunctionContext;
    }
 
    bool isImmediateFunctionContext() const {
      return Context == ExpressionEvaluationContext::ImmediateFunctionContext ||
             (Context == ExpressionEvaluationContext::DiscardedStatement &&
              InImmediateFunctionContext) ||
             // C++23 [expr.const]p14:
             // An expression or conversion is in an immediate function
             // context if it is potentially evaluated and either:
             //   * its innermost enclosing non-block scope is a function
             //     parameter scope of an immediate function, or
             //   * its enclosing statement is enclosed by the compound-
             //     statement of a consteval if statement.
             (Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
              InImmediateFunctionContext);
    }
 
    bool isDiscardedStatementContext() const {
      return Context == ExpressionEvaluationContext::DiscardedStatement ||
             (Context ==
                  ExpressionEvaluationContext::ImmediateFunctionContext &&
              InDiscardedStatement);
    }
  };
 
  /// A stack of expression evaluation contexts.
  SmallVector<ExpressionEvaluationContextRecord, 8> ExprEvalContexts;
 
  // Set of failed immediate invocations to avoid double diagnosing.
  llvm::SmallPtrSet<ConstantExpr *, 4> FailedImmediateInvocations;
 
  /// Emit a warning for all pending noderef expressions that we recorded.
  void WarnOnPendingNoDerefs(ExpressionEvaluationContextRecord &Rec);
 
  /// Compute the mangling number context for a lambda expression or
  /// block literal. Also return the extra mangling decl if any.
  ///
  /// \param DC - The DeclContext containing the lambda expression or
  /// block literal.
  std::tuple<MangleNumberingContext *, Decl *>
  getCurrentMangleNumberContext(const DeclContext *DC);
 
 
  /// SpecialMemberOverloadResult - The overloading result for a special member
  /// function.
  ///
  /// This is basically a wrapper around PointerIntPair. The lowest bits of the
  /// integer are used to determine whether overload resolution succeeded.
  class SpecialMemberOverloadResult {
  public:
    enum Kind {
      NoMemberOrDeleted,
      Ambiguous,
      Success
    };
 
  private:
    llvm::PointerIntPair<CXXMethodDecl *, 2> Pair;
 
  public:
    SpecialMemberOverloadResult() {}
    SpecialMemberOverloadResult(CXXMethodDecl *MD)
        : Pair(MD, MD->isDeleted() ? NoMemberOrDeleted : Success) {}
 
    CXXMethodDecl *getMethod() const { return Pair.getPointer(); }
    void setMethod(CXXMethodDecl *MD) { Pair.setPointer(MD); }
 
    Kind getKind() const { return static_cast<Kind>(Pair.getInt()); }
    void setKind(Kind K) { Pair.setInt(K); }
  };
 
  class SpecialMemberOverloadResultEntry
      : public llvm::FastFoldingSetNode,
        public SpecialMemberOverloadResult {
  public:
    SpecialMemberOverloadResultEntry(const llvm::FoldingSetNodeID &ID)
      : FastFoldingSetNode(ID)
    {}
  };
 
  /// A cache of special member function overload resolution results
  /// for C++ records.
  llvm::FoldingSet<SpecialMemberOverloadResultEntry> SpecialMemberCache;
 
  /// A cache of the flags available in enumerations with the flag_bits
  /// attribute.
  mutable llvm::DenseMap<const EnumDecl*, llvm::APInt> FlagBitsCache;
 
  /// The kind of translation unit we are processing.
  ///
  /// When we're processing a complete translation unit, Sema will perform
  /// end-of-translation-unit semantic tasks (such as creating
  /// initializers for tentative definitions in C) once parsing has
  /// completed. Modules and precompiled headers perform different kinds of
  /// checks.
  const TranslationUnitKind TUKind;
 
  llvm::BumpPtrAllocator BumpAlloc;
 
  /// The number of SFINAE diagnostics that have been trapped.
  unsigned NumSFINAEErrors;
 
  typedef llvm::DenseMap<ParmVarDecl *, llvm::TinyPtrVector<ParmVarDecl *>>
    UnparsedDefaultArgInstantiationsMap;
 
  /// A mapping from parameters with unparsed default arguments to the
  /// set of instantiations of each parameter.
  ///
  /// This mapping is a temporary data structure used when parsing
  /// nested class templates or nested classes of class templates,
  /// where we might end up instantiating an inner class before the
  /// default arguments of its methods have been parsed.
  UnparsedDefaultArgInstantiationsMap UnparsedDefaultArgInstantiations;
 
  // Contains the locations of the beginning of unparsed default
  // argument locations.
  llvm::DenseMap<ParmVarDecl *, SourceLocation> UnparsedDefaultArgLocs;
 
  /// UndefinedInternals - all the used, undefined objects which require a
  /// definition in this translation unit.
  llvm::MapVector<NamedDecl *, SourceLocation> UndefinedButUsed;
 
  /// Determine if VD, which must be a variable or function, is an external
  /// symbol that nonetheless can't be referenced from outside this translation
  /// unit because its type has no linkage and it's not extern "C".
  bool isExternalWithNoLinkageType(const ValueDecl *VD) const;
 
  /// Obtain a sorted list of functions that are undefined but ODR-used.
  void getUndefinedButUsed(
      SmallVectorImpl<std::pair<NamedDecl *, SourceLocation> > &Undefined);
 
  /// Retrieves list of suspicious delete-expressions that will be checked at
  /// the end of translation unit.
  const llvm::MapVector<FieldDecl *, DeleteLocs> &
  getMismatchingDeleteExpressions() const;
 
  class GlobalMethodPool {
  public:
    using Lists = std::pair<ObjCMethodList, ObjCMethodList>;
    using iterator = llvm::DenseMap<Selector, Lists>::iterator;
    iterator begin() { return Methods.begin(); }
    iterator end() { return Methods.end(); }
    iterator find(Selector Sel) { return Methods.find(Sel); }
    std::pair<iterator, bool> insert(std::pair<Selector, Lists> &&Val) {
      return Methods.insert(Val);
    }
    int count(Selector Sel) const { return Methods.count(Sel); }
    bool empty() const { return Methods.empty(); }
 
  private:
    llvm::DenseMap<Selector, Lists> Methods;
  };
 
  /// Method Pool - allows efficient lookup when typechecking messages to "id".
  /// We need to maintain a list, since selectors can have differing signatures
  /// across classes. In Cocoa, this happens to be extremely uncommon (only 1%
  /// of selectors are "overloaded").
  /// At the head of the list it is recorded whether there were 0, 1, or >= 2
  /// methods inside categories with a particular selector.
  GlobalMethodPool MethodPool;
 
  /// Method selectors used in a \@selector expression. Used for implementation
  /// of -Wselector.
  llvm::MapVector<Selector, SourceLocation> ReferencedSelectors;
 
  /// List of SourceLocations where 'self' is implicitly retained inside a
  /// block.
  llvm::SmallVector<std::pair<SourceLocation, const BlockDecl *>, 1>
      ImplicitlyRetainedSelfLocs;
 
  /// Kinds of C++ special members.
  enum CXXSpecialMember {
    CXXDefaultConstructor,
    CXXCopyConstructor,
    CXXMoveConstructor,
    CXXCopyAssignment,
    CXXMoveAssignment,
    CXXDestructor,
    CXXInvalid
  };
 
  typedef llvm::PointerIntPair<CXXRecordDecl *, 3, CXXSpecialMember>
      SpecialMemberDecl;
 
  /// The C++ special members which we are currently in the process of
  /// declaring. If this process recursively triggers the declaration of the
  /// same special member, we should act as if it is not yet declared.
  llvm::SmallPtrSet<SpecialMemberDecl, 4> SpecialMembersBeingDeclared;
 
  /// Kinds of defaulted comparison operator functions.
  enum class DefaultedComparisonKind : unsigned char {
    /// This is not a defaultable comparison operator.
    None,
    /// This is an operator== that should be implemented as a series of
    /// subobject comparisons.
    Equal,
    /// This is an operator<=> that should be implemented as a series of
    /// subobject comparisons.
    ThreeWay,
    /// This is an operator!= that should be implemented as a rewrite in terms
    /// of a == comparison.
    NotEqual,
    /// This is an <, <=, >, or >= that should be implemented as a rewrite in
    /// terms of a <=> comparison.
    Relational,
  };
 
  /// The function definitions which were renamed as part of typo-correction
  /// to match their respective declarations. We want to keep track of them
  /// to ensure that we don't emit a "redefinition" error if we encounter a
  /// correctly named definition after the renamed definition.
  llvm::SmallPtrSet<const NamedDecl *, 4> TypoCorrectedFunctionDefinitions;
 
  /// Stack of types that correspond to the parameter entities that are
  /// currently being copy-initialized. Can be empty.
  llvm::SmallVector<QualType, 4> CurrentParameterCopyTypes;
 
  void ReadMethodPool(Selector Sel);
  void updateOutOfDateSelector(Selector Sel);
 
  /// Private Helper predicate to check for 'self'.
  bool isSelfExpr(Expr *RExpr);
  bool isSelfExpr(Expr *RExpr, const ObjCMethodDecl *Method);
 
  /// Cause the active diagnostic on the DiagosticsEngine to be
  /// emitted. This is closely coupled to the SemaDiagnosticBuilder class and
  /// should not be used elsewhere.
  void EmitCurrentDiagnostic(unsigned DiagID);
 
  /// Records and restores the CurFPFeatures state on entry/exit of compound
  /// statements.
  class FPFeaturesStateRAII {
  public:
    FPFeaturesStateRAII(Sema &S);
    ~FPFeaturesStateRAII();
    FPOptionsOverride getOverrides() { return OldOverrides; }
 
  private:
    Sema& S;
    FPOptions OldFPFeaturesState;
    FPOptionsOverride OldOverrides;
    LangOptions::FPEvalMethodKind OldEvalMethod;
    SourceLocation OldFPPragmaLocation;
  };
 
  void addImplicitTypedef(StringRef Name, QualType T);
 
  bool WarnedStackExhausted = false;
 
  /// Increment when we find a reference; decrement when we find an ignored
  /// assignment.  Ultimately the value is 0 if every reference is an ignored
  /// assignment.
  llvm::DenseMap<const VarDecl *, int> RefsMinusAssignments;
 
  /// Indicate RISC-V vector builtin functions enabled or not.
  bool DeclareRISCVVBuiltins = false;
 
  /// Indicate RISC-V SiFive vector builtin functions enabled or not.
  bool DeclareRISCVSiFiveVectorBuiltins = false;
 
private:
  std::unique_ptr<sema::RISCVIntrinsicManager> RVIntrinsicManager;
 
  std::optional<std::unique_ptr<DarwinSDKInfo>> CachedDarwinSDKInfo;
 
  bool WarnedDarwinSDKInfoMissing = false;
 
public:
  Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer,
       TranslationUnitKind TUKind = TU_Complete,
       CodeCompleteConsumer *CompletionConsumer = nullptr);
  ~Sema();
 
  /// Perform initialization that occurs after the parser has been
  /// initialized but before it parses anything.
  void Initialize();
 
  /// This virtual key function only exists to limit the emission of debug info
  /// describing the Sema class. GCC and Clang only emit debug info for a class
  /// with a vtable when the vtable is emitted. Sema is final and not
  /// polymorphic, but the debug info size savings are so significant that it is
  /// worth adding a vtable just to take advantage of this optimization.
  virtual void anchor();
 
  const LangOptions &getLangOpts() const { return LangOpts; }
  OpenCLOptions &getOpenCLOptions() { return OpenCLFeatures; }
  FPOptions     &getCurFPFeatures() { return CurFPFeatures; }
 
  DiagnosticsEngine &getDiagnostics() const { return Diags; }
  SourceManager &getSourceManager() const { return SourceMgr; }
  Preprocessor &getPreprocessor() const { return PP; }
  ASTContext &getASTContext() const { return Context; }
  ASTConsumer &getASTConsumer() const { return Consumer; }
  ASTMutationListener *getASTMutationListener() const;
  ExternalSemaSource *getExternalSource() const { return ExternalSource.get(); }
 
  DarwinSDKInfo *getDarwinSDKInfoForAvailabilityChecking(SourceLocation Loc,
                                                         StringRef Platform);
  DarwinSDKInfo *getDarwinSDKInfoForAvailabilityChecking();
 
  ///Registers an external source. If an external source already exists,
  /// creates a multiplex external source and appends to it.
  ///
  ///\param[in] E - A non-null external sema source.
  ///
  void addExternalSource(ExternalSemaSource *E);
 
  void PrintStats() const;
 
  /// Warn that the stack is nearly exhausted.
  void warnStackExhausted(SourceLocation Loc);
 
  /// Run some code with "sufficient" stack space. (Currently, at least 256K is
  /// guaranteed). Produces a warning if we're low on stack space and allocates
  /// more in that case. Use this in code that may recurse deeply (for example,
  /// in template instantiation) to avoid stack overflow.
  void runWithSufficientStackSpace(SourceLocation Loc,
                                   llvm::function_ref<void()> Fn);
 
  /// Helper class that creates diagnostics with optional
  /// template instantiation stacks.
  ///
  /// This class provides a wrapper around the basic DiagnosticBuilder
  /// class that emits diagnostics. ImmediateDiagBuilder is
  /// responsible for emitting the diagnostic (as DiagnosticBuilder
  /// does) and, if the diagnostic comes from inside a template
  /// instantiation, printing the template instantiation stack as
  /// well.
  class ImmediateDiagBuilder : public DiagnosticBuilder {
    Sema &SemaRef;
    unsigned DiagID;
 
  public:
    ImmediateDiagBuilder(DiagnosticBuilder &DB, Sema &SemaRef, unsigned DiagID)
        : DiagnosticBuilder(DB), SemaRef(SemaRef), DiagID(DiagID) {}
    ImmediateDiagBuilder(DiagnosticBuilder &&DB, Sema &SemaRef, unsigned DiagID)
        : DiagnosticBuilder(DB), SemaRef(SemaRef), DiagID(DiagID) {}
 
    // This is a cunning lie. DiagnosticBuilder actually performs move
    // construction in its copy constructor (but due to varied uses, it's not
    // possible to conveniently express this as actual move construction). So
    // the default copy ctor here is fine, because the base class disables the
    // source anyway, so the user-defined ~ImmediateDiagBuilder is a safe no-op
    // in that case anwyay.
    ImmediateDiagBuilder(const ImmediateDiagBuilder &) = default;
 
    ~ImmediateDiagBuilder() {
      // If we aren't active, there is nothing to do.
      if (!isActive()) return;
 
      // Otherwise, we need to emit the diagnostic. First clear the diagnostic
      // builder itself so it won't emit the diagnostic in its own destructor.
      //
      // This seems wasteful, in that as written the DiagnosticBuilder dtor will
      // do its own needless checks to see if the diagnostic needs to be
      // emitted. However, because we take care to ensure that the builder
      // objects never escape, a sufficiently smart compiler will be able to
      // eliminate that code.
      Clear();
 
      // Dispatch to Sema to emit the diagnostic.
      SemaRef.EmitCurrentDiagnostic(DiagID);
    }
 
    /// Teach operator<< to produce an object of the correct type.
    template <typename T>
    friend const ImmediateDiagBuilder &
    operator<<(const ImmediateDiagBuilder &Diag, const T &Value) {
      const DiagnosticBuilder &BaseDiag = Diag;
      BaseDiag << Value;
      return Diag;
    }
 
    // It is necessary to limit this to rvalue reference to avoid calling this
    // function with a bitfield lvalue argument since non-const reference to
    // bitfield is not allowed.
    template <typename T,
              typename = std::enable_if_t<!std::is_lvalue_reference<T>::value>>
    const ImmediateDiagBuilder &operator<<(T &&V) const {
      const DiagnosticBuilder &BaseDiag = *this;
      BaseDiag << std::move(V);
      return *this;
    }
  };
 
  /// A generic diagnostic builder for errors which may or may not be deferred.
  ///
  /// In CUDA, there exist constructs (e.g. variable-length arrays, try/catch)
  /// which are not allowed to appear inside __device__ functions and are
  /// allowed to appear in __host__ __device__ functions only if the host+device
  /// function is never codegen'ed.
  ///
  /// To handle this, we use the notion of "deferred diagnostics", where we
  /// attach a diagnostic to a FunctionDecl that's emitted iff it's codegen'ed.
  ///
  /// This class lets you emit either a regular diagnostic, a deferred
  /// diagnostic, or no diagnostic at all, according to an argument you pass to
  /// its constructor, thus simplifying the process of creating these "maybe
  /// deferred" diagnostics.
  class SemaDiagnosticBuilder {
  public:
    enum Kind {
      /// Emit no diagnostics.
      K_Nop,
      /// Emit the diagnostic immediately (i.e., behave like Sema::Diag()).
      K_Immediate,
      /// Emit the diagnostic immediately, and, if it's a warning or error, also
      /// emit a call stack showing how this function can be reached by an a
      /// priori known-emitted function.
      K_ImmediateWithCallStack,
      /// Create a deferred diagnostic, which is emitted only if the function
      /// it's attached to is codegen'ed.  Also emit a call stack as with
      /// K_ImmediateWithCallStack.
      K_Deferred
    };
 
    SemaDiagnosticBuilder(Kind K, SourceLocation Loc, unsigned DiagID,
                          const FunctionDecl *Fn, Sema &S);
    SemaDiagnosticBuilder(SemaDiagnosticBuilder &&D);
    SemaDiagnosticBuilder(const SemaDiagnosticBuilder &) = default;
 
    // The copy and move assignment operator is defined as deleted pending
    // further motivation.
    SemaDiagnosticBuilder &operator=(const SemaDiagnosticBuilder &) = delete;
    SemaDiagnosticBuilder &operator=(SemaDiagnosticBuilder &&) = delete;
 
    ~SemaDiagnosticBuilder();
 
    bool isImmediate() const { return ImmediateDiag.has_value(); }
 
    /// Convertible to bool: True if we immediately emitted an error, false if
    /// we didn't emit an error or we created a deferred error.
    ///
    /// Example usage:
    ///
    ///   if (SemaDiagnosticBuilder(...) << foo << bar)
    ///     return ExprError();
    ///
    /// But see CUDADiagIfDeviceCode() and CUDADiagIfHostCode() -- you probably
    /// want to use these instead of creating a SemaDiagnosticBuilder yourself.
    operator bool() const { return isImmediate(); }
 
    template <typename T>
    friend const SemaDiagnosticBuilder &
    operator<<(const SemaDiagnosticBuilder &Diag, const T &Value) {
      if (Diag.ImmediateDiag)
        *Diag.ImmediateDiag << Value;
      else if (Diag.PartialDiagId)
        Diag.S.DeviceDeferredDiags[Diag.Fn][*Diag.PartialDiagId].second
            << Value;
      return Diag;
    }
 
    // It is necessary to limit this to rvalue reference to avoid calling this
    // function with a bitfield lvalue argument since non-const reference to
    // bitfield is not allowed.
    template <typename T,
              typename = std::enable_if_t<!std::is_lvalue_reference<T>::value>>
    const SemaDiagnosticBuilder &operator<<(T &&V) const {
      if (ImmediateDiag)
        *ImmediateDiag << std::move(V);
      else if (PartialDiagId)
        S.DeviceDeferredDiags[Fn][*PartialDiagId].second << std::move(V);
      return *this;
    }
 
    friend const SemaDiagnosticBuilder &
    operator<<(const SemaDiagnosticBuilder &Diag, const PartialDiagnostic &PD) {
      if (Diag.ImmediateDiag)
        PD.Emit(*Diag.ImmediateDiag);
      else if (Diag.PartialDiagId)
        Diag.S.DeviceDeferredDiags[Diag.Fn][*Diag.PartialDiagId].second = PD;
      return Diag;
    }
 
    void AddFixItHint(const FixItHint &Hint) const {
      if (ImmediateDiag)
        ImmediateDiag->AddFixItHint(Hint);
      else if (PartialDiagId)
        S.DeviceDeferredDiags[Fn][*PartialDiagId].second.AddFixItHint(Hint);
    }
 
    friend ExprResult ExprError(const SemaDiagnosticBuilder &) {
      return ExprError();
    }
    friend StmtResult StmtError(const SemaDiagnosticBuilder &) {
      return StmtError();
    }
    operator ExprResult() const { return ExprError(); }
    operator StmtResult() const { return StmtError(); }
    operator TypeResult() const { return TypeError(); }
    operator DeclResult() const { return DeclResult(true); }
    operator MemInitResult() const { return MemInitResult(true); }
 
  private:
    Sema &S;
    SourceLocation Loc;
    unsigned DiagID;
    const FunctionDecl *Fn;
    bool ShowCallStack;
 
    // Invariant: At most one of these Optionals has a value.
    // FIXME: Switch these to a Variant once that exists.
    std::optional<ImmediateDiagBuilder> ImmediateDiag;
    std::optional<unsigned> PartialDiagId;
  };
 
  /// Is the last error level diagnostic immediate. This is used to determined
  /// whether the next info diagnostic should be immediate.
  bool IsLastErrorImmediate = true;
 
  /// Emit a diagnostic.
  SemaDiagnosticBuilder Diag(SourceLocation Loc, unsigned DiagID,
                             bool DeferHint = false);
 
  /// Emit a partial diagnostic.
  SemaDiagnosticBuilder Diag(SourceLocation Loc, const PartialDiagnostic &PD,
                             bool DeferHint = false);
 
  /// Build a partial diagnostic.
  PartialDiagnostic PDiag(unsigned DiagID = 0); // in SemaInternal.h
 
  /// Whether deferrable diagnostics should be deferred.
  bool DeferDiags = false;
 
  /// RAII class to control scope of DeferDiags.
  class DeferDiagsRAII {
    Sema &S;
    bool SavedDeferDiags = false;
 
  public:
    DeferDiagsRAII(Sema &S, bool DeferDiags)
        : S(S), SavedDeferDiags(S.DeferDiags) {
      S.DeferDiags = DeferDiags;
    }
    ~DeferDiagsRAII() { S.DeferDiags = SavedDeferDiags; }
  };
 
  /// Whether uncompilable error has occurred. This includes error happens
  /// in deferred diagnostics.
  bool hasUncompilableErrorOccurred() const;
 
  bool findMacroSpelling(SourceLocation &loc, StringRef name);
 
  /// Get a string to suggest for zero-initialization of a type.
  std::string
  getFixItZeroInitializerForType(QualType T, SourceLocation Loc) const;
  std::string getFixItZeroLiteralForType(QualType T, SourceLocation Loc) const;
 
  /// Calls \c Lexer::getLocForEndOfToken()
  SourceLocation getLocForEndOfToken(SourceLocation Loc, unsigned Offset = 0);
 
  /// Retrieve the module loader associated with the preprocessor.
  ModuleLoader &getModuleLoader() const;
 
  /// Invent a new identifier for parameters of abbreviated templates.
  IdentifierInfo *
  InventAbbreviatedTemplateParameterTypeName(IdentifierInfo *ParamName,
                                             unsigned Index);
 
  void emitAndClearUnusedLocalTypedefWarnings();
 
  private:
    /// Function or variable declarations to be checked for whether the deferred
    /// diagnostics should be emitted.
    llvm::SmallSetVector<Decl *, 4> DeclsToCheckForDeferredDiags;
 
  public:
  // Emit all deferred diagnostics.
  void emitDeferredDiags();
 
  enum TUFragmentKind {
    /// The global module fragment, between 'module;' and a module-declaration.
    Global,
    /// A normal translation unit fragment. For a non-module unit, this is the
    /// entire translation unit. Otherwise, it runs from the module-declaration
    /// to the private-module-fragment (if any) or the end of the TU (if not).
    Normal,
    /// The private module fragment, between 'module :private;' and the end of
    /// the translation unit.
    Private
  };
 
  void ActOnStartOfTranslationUnit();
  void ActOnEndOfTranslationUnit();
  void ActOnEndOfTranslationUnitFragment(TUFragmentKind Kind);
 
  void CheckDelegatingCtorCycles();
 
  Scope *getScopeForContext(DeclContext *Ctx);
 
  void PushFunctionScope();
  void PushBlockScope(Scope *BlockScope, BlockDecl *Block);
  sema::LambdaScopeInfo *PushLambdaScope();
 
  /// This is used to inform Sema what the current TemplateParameterDepth
  /// is during Parsing.  Currently it is used to pass on the depth
  /// when parsing generic lambda 'auto' parameters.
  void RecordParsingTemplateParameterDepth(unsigned Depth);
 
  void PushCapturedRegionScope(Scope *RegionScope, CapturedDecl *CD,
                               RecordDecl *RD, CapturedRegionKind K,
                               unsigned OpenMPCaptureLevel = 0);
 
  /// Custom deleter to allow FunctionScopeInfos to be kept alive for a short
  /// time after they've been popped.
  class PoppedFunctionScopeDeleter {
    Sema *Self;
 
  public:
    explicit PoppedFunctionScopeDeleter(Sema *Self) : Self(Self) {}
    void operator()(sema::FunctionScopeInfo *Scope) const;
  };
 
  using PoppedFunctionScopePtr =
      std::unique_ptr<sema::FunctionScopeInfo, PoppedFunctionScopeDeleter>;
 
  PoppedFunctionScopePtr
  PopFunctionScopeInfo(const sema::AnalysisBasedWarnings::Policy *WP = nullptr,
                       const Decl *D = nullptr,
                       QualType BlockType = QualType());
 
  sema::FunctionScopeInfo *getCurFunction() const {
    return FunctionScopes.empty() ? nullptr : FunctionScopes.back();
  }
 
  sema::FunctionScopeInfo *getEnclosingFunction() const;
 
  void setFunctionHasBranchIntoScope();
  void setFunctionHasBranchProtectedScope();
  void setFunctionHasIndirectGoto();
  void setFunctionHasMustTail();
 
  void PushCompoundScope(bool IsStmtExpr);
  void PopCompoundScope();
 
  sema::CompoundScopeInfo &getCurCompoundScope() const;
 
  bool hasAnyUnrecoverableErrorsInThisFunction() const;
 
  /// Retrieve the current block, if any.
  sema::BlockScopeInfo *getCurBlock();
 
  /// Get the innermost lambda enclosing the current location, if any. This
  /// looks through intervening non-lambda scopes such as local functions and
  /// blocks.
  sema::LambdaScopeInfo *getEnclosingLambda() const;
 
  /// Retrieve the current lambda scope info, if any.
  /// \param IgnoreNonLambdaCapturingScope true if should find the top-most
  /// lambda scope info ignoring all inner capturing scopes that are not
  /// lambda scopes.
  sema::LambdaScopeInfo *
  getCurLambda(bool IgnoreNonLambdaCapturingScope = false);
 
  /// Retrieve the current generic lambda info, if any.
  sema::LambdaScopeInfo *getCurGenericLambda();
 
  /// Retrieve the current captured region, if any.
  sema::CapturedRegionScopeInfo *getCurCapturedRegion();
 
  /// Retrieve the current function, if any, that should be analyzed for
  /// potential availability violations.
  sema::FunctionScopeInfo *getCurFunctionAvailabilityContext();
 
  /// WeakTopLevelDeclDecls - access to \#pragma weak-generated Decls
  SmallVectorImpl<Decl *> &WeakTopLevelDecls() { return WeakTopLevelDecl; }
 
  /// Called before parsing a function declarator belonging to a function
  /// declaration.
  void ActOnStartFunctionDeclarationDeclarator(Declarator &D,
                                               unsigned TemplateParameterDepth);
 
  /// Called after parsing a function declarator belonging to a function
  /// declaration.
  void ActOnFinishFunctionDeclarationDeclarator(Declarator &D);
 
  void ActOnComment(SourceRange Comment);
 
  //===--------------------------------------------------------------------===//
  // Type Analysis / Processing: SemaType.cpp.
  //
 
  QualType BuildQualifiedType(QualType T, SourceLocation Loc, Qualifiers Qs,
                              const DeclSpec *DS = nullptr);
  QualType BuildQualifiedType(QualType T, SourceLocation Loc, unsigned CVRA,
                              const DeclSpec *DS = nullptr);
  QualType BuildPointerType(QualType T,
                            SourceLocation Loc, DeclarationName Entity);
  QualType BuildReferenceType(QualType T, bool LValueRef,
                              SourceLocation Loc, DeclarationName Entity);
  QualType BuildArrayType(QualType T, ArraySizeModifier ASM, Expr *ArraySize,
                          unsigned Quals, SourceRange Brackets,
                          DeclarationName Entity);
  QualType BuildVectorType(QualType T, Expr *VecSize, SourceLocation AttrLoc);
  QualType BuildExtVectorType(QualType T, Expr *ArraySize,
                              SourceLocation AttrLoc);
  QualType BuildMatrixType(QualType T, Expr *NumRows, Expr *NumColumns,
                           SourceLocation AttrLoc);
 
  QualType BuildAddressSpaceAttr(QualType &T, LangAS ASIdx, Expr *AddrSpace,
                                 SourceLocation AttrLoc);
 
  /// Same as above, but constructs the AddressSpace index if not provided.
  QualType BuildAddressSpaceAttr(QualType &T, Expr *AddrSpace,
                                 SourceLocation AttrLoc);
 
  CodeAlignAttr *BuildCodeAlignAttr(const AttributeCommonInfo &CI, Expr *E);
  bool CheckRebuiltCodeAlignStmtAttributes(ArrayRef<const Attr *> Attrs);
 
  bool CheckQualifiedFunctionForTypeId(QualType T, SourceLocation Loc);
 
  bool CheckFunctionReturnType(QualType T, SourceLocation Loc);
 
  /// Build a function type.
  ///
  /// This routine checks the function type according to C++ rules and
  /// under the assumption that the result type and parameter types have
  /// just been instantiated from a template. It therefore duplicates
  /// some of the behavior of GetTypeForDeclarator, but in a much
  /// simpler form that is only suitable for this narrow use case.
  ///
  /// \param T The return type of the function.
  ///
  /// \param ParamTypes The parameter types of the function. This array
  /// will be modified to account for adjustments to the types of the
  /// function parameters.
  ///
  /// \param Loc The location of the entity whose type involves this
  /// function type or, if there is no such entity, the location of the
  /// type that will have function type.
  ///
  /// \param Entity The name of the entity that involves the function
  /// type, if known.
  ///
  /// \param EPI Extra information about the function type. Usually this will
  /// be taken from an existing function with the same prototype.
  ///
  /// \returns A suitable function type, if there are no errors. The
  /// unqualified type will always be a FunctionProtoType.
  /// Otherwise, returns a NULL type.
  QualType BuildFunctionType(QualType T,
                             MutableArrayRef<QualType> ParamTypes,
                             SourceLocation Loc, DeclarationName Entity,
                             const FunctionProtoType::ExtProtoInfo &EPI);
 
  QualType BuildMemberPointerType(QualType T, QualType Class,
                                  SourceLocation Loc,
                                  DeclarationName Entity);
  QualType BuildBlockPointerType(QualType T,
                                 SourceLocation Loc, DeclarationName Entity);
  QualType BuildParenType(QualType T);
  QualType BuildAtomicType(QualType T, SourceLocation Loc);
  QualType BuildReadPipeType(QualType T,
                         SourceLocation Loc);
  QualType BuildWritePipeType(QualType T,
                         SourceLocation Loc);
  QualType BuildBitIntType(bool IsUnsigned, Expr *BitWidth, SourceLocation Loc);
 
  TypeSourceInfo *GetTypeForDeclarator(Declarator &D, Scope *S);
  TypeSourceInfo *GetTypeForDeclaratorCast(Declarator &D, QualType FromTy);
 
  /// Package the given type and TSI into a ParsedType.
  ParsedType CreateParsedType(QualType T, TypeSourceInfo *TInfo);
  DeclarationNameInfo GetNameForDeclarator(Declarator &D);
  DeclarationNameInfo GetNameFromUnqualifiedId(const UnqualifiedId &Name);
  static QualType GetTypeFromParser(ParsedType Ty,
                                    TypeSourceInfo **TInfo = nullptr);
  CanThrowResult canThrow(const Stmt *E);
  /// Determine whether the callee of a particular function call can throw.
  /// E, D and Loc are all optional.
  static CanThrowResult canCalleeThrow(Sema &S, const Expr *E, const Decl *D,
                                       SourceLocation Loc = SourceLocation());
  const FunctionProtoType *ResolveExceptionSpec(SourceLocation Loc,
                                                const FunctionProtoType *FPT);
  void UpdateExceptionSpec(FunctionDecl *FD,
                           const FunctionProtoType::ExceptionSpecInfo &ESI);
  bool CheckSpecifiedExceptionType(QualType &T, SourceRange Range);
  bool CheckDistantExceptionSpec(QualType T);
  bool CheckEquivalentExceptionSpec(FunctionDecl *Old, FunctionDecl *New);
  bool CheckEquivalentExceptionSpec(
      const FunctionProtoType *Old, SourceLocation OldLoc,
      const FunctionProtoType *New, SourceLocation NewLoc);
  bool CheckEquivalentExceptionSpec(
      const PartialDiagnostic &DiagID, const PartialDiagnostic & NoteID,
      const FunctionProtoType *Old, SourceLocation OldLoc,
      const FunctionProtoType *New, SourceLocation NewLoc);
  bool handlerCanCatch(QualType HandlerType, QualType ExceptionType);
  bool CheckExceptionSpecSubset(
      const PartialDiagnostic &DiagID, const PartialDiagnostic &NestedDiagID,
      const PartialDiagnostic &NoteID, const PartialDiagnostic &NoThrowDiagID,
      const FunctionProtoType *Superset, bool SkipSupersetFirstParameter,
      SourceLocation SuperLoc, const FunctionProtoType *Subset,
      bool SkipSubsetFirstParameter, SourceLocation SubLoc);
  bool CheckParamExceptionSpec(
      const PartialDiagnostic &NestedDiagID, const PartialDiagnostic &NoteID,
      const FunctionProtoType *Target, bool SkipTargetFirstParameter,
      SourceLocation TargetLoc, const FunctionProtoType *Source,
      bool SkipSourceFirstParameter, SourceLocation SourceLoc);
 
  TypeResult ActOnTypeName(Scope *S, Declarator &D);
 
  /// The parser has parsed the context-sensitive type 'instancetype'
  /// in an Objective-C message declaration. Return the appropriate type.
  ParsedType ActOnObjCInstanceType(SourceLocation Loc);
 
  /// Abstract class used to diagnose incomplete types.
  struct TypeDiagnoser {
    TypeDiagnoser() {}
 
    virtual void diagnose(Sema &S, SourceLocation Loc, QualType T) = 0;
    virtual ~TypeDiagnoser() {}
  };
 
  static int getPrintable(int I) { return I; }
  static unsigned getPrintable(unsigned I) { return I; }
  static bool getPrintable(bool B) { return B; }
  static const char * getPrintable(const char *S) { return S; }
  static StringRef getPrintable(StringRef S) { return S; }
  static const std::string &getPrintable(const std::string &S) { return S; }
  static const IdentifierInfo *getPrintable(const IdentifierInfo *II) {
    return II;
  }
  static DeclarationName getPrintable(DeclarationName N) { return N; }
  static QualType getPrintable(QualType T) { return T; }
  static SourceRange getPrintable(SourceRange R) { return R; }
  static SourceRange getPrintable(SourceLocation L) { return L; }
  static SourceRange getPrintable(const Expr *E) { return E->getSourceRange(); }
  static SourceRange getPrintable(TypeLoc TL) { return TL.getSourceRange();}
 
  template <typename... Ts> class BoundTypeDiagnoser : public TypeDiagnoser {
  protected:
    unsigned DiagID;
    std::tuple<const Ts &...> Args;
 
    template <std::size_t... Is>
    void emit(const SemaDiagnosticBuilder &DB,
              std::index_sequence<Is...>) const {
      // Apply all tuple elements to the builder in order.
      bool Dummy[] = {false, (DB << getPrintable(std::get<Is>(Args)))...};
      (void)Dummy;
    }
 
  public:
    BoundTypeDiagnoser(unsigned DiagID, const Ts &...Args)
        : TypeDiagnoser(), DiagID(DiagID), Args(Args...) {
      assert(DiagID != 0 && "no diagnostic for type diagnoser");
    }
 
    void diagnose(Sema &S, SourceLocation Loc, QualType T) override {
      const SemaDiagnosticBuilder &DB = S.Diag(Loc, DiagID);
      emit(DB, std::index_sequence_for<Ts...>());
      DB << T;
    }
  };
 
  /// Do a check to make sure \p Name looks like a legal argument for the
  /// swift_name attribute applied to decl \p D.  Raise a diagnostic if the name
  /// is invalid for the given declaration.
  ///
  /// \p AL is used to provide caret diagnostics in case of a malformed name.
  ///
  /// \returns true if the name is a valid swift name for \p D, false otherwise.
  bool DiagnoseSwiftName(Decl *D, StringRef Name, SourceLocation Loc,
                         const ParsedAttr &AL, bool IsAsync);
 
  /// A derivative of BoundTypeDiagnoser for which the diagnostic's type
  /// parameter is preceded by a 0/1 enum that is 1 if the type is sizeless.
  /// For example, a diagnostic with no other parameters would generally have
  /// the form "...%select{incomplete|sizeless}0 type %1...".
  template <typename... Ts>
  class SizelessTypeDiagnoser : public BoundTypeDiagnoser<Ts...> {
  public:
    SizelessTypeDiagnoser(unsigned DiagID, const Ts &... Args)
        : BoundTypeDiagnoser<Ts...>(DiagID, Args...) {}
 
    void diagnose(Sema &S, SourceLocation Loc, QualType T) override {
      const SemaDiagnosticBuilder &DB = S.Diag(Loc, this->DiagID);
      this->emit(DB, std::index_sequence_for<Ts...>());
      DB << T->isSizelessType() << T;
    }
  };
 
  enum class CompleteTypeKind {
    /// Apply the normal rules for complete types.  In particular,
    /// treat all sizeless types as incomplete.
    Normal,
 
    /// Relax the normal rules for complete types so that they include
    /// sizeless built-in types.
    AcceptSizeless,
 
    // FIXME: Eventually we should flip the default to Normal and opt in
    // to AcceptSizeless rather than opt out of it.
    Default = AcceptSizeless
  };
 
  enum class AcceptableKind { Visible, Reachable };
 
private:
  /// Methods for marking which expressions involve dereferencing a pointer
  /// marked with the 'noderef' attribute. Expressions are checked bottom up as
  /// they are parsed, meaning that a noderef pointer may not be accessed. For
  /// example, in `&*p` where `p` is a noderef pointer, we will first parse the
  /// `*p`, but need to check that `address of` is called on it. This requires
  /// keeping a container of all pending expressions and checking if the address
  /// of them are eventually taken.
  void CheckSubscriptAccessOfNoDeref(const ArraySubscriptExpr *E);
  void CheckAddressOfNoDeref(const Expr *E);
  void CheckMemberAccessOfNoDeref(const MemberExpr *E);
 
  bool RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
                               CompleteTypeKind Kind, TypeDiagnoser *Diagnoser);
 
  struct ModuleScope {
    SourceLocation BeginLoc;
    clang::Module *Module = nullptr;
    VisibleModuleSet OuterVisibleModules;
  };
  /// The modules we're currently parsing.
  llvm::SmallVector<ModuleScope, 16> ModuleScopes;
 
  /// For an interface unit, this is the implicitly imported interface unit.
  clang::Module *ThePrimaryInterface = nullptr;
 
  /// The explicit global module fragment of the current translation unit.
  /// The explicit Global Module Fragment, as specified in C++
  /// [module.global.frag].
  clang::Module *TheGlobalModuleFragment = nullptr;
 
  /// The implicit global module fragments of the current translation unit.
  ///
  /// The contents in the implicit global module fragment can't be discarded.
  clang::Module *TheImplicitGlobalModuleFragment = nullptr;
 
  /// Namespace definitions that we will export when they finish.
  llvm::SmallPtrSet<const NamespaceDecl*, 8> DeferredExportedNamespaces;
 
  /// In a C++ standard module, inline declarations require a definition to be
  /// present at the end of a definition domain.  This set holds the decls to
  /// be checked at the end of the TU.
  llvm::SmallPtrSet<const FunctionDecl *, 8> PendingInlineFuncDecls;
 
  /// Helper function to judge if we are in module purview.
  /// Return false if we are not in a module.
  bool isCurrentModulePurview() const;
 
  /// Enter the scope of the explicit global module fragment.
  Module *PushGlobalModuleFragment(SourceLocation BeginLoc);
  /// Leave the scope of the explicit global module fragment.
  void PopGlobalModuleFragment();
 
  /// Enter the scope of an implicit global module fragment.
  Module *PushImplicitGlobalModuleFragment(SourceLocation BeginLoc);
  /// Leave the scope of an implicit global module fragment.
  void PopImplicitGlobalModuleFragment();
 
  VisibleModuleSet VisibleModules;
 
  /// Cache for module units which is usable for current module.
  llvm::DenseSet<const Module *> UsableModuleUnitsCache;
 
  bool isUsableModule(const Module *M);
 
  bool isAcceptableSlow(const NamedDecl *D, AcceptableKind Kind);
 
public:
  /// Get the module unit whose scope we are currently within.
  Module *getCurrentModule() const {
    return ModuleScopes.empty() ? nullptr : ModuleScopes.back().Module;
  }
 
  /// Is the module scope we are an implementation unit?
  bool currentModuleIsImplementation() const {
    return ModuleScopes.empty()
               ? false
               : ModuleScopes.back().Module->isModuleImplementation();
  }
 
  /// Is the module scope we are in a C++ Header Unit?
  bool currentModuleIsHeaderUnit() const {
    return ModuleScopes.empty() ? false
                                : ModuleScopes.back().Module->isHeaderUnit();
  }
 
  /// Get the module owning an entity.
  Module *getOwningModule(const Decl *Entity) {
    return Entity->getOwningModule();
  }
 
  /// Make a merged definition of an existing hidden definition \p ND
  /// visible at the specified location.
  void makeMergedDefinitionVisible(NamedDecl *ND);
 
  bool isModuleVisible(const Module *M, bool ModulePrivate = false);
 
  // When loading a non-modular PCH files, this is used to restore module
  // visibility.
  void makeModuleVisible(Module *Mod, SourceLocation ImportLoc) {
    VisibleModules.setVisible(Mod, ImportLoc);
  }
 
  /// Determine whether a declaration is visible to name lookup.
  bool isVisible(const NamedDecl *D) {
    return D->isUnconditionallyVisible() ||
           isAcceptableSlow(D, AcceptableKind::Visible);
  }
 
  /// Determine whether a declaration is reachable.
  bool isReachable(const NamedDecl *D) {
    // All visible declarations are reachable.
    return D->isUnconditionallyVisible() ||
           isAcceptableSlow(D, AcceptableKind::Reachable);
  }
 
  /// Determine whether a declaration is acceptable (visible/reachable).
  bool isAcceptable(const NamedDecl *D, AcceptableKind Kind) {
    return Kind == AcceptableKind::Visible ? isVisible(D) : isReachable(D);
  }
 
  /// Determine whether any declaration of an entity is visible.
  bool
  hasVisibleDeclaration(const NamedDecl *D,
                        llvm::SmallVectorImpl<Module *> *Modules = nullptr) {
    return isVisible(D) || hasVisibleDeclarationSlow(D, Modules);
  }
 
  bool hasVisibleDeclarationSlow(const NamedDecl *D,
                                 llvm::SmallVectorImpl<Module *> *Modules);
  /// Determine whether any declaration of an entity is reachable.
  bool
  hasReachableDeclaration(const NamedDecl *D,
                          llvm::SmallVectorImpl<Module *> *Modules = nullptr) {
    return isReachable(D) || hasReachableDeclarationSlow(D, Modules);
  }
  bool hasReachableDeclarationSlow(
      const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
  bool hasVisibleMergedDefinition(const NamedDecl *Def);
  bool hasMergedDefinitionInCurrentModule(const NamedDecl *Def);
 
  /// Determine if \p D and \p Suggested have a structurally compatible
  /// layout as described in C11 6.2.7/1.
  bool hasStructuralCompatLayout(Decl *D, Decl *Suggested);
 
  /// Determine if \p D has a visible definition. If not, suggest a declaration
  /// that should be made visible to expose the definition.
  bool hasVisibleDefinition(NamedDecl *D, NamedDecl **Suggested,
                            bool OnlyNeedComplete = false);
  bool hasVisibleDefinition(const NamedDecl *D) {
    NamedDecl *Hidden;
    return hasVisibleDefinition(const_cast<NamedDecl*>(D), &Hidden);
  }
 
  /// Determine if \p D has a reachable definition. If not, suggest a
  /// declaration that should be made reachable to expose the definition.
  bool hasReachableDefinition(NamedDecl *D, NamedDecl **Suggested,
                              bool OnlyNeedComplete = false);
  bool hasReachableDefinition(NamedDecl *D) {
    NamedDecl *Hidden;
    return hasReachableDefinition(D, &Hidden);
  }
 
  bool hasAcceptableDefinition(NamedDecl *D, NamedDecl **Suggested,
                               AcceptableKind Kind,
                               bool OnlyNeedComplete = false);
  bool hasAcceptableDefinition(NamedDecl *D, AcceptableKind Kind) {
    NamedDecl *Hidden;
    return hasAcceptableDefinition(D, &Hidden, Kind);
  }
 
  /// Determine if the template parameter \p D has a visible default argument.
  bool
  hasVisibleDefaultArgument(const NamedDecl *D,
                            llvm::SmallVectorImpl<Module *> *Modules = nullptr);
  /// Determine if the template parameter \p D has a reachable default argument.
  bool hasReachableDefaultArgument(
      const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
  /// Determine if the template parameter \p D has a reachable default argument.
  bool hasAcceptableDefaultArgument(const NamedDecl *D,
                                    llvm::SmallVectorImpl<Module *> *Modules,
                                    Sema::AcceptableKind Kind);
 
  /// Determine if there is a visible declaration of \p D that is an explicit
  /// specialization declaration for a specialization of a template. (For a
  /// member specialization, use hasVisibleMemberSpecialization.)
  bool hasVisibleExplicitSpecialization(
      const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
  /// Determine if there is a reachable declaration of \p D that is an explicit
  /// specialization declaration for a specialization of a template. (For a
  /// member specialization, use hasReachableMemberSpecialization.)
  bool hasReachableExplicitSpecialization(
      const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
  /// Determine if there is a visible declaration of \p D that is a member
  /// specialization declaration (as opposed to an instantiated declaration).
  bool hasVisibleMemberSpecialization(
      const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
  /// Determine if there is a reachable declaration of \p D that is a member
  /// specialization declaration (as opposed to an instantiated declaration).
  bool hasReachableMemberSpecialization(
      const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
  /// Determine if \p A and \p B are equivalent internal linkage declarations
  /// from different modules, and thus an ambiguity error can be downgraded to
  /// an extension warning.
  bool isEquivalentInternalLinkageDeclaration(const NamedDecl *A,
                                              const NamedDecl *B);
  void diagnoseEquivalentInternalLinkageDeclarations(
      SourceLocation Loc, const NamedDecl *D,
      ArrayRef<const NamedDecl *> Equiv);
 
  bool isUsualDeallocationFunction(const CXXMethodDecl *FD);
 
  // Check whether the size of array element of type \p EltTy is a multiple of
  // its alignment and return false if it isn't.
  bool checkArrayElementAlignment(QualType EltTy, SourceLocation Loc);
 
  bool isCompleteType(SourceLocation Loc, QualType T,
                      CompleteTypeKind Kind = CompleteTypeKind::Default) {
    return !RequireCompleteTypeImpl(Loc, T, Kind, nullptr);
  }
  bool RequireCompleteType(SourceLocation Loc, QualType T,
                           CompleteTypeKind Kind, TypeDiagnoser &Diagnoser);
  bool RequireCompleteType(SourceLocation Loc, QualType T,
                           CompleteTypeKind Kind, unsigned DiagID);
 
  bool RequireCompleteType(SourceLocation Loc, QualType T,
                           TypeDiagnoser &Diagnoser) {
    return RequireCompleteType(Loc, T, CompleteTypeKind::Default, Diagnoser);
  }
  bool RequireCompleteType(SourceLocation Loc, QualType T, unsigned DiagID) {
    return RequireCompleteType(Loc, T, CompleteTypeKind::Default, DiagID);
  }
 
  template <typename... Ts>
  bool RequireCompleteType(SourceLocation Loc, QualType T, unsigned DiagID,
                           const Ts &...Args) {
    BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
    return RequireCompleteType(Loc, T, Diagnoser);
  }
 
  template <typename... Ts>
  bool RequireCompleteSizedType(SourceLocation Loc, QualType T, unsigned DiagID,
                                const Ts &... Args) {
    SizelessTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
    return RequireCompleteType(Loc, T, CompleteTypeKind::Normal, Diagnoser);
  }
 
  /// Get the type of expression E, triggering instantiation to complete the
  /// type if necessary -- that is, if the expression refers to a templated
  /// static data member of incomplete array type.
  ///
  /// May still return an incomplete type if instantiation was not possible or
  /// if the type is incomplete for a different reason. Use
  /// RequireCompleteExprType instead if a diagnostic is expected for an
  /// incomplete expression type.
  QualType getCompletedType(Expr *E);
 
  void completeExprArrayBound(Expr *E);
  bool RequireCompleteExprType(Expr *E, CompleteTypeKind Kind,
                               TypeDiagnoser &Diagnoser);
  bool RequireCompleteExprType(Expr *E, unsigned DiagID);
 
  template <typename... Ts>
  bool RequireCompleteExprType(Expr *E, unsigned DiagID, const Ts &...Args) {
    BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
    return RequireCompleteExprType(E, CompleteTypeKind::Default, Diagnoser);
  }
 
  template <typename... Ts>
  bool RequireCompleteSizedExprType(Expr *E, unsigned DiagID,
                                    const Ts &... Args) {
    SizelessTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
    return RequireCompleteExprType(E, CompleteTypeKind::Normal, Diagnoser);
  }
 
  bool RequireLiteralType(SourceLocation Loc, QualType T,
                          TypeDiagnoser &Diagnoser);
  bool RequireLiteralType(SourceLocation Loc, QualType T, unsigned DiagID);
 
  template <typename... Ts>
  bool RequireLiteralType(SourceLocation Loc, QualType T, unsigned DiagID,
                          const Ts &...Args) {
    BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
    return RequireLiteralType(Loc, T, Diagnoser);
  }
 
  QualType getElaboratedType(ElaboratedTypeKeyword Keyword,
                             const CXXScopeSpec &SS, QualType T,
                             TagDecl *OwnedTagDecl = nullptr);
 
  // Returns the underlying type of a decltype with the given expression.
  QualType getDecltypeForExpr(Expr *E);
 
  QualType BuildTypeofExprType(Expr *E, TypeOfKind Kind);
  /// If AsUnevaluated is false, E is treated as though it were an evaluated
  /// context, such as when building a type for decltype(auto).
  QualType BuildDecltypeType(Expr *E, bool AsUnevaluated = true);
 
  using UTTKind = UnaryTransformType::UTTKind;
  QualType BuildUnaryTransformType(QualType BaseType, UTTKind UKind,
                                   SourceLocation Loc);
  QualType BuiltinEnumUnderlyingType(QualType BaseType, SourceLocation Loc);
  QualType BuiltinAddPointer(QualType BaseType, SourceLocation Loc);
  QualType BuiltinRemovePointer(QualType BaseType, SourceLocation Loc);
  QualType BuiltinDecay(QualType BaseType, SourceLocation Loc);
  QualType BuiltinAddReference(QualType BaseType, UTTKind UKind,
                               SourceLocation Loc);
  QualType BuiltinRemoveExtent(QualType BaseType, UTTKind UKind,
                               SourceLocation Loc);
  QualType BuiltinRemoveReference(QualType BaseType, UTTKind UKind,
                                  SourceLocation Loc);
  QualType BuiltinChangeCVRQualifiers(QualType BaseType, UTTKind UKind,
                                      SourceLocation Loc);
  QualType BuiltinChangeSignedness(QualType BaseType, UTTKind UKind,
                                   SourceLocation Loc);
 
  //===--------------------------------------------------------------------===//
  // Symbol table / Decl tracking callbacks: SemaDecl.cpp.
  //
 
  struct SkipBodyInfo {
    SkipBodyInfo() = default;
    bool ShouldSkip = false;
    bool CheckSameAsPrevious = false;
    NamedDecl *Previous = nullptr;
    NamedDecl *New = nullptr;
  };
 
  DeclGroupPtrTy ConvertDeclToDeclGroup(Decl *Ptr, Decl *OwnedType = nullptr);
 
  void DiagnoseUseOfUnimplementedSelectors();
 
  bool isSimpleTypeSpecifier(tok::TokenKind Kind) const;
 
  ParsedType getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
                         Scope *S, CXXScopeSpec *SS = nullptr,
                         bool isClassName = false, bool HasTrailingDot = false,
                         ParsedType ObjectType = nullptr,
                         bool IsCtorOrDtorName = false,
                         bool WantNontrivialTypeSourceInfo = false,
                         bool IsClassTemplateDeductionContext = true,
                         ImplicitTypenameContext AllowImplicitTypename =
                             ImplicitTypenameContext::No,
                         IdentifierInfo **CorrectedII = nullptr);
  TypeSpecifierType isTagName(IdentifierInfo &II, Scope *S);
  bool isMicrosoftMissingTypename(const CXXScopeSpec *SS, Scope *S);
  void DiagnoseUnknownTypeName(IdentifierInfo *&II,
                               SourceLocation IILoc,
                               Scope *S,
                               CXXScopeSpec *SS,
                               ParsedType &SuggestedType,
                               bool IsTemplateName = false);
 
  /// Attempt to behave like MSVC in situations where lookup of an unqualified
  /// type name has failed in a dependent context. In these situations, we
  /// automatically form a DependentTypeName that will retry lookup in a related
  /// scope during instantiation.
  ParsedType ActOnMSVCUnknownTypeName(const IdentifierInfo &II,
                                      SourceLocation NameLoc,
                                      bool IsTemplateTypeArg);
 
  /// Describes the result of the name lookup and resolution performed
  /// by \c ClassifyName().
  enum NameClassificationKind {
    /// This name is not a type or template in this context, but might be
    /// something else.
    NC_Unknown,
    /// Classification failed; an error has been produced.
    NC_Error,
    /// The name has been typo-corrected to a keyword.
    NC_Keyword,
    /// The name was classified as a type.
    NC_Type,
    /// The name was classified as a specific non-type, non-template
    /// declaration. ActOnNameClassifiedAsNonType should be called to
    /// convert the declaration to an expression.
    NC_NonType,
    /// The name was classified as an ADL-only function name.
    /// ActOnNameClassifiedAsUndeclaredNonType should be called to convert the
    /// result to an expression.
    NC_UndeclaredNonType,
    /// The name denotes a member of a dependent type that could not be
    /// resolved. ActOnNameClassifiedAsDependentNonType should be called to
    /// convert the result to an expression.
    NC_DependentNonType,
    /// The name was classified as an overload set, and an expression
    /// representing that overload set has been formed.
    /// ActOnNameClassifiedAsOverloadSet should be called to form a suitable
    /// expression referencing the overload set.
    NC_OverloadSet,
    /// The name was classified as a template whose specializations are types.
    NC_TypeTemplate,
    /// The name was classified as a variable template name.
    NC_VarTemplate,
    /// The name was classified as a function template name.
    NC_FunctionTemplate,
    /// The name was classified as an ADL-only function template name.
    NC_UndeclaredTemplate,
    /// The name was classified as a concept name.
    NC_Concept,
  };
 
  class NameClassification {
    NameClassificationKind Kind;
    union {
      ExprResult Expr;
      NamedDecl *NonTypeDecl;
      TemplateName Template;
      ParsedType Type;
    };
 
    explicit NameClassification(NameClassificationKind Kind) : Kind(Kind) {}
 
  public:
    NameClassification(ParsedType Type) : Kind(NC_Type), Type(Type) {}
 
    NameClassification(const IdentifierInfo *Keyword) : Kind(NC_Keyword) {}
 
    static NameClassification Error() {
      return NameClassification(NC_Error);
    }
 
    static NameClassification Unknown() {
      return NameClassification(NC_Unknown);
    }
 
    static NameClassification OverloadSet(ExprResult E) {
      NameClassification Result(NC_OverloadSet);
      Result.Expr = E;
      return Result;
    }
 
    static NameClassification NonType(NamedDecl *D) {
      NameClassification Result(NC_NonType);
      Result.NonTypeDecl = D;
      return Result;
    }
 
    static NameClassification UndeclaredNonType() {
      return NameClassification(NC_UndeclaredNonType);
    }
 
    static NameClassification DependentNonType() {
      return NameClassification(NC_DependentNonType);
    }
 
    static NameClassification TypeTemplate(TemplateName Name) {
      NameClassification Result(NC_TypeTemplate);
      Result.Template = Name;
      return Result;
    }
 
    static NameClassification VarTemplate(TemplateName Name) {
      NameClassification Result(NC_VarTemplate);
      Result.Template = Name;
      return Result;
    }
 
    static NameClassification FunctionTemplate(TemplateName Name) {
      NameClassification Result(NC_FunctionTemplate);
      Result.Template = Name;
      return Result;
    }
 
    static NameClassification Concept(TemplateName Name) {
      NameClassification Result(NC_Concept);
      Result.Template = Name;
      return Result;
    }
 
    static NameClassification UndeclaredTemplate(TemplateName Name) {
      NameClassification Result(NC_UndeclaredTemplate);
      Result.Template = Name;
      return Result;
    }
 
    NameClassificationKind getKind() const { return Kind; }
 
    ExprResult getExpression() const {
      assert(Kind == NC_OverloadSet);
      return Expr;
    }
 
    ParsedType getType() const {
      assert(Kind == NC_Type);
      return Type;
    }
 
    NamedDecl *getNonTypeDecl() const {
      assert(Kind == NC_NonType);
      return NonTypeDecl;
    }
 
    TemplateName getTemplateName() const {
      assert(Kind == NC_TypeTemplate || Kind == NC_FunctionTemplate ||
             Kind == NC_VarTemplate || Kind == NC_Concept ||
             Kind == NC_UndeclaredTemplate);
      return Template;
    }
 
    TemplateNameKind getTemplateNameKind() const {
      switch (Kind) {
      case NC_TypeTemplate:
        return TNK_Type_template;
      case NC_FunctionTemplate:
        return TNK_Function_template;
      case NC_VarTemplate:
        return TNK_Var_template;
      case NC_Concept:
        return TNK_Concept_template;
      case NC_UndeclaredTemplate:
        return TNK_Undeclared_template;
      default:
        llvm_unreachable("unsupported name classification.");
      }
    }
  };
 
  /// Perform name lookup on the given name, classifying it based on
  /// the results of name lookup and the following token.
  ///
  /// This routine is used by the parser to resolve identifiers and help direct
  /// parsing. When the identifier cannot be found, this routine will attempt
  /// to correct the typo and classify based on the resulting name.
  ///
  /// \param S The scope in which we're performing name lookup.
  ///
  /// \param SS The nested-name-specifier that precedes the name.
  ///
  /// \param Name The identifier. If typo correction finds an alternative name,
  /// this pointer parameter will be updated accordingly.
  ///
  /// \param NameLoc The location of the identifier.
  ///
  /// \param NextToken The token following the identifier. Used to help
  /// disambiguate the name.
  ///
  /// \param CCC The correction callback, if typo correction is desired.
  NameClassification ClassifyName(Scope *S, CXXScopeSpec &SS,
                                  IdentifierInfo *&Name, SourceLocation NameLoc,
                                  const Token &NextToken,
                                  CorrectionCandidateCallback *CCC = nullptr);
 
  /// Act on the result of classifying a name as an undeclared (ADL-only)
  /// non-type declaration.
  ExprResult ActOnNameClassifiedAsUndeclaredNonType(IdentifierInfo *Name,
                                                    SourceLocation NameLoc);
  /// Act on the result of classifying a name as an undeclared member of a
  /// dependent base class.
  ExprResult ActOnNameClassifiedAsDependentNonType(const CXXScopeSpec &SS,
                                                   IdentifierInfo *Name,
                                                   SourceLocation NameLoc,
                                                   bool IsAddressOfOperand);
  /// Act on the result of classifying a name as a specific non-type
  /// declaration.
  ExprResult ActOnNameClassifiedAsNonType(Scope *S, const CXXScopeSpec &SS,
                                          NamedDecl *Found,
                                          SourceLocation NameLoc,
                                          const Token &NextToken);
  /// Act on the result of classifying a name as an overload set.
  ExprResult ActOnNameClassifiedAsOverloadSet(Scope *S, Expr *OverloadSet);
 
  /// Describes the detailed kind of a template name. Used in diagnostics.
  enum class TemplateNameKindForDiagnostics {
    ClassTemplate,
    FunctionTemplate,
    VarTemplate,
    AliasTemplate,
    TemplateTemplateParam,
    Concept,
    DependentTemplate
  };
  TemplateNameKindForDiagnostics
  getTemplateNameKindForDiagnostics(TemplateName Name);
 
  /// Determine whether it's plausible that E was intended to be a
  /// template-name.
  bool mightBeIntendedToBeTemplateName(ExprResult E, bool &Dependent) {
    if (!getLangOpts().CPlusPlus || E.isInvalid())
      return false;
    Dependent = false;
    if (auto *DRE = dyn_cast<DeclRefExpr>(E.get()))
      return !DRE->hasExplicitTemplateArgs();
    if (auto *ME = dyn_cast<MemberExpr>(E.get()))
      return !ME->hasExplicitTemplateArgs();
    Dependent = true;
    if (auto *DSDRE = dyn_cast<DependentScopeDeclRefExpr>(E.get()))
      return !DSDRE->hasExplicitTemplateArgs();
    if (auto *DSME = dyn_cast<CXXDependentScopeMemberExpr>(E.get()))
      return !DSME->hasExplicitTemplateArgs();
    // Any additional cases recognized here should also be handled by
    // diagnoseExprIntendedAsTemplateName.
    return false;
  }
  void diagnoseExprIntendedAsTemplateName(Scope *S, ExprResult TemplateName,
                                          SourceLocation Less,
                                          SourceLocation Greater);
 
  void warnOnReservedIdentifier(const NamedDecl *D);
 
  Decl *ActOnDeclarator(Scope *S, Declarator &D);
 
  NamedDecl *HandleDeclarator(Scope *S, Declarator &D,
                              MultiTemplateParamsArg TemplateParameterLists);
  bool tryToFixVariablyModifiedVarType(TypeSourceInfo *&TInfo,
                                       QualType &T, SourceLocation Loc,
                                       unsigned FailedFoldDiagID);
  void RegisterLocallyScopedExternCDecl(NamedDecl *ND, Scope *S);
  bool DiagnoseClassNameShadow(DeclContext *DC, DeclarationNameInfo Info);
  bool diagnoseQualifiedDeclaration(CXXScopeSpec &SS, DeclContext *DC,
                                    DeclarationName Name, SourceLocation Loc,
                                    bool IsTemplateId);
  void
  diagnoseIgnoredQualifiers(unsigned DiagID, unsigned Quals,
                            SourceLocation FallbackLoc,
                            SourceLocation ConstQualLoc = SourceLocation(),
                            SourceLocation VolatileQualLoc = SourceLocation(),
                            SourceLocation RestrictQualLoc = SourceLocation(),
                            SourceLocation AtomicQualLoc = SourceLocation(),
                            SourceLocation UnalignedQualLoc = SourceLocation());
 
  static bool adjustContextForLocalExternDecl(DeclContext *&DC);
  void DiagnoseFunctionSpecifiers(const DeclSpec &DS);
  NamedDecl *getShadowedDeclaration(const TypedefNameDecl *D,
                                    const LookupResult &R);
  NamedDecl *getShadowedDeclaration(const VarDecl *D, const LookupResult &R);
  NamedDecl *getShadowedDeclaration(const BindingDecl *D,
                                    const LookupResult &R);
  void CheckShadow(NamedDecl *D, NamedDecl *ShadowedDecl,
                   const LookupResult &R);
  void CheckShadow(Scope *S, VarDecl *D);
 
  /// Warn if 'E', which is an expression that is about to be modified, refers
  /// to a shadowing declaration.
  void CheckShadowingDeclModification(Expr *E, SourceLocation Loc);
 
  void DiagnoseShadowingLambdaDecls(const sema::LambdaScopeInfo *LSI);
 
private:
  /// Map of current shadowing declarations to shadowed declarations. Warn if
  /// it looks like the user is trying to modify the shadowing declaration.
  llvm::DenseMap<const NamedDecl *, const NamedDecl *> ShadowingDecls;
 
public:
  void CheckCastAlign(Expr *Op, QualType T, SourceRange TRange);
  void handleTagNumbering(const TagDecl *Tag, Scope *TagScope);
  void setTagNameForLinkagePurposes(TagDecl *TagFromDeclSpec,
                                    TypedefNameDecl *NewTD);
  void CheckTypedefForVariablyModifiedType(Scope *S, TypedefNameDecl *D);
  NamedDecl* ActOnTypedefDeclarator(Scope* S, Declarator& D, DeclContext* DC,
                                    TypeSourceInfo *TInfo,
                                    LookupResult &Previous);
  NamedDecl* ActOnTypedefNameDecl(Scope* S, DeclContext* DC, TypedefNameDecl *D,
                                  LookupResult &Previous, bool &Redeclaration);
  NamedDecl *ActOnVariableDeclarator(
      Scope *S, Declarator &D, DeclContext *DC, TypeSourceInfo *TInfo,
      LookupResult &Previous, MultiTemplateParamsArg TemplateParamLists,
      bool &AddToScope, ArrayRef<BindingDecl *> Bindings = std::nullopt);
  NamedDecl *
  ActOnDecompositionDeclarator(Scope *S, Declarator &D,
                               MultiTemplateParamsArg TemplateParamLists);
  void DiagPlaceholderVariableDefinition(SourceLocation Loc);
  bool DiagRedefinedPlaceholderFieldDecl(SourceLocation Loc,
                                         RecordDecl *ClassDecl,
                                         const IdentifierInfo *Name);
  // Returns true if the variable declaration is a redeclaration
  bool CheckVariableDeclaration(VarDecl *NewVD, LookupResult &Previous);
  void CheckVariableDeclarationType(VarDecl *NewVD);
  bool DeduceVariableDeclarationType(VarDecl *VDecl, bool DirectInit,
                                     Expr *Init);
  void CheckCompleteVariableDeclaration(VarDecl *VD);
  void CheckCompleteDecompositionDeclaration(DecompositionDecl *DD);
  void MaybeSuggestAddingStaticToDecl(const FunctionDecl *D);
 
  NamedDecl* ActOnFunctionDeclarator(Scope* S, Declarator& D, DeclContext* DC,
                                     TypeSourceInfo *TInfo,
                                     LookupResult &Previous,
                                     MultiTemplateParamsArg TemplateParamLists,
                                     bool &AddToScope);
  bool AddOverriddenMethods(CXXRecordDecl *DC, CXXMethodDecl *MD);
 
  enum class CheckConstexprKind {
    /// Diagnose issues that are non-constant or that are extensions.
    Diagnose,
    /// Identify whether this function satisfies the formal rules for constexpr
    /// functions in the current lanugage mode (with no extensions).
    CheckValid
  };
 
  bool CheckConstexprFunctionDefinition(const FunctionDecl *FD,
                                        CheckConstexprKind Kind);
 
  void DiagnoseHiddenVirtualMethods(CXXMethodDecl *MD);
  void FindHiddenVirtualMethods(CXXMethodDecl *MD,
                          SmallVectorImpl<CXXMethodDecl*> &OverloadedMethods);
  void NoteHiddenVirtualMethods(CXXMethodDecl *MD,
                          SmallVectorImpl<CXXMethodDecl*> &OverloadedMethods);
  // Returns true if the function declaration is a redeclaration
  bool CheckFunctionDeclaration(Scope *S,
                                FunctionDecl *NewFD, LookupResult &Previous,
                                bool IsMemberSpecialization, bool DeclIsDefn);
  bool shouldLinkDependentDeclWithPrevious(Decl *D, Decl *OldDecl);
  bool canFullyTypeCheckRedeclaration(ValueDecl *NewD, ValueDecl *OldD,
                                      QualType NewT, QualType OldT);
  void CheckMain(FunctionDecl *FD, const DeclSpec &D);
  void CheckMSVCRTEntryPoint(FunctionDecl *FD);
  void ActOnHLSLTopLevelFunction(FunctionDecl *FD);
  void CheckHLSLEntryPoint(FunctionDecl *FD);
  void CheckHLSLSemanticAnnotation(FunctionDecl *EntryPoint, const Decl *Param,
                                   const HLSLAnnotationAttr *AnnotationAttr);
  void DiagnoseHLSLAttrStageMismatch(
      const Attr *A, HLSLShaderAttr::ShaderType Stage,
      std::initializer_list<HLSLShaderAttr::ShaderType> AllowedStages);
  Attr *getImplicitCodeSegOrSectionAttrForFunction(const FunctionDecl *FD,
                                                   bool IsDefinition);
  void CheckFunctionOrTemplateParamDeclarator(Scope *S, Declarator &D);
  Decl *ActOnParamDeclarator(Scope *S, Declarator &D,
                             SourceLocation ExplicitThisLoc = {});
  ParmVarDecl *BuildParmVarDeclForTypedef(DeclContext *DC,
                                          SourceLocation Loc,
                                          QualType T);
  ParmVarDecl *CheckParameter(DeclContext *DC, SourceLocation StartLoc,
                              SourceLocation NameLoc, IdentifierInfo *Name,
                              QualType T, TypeSourceInfo *TSInfo,
                              StorageClass SC);
  void ActOnParamDefaultArgument(Decl *param,
                                 SourceLocation EqualLoc,
                                 Expr *defarg);
  void ActOnParamUnparsedDefaultArgument(Decl *param, SourceLocation EqualLoc,
                                         SourceLocation ArgLoc);
  void ActOnParamDefaultArgumentError(Decl *param, SourceLocation EqualLoc,
                                      Expr* DefaultArg);
  ExprResult ConvertParamDefaultArgument(ParmVarDecl *Param, Expr *DefaultArg,
                                         SourceLocation EqualLoc);
  void SetParamDefaultArgument(ParmVarDecl *Param, Expr *DefaultArg,
                               SourceLocation EqualLoc);
 
  // Contexts where using non-trivial C union types can be disallowed. This is
  // passed to err_non_trivial_c_union_in_invalid_context.
  enum NonTrivialCUnionContext {
    // Function parameter.
    NTCUC_FunctionParam,
    // Function return.
    NTCUC_FunctionReturn,
    // Default-initialized object.
    NTCUC_DefaultInitializedObject,
    // Variable with automatic storage duration.
    NTCUC_AutoVar,
    // Initializer expression that might copy from another object.
    NTCUC_CopyInit,
    // Assignment.
    NTCUC_Assignment,
    // Compound literal.
    NTCUC_CompoundLiteral,
    // Block capture.
    NTCUC_BlockCapture,
    // lvalue-to-rvalue conversion of volatile type.
    NTCUC_LValueToRValueVolatile,
  };
 
  /// Emit diagnostics if the initializer or any of its explicit or
  /// implicitly-generated subexpressions require copying or
  /// default-initializing a type that is or contains a C union type that is
  /// non-trivial to copy or default-initialize.
  void checkNonTrivialCUnionInInitializer(const Expr *Init, SourceLocation Loc);
 
  // These flags are passed to checkNonTrivialCUnion.
  enum NonTrivialCUnionKind {
    NTCUK_Init = 0x1,
    NTCUK_Destruct = 0x2,
    NTCUK_Copy = 0x4,
  };
 
  /// Emit diagnostics if a non-trivial C union type or a struct that contains
  /// a non-trivial C union is used in an invalid context.
  void checkNonTrivialCUnion(QualType QT, SourceLocation Loc,
                             NonTrivialCUnionContext UseContext,
                             unsigned NonTrivialKind);
 
  void AddInitializerToDecl(Decl *dcl, Expr *init, bool DirectInit);
  void ActOnUninitializedDecl(Decl *dcl);
  void ActOnInitializerError(Decl *Dcl);
 
  void ActOnPureSpecifier(Decl *D, SourceLocation PureSpecLoc);
  void ActOnCXXForRangeDecl(Decl *D);
  StmtResult ActOnCXXForRangeIdentifier(Scope *S, SourceLocation IdentLoc,
                                        IdentifierInfo *Ident,
                                        ParsedAttributes &Attrs);
  void SetDeclDeleted(Decl *dcl, SourceLocation DelLoc);
  void SetDeclDefaulted(Decl *dcl, SourceLocation DefaultLoc);
  void CheckStaticLocalForDllExport(VarDecl *VD);
  void CheckThreadLocalForLargeAlignment(VarDecl *VD);
  void FinalizeDeclaration(Decl *D);
  DeclGroupPtrTy FinalizeDeclaratorGroup(Scope *S, const DeclSpec &DS,
                                         ArrayRef<Decl *> Group);
  DeclGroupPtrTy BuildDeclaratorGroup(MutableArrayRef<Decl *> Group);
 
  /// Should be called on all declarations that might have attached
  /// documentation comments.
  void ActOnDocumentableDecl(Decl *D);
  void ActOnDocumentableDecls(ArrayRef<Decl *> Group);
 
  enum class FnBodyKind {
    /// C++ [dcl.fct.def.general]p1
    /// function-body:
    ///   ctor-initializer[opt] compound-statement
    ///   function-try-block
    Other,
    ///   = default ;
    Default,
    ///   = delete ;
    Delete
  };
 
  void ActOnFinishKNRParamDeclarations(Scope *S, Declarator &D,
                                       SourceLocation LocAfterDecls);
  void CheckForFunctionRedefinition(
      FunctionDecl *FD, const FunctionDecl *EffectiveDefinition = nullptr,
      SkipBodyInfo *SkipBody = nullptr);
  Decl *ActOnStartOfFunctionDef(Scope *S, Declarator &D,
                                MultiTemplateParamsArg TemplateParamLists,
                                SkipBodyInfo *SkipBody = nullptr,
                                FnBodyKind BodyKind = FnBodyKind::Other);
  Decl *ActOnStartOfFunctionDef(Scope *S, Decl *D,
                                SkipBodyInfo *SkipBody = nullptr,
                                FnBodyKind BodyKind = FnBodyKind::Other);
  void SetFunctionBodyKind(Decl *D, SourceLocation Loc, FnBodyKind BodyKind);
  void ActOnStartTrailingRequiresClause(Scope *S, Declarator &D);
  ExprResult ActOnFinishTrailingRequiresClause(ExprResult ConstraintExpr);
  ExprResult ActOnRequiresClause(ExprResult ConstraintExpr);
  void ActOnStartOfObjCMethodDef(Scope *S, Decl *D);
  bool isObjCMethodDecl(Decl *D) {
    return D && isa<ObjCMethodDecl>(D);
  }
 
  /// Determine whether we can delay parsing the body of a function or
  /// function template until it is used, assuming we don't care about emitting
  /// code for that function.
  ///
  /// This will be \c false if we may need the body of the function in the
  /// middle of parsing an expression (where it's impractical to switch to
  /// parsing a different function), for instance, if it's constexpr in C++11
  /// or has an 'auto' return type in C++14. These cases are essentially bugs.
  bool canDelayFunctionBody(const Declarator &D);
 
  /// Determine whether we can skip parsing the body of a function
  /// definition, assuming we don't care about analyzing its body or emitting
  /// code for that function.
  ///
  /// This will be \c false only if we may need the body of the function in
  /// order to parse the rest of the program (for instance, if it is
  /// \c constexpr in C++11 or has an 'auto' return type in C++14).
  bool canSkipFunctionBody(Decl *D);
 
  /// Determine whether \param D is function like (function or function
  /// template) for parsing.
  bool isDeclaratorFunctionLike(Declarator &D);
 
  void computeNRVO(Stmt *Body, sema::FunctionScopeInfo *Scope);
  Decl *ActOnFinishFunctionBody(Decl *Decl, Stmt *Body);
  Decl *ActOnFinishFunctionBody(Decl *Decl, Stmt *Body, bool IsInstantiation);
  Decl *ActOnSkippedFunctionBody(Decl *Decl);
  void ActOnFinishInlineFunctionDef(FunctionDecl *D);
 
  /// ActOnFinishDelayedAttribute - Invoked when we have finished parsing an
  /// attribute for which parsing is delayed.
  void ActOnFinishDelayedAttribute(Scope *S, Decl *D, ParsedAttributes &Attrs);
 
  /// Diagnose any unused parameters in the given sequence of
  /// ParmVarDecl pointers.
  void DiagnoseUnusedParameters(ArrayRef<ParmVarDecl *> Parameters);
 
  /// Diagnose whether the size of parameters or return value of a
  /// function or obj-c method definition is pass-by-value and larger than a
  /// specified threshold.
  void
  DiagnoseSizeOfParametersAndReturnValue(ArrayRef<ParmVarDecl *> Parameters,
                                         QualType ReturnTy, NamedDecl *D);
 
  void DiagnoseInvalidJumps(Stmt *Body);
  Decl *ActOnFileScopeAsmDecl(Expr *expr,
                              SourceLocation AsmLoc,
                              SourceLocation RParenLoc);
 
  Decl *ActOnTopLevelStmtDecl(Stmt *Statement);
 
  /// Handle a C++11 empty-declaration and attribute-declaration.
  Decl *ActOnEmptyDeclaration(Scope *S, const ParsedAttributesView &AttrList,
                              SourceLocation SemiLoc);
 
  enum class ModuleDeclKind {
    Interface,               ///< 'export module X;'
    Implementation,          ///< 'module X;'
    PartitionInterface,      ///< 'export module X:Y;'
    PartitionImplementation, ///< 'module X:Y;'
  };
 
  /// An enumeration to represent the transition of states in parsing module
  /// fragments and imports.  If we are not parsing a C++20 TU, or we find
  /// an error in state transition, the state is set to NotACXX20Module.
  enum class ModuleImportState {
    FirstDecl,      ///< Parsing the first decl in a TU.
    GlobalFragment, ///< after 'module;' but before 'module X;'
    ImportAllowed,  ///< after 'module X;' but before any non-import decl.
    ImportFinished, ///< after any non-import decl.
    PrivateFragmentImportAllowed,  ///< after 'module :private;' but before any
                                   ///< non-import decl.
    PrivateFragmentImportFinished, ///< after 'module :private;' but a
                                   ///< non-import decl has already been seen.
    NotACXX20Module ///< Not a C++20 TU, or an invalid state was found.
  };
 
private:
  /// The parser has begun a translation unit to be compiled as a C++20
  /// Header Unit, helper for ActOnStartOfTranslationUnit() only.
  void HandleStartOfHeaderUnit();
 
public:
  /// The parser has processed a module-declaration that begins the definition
  /// of a module interface or implementation.
  DeclGroupPtrTy ActOnModuleDecl(SourceLocation StartLoc,
                                 SourceLocation ModuleLoc, ModuleDeclKind MDK,
                                 ModuleIdPath Path, ModuleIdPath Partition,
                                 ModuleImportState &ImportState);
 
  /// The parser has processed a global-module-fragment declaration that begins
  /// the definition of the global module fragment of the current module unit.
  /// \param ModuleLoc The location of the 'module' keyword.
  DeclGroupPtrTy ActOnGlobalModuleFragmentDecl(SourceLocation ModuleLoc);
 
  /// The parser has processed a private-module-fragment declaration that begins
  /// the definition of the private module fragment of the current module unit.
  /// \param ModuleLoc The location of the 'module' keyword.
  /// \param PrivateLoc The location of the 'private' keyword.
  DeclGroupPtrTy ActOnPrivateModuleFragmentDecl(SourceLocation ModuleLoc,
                                                SourceLocation PrivateLoc);
 
  /// The parser has processed a module import declaration.
  ///
  /// \param StartLoc The location of the first token in the declaration. This
  ///        could be the location of an '@', 'export', or 'import'.
  /// \param ExportLoc The location of the 'export' keyword, if any.
  /// \param ImportLoc The location of the 'import' keyword.
  /// \param Path The module toplevel name as an access path.
  /// \param IsPartition If the name is for a partition.
  DeclResult ActOnModuleImport(SourceLocation StartLoc,
                               SourceLocation ExportLoc,
                               SourceLocation ImportLoc, ModuleIdPath Path,
                               bool IsPartition = false);
  DeclResult ActOnModuleImport(SourceLocation StartLoc,
                               SourceLocation ExportLoc,
                               SourceLocation ImportLoc, Module *M,
                               ModuleIdPath Path = {});
 
  /// The parser has processed a module import translated from a
  /// #include or similar preprocessing directive.
  void ActOnModuleInclude(SourceLocation DirectiveLoc, Module *Mod);
  void BuildModuleInclude(SourceLocation DirectiveLoc, Module *Mod);
 
  /// The parsed has entered a submodule.
  void ActOnModuleBegin(SourceLocation DirectiveLoc, Module *Mod);
  /// The parser has left a submodule.
  void ActOnModuleEnd(SourceLocation DirectiveLoc, Module *Mod);
 
  /// Create an implicit import of the given module at the given
  /// source location, for error recovery, if possible.
  ///
  /// This routine is typically used when an entity found by name lookup
  /// is actually hidden within a module that we know about but the user
  /// has forgotten to import.
  void createImplicitModuleImportForErrorRecovery(SourceLocation Loc,
                                                  Module *Mod);
 
  /// Kinds of missing import. Note, the values of these enumerators correspond
  /// to %select values in diagnostics.
  enum class MissingImportKind {
    Declaration,
    Definition,
    DefaultArgument,
    ExplicitSpecialization,
    PartialSpecialization
  };
 
  /// Diagnose that the specified declaration needs to be visible but
  /// isn't, and suggest a module import that would resolve the problem.
  void diagnoseMissingImport(SourceLocation Loc, const NamedDecl *Decl,
                             MissingImportKind MIK, bool Recover = true);
  void diagnoseMissingImport(SourceLocation Loc, const NamedDecl *Decl,
                             SourceLocation DeclLoc, ArrayRef<Module *> Modules,
                             MissingImportKind MIK, bool Recover);
 
  Decl *ActOnStartExportDecl(Scope *S, SourceLocation ExportLoc,
                             SourceLocation LBraceLoc);
  Decl *ActOnFinishExportDecl(Scope *S, Decl *ExportDecl,
                              SourceLocation RBraceLoc);
 
  /// We've found a use of a templated declaration that would trigger an
  /// implicit instantiation. Check that any relevant explicit specializations
  /// and partial specializations are visible/reachable, and diagnose if not.
  void checkSpecializationVisibility(SourceLocation Loc, NamedDecl *Spec);
  void checkSpecializationReachability(SourceLocation Loc, NamedDecl *Spec);
 
  /// Retrieve a suitable printing policy for diagnostics.
  PrintingPolicy getPrintingPolicy() const {
    return getPrintingPolicy(Context, PP);
  }
 
  /// Retrieve a suitable printing policy for diagnostics.
  static PrintingPolicy getPrintingPolicy(const ASTContext &Ctx,
                                          const Preprocessor &PP);
 
  /// Scope actions.
  void ActOnPopScope(SourceLocation Loc, Scope *S);
  void ActOnTranslationUnitScope(Scope *S);
 
  Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                   const ParsedAttributesView &DeclAttrs,
                                   RecordDecl *&AnonRecord);
  Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                   const ParsedAttributesView &DeclAttrs,
                                   MultiTemplateParamsArg TemplateParams,
                                   bool IsExplicitInstantiation,
                                   RecordDecl *&AnonRecord);
 
  Decl *BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS,
                                    AccessSpecifier AS,
                                    RecordDecl *Record,
                                    const PrintingPolicy &Policy);
 
  /// Called once it is known whether
  /// a tag declaration is an anonymous union or struct.
  void ActOnDefinedDeclarationSpecifier(Decl *D);
 
  void DiagPlaceholderFieldDeclDefinitions(RecordDecl *Record);
 
  Decl *BuildMicrosoftCAnonymousStruct(Scope *S, DeclSpec &DS,
                                       RecordDecl *Record);
 
  /// Common ways to introduce type names without a tag for use in diagnostics.
  /// Keep in sync with err_tag_reference_non_tag.
  enum NonTagKind {
    NTK_NonStruct,
    NTK_NonClass,
    NTK_NonUnion,
    NTK_NonEnum,
    NTK_Typedef,
    NTK_TypeAlias,
    NTK_Template,
    NTK_TypeAliasTemplate,
    NTK_TemplateTemplateArgument,
  };
 
  /// Given a non-tag type declaration, returns an enum useful for indicating
  /// what kind of non-tag type this is.
  NonTagKind getNonTagTypeDeclKind(const Decl *D, TagTypeKind TTK);
 
  bool isAcceptableTagRedeclaration(const TagDecl *Previous,
                                    TagTypeKind NewTag, bool isDefinition,
                                    SourceLocation NewTagLoc,
                                    const IdentifierInfo *Name);
 
  enum TagUseKind {
    TUK_Reference,   // Reference to a tag:  'struct foo *X;'
    TUK_Declaration, // Fwd decl of a tag:   'struct foo;'
    TUK_Definition,  // Definition of a tag: 'struct foo { int X; } Y;'
    TUK_Friend       // Friend declaration:  'friend struct foo;'
  };
 
  enum OffsetOfKind {
    // Not parsing a type within __builtin_offsetof.
    OOK_Outside,
    // Parsing a type within __builtin_offsetof.
    OOK_Builtin,
    // Parsing a type within macro "offsetof", defined in __buitin_offsetof
    // To improve our diagnostic message.
    OOK_Macro,
  };
 
  DeclResult ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                      SourceLocation KWLoc, CXXScopeSpec &SS,
                      IdentifierInfo *Name, SourceLocation NameLoc,
                      const ParsedAttributesView &Attr, AccessSpecifier AS,
                      SourceLocation ModulePrivateLoc,
                      MultiTemplateParamsArg TemplateParameterLists,
                      bool &OwnedDecl, bool &IsDependent,
                      SourceLocation ScopedEnumKWLoc,
                      bool ScopedEnumUsesClassTag, TypeResult UnderlyingType,
                      bool IsTypeSpecifier, bool IsTemplateParamOrArg,
                      OffsetOfKind OOK, SkipBodyInfo *SkipBody = nullptr);
 
  DeclResult ActOnTemplatedFriendTag(Scope *S, SourceLocation FriendLoc,
                                     unsigned TagSpec, SourceLocation TagLoc,
                                     CXXScopeSpec &SS, IdentifierInfo *Name,
                                     SourceLocation NameLoc,
                                     const ParsedAttributesView &Attr,
                                     MultiTemplateParamsArg TempParamLists);
 
  TypeResult ActOnDependentTag(Scope *S,
                               unsigned TagSpec,
                               TagUseKind TUK,
                               const CXXScopeSpec &SS,
                               IdentifierInfo *Name,
                               SourceLocation TagLoc,
                               SourceLocation NameLoc);
 
  void ActOnDefs(Scope *S, Decl *TagD, SourceLocation DeclStart,
                 IdentifierInfo *ClassName,
                 SmallVectorImpl<Decl *> &Decls);
  Decl *ActOnField(Scope *S, Decl *TagD, SourceLocation DeclStart,
                   Declarator &D, Expr *BitfieldWidth);
 
  FieldDecl *HandleField(Scope *S, RecordDecl *TagD, SourceLocation DeclStart,
                         Declarator &D, Expr *BitfieldWidth,
                         InClassInitStyle InitStyle,
                         AccessSpecifier AS);
  MSPropertyDecl *HandleMSProperty(Scope *S, RecordDecl *TagD,
                                   SourceLocation DeclStart, Declarator &D,
                                   Expr *BitfieldWidth,
                                   InClassInitStyle InitStyle,
                                   AccessSpecifier AS,
                                   const ParsedAttr &MSPropertyAttr);
 
  FieldDecl *CheckFieldDecl(DeclarationName Name, QualType T,
                            TypeSourceInfo *TInfo,
                            RecordDecl *Record, SourceLocation Loc,
                            bool Mutable, Expr *BitfieldWidth,
                            InClassInitStyle InitStyle,
                            SourceLocation TSSL,
                            AccessSpecifier AS, NamedDecl *PrevDecl,
                            Declarator *D = nullptr);
 
  bool CheckNontrivialField(FieldDecl *FD);
  void DiagnoseNontrivial(const CXXRecordDecl *Record, CXXSpecialMember CSM);
 
  enum TrivialABIHandling {
    /// The triviality of a method unaffected by "trivial_abi".
    TAH_IgnoreTrivialABI,
 
    /// The triviality of a method affected by "trivial_abi".
    TAH_ConsiderTrivialABI
  };
 
  bool SpecialMemberIsTrivial(CXXMethodDecl *MD, CXXSpecialMember CSM,
                              TrivialABIHandling TAH = TAH_IgnoreTrivialABI,
                              bool Diagnose = false);
 
  /// For a defaulted function, the kind of defaulted function that it is.
  class DefaultedFunctionKind {
    CXXSpecialMember SpecialMember : 8;
    DefaultedComparisonKind Comparison : 8;
 
  public:
    DefaultedFunctionKind()
        : SpecialMember(CXXInvalid), Comparison(DefaultedComparisonKind::None) {
    }
    DefaultedFunctionKind(CXXSpecialMember CSM)
        : SpecialMember(CSM), Comparison(DefaultedComparisonKind::None) {}
    DefaultedFunctionKind(DefaultedComparisonKind Comp)
        : SpecialMember(CXXInvalid), Comparison(Comp) {}
 
    bool isSpecialMember() const { return SpecialMember != CXXInvalid; }
    bool isComparison() const {
      return Comparison != DefaultedComparisonKind::None;
    }
 
    explicit operator bool() const {
      return isSpecialMember() || isComparison();
    }
 
    CXXSpecialMember asSpecialMember() const { return SpecialMember; }
    DefaultedComparisonKind asComparison() const { return Comparison; }
 
    /// Get the index of this function kind for use in diagnostics.
    unsigned getDiagnosticIndex() const {
      static_assert(CXXInvalid > CXXDestructor,
                    "invalid should have highest index");
      static_assert((unsigned)DefaultedComparisonKind::None == 0,
                    "none should be equal to zero");
      return SpecialMember + (unsigned)Comparison;
    }
  };
 
  DefaultedFunctionKind getDefaultedFunctionKind(const FunctionDecl *FD);
 
  CXXSpecialMember getSpecialMember(const CXXMethodDecl *MD) {
    return getDefaultedFunctionKind(MD).asSpecialMember();
  }
  DefaultedComparisonKind getDefaultedComparisonKind(const FunctionDecl *FD) {
    return getDefaultedFunctionKind(FD).asComparison();
  }
 
  void ActOnLastBitfield(SourceLocation DeclStart,
                         SmallVectorImpl<Decl *> &AllIvarDecls);
  Decl *ActOnIvar(Scope *S, SourceLocation DeclStart, Declarator &D,
                  Expr *BitWidth, tok::ObjCKeywordKind visibility);
 
  // This is used for both record definitions and ObjC interface declarations.
  void ActOnFields(Scope *S, SourceLocation RecLoc, Decl *TagDecl,
                   ArrayRef<Decl *> Fields, SourceLocation LBrac,
                   SourceLocation RBrac, const ParsedAttributesView &AttrList);
 
  /// ActOnTagStartDefinition - Invoked when we have entered the
  /// scope of a tag's definition (e.g., for an enumeration, class,
  /// struct, or union).
  void ActOnTagStartDefinition(Scope *S, Decl *TagDecl);
 
  /// Perform ODR-like check for C/ObjC when merging tag types from modules.
  /// Differently from C++, actually parse the body and reject / error out
  /// in case of a structural mismatch.
  bool ActOnDuplicateDefinition(Decl *Prev, SkipBodyInfo &SkipBody);
 
  /// Check ODR hashes for C/ObjC when merging types from modules.
  /// Differently from C++, actually parse the body and reject in case
  /// of a mismatch.
  template <typename T,
            typename = std::enable_if_t<std::is_base_of<NamedDecl, T>::value>>
  bool ActOnDuplicateODRHashDefinition(T *Duplicate, T *Previous) {
    if (Duplicate->getODRHash() != Previous->getODRHash())
      return false;
 
    // Make the previous decl visible.
    makeMergedDefinitionVisible(Previous);
    return true;
  }
 
  typedef void *SkippedDefinitionContext;
 
  /// Invoked when we enter a tag definition that we're skipping.
  SkippedDefinitionContext ActOnTagStartSkippedDefinition(Scope *S, Decl *TD);
 
  void ActOnObjCContainerStartDefinition(ObjCContainerDecl *IDecl);
 
  /// ActOnStartCXXMemberDeclarations - Invoked when we have parsed a
  /// C++ record definition's base-specifiers clause and are starting its
  /// member declarations.
  void ActOnStartCXXMemberDeclarations(Scope *S, Decl *TagDecl,
                                       SourceLocation FinalLoc,
                                       bool IsFinalSpelledSealed,
                                       bool IsAbstract,
                                       SourceLocation LBraceLoc);
 
  /// ActOnTagFinishDefinition - Invoked once we have finished parsing
  /// the definition of a tag (enumeration, class, struct, or union).
  void ActOnTagFinishDefinition(Scope *S, Decl *TagDecl,
                                SourceRange BraceRange);
 
  void ActOnTagFinishSkippedDefinition(SkippedDefinitionContext Context);
 
  void ActOnObjCContainerFinishDefinition();
 
  /// Invoked when we must temporarily exit the objective-c container
  /// scope for parsing/looking-up C constructs.
  ///
  /// Must be followed by a call to \see ActOnObjCReenterContainerContext
  void ActOnObjCTemporaryExitContainerContext(ObjCContainerDecl *ObjCCtx);
  void ActOnObjCReenterContainerContext(ObjCContainerDecl *ObjCCtx);
 
  /// ActOnTagDefinitionError - Invoked when there was an unrecoverable
  /// error parsing the definition of a tag.
  void ActOnTagDefinitionError(Scope *S, Decl *TagDecl);
 
  EnumConstantDecl *CheckEnumConstant(EnumDecl *Enum,
                                      EnumConstantDecl *LastEnumConst,
                                      SourceLocation IdLoc,
                                      IdentifierInfo *Id,
                                      Expr *val);
  bool CheckEnumUnderlyingType(TypeSourceInfo *TI);
  bool CheckEnumRedeclaration(SourceLocation EnumLoc, bool IsScoped,
                              QualType EnumUnderlyingTy, bool IsFixed,
                              const EnumDecl *Prev);
 
  /// Determine whether the body of an anonymous enumeration should be skipped.
  /// \param II The name of the first enumerator.
  SkipBodyInfo shouldSkipAnonEnumBody(Scope *S, IdentifierInfo *II,
                                      SourceLocation IILoc);
 
  Decl *ActOnEnumConstant(Scope *S, Decl *EnumDecl, Decl *LastEnumConstant,
                          SourceLocation IdLoc, IdentifierInfo *Id,
                          const ParsedAttributesView &Attrs,
                          SourceLocation EqualLoc, Expr *Val);
  void ActOnEnumBody(SourceLocation EnumLoc, SourceRange BraceRange,
                     Decl *EnumDecl, ArrayRef<Decl *> Elements, Scope *S,
                     const ParsedAttributesView &Attr);
 
  /// Set the current declaration context until it gets popped.
  void PushDeclContext(Scope *S, DeclContext *DC);
  void PopDeclContext();
 
  /// EnterDeclaratorContext - Used when we must lookup names in the context
  /// of a declarator's nested name specifier.
  void EnterDeclaratorContext(Scope *S, DeclContext *DC);
  void ExitDeclaratorContext(Scope *S);
 
  /// Enter a template parameter scope, after it's been associated with a particular
  /// DeclContext. Causes lookup within the scope to chain through enclosing contexts
  /// in the correct order.
  void EnterTemplatedContext(Scope *S, DeclContext *DC);
 
  /// Push the parameters of D, which must be a function, into scope.
  void ActOnReenterFunctionContext(Scope* S, Decl* D);
  void ActOnExitFunctionContext();
 
  /// If \p AllowLambda is true, treat lambda as function.
  DeclContext *getFunctionLevelDeclContext(bool AllowLambda = false) const;
 
  /// Returns a pointer to the innermost enclosing function, or nullptr if the
  /// current context is not inside a function. If \p AllowLambda is true,
  /// this can return the call operator of an enclosing lambda, otherwise
  /// lambdas are skipped when looking for an enclosing function.
  FunctionDecl *getCurFunctionDecl(bool AllowLambda = false) const;
 
  /// getCurMethodDecl - If inside of a method body, this returns a pointer to
  /// the method decl for the method being parsed.  If we're currently
  /// in a 'block', this returns the containing context.
  ObjCMethodDecl *getCurMethodDecl();
 
  /// getCurFunctionOrMethodDecl - Return the Decl for the current ObjC method
  /// or C function we're in, otherwise return null.  If we're currently
  /// in a 'block', this returns the containing context.
  NamedDecl *getCurFunctionOrMethodDecl() const;
 
  /// Add this decl to the scope shadowed decl chains.
  void PushOnScopeChains(NamedDecl *D, Scope *S, bool AddToContext = true);
 
  /// isDeclInScope - If 'Ctx' is a function/method, isDeclInScope returns true
  /// if 'D' is in Scope 'S', otherwise 'S' is ignored and isDeclInScope returns
  /// true if 'D' belongs to the given declaration context.
  ///
  /// \param AllowInlineNamespace If \c true, allow the declaration to be in the
  ///        enclosing namespace set of the context, rather than contained
  ///        directly within it.
  bool isDeclInScope(NamedDecl *D, DeclContext *Ctx, Scope *S = nullptr,
                     bool AllowInlineNamespace = false) const;
 
  /// Finds the scope corresponding to the given decl context, if it
  /// happens to be an enclosing scope.  Otherwise return NULL.
  static Scope *getScopeForDeclContext(Scope *S, DeclContext *DC);
 
  /// Subroutines of ActOnDeclarator().
  TypedefDecl *ParseTypedefDecl(Scope *S, Declarator &D, QualType T,
                                TypeSourceInfo *TInfo);
  bool isIncompatibleTypedef(TypeDecl *Old, TypedefNameDecl *New);
 
  /// Describes the kind of merge to perform for availability
  /// attributes (including "deprecated", "unavailable", and "availability").
  enum AvailabilityMergeKind {
    /// Don't merge availability attributes at all.
    AMK_None,
    /// Merge availability attributes for a redeclaration, which requires
    /// an exact match.
    AMK_Redeclaration,
    /// Merge availability attributes for an override, which requires
    /// an exact match or a weakening of constraints.
    AMK_Override,
    /// Merge availability attributes for an implementation of
    /// a protocol requirement.
    AMK_ProtocolImplementation,
    /// Merge availability attributes for an implementation of
    /// an optional protocol requirement.
    AMK_OptionalProtocolImplementation
  };
 
  /// Describes the kind of priority given to an availability attribute.
  ///
  /// The sum of priorities deteremines the final priority of the attribute.
  /// The final priority determines how the attribute will be merged.
  /// An attribute with a lower priority will always remove higher priority
  /// attributes for the specified platform when it is being applied. An
  /// attribute with a higher priority will not be applied if the declaration
  /// already has an availability attribute with a lower priority for the
  /// specified platform. The final prirority values are not expected to match
  /// the values in this enumeration, but instead should be treated as a plain
  /// integer value. This enumeration just names the priority weights that are
  /// used to calculate that final vaue.
  enum AvailabilityPriority : int {
    /// The availability attribute was specified explicitly next to the
    /// declaration.
    AP_Explicit = 0,
 
    /// The availability attribute was applied using '#pragma clang attribute'.
    AP_PragmaClangAttribute = 1,
 
    /// The availability attribute for a specific platform was inferred from
    /// an availability attribute for another platform.
    AP_InferredFromOtherPlatform = 2
  };
 
  /// Attribute merging methods. Return true if a new attribute was added.
  AvailabilityAttr *
  mergeAvailabilityAttr(NamedDecl *D, const AttributeCommonInfo &CI,
                        IdentifierInfo *Platform, bool Implicit,
                        VersionTuple Introduced, VersionTuple Deprecated,
                        VersionTuple Obsoleted, bool IsUnavailable,
                        StringRef Message, bool IsStrict, StringRef Replacement,
                        AvailabilityMergeKind AMK, int Priority);
  TypeVisibilityAttr *
  mergeTypeVisibilityAttr(Decl *D, const AttributeCommonInfo &CI,
                          TypeVisibilityAttr::VisibilityType Vis);
  VisibilityAttr *mergeVisibilityAttr(Decl *D, const AttributeCommonInfo &CI,
                                      VisibilityAttr::VisibilityType Vis);
  UuidAttr *mergeUuidAttr(Decl *D, const AttributeCommonInfo &CI,
                          StringRef UuidAsWritten, MSGuidDecl *GuidDecl);
  DLLImportAttr *mergeDLLImportAttr(Decl *D, const AttributeCommonInfo &CI);
  DLLExportAttr *mergeDLLExportAttr(Decl *D, const AttributeCommonInfo &CI);
  MSInheritanceAttr *mergeMSInheritanceAttr(Decl *D,
                                            const AttributeCommonInfo &CI,
                                            bool BestCase,
                                            MSInheritanceModel Model);
  ErrorAttr *mergeErrorAttr(Decl *D, const AttributeCommonInfo &CI,
                            StringRef NewUserDiagnostic);
  FormatAttr *mergeFormatAttr(Decl *D, const AttributeCommonInfo &CI,
                              IdentifierInfo *Format, int FormatIdx,
                              int FirstArg);
  SectionAttr *mergeSectionAttr(Decl *D, const AttributeCommonInfo &CI,
                                StringRef Name);
  CodeSegAttr *mergeCodeSegAttr(Decl *D, const AttributeCommonInfo &CI,
                                StringRef Name);
  AlwaysInlineAttr *mergeAlwaysInlineAttr(Decl *D,
                                          const AttributeCommonInfo &CI,
                                          const IdentifierInfo *Ident);
  MinSizeAttr *mergeMinSizeAttr(Decl *D, const AttributeCommonInfo &CI);
  SwiftNameAttr *mergeSwiftNameAttr(Decl *D, const SwiftNameAttr &SNA,
                                    StringRef Name);
  OptimizeNoneAttr *mergeOptimizeNoneAttr(Decl *D,
                                          const AttributeCommonInfo &CI);
  InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D, const ParsedAttr &AL);
  InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D,
                                                const InternalLinkageAttr &AL);
  WebAssemblyImportNameAttr *mergeImportNameAttr(
      Decl *D, const WebAssemblyImportNameAttr &AL);
  WebAssemblyImportModuleAttr *mergeImportModuleAttr(
      Decl *D, const WebAssemblyImportModuleAttr &AL);
  EnforceTCBAttr *mergeEnforceTCBAttr(Decl *D, const EnforceTCBAttr &AL);
  EnforceTCBLeafAttr *mergeEnforceTCBLeafAttr(Decl *D,
                                              const EnforceTCBLeafAttr &AL);
  BTFDeclTagAttr *mergeBTFDeclTagAttr(Decl *D, const BTFDeclTagAttr &AL);
  HLSLNumThreadsAttr *mergeHLSLNumThreadsAttr(Decl *D,
                                              const AttributeCommonInfo &AL,
                                              int X, int Y, int Z);
  HLSLShaderAttr *mergeHLSLShaderAttr(Decl *D, const AttributeCommonInfo &AL,
                                      HLSLShaderAttr::ShaderType ShaderType);
  HLSLParamModifierAttr *
  mergeHLSLParamModifierAttr(Decl *D, const AttributeCommonInfo &AL,
                             HLSLParamModifierAttr::Spelling Spelling);
 
  void mergeDeclAttributes(NamedDecl *New, Decl *Old,
                           AvailabilityMergeKind AMK = AMK_Redeclaration);
  void MergeTypedefNameDecl(Scope *S, TypedefNameDecl *New,
                            LookupResult &OldDecls);
  bool MergeFunctionDecl(FunctionDecl *New, NamedDecl *&Old, Scope *S,
                         bool MergeTypeWithOld, bool NewDeclIsDefn);
  bool MergeCompatibleFunctionDecls(FunctionDecl *New, FunctionDecl *Old,
                                    Scope *S, bool MergeTypeWithOld);
  void mergeObjCMethodDecls(ObjCMethodDecl *New, ObjCMethodDecl *Old);
  void MergeVarDecl(VarDecl *New, LookupResult &Previous);
  void MergeVarDeclTypes(VarDecl *New, VarDecl *Old, bool MergeTypeWithOld);
  void MergeVarDeclExceptionSpecs(VarDecl *New, VarDecl *Old);
  bool checkVarDeclRedefinition(VarDecl *OldDefn, VarDecl *NewDefn);
  void notePreviousDefinition(const NamedDecl *Old, SourceLocation New);
  bool MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old, Scope *S);
 
  // AssignmentAction - This is used by all the assignment diagnostic functions
  // to represent what is actually causing the operation
  enum AssignmentAction {
    AA_Assigning,
    AA_Passing,
    AA_Returning,
    AA_Converting,
    AA_Initializing,
    AA_Sending,
    AA_Casting,
    AA_Passing_CFAudited
  };
 
  /// C++ Overloading.
  enum OverloadKind {
    /// This is a legitimate overload: the existing declarations are
    /// functions or function templates with different signatures.
    Ovl_Overload,
 
    /// This is not an overload because the signature exactly matches
    /// an existing declaration.
    Ovl_Match,
 
    /// This is not an overload because the lookup results contain a
    /// non-function.
    Ovl_NonFunction
  };
  OverloadKind CheckOverload(Scope *S,
                             FunctionDecl *New,
                             const LookupResult &OldDecls,
                             NamedDecl *&OldDecl,
                             bool UseMemberUsingDeclRules);
  bool IsOverload(FunctionDecl *New, FunctionDecl *Old,
                  bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true);
 
  // Checks whether MD constitutes an override the base class method BaseMD.
  // When checking for overrides, the object object members are ignored.
  bool IsOverride(FunctionDecl *MD, FunctionDecl *BaseMD,
                  bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true);
 
  // Calculates whether the expression Constraint depends on an enclosing
  // template, for the purposes of [temp.friend] p9.
  // TemplateDepth is the 'depth' of the friend function, which is used to
  // compare whether a declaration reference is referring to a containing
  // template, or just the current friend function. A 'lower' TemplateDepth in
  // the AST refers to a 'containing' template. As the constraint is
  // uninstantiated, this is relative to the 'top' of the TU.
  bool
  ConstraintExpressionDependsOnEnclosingTemplate(const FunctionDecl *Friend,
                                                 unsigned TemplateDepth,
                                                 const Expr *Constraint);
 
  // Calculates whether the friend function depends on an enclosing template for
  // the purposes of [temp.friend] p9.
  bool FriendConstraintsDependOnEnclosingTemplate(const FunctionDecl *FD);
 
  enum class AllowedExplicit {
    /// Allow no explicit functions to be used.
    None,
    /// Allow explicit conversion functions but not explicit constructors.
    Conversions,
    /// Allow both explicit conversion functions and explicit constructors.
    All
  };
 
  ImplicitConversionSequence
  TryImplicitConversion(Expr *From, QualType ToType,
                        bool SuppressUserConversions,
                        AllowedExplicit AllowExplicit,
                        bool InOverloadResolution,
                        bool CStyle,
                        bool AllowObjCWritebackConversion);
 
  bool IsIntegralPromotion(Expr *From, QualType FromType, QualType ToType);
  bool IsFloatingPointPromotion(QualType FromType, QualType ToType);
  bool IsComplexPromotion(QualType FromType, QualType ToType);
  bool IsPointerConversion(Expr *From, QualType FromType, QualType ToType,
                           bool InOverloadResolution,
                           QualType& ConvertedType, bool &IncompatibleObjC);
  bool isObjCPointerConversion(QualType FromType, QualType ToType,
                               QualType& ConvertedType, bool &IncompatibleObjC);
  bool isObjCWritebackConversion(QualType FromType, QualType ToType,
                                 QualType &ConvertedType);
  bool IsBlockPointerConversion(QualType FromType, QualType ToType,
                                QualType& ConvertedType);
 
  bool FunctionParamTypesAreEqual(ArrayRef<QualType> Old,
                                  ArrayRef<QualType> New,
                                  unsigned *ArgPos = nullptr,
                                  bool Reversed = false);
 
  bool FunctionParamTypesAreEqual(const FunctionProtoType *OldType,
                                  const FunctionProtoType *NewType,
                                  unsigned *ArgPos = nullptr,
                                  bool Reversed = false);
 
  bool FunctionNonObjectParamTypesAreEqual(const FunctionDecl *OldFunction,
                                           const FunctionDecl *NewFunction,
                                           unsigned *ArgPos = nullptr,
                                           bool Reversed = false);
 
  void HandleFunctionTypeMismatch(PartialDiagnostic &PDiag,
                                  QualType FromType, QualType ToType);
 
  void maybeExtendBlockObject(ExprResult &E);
  CastKind PrepareCastToObjCObjectPointer(ExprResult &E);
  bool CheckPointerConversion(Expr *From, QualType ToType,
                              CastKind &Kind,
                              CXXCastPath& BasePath,
                              bool IgnoreBaseAccess,
                              bool Diagnose = true);
  bool IsMemberPointerConversion(Expr *From, QualType FromType, QualType ToType,
                                 bool InOverloadResolution,
                                 QualType &ConvertedType);
  bool CheckMemberPointerConversion(Expr *From, QualType ToType,
                                    CastKind &Kind,
                                    CXXCastPath &BasePath,
                                    bool IgnoreBaseAccess);
  bool IsQualificationConversion(QualType FromType, QualType ToType,
                                 bool CStyle, bool &ObjCLifetimeConversion);
  bool IsFunctionConversion(QualType FromType, QualType ToType,
                            QualType &ResultTy);
  bool DiagnoseMultipleUserDefinedConversion(Expr *From, QualType ToType);
  bool isSameOrCompatibleFunctionType(QualType Param, QualType Arg);
 
  bool CanPerformAggregateInitializationForOverloadResolution(
      const InitializedEntity &Entity, InitListExpr *From);
 
  bool IsStringInit(Expr *Init, const ArrayType *AT);
 
  bool CanPerformCopyInitialization(const InitializedEntity &Entity,
                                    ExprResult Init);
  ExprResult PerformCopyInitialization(const InitializedEntity &Entity,
                                       SourceLocation EqualLoc,
                                       ExprResult Init,
                                       bool TopLevelOfInitList = false,
                                       bool AllowExplicit = false);
  ExprResult InitializeExplicitObjectArgument(Sema &S, Expr *Obj,
                                              FunctionDecl *Fun);
  ExprResult PerformImplicitObjectArgumentInitialization(
      Expr *From, NestedNameSpecifier *Qualifier, NamedDecl *FoundDecl,
      CXXMethodDecl *Method);
 
  /// Check that the lifetime of the initializer (and its subobjects) is
  /// sufficient for initializing the entity, and perform lifetime extension
  /// (when permitted) if not.
  void checkInitializerLifetime(const InitializedEntity &Entity, Expr *Init);
 
  ExprResult PerformContextuallyConvertToBool(Expr *From);
  ExprResult PerformContextuallyConvertToObjCPointer(Expr *From);
 
  /// Contexts in which a converted constant expression is required.
  enum CCEKind {
    CCEK_CaseValue,    ///< Expression in a case label.
    CCEK_Enumerator,   ///< Enumerator value with fixed underlying type.
    CCEK_TemplateArg,  ///< Value of a non-type template parameter.
    CCEK_ArrayBound,   ///< Array bound in array declarator or new-expression.
    CCEK_ExplicitBool, ///< Condition in an explicit(bool) specifier.
    CCEK_Noexcept,     ///< Condition in a noexcept(bool) specifier.
    CCEK_StaticAssertMessageSize, ///< Call to size() in a static assert
                                  ///< message.
    CCEK_StaticAssertMessageData, ///< Call to data() in a static assert
                                  ///< message.
  };
 
  ExprResult BuildConvertedConstantExpression(Expr *From, QualType T,
                                              CCEKind CCE,
                                              NamedDecl *Dest = nullptr);
 
  ExprResult CheckConvertedConstantExpression(Expr *From, QualType T,
                                              llvm::APSInt &Value, CCEKind CCE);
  ExprResult CheckConvertedConstantExpression(Expr *From, QualType T,
                                              APValue &Value, CCEKind CCE,
                                              NamedDecl *Dest = nullptr);
 
  ExprResult
  EvaluateConvertedConstantExpression(Expr *E, QualType T, APValue &Value,
                                      CCEKind CCE, bool RequireInt,
                                      const APValue &PreNarrowingValue);
 
  /// Abstract base class used to perform a contextual implicit
  /// conversion from an expression to any type passing a filter.
  class ContextualImplicitConverter {
  public:
    bool Suppress;
    bool SuppressConversion;
 
    ContextualImplicitConverter(bool Suppress = false,
                                bool SuppressConversion = false)
        : Suppress(Suppress), SuppressConversion(SuppressConversion) {}
 
    /// Determine whether the specified type is a valid destination type
    /// for this conversion.
    virtual bool match(QualType T) = 0;
 
    /// Emits a diagnostic complaining that the expression does not have
    /// integral or enumeration type.
    virtual SemaDiagnosticBuilder
    diagnoseNoMatch(Sema &S, SourceLocation Loc, QualType T) = 0;
 
    /// Emits a diagnostic when the expression has incomplete class type.
    virtual SemaDiagnosticBuilder
    diagnoseIncomplete(Sema &S, SourceLocation Loc, QualType T) = 0;
 
    /// Emits a diagnostic when the only matching conversion function
    /// is explicit.
    virtual SemaDiagnosticBuilder diagnoseExplicitConv(
        Sema &S, SourceLocation Loc, QualType T, QualType ConvTy) = 0;
 
    /// Emits a note for the explicit conversion function.
    virtual SemaDiagnosticBuilder
    noteExplicitConv(Sema &S, CXXConversionDecl *Conv, QualType ConvTy) = 0;
 
    /// Emits a diagnostic when there are multiple possible conversion
    /// functions.
    virtual SemaDiagnosticBuilder
    diagnoseAmbiguous(Sema &S, SourceLocation Loc, QualType T) = 0;
 
    /// Emits a note for one of the candidate conversions.
    virtual SemaDiagnosticBuilder
    noteAmbiguous(Sema &S, CXXConversionDecl *Conv, QualType ConvTy) = 0;
 
    /// Emits a diagnostic when we picked a conversion function
    /// (for cases when we are not allowed to pick a conversion function).
    virtual SemaDiagnosticBuilder diagnoseConversion(
        Sema &S, SourceLocation Loc, QualType T, QualType ConvTy) = 0;
 
    virtual ~ContextualImplicitConverter() {}
  };
 
  class ICEConvertDiagnoser : public ContextualImplicitConverter {
    bool AllowScopedEnumerations;
 
  public:
    ICEConvertDiagnoser(bool AllowScopedEnumerations,
                        bool Suppress, bool SuppressConversion)
        : ContextualImplicitConverter(Suppress, SuppressConversion),
          AllowScopedEnumerations(AllowScopedEnumerations) {}
 
    /// Match an integral or (possibly scoped) enumeration type.
    bool match(QualType T) override;
 
    SemaDiagnosticBuilder
    diagnoseNoMatch(Sema &S, SourceLocation Loc, QualType T) override {
      return diagnoseNotInt(S, Loc, T);
    }
 
    /// Emits a diagnostic complaining that the expression does not have
    /// integral or enumeration type.
    virtual SemaDiagnosticBuilder
    diagnoseNotInt(Sema &S, SourceLocation Loc, QualType T) = 0;
  };
 
  /// Perform a contextual implicit conversion.
  ExprResult PerformContextualImplicitConversion(
      SourceLocation Loc, Expr *FromE, ContextualImplicitConverter &Converter);
 
 
  enum ObjCSubscriptKind {
    OS_Array,
    OS_Dictionary,
    OS_Error
  };
  ObjCSubscriptKind CheckSubscriptingKind(Expr *FromE);
 
  // Note that LK_String is intentionally after the other literals, as
  // this is used for diagnostics logic.
  enum ObjCLiteralKind {
    LK_Array,
    LK_Dictionary,
    LK_Numeric,
    LK_Boxed,
    LK_String,
    LK_Block,
    LK_None
  };
  ObjCLiteralKind CheckLiteralKind(Expr *FromE);
 
  ExprResult PerformObjectMemberConversion(Expr *From,
                                           NestedNameSpecifier *Qualifier,
                                           NamedDecl *FoundDecl,
                                           NamedDecl *Member);
 
  // Members have to be NamespaceDecl* or TranslationUnitDecl*.
  // TODO: make this is a typesafe union.
  typedef llvm::SmallSetVector<DeclContext   *, 16> AssociatedNamespaceSet;
  typedef llvm::SmallSetVector<CXXRecordDecl *, 16> AssociatedClassSet;
 
  using ADLCallKind = CallExpr::ADLCallKind;
 
  void AddOverloadCandidate(
      FunctionDecl *Function, DeclAccessPair FoundDecl, ArrayRef<Expr *> Args,
      OverloadCandidateSet &CandidateSet, bool SuppressUserConversions = false,
      bool PartialOverloading = false, bool AllowExplicit = true,
      bool AllowExplicitConversion = false,
      ADLCallKind IsADLCandidate = ADLCallKind::NotADL,
      ConversionSequenceList EarlyConversions = std::nullopt,
      OverloadCandidateParamOrder PO = {},
      bool AggregateCandidateDeduction = false);
  void AddFunctionCandidates(const UnresolvedSetImpl &Functions,
                      ArrayRef<Expr *> Args,
                      OverloadCandidateSet &CandidateSet,
                      TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr,
                      bool SuppressUserConversions = false,
                      bool PartialOverloading = false,
                      bool FirstArgumentIsBase = false);
  void AddMethodCandidate(DeclAccessPair FoundDecl,
                          QualType ObjectType,
                          Expr::Classification ObjectClassification,
                          ArrayRef<Expr *> Args,
                          OverloadCandidateSet& CandidateSet,
                          bool SuppressUserConversion = false,
                          OverloadCandidateParamOrder PO = {});
  void
  AddMethodCandidate(CXXMethodDecl *Method, DeclAccessPair FoundDecl,
                     CXXRecordDecl *ActingContext, QualType ObjectType,
                     Expr::Classification ObjectClassification,
                     ArrayRef<Expr *> Args, OverloadCandidateSet &CandidateSet,
                     bool SuppressUserConversions = false,
                     bool PartialOverloading = false,
                     ConversionSequenceList EarlyConversions = std::nullopt,
                     OverloadCandidateParamOrder PO = {});
  void AddMethodTemplateCandidate(FunctionTemplateDecl *MethodTmpl,
                                  DeclAccessPair FoundDecl,
                                  CXXRecordDecl *ActingContext,
                                 TemplateArgumentListInfo *ExplicitTemplateArgs,
                                  QualType ObjectType,
                                  Expr::Classification ObjectClassification,
                                  ArrayRef<Expr *> Args,
                                  OverloadCandidateSet& CandidateSet,
                                  bool SuppressUserConversions = false,
                                  bool PartialOverloading = false,
                                  OverloadCandidateParamOrder PO = {});
  void AddTemplateOverloadCandidate(
      FunctionTemplateDecl *FunctionTemplate, DeclAccessPair FoundDecl,
      TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
      OverloadCandidateSet &CandidateSet, bool SuppressUserConversions = false,
      bool PartialOverloading = false, bool AllowExplicit = true,
      ADLCallKind IsADLCandidate = ADLCallKind::NotADL,
      OverloadCandidateParamOrder PO = {},
      bool AggregateCandidateDeduction = false);
  bool CheckNonDependentConversions(
      FunctionTemplateDecl *FunctionTemplate, ArrayRef<QualType> ParamTypes,
      ArrayRef<Expr *> Args, OverloadCandidateSet &CandidateSet,
      ConversionSequenceList &Conversions, bool SuppressUserConversions,
      CXXRecordDecl *ActingContext = nullptr, QualType ObjectType = QualType(),
      Expr::Classification ObjectClassification = {},
      OverloadCandidateParamOrder PO = {});
  void AddConversionCandidate(
      CXXConversionDecl *Conversion, DeclAccessPair FoundDecl,
      CXXRecordDecl *ActingContext, Expr *From, QualType ToType,
      OverloadCandidateSet &CandidateSet, bool AllowObjCConversionOnExplicit,
      bool AllowExplicit, bool AllowResultConversion = true);
  void AddTemplateConversionCandidate(
      FunctionTemplateDecl *FunctionTemplate, DeclAccessPair FoundDecl,
      CXXRecordDecl *ActingContext, Expr *From, QualType ToType,
      OverloadCandidateSet &CandidateSet, bool AllowObjCConversionOnExplicit,
      bool AllowExplicit, bool AllowResultConversion = true);
  void AddSurrogateCandidate(CXXConversionDecl *Conversion,
                             DeclAccessPair FoundDecl,
                             CXXRecordDecl *ActingContext,
                             const FunctionProtoType *Proto,
                             Expr *Object, ArrayRef<Expr *> Args,
                             OverloadCandidateSet& CandidateSet);
  void AddNonMemberOperatorCandidates(
      const UnresolvedSetImpl &Functions, ArrayRef<Expr *> Args,
      OverloadCandidateSet &CandidateSet,
      TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr);
  void AddMemberOperatorCandidates(OverloadedOperatorKind Op,
                                   SourceLocation OpLoc, ArrayRef<Expr *> Args,
                                   OverloadCandidateSet &CandidateSet,
                                   OverloadCandidateParamOrder PO = {});
  void AddBuiltinCandidate(QualType *ParamTys, ArrayRef<Expr *> Args,
                           OverloadCandidateSet& CandidateSet,
                           bool IsAssignmentOperator = false,
                           unsigned NumContextualBoolArguments = 0);
  void AddBuiltinOperatorCandidates(OverloadedOperatorKind Op,
                                    SourceLocation OpLoc, ArrayRef<Expr *> Args,
                                    OverloadCandidateSet& CandidateSet);
  void AddArgumentDependentLookupCandidates(DeclarationName Name,
                                            SourceLocation Loc,
                                            ArrayRef<Expr *> Args,
                                TemplateArgumentListInfo *ExplicitTemplateArgs,
                                            OverloadCandidateSet& CandidateSet,
                                            bool PartialOverloading = false);
 
  // Emit as a 'note' the specific overload candidate
  void NoteOverloadCandidate(
      const NamedDecl *Found, const FunctionDecl *Fn,
      OverloadCandidateRewriteKind RewriteKind = OverloadCandidateRewriteKind(),
      QualType DestType = QualType(), bool TakingAddress = false);
 
  // Emit as a series of 'note's all template and non-templates identified by
  // the expression Expr
  void NoteAllOverloadCandidates(Expr *E, QualType DestType = QualType(),
                                 bool TakingAddress = false);
 
  /// Check the enable_if expressions on the given function. Returns the first
  /// failing attribute, or NULL if they were all successful.
  EnableIfAttr *CheckEnableIf(FunctionDecl *Function, SourceLocation CallLoc,
                              ArrayRef<Expr *> Args,
                              bool MissingImplicitThis = false);
 
  /// Find the failed Boolean condition within a given Boolean
  /// constant expression, and describe it with a string.
  std::pair<Expr *, std::string> findFailedBooleanCondition(Expr *Cond);
 
  /// Emit diagnostics for the diagnose_if attributes on Function, ignoring any
  /// non-ArgDependent DiagnoseIfAttrs.
  ///
  /// Argument-dependent diagnose_if attributes should be checked each time a
  /// function is used as a direct callee of a function call.
  ///
  /// Returns true if any errors were emitted.
  bool diagnoseArgDependentDiagnoseIfAttrs(const FunctionDecl *Function,
                                           const Expr *ThisArg,
                                           ArrayRef<const Expr *> Args,
                                           SourceLocation Loc);
 
  /// Emit diagnostics for the diagnose_if attributes on Function, ignoring any
  /// ArgDependent DiagnoseIfAttrs.
  ///
  /// Argument-independent diagnose_if attributes should be checked on every use
  /// of a function.
  ///
  /// Returns true if any errors were emitted.
  bool diagnoseArgIndependentDiagnoseIfAttrs(const NamedDecl *ND,
                                             SourceLocation Loc);
 
  /// Returns whether the given function's address can be taken or not,
  /// optionally emitting a diagnostic if the address can't be taken.
  ///
  /// Returns false if taking the address of the function is illegal.
  bool checkAddressOfFunctionIsAvailable(const FunctionDecl *Function,
                                         bool Complain = false,
                                         SourceLocation Loc = SourceLocation());
 
  // [PossiblyAFunctionType]  -->   [Return]
  // NonFunctionType --> NonFunctionType
  // R (A) --> R(A)
  // R (*)(A) --> R (A)
  // R (&)(A) --> R (A)
  // R (S::*)(A) --> R (A)
  QualType ExtractUnqualifiedFunctionType(QualType PossiblyAFunctionType);
 
  FunctionDecl *
  ResolveAddressOfOverloadedFunction(Expr *AddressOfExpr,
                                     QualType TargetType,
                                     bool Complain,
                                     DeclAccessPair &Found,
                                     bool *pHadMultipleCandidates = nullptr);
 
  FunctionDecl *
  resolveAddressOfSingleOverloadCandidate(Expr *E, DeclAccessPair &FoundResult);
 
  bool resolveAndFixAddressOfSingleOverloadCandidate(
      ExprResult &SrcExpr, bool DoFunctionPointerConversion = false);
 
  FunctionDecl *ResolveSingleFunctionTemplateSpecialization(
      OverloadExpr *ovl, bool Complain = false, DeclAccessPair *Found = nullptr,
      TemplateSpecCandidateSet *FailedTSC = nullptr);
 
  bool ResolveAndFixSingleFunctionTemplateSpecialization(
      ExprResult &SrcExpr, bool DoFunctionPointerConversion = false,
      bool Complain = false, SourceRange OpRangeForComplaining = SourceRange(),
      QualType DestTypeForComplaining = QualType(),
      unsigned DiagIDForComplaining = 0);
 
  ExprResult FixOverloadedFunctionReference(Expr *E, DeclAccessPair FoundDecl,
                                            FunctionDecl *Fn);
  ExprResult FixOverloadedFunctionReference(ExprResult,
                                            DeclAccessPair FoundDecl,
                                            FunctionDecl *Fn);
 
  void AddOverloadedCallCandidates(UnresolvedLookupExpr *ULE,
                                   ArrayRef<Expr *> Args,
                                   OverloadCandidateSet &CandidateSet,
                                   bool PartialOverloading = false);
  void AddOverloadedCallCandidates(
      LookupResult &R, TemplateArgumentListInfo *ExplicitTemplateArgs,
      ArrayRef<Expr *> Args, OverloadCandidateSet &CandidateSet);
 
  // An enum used to represent the different possible results of building a
  // range-based for loop.
  enum ForRangeStatus {
    FRS_Success,
    FRS_NoViableFunction,
    FRS_DiagnosticIssued
  };
 
  ForRangeStatus BuildForRangeBeginEndCall(SourceLocation Loc,
                                           SourceLocation RangeLoc,
                                           const DeclarationNameInfo &NameInfo,
                                           LookupResult &MemberLookup,
                                           OverloadCandidateSet *CandidateSet,
                                           Expr *Range, ExprResult *CallExpr);
 
  ExprResult BuildOverloadedCallExpr(Scope *S, Expr *Fn,
                                     UnresolvedLookupExpr *ULE,
                                     SourceLocation LParenLoc,
                                     MultiExprArg Args,
                                     SourceLocation RParenLoc,
                                     Expr *ExecConfig,
                                     bool AllowTypoCorrection=true,
                                     bool CalleesAddressIsTaken=false);
 
  bool buildOverloadedCallSet(Scope *S, Expr *Fn, UnresolvedLookupExpr *ULE,
                              MultiExprArg Args, SourceLocation RParenLoc,
                              OverloadCandidateSet *CandidateSet,
                              ExprResult *Result);
 
  ExprResult CreateUnresolvedLookupExpr(CXXRecordDecl *NamingClass,
                                        NestedNameSpecifierLoc NNSLoc,
                                        DeclarationNameInfo DNI,
                                        const UnresolvedSetImpl &Fns,
                                        bool PerformADL = true);
 
  ExprResult CreateOverloadedUnaryOp(SourceLocation OpLoc,
                                     UnaryOperatorKind Opc,
                                     const UnresolvedSetImpl &Fns,
                                     Expr *input, bool RequiresADL = true);
 
  void LookupOverloadedBinOp(OverloadCandidateSet &CandidateSet,
                             OverloadedOperatorKind Op,
                             const UnresolvedSetImpl &Fns,
                             ArrayRef<Expr *> Args, bool RequiresADL = true);
  ExprResult CreateOverloadedBinOp(SourceLocation OpLoc,
                                   BinaryOperatorKind Opc,
                                   const UnresolvedSetImpl &Fns,
                                   Expr *LHS, Expr *RHS,
                                   bool RequiresADL = true,
                                   bool AllowRewrittenCandidates = true,
                                   FunctionDecl *DefaultedFn = nullptr);
  ExprResult BuildSynthesizedThreeWayComparison(SourceLocation OpLoc,
                                                const UnresolvedSetImpl &Fns,
                                                Expr *LHS, Expr *RHS,
                                                FunctionDecl *DefaultedFn);
 
  ExprResult CreateOverloadedArraySubscriptExpr(SourceLocation LLoc,
                                                SourceLocation RLoc, Expr *Base,
                                                MultiExprArg Args);
 
  ExprResult BuildCallToMemberFunction(Scope *S, Expr *MemExpr,
                                       SourceLocation LParenLoc,
                                       MultiExprArg Args,
                                       SourceLocation RParenLoc,
                                       Expr *ExecConfig = nullptr,
                                       bool IsExecConfig = false,
                                       bool AllowRecovery = false);
  ExprResult
  BuildCallToObjectOfClassType(Scope *S, Expr *Object, SourceLocation LParenLoc,
                               MultiExprArg Args,
                               SourceLocation RParenLoc);
 
  ExprResult BuildOverloadedArrowExpr(Scope *S, Expr *Base,
                                      SourceLocation OpLoc,
                                      bool *NoArrowOperatorFound = nullptr);
 
  /// CheckCallReturnType - Checks that a call expression's return type is
  /// complete. Returns true on failure. The location passed in is the location
  /// that best represents the call.
  bool CheckCallReturnType(QualType ReturnType, SourceLocation Loc,
                           CallExpr *CE, FunctionDecl *FD);
 
  /// Helpers for dealing with blocks and functions.
  bool CheckParmsForFunctionDef(ArrayRef<ParmVarDecl *> Parameters,
                                bool CheckParameterNames);
  void CheckCXXDefaultArguments(FunctionDecl *FD);
  void CheckExtraCXXDefaultArguments(Declarator &D);
  Scope *getNonFieldDeclScope(Scope *S);
 
  /// \name Name lookup
  ///