Sema.h

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//===--- Sema.h - Semantic Analysis & AST Building --------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/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/ExprObjC.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/TypeLoc.h"
#include "clang/AST/TypeOrdering.h"
#include "clang/Basic/ExpressionTraits.h"
#include "clang/Basic/Module.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/TypoCorrection.h"
#include "clang/Sema/Weak.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/TinyPtrVector.h"
#include <deque>
#include <memory>
#include <string>
#include <vector>

namespace llvm {
  class APSInt;
  template <typename ValueT> struct DenseMapInfo;
  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 OverloadCandidate;
  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 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;
  }
};

/// Sema - This implements semantic analysis and AST building for C.
class Sema {
  Sema(const Sema &) = delete;
  void operator=(const Sema &) = delete;

  ///Source of additional semantic information.
  ExternalSemaSource *ExternalSource;

  ///Whether Sema has generated a multiplexer and has to delete it.
  bool isMultiplexExternalSource;

  static bool mightHaveNonExternalLinkage(const DeclaratorDecl *FD);

  bool isVisibleSlow(const NamedDecl *D);

  /// 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);

public:
  typedef OpaquePtr<DeclGroupRef> DeclGroupPtrTy;
  typedef OpaquePtr<TemplateName> TemplateTy;
  typedef OpaquePtr<QualType> TypeTy;

  OpenCLOptions OpenCLFeatures;
  FPOptions FPFeatures;

  const LangOptions &LangOpts;
  Preprocessor &PP;
  ASTContext &Context;
  ASTConsumer &Consumer;
  DiagnosticsEngine &Diags;
  SourceManager &SourceMgr;

  /// 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;

  /// pragma clang section kind
  enum PragmaClangSectionKind {
    PCSK_Invalid      = 0,
    PCSK_BSS          = 1,
    PCSK_Data         = 2,
    PCSK_Rodata       = 3,
    PCSK_Text         = 4
   };

  enum PragmaClangSectionAction {
    PCSA_Set     = 0,
    PCSA_Clear   = 1
  };

  struct PragmaClangSection {
    std::string SectionName;
    bool Valid = false;
    SourceLocation PragmaLocation;

    void Act(SourceLocation PragmaLocation,
             PragmaClangSectionAction Action,
             StringLiteral* Name);
   };

   PragmaClangSection PragmaClangBSSSection;
   PragmaClangSection PragmaClangDataSection;
   PragmaClangSection PragmaClangRodataSection;
   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)
  };

  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);

    // 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<MSVtorDispAttr::Mode> VtorDispStack;
  // #pragma pack.
  // Sentinel to represent when the stack is set to mac68k alignment.
  static const unsigned kMac68kAlignmentSentinel = ~0U;
  PragmaStack<unsigned> PackStack;
  // The current #pragma pack values and locations at each #include.
  struct PackIncludeState {
    unsigned CurrentValue;
    SourceLocation CurrentPragmaLocation;
    bool HasNonDefaultValue, ShouldWarnOnInclude;
  };
  SmallVector<PackIncludeState, 8> PackIncludeStack;
  // Segment #pragmas.
  PragmaStack<StringLiteral *> DataSegStack;
  PragmaStack<StringLiteral *> BSSSegStack;
  PragmaStack<StringLiteral *> ConstSegStack;
  PragmaStack<StringLiteral *> CodeSegStack;

  // 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;

  /// 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;
    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;

  /// 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.  The
  /// element type here is ExprWithCleanups::Object.
  SmallVector<BlockDecl*, 8> ExprCleanupObjects;

  /// Store a list 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.
  llvm::SmallPtrSet<Expr*, 2> MaybeODRUseExprs;

  std::unique_ptr<sema::FunctionScopeInfo> PreallocatedFunctionScope;

  /// Stack containing information about each of the nested
  /// function, block, and method scopes that are currently active.
  SmallVector<sema::FunctionScopeInfo *, 4> FunctionScopes;

  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<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;

  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;

  /// All the members seen during a class definition which were both
  /// explicitly defaulted and had explicitly-specified exception
  /// specifications, along with the function type containing their
  /// user-specified exception specification. Those exception specifications
  /// were overridden with the default specifications, but we still need to
  /// check whether they are compatible with the default specification, and
  /// we can't do that until the nesting set of class definitions is complete.
  SmallVector<std::pair<CXXMethodDecl*, const FunctionProtoType*>, 2>
    DelayedDefaultedMemberExceptionSpecs;

  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;
    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;

  public:
    DelayedDiagnostics() : CurPool(nullptr) {}

    /// 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;

  /// A RAII object to temporarily push a declaration context.
  class ContextRAII {
  private:
    Sema &S;
    DeclContext *SavedContext;
    ProcessingContextState SavedContextState;
    QualType SavedCXXThisTypeOverride;

  public:
    ContextRAII(Sema &S, DeclContext *ContextToPush, bool NewThisContext = true)
      : S(S), SavedContext(S.CurContext),
        SavedContextState(S.DelayedDiagnostics.pushUndelayed()),
        SavedCXXThisTypeOverride(S.CXXThisTypeOverride)
    {
      assert(ContextToPush && "pushing null context");
      S.CurContext = ContextToPush;
      if (NewThisContext)
        S.CXXThisTypeOverride = QualType();
    }

    void pop() {
      if (!SavedContext) return;
      S.CurContext = SavedContext;
      S.DelayedDiagnostics.popUndelayed(SavedContextState);
      S.CXXThisTypeOverride = SavedCXXThisTypeOverride;
      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) {
      S.PushFunctionScope();
      S.PushExpressionEvaluationContext(
          Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
      if (auto *FD = dyn_cast<FunctionDecl>(DC))
        FD->setWillHaveBody(true);
      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.PopExpressionEvaluationContext();
      S.PopFunctionScopeInfo();
    }
  };

  /// WeakUndeclaredIdentifiers - Identifiers contained in
  /// \#pragma weak before declared. rare. may alias another
  /// identifier, declared or undeclared
  llvm::MapVector<IdentifierInfo *, WeakInfo> 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::experimental" namespace, where the experimental parts
  /// of the standard library resides.
  NamespaceDecl *StdExperimentalNamespaceCache;

  /// 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 MSVC "_GUID" struct, which is defined in MSVC header files.
  RecordDecl *MSVCGuidDecl;

  /// 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;

  /// A flag to indicate that we're in a context that permits abstract
  /// references to fields.  This is really a
  bool AllowAbstractFieldReference;

  /// 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,

    /// 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
  };

  /// 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;

    /// Whether we are in a decltype expression.
    bool IsDecltype;

    /// 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;

    llvm::SmallPtrSet<Expr*, 2> 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;

    /// The context information used to mangle lambda expressions
    /// and block literals within this context.
    ///
    /// This mangling information is allocated lazily, since most contexts
    /// do not have lambda expressions or block literals.
    std::unique_ptr<MangleNumberingContext> MangleNumbering;

    /// 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;

    /// \brief Describes whether we are in an expression constext which we have
    /// to handle differently.
    enum ExpressionKind {
      EK_Decltype, EK_TemplateArgument, EK_Other
    } ExprContext;

    ExpressionEvaluationContextRecord(ExpressionEvaluationContext Context,
                                      unsigned NumCleanupObjects,
                                      CleanupInfo ParentCleanup,
                                      Decl *ManglingContextDecl,
                                      ExpressionKind ExprContext)
        : Context(Context), ParentCleanup(ParentCleanup),
          NumCleanupObjects(NumCleanupObjects), NumTypos(0),
          ManglingContextDecl(ManglingContextDecl), MangleNumbering(),
          ExprContext(ExprContext) {}

    /// Retrieve the mangling numbering context, used to consistently
    /// number constructs like lambdas for mangling.
    MangleNumberingContext &getMangleNumberingContext(ASTContext &Ctx);

    bool isUnevaluated() const {
      return Context == ExpressionEvaluationContext::Unevaluated ||
             Context == ExpressionEvaluationContext::UnevaluatedAbstract ||
             Context == ExpressionEvaluationContext::UnevaluatedList;
    }
    bool isConstantEvaluated() const {
      return Context == ExpressionEvaluationContext::ConstantEvaluated;
    }
  };

  /// A stack of expression evaluation contexts.
  SmallVector<ExpressionEvaluationContextRecord, 8> ExprEvalContexts;

  /// 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.
  ///
  /// \param DC - The DeclContext containing the lambda expression or
  /// block literal.
  /// \param[out] ManglingContextDecl - Returns the ManglingContextDecl
  /// associated with the context, if relevant.
  MangleNumberingContext *getCurrentMangleNumberContext(
    const DeclContext *DC,
    Decl *&ManglingContextDecl);


  /// 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() : Pair() {}
    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.
  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(ValueDecl *VD);

  /// 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;

  typedef std::pair<ObjCMethodList, ObjCMethodList> GlobalMethods;
  typedef llvm::DenseMap<Selector, GlobalMethods> GlobalMethodPool;

  /// 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;

  /// 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;

  /// 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 FP_CONTRACT state on entry/exit of compound
  /// statements.
  class FPContractStateRAII {
  public:
    FPContractStateRAII(Sema &S) : S(S), OldFPFeaturesState(S.FPFeatures) {}
    ~FPContractStateRAII() { S.FPFeatures = OldFPFeaturesState; }

  private:
    Sema& S;
    FPOptions OldFPFeaturesState;
  };

  void addImplicitTypedef(StringRef Name, QualType T);

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();

  const LangOptions &getLangOpts() const { return LangOpts; }
  OpenCLOptions &getOpenCLOptions() { return OpenCLFeatures; }
  FPOptions     &getFPOptions() { return FPFeatures; }

  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; }

  ///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;

  /// Helper class that creates diagnostics with optional
  /// template instantiation stacks.
  ///
  /// This class provides a wrapper around the basic DiagnosticBuilder
  /// class that emits diagnostics. SemaDiagnosticBuilder 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 SemaDiagnosticBuilder : public DiagnosticBuilder {
    Sema &SemaRef;
    unsigned DiagID;

  public:
    SemaDiagnosticBuilder(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 ~SemaDiagnosticBuilder is a safe no-op
    // in that case anwyay.
    SemaDiagnosticBuilder(const SemaDiagnosticBuilder&) = default;

    ~SemaDiagnosticBuilder() {
      // If we aren't active, there is nothing to do.
      if (!isActive()) return;

      // Otherwise, we need to emit the diagnostic. First flush the underlying
      // DiagnosticBuilder data, and 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.
      FlushCounts();
      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 SemaDiagnosticBuilder &operator<<(
        const SemaDiagnosticBuilder &Diag, const T &Value) {
      const DiagnosticBuilder &BaseDiag = Diag;
      BaseDiag << Value;
      return Diag;
    }
  };

  /// Emit a diagnostic.
  SemaDiagnosticBuilder Diag(SourceLocation Loc, unsigned DiagID) {
    DiagnosticBuilder DB = Diags.Report(Loc, DiagID);
    return SemaDiagnosticBuilder(DB, *this, DiagID);
  }

  /// Emit a partial diagnostic.
  SemaDiagnosticBuilder Diag(SourceLocation Loc, const PartialDiagnostic& PD);

  /// Build a partial diagnostic.
  PartialDiagnostic PDiag(unsigned DiagID = 0); // in SemaInternal.h

  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;

  void emitAndClearUnusedLocalTypedefWarnings();

  void ActOnStartOfTranslationUnit();
  void ActOnEndOfTranslationUnit();

  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);
  void
  PopFunctionScopeInfo(const sema::AnalysisBasedWarnings::Policy *WP = nullptr,
                       const Decl *D = nullptr,
                       const BlockExpr *blkExpr = nullptr);

  sema::FunctionScopeInfo *getCurFunction() const {
    return FunctionScopes.empty() ? nullptr : FunctionScopes.back();
  }

  sema::FunctionScopeInfo *getEnclosingFunction() const;

  void setFunctionHasBranchIntoScope();
  void setFunctionHasBranchProtectedScope();
  void setFunctionHasIndirectGoto();

  void PushCompoundScope(bool IsStmtExpr);
  void PopCompoundScope();

  sema::CompoundScopeInfo &getCurCompoundScope() const;

  bool hasAnyUnrecoverableErrorsInThisFunction() const;

  /// Retrieve the current block, if any.
  sema::BlockScopeInfo *getCurBlock();

  /// 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();

  /// WeakTopLevelDeclDecls - access to \#pragma weak-generated Decls
  SmallVectorImpl<Decl *> &WeakTopLevelDecls() { return WeakTopLevelDecl; }

  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, ArrayType::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 BuildAddressSpaceAttr(QualType &T, Expr *AddrSpace,
                                 SourceLocation AttrLoc);

  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);

  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 Expr *E);
  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 FunctionProtoType *Superset,
                                SourceLocation SuperLoc,
                                const FunctionProtoType *Subset,
                                SourceLocation SubLoc);
  bool CheckParamExceptionSpec(const PartialDiagnostic &NestedDiagID,
                               const PartialDiagnostic &NoteID,
                               const FunctionProtoType *Target,
                               SourceLocation TargetLoc,
                               const FunctionProtoType *Source,
                               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 {
    unsigned DiagID;
    std::tuple<const Ts &...> Args;

    template <std::size_t... Is>
    void emit(const SemaDiagnosticBuilder &DB,
              llvm::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, llvm::index_sequence_for<Ts...>());
      DB << T;
    }
  };

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,
                               TypeDiagnoser *Diagnoser);

  struct ModuleScope {
    clang::Module *Module = nullptr;
    bool ModuleInterface = false;
    VisibleModuleSet OuterVisibleModules;
  };
  /// The modules we're currently parsing.
  llvm::SmallVector<ModuleScope, 16> ModuleScopes;

  /// Get the module whose scope we are currently within.
  Module *getCurrentModule() const {
    return ModuleScopes.empty() ? nullptr : ModuleScopes.back().Module;
  }

  VisibleModuleSet VisibleModules;

public:
  /// Get the module owning an entity.
  Module *getOwningModule(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);

  /// Determine whether a declaration is visible to name lookup.
  bool isVisible(const NamedDecl *D) {
    return !D->isHidden() || isVisibleSlow(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);

  bool hasVisibleMergedDefinition(NamedDecl *Def);
  bool hasMergedDefinitionInCurrentModule(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 the template parameter \p D has a visible default argument.
  bool
  hasVisibleDefaultArgument(const NamedDecl *D,
                            llvm::SmallVectorImpl<Module *> *Modules = nullptr);

  /// 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 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 \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);

  bool isCompleteType(SourceLocation Loc, QualType T) {
    return !RequireCompleteTypeImpl(Loc, T, nullptr);
  }
  bool RequireCompleteType(SourceLocation Loc, QualType T,
                           TypeDiagnoser &Diagnoser);
  bool RequireCompleteType(SourceLocation Loc, QualType T,
                           unsigned 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);
  }

  void completeExprArrayBound(Expr *E);
  bool RequireCompleteExprType(Expr *E, 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, 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);

  QualType BuildTypeofExprType(Expr *E, SourceLocation Loc);
  /// 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, SourceLocation Loc,
                             bool AsUnevaluated = true);
  QualType BuildUnaryTransformType(QualType BaseType,
                                   UnaryTransformType::UTTKind UKind,
                                   SourceLocation Loc);

  //===--------------------------------------------------------------------===//
  // Symbol table / Decl tracking callbacks: SemaDecl.cpp.
  //

  struct SkipBodyInfo {
    SkipBodyInfo()
        : ShouldSkip(false), CheckSameAsPrevious(false), Previous(nullptr),
          New(nullptr) {}
    bool ShouldSkip;
    bool CheckSameAsPrevious;
    NamedDecl *Previous;
    NamedDecl *New;
  };

  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,
                         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 {
    NC_Unknown,
    NC_Error,
    NC_Keyword,
    NC_Type,
    NC_Expression,
    NC_NestedNameSpecifier,
    NC_TypeTemplate,
    NC_VarTemplate,
    NC_FunctionTemplate
  };

  class NameClassification {
    NameClassificationKind Kind;
    ExprResult Expr;
    TemplateName Template;
    ParsedType Type;

    explicit NameClassification(NameClassificationKind Kind) : Kind(Kind) {}

  public:
    NameClassification(ExprResult Expr) : Kind(NC_Expression), Expr(Expr) {}

    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 NestedNameSpecifier() {
      return NameClassification(NC_NestedNameSpecifier);
    }

    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;
    }

    NameClassificationKind getKind() const { return Kind; }

    ParsedType getType() const {
      assert(Kind == NC_Type);
      return Type;
    }

    ExprResult getExpression() const {
      assert(Kind == NC_Expression);
      return Expr;
    }

    TemplateName getTemplateName() const {
      assert(Kind == NC_TypeTemplate || Kind == NC_FunctionTemplate ||
             Kind == NC_VarTemplate);
      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;
      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 IsAddressOfOperand True if this name is the operand of a unary
  ///        address of ('&') expression, assuming it is classified as an
  ///        expression.
  ///
  /// \param CCC The correction callback, if typo correction is desired.
  NameClassification
  ClassifyName(Scope *S, CXXScopeSpec &SS, IdentifierInfo *&Name,
               SourceLocation NameLoc, const Token &NextToken,
               bool IsAddressOfOperand,
               std::unique_ptr<CorrectionCandidateCallback> CCC = nullptr);

  /// Describes the detailed kind of a template name. Used in diagnostics.
  enum class TemplateNameKindForDiagnostics {
    ClassTemplate,
    FunctionTemplate,
    VarTemplate,
    AliasTemplate,
    TemplateTemplateParam,
    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);

  Decl *ActOnDeclarator(Scope *S, Declarator &D);

  NamedDecl *HandleDeclarator(Scope *S, Declarator &D,
                              MultiTemplateParamsArg TemplateParameterLists);
  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);
  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 = None);
  NamedDecl *
  ActOnDecompositionDeclarator(Scope *S, Declarator &D,
                               MultiTemplateParamsArg TemplateParamLists);
  // 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);

  bool CheckConstexprFunctionDecl(const FunctionDecl *FD);
  bool CheckConstexprFunctionBody(const FunctionDecl *FD, Stmt *Body);

  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 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);
  Attr *getImplicitCodeSegOrSectionAttrForFunction(const FunctionDecl *FD, bool IsDefinition);
  Decl *ActOnParamDeclarator(Scope *S, Declarator &D);
  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);
  bool SetParamDefaultArgument(ParmVarDecl *Param, Expr *DefaultArg,
                               SourceLocation EqualLoc);

  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,
                                        SourceLocation AttrEnd);
  void SetDeclDeleted(Decl *dcl, SourceLocation DelLoc);
  void SetDeclDefaulted(Decl *dcl, SourceLocation DefaultLoc);
  void CheckStaticLocalForDllExport(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);

  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);
  Decl *ActOnStartOfFunctionDef(Scope *S, Decl *D,
                                SkipBodyInfo *SkipBody = nullptr);
  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);

  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);

  /// 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;'
    Partition,      ///< 'module partition X;'
  };

  /// 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);

  /// The parser has processed a module import declaration.
  ///
  /// \param AtLoc The location of the '@' symbol, if any.
  ///
  /// \param ImportLoc The location of the 'import' keyword.
  ///
  /// \param Path The module access path.
  DeclResult ActOnModuleImport(SourceLocation AtLoc, SourceLocation ImportLoc,
                               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, NamedDecl *Decl,
                             MissingImportKind MIK, bool Recover = true);
  void diagnoseMissingImport(SourceLocation Loc, 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, and diagnose if not.
  void checkSpecializationVisibility(SourceLocation Loc, NamedDecl *Spec);

  /// We've found a use of a template specialization that would select a
  /// partial specialization. Check that the partial specialization is visible,
  /// and diagnose if not.
  void checkPartialSpecializationVisibility(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,
                                   RecordDecl *&AnonRecord);
  Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                   MultiTemplateParamsArg TemplateParams,
                                   bool IsExplicitInstantiation,
                                   RecordDecl *&AnonRecord);

  Decl *BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS,
                                    AccessSpecifier AS,
                                    RecordDecl *Record,
                                    const PrintingPolicy &Policy);

  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;'
  };

  Decl *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,
                 SkipBodyInfo *SkipBody = nullptr);

  Decl *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);
  CXXSpecialMember getSpecialMember(const CXXMethodDecl *MD);
  void ActOnLastBitfield(SourceLocation DeclStart,
                         SmallVectorImpl<Decl *> &AllIvarDecls);
  Decl *ActOnIvar(Scope *S, SourceLocation DeclStart,
                  Declarator &D, Expr *BitfieldWidth,
                  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(DeclSpec &DS, Decl *Prev,
                                SkipBodyInfo &SkipBody);

  typedef void *SkippedDefinitionContext;

  /// Invoked when we enter a tag definition that we're skipping.
  SkippedDefinitionContext ActOnTagStartSkippedDefinition(Scope *S, Decl *TD);

  Decl *ActOnObjCContainerStartDefinition(Decl *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,
                                       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(DeclContext *DC);
  void ActOnObjCReenterContainerContext(DeclContext *DC);

  /// 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);

  DeclContext *getContainingDC(DeclContext *DC);

  /// 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);

  /// Push the parameters of D, which must be a function, into scope.
  void ActOnReenterFunctionContext(Scope* S, Decl* D);
  void ActOnExitFunctionContext();

  DeclContext *getFunctionLevelDeclContext();

  /// getCurFunctionDecl - If inside of a function body, this returns a pointer
  /// to the function decl for the function being parsed.  If we're currently
  /// in a 'block', this returns the containing context.
  FunctionDecl *getCurFunctionDecl();

  /// 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();

  /// Add this decl to the scope shadowed decl chains.
  void PushOnScopeChains(NamedDecl *D, Scope *S, bool AddToContext = true);

  /// Make the given externally-produced declaration visible at the
  /// top level scope.
  ///
  /// \param D The externally-produced declaration to push.
  ///
  /// \param Name The name of the externally-produced declaration.
  void pushExternalDeclIntoScope(NamedDecl *D, DeclarationName Name);

  /// 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);

  /// 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,
  };

  /// Attribute merging methods. Return true if a new attribute was added.
  AvailabilityAttr *mergeAvailabilityAttr(NamedDecl *D, SourceRange Range,
                                          IdentifierInfo *Platform,
                                          bool Implicit,
                                          VersionTuple Introduced,
                                          VersionTuple Deprecated,
                                          VersionTuple Obsoleted,
                                          bool IsUnavailable,
                                          StringRef Message,
                                          bool IsStrict, StringRef Replacement,
                                          AvailabilityMergeKind AMK,
                                          unsigned AttrSpellingListIndex);
  TypeVisibilityAttr *mergeTypeVisibilityAttr(Decl *D, SourceRange Range,
                                       TypeVisibilityAttr::VisibilityType Vis,
                                              unsigned AttrSpellingListIndex);
  VisibilityAttr *mergeVisibilityAttr(Decl *D, SourceRange Range,
                                      VisibilityAttr::VisibilityType Vis,
                                      unsigned AttrSpellingListIndex);
  UuidAttr *mergeUuidAttr(Decl *D, SourceRange Range,
                          unsigned AttrSpellingListIndex, StringRef Uuid);
  DLLImportAttr *mergeDLLImportAttr(Decl *D, SourceRange Range,
                                    unsigned AttrSpellingListIndex);
  DLLExportAttr *mergeDLLExportAttr(Decl *D, SourceRange Range,
                                    unsigned AttrSpellingListIndex);
  MSInheritanceAttr *
  mergeMSInheritanceAttr(Decl *D, SourceRange Range, bool BestCase,
                         unsigned AttrSpellingListIndex,
                         MSInheritanceAttr::Spelling SemanticSpelling);
  FormatAttr *mergeFormatAttr(Decl *D, SourceRange Range,
                              IdentifierInfo *Format, int FormatIdx,
                              int FirstArg, unsigned AttrSpellingListIndex);
  SectionAttr *mergeSectionAttr(Decl *D, SourceRange Range, StringRef Name,
                                unsigned AttrSpellingListIndex);
  CodeSegAttr *mergeCodeSegAttr(Decl *D, SourceRange Range, StringRef Name,
                                unsigned AttrSpellingListIndex);
  AlwaysInlineAttr *mergeAlwaysInlineAttr(Decl *D, SourceRange Range,
                                          IdentifierInfo *Ident,
                                          unsigned AttrSpellingListIndex);
  MinSizeAttr *mergeMinSizeAttr(Decl *D, SourceRange Range,
                                unsigned AttrSpellingListIndex);
  OptimizeNoneAttr *mergeOptimizeNoneAttr(Decl *D, SourceRange Range,
                                          unsigned AttrSpellingListIndex);
  InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D, const ParsedAttr &AL);
  InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D,
                                                const InternalLinkageAttr &AL);
  CommonAttr *mergeCommonAttr(Decl *D, const ParsedAttr &AL);
  CommonAttr *mergeCommonAttr(Decl *D, const CommonAttr &AL);

  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 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 IsForUsingDecl);
  bool IsOverload(FunctionDecl *New, FunctionDecl *Old, bool IsForUsingDecl,
                  bool ConsiderCudaAttrs = true);

  /// Checks availability of the function depending on the current
  /// function context.Inside an unavailable function,unavailability is ignored.
  ///
  /// \returns true if \p FD is unavailable and current context is inside
  /// an available function, false otherwise.
  bool isFunctionConsideredUnavailable(FunctionDecl *FD);

  ImplicitConversionSequence
  TryImplicitConversion(Expr *From, QualType ToType,
                        bool SuppressUserConversions,
                        bool 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(const FunctionProtoType *OldType,
                                  const FunctionProtoType *NewType,
                                  unsigned *ArgPos = nullptr);
  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(CanQualType Param, CanQualType Arg);

  ExprResult PerformMoveOrCopyInitialization(const InitializedEntity &Entity,
                                             const VarDecl *NRVOCandidate,
                                             QualType ResultType,
                                             Expr *Value,
                                             bool AllowNRVO = true);

  bool CanPerformCopyInitialization(const InitializedEntity &Entity,
                                    ExprResult Init);
  ExprResult PerformCopyInitialization(const InitializedEntity &Entity,
                                       SourceLocation EqualLoc,
                                       ExprResult Init,
                                       bool TopLevelOfInitList = false,
                                       bool AllowExplicit = false);
  ExprResult PerformObjectArgumentInitialization(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_NewExpr,     ///< Constant expression in a noptr-new-declarator.
    CCEK_ConstexprIf  ///< Condition in a constexpr if statement.
  };
  ExprResult CheckConvertedConstantExpression(Expr *From, QualType T,
                                              llvm::APSInt &Value, CCEKind CCE);
  ExprResult CheckConvertedConstantExpression(Expr *From, QualType T,
                                              APValue &Value, CCEKind CCE);

  /// 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 = false,
                            ADLCallKind IsADLCandidate = ADLCallKind::NotADL,
                            ConversionSequenceList EarlyConversions = None);
  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);
  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 = None);
  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);
  void AddTemplateOverloadCandidate(
      FunctionTemplateDecl *FunctionTemplate, DeclAccessPair FoundDecl,
      TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
      OverloadCandidateSet &CandidateSet, bool SuppressUserConversions = false,
      bool PartialOverloading = false,
      ADLCallKind IsADLCandidate = ADLCallKind::NotADL);
  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 = {});
  void AddConversionCandidate(CXXConversionDecl *Conversion,
                              DeclAccessPair FoundDecl,
                              CXXRecordDecl *ActingContext,
                              Expr *From, QualType ToType,
                              OverloadCandidateSet& CandidateSet,
                              bool AllowObjCConversionOnExplicit,
                              bool AllowResultConversion = true);
  void AddTemplateConversionCandidate(FunctionTemplateDecl *FunctionTemplate,
                                      DeclAccessPair FoundDecl,
                                      CXXRecordDecl *ActingContext,
                                      Expr *From, QualType ToType,
                                      OverloadCandidateSet &CandidateSet,
                                      bool AllowObjCConversionOnExplicit,
                                      bool AllowResultConversion = true);
  void AddSurrogateCandidate(CXXConversionDecl *Conversion,
                             DeclAccessPair FoundDecl,
                             CXXRecordDecl *ActingContext,
                             const FunctionProtoType *Proto,
                             Expr *Object, ArrayRef<Expr *> Args,
                             OverloadCandidateSet& CandidateSet);
  void AddMemberOperatorCandidates(OverloadedOperatorKind Op,
                                   SourceLocation OpLoc, ArrayRef<Expr *> Args,
                                   OverloadCandidateSet& CandidateSet,
                                   SourceRange OpRange = SourceRange());
  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(NamedDecl *Found, FunctionDecl *Fn,
                             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, 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 *
  resolveAddressOfOnlyViableOverloadCandidate(Expr *E,
                                              DeclAccessPair &FoundResult);

  bool resolveAndFixAddressOfOnlyViableOverloadCandidate(
      ExprResult &SrcExpr, bool DoFunctionPointerConversion = false);

  FunctionDecl *
  ResolveSingleFunctionTemplateSpecialization(OverloadExpr *ovl,
                                              bool Complain = false,
                                              DeclAccessPair *Found = nullptr);

  bool ResolveAndFixSingleFunctionTemplateSpecialization(
                      ExprResult &SrcExpr,
                      bool DoFunctionPointerConverion = false,
                      bool Complain = false,
                      SourceRange OpRangeForComplaining = SourceRange(),
                      QualType DestTypeForComplaining = QualType(),
                      unsigned DiagIDForComplaining = 0);


  Expr *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);

  // 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 CreateOverloadedUnaryOp(SourceLocation OpLoc,
                                     UnaryOperatorKind Opc,
                                     const UnresolvedSetImpl &Fns,
                                     Expr *input, bool RequiresADL = true);

  ExprResult CreateOverloadedBinOp(SourceLocation OpLoc,
                                   BinaryOperatorKind Opc,
                                   const UnresolvedSetImpl &Fns,
                                   Expr *LHS, Expr *RHS,
                                   bool RequiresADL = true);

  ExprResult CreateOverloadedArraySubscriptExpr(SourceLocation LLoc,
                                                SourceLocation RLoc,
                                                Expr *Base,Expr *Idx);

  ExprResult
  BuildCallToMemberFunction(Scope *S, Expr *MemExpr,
                            SourceLocation LParenLoc,
                            MultiExprArg Args,
                            SourceLocation RParenLoc);
  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
  ///
  /// These routines provide name lookup that is used during semantic
  /// analysis to resolve the various kinds of names (identifiers,
  /// overloaded operator names, constructor names, etc.) into zero or
  /// more declarations within a particular scope. The major entry
  /// points are LookupName, which performs unqualified name lookup,
  /// and LookupQualifiedName, which performs qualified name lookup.
  ///
  /// All name lookup is performed based on some specific criteria,
  /// which specify what names will be visible to name lookup and how
  /// far name lookup should work. These criteria are important both
  /// for capturing language semantics (certain lookups will ignore
  /// certain names, for example) and for performance, since name
  /// lookup is often a bottleneck in the compilation of C++. Name
  /// lookup criteria is specified via the LookupCriteria enumeration.
  ///
  /// The results of name lookup can vary based on the kind of name
  /// lookup performed, the current language, and the translation
  /// unit. In C, for example, name lookup will either return nothing
  /// (no entity found) or a single declaration. In C++, name lookup
  /// can additionally refer to a set of overloaded functions or
  /// result in an ambiguity. All of the possible results of name
  /// lookup are captured by the LookupResult class, which provides
  /// the ability to distinguish among them.
  //@{

  /// Describes the kind of name lookup to perform.
  enum LookupNameKind {
    /// Ordinary name lookup, which finds ordinary names (functions,
    /// variables, typedefs, etc.) in C and most kinds of names
    /// (functions, variables, members, types, etc.) in C++.
    LookupOrdinaryName = 0,
    /// Tag name lookup, which finds the names of enums, classes,
    /// structs, and unions.
    LookupTagName,
    /// Label name lookup.
    LookupLabel,
    /// Member name lookup, which finds the names of
    /// class/struct/union members.
    LookupMemberName,
    /// Look up of an operator name (e.g., operator+) for use with
    /// operator overloading. This lookup is similar to ordinary name
    /// lookup, but will ignore any declarations that are class members.
    LookupOperatorName,
    /// Look up of a name that precedes the '::' scope resolution
    /// operator in C++. This lookup completely ignores operator, object,
    /// function, and enumerator names (C++ [basic.lookup.qual]p1).
    LookupNestedNameSpecifierName,
    /// Look up a namespace name within a C++ using directive or
    /// namespace alias definition, ignoring non-namespace names (C++
    /// [basic.lookup.udir]p1).
    LookupNamespaceName,
    /// Look up all declarations in a scope with the given name,
    /// including resolved using declarations.  This is appropriate
    /// for checking redeclarations for a using declaration.
    LookupUsingDeclName,
    /// Look up an ordinary name that is going to be redeclared as a
    /// name with linkage. This lookup ignores any declarations that
    /// are outside of the current scope unless they have linkage. See
    /// C99 6.2.2p4-5 and C++ [basic.link]p6.
    LookupRedeclarationWithLinkage,
    /// Look up a friend of a local class. This lookup does not look
    /// outside the innermost non-class scope. See C++11 [class.friend]p11.
    LookupLocalFriendName,
    /// Look up the name of an Objective-C protocol.
    LookupObjCProtocolName,
    /// Look up implicit 'self' parameter of an objective-c method.
    LookupObjCImplicitSelfParam,
    /// Look up the name of an OpenMP user-defined reduction operation.
    LookupOMPReductionName,
    /// Look up any declaration with any name.
    LookupAnyName
  };

  /// Specifies whether (or how) name lookup is being performed for a
  /// redeclaration (vs. a reference).
  enum RedeclarationKind {
    /// The lookup is a reference to this name that is not for the
    /// purpose of redeclaring the name.
    NotForRedeclaration = 0,
    /// The lookup results will be used for redeclaration of a name,
    /// if an entity by that name already exists and is visible.
    ForVisibleRedeclaration,
    /// The lookup results will be used for redeclaration of a name
    /// with external linkage; non-visible lookup results with external linkage
    /// may also be found.
    ForExternalRedeclaration
  };

  RedeclarationKind forRedeclarationInCurContext() {
    // A declaration with an owning module for linkage can never link against
    // anything that is not visible. We don't need to check linkage here; if
    // the context has internal linkage, redeclaration lookup won't find things
    // from other TUs, and we can't safely compute linkage yet in general.
    if (cast<Decl>(CurContext)
            ->getOwningModuleForLinkage(/*IgnoreLinkage*/true))
      return ForVisibleRedeclaration;
    return ForExternalRedeclaration;
  }

  /// The possible outcomes of name lookup for a literal operator.
  enum LiteralOperatorLookupResult {
    /// The lookup resulted in an error.
    LOLR_Error,
    /// The lookup found no match but no diagnostic was issued.
    LOLR_ErrorNoDiagnostic,
    /// The lookup found a single 'cooked' literal operator, which
    /// expects a normal literal to be built and passed to it.
    LOLR_Cooked,
    /// The lookup found a single 'raw' literal operator, which expects
    /// a string literal containing the spelling of the literal token.
    LOLR_Raw,
    /// The lookup found an overload set of literal operator templates,
    /// which expect the characters of the spelling of the literal token to be
    /// passed as a non-type template argument pack.
    LOLR_Template,
    /// The lookup found an overload set of literal operator templates,
    /// which expect the character type and characters of the spelling of the
    /// string literal token to be passed as template arguments.
    LOLR_StringTemplate
  };

  SpecialMemberOverloadResult LookupSpecialMember(CXXRecordDecl *D,
                                                  CXXSpecialMember SM,
                                                  bool ConstArg,
                                                  bool VolatileArg,
                                                  bool RValueThis,
                                                  bool ConstThis,
                                                  bool VolatileThis);

  typedef std::function<void(const TypoCorrection &)> TypoDiagnosticGenerator;
  typedef std::function<ExprResult(Sema &, TypoExpr *, TypoCorrection)>
      TypoRecoveryCallback;

private:
  bool CppLookupName(LookupResult &R, Scope *S);

  struct TypoExprState {
    std::unique_ptr<TypoCorrectionConsumer> Consumer;
    TypoDiagnosticGenerator DiagHandler;
    TypoRecoveryCallback RecoveryHandler;
    TypoExprState();
    TypoExprState(TypoExprState &&other) noexcept;
    TypoExprState &operator=(TypoExprState &&other) noexcept;
  };

  /// The set of unhandled TypoExprs and their associated state.
  llvm::MapVector<TypoExpr *, TypoExprState> DelayedTypos;

  /// Creates a new TypoExpr AST node.
  TypoExpr *createDelayedTypo(std::unique_ptr<TypoCorrectionConsumer> TCC,
                              TypoDiagnosticGenerator TDG,
                              TypoRecoveryCallback TRC);

  // The set of known/encountered (unique, canonicalized) NamespaceDecls.
  //
  // The boolean value will be true to indicate that the namespace was loaded
  // from an AST/PCH file, or false otherwise.
  llvm::MapVector<NamespaceDecl*, bool> KnownNamespaces;

  /// Whether we have already loaded known namespaces from an extenal
  /// source.
  bool LoadedExternalKnownNamespaces;

  /// Helper for CorrectTypo and CorrectTypoDelayed used to create and
  /// populate a new TypoCorrectionConsumer. Returns nullptr if typo correction
  /// should be skipped entirely.
  std::unique_ptr<TypoCorrectionConsumer>
  makeTypoCorrectionConsumer(const DeclarationNameInfo &Typo,
                             Sema::LookupNameKind LookupKind, Scope *S,
                             CXXScopeSpec *SS,
                             std::unique_ptr<CorrectionCandidateCallback> CCC,
                             DeclContext *MemberContext, bool EnteringContext,
                             const ObjCObjectPointerType *OPT,
                             bool ErrorRecovery);

public:
  const TypoExprState &getTypoExprState(TypoExpr *TE) const;

  /// Clears the state of the given TypoExpr.
  void clearDelayedTypo(TypoExpr *TE);

  /// Look up a name, looking for a single declaration.  Return
  /// null if the results were absent, ambiguous, or overloaded.
  ///
  /// It is preferable to use the elaborated form and explicitly handle
  /// ambiguity and overloaded.
  NamedDecl *LookupSingleName(Scope *S, DeclarationName Name,
                              SourceLocation Loc,
                              LookupNameKind NameKind,
                              RedeclarationKind Redecl
                                = NotForRedeclaration);
  bool LookupName(LookupResult &R, Scope *S,
                  bool AllowBuiltinCreation = false);
  bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                           bool InUnqualifiedLookup = false);
  bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                           CXXScopeSpec &SS);
  bool LookupParsedName(LookupResult &R, Scope *S, CXXScopeSpec *SS,
                        bool AllowBuiltinCreation = false,
                        bool EnteringContext = false);
  ObjCProtocolDecl *LookupProtocol(IdentifierInfo *II, SourceLocation IdLoc,
                                   RedeclarationKind Redecl
                                     = NotForRedeclaration);
  bool LookupInSuper(LookupResult &R, CXXRecordDecl *Class);

  void LookupOverloadedOperatorName(OverloadedOperatorKind Op, Scope *S,
                                    QualType T1, QualType T2,
                                    UnresolvedSetImpl &Functions);

  LabelDecl *LookupOrCreateLabel(IdentifierInfo *II, SourceLocation IdentLoc,
                                 SourceLocation GnuLabelLoc = SourceLocation());

  DeclContextLookupResult LookupConstructors(CXXRecordDecl *Class);
  CXXConstructorDecl *LookupDefaultConstructor(CXXRecordDecl *Class);
  CXXConstructorDecl *LookupCopyingConstructor(CXXRecordDecl *Class,
                                               unsigned Quals);
  CXXMethodDecl *LookupCopyingAssignment(CXXRecordDecl *Class, unsigned Quals,
                                         bool RValueThis, unsigned ThisQuals);
  CXXConstructorDecl *LookupMovingConstructor(CXXRecordDecl *Class,
                                              unsigned Quals);
  CXXMethodDecl *LookupMovingAssignment(CXXRecordDecl *Class, unsigned Quals,
                                        bool RValueThis, unsigned ThisQuals);
  CXXDestructorDecl *LookupDestructor(CXXRecordDecl *Class);

  bool checkLiteralOperatorId(const CXXScopeSpec &SS, const UnqualifiedId &Id);
  LiteralOperatorLookupResult LookupLiteralOperator(Scope *S, LookupResult &R,
                                                    ArrayRef<QualType> ArgTys,
                                                    bool AllowRaw,
                                                    bool AllowTemplate,
                                                    bool AllowStringTemplate,
                                                    bool DiagnoseMissing);
  bool isKnownName(StringRef name);

  void ArgumentDependentLookup(DeclarationName Name, SourceLocation Loc,
                               ArrayRef<Expr *> Args, ADLResult &Functions);

  void LookupVisibleDecls(Scope *S, LookupNameKind Kind,
                          VisibleDeclConsumer &Consumer,
                          bool IncludeGlobalScope = true,
                          bool LoadExternal = true);
  void LookupVisibleDecls(DeclContext *Ctx, LookupNameKind Kind,
                          VisibleDeclConsumer &Consumer,
                          bool IncludeGlobalScope = true,
                          bool IncludeDependentBases = false,
                          bool LoadExternal = true);

  enum CorrectTypoKind {
    CTK_NonError,     // CorrectTypo used in a non error recovery situation.
    CTK_ErrorRecovery // CorrectTypo used in normal error recovery.
  };

  TypoCorrection CorrectTypo(const DeclarationNameInfo &Typo,
                             Sema::LookupNameKind LookupKind,
                             Scope *S, CXXScopeSpec *SS,
                             std::unique_ptr<CorrectionCandidateCallback> CCC,
                             CorrectTypoKind Mode,
                             DeclContext *MemberContext = nullptr,
                             bool EnteringContext = false,
                             const ObjCObjectPointerType *OPT = nullptr,
                             bool RecordFailure = true);

  TypoExpr *CorrectTypoDelayed(const DeclarationNameInfo &Typo,
                               Sema::LookupNameKind LookupKind, Scope *S,
                               CXXScopeSpec *SS,
                               std::unique_ptr<CorrectionCandidateCallback> CCC,
                               TypoDiagnosticGenerator TDG,
                               TypoRecoveryCallback TRC, CorrectTypoKind Mode,
                               DeclContext *MemberContext = nullptr,
                               bool EnteringContext = false,
                               const ObjCObjectPointerType *OPT = nullptr);

  /// Process any TypoExprs in the given Expr and its children,
  /// generating diagnostics as appropriate and returning a new Expr if there
  /// were typos that were all successfully corrected and ExprError if one or
  /// more typos could not be corrected.
  ///
  /// \param E The Expr to check for TypoExprs.
  ///
  /// \param InitDecl A VarDecl to avoid because the Expr being corrected is its
  /// initializer.
  ///
  /// \param Filter A function applied to a newly rebuilt Expr to determine if
  /// it is an acceptable/usable result from a single combination of typo
  /// corrections. As long as the filter returns ExprError, different
  /// combinations of corrections will be tried until all are exhausted.
  ExprResult
  CorrectDelayedTyposInExpr(Expr *E, VarDecl *InitDecl = nullptr,
                            llvm::function_ref<ExprResult(Expr *)> Filter =
                                [](Expr *E) -> ExprResult { return E; });

  ExprResult
  CorrectDelayedTyposInExpr(Expr *E,
                            llvm::function_ref<ExprResult(Expr *)> Filter) {
    return CorrectDelayedTyposInExpr(E, nullptr, Filter);
  }

  ExprResult
  CorrectDelayedTyposInExpr(ExprResult ER, VarDecl *InitDecl = nullptr,
                            llvm::function_ref<ExprResult(Expr *)> Filter =
                                [](Expr *E) -> ExprResult { return E; }) {
    return ER.isInvalid() ? ER : CorrectDelayedTyposInExpr(ER.get(), Filter);
  }

  ExprResult
  CorrectDelayedTyposInExpr(ExprResult ER,
                            llvm::function_ref<ExprResult(Expr *)> Filter) {
    return CorrectDelayedTyposInExpr(ER, nullptr, Filter);
  }

  void diagnoseTypo(const TypoCorrection &Correction,
                    const PartialDiagnostic &TypoDiag,
                    bool ErrorRecovery = true);

  void diagnoseTypo(const TypoCorrection &Correction,
                    const PartialDiagnostic &TypoDiag,
                    const PartialDiagnostic &PrevNote,
                    bool ErrorRecovery = true);

  void MarkTypoCorrectedFunctionDefinition(const NamedDecl *F);

  void FindAssociatedClassesAndNamespaces(SourceLocation InstantiationLoc,
                                          ArrayRef<Expr *> Args,
                                   AssociatedNamespaceSet &AssociatedNamespaces,
                                   AssociatedClassSet &AssociatedClasses);

  void FilterLookupForScope(LookupResult &R, DeclContext *Ctx, Scope *S,
                            bool ConsiderLinkage, bool AllowInlineNamespace);

  bool CheckRedeclarationModuleOwnership(NamedDecl *New, NamedDecl *Old);

  void DiagnoseAmbiguousLookup(LookupResult &Result);
  //@}

  ObjCInterfaceDecl *getObjCInterfaceDecl(IdentifierInfo *&Id,
                                          SourceLocation IdLoc,
                                          bool TypoCorrection = false);
  NamedDecl *LazilyCreateBuiltin(IdentifierInfo *II, unsigned ID,
                                 Scope *S, bool ForRedeclaration,
                                 SourceLocation Loc);
  NamedDecl *ImplicitlyDefineFunction(SourceLocation Loc, IdentifierInfo &II,
                                      Scope *S);
  void AddKnownFunctionAttributes(FunctionDecl *FD);

  // More parsing and symbol table subroutines.

  void ProcessPragmaWeak(Scope *S, Decl *D);
  // Decl attributes - this routine is the top level dispatcher.
  void ProcessDeclAttributes(Scope *S, Decl *D, const Declarator &PD);
  // Helper for delayed processing of attributes.
  void ProcessDeclAttributeDelayed(Decl *D,
                                   const ParsedAttributesView &AttrList);
  void ProcessDeclAttributeList(Scope *S, Decl *D, const ParsedAttributesView &AL,
                             bool IncludeCXX11Attributes = true);
  bool ProcessAccessDeclAttributeList(AccessSpecDecl *ASDecl,
                                   const ParsedAttributesView &AttrList);

  void checkUnusedDeclAttributes(Declarator &D);

  /// Determine if type T is a valid subject for a nonnull and similar
  /// attributes. By default, we look through references (the behavior used by
  /// nonnull), but if the second parameter is true, then we treat a reference
  /// type as valid.
  bool isValidPointerAttrType(QualType T, bool RefOkay = false);

  bool CheckRegparmAttr(const ParsedAttr &attr, unsigned &value);
  bool CheckCallingConvAttr(const ParsedAttr &attr, CallingConv &CC,
                            const FunctionDecl *FD = nullptr);
  bool CheckAttrTarget(const ParsedAttr &CurrAttr);
  bool CheckAttrNoArgs(const ParsedAttr &CurrAttr);
  bool checkStringLiteralArgumentAttr(const ParsedAttr &Attr, unsigned ArgNum,
                                      StringRef &Str,
                                      SourceLocation *ArgLocation = nullptr);
  bool checkSectionName(SourceLocation LiteralLoc, StringRef Str);
  bool checkTargetAttr(SourceLocation LiteralLoc, StringRef Str);
  bool checkMSInheritanceAttrOnDefinition(
      CXXRecordDecl *RD, SourceRange Range, bool BestCase,
      MSInheritanceAttr::Spelling SemanticSpelling);

  void CheckAlignasUnderalignment(Decl *D);

  /// Adjust the calling convention of a method to be the ABI default if it
  /// wasn't specified explicitly.  This handles method types formed from
  /// function type typedefs and typename template arguments.
  void adjustMemberFunctionCC(QualType &T, bool IsStatic, bool IsCtorOrDtor,
                              SourceLocation Loc);

  // Check if there is an explicit attribute, but only look through parens.
  // The intent is to look for an attribute on the current declarator, but not
  // one that came from a typedef.
  bool hasExplicitCallingConv(QualType &T);

  /// Get the outermost AttributedType node that sets a calling convention.
  /// Valid types should not have multiple attributes with different CCs.
  const AttributedType *getCallingConvAttributedType(QualType T) const;

  /// Stmt attributes - this routine is the top level dispatcher.
  StmtResult ProcessStmtAttributes(Stmt *Stmt,
                                   const ParsedAttributesView &Attrs,
                                   SourceRange Range);

  void WarnConflictingTypedMethods(ObjCMethodDecl *Method,
                                   ObjCMethodDecl *MethodDecl,
                                   bool IsProtocolMethodDecl);

  void CheckConflictingOverridingMethod(ObjCMethodDecl *Method,
                                   ObjCMethodDecl *Overridden,
                                   bool IsProtocolMethodDecl);

  /// WarnExactTypedMethods - This routine issues a warning if method
  /// implementation declaration matches exactly that of its declaration.
  void WarnExactTypedMethods(ObjCMethodDecl *Method,
                             ObjCMethodDecl *MethodDecl,
                             bool IsProtocolMethodDecl);

  typedef llvm::SmallPtrSet<Selector, 8> SelectorSet;

  /// CheckImplementationIvars - This routine checks if the instance variables
  /// listed in the implelementation match those listed in the interface.
  void CheckImplementationIvars(ObjCImplementationDecl *ImpDecl,
                                ObjCIvarDecl **Fields, unsigned nIvars,
                                SourceLocation Loc);

  /// ImplMethodsVsClassMethods - This is main routine to warn if any method
  /// remains unimplemented in the class or category \@implementation.
  void ImplMethodsVsClassMethods(Scope *S, ObjCImplDecl* IMPDecl,
                                 ObjCContainerDecl* IDecl,
                                 bool IncompleteImpl = false);

  /// DiagnoseUnimplementedProperties - This routine warns on those properties
  /// which must be implemented by this implementation.
  void DiagnoseUnimplementedProperties(Scope *S, ObjCImplDecl* IMPDecl,
                                       ObjCContainerDecl *CDecl,
                                       bool SynthesizeProperties);

  /// Diagnose any null-resettable synthesized setters.
  void diagnoseNullResettableSynthesizedSetters(const ObjCImplDecl *impDecl);

  /// DefaultSynthesizeProperties - This routine default synthesizes all
  /// properties which must be synthesized in the class's \@implementation.
  void DefaultSynthesizeProperties(Scope *S, ObjCImplDecl *IMPDecl,
                                   ObjCInterfaceDecl *IDecl,
                                   SourceLocation AtEnd);
  void DefaultSynthesizeProperties(Scope *S, Decl *D, SourceLocation AtEnd);

  /// IvarBacksCurrentMethodAccessor - This routine returns 'true' if 'IV' is
  /// an ivar synthesized for 'Method' and 'Method' is a property accessor
  /// declared in class 'IFace'.
  bool IvarBacksCurrentMethodAccessor(ObjCInterfaceDecl *IFace,
                                      ObjCMethodDecl *Method, ObjCIvarDecl *IV);

  /// DiagnoseUnusedBackingIvarInAccessor - Issue an 'unused' warning if ivar which
  /// backs the property is not used in the property's accessor.
  void DiagnoseUnusedBackingIvarInAccessor(Scope *S,
                                           const ObjCImplementationDecl *ImplD);

  /// GetIvarBackingPropertyAccessor - If method is a property setter/getter and
  /// it property has a backing ivar, returns this ivar; otherwise, returns NULL.
  /// It also returns ivar's property on success.
  ObjCIvarDecl *GetIvarBackingPropertyAccessor(const ObjCMethodDecl *Method,
                                               const ObjCPropertyDecl *&PDecl) const;

  /// Called by ActOnProperty to handle \@property declarations in
  /// class extensions.
  ObjCPropertyDecl *HandlePropertyInClassExtension(Scope *S,
                      SourceLocation AtLoc,
                      SourceLocation LParenLoc,
                      FieldDeclarator &FD,
                      Selector GetterSel,
                      SourceLocation GetterNameLoc,
                      Selector SetterSel,
                      SourceLocation SetterNameLoc,
                      const bool isReadWrite,
                      unsigned &Attributes,
                      const unsigned AttributesAsWritten,
                      QualType T,
                      TypeSourceInfo *TSI,
                      tok::ObjCKeywordKind MethodImplKind);

  /// Called by ActOnProperty and HandlePropertyInClassExtension to
  /// handle creating the ObjcPropertyDecl for a category or \@interface.
  ObjCPropertyDecl *CreatePropertyDecl(Scope *S,
                                       ObjCContainerDecl *CDecl,
                                       SourceLocation AtLoc,
                                       SourceLocation LParenLoc,
                                       FieldDeclarator &FD,
                                       Selector GetterSel,
                                       SourceLocation GetterNameLoc,
                                       Selector SetterSel,
                                       SourceLocation SetterNameLoc,
                                       const bool isReadWrite,
                                       const unsigned Attributes,
                                       const unsigned AttributesAsWritten,
                                       QualType T,
                                       TypeSourceInfo *TSI,
                                       tok::ObjCKeywordKind MethodImplKind,
                                       DeclContext *lexicalDC = nullptr);

  /// AtomicPropertySetterGetterRules - This routine enforces the rule (via
  /// warning) when atomic property has one but not the other user-declared
  /// setter or getter.
  void AtomicPropertySetterGetterRules(ObjCImplDecl* IMPDecl,
                                       ObjCInterfaceDecl* IDecl);

  void DiagnoseOwningPropertyGetterSynthesis(const ObjCImplementationDecl *D);

  void DiagnoseMissingDesignatedInitOverrides(
                                          const ObjCImplementationDecl *ImplD,
                                          const ObjCInterfaceDecl *IFD);

  void DiagnoseDuplicateIvars(ObjCInterfaceDecl *ID, ObjCInterfaceDecl *SID);

  enum MethodMatchStrategy {
    MMS_loose,
    MMS_strict
  };

  /// MatchTwoMethodDeclarations - Checks if two methods' type match and returns
  /// true, or false, accordingly.
  bool MatchTwoMethodDeclarations(const ObjCMethodDecl *Method,
                                  const ObjCMethodDecl *PrevMethod,
                                  MethodMatchStrategy strategy = MMS_strict);

  /// MatchAllMethodDeclarations - Check methods declaraed in interface or
  /// or protocol against those declared in their implementations.
  void MatchAllMethodDeclarations(const SelectorSet &InsMap,
                                  const SelectorSet &ClsMap,
                                  SelectorSet &InsMapSeen,
                                  SelectorSet &ClsMapSeen,
                                  ObjCImplDecl* IMPDecl,
                                  ObjCContainerDecl* IDecl,
                                  bool &IncompleteImpl,
                                  bool ImmediateClass,
                                  bool WarnCategoryMethodImpl=false);

  /// CheckCategoryVsClassMethodMatches - Checks that methods implemented in
  /// category matches with those implemented in its primary class and
  /// warns each time an exact match is found.
  void CheckCategoryVsClassMethodMatches(ObjCCategoryImplDecl *CatIMP);

  /// Add the given method to the list of globally-known methods.
  void addMethodToGlobalList(ObjCMethodList *List, ObjCMethodDecl *Method);

private:
  /// AddMethodToGlobalPool - Add an instance or factory method to the global
  /// pool. See descriptoin of AddInstanceMethodToGlobalPool.
  void AddMethodToGlobalPool(ObjCMethodDecl *Method, bool impl, bool instance);

  /// LookupMethodInGlobalPool - Returns the instance or factory method and
  /// optionally warns if there are multiple signatures.
  ObjCMethodDecl *LookupMethodInGlobalPool(Selector Sel, SourceRange R,
                                           bool receiverIdOrClass,
                                           bool instance);

public:
  /// - Returns instance or factory methods in global method pool for
  /// given selector. It checks the desired kind first, if none is found, and
  /// parameter checkTheOther is set, it then checks the other kind. If no such
  /// method or only one method is found, function returns false; otherwise, it
  /// returns true.
  bool
  CollectMultipleMethodsInGlobalPool(Selector Sel,
                                     SmallVectorImpl<ObjCMethodDecl*>& Methods,
                                     bool InstanceFirst, bool CheckTheOther,
                                     const ObjCObjectType *TypeBound = nullptr);

  bool
  AreMultipleMethodsInGlobalPool(Selector Sel, ObjCMethodDecl *BestMethod,
                                 SourceRange R, bool receiverIdOrClass,
                                 SmallVectorImpl<ObjCMethodDecl*>& Methods);

  void
  DiagnoseMultipleMethodInGlobalPool(SmallVectorImpl<ObjCMethodDecl*> &Methods,
                                     Selector Sel, SourceRange R,
                                     bool receiverIdOrClass);

private:
  /// - Returns a selector which best matches given argument list or
  /// nullptr if none could be found
  ObjCMethodDecl *SelectBestMethod(Selector Sel, MultiExprArg Args,
                                   bool IsInstance,
                                   SmallVectorImpl<ObjCMethodDecl*>& Methods);


  /// Record the typo correction failure and return an empty correction.
  TypoCorrection FailedCorrection(IdentifierInfo *Typo, SourceLocation TypoLoc,
                                  bool RecordFailure = true) {
    if (RecordFailure)
      TypoCorrectionFailures[Typo].insert(TypoLoc);
    return TypoCorrection();
  }

public:
  /// AddInstanceMethodToGlobalPool - All instance methods in a translation
  /// unit are added to a global pool. This allows us to efficiently associate
  /// a selector with a method declaraation for purposes of typechecking
  /// messages sent to "id" (where the class of the object is unknown).
  void AddInstanceMethodToGlobalPool(ObjCMethodDecl *Method, bool impl=false) {
    AddMethodToGlobalPool(Method, impl, /*instance*/true);
  }

  /// AddFactoryMethodToGlobalPool - Same as above, but for factory methods.
  void AddFactoryMethodToGlobalPool(ObjCMethodDecl *Method, bool impl=false) {
    AddMethodToGlobalPool(Method, impl, /*instance*/false);
  }

  /// AddAnyMethodToGlobalPool - Add any method, instance or factory to global
  /// pool.
  void AddAnyMethodToGlobalPool(Decl *D);

  /// LookupInstanceMethodInGlobalPool - Returns the method and warns if
  /// there are multiple signatures.
  ObjCMethodDecl *LookupInstanceMethodInGlobalPool(Selector Sel, SourceRange R,
                                                   bool receiverIdOrClass=false) {
    return LookupMethodInGlobalPool(Sel, R, receiverIdOrClass,
                                    /*instance*/true);
  }

  /// LookupFactoryMethodInGlobalPool - Returns the method and warns if
  /// there are multiple signatures.
  ObjCMethodDecl *LookupFactoryMethodInGlobalPool(Selector Sel, SourceRange R,
                                                  bool receiverIdOrClass=false) {
    return LookupMethodInGlobalPool(Sel, R, receiverIdOrClass,
                                    /*instance*/false);
  }

  const ObjCMethodDecl *SelectorsForTypoCorrection(Selector Sel,
                              QualType ObjectType=QualType());
  /// LookupImplementedMethodInGlobalPool - Returns the method which has an
  /// implementation.
  ObjCMethodDecl *LookupImplementedMethodInGlobalPool(Selector Sel);

  /// CollectIvarsToConstructOrDestruct - Collect those ivars which require
  /// initialization.
  void CollectIvarsToConstructOrDestruct(ObjCInterfaceDecl *OI,
                                  SmallVectorImpl<ObjCIvarDecl*> &Ivars);

  //===--------------------------------------------------------------------===//
  // Statement Parsing Callbacks: SemaStmt.cpp.
public:
  class FullExprArg {
  public:
    FullExprArg() : E(nullptr) { }
    FullExprArg(Sema &actions) : E(nullptr) { }

    ExprResult release() {
      return E;
    }

    Expr *get() const { return E; }

    Expr *operator->() {
      return E;
    }

  private:
    // FIXME: No need to make the entire Sema class a friend when it's just
    // Sema::MakeFullExpr that needs access to the constructor below.
    friend class Sema;

    explicit FullExprArg(Expr *expr) : E(expr) {}

    Expr *E;
  };

  FullExprArg MakeFullExpr(Expr *Arg) {
    return MakeFullExpr(Arg, Arg ? Arg->getExprLoc() : SourceLocation());
  }
  FullExprArg MakeFullExpr(Expr *Arg, SourceLocation CC) {
    return FullExprArg(ActOnFinishFullExpr(Arg, CC).get());
  }
  FullExprArg MakeFullDiscardedValueExpr(Expr *Arg) {
    ExprResult FE =
      ActOnFinishFullExpr(Arg, Arg ? Arg->getExprLoc() : SourceLocation(),
                          /*DiscardedValue*/ true);
    return FullExprArg(FE.get());
  }

  StmtResult ActOnExprStmt(ExprResult Arg);
  StmtResult ActOnExprStmtError();

  StmtResult ActOnNullStmt(SourceLocation SemiLoc,
                           bool HasLeadingEmptyMacro = false);

  void ActOnStartOfCompoundStmt(bool IsStmtExpr);
  void ActOnFinishOfCompoundStmt();
  StmtResult ActOnCompoundStmt(SourceLocation L, SourceLocation R,
                               ArrayRef<Stmt *> Elts, bool isStmtExpr);

  /// A RAII object to enter scope of a compound statement.
  class CompoundScopeRAII {
  public:
    CompoundScopeRAII(Sema &S, bool IsStmtExpr = false) : S(S) {
      S.ActOnStartOfCompoundStmt(IsStmtExpr);
    }

    ~CompoundScopeRAII() {
      S.ActOnFinishOfCompoundStmt();
    }

  private:
    Sema &S;
  };

  /// An RAII helper that pops function a function scope on exit.
  struct FunctionScopeRAII {
    Sema &S;
    bool Active;
    FunctionScopeRAII(Sema &S) : S(S), Active(true) {}
    ~FunctionScopeRAII() {
      if (Active)
        S.PopFunctionScopeInfo();
    }
    void disable() { Active = false; }
  };

  StmtResult ActOnDeclStmt(DeclGroupPtrTy Decl,
                                   SourceLocation StartLoc,
                                   SourceLocation EndLoc);
  void ActOnForEachDeclStmt(DeclGroupPtrTy Decl);
  StmtResult ActOnForEachLValueExpr(Expr *E);
  ExprResult ActOnCaseExpr(SourceLocation CaseLoc, ExprResult Val);
  StmtResult ActOnCaseStmt(SourceLocation CaseLoc, ExprResult LHS,
                           SourceLocation DotDotDotLoc, ExprResult RHS,
                           SourceLocation ColonLoc);
  void ActOnCaseStmtBody(Stmt *CaseStmt, Stmt *SubStmt);

  StmtResult ActOnDefaultStmt(SourceLocation DefaultLoc,
                                      SourceLocation ColonLoc,
                                      Stmt *SubStmt, Scope *CurScope);
  StmtResult ActOnLabelStmt(SourceLocation IdentLoc, LabelDecl *TheDecl,
                            SourceLocation ColonLoc, Stmt *SubStmt);

  StmtResult ActOnAttributedStmt(SourceLocation AttrLoc,
                                 ArrayRef<const Attr*> Attrs,
                                 Stmt *SubStmt);

  class ConditionResult;
  StmtResult ActOnIfStmt(SourceLocation IfLoc, bool IsConstexpr,
                         Stmt *InitStmt,
                         ConditionResult Cond, Stmt *ThenVal,
                         SourceLocation ElseLoc, Stmt *ElseVal);
  StmtResult BuildIfStmt(SourceLocation IfLoc, bool IsConstexpr,
                         Stmt *InitStmt,
                         ConditionResult Cond, Stmt *ThenVal,
                         SourceLocation ElseLoc, Stmt *ElseVal);
  StmtResult ActOnStartOfSwitchStmt(SourceLocation SwitchLoc,
                                    Stmt *InitStmt,
                                    ConditionResult Cond);
  StmtResult ActOnFinishSwitchStmt(SourceLocation SwitchLoc,
                                           Stmt *Switch, Stmt *Body);
  StmtResult ActOnWhileStmt(SourceLocation WhileLoc, ConditionResult Cond,
                            Stmt *Body);
  StmtResult ActOnDoStmt(SourceLocation DoLoc, Stmt *Body,
                         SourceLocation WhileLoc, SourceLocation CondLParen,
                         Expr *Cond, SourceLocation CondRParen);

  StmtResult ActOnForStmt(SourceLocation ForLoc,
                          SourceLocation LParenLoc,
                          Stmt *First,
                          ConditionResult Second,
                          FullExprArg Third,
                          SourceLocation RParenLoc,
                          Stmt *Body);
  ExprResult CheckObjCForCollectionOperand(SourceLocation forLoc,
                                           Expr *collection);
  StmtResult ActOnObjCForCollectionStmt(SourceLocation ForColLoc,
                                        Stmt *First, Expr *collection,
                                        SourceLocation RParenLoc);
  StmtResult FinishObjCForCollectionStmt(Stmt *ForCollection, Stmt *Body);

  enum BuildForRangeKind {
    /// Initial building of a for-range statement.
    BFRK_Build,
    /// Instantiation or recovery rebuild of a for-range statement. Don't
    /// attempt any typo-correction.
    BFRK_Rebuild,
    /// Determining whether a for-range statement could be built. Avoid any
    /// unnecessary or irreversible actions.
    BFRK_Check
  };

  StmtResult ActOnCXXForRangeStmt(Scope *S, SourceLocation ForLoc,
                                  SourceLocation CoawaitLoc,
                                  Stmt *InitStmt,
                                  Stmt *LoopVar,
                                  SourceLocation ColonLoc, Expr *Collection,
                                  SourceLocation RParenLoc,
                                  BuildForRangeKind Kind);
  StmtResult BuildCXXForRangeStmt(SourceLocation ForLoc,
                                  SourceLocation CoawaitLoc,
                                  Stmt *InitStmt,
                                  SourceLocation ColonLoc,
                                  Stmt *RangeDecl, Stmt *Begin, Stmt *End,
                                  Expr *Cond, Expr *Inc,
                                  Stmt *LoopVarDecl,
                                  SourceLocation RParenLoc,
                                  BuildForRangeKind Kind);
  StmtResult FinishCXXForRangeStmt(Stmt *ForRange, Stmt *Body);

  StmtResult ActOnGotoStmt(SourceLocation GotoLoc,
                           SourceLocation LabelLoc,
                           LabelDecl *TheDecl);
  StmtResult ActOnIndirectGotoStmt(SourceLocation GotoLoc,
                                   SourceLocation StarLoc,
                                   Expr *DestExp);
  StmtResult ActOnContinueStmt(SourceLocation ContinueLoc, Scope *CurScope);
  StmtResult ActOnBreakStmt(SourceLocation BreakLoc, Scope *CurScope);

  void ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
                                CapturedRegionKind Kind, unsigned NumParams);
  typedef std::pair<StringRef, QualType> CapturedParamNameType;
  void ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
                                CapturedRegionKind Kind,
                                ArrayRef<CapturedParamNameType> Params);
  StmtResult ActOnCapturedRegionEnd(Stmt *S);
  void ActOnCapturedRegionError();
  RecordDecl *CreateCapturedStmtRecordDecl(CapturedDecl *&CD,
                                           SourceLocation Loc,
                                           unsigned NumParams);

  enum CopyElisionSemanticsKind {
    CES_Strict = 0,
    CES_AllowParameters = 1,
    CES_AllowDifferentTypes = 2,
    CES_AllowExceptionVariables = 4,
    CES_FormerDefault = (CES_AllowParameters),
    CES_Default = (CES_AllowParameters | CES_AllowDifferentTypes),
    CES_AsIfByStdMove = (CES_AllowParameters | CES_AllowDifferentTypes |
                         CES_AllowExceptionVariables),
  };

  VarDecl *getCopyElisionCandidate(QualType ReturnType, Expr *E,
                                   CopyElisionSemanticsKind CESK);
  bool isCopyElisionCandidate(QualType ReturnType, const VarDecl *VD,
                              CopyElisionSemanticsKind CESK);

  StmtResult ActOnReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
                             Scope *CurScope);
  StmtResult BuildReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp);
  StmtResult ActOnCapScopeReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp);

  StmtResult ActOnGCCAsmStmt(SourceLocation AsmLoc, bool IsSimple,
                             bool IsVolatile, unsigned NumOutputs,
                             unsigned NumInputs, IdentifierInfo **Names,
                             MultiExprArg Constraints, MultiExprArg Exprs,
                             Expr *AsmString, MultiExprArg Clobbers,
                             SourceLocation RParenLoc);

  void FillInlineAsmIdentifierInfo(Expr *Res,
                                   llvm::InlineAsmIdentifierInfo &Info);
  ExprResult LookupInlineAsmIdentifier(CXXScopeSpec &SS,
                                       SourceLocation TemplateKWLoc,
                                       UnqualifiedId &Id,
                                       bool IsUnevaluatedContext);
  bool LookupInlineAsmField(StringRef Base, StringRef Member,
                            unsigned &Offset, SourceLocation AsmLoc);
  ExprResult LookupInlineAsmVarDeclField(Expr *RefExpr, StringRef Member,
                                         SourceLocation AsmLoc);
  StmtResult ActOnMSAsmStmt(SourceLocation AsmLoc, SourceLocation LBraceLoc,
                            ArrayRef<Token> AsmToks,
                            StringRef AsmString,
                            unsigned NumOutputs, unsigned NumInputs,
                            ArrayRef<StringRef> Constraints,
                            ArrayRef<StringRef> Clobbers,
                            ArrayRef<Expr*> Exprs,
                            SourceLocation EndLoc);
  LabelDecl *GetOrCreateMSAsmLabel(StringRef ExternalLabelName,
                                   SourceLocation Location,
                                   bool AlwaysCreate);

  VarDecl *BuildObjCExceptionDecl(TypeSourceInfo *TInfo, QualType ExceptionType,
                                  SourceLocation StartLoc,
                                  SourceLocation IdLoc, IdentifierInfo *Id,
                                  bool Invalid = false);

  Decl *ActOnObjCExceptionDecl(Scope *S, Declarator &D);

  StmtResult ActOnObjCAtCatchStmt(SourceLocation AtLoc, SourceLocation RParen,
                                  Decl *Parm, Stmt *Body);

  StmtResult ActOnObjCAtFinallyStmt(SourceLocation AtLoc, Stmt *Body);

  StmtResult ActOnObjCAtTryStmt(SourceLocation AtLoc, Stmt *Try,
                                MultiStmtArg Catch, Stmt *Finally);

  StmtResult BuildObjCAtThrowStmt(SourceLocation AtLoc, Expr *Throw);
  StmtResult ActOnObjCAtThrowStmt(SourceLocation AtLoc, Expr *Throw,
                                  Scope *CurScope);
  ExprResult ActOnObjCAtSynchronizedOperand(SourceLocation atLoc,
                                            Expr *operand);
  StmtResult ActOnObjCAtSynchronizedStmt(SourceLocation AtLoc,
                                         Expr *SynchExpr,
                                         Stmt *SynchBody);

  StmtResult ActOnObjCAutoreleasePoolStmt(SourceLocation AtLoc, Stmt *Body);

  VarDecl *BuildExceptionDeclaration(Scope *S, TypeSourceInfo *TInfo,
                                     SourceLocation StartLoc,
                                     SourceLocation IdLoc,
                                     IdentifierInfo *Id);

  Decl *ActOnExceptionDeclarator(Scope *S, Declarator &D);

  StmtResult ActOnCXXCatchBlock(SourceLocation CatchLoc,
                                Decl *ExDecl, Stmt *HandlerBlock);
  StmtResult ActOnCXXTryBlock(SourceLocation TryLoc, Stmt *TryBlock,
                              ArrayRef<Stmt *> Handlers);

  StmtResult ActOnSEHTryBlock(bool IsCXXTry, // try (true) or __try (false) ?
                              SourceLocation TryLoc, Stmt *TryBlock,
                              Stmt *Handler);
  StmtResult ActOnSEHExceptBlock(SourceLocation Loc,
                                 Expr *FilterExpr,
                                 Stmt *Block);
  void ActOnStartSEHFinallyBlock();
  void ActOnAbortSEHFinallyBlock();
  StmtResult ActOnFinishSEHFinallyBlock(SourceLocation Loc, Stmt *Block);
  StmtResult ActOnSEHLeaveStmt(SourceLocation Loc, Scope *CurScope);

  void DiagnoseReturnInConstructorExceptionHandler(CXXTryStmt *TryBlock);

  bool ShouldWarnIfUnusedFileScopedDecl(const DeclaratorDecl *D) const;

  /// If it's a file scoped decl that must warn if not used, keep track
  /// of it.
  void MarkUnusedFileScopedDecl(const DeclaratorDecl *D);

  /// DiagnoseUnusedExprResult - If the statement passed in is an expression
  /// whose result is unused, warn.
  void DiagnoseUnusedExprResult(const Stmt *S);
  void DiagnoseUnusedNestedTypedefs(const RecordDecl *D);
  void DiagnoseUnusedDecl(const NamedDecl *ND);

  /// Emit \p DiagID if statement located on \p StmtLoc has a suspicious null
  /// statement as a \p Body, and it is located on the same line.
  ///
  /// This helps prevent bugs due to typos, such as:
  ///     if (condition);
  ///       do_stuff();
  void DiagnoseEmptyStmtBody(SourceLocation StmtLoc,
                             const Stmt *Body,
                             unsigned DiagID);

  /// Warn if a for/while loop statement \p S, which is followed by
  /// \p PossibleBody, has a suspicious null statement as a body.
  void DiagnoseEmptyLoopBody(const Stmt *S,
                             const Stmt *PossibleBody);

  /// Warn if a value is moved to itself.
  void DiagnoseSelfMove(const Expr *LHSExpr, const Expr *RHSExpr,
                        SourceLocation OpLoc);

  /// Warn if we're implicitly casting from a _Nullable pointer type to a
  /// _Nonnull one.
  void diagnoseNullableToNonnullConversion(QualType DstType, QualType SrcType,
                                           SourceLocation Loc);

  /// Warn when implicitly casting 0 to nullptr.
  void diagnoseZeroToNullptrConversion(CastKind Kind, const Expr *E);

  ParsingDeclState PushParsingDeclaration(sema::DelayedDiagnosticPool &pool) {
    return DelayedDiagnostics.push(pool);
  }
  void PopParsingDeclaration(ParsingDeclState state, Decl *decl);

  typedef ProcessingContextState ParsingClassState;
  ParsingClassState PushParsingClass() {
    return DelayedDiagnostics.pushUndelayed();
  }
  void PopParsingClass(ParsingClassState state) {
    DelayedDiagnostics.popUndelayed(state);
  }

  void redelayDiagnostics(sema::DelayedDiagnosticPool &pool);

  void DiagnoseAvailabilityOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                                  const ObjCInterfaceDecl *UnknownObjCClass,
                                  bool ObjCPropertyAccess,
                                  bool AvoidPartialAvailabilityChecks = false,
                                  ObjCInterfaceDecl *ClassReceiver = nullptr);

  bool makeUnavailableInSystemHeader(SourceLocation loc,
                                     UnavailableAttr::ImplicitReason reason);

  /// Issue any -Wunguarded-availability warnings in \c FD
  void DiagnoseUnguardedAvailabilityViolations(Decl *FD);

  //===--------------------------------------------------------------------===//
  // Expression Parsing Callbacks: SemaExpr.cpp.

  bool CanUseDecl(NamedDecl *D, bool TreatUnavailableAsInvalid);
  bool DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                         const ObjCInterfaceDecl *UnknownObjCClass = nullptr,
                         bool ObjCPropertyAccess = false,
                         bool AvoidPartialAvailabilityChecks = false,
                         ObjCInterfaceDecl *ClassReciever = nullptr);
  void NoteDeletedFunction(FunctionDecl *FD);
  void NoteDeletedInheritingConstructor(CXXConstructorDecl *CD);
  std::string getDeletedOrUnavailableSuffix(const FunctionDecl *FD);
  bool DiagnosePropertyAccessorMismatch(ObjCPropertyDecl *PD,
                                        ObjCMethodDecl *Getter,
                                        SourceLocation Loc);
  void DiagnoseSentinelCalls(NamedDecl *D, SourceLocation Loc,
                             ArrayRef<Expr *> Args);

  void PushExpressionEvaluationContext(
      ExpressionEvaluationContext NewContext, Decl *LambdaContextDecl = nullptr,
      ExpressionEvaluationContextRecord::ExpressionKind Type =
          ExpressionEvaluationContextRecord::EK_Other);
  enum ReuseLambdaContextDecl_t { ReuseLambdaContextDecl };
  void PushExpressionEvaluationContext(
      ExpressionEvaluationContext NewContext, ReuseLambdaContextDecl_t,
      ExpressionEvaluationContextRecord::ExpressionKind Type =
          ExpressionEvaluationContextRecord::EK_Other);
  void PopExpressionEvaluationContext();

  void DiscardCleanupsInEvaluationContext();

  ExprResult TransformToPotentiallyEvaluated(Expr *E);
  ExprResult HandleExprEvaluationContextForTypeof(Expr *E);

  ExprResult ActOnConstantExpression(ExprResult Res);

  // Functions for marking a declaration referenced.  These functions also
  // contain the relevant logic for marking if a reference to a function or
  // variable is an odr-use (in the C++11 sense).  There are separate variants
  // for expressions referring to a decl; these exist because odr-use marking
  // needs to be delayed for some constant variables when we build one of the
  // named expressions.
  //
  // MightBeOdrUse indicates whether the use could possibly be an odr-use, and
  // should usually be true. This only needs to be set to false if the lack of
  // odr-use cannot be determined from the current context (for instance,
  // because the name denotes a virtual function and was written without an
  // explicit nested-name-specifier).
  void MarkAnyDeclReferenced(SourceLocation Loc, Decl *D, bool MightBeOdrUse);
  void MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
                              bool MightBeOdrUse = true);
  void MarkVariableReferenced(SourceLocation Loc, VarDecl *Var);
  void MarkDeclRefReferenced(DeclRefExpr *E, const Expr *Base = nullptr);
  void MarkMemberReferenced(MemberExpr *E);

  void UpdateMarkingForLValueToRValue(Expr *E);
  void CleanupVarDeclMarking();

  enum TryCaptureKind {
    TryCapture_Implicit, TryCapture_ExplicitByVal, TryCapture_ExplicitByRef
  };

  /// Try to capture the given variable.
  ///
  /// \param Var The variable to capture.
  ///
  /// \param Loc The location at which the capture occurs.
  ///
  /// \param Kind The kind of capture, which may be implicit (for either a
  /// block or a lambda), or explicit by-value or by-reference (for a lambda).
  ///
  /// \param EllipsisLoc The location of the ellipsis, if one is provided in
  /// an explicit lambda capture.
  ///
  /// \param BuildAndDiagnose Whether we are actually supposed to add the
  /// captures or diagnose errors. If false, this routine merely check whether
  /// the capture can occur without performing the capture itself or complaining
  /// if the variable cannot be captured.
  ///
  /// \param CaptureType Will be set to the type of the field used to capture
  /// this variable in the innermost block or lambda. Only valid when the
  /// variable can be captured.
  ///
  /// \param DeclRefType Will be set to the type of a reference to the capture
  /// from within the current scope. Only valid when the variable can be
  /// captured.
  ///
  /// \param FunctionScopeIndexToStopAt If non-null, it points to the index
  /// of the FunctionScopeInfo stack beyond which we do not attempt to capture.
  /// This is useful when enclosing lambdas must speculatively capture
  /// variables that may or may not be used in certain specializations of
  /// a nested generic lambda.
  ///
  /// \returns true if an error occurred (i.e., the variable cannot be
  /// captured) and false if the capture succeeded.
  bool tryCaptureVariable(VarDecl *Var, SourceLocation Loc, TryCaptureKind Kind,
                          SourceLocation EllipsisLoc, bool BuildAndDiagnose,
                          QualType &CaptureType,
                          QualType &DeclRefType,
                          const unsigned *const FunctionScopeIndexToStopAt);

  /// Try to capture the given variable.
  bool tryCaptureVariable(VarDecl *Var, SourceLocation Loc,
                          TryCaptureKind Kind = TryCapture_Implicit,
                          SourceLocation EllipsisLoc = SourceLocation());

  /// Checks if the variable must be captured.
  bool NeedToCaptureVariable(VarDecl *Var, SourceLocation Loc);

  /// Given a variable, determine the type that a reference to that
  /// variable will have in the given scope.
  QualType getCapturedDeclRefType(VarDecl *Var, SourceLocation Loc);

  /// Mark all of the declarations referenced within a particular AST node as
  /// referenced. Used when template instantiation instantiates a non-dependent
  /// type -- entities referenced by the type are now referenced.
  void MarkDeclarationsReferencedInType(SourceLocation Loc, QualType T);
  void MarkDeclarationsReferencedInExpr(Expr *E,
                                        bool SkipLocalVariables = false);

  /// Try to recover by turning the given expression into a
  /// call.  Returns true if recovery was attempted or an error was
  /// emitted; this may also leave the ExprResult invalid.
  bool tryToRecoverWithCall(ExprResult &E, const PartialDiagnostic &PD,
                            bool ForceComplain = false,
                            bool (*IsPlausibleResult)(QualType) = nullptr);

  /// Figure out if an expression could be turned into a call.
  bool tryExprAsCall(Expr &E, QualType &ZeroArgCallReturnTy,
                     UnresolvedSetImpl &NonTemplateOverloads);

  /// Conditionally issue a diagnostic based on the current
  /// evaluation context.
  ///
  /// \param Statement If Statement is non-null, delay reporting the
  /// diagnostic until the function body is parsed, and then do a basic
  /// reachability analysis to determine if the statement is reachable.
  /// If it is unreachable, the diagnostic will not be emitted.
  bool DiagRuntimeBehavior(SourceLocation Loc, const Stmt *Statement,
                           const PartialDiagnostic &PD);

  // Primary Expressions.
  SourceRange getExprRange(Expr *E) const;

  ExprResult ActOnIdExpression(
      Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
      UnqualifiedId &Id, bool HasTrailingLParen, bool IsAddressOfOperand,
      std::unique_ptr<CorrectionCandidateCallback> CCC = nullptr,
      bool IsInlineAsmIdentifier = false, Token *KeywordReplacement = nullptr);

  void DecomposeUnqualifiedId(const UnqualifiedId &Id,
                              TemplateArgumentListInfo &Buffer,
                              DeclarationNameInfo &NameInfo,
                              const TemplateArgumentListInfo *&TemplateArgs);

  bool
  DiagnoseEmptyLookup(Scope *S, CXXScopeSpec &SS, LookupResult &R,
                      std::unique_ptr<CorrectionCandidateCallback> CCC,
                      TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr,
                      ArrayRef<Expr *> Args = None, TypoExpr **Out = nullptr);

  ExprResult LookupInObjCMethod(LookupResult &LookUp, Scope *S,
                                IdentifierInfo *II,
                                bool AllowBuiltinCreation=false);

  ExprResult ActOnDependentIdExpression(const CXXScopeSpec &SS,
                                        SourceLocation TemplateKWLoc,
                                        const DeclarationNameInfo &NameInfo,
                                        bool isAddressOfOperand,
                                const TemplateArgumentListInfo *TemplateArgs);

  ExprResult BuildDeclRefExpr(ValueDecl *D, QualType Ty,
                              ExprValueKind VK,
                              SourceLocation Loc,
                              const CXXScopeSpec *SS = nullptr);
  ExprResult
  BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                   const DeclarationNameInfo &NameInfo,
                   const CXXScopeSpec *SS = nullptr,
                   NamedDecl *FoundD = nullptr,
                   const TemplateArgumentListInfo *TemplateArgs = nullptr);
  ExprResult
  BuildAnonymousStructUnionMemberReference(
      const CXXScopeSpec &SS,
      SourceLocation nameLoc,
      IndirectFieldDecl *indirectField,
      DeclAccessPair FoundDecl = DeclAccessPair::make(nullptr, AS_none),
      Expr *baseObjectExpr = nullptr,
      SourceLocation opLoc = SourceLocation());

  ExprResult BuildPossibleImplicitMemberExpr(const CXXScopeSpec &SS,
                                             SourceLocation TemplateKWLoc,
                                             LookupResult &R,
                                const TemplateArgumentListInfo *TemplateArgs,
                                             const Scope *S);
  ExprResult BuildImplicitMemberExpr(const CXXScopeSpec &SS,
                                     SourceLocation TemplateKWLoc,
                                     LookupResult &R,
                                const TemplateArgumentListInfo *TemplateArgs,
                                     bool IsDefiniteInstance,
                                     const Scope *S);
  bool UseArgumentDependentLookup(const CXXScopeSpec &SS,
                                  const LookupResult &R,
                                  bool HasTrailingLParen);

  ExprResult
  BuildQualifiedDeclarationNameExpr(CXXScopeSpec &SS,
                                    const DeclarationNameInfo &NameInfo,
                                    bool IsAddressOfOperand, const Scope *S,
                                    TypeSourceInfo **RecoveryTSI = nullptr);

  ExprResult BuildDependentDeclRefExpr(const CXXScopeSpec &SS,
                                       SourceLocation TemplateKWLoc,
                                const DeclarationNameInfo &NameInfo,
                                const TemplateArgumentListInfo *TemplateArgs);

  ExprResult BuildDeclarationNameExpr(const CXXScopeSpec &SS,
                                      LookupResult &R,
                                      bool NeedsADL,
                                      bool AcceptInvalidDecl = false);
  ExprResult BuildDeclarationNameExpr(
      const CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo, NamedDecl *D,
      NamedDecl *FoundD = nullptr,
      const TemplateArgumentListInfo *TemplateArgs = nullptr,
      bool AcceptInvalidDecl = false);

  ExprResult BuildLiteralOperatorCall(LookupResult &R,
                      DeclarationNameInfo &SuffixInfo,
                      ArrayRef<Expr *> Args,
                      SourceLocation LitEndLoc,
                      TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr);

  ExprResult BuildPredefinedExpr(SourceLocation Loc,
                                 PredefinedExpr::IdentKind IK);
  ExprResult ActOnPredefinedExpr(SourceLocation Loc, tok::TokenKind Kind);
  ExprResult ActOnIntegerConstant(SourceLocation Loc, uint64_t Val);

  bool CheckLoopHintExpr(Expr *E, SourceLocation Loc);

  ExprResult ActOnNumericConstant(const Token &Tok, Scope *UDLScope = nullptr);
  ExprResult ActOnCharacterConstant(const Token &Tok,
                                    Scope *UDLScope = nullptr);
  ExprResult ActOnParenExpr(SourceLocation L, SourceLocation R, Expr *E);
  ExprResult ActOnParenListExpr(SourceLocation L,
                                SourceLocation R,
                                MultiExprArg Val);

  /// ActOnStringLiteral - The specified tokens were lexed as pasted string
  /// fragments (e.g. "foo" "bar" L"baz").
  ExprResult ActOnStringLiteral(ArrayRef<Token> StringToks,
                                Scope *UDLScope = nullptr);

  ExprResult ActOnGenericSelectionExpr(SourceLocation KeyLoc,
                                       SourceLocation DefaultLoc,
                                       SourceLocation RParenLoc,
                                       Expr *ControllingExpr,
                                       ArrayRef<ParsedType> ArgTypes,
                                       ArrayRef<Expr *> ArgExprs);
  ExprResult CreateGenericSelectionExpr(SourceLocation KeyLoc,
                                        SourceLocation DefaultLoc,
                                        SourceLocation RParenLoc,
                                        Expr *ControllingExpr,
                                        ArrayRef<TypeSourceInfo *> Types,
                                        ArrayRef<Expr *> Exprs);

  // Binary/Unary Operators.  'Tok' is the token for the operator.
  ExprResult CreateBuiltinUnaryOp(SourceLocation OpLoc, UnaryOperatorKind Opc,
                                  Expr *InputExpr);
  ExprResult BuildUnaryOp(Scope *S, SourceLocation OpLoc,
                          UnaryOperatorKind Opc, Expr *Input);
  ExprResult ActOnUnaryOp(Scope *S, SourceLocation OpLoc,
                          tok::TokenKind Op, Expr *Input);

  bool isQualifiedMemberAccess(Expr *E);
  QualType CheckAddressOfOperand(ExprResult &Operand, SourceLocation OpLoc);

  ExprResult CreateUnaryExprOrTypeTraitExpr(TypeSourceInfo *TInfo,
                                            SourceLocation OpLoc,
                                            UnaryExprOrTypeTrait ExprKind,
                                            SourceRange R);
  ExprResult CreateUnaryExprOrTypeTraitExpr(Expr *E, SourceLocation OpLoc,
                                            UnaryExprOrTypeTrait ExprKind);
  ExprResult
    ActOnUnaryExprOrTypeTraitExpr(SourceLocation OpLoc,
                                  UnaryExprOrTypeTrait ExprKind,
                                  bool IsType, void *TyOrEx,
                                  SourceRange ArgRange);

  ExprResult CheckPlaceholderExpr(Expr *E);
  bool CheckVecStepExpr(Expr *E);

  bool CheckUnaryExprOrTypeTraitOperand(Expr *E, UnaryExprOrTypeTrait ExprKind);
  bool CheckUnaryExprOrTypeTraitOperand(QualType ExprType, SourceLocation OpLoc,
                                        SourceRange ExprRange,
                                        UnaryExprOrTypeTrait ExprKind);
  ExprResult ActOnSizeofParameterPackExpr(Scope *S,
                                          SourceLocation OpLoc,
                                          IdentifierInfo &Name,
                                          SourceLocation NameLoc,
                                          SourceLocation RParenLoc);
  ExprResult ActOnPostfixUnaryOp(Scope *S, SourceLocation OpLoc,
                                 tok::TokenKind Kind, Expr *Input);

  ExprResult ActOnArraySubscriptExpr(Scope *S, Expr *Base, SourceLocation LLoc,
                                     Expr *Idx, SourceLocation RLoc);
  ExprResult CreateBuiltinArraySubscriptExpr(Expr *Base, SourceLocation LLoc,
                                             Expr *Idx, SourceLocation RLoc);
  ExprResult ActOnOMPArraySectionExpr(Expr *Base, SourceLocation LBLoc,
                                      Expr *LowerBound, SourceLocation ColonLoc,
                                      Expr *Length, SourceLocation RBLoc);

  // This struct is for use by ActOnMemberAccess to allow
  // BuildMemberReferenceExpr to be able to reinvoke ActOnMemberAccess after
  // changing the access operator from a '.' to a '->' (to see if that is the
  // change needed to fix an error about an unknown member, e.g. when the class
  // defines a custom operator->).
  struct ActOnMemberAccessExtraArgs {
    Scope *S;
    UnqualifiedId &Id;
    Decl *ObjCImpDecl;
  };

  ExprResult BuildMemberReferenceExpr(
      Expr *Base, QualType BaseType, SourceLocation OpLoc, bool IsArrow,
      CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
      NamedDecl *FirstQualifierInScope, const DeclarationNameInfo &NameInfo,
      const TemplateArgumentListInfo *TemplateArgs,
      const Scope *S,
      ActOnMemberAccessExtraArgs *ExtraArgs = nullptr);

  ExprResult
  BuildMemberReferenceExpr(Expr *Base, QualType BaseType, SourceLocation OpLoc,
                           bool IsArrow, const CXXScopeSpec &SS,
                           SourceLocation TemplateKWLoc,
                           NamedDecl *FirstQualifierInScope, LookupResult &R,
                           const TemplateArgumentListInfo *TemplateArgs,
                           const Scope *S,
                           bool SuppressQualifierCheck = false,
                           ActOnMemberAccessExtraArgs *ExtraArgs = nullptr);

  ExprResult BuildFieldReferenceExpr(Expr *BaseExpr, bool IsArrow,
                                     SourceLocation OpLoc,
                                     const CXXScopeSpec &SS, FieldDecl *Field,
                                     DeclAccessPair FoundDecl,
                                     const DeclarationNameInfo &MemberNameInfo);

  ExprResult PerformMemberExprBaseConversion(Expr *Base, bool IsArrow);

  bool CheckQualifiedMemberReference(Expr *BaseExpr, QualType BaseType,
                                     const CXXScopeSpec &SS,
                                     const LookupResult &R);

  ExprResult ActOnDependentMemberExpr(Expr *Base, QualType BaseType,
                                      bool IsArrow, SourceLocation OpLoc,
                                      const CXXScopeSpec &SS,
                                      SourceLocation TemplateKWLoc,
                                      NamedDecl *FirstQualifierInScope,
                               const DeclarationNameInfo &NameInfo,
                               const TemplateArgumentListInfo *TemplateArgs);

  ExprResult ActOnMemberAccessExpr(Scope *S, Expr *Base,
                                   SourceLocation OpLoc,
                                   tok::TokenKind OpKind,
                                   CXXScopeSpec &SS,
                                   SourceLocation TemplateKWLoc,
                                   UnqualifiedId &Member,
                                   Decl *ObjCImpDecl);

  void ActOnDefaultCtorInitializers(Decl *CDtorDecl);
  bool ConvertArgumentsForCall(CallExpr *Call, Expr *Fn,
                               FunctionDecl *FDecl,
                               const FunctionProtoType *Proto,
                               ArrayRef<Expr *> Args,
                               SourceLocation RParenLoc,
                               bool ExecConfig = false);
  void CheckStaticArrayArgument(SourceLocation CallLoc,
                                ParmVarDecl *Param,
                                const Expr *ArgExpr);

  /// ActOnCallExpr - Handle a call to Fn with the specified array of arguments.
  /// This provides the location of the left/right parens and a list of comma
  /// locations.
  ExprResult ActOnCallExpr(Scope *S, Expr *Fn, SourceLocation LParenLoc,
                           MultiExprArg ArgExprs, SourceLocation RParenLoc,
                           Expr *ExecConfig = nullptr,
                           bool IsExecConfig = false);
  ExprResult
  BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl, SourceLocation LParenLoc,
                        ArrayRef<Expr *> Arg, SourceLocation RParenLoc,
                        Expr *Config = nullptr, bool IsExecConfig = false,
                        ADLCallKind UsesADL = ADLCallKind::NotADL);

  ExprResult ActOnCUDAExecConfigExpr(Scope *S, SourceLocation LLLLoc,
                                     MultiExprArg ExecConfig,
                                     SourceLocation GGGLoc);

  ExprResult ActOnCastExpr(Scope *S, SourceLocation LParenLoc,
                           Declarator &D, ParsedType &Ty,
                           SourceLocation RParenLoc, Expr *CastExpr);
  ExprResult BuildCStyleCastExpr(SourceLocation LParenLoc,
                                 TypeSourceInfo *Ty,
                                 SourceLocation RParenLoc,
                                 Expr *Op);
  CastKind PrepareScalarCast(ExprResult &src, QualType destType);

  /// Build an altivec or OpenCL literal.
  ExprResult BuildVectorLiteral(SourceLocation LParenLoc,
                                SourceLocation RParenLoc, Expr *E,
                                TypeSourceInfo *TInfo);

  ExprResult MaybeConvertParenListExprToParenExpr(Scope *S, Expr *ME);

  ExprResult ActOnCompoundLiteral(SourceLocation LParenLoc,
                                  ParsedType Ty,
                                  SourceLocation RParenLoc,
                                  Expr *InitExpr);

  ExprResult BuildCompoundLiteralExpr(SourceLocation LParenLoc,
                                      TypeSourceInfo *TInfo,
                                      SourceLocation RParenLoc,
                                      Expr *LiteralExpr);

  ExprResult ActOnInitList(SourceLocation LBraceLoc,
                           MultiExprArg InitArgList,
                           SourceLocation RBraceLoc);

  ExprResult ActOnDesignatedInitializer(Designation &Desig,
                                        SourceLocation Loc,
                                        bool GNUSyntax,
                                        ExprResult Init);

private:
  static BinaryOperatorKind ConvertTokenKindToBinaryOpcode(tok::TokenKind Kind);

public:
  ExprResult ActOnBinOp(Scope *S, SourceLocation TokLoc,
                        tok::TokenKind Kind, Expr *LHSExpr, Expr *RHSExpr);
  ExprResult BuildBinOp(Scope *S, SourceLocation OpLoc,
                        BinaryOperatorKind Opc, Expr *LHSExpr, Expr *RHSExpr);
  ExprResult CreateBuiltinBinOp(SourceLocation OpLoc, BinaryOperatorKind Opc,
                                Expr *LHSExpr, Expr *RHSExpr);

  void DiagnoseCommaOperator(const Expr *LHS, SourceLocation Loc);

  /// ActOnConditionalOp - Parse a ?: operation.  Note that 'LHS' may be null
  /// in the case of a the GNU conditional expr extension.
  ExprResult ActOnConditionalOp(SourceLocation QuestionLoc,
                                SourceLocation ColonLoc,
                                Expr *CondExpr, Expr *LHSExpr, Expr *RHSExpr);

  /// ActOnAddrLabel - Parse the GNU address of label extension: "&&foo".
  ExprResult ActOnAddrLabel(SourceLocation OpLoc, SourceLocation LabLoc,
                            LabelDecl *TheDecl);

  void ActOnStartStmtExpr();
  ExprResult ActOnStmtExpr(SourceLocation LPLoc, Stmt *SubStmt,
                           SourceLocation RPLoc); // "({..})"
  void ActOnStmtExprError();

  // __builtin_offsetof(type, identifier(.identifier|[expr])*)
  struct OffsetOfComponent {
    SourceLocation LocStart, LocEnd;
    bool isBrackets;  // true if [expr], false if .ident
    union {
      IdentifierInfo *IdentInfo;
      Expr *E;
    } U;
  };

  /// __builtin_offsetof(type, a.b[123][456].c)
  ExprResult BuildBuiltinOffsetOf(SourceLocation BuiltinLoc,
                                  TypeSourceInfo *TInfo,
                                  ArrayRef<OffsetOfComponent> Components,
                                  SourceLocation RParenLoc);
  ExprResult ActOnBuiltinOffsetOf(Scope *S,
                                  SourceLocation BuiltinLoc,
                                  SourceLocation TypeLoc,
                                  ParsedType ParsedArgTy,
                                  ArrayRef<OffsetOfComponent> Components,
                                  SourceLocation RParenLoc);

  // __builtin_choose_expr(constExpr, expr1, expr2)
  ExprResult ActOnChooseExpr(SourceLocation BuiltinLoc,
                             Expr *CondExpr, Expr *LHSExpr,
                             Expr *RHSExpr, SourceLocation RPLoc);

  // __builtin_va_arg(expr, type)
  ExprResult ActOnVAArg(SourceLocation BuiltinLoc, Expr *E, ParsedType Ty,
                        SourceLocation RPLoc);
  ExprResult BuildVAArgExpr(SourceLocation BuiltinLoc, Expr *E,
                            TypeSourceInfo *TInfo, SourceLocation RPLoc);

  // __null
  ExprResult ActOnGNUNullExpr(SourceLocation TokenLoc);

  bool CheckCaseExpression(Expr *E);

  /// Describes the result of an "if-exists" condition check.
  enum IfExistsResult {
    /// The symbol exists.
    IER_Exists,

    /// The symbol does not exist.
    IER_DoesNotExist,

    /// The name is a dependent name, so the results will differ
    /// from one instantiation to the next.
    IER_Dependent,

    /// An error occurred.
    IER_Error
  };

  IfExistsResult
  CheckMicrosoftIfExistsSymbol(Scope *S, CXXScopeSpec &SS,
                               const DeclarationNameInfo &TargetNameInfo);

  IfExistsResult
  CheckMicrosoftIfExistsSymbol(Scope *S, SourceLocation KeywordLoc,
                               bool IsIfExists, CXXScopeSpec &SS,
                               UnqualifiedId &Name);

  StmtResult BuildMSDependentExistsStmt(SourceLocation KeywordLoc,
                                        bool IsIfExists,
                                        NestedNameSpecifierLoc QualifierLoc,
                                        DeclarationNameInfo NameInfo,
                                        Stmt *Nested);
  StmtResult ActOnMSDependentExistsStmt(SourceLocation KeywordLoc,
                                        bool IsIfExists,
                                        CXXScopeSpec &SS, UnqualifiedId &Name,
                                        Stmt *Nested);

  //===------------------------- "Block" Extension ------------------------===//

  /// ActOnBlockStart - This callback is invoked when a block literal is
  /// started.
  void ActOnBlockStart(SourceLocation CaretLoc, Scope *CurScope);

  /// ActOnBlockArguments - This callback allows processing of block arguments.
  /// If there are no arguments, this is still invoked.
  void ActOnBlockArguments(SourceLocation CaretLoc, Declarator &ParamInfo,
                           Scope *CurScope);

  /// ActOnBlockError - If there is an error parsing a block, this callback
  /// is invoked to pop the information about the block from the action impl.
  void ActOnBlockError(SourceLocation CaretLoc, Scope *CurScope);

  /// ActOnBlockStmtExpr - This is called when the body of a block statement
  /// literal was successfully completed.  ^(int x){...}
  ExprResult ActOnBlockStmtExpr(SourceLocation CaretLoc, Stmt *Body,
                                Scope *CurScope);

  //===---------------------------- Clang Extensions ----------------------===//

  /// __builtin_convertvector(...)
  ExprResult ActOnConvertVectorExpr(Expr *E, ParsedType ParsedDestTy,
                                    SourceLocation BuiltinLoc,
                                    SourceLocation RParenLoc);

  //===---------------------------- OpenCL Features -----------------------===//

  /// __builtin_astype(...)
  ExprResult ActOnAsTypeExpr(Expr *E, ParsedType ParsedDestTy,
                             SourceLocation BuiltinLoc,
                             SourceLocation RParenLoc);

  //===---------------------------- C++ Features --------------------------===//

  // Act on C++ namespaces
  Decl *ActOnStartNamespaceDef(Scope *S, SourceLocation InlineLoc,
                               SourceLocation NamespaceLoc,
                               SourceLocation IdentLoc, IdentifierInfo *Ident,
                               SourceLocation LBrace,
                               const ParsedAttributesView &AttrList,
                               UsingDirectiveDecl *&UsingDecl);
  void ActOnFinishNamespaceDef(Decl *Dcl, SourceLocation RBrace);

  NamespaceDecl *getStdNamespace() const;
  NamespaceDecl *getOrCreateStdNamespace();

  NamespaceDecl *lookupStdExperimentalNamespace();

  CXXRecordDecl *getStdBadAlloc() const;
  EnumDecl *getStdAlignValT() const;

private:
  // A cache representing if we've fully checked the various comparison category
  // types stored in ASTContext. The bit-index corresponds to the integer value
  // of a ComparisonCategoryType enumerator.
  llvm::SmallBitVector FullyCheckedComparisonCategories;

  ValueDecl *tryLookupCtorInitMemberDecl(CXXRecordDecl *ClassDecl,
                                         CXXScopeSpec &SS,
                                         ParsedType TemplateTypeTy,
                                         IdentifierInfo *MemberOrBase);

public:
  /// Lookup the specified comparison category types in the standard
  ///   library, an check the VarDecls possibly returned by the operator<=>
  ///   builtins for that type.
  ///
  /// \return The type of the comparison category type corresponding to the
  ///   specified Kind, or a null type if an error occurs
  QualType CheckComparisonCategoryType(ComparisonCategoryType Kind,
                                       SourceLocation Loc);

  /// Tests whether Ty is an instance of std::initializer_list and, if
  /// it is and Element is not NULL, assigns the element type to Element.
  bool isStdInitializerList(QualType Ty, QualType *Element);

  /// Looks for the std::initializer_list template and instantiates it
  /// with Element, or emits an error if it's not found.
  ///
  /// \returns The instantiated template, or null on error.
  QualType BuildStdInitializerList(QualType Element, SourceLocation Loc);

  /// Determine whether Ctor is an initializer-list constructor, as
  /// defined in [dcl.init.list]p2.
  bool isInitListConstructor(const FunctionDecl *Ctor);

  Decl *ActOnUsingDirective(Scope *CurScope, SourceLocation UsingLoc,
                            SourceLocation NamespcLoc, CXXScopeSpec &SS,
                            SourceLocation IdentLoc,
                            IdentifierInfo *NamespcName,
                            const ParsedAttributesView &AttrList);

  void PushUsingDirective(Scope *S, UsingDirectiveDecl *UDir);

  Decl *ActOnNamespaceAliasDef(Scope *CurScope,
                               SourceLocation NamespaceLoc,
                               SourceLocation AliasLoc,
                               IdentifierInfo *Alias,
                               CXXScopeSpec &SS,
                               SourceLocation IdentLoc,
                               IdentifierInfo *Ident);

  void HideUsingShadowDecl(Scope *S, UsingShadowDecl *Shadow);
  bool CheckUsingShadowDecl(UsingDecl *UD, NamedDecl *Target,
                            const LookupResult &PreviousDecls,
                            UsingShadowDecl *&PrevShadow);
  UsingShadowDecl *BuildUsingShadowDecl(Scope *S, UsingDecl *UD,
                                        NamedDecl *Target,
                                        UsingShadowDecl *PrevDecl);

  bool CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
                                   bool HasTypenameKeyword,
                                   const CXXScopeSpec &SS,
                                   SourceLocation NameLoc,
                                   const LookupResult &Previous);
  bool CheckUsingDeclQualifier(SourceLocation UsingLoc,
                               bool HasTypename,
                               const CXXScopeSpec &SS,
                               const DeclarationNameInfo &NameInfo,
                               SourceLocation NameLoc);

  NamedDecl *BuildUsingDeclaration(
      Scope *S, AccessSpecifier AS, SourceLocation UsingLoc,
      bool HasTypenameKeyword, SourceLocation TypenameLoc, CXXScopeSpec &SS,
      DeclarationNameInfo NameInfo, SourceLocation EllipsisLoc,
      const ParsedAttributesView &AttrList, bool IsInstantiation);
  NamedDecl *BuildUsingPackDecl(NamedDecl *InstantiatedFrom,
                                ArrayRef<NamedDecl *> Expansions);

  bool CheckInheritingConstructorUsingDecl(UsingDecl *UD);

  /// Given a derived-class using shadow declaration for a constructor and the
  /// correspnding base class constructor, find or create the implicit
  /// synthesized derived class constructor to use for this initialization.
  CXXConstructorDecl *
  findInheritingConstructor(SourceLocation Loc, CXXConstructorDecl *BaseCtor,
                            ConstructorUsingShadowDecl *DerivedShadow);

  Decl *ActOnUsingDeclaration(Scope *CurScope, AccessSpecifier AS,
                              SourceLocation UsingLoc,
                              SourceLocation TypenameLoc, CXXScopeSpec &SS,
                              UnqualifiedId &Name, SourceLocation EllipsisLoc,
                              const ParsedAttributesView &AttrList);
  Decl *ActOnAliasDeclaration(Scope *CurScope, AccessSpecifier AS,
                              MultiTemplateParamsArg TemplateParams,
                              SourceLocation UsingLoc, UnqualifiedId &Name,
                              const ParsedAttributesView &AttrList,
                              TypeResult Type, Decl *DeclFromDeclSpec);

  /// BuildCXXConstructExpr - Creates a complete call to a constructor,
  /// including handling of its default argument expressions.
  ///
  /// \param ConstructKind - a CXXConstructExpr::ConstructionKind
  ExprResult
  BuildCXXConstructExpr(SourceLocation ConstructLoc, QualType DeclInitType,
                        NamedDecl *FoundDecl,
                        CXXConstructorDecl *Constructor, MultiExprArg Exprs,
                        bool HadMultipleCandidates, bool IsListInitialization,
                        bool IsStdInitListInitialization,
                        bool RequiresZeroInit, unsigned ConstructKind,
                        SourceRange ParenRange);

  /// Build a CXXConstructExpr whose constructor has already been resolved if
  /// it denotes an inherited constructor.
  ExprResult
  BuildCXXConstructExpr(SourceLocation ConstructLoc, QualType DeclInitType,
                        CXXConstructorDecl *Constructor, bool Elidable,
                        MultiExprArg Exprs,
                        bool HadMultipleCandidates, bool IsListInitialization,
                        bool IsStdInitListInitialization,
                        bool RequiresZeroInit, unsigned ConstructKind,
                        SourceRange ParenRange);

  // FIXME: Can we remove this and have the above BuildCXXConstructExpr check if
  // the constructor can be elidable?
  ExprResult
  BuildCXXConstructExpr(SourceLocation ConstructLoc, QualType DeclInitType,
                        NamedDecl *FoundDecl,
                        CXXConstructorDecl *Constructor, bool Elidable,
                        MultiExprArg Exprs, bool HadMultipleCandidates,
                        bool IsListInitialization,
                        bool IsStdInitListInitialization, bool RequiresZeroInit,
                        unsigned ConstructKind, SourceRange ParenRange);

  ExprResult BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field);


  /// Instantiate or parse a C++ default argument expression as necessary.
  /// Return true on error.
  bool CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
                              ParmVarDecl *Param);

  /// BuildCXXDefaultArgExpr - Creates a CXXDefaultArgExpr, instantiating
  /// the default expr if needed.
  ExprResult BuildCXXDefaultArgExpr(SourceLocation CallLoc,
                                    FunctionDecl *FD,
                                    ParmVarDecl *Param);

  /// FinalizeVarWithDestructor - Prepare for calling destructor on the
  /// constructed variable.
  void FinalizeVarWithDestructor(VarDecl *VD, const RecordType *DeclInitType);

  /// Helper class that collects exception specifications for
  /// implicitly-declared special member functions.
  class ImplicitExceptionSpecification {
    // Pointer to allow copying
    Sema *Self;
    // We order exception specifications thus:
    // noexcept is the most restrictive, but is only used in C++11.
    // throw() comes next.
    // Then a throw(collected exceptions)
    // Finally no specification, which is expressed as noexcept(false).
    // throw(...) is used instead if any called function uses it.
    ExceptionSpecificationType ComputedEST;
    llvm::SmallPtrSet<CanQualType, 4> ExceptionsSeen;
    SmallVector<QualType, 4> Exceptions;

    void ClearExceptions() {
      ExceptionsSeen.clear();
      Exceptions.clear();
    }

  public:
    explicit ImplicitExceptionSpecification(Sema &Self)
      : Self(&Self), ComputedEST(EST_BasicNoexcept) {
      if (!Self.getLangOpts().CPlusPlus11)
        ComputedEST = EST_DynamicNone;
    }

    /// Get the computed exception specification type.
    ExceptionSpecificationType getExceptionSpecType() const {
      assert(!isComputedNoexcept(ComputedEST) &&
             "noexcept(expr) should not be a possible result");
      return ComputedEST;
    }

    /// The number of exceptions in the exception specification.
    unsigned size() const { return Exceptions.size(); }

    /// The set of exceptions in the exception specification.
    const QualType *data() const { return Exceptions.data(); }

    /// Integrate another called method into the collected data.
    void CalledDecl(SourceLocation CallLoc, const CXXMethodDecl *Method);

    /// Integrate an invoked expression into the collected data.
    void CalledExpr(Expr *E);

    /// Overwrite an EPI's exception specification with this
    /// computed exception specification.
    FunctionProtoType::ExceptionSpecInfo getExceptionSpec() const {
      FunctionProtoType::ExceptionSpecInfo ESI;
      ESI.Type = getExceptionSpecType();
      if (ESI.Type == EST_Dynamic) {
        ESI.Exceptions = Exceptions;
      } else if (ESI.Type == EST_None) {
        /// C++11 [except.spec]p14:
        ///   The exception-specification is noexcept(false) if the set of
        ///   potential exceptions of the special member function contains "any"
        ESI.Type = EST_NoexceptFalse;
        ESI.NoexceptExpr = Self->ActOnCXXBoolLiteral(SourceLocation(),
                                                     tok::kw_false).get();
      }
      return ESI;
    }
  };

  /// Determine what sort of exception specification a defaulted
  /// copy constructor of a class will have.
  ImplicitExceptionSpecification
  ComputeDefaultedDefaultCtorExceptionSpec(SourceLocation Loc,
                                           CXXMethodDecl *MD);

  /// Determine what sort of exception specification a defaulted
  /// default constructor of a class will have, and whether the parameter
  /// will be const.
  ImplicitExceptionSpecification
  ComputeDefaultedCopyCtorExceptionSpec(CXXMethodDecl *MD);

  /// Determine what sort of exception specification a defautled
  /// copy assignment operator of a class will have, and whether the
  /// parameter will be const.
  ImplicitExceptionSpecification
  ComputeDefaultedCopyAssignmentExceptionSpec(CXXMethodDecl *MD);

  /// Determine what sort of exception specification a defaulted move
  /// constructor of a class will have.
  ImplicitExceptionSpecification
  ComputeDefaultedMoveCtorExceptionSpec(CXXMethodDecl *MD);

  /// Determine what sort of exception specification a defaulted move
  /// assignment operator of a class will have.
  ImplicitExceptionSpecification
  ComputeDefaultedMoveAssignmentExceptionSpec(CXXMethodDecl *MD);

  /// Determine what sort of exception specification a defaulted
  /// destructor of a class will have.
  ImplicitExceptionSpecification
  ComputeDefaultedDtorExceptionSpec(CXXMethodDecl *MD);

  /// Determine what sort of exception specification an inheriting
  /// constructor of a class will have.
  ImplicitExceptionSpecification
  ComputeInheritingCtorExceptionSpec(SourceLocation Loc,
                                     CXXConstructorDecl *CD);

  /// Evaluate the implicit exception specification for a defaulted
  /// special member function.
  void EvaluateImplicitExceptionSpec(SourceLocation Loc, CXXMethodDecl *MD);

  /// Check the given noexcept-specifier, convert its expression, and compute
  /// the appropriate ExceptionSpecificationType.
  ExprResult ActOnNoexceptSpec(SourceLocation NoexceptLoc, Expr *NoexceptExpr,
                               ExceptionSpecificationType &EST);

  /// Check the given exception-specification and update the
  /// exception specification information with the results.
  void checkExceptionSpecification(bool IsTopLevel,
                                   ExceptionSpecificationType EST,
                                   ArrayRef<ParsedType> DynamicExceptions,
                                   ArrayRef<SourceRange> DynamicExceptionRanges,
                                   Expr *NoexceptExpr,
                                   SmallVectorImpl<QualType> &Exceptions,
                                   FunctionProtoType::ExceptionSpecInfo &ESI);

  /// Determine if we're in a case where we need to (incorrectly) eagerly
  /// parse an exception specification to work around a libstdc++ bug.
  bool isLibstdcxxEagerExceptionSpecHack(const Declarator &D);

  /// Add an exception-specification to the given member function
  /// (or member function template). The exception-specification was parsed
  /// after the method itself was declared.
  void actOnDelayedExceptionSpecification(Decl *Method,
         ExceptionSpecificationType EST,
         SourceRange SpecificationRange,
         ArrayRef<ParsedType> DynamicExceptions,
         ArrayRef<SourceRange> DynamicExceptionRanges,
         Expr *NoexceptExpr);

  class InheritedConstructorInfo;

  /// Determine if a special member function should have a deleted
  /// definition when it is defaulted.
  bool ShouldDeleteSpecialMember(CXXMethodDecl *MD, CXXSpecialMember CSM,
                                 InheritedConstructorInfo *ICI = nullptr,
                                 bool Diagnose = false);

  /// Declare the implicit default constructor for the given class.
  ///
  /// \param ClassDecl The class declaration into which the implicit
  /// default constructor will be added.
  ///
  /// \returns The implicitly-declared default constructor.
  CXXConstructorDecl *DeclareImplicitDefaultConstructor(
                                                     CXXRecordDecl *ClassDecl);

  /// DefineImplicitDefaultConstructor - Checks for feasibility of
  /// defining this constructor as the default constructor.
  void DefineImplicitDefaultConstructor(SourceLocation CurrentLocation,
                                        CXXConstructorDecl *Constructor);

  /// Declare the implicit destructor for the given class.
  ///
  /// \param ClassDecl The class declaration into which the implicit
  /// destructor will be added.
  ///
  /// \returns The implicitly-declared destructor.
  CXXDestructorDecl *DeclareImplicitDestructor(CXXRecordDecl *ClassDecl);

  /// DefineImplicitDestructor - Checks for feasibility of
  /// defining this destructor as the default destructor.
  void DefineImplicitDestructor(SourceLocation CurrentLocation,
                                CXXDestructorDecl *Destructor);

  /// Build an exception spec for destructors that don't have one.
  ///
  /// C++11 says that user-defined destructors with no exception spec get one
  /// that looks as if the destructor was implicitly declared.
  void AdjustDestructorExceptionSpec(CXXDestructorDecl *Destructor);

  /// Define the specified inheriting constructor.
  void DefineInheritingConstructor(SourceLocation UseLoc,
                                   CXXConstructorDecl *Constructor);

  /// Declare the implicit copy constructor for the given class.
  ///
  /// \param ClassDecl The class declaration into which the implicit
  /// copy constructor will be added.
  ///
  /// \returns The implicitly-declared copy constructor.
  CXXConstructorDecl *DeclareImplicitCopyConstructor(CXXRecordDecl *ClassDecl);

  /// DefineImplicitCopyConstructor - Checks for feasibility of
  /// defining this constructor as the copy constructor.
  void DefineImplicitCopyConstructor(SourceLocation CurrentLocation,
                                     CXXConstructorDecl *Constructor);

  /// Declare the implicit move constructor for the given class.
  ///
  /// \param ClassDecl The Class declaration into which the implicit
  /// move constructor will be added.
  ///
  /// \returns The implicitly-declared move constructor, or NULL if it wasn't
  /// declared.
  CXXConstructorDecl *DeclareImplicitMoveConstructor(CXXRecordDecl *ClassDecl);

  /// DefineImplicitMoveConstructor - Checks for feasibility of
  /// defining this constructor as the move constructor.
  void DefineImplicitMoveConstructor(SourceLocation CurrentLocation,
                                     CXXConstructorDecl *Constructor);

  /// Declare the implicit copy assignment operator for the given class.
  ///
  /// \param ClassDecl The class declaration into which the implicit
  /// copy assignment operator will be added.
  ///
  /// \returns The implicitly-declared copy assignment operator.
  CXXMethodDecl *DeclareImplicitCopyAssignment(CXXRecordDecl *ClassDecl);

  /// Defines an implicitly-declared copy assignment operator.
  void DefineImplicitCopyAssignment(SourceLocation CurrentLocation,
                                    CXXMethodDecl *MethodDecl);

  /// Declare the implicit move assignment operator for the given class.
  ///
  /// \param ClassDecl The Class declaration into which the implicit
  /// move assignment operator will be added.
  ///
  /// \returns The implicitly-declared move assignment operator, or NULL if it
  /// wasn't declared.
  CXXMethodDecl *DeclareImplicitMoveAssignment(CXXRecordDecl *ClassDecl);

  /// Defines an implicitly-declared move assignment operator.
  void DefineImplicitMoveAssignment(SourceLocation CurrentLocation,
                                    CXXMethodDecl *MethodDecl);

  /// Force the declaration of any implicitly-declared members of this
  /// class.
  void ForceDeclarationOfImplicitMembers(CXXRecordDecl *Class);

  /// Check a completed declaration of an implicit special member.
  void CheckImplicitSpecialMemberDeclaration(Scope *S, FunctionDecl *FD);

  /// Determine whether the given function is an implicitly-deleted
  /// special member function.
  bool isImplicitlyDeleted(FunctionDecl *FD);

  /// Check whether 'this' shows up in the type of a static member
  /// function after the (naturally empty) cv-qualifier-seq would be.
  ///
  /// \returns true if an error occurred.
  bool checkThisInStaticMemberFunctionType(CXXMethodDecl *Method);

  /// Whether this' shows up in the exception specification of a static
  /// member function.
  bool checkThisInStaticMemberFunctionExceptionSpec(CXXMethodDecl *Method);

  /// Check whether 'this' shows up in the attributes of the given
  /// static member function.
  ///
  /// \returns true if an error occurred.
  bool checkThisInStaticMemberFunctionAttributes(CXXMethodDecl *Method);

  /// MaybeBindToTemporary - If the passed in expression has a record type with
  /// a non-trivial destructor, this will return CXXBindTemporaryExpr. Otherwise
  /// it simply returns the passed in expression.
  ExprResult MaybeBindToTemporary(Expr *E);

  bool CompleteConstructorCall(CXXConstructorDecl *Constructor,
                               MultiExprArg ArgsPtr,
                               SourceLocation Loc,
                               SmallVectorImpl<Expr*> &ConvertedArgs,
                               bool AllowExplicit = false,
                               bool IsListInitialization = false);

  ParsedType getInheritingConstructorName(CXXScopeSpec &SS,
                                          SourceLocation NameLoc,
                                          IdentifierInfo &Name);

  ParsedType getConstructorName(IdentifierInfo &II, SourceLocation NameLoc,
                                Scope *S, CXXScopeSpec &SS,
                                bool EnteringContext);
  ParsedType getDestructorName(SourceLocation TildeLoc,
                               IdentifierInfo &II, SourceLocation NameLoc,
                               Scope *S, CXXScopeSpec &SS,
                               ParsedType ObjectType,
                               bool EnteringContext);

  ParsedType getDestructorTypeForDecltype(const DeclSpec &DS,
                                          ParsedType ObjectType);

  // Checks that reinterpret casts don't have undefined behavior.
  void CheckCompatibleReinterpretCast(QualType SrcType, QualType DestType,
                                      bool IsDereference, SourceRange Range);

  /// ActOnCXXNamedCast - Parse {dynamic,static,reinterpret,const}_cast's.
  ExprResult ActOnCXXNamedCast(SourceLocation OpLoc,
                               tok::TokenKind Kind,
                               SourceLocation LAngleBracketLoc,
                               Declarator &D,
                               SourceLocation RAngleBracketLoc,
                               SourceLocation LParenLoc,
                               Expr *E,
                               SourceLocation RParenLoc);

  ExprResult BuildCXXNamedCast(SourceLocation OpLoc,
                               tok::TokenKind Kind,
                               TypeSourceInfo *Ty,
                               Expr *E,
                               SourceRange AngleBrackets,
                               SourceRange Parens);

  ExprResult BuildCXXTypeId(QualType TypeInfoType,
                            SourceLocation TypeidLoc,
                            TypeSourceInfo *Operand,
                            SourceLocation RParenLoc);
  ExprResult BuildCXXTypeId(QualType TypeInfoType,
                            SourceLocation TypeidLoc,
                            Expr *Operand,
                            SourceLocation RParenLoc);

  /// ActOnCXXTypeid - Parse typeid( something ).
  ExprResult ActOnCXXTypeid(SourceLocation OpLoc,
                            SourceLocation LParenLoc, bool isType,
                            void *TyOrExpr,
                            SourceLocation RParenLoc);

  ExprResult BuildCXXUuidof(QualType TypeInfoType,
                            SourceLocation TypeidLoc,
                            TypeSourceInfo *Operand,
                            SourceLocation RParenLoc);
  ExprResult BuildCXXUuidof(QualType TypeInfoType,
                            SourceLocation TypeidLoc,
                            Expr *Operand,
                            SourceLocation RParenLoc);

  /// ActOnCXXUuidof - Parse __uuidof( something ).
  ExprResult ActOnCXXUuidof(SourceLocation OpLoc,
                            SourceLocation LParenLoc, bool isType,
                            void *TyOrExpr,
                            SourceLocation RParenLoc);

  /// Handle a C++1z fold-expression: ( expr op ... op expr ).
  ExprResult ActOnCXXFoldExpr(SourceLocation LParenLoc, Expr *LHS,
                              tok::TokenKind Operator,
                              SourceLocation EllipsisLoc, Expr *RHS,
                              SourceLocation RParenLoc);
  ExprResult BuildCXXFoldExpr(SourceLocation LParenLoc, Expr *LHS,
                              BinaryOperatorKind Operator,
                              SourceLocation EllipsisLoc, Expr *RHS,
                              SourceLocation RParenLoc);
  ExprResult BuildEmptyCXXFoldExpr(SourceLocation EllipsisLoc,
                                   BinaryOperatorKind Operator);

  //// ActOnCXXThis -  Parse 'this' pointer.
  ExprResult ActOnCXXThis(SourceLocation loc);

  /// Try to retrieve the type of the 'this' pointer.
  ///
  /// \returns The type of 'this', if possible. Otherwise, returns a NULL type.
  QualType getCurrentThisType();

  /// When non-NULL, the C++ 'this' expression is allowed despite the
  /// current context not being a non-static member function. In such cases,
  /// this provides the type used for 'this'.
  QualType CXXThisTypeOverride;

  /// RAII object used to temporarily allow the C++ 'this' expression
  /// to be used, with the given qualifiers on the current class type.
  class CXXThisScopeRAII {
    Sema &S;
    QualType OldCXXThisTypeOverride;
    bool Enabled;

  public:
    /// Introduce a new scope where 'this' may be allowed (when enabled),
    /// using the given declaration (which is either a class template or a
    /// class) along with the given qualifiers.
    /// along with the qualifiers placed on '*this'.
    CXXThisScopeRAII(Sema &S, Decl *ContextDecl, Qualifiers CXXThisTypeQuals,
                     bool Enabled = true);

    ~CXXThisScopeRAII();
  };

  /// Make sure the value of 'this' is actually available in the current
  /// context, if it is a potentially evaluated context.
  ///
  /// \param Loc The location at which the capture of 'this' occurs.
  ///
  /// \param Explicit Whether 'this' is explicitly captured in a lambda
  /// capture list.
  ///
  /// \param FunctionScopeIndexToStopAt If non-null, it points to the index
  /// of the FunctionScopeInfo stack beyond which we do not attempt to capture.
  /// This is useful when enclosing lambdas must speculatively capture
  /// 'this' that may or may not be used in certain specializations of
  /// a nested generic lambda (depending on whether the name resolves to
  /// a non-static member function or a static function).
  /// \return returns 'true' if failed, 'false' if success.
  bool CheckCXXThisCapture(SourceLocation Loc, bool Explicit = false,
      bool BuildAndDiagnose = true,
      const unsigned *const FunctionScopeIndexToStopAt = nullptr,
      bool ByCopy = false);

  /// Determine whether the given type is the type of *this that is used
  /// outside of the body of a member function for a type that is currently
  /// being defined.
  bool isThisOutsideMemberFunctionBody(QualType BaseType);

  /// ActOnCXXBoolLiteral - Parse {true,false} literals.
  ExprResult ActOnCXXBoolLiteral(SourceLocation OpLoc, tok::TokenKind Kind);


  /// ActOnObjCBoolLiteral - Parse {__objc_yes,__objc_no} literals.
  ExprResult ActOnObjCBoolLiteral(SourceLocation OpLoc, tok::TokenKind Kind);

  ExprResult
  ActOnObjCAvailabilityCheckExpr(llvm::ArrayRef<AvailabilitySpec> AvailSpecs,
                                 SourceLocation AtLoc, SourceLocation RParen);

  /// ActOnCXXNullPtrLiteral - Parse 'nullptr'.
  ExprResult ActOnCXXNullPtrLiteral(SourceLocation Loc);

  //// ActOnCXXThrow -  Parse throw expressions.
  ExprResult ActOnCXXThrow(Scope *S, SourceLocation OpLoc, Expr *expr);
  ExprResult BuildCXXThrow(SourceLocation OpLoc, Expr *Ex,
                           bool IsThrownVarInScope);
  bool CheckCXXThrowOperand(SourceLocation ThrowLoc, QualType ThrowTy, Expr *E);