--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/lib/Lex/Preprocessor.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,1420 @@
+//===- Preprocessor.cpp - C Language Family Preprocessor Implementation ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements the Preprocessor interface.
+//
+//===----------------------------------------------------------------------===//
+//
+// Options to support:
+//   -H       - Print the name of each header file used.
+//   -d[DNI] - Dump various things.
+//   -fworking-directory - #line's with preprocessor's working dir.
+//   -fpreprocessed
+//   -dependency-file,-M,-MM,-MF,-MG,-MP,-MT,-MQ,-MD,-MMD
+//   -W*
+//   -w
+//
+// Messages to emit:
+//   "Multiple include guards may be useful for:\n"
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Lex/Preprocessor.h"
+#include "clang/Basic/Builtins.h"
+#include "clang/Basic/FileManager.h"
+#include "clang/Basic/FileSystemStatCache.h"
+#include "clang/Basic/IdentifierTable.h"
+#include "clang/Basic/LLVM.h"
+#include "clang/Basic/LangOptions.h"
+#include "clang/Basic/Module.h"
+#include "clang/Basic/SourceLocation.h"
+#include "clang/Basic/SourceManager.h"
+#include "clang/Basic/TargetInfo.h"
+#include "clang/Lex/CodeCompletionHandler.h"
+#include "clang/Lex/ExternalPreprocessorSource.h"
+#include "clang/Lex/HeaderSearch.h"
+#include "clang/Lex/LexDiagnostic.h"
+#include "clang/Lex/Lexer.h"
+#include "clang/Lex/LiteralSupport.h"
+#include "clang/Lex/MacroArgs.h"
+#include "clang/Lex/MacroInfo.h"
+#include "clang/Lex/ModuleLoader.h"
+#include "clang/Lex/Pragma.h"
+#include "clang/Lex/PreprocessingRecord.h"
+#include "clang/Lex/PreprocessorLexer.h"
+#include "clang/Lex/PreprocessorOptions.h"
+#include "clang/Lex/ScratchBuffer.h"
+#include "clang/Lex/Token.h"
+#include "clang/Lex/TokenLexer.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "llvm/Support/Capacity.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <cassert>
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+using namespace clang;
+
+LLVM_INSTANTIATE_REGISTRY(PragmaHandlerRegistry)
+
+ExternalPreprocessorSource::~ExternalPreprocessorSource() = default;
+
+Preprocessor::Preprocessor(std::shared_ptr<PreprocessorOptions> PPOpts,
+                           DiagnosticsEngine &diags, LangOptions &opts,
+                           SourceManager &SM, HeaderSearch &Headers,
+                           ModuleLoader &TheModuleLoader,
+                           IdentifierInfoLookup *IILookup, bool OwnsHeaders,
+                           TranslationUnitKind TUKind)
+    : PPOpts(std::move(PPOpts)), Diags(&diags), LangOpts(opts),
+      FileMgr(Headers.getFileMgr()), SourceMgr(SM),
+      ScratchBuf(new ScratchBuffer(SourceMgr)), HeaderInfo(Headers),
+      TheModuleLoader(TheModuleLoader), ExternalSource(nullptr),
+      // As the language options may have not been loaded yet (when
+      // deserializing an ASTUnit), adding keywords to the identifier table is
+      // deferred to Preprocessor::Initialize().
+      Identifiers(IILookup), PragmaHandlers(new PragmaNamespace(StringRef())),
+      TUKind(TUKind), SkipMainFilePreamble(0, true),
+      CurSubmoduleState(&NullSubmoduleState) {
+  OwnsHeaderSearch = OwnsHeaders;
+
+  // Default to discarding comments.
+  KeepComments = false;
+  KeepMacroComments = false;
+  SuppressIncludeNotFoundError = false;
+
+  // Macro expansion is enabled.
+  DisableMacroExpansion = false;
+  MacroExpansionInDirectivesOverride = false;
+  InMacroArgs = false;
+  ArgMacro = nullptr;
+  InMacroArgPreExpansion = false;
+  NumCachedTokenLexers = 0;
+  PragmasEnabled = true;
+  ParsingIfOrElifDirective = false;
+  PreprocessedOutput = false;
+
+  // We haven't read anything from the external source.
+  ReadMacrosFromExternalSource = false;
+
+  BuiltinInfo = std::make_unique<Builtin::Context>();
+
+  // "Poison" __VA_ARGS__, __VA_OPT__ which can only appear in the expansion of
+  // a macro. They get unpoisoned where it is allowed.
+  (Ident__VA_ARGS__ = getIdentifierInfo("__VA_ARGS__"))->setIsPoisoned();
+  SetPoisonReason(Ident__VA_ARGS__,diag::ext_pp_bad_vaargs_use);
+  if (getLangOpts().CPlusPlus2a) {
+    (Ident__VA_OPT__ = getIdentifierInfo("__VA_OPT__"))->setIsPoisoned();
+    SetPoisonReason(Ident__VA_OPT__,diag::ext_pp_bad_vaopt_use);
+  } else {
+    Ident__VA_OPT__ = nullptr;
+  }
+
+  // Initialize the pragma handlers.
+  RegisterBuiltinPragmas();
+
+  // Initialize builtin macros like __LINE__ and friends.
+  RegisterBuiltinMacros();
+
+  if(LangOpts.Borland) {
+    Ident__exception_info        = getIdentifierInfo("_exception_info");
+    Ident___exception_info       = getIdentifierInfo("__exception_info");
+    Ident_GetExceptionInfo       = getIdentifierInfo("GetExceptionInformation");
+    Ident__exception_code        = getIdentifierInfo("_exception_code");
+    Ident___exception_code       = getIdentifierInfo("__exception_code");
+    Ident_GetExceptionCode       = getIdentifierInfo("GetExceptionCode");
+    Ident__abnormal_termination  = getIdentifierInfo("_abnormal_termination");
+    Ident___abnormal_termination = getIdentifierInfo("__abnormal_termination");
+    Ident_AbnormalTermination    = getIdentifierInfo("AbnormalTermination");
+  } else {
+    Ident__exception_info = Ident__exception_code = nullptr;
+    Ident__abnormal_termination = Ident___exception_info = nullptr;
+    Ident___exception_code = Ident___abnormal_termination = nullptr;
+    Ident_GetExceptionInfo = Ident_GetExceptionCode = nullptr;
+    Ident_AbnormalTermination = nullptr;
+  }
+
+  // If using a PCH where a #pragma hdrstop is expected, start skipping tokens.
+  if (usingPCHWithPragmaHdrStop())
+    SkippingUntilPragmaHdrStop = true;
+
+  // If using a PCH with a through header, start skipping tokens.
+  if (!this->PPOpts->PCHThroughHeader.empty() &&
+      !this->PPOpts->ImplicitPCHInclude.empty())
+    SkippingUntilPCHThroughHeader = true;
+
+  if (this->PPOpts->GeneratePreamble)
+    PreambleConditionalStack.startRecording();
+
+  ExcludedConditionalDirectiveSkipMappings =
+      this->PPOpts->ExcludedConditionalDirectiveSkipMappings;
+  if (ExcludedConditionalDirectiveSkipMappings)
+    ExcludedConditionalDirectiveSkipMappings->clear();
+
+  MaxTokens = LangOpts.MaxTokens;
+}
+
+Preprocessor::~Preprocessor() {
+  assert(BacktrackPositions.empty() && "EnableBacktrack/Backtrack imbalance!");
+
+  IncludeMacroStack.clear();
+
+  // Destroy any macro definitions.
+  while (MacroInfoChain *I = MIChainHead) {
+    MIChainHead = I->Next;
+    I->~MacroInfoChain();
+  }
+
+  // Free any cached macro expanders.
+  // This populates MacroArgCache, so all TokenLexers need to be destroyed
+  // before the code below that frees up the MacroArgCache list.
+  std::fill(TokenLexerCache, TokenLexerCache + NumCachedTokenLexers, nullptr);
+  CurTokenLexer.reset();
+
+  // Free any cached MacroArgs.
+  for (MacroArgs *ArgList = MacroArgCache; ArgList;)
+    ArgList = ArgList->deallocate();
+
+  // Delete the header search info, if we own it.
+  if (OwnsHeaderSearch)
+    delete &HeaderInfo;
+}
+
+void Preprocessor::Initialize(const TargetInfo &Target,
+                              const TargetInfo *AuxTarget) {
+  assert((!this->Target || this->Target == &Target) &&
+         "Invalid override of target information");
+  this->Target = &Target;
+
+  assert((!this->AuxTarget || this->AuxTarget == AuxTarget) &&
+         "Invalid override of aux target information.");
+  this->AuxTarget = AuxTarget;
+
+  // Initialize information about built-ins.
+  BuiltinInfo->InitializeTarget(Target, AuxTarget);
+  HeaderInfo.setTarget(Target);
+
+  // Populate the identifier table with info about keywords for the current language.
+  Identifiers.AddKeywords(LangOpts);
+}
+
+void Preprocessor::InitializeForModelFile() {
+  NumEnteredSourceFiles = 0;
+
+  // Reset pragmas
+  PragmaHandlersBackup = std::move(PragmaHandlers);
+  PragmaHandlers = std::make_unique<PragmaNamespace>(StringRef());
+  RegisterBuiltinPragmas();
+
+  // Reset PredefinesFileID
+  PredefinesFileID = FileID();
+}
+
+void Preprocessor::FinalizeForModelFile() {
+  NumEnteredSourceFiles = 1;
+
+  PragmaHandlers = std::move(PragmaHandlersBackup);
+}
+
+void Preprocessor::DumpToken(const Token &Tok, bool DumpFlags) const {
+  llvm::errs() << tok::getTokenName(Tok.getKind()) << " '"
+               << getSpelling(Tok) << "'";
+
+  if (!DumpFlags) return;
+
+  llvm::errs() << "\t";
+  if (Tok.isAtStartOfLine())
+    llvm::errs() << " [StartOfLine]";
+  if (Tok.hasLeadingSpace())
+    llvm::errs() << " [LeadingSpace]";
+  if (Tok.isExpandDisabled())
+    llvm::errs() << " [ExpandDisabled]";
+  if (Tok.needsCleaning()) {
+    const char *Start = SourceMgr.getCharacterData(Tok.getLocation());
+    llvm::errs() << " [UnClean='" << StringRef(Start, Tok.getLength())
+                 << "']";
+  }
+
+  llvm::errs() << "\tLoc=<";
+  DumpLocation(Tok.getLocation());
+  llvm::errs() << ">";
+}
+
+void Preprocessor::DumpLocation(SourceLocation Loc) const {
+  Loc.print(llvm::errs(), SourceMgr);
+}
+
+void Preprocessor::DumpMacro(const MacroInfo &MI) const {
+  llvm::errs() << "MACRO: ";
+  for (unsigned i = 0, e = MI.getNumTokens(); i != e; ++i) {
+    DumpToken(MI.getReplacementToken(i));
+    llvm::errs() << "  ";
+  }
+  llvm::errs() << "\n";
+}
+
+void Preprocessor::PrintStats() {
+  llvm::errs() << "\n*** Preprocessor Stats:\n";
+  llvm::errs() << NumDirectives << " directives found:\n";
+  llvm::errs() << "  " << NumDefined << " #define.\n";
+  llvm::errs() << "  " << NumUndefined << " #undef.\n";
+  llvm::errs() << "  #include/#include_next/#import:\n";
+  llvm::errs() << "    " << NumEnteredSourceFiles << " source files entered.\n";
+  llvm::errs() << "    " << MaxIncludeStackDepth << " max include stack depth\n";
+  llvm::errs() << "  " << NumIf << " #if/#ifndef/#ifdef.\n";
+  llvm::errs() << "  " << NumElse << " #else/#elif.\n";
+  llvm::errs() << "  " << NumEndif << " #endif.\n";
+  llvm::errs() << "  " << NumPragma << " #pragma.\n";
+  llvm::errs() << NumSkipped << " #if/#ifndef#ifdef regions skipped\n";
+
+  llvm::errs() << NumMacroExpanded << "/" << NumFnMacroExpanded << "/"
+             << NumBuiltinMacroExpanded << " obj/fn/builtin macros expanded, "
+             << NumFastMacroExpanded << " on the fast path.\n";
+  llvm::errs() << (NumFastTokenPaste+NumTokenPaste)
+             << " token paste (##) operations performed, "
+             << NumFastTokenPaste << " on the fast path.\n";
+
+  llvm::errs() << "\nPreprocessor Memory: " << getTotalMemory() << "B total";
+
+  llvm::errs() << "\n  BumpPtr: " << BP.getTotalMemory();
+  llvm::errs() << "\n  Macro Expanded Tokens: "
+               << llvm::capacity_in_bytes(MacroExpandedTokens);
+  llvm::errs() << "\n  Predefines Buffer: " << Predefines.capacity();
+  // FIXME: List information for all submodules.
+  llvm::errs() << "\n  Macros: "
+               << llvm::capacity_in_bytes(CurSubmoduleState->Macros);
+  llvm::errs() << "\n  #pragma push_macro Info: "
+               << llvm::capacity_in_bytes(PragmaPushMacroInfo);
+  llvm::errs() << "\n  Poison Reasons: "
+               << llvm::capacity_in_bytes(PoisonReasons);
+  llvm::errs() << "\n  Comment Handlers: "
+               << llvm::capacity_in_bytes(CommentHandlers) << "\n";
+}
+
+Preprocessor::macro_iterator
+Preprocessor::macro_begin(bool IncludeExternalMacros) const {
+  if (IncludeExternalMacros && ExternalSource &&
+      !ReadMacrosFromExternalSource) {
+    ReadMacrosFromExternalSource = true;
+    ExternalSource->ReadDefinedMacros();
+  }
+
+  // Make sure we cover all macros in visible modules.
+  for (const ModuleMacro &Macro : ModuleMacros)
+    CurSubmoduleState->Macros.insert(std::make_pair(Macro.II, MacroState()));
+
+  return CurSubmoduleState->Macros.begin();
+}
+
+size_t Preprocessor::getTotalMemory() const {
+  return BP.getTotalMemory()
+    + llvm::capacity_in_bytes(MacroExpandedTokens)
+    + Predefines.capacity() /* Predefines buffer. */
+    // FIXME: Include sizes from all submodules, and include MacroInfo sizes,
+    // and ModuleMacros.
+    + llvm::capacity_in_bytes(CurSubmoduleState->Macros)
+    + llvm::capacity_in_bytes(PragmaPushMacroInfo)
+    + llvm::capacity_in_bytes(PoisonReasons)
+    + llvm::capacity_in_bytes(CommentHandlers);
+}
+
+Preprocessor::macro_iterator
+Preprocessor::macro_end(bool IncludeExternalMacros) const {
+  if (IncludeExternalMacros && ExternalSource &&
+      !ReadMacrosFromExternalSource) {
+    ReadMacrosFromExternalSource = true;
+    ExternalSource->ReadDefinedMacros();
+  }
+
+  return CurSubmoduleState->Macros.end();
+}
+
+/// Compares macro tokens with a specified token value sequence.
+static bool MacroDefinitionEquals(const MacroInfo *MI,
+                                  ArrayRef<TokenValue> Tokens) {
+  return Tokens.size() == MI->getNumTokens() &&
+      std::equal(Tokens.begin(), Tokens.end(), MI->tokens_begin());
+}
+
+StringRef Preprocessor::getLastMacroWithSpelling(
+                                    SourceLocation Loc,
+                                    ArrayRef<TokenValue> Tokens) const {
+  SourceLocation BestLocation;
+  StringRef BestSpelling;
+  for (Preprocessor::macro_iterator I = macro_begin(), E = macro_end();
+       I != E; ++I) {
+    const MacroDirective::DefInfo
+      Def = I->second.findDirectiveAtLoc(Loc, SourceMgr);
+    if (!Def || !Def.getMacroInfo())
+      continue;
+    if (!Def.getMacroInfo()->isObjectLike())
+      continue;
+    if (!MacroDefinitionEquals(Def.getMacroInfo(), Tokens))
+      continue;
+    SourceLocation Location = Def.getLocation();
+    // Choose the macro defined latest.
+    if (BestLocation.isInvalid() ||
+        (Location.isValid() &&
+         SourceMgr.isBeforeInTranslationUnit(BestLocation, Location))) {
+      BestLocation = Location;
+      BestSpelling = I->first->getName();
+    }
+  }
+  return BestSpelling;
+}
+
+void Preprocessor::recomputeCurLexerKind() {
+  if (CurLexer)
+    CurLexerKind = CLK_Lexer;
+  else if (CurTokenLexer)
+    CurLexerKind = CLK_TokenLexer;
+  else
+    CurLexerKind = CLK_CachingLexer;
+}
+
+bool Preprocessor::SetCodeCompletionPoint(const FileEntry *File,
+                                          unsigned CompleteLine,
+                                          unsigned CompleteColumn) {
+  assert(File);
+  assert(CompleteLine && CompleteColumn && "Starts from 1:1");
+  assert(!CodeCompletionFile && "Already set");
+
+  using llvm::MemoryBuffer;
+
+  // Load the actual file's contents.
+  bool Invalid = false;
+  const MemoryBuffer *Buffer = SourceMgr.getMemoryBufferForFile(File, &Invalid);
+  if (Invalid)
+    return true;
+
+  // Find the byte position of the truncation point.
+  const char *Position = Buffer->getBufferStart();
+  for (unsigned Line = 1; Line < CompleteLine; ++Line) {
+    for (; *Position; ++Position) {
+      if (*Position != '\r' && *Position != '\n')
+        continue;
+
+      // Eat \r\n or \n\r as a single line.
+      if ((Position[1] == '\r' || Position[1] == '\n') &&
+          Position[0] != Position[1])
+        ++Position;
+      ++Position;
+      break;
+    }
+  }
+
+  Position += CompleteColumn - 1;
+
+  // If pointing inside the preamble, adjust the position at the beginning of
+  // the file after the preamble.
+  if (SkipMainFilePreamble.first &&
+      SourceMgr.getFileEntryForID(SourceMgr.getMainFileID()) == File) {
+    if (Position - Buffer->getBufferStart() < SkipMainFilePreamble.first)
+      Position = Buffer->getBufferStart() + SkipMainFilePreamble.first;
+  }
+
+  if (Position > Buffer->getBufferEnd())
+    Position = Buffer->getBufferEnd();
+
+  CodeCompletionFile = File;
+  CodeCompletionOffset = Position - Buffer->getBufferStart();
+
+  auto NewBuffer = llvm::WritableMemoryBuffer::getNewUninitMemBuffer(
+      Buffer->getBufferSize() + 1, Buffer->getBufferIdentifier());
+  char *NewBuf = NewBuffer->getBufferStart();
+  char *NewPos = std::copy(Buffer->getBufferStart(), Position, NewBuf);
+  *NewPos = '\0';
+  std::copy(Position, Buffer->getBufferEnd(), NewPos+1);
+  SourceMgr.overrideFileContents(File, std::move(NewBuffer));
+
+  return false;
+}
+
+void Preprocessor::CodeCompleteIncludedFile(llvm::StringRef Dir,
+                                            bool IsAngled) {
+  if (CodeComplete)
+    CodeComplete->CodeCompleteIncludedFile(Dir, IsAngled);
+  setCodeCompletionReached();
+}
+
+void Preprocessor::CodeCompleteNaturalLanguage() {
+  if (CodeComplete)
+    CodeComplete->CodeCompleteNaturalLanguage();
+  setCodeCompletionReached();
+}
+
+/// getSpelling - This method is used to get the spelling of a token into a
+/// SmallVector. Note that the returned StringRef may not point to the
+/// supplied buffer if a copy can be avoided.
+StringRef Preprocessor::getSpelling(const Token &Tok,
+                                          SmallVectorImpl<char> &Buffer,
+                                          bool *Invalid) const {
+  // NOTE: this has to be checked *before* testing for an IdentifierInfo.
+  if (Tok.isNot(tok::raw_identifier) && !Tok.hasUCN()) {
+    // Try the fast path.
+    if (const IdentifierInfo *II = Tok.getIdentifierInfo())
+      return II->getName();
+  }
+
+  // Resize the buffer if we need to copy into it.
+  if (Tok.needsCleaning())
+    Buffer.resize(Tok.getLength());
+
+  const char *Ptr = Buffer.data();
+  unsigned Len = getSpelling(Tok, Ptr, Invalid);
+  return StringRef(Ptr, Len);
+}
+
+/// CreateString - Plop the specified string into a scratch buffer and return a
+/// location for it.  If specified, the source location provides a source
+/// location for the token.
+void Preprocessor::CreateString(StringRef Str, Token &Tok,
+                                SourceLocation ExpansionLocStart,
+                                SourceLocation ExpansionLocEnd) {
+  Tok.setLength(Str.size());
+
+  const char *DestPtr;
+  SourceLocation Loc = ScratchBuf->getToken(Str.data(), Str.size(), DestPtr);
+
+  if (ExpansionLocStart.isValid())
+    Loc = SourceMgr.createExpansionLoc(Loc, ExpansionLocStart,
+                                       ExpansionLocEnd, Str.size());
+  Tok.setLocation(Loc);
+
+  // If this is a raw identifier or a literal token, set the pointer data.
+  if (Tok.is(tok::raw_identifier))
+    Tok.setRawIdentifierData(DestPtr);
+  else if (Tok.isLiteral())
+    Tok.setLiteralData(DestPtr);
+}
+
+SourceLocation Preprocessor::SplitToken(SourceLocation Loc, unsigned Length) {
+  auto &SM = getSourceManager();
+  SourceLocation SpellingLoc = SM.getSpellingLoc(Loc);
+  std::pair<FileID, unsigned> LocInfo = SM.getDecomposedLoc(SpellingLoc);
+  bool Invalid = false;
+  StringRef Buffer = SM.getBufferData(LocInfo.first, &Invalid);
+  if (Invalid)
+    return SourceLocation();
+
+  // FIXME: We could consider re-using spelling for tokens we see repeatedly.
+  const char *DestPtr;
+  SourceLocation Spelling =
+      ScratchBuf->getToken(Buffer.data() + LocInfo.second, Length, DestPtr);
+  return SM.createTokenSplitLoc(Spelling, Loc, Loc.getLocWithOffset(Length));
+}
+
+Module *Preprocessor::getCurrentModule() {
+  if (!getLangOpts().isCompilingModule())
+    return nullptr;
+
+  return getHeaderSearchInfo().lookupModule(getLangOpts().CurrentModule);
+}
+
+//===----------------------------------------------------------------------===//
+// Preprocessor Initialization Methods
+//===----------------------------------------------------------------------===//
+
+/// EnterMainSourceFile - Enter the specified FileID as the main source file,
+/// which implicitly adds the builtin defines etc.
+void Preprocessor::EnterMainSourceFile() {
+  // We do not allow the preprocessor to reenter the main file.  Doing so will
+  // cause FileID's to accumulate information from both runs (e.g. #line
+  // information) and predefined macros aren't guaranteed to be set properly.
+  assert(NumEnteredSourceFiles == 0 && "Cannot reenter the main file!");
+  FileID MainFileID = SourceMgr.getMainFileID();
+
+  // If MainFileID is loaded it means we loaded an AST file, no need to enter
+  // a main file.
+  if (!SourceMgr.isLoadedFileID(MainFileID)) {
+    // Enter the main file source buffer.
+    EnterSourceFile(MainFileID, nullptr, SourceLocation());
+
+    // If we've been asked to skip bytes in the main file (e.g., as part of a
+    // precompiled preamble), do so now.
+    if (SkipMainFilePreamble.first > 0)
+      CurLexer->SetByteOffset(SkipMainFilePreamble.first,
+                              SkipMainFilePreamble.second);
+
+    // Tell the header info that the main file was entered.  If the file is later
+    // #imported, it won't be re-entered.
+    if (const FileEntry *FE = SourceMgr.getFileEntryForID(MainFileID))
+      HeaderInfo.IncrementIncludeCount(FE);
+  }
+
+  // Preprocess Predefines to populate the initial preprocessor state.
+  std::unique_ptr<llvm::MemoryBuffer> SB =
+    llvm::MemoryBuffer::getMemBufferCopy(Predefines, "<built-in>");
+  assert(SB && "Cannot create predefined source buffer");
+  FileID FID = SourceMgr.createFileID(std::move(SB));
+  assert(FID.isValid() && "Could not create FileID for predefines?");
+  setPredefinesFileID(FID);
+
+  // Start parsing the predefines.
+  EnterSourceFile(FID, nullptr, SourceLocation());
+
+  if (!PPOpts->PCHThroughHeader.empty()) {
+    // Lookup and save the FileID for the through header. If it isn't found
+    // in the search path, it's a fatal error.
+    const DirectoryLookup *CurDir;
+    Optional<FileEntryRef> File = LookupFile(
+        SourceLocation(), PPOpts->PCHThroughHeader,
+        /*isAngled=*/false, /*FromDir=*/nullptr, /*FromFile=*/nullptr, CurDir,
+        /*SearchPath=*/nullptr, /*RelativePath=*/nullptr,
+        /*SuggestedModule=*/nullptr, /*IsMapped=*/nullptr,
+        /*IsFrameworkFound=*/nullptr);
+    if (!File) {
+      Diag(SourceLocation(), diag::err_pp_through_header_not_found)
+          << PPOpts->PCHThroughHeader;
+      return;
+    }
+    setPCHThroughHeaderFileID(
+        SourceMgr.createFileID(*File, SourceLocation(), SrcMgr::C_User));
+  }
+
+  // Skip tokens from the Predefines and if needed the main file.
+  if ((usingPCHWithThroughHeader() && SkippingUntilPCHThroughHeader) ||
+      (usingPCHWithPragmaHdrStop() && SkippingUntilPragmaHdrStop))
+    SkipTokensWhileUsingPCH();
+}
+
+void Preprocessor::setPCHThroughHeaderFileID(FileID FID) {
+  assert(PCHThroughHeaderFileID.isInvalid() &&
+         "PCHThroughHeaderFileID already set!");
+  PCHThroughHeaderFileID = FID;
+}
+
+bool Preprocessor::isPCHThroughHeader(const FileEntry *FE) {
+  assert(PCHThroughHeaderFileID.isValid() &&
+         "Invalid PCH through header FileID");
+  return FE == SourceMgr.getFileEntryForID(PCHThroughHeaderFileID);
+}
+
+bool Preprocessor::creatingPCHWithThroughHeader() {
+  return TUKind == TU_Prefix && !PPOpts->PCHThroughHeader.empty() &&
+         PCHThroughHeaderFileID.isValid();
+}
+
+bool Preprocessor::usingPCHWithThroughHeader() {
+  return TUKind != TU_Prefix && !PPOpts->PCHThroughHeader.empty() &&
+         PCHThroughHeaderFileID.isValid();
+}
+
+bool Preprocessor::creatingPCHWithPragmaHdrStop() {
+  return TUKind == TU_Prefix && PPOpts->PCHWithHdrStop;
+}
+
+bool Preprocessor::usingPCHWithPragmaHdrStop() {
+  return TUKind != TU_Prefix && PPOpts->PCHWithHdrStop;
+}
+
+/// Skip tokens until after the #include of the through header or
+/// until after a #pragma hdrstop is seen. Tokens in the predefines file
+/// and the main file may be skipped. If the end of the predefines file
+/// is reached, skipping continues into the main file. If the end of the
+/// main file is reached, it's a fatal error.
+void Preprocessor::SkipTokensWhileUsingPCH() {
+  bool ReachedMainFileEOF = false;
+  bool UsingPCHThroughHeader = SkippingUntilPCHThroughHeader;
+  bool UsingPragmaHdrStop = SkippingUntilPragmaHdrStop;
+  Token Tok;
+  while (true) {
+    bool InPredefines =
+        (CurLexer && CurLexer->getFileID() == getPredefinesFileID());
+    switch (CurLexerKind) {
+    case CLK_Lexer:
+      CurLexer->Lex(Tok);
+     break;
+    case CLK_TokenLexer:
+      CurTokenLexer->Lex(Tok);
+      break;
+    case CLK_CachingLexer:
+      CachingLex(Tok);
+      break;
+    case CLK_LexAfterModuleImport:
+      LexAfterModuleImport(Tok);
+      break;
+    }
+    if (Tok.is(tok::eof) && !InPredefines) {
+      ReachedMainFileEOF = true;
+      break;
+    }
+    if (UsingPCHThroughHeader && !SkippingUntilPCHThroughHeader)
+      break;
+    if (UsingPragmaHdrStop && !SkippingUntilPragmaHdrStop)
+      break;
+  }
+  if (ReachedMainFileEOF) {
+    if (UsingPCHThroughHeader)
+      Diag(SourceLocation(), diag::err_pp_through_header_not_seen)
+          << PPOpts->PCHThroughHeader << 1;
+    else if (!PPOpts->PCHWithHdrStopCreate)
+      Diag(SourceLocation(), diag::err_pp_pragma_hdrstop_not_seen);
+  }
+}
+
+void Preprocessor::replayPreambleConditionalStack() {
+  // Restore the conditional stack from the preamble, if there is one.
+  if (PreambleConditionalStack.isReplaying()) {
+    assert(CurPPLexer &&
+           "CurPPLexer is null when calling replayPreambleConditionalStack.");
+    CurPPLexer->setConditionalLevels(PreambleConditionalStack.getStack());
+    PreambleConditionalStack.doneReplaying();
+    if (PreambleConditionalStack.reachedEOFWhileSkipping())
+      SkipExcludedConditionalBlock(
+          PreambleConditionalStack.SkipInfo->HashTokenLoc,
+          PreambleConditionalStack.SkipInfo->IfTokenLoc,
+          PreambleConditionalStack.SkipInfo->FoundNonSkipPortion,
+          PreambleConditionalStack.SkipInfo->FoundElse,
+          PreambleConditionalStack.SkipInfo->ElseLoc);
+  }
+}
+
+void Preprocessor::EndSourceFile() {
+  // Notify the client that we reached the end of the source file.
+  if (Callbacks)
+    Callbacks->EndOfMainFile();
+}
+
+//===----------------------------------------------------------------------===//
+// Lexer Event Handling.
+//===----------------------------------------------------------------------===//
+
+/// LookUpIdentifierInfo - Given a tok::raw_identifier token, look up the
+/// identifier information for the token and install it into the token,
+/// updating the token kind accordingly.
+IdentifierInfo *Preprocessor::LookUpIdentifierInfo(Token &Identifier) const {
+  assert(!Identifier.getRawIdentifier().empty() && "No raw identifier data!");
+
+  // Look up this token, see if it is a macro, or if it is a language keyword.
+  IdentifierInfo *II;
+  if (!Identifier.needsCleaning() && !Identifier.hasUCN()) {
+    // No cleaning needed, just use the characters from the lexed buffer.
+    II = getIdentifierInfo(Identifier.getRawIdentifier());
+  } else {
+    // Cleaning needed, alloca a buffer, clean into it, then use the buffer.
+    SmallString<64> IdentifierBuffer;
+    StringRef CleanedStr = getSpelling(Identifier, IdentifierBuffer);
+
+    if (Identifier.hasUCN()) {
+      SmallString<64> UCNIdentifierBuffer;
+      expandUCNs(UCNIdentifierBuffer, CleanedStr);
+      II = getIdentifierInfo(UCNIdentifierBuffer);
+    } else {
+      II = getIdentifierInfo(CleanedStr);
+    }
+  }
+
+  // Update the token info (identifier info and appropriate token kind).
+  Identifier.setIdentifierInfo(II);
+  if (getLangOpts().MSVCCompat && II->isCPlusPlusOperatorKeyword() &&
+      getSourceManager().isInSystemHeader(Identifier.getLocation()))
+    Identifier.setKind(tok::identifier);
+  else
+    Identifier.setKind(II->getTokenID());
+
+  return II;
+}
+
+void Preprocessor::SetPoisonReason(IdentifierInfo *II, unsigned DiagID) {
+  PoisonReasons[II] = DiagID;
+}
+
+void Preprocessor::PoisonSEHIdentifiers(bool Poison) {
+  assert(Ident__exception_code && Ident__exception_info);
+  assert(Ident___exception_code && Ident___exception_info);
+  Ident__exception_code->setIsPoisoned(Poison);
+  Ident___exception_code->setIsPoisoned(Poison);
+  Ident_GetExceptionCode->setIsPoisoned(Poison);
+  Ident__exception_info->setIsPoisoned(Poison);
+  Ident___exception_info->setIsPoisoned(Poison);
+  Ident_GetExceptionInfo->setIsPoisoned(Poison);
+  Ident__abnormal_termination->setIsPoisoned(Poison);
+  Ident___abnormal_termination->setIsPoisoned(Poison);
+  Ident_AbnormalTermination->setIsPoisoned(Poison);
+}
+
+void Preprocessor::HandlePoisonedIdentifier(Token & Identifier) {
+  assert(Identifier.getIdentifierInfo() &&
+         "Can't handle identifiers without identifier info!");
+  llvm::DenseMap<IdentifierInfo*,unsigned>::const_iterator it =
+    PoisonReasons.find(Identifier.getIdentifierInfo());
+  if(it == PoisonReasons.end())
+    Diag(Identifier, diag::err_pp_used_poisoned_id);
+  else
+    Diag(Identifier,it->second) << Identifier.getIdentifierInfo();
+}
+
+/// Returns a diagnostic message kind for reporting a future keyword as
+/// appropriate for the identifier and specified language.
+static diag::kind getFutureCompatDiagKind(const IdentifierInfo &II,
+                                          const LangOptions &LangOpts) {
+  assert(II.isFutureCompatKeyword() && "diagnostic should not be needed");
+
+  if (LangOpts.CPlusPlus)
+    return llvm::StringSwitch<diag::kind>(II.getName())
+#define CXX11_KEYWORD(NAME, FLAGS)                                             \
+        .Case(#NAME, diag::warn_cxx11_keyword)
+#define CXX2A_KEYWORD(NAME, FLAGS)                                             \
+        .Case(#NAME, diag::warn_cxx2a_keyword)
+#include "clang/Basic/TokenKinds.def"
+        ;
+
+  llvm_unreachable(
+      "Keyword not known to come from a newer Standard or proposed Standard");
+}
+
+void Preprocessor::updateOutOfDateIdentifier(IdentifierInfo &II) const {
+  assert(II.isOutOfDate() && "not out of date");
+  getExternalSource()->updateOutOfDateIdentifier(II);
+}
+
+/// HandleIdentifier - This callback is invoked when the lexer reads an
+/// identifier.  This callback looks up the identifier in the map and/or
+/// potentially macro expands it or turns it into a named token (like 'for').
+///
+/// Note that callers of this method are guarded by checking the
+/// IdentifierInfo's 'isHandleIdentifierCase' bit.  If this method changes, the
+/// IdentifierInfo methods that compute these properties will need to change to
+/// match.
+bool Preprocessor::HandleIdentifier(Token &Identifier) {
+  assert(Identifier.getIdentifierInfo() &&
+         "Can't handle identifiers without identifier info!");
+
+  IdentifierInfo &II = *Identifier.getIdentifierInfo();
+
+  // If the information about this identifier is out of date, update it from
+  // the external source.
+  // We have to treat __VA_ARGS__ in a special way, since it gets
+  // serialized with isPoisoned = true, but our preprocessor may have
+  // unpoisoned it if we're defining a C99 macro.
+  if (II.isOutOfDate()) {
+    bool CurrentIsPoisoned = false;
+    const bool IsSpecialVariadicMacro =
+        &II == Ident__VA_ARGS__ || &II == Ident__VA_OPT__;
+    if (IsSpecialVariadicMacro)
+      CurrentIsPoisoned = II.isPoisoned();
+
+    updateOutOfDateIdentifier(II);
+    Identifier.setKind(II.getTokenID());
+
+    if (IsSpecialVariadicMacro)
+      II.setIsPoisoned(CurrentIsPoisoned);
+  }
+
+  // If this identifier was poisoned, and if it was not produced from a macro
+  // expansion, emit an error.
+  if (II.isPoisoned() && CurPPLexer) {
+    HandlePoisonedIdentifier(Identifier);
+  }
+
+  // If this is a macro to be expanded, do it.
+  if (MacroDefinition MD = getMacroDefinition(&II)) {
+    auto *MI = MD.getMacroInfo();
+    assert(MI && "macro definition with no macro info?");
+    if (!DisableMacroExpansion) {
+      if (!Identifier.isExpandDisabled() && MI->isEnabled()) {
+        // C99 6.10.3p10: If the preprocessing token immediately after the
+        // macro name isn't a '(', this macro should not be expanded.
+        if (!MI->isFunctionLike() || isNextPPTokenLParen())
+          return HandleMacroExpandedIdentifier(Identifier, MD);
+      } else {
+        // C99 6.10.3.4p2 says that a disabled macro may never again be
+        // expanded, even if it's in a context where it could be expanded in the
+        // future.
+        Identifier.setFlag(Token::DisableExpand);
+        if (MI->isObjectLike() || isNextPPTokenLParen())
+          Diag(Identifier, diag::pp_disabled_macro_expansion);
+      }
+    }
+  }
+
+  // If this identifier is a keyword in a newer Standard or proposed Standard,
+  // produce a warning. Don't warn if we're not considering macro expansion,
+  // since this identifier might be the name of a macro.
+  // FIXME: This warning is disabled in cases where it shouldn't be, like
+  //   "#define constexpr constexpr", "int constexpr;"
+  if (II.isFutureCompatKeyword() && !DisableMacroExpansion) {
+    Diag(Identifier, getFutureCompatDiagKind(II, getLangOpts()))
+        << II.getName();
+    // Don't diagnose this keyword again in this translation unit.
+    II.setIsFutureCompatKeyword(false);
+  }
+
+  // If this is an extension token, diagnose its use.
+  // We avoid diagnosing tokens that originate from macro definitions.
+  // FIXME: This warning is disabled in cases where it shouldn't be,
+  // like "#define TY typeof", "TY(1) x".
+  if (II.isExtensionToken() && !DisableMacroExpansion)
+    Diag(Identifier, diag::ext_token_used);
+
+  // If this is the 'import' contextual keyword following an '@', note
+  // that the next token indicates a module name.
+  //
+  // Note that we do not treat 'import' as a contextual
+  // keyword when we're in a caching lexer, because caching lexers only get
+  // used in contexts where import declarations are disallowed.
+  //
+  // Likewise if this is the C++ Modules TS import keyword.
+  if (((LastTokenWasAt && II.isModulesImport()) ||
+       Identifier.is(tok::kw_import)) &&
+      !InMacroArgs && !DisableMacroExpansion &&
+      (getLangOpts().Modules || getLangOpts().DebuggerSupport) &&
+      CurLexerKind != CLK_CachingLexer) {
+    ModuleImportLoc = Identifier.getLocation();
+    ModuleImportPath.clear();
+    ModuleImportExpectsIdentifier = true;
+    CurLexerKind = CLK_LexAfterModuleImport;
+  }
+  return true;
+}
+
+void Preprocessor::Lex(Token &Result) {
+  ++LexLevel;
+
+  // We loop here until a lex function returns a token; this avoids recursion.
+  bool ReturnedToken;
+  do {
+    switch (CurLexerKind) {
+    case CLK_Lexer:
+      ReturnedToken = CurLexer->Lex(Result);
+      break;
+    case CLK_TokenLexer:
+      ReturnedToken = CurTokenLexer->Lex(Result);
+      break;
+    case CLK_CachingLexer:
+      CachingLex(Result);
+      ReturnedToken = true;
+      break;
+    case CLK_LexAfterModuleImport:
+      ReturnedToken = LexAfterModuleImport(Result);
+      break;
+    }
+  } while (!ReturnedToken);
+
+  if (Result.is(tok::unknown) && TheModuleLoader.HadFatalFailure)
+    return;
+
+  if (Result.is(tok::code_completion) && Result.getIdentifierInfo()) {
+    // Remember the identifier before code completion token.
+    setCodeCompletionIdentifierInfo(Result.getIdentifierInfo());
+    setCodeCompletionTokenRange(Result.getLocation(), Result.getEndLoc());
+    // Set IdenfitierInfo to null to avoid confusing code that handles both
+    // identifiers and completion tokens.
+    Result.setIdentifierInfo(nullptr);
+  }
+
+  // Update ImportSeqState to track our position within a C++20 import-seq
+  // if this token is being produced as a result of phase 4 of translation.
+  if (getLangOpts().CPlusPlusModules && LexLevel == 1 &&
+      !Result.getFlag(Token::IsReinjected)) {
+    switch (Result.getKind()) {
+    case tok::l_paren: case tok::l_square: case tok::l_brace:
+      ImportSeqState.handleOpenBracket();
+      break;
+    case tok::r_paren: case tok::r_square:
+      ImportSeqState.handleCloseBracket();
+      break;
+    case tok::r_brace:
+      ImportSeqState.handleCloseBrace();
+      break;
+    case tok::semi:
+      ImportSeqState.handleSemi();
+      break;
+    case tok::header_name:
+    case tok::annot_header_unit:
+      ImportSeqState.handleHeaderName();
+      break;
+    case tok::kw_export:
+      ImportSeqState.handleExport();
+      break;
+    case tok::identifier:
+      if (Result.getIdentifierInfo()->isModulesImport()) {
+        ImportSeqState.handleImport();
+        if (ImportSeqState.afterImportSeq()) {
+          ModuleImportLoc = Result.getLocation();
+          ModuleImportPath.clear();
+          ModuleImportExpectsIdentifier = true;
+          CurLexerKind = CLK_LexAfterModuleImport;
+        }
+        break;
+      }
+      LLVM_FALLTHROUGH;
+    default:
+      ImportSeqState.handleMisc();
+      break;
+    }
+  }
+
+  LastTokenWasAt = Result.is(tok::at);
+  --LexLevel;
+
+  if (LexLevel == 0 && !Result.getFlag(Token::IsReinjected)) {
+    ++TokenCount;
+    if (OnToken)
+      OnToken(Result);
+  }
+}
+
+/// Lex a header-name token (including one formed from header-name-tokens if
+/// \p AllowConcatenation is \c true).
+///
+/// \param FilenameTok Filled in with the next token. On success, this will
+///        be either a header_name token. On failure, it will be whatever other
+///        token was found instead.
+/// \param AllowMacroExpansion If \c true, allow the header name to be formed
+///        by macro expansion (concatenating tokens as necessary if the first
+///        token is a '<').
+/// \return \c true if we reached EOD or EOF while looking for a > token in
+///         a concatenated header name and diagnosed it. \c false otherwise.
+bool Preprocessor::LexHeaderName(Token &FilenameTok, bool AllowMacroExpansion) {
+  // Lex using header-name tokenization rules if tokens are being lexed from
+  // a file. Just grab a token normally if we're in a macro expansion.
+  if (CurPPLexer)
+    CurPPLexer->LexIncludeFilename(FilenameTok);
+  else
+    Lex(FilenameTok);
+
+  // This could be a <foo/bar.h> file coming from a macro expansion.  In this
+  // case, glue the tokens together into an angle_string_literal token.
+  SmallString<128> FilenameBuffer;
+  if (FilenameTok.is(tok::less) && AllowMacroExpansion) {
+    bool StartOfLine = FilenameTok.isAtStartOfLine();
+    bool LeadingSpace = FilenameTok.hasLeadingSpace();
+    bool LeadingEmptyMacro = FilenameTok.hasLeadingEmptyMacro();
+
+    SourceLocation Start = FilenameTok.getLocation();
+    SourceLocation End;
+    FilenameBuffer.push_back('<');
+
+    // Consume tokens until we find a '>'.
+    // FIXME: A header-name could be formed starting or ending with an
+    // alternative token. It's not clear whether that's ill-formed in all
+    // cases.
+    while (FilenameTok.isNot(tok::greater)) {
+      Lex(FilenameTok);
+      if (FilenameTok.isOneOf(tok::eod, tok::eof)) {
+        Diag(FilenameTok.getLocation(), diag::err_expected) << tok::greater;
+        Diag(Start, diag::note_matching) << tok::less;
+        return true;
+      }
+
+      End = FilenameTok.getLocation();
+
+      // FIXME: Provide code completion for #includes.
+      if (FilenameTok.is(tok::code_completion)) {
+        setCodeCompletionReached();
+        Lex(FilenameTok);
+        continue;
+      }
+
+      // Append the spelling of this token to the buffer. If there was a space
+      // before it, add it now.
+      if (FilenameTok.hasLeadingSpace())
+        FilenameBuffer.push_back(' ');
+
+      // Get the spelling of the token, directly into FilenameBuffer if
+      // possible.
+      size_t PreAppendSize = FilenameBuffer.size();
+      FilenameBuffer.resize(PreAppendSize + FilenameTok.getLength());
+
+      const char *BufPtr = &FilenameBuffer[PreAppendSize];
+      unsigned ActualLen = getSpelling(FilenameTok, BufPtr);
+
+      // If the token was spelled somewhere else, copy it into FilenameBuffer.
+      if (BufPtr != &FilenameBuffer[PreAppendSize])
+        memcpy(&FilenameBuffer[PreAppendSize], BufPtr, ActualLen);
+
+      // Resize FilenameBuffer to the correct size.
+      if (FilenameTok.getLength() != ActualLen)
+        FilenameBuffer.resize(PreAppendSize + ActualLen);
+    }
+
+    FilenameTok.startToken();
+    FilenameTok.setKind(tok::header_name);
+    FilenameTok.setFlagValue(Token::StartOfLine, StartOfLine);
+    FilenameTok.setFlagValue(Token::LeadingSpace, LeadingSpace);
+    FilenameTok.setFlagValue(Token::LeadingEmptyMacro, LeadingEmptyMacro);
+    CreateString(FilenameBuffer, FilenameTok, Start, End);
+  } else if (FilenameTok.is(tok::string_literal) && AllowMacroExpansion) {
+    // Convert a string-literal token of the form " h-char-sequence "
+    // (produced by macro expansion) into a header-name token.
+    //
+    // The rules for header-names don't quite match the rules for
+    // string-literals, but all the places where they differ result in
+    // undefined behavior, so we can and do treat them the same.
+    //
+    // A string-literal with a prefix or suffix is not translated into a
+    // header-name. This could theoretically be observable via the C++20
+    // context-sensitive header-name formation rules.
+    StringRef Str = getSpelling(FilenameTok, FilenameBuffer);
+    if (Str.size() >= 2 && Str.front() == '"' && Str.back() == '"')
+      FilenameTok.setKind(tok::header_name);
+  }
+
+  return false;
+}
+
+/// Collect the tokens of a C++20 pp-import-suffix.
+void Preprocessor::CollectPpImportSuffix(SmallVectorImpl<Token> &Toks) {
+  // FIXME: For error recovery, consider recognizing attribute syntax here
+  // and terminating / diagnosing a missing semicolon if we find anything
+  // else? (Can we leave that to the parser?)
+  unsigned BracketDepth = 0;
+  while (true) {
+    Toks.emplace_back();
+    Lex(Toks.back());
+
+    switch (Toks.back().getKind()) {
+    case tok::l_paren: case tok::l_square: case tok::l_brace:
+      ++BracketDepth;
+      break;
+
+    case tok::r_paren: case tok::r_square: case tok::r_brace:
+      if (BracketDepth == 0)
+        return;
+      --BracketDepth;
+      break;
+
+    case tok::semi:
+      if (BracketDepth == 0)
+        return;
+    break;
+
+    case tok::eof:
+      return;
+
+    default:
+      break;
+    }
+  }
+}
+
+
+/// Lex a token following the 'import' contextual keyword.
+///
+///     pp-import: [C++20]
+///           import header-name pp-import-suffix[opt] ;
+///           import header-name-tokens pp-import-suffix[opt] ;
+/// [ObjC]    @ import module-name ;
+/// [Clang]   import module-name ;
+///
+///     header-name-tokens:
+///           string-literal
+///           < [any sequence of preprocessing-tokens other than >] >
+///
+///     module-name:
+///           module-name-qualifier[opt] identifier
+///
+///     module-name-qualifier
+///           module-name-qualifier[opt] identifier .
+///
+/// We respond to a pp-import by importing macros from the named module.
+bool Preprocessor::LexAfterModuleImport(Token &Result) {
+  // Figure out what kind of lexer we actually have.
+  recomputeCurLexerKind();
+
+  // Lex the next token. The header-name lexing rules are used at the start of
+  // a pp-import.
+  //
+  // For now, we only support header-name imports in C++20 mode.
+  // FIXME: Should we allow this in all language modes that support an import
+  // declaration as an extension?
+  if (ModuleImportPath.empty() && getLangOpts().CPlusPlusModules) {
+    if (LexHeaderName(Result))
+      return true;
+  } else {
+    Lex(Result);
+  }
+
+  // Allocate a holding buffer for a sequence of tokens and introduce it into
+  // the token stream.
+  auto EnterTokens = [this](ArrayRef<Token> Toks) {
+    auto ToksCopy = std::make_unique<Token[]>(Toks.size());
+    std::copy(Toks.begin(), Toks.end(), ToksCopy.get());
+    EnterTokenStream(std::move(ToksCopy), Toks.size(),
+                     /*DisableMacroExpansion*/ true, /*IsReinject*/ false);
+  };
+
+  // Check for a header-name.
+  SmallVector<Token, 32> Suffix;
+  if (Result.is(tok::header_name)) {
+    // Enter the header-name token into the token stream; a Lex action cannot
+    // both return a token and cache tokens (doing so would corrupt the token
+    // cache if the call to Lex comes from CachingLex / PeekAhead).
+    Suffix.push_back(Result);
+
+    // Consume the pp-import-suffix and expand any macros in it now. We'll add
+    // it back into the token stream later.
+    CollectPpImportSuffix(Suffix);
+    if (Suffix.back().isNot(tok::semi)) {
+      // This is not a pp-import after all.
+      EnterTokens(Suffix);
+      return false;
+    }
+
+    // C++2a [cpp.module]p1:
+    //   The ';' preprocessing-token terminating a pp-import shall not have
+    //   been produced by macro replacement.
+    SourceLocation SemiLoc = Suffix.back().getLocation();
+    if (SemiLoc.isMacroID())
+      Diag(SemiLoc, diag::err_header_import_semi_in_macro);
+
+    // Reconstitute the import token.
+    Token ImportTok;
+    ImportTok.startToken();
+    ImportTok.setKind(tok::kw_import);
+    ImportTok.setLocation(ModuleImportLoc);
+    ImportTok.setIdentifierInfo(getIdentifierInfo("import"));
+    ImportTok.setLength(6);
+
+    auto Action = HandleHeaderIncludeOrImport(
+        /*HashLoc*/ SourceLocation(), ImportTok, Suffix.front(), SemiLoc);
+    switch (Action.Kind) {
+    case ImportAction::None:
+      break;
+
+    case ImportAction::ModuleBegin:
+      // Let the parser know we're textually entering the module.
+      Suffix.emplace_back();
+      Suffix.back().startToken();
+      Suffix.back().setKind(tok::annot_module_begin);
+      Suffix.back().setLocation(SemiLoc);
+      Suffix.back().setAnnotationEndLoc(SemiLoc);
+      Suffix.back().setAnnotationValue(Action.ModuleForHeader);
+      LLVM_FALLTHROUGH;
+
+    case ImportAction::ModuleImport:
+    case ImportAction::SkippedModuleImport:
+      // We chose to import (or textually enter) the file. Convert the
+      // header-name token into a header unit annotation token.
+      Suffix[0].setKind(tok::annot_header_unit);
+      Suffix[0].setAnnotationEndLoc(Suffix[0].getLocation());
+      Suffix[0].setAnnotationValue(Action.ModuleForHeader);
+      // FIXME: Call the moduleImport callback?
+      break;
+    case ImportAction::Failure:
+      assert(TheModuleLoader.HadFatalFailure &&
+             "This should be an early exit only to a fatal error");
+      Result.setKind(tok::eof);
+      CurLexer->cutOffLexing();
+      EnterTokens(Suffix);
+      return true;
+    }
+
+    EnterTokens(Suffix);
+    return false;
+  }
+
+  // The token sequence
+  //
+  //   import identifier (. identifier)*
+  //
+  // indicates a module import directive. We already saw the 'import'
+  // contextual keyword, so now we're looking for the identifiers.
+  if (ModuleImportExpectsIdentifier && Result.getKind() == tok::identifier) {
+    // We expected to see an identifier here, and we did; continue handling
+    // identifiers.
+    ModuleImportPath.push_back(std::make_pair(Result.getIdentifierInfo(),
+                                              Result.getLocation()));
+    ModuleImportExpectsIdentifier = false;
+    CurLexerKind = CLK_LexAfterModuleImport;
+    return true;
+  }
+
+  // If we're expecting a '.' or a ';', and we got a '.', then wait until we
+  // see the next identifier. (We can also see a '[[' that begins an
+  // attribute-specifier-seq here under the C++ Modules TS.)
+  if (!ModuleImportExpectsIdentifier && Result.getKind() == tok::period) {
+    ModuleImportExpectsIdentifier = true;
+    CurLexerKind = CLK_LexAfterModuleImport;
+    return true;
+  }
+
+  // If we didn't recognize a module name at all, this is not a (valid) import.
+  if (ModuleImportPath.empty() || Result.is(tok::eof))
+    return true;
+
+  // Consume the pp-import-suffix and expand any macros in it now, if we're not
+  // at the semicolon already.
+  SourceLocation SemiLoc = Result.getLocation();
+  if (Result.isNot(tok::semi)) {
+    Suffix.push_back(Result);
+    CollectPpImportSuffix(Suffix);
+    if (Suffix.back().isNot(tok::semi)) {
+      // This is not an import after all.
+      EnterTokens(Suffix);
+      return false;
+    }
+    SemiLoc = Suffix.back().getLocation();
+  }
+
+  // Under the Modules TS, the dot is just part of the module name, and not
+  // a real hierarchy separator. Flatten such module names now.
+  //
+  // FIXME: Is this the right level to be performing this transformation?
+  std::string FlatModuleName;
+  if (getLangOpts().ModulesTS || getLangOpts().CPlusPlusModules) {
+    for (auto &Piece : ModuleImportPath) {
+      if (!FlatModuleName.empty())
+        FlatModuleName += ".";
+      FlatModuleName += Piece.first->getName();
+    }
+    SourceLocation FirstPathLoc = ModuleImportPath[0].second;
+    ModuleImportPath.clear();
+    ModuleImportPath.push_back(
+        std::make_pair(getIdentifierInfo(FlatModuleName), FirstPathLoc));
+  }
+
+  Module *Imported = nullptr;
+  if (getLangOpts().Modules) {
+    Imported = TheModuleLoader.loadModule(ModuleImportLoc,
+                                          ModuleImportPath,
+                                          Module::Hidden,
+                                          /*IsInclusionDirective=*/false);
+    if (Imported)
+      makeModuleVisible(Imported, SemiLoc);
+  }
+  if (Callbacks)
+    Callbacks->moduleImport(ModuleImportLoc, ModuleImportPath, Imported);
+
+  if (!Suffix.empty()) {
+    EnterTokens(Suffix);
+    return false;
+  }
+  return true;
+}
+
+void Preprocessor::makeModuleVisible(Module *M, SourceLocation Loc) {
+  CurSubmoduleState->VisibleModules.setVisible(
+      M, Loc, [](Module *) {},
+      [&](ArrayRef<Module *> Path, Module *Conflict, StringRef Message) {
+        // FIXME: Include the path in the diagnostic.
+        // FIXME: Include the import location for the conflicting module.
+        Diag(ModuleImportLoc, diag::warn_module_conflict)
+            << Path[0]->getFullModuleName()
+            << Conflict->getFullModuleName()
+            << Message;
+      });
+
+  // Add this module to the imports list of the currently-built submodule.
+  if (!BuildingSubmoduleStack.empty() && M != BuildingSubmoduleStack.back().M)
+    BuildingSubmoduleStack.back().M->Imports.insert(M);
+}
+
+bool Preprocessor::FinishLexStringLiteral(Token &Result, std::string &String,
+                                          const char *DiagnosticTag,
+                                          bool AllowMacroExpansion) {
+  // We need at least one string literal.
+  if (Result.isNot(tok::string_literal)) {
+    Diag(Result, diag::err_expected_string_literal)
+      << /*Source='in...'*/0 << DiagnosticTag;
+    return false;
+  }
+
+  // Lex string literal tokens, optionally with macro expansion.
+  SmallVector<Token, 4> StrToks;
+  do {
+    StrToks.push_back(Result);
+
+    if (Result.hasUDSuffix())
+      Diag(Result, diag::err_invalid_string_udl);
+
+    if (AllowMacroExpansion)
+      Lex(Result);
+    else
+      LexUnexpandedToken(Result);
+  } while (Result.is(tok::string_literal));
+
+  // Concatenate and parse the strings.
+  StringLiteralParser Literal(StrToks, *this);
+  assert(Literal.isAscii() && "Didn't allow wide strings in");
+
+  if (Literal.hadError)
+    return false;
+
+  if (Literal.Pascal) {
+    Diag(StrToks[0].getLocation(), diag::err_expected_string_literal)
+      << /*Source='in...'*/0 << DiagnosticTag;
+    return false;
+  }
+
+  String = std::string(Literal.GetString());
+  return true;
+}
+
+bool Preprocessor::parseSimpleIntegerLiteral(Token &Tok, uint64_t &Value) {
+  assert(Tok.is(tok::numeric_constant));
+  SmallString<8> IntegerBuffer;
+  bool NumberInvalid = false;
+  StringRef Spelling = getSpelling(Tok, IntegerBuffer, &NumberInvalid);
+  if (NumberInvalid)
+    return false;
+  NumericLiteralParser Literal(Spelling, Tok.getLocation(), *this);
+  if (Literal.hadError || !Literal.isIntegerLiteral() || Literal.hasUDSuffix())
+    return false;
+  llvm::APInt APVal(64, 0);
+  if (Literal.GetIntegerValue(APVal))
+    return false;
+  Lex(Tok);
+  Value = APVal.getLimitedValue();
+  return true;
+}
+
+void Preprocessor::addCommentHandler(CommentHandler *Handler) {
+  assert(Handler && "NULL comment handler");
+  assert(llvm::find(CommentHandlers, Handler) == CommentHandlers.end() &&
+         "Comment handler already registered");
+  CommentHandlers.push_back(Handler);
+}
+
+void Preprocessor::removeCommentHandler(CommentHandler *Handler) {
+  std::vector<CommentHandler *>::iterator Pos =
+      llvm::find(CommentHandlers, Handler);
+  assert(Pos != CommentHandlers.end() && "Comment handler not registered");
+  CommentHandlers.erase(Pos);
+}
+
+bool Preprocessor::HandleComment(Token &result, SourceRange Comment) {
+  bool AnyPendingTokens = false;
+  for (std::vector<CommentHandler *>::iterator H = CommentHandlers.begin(),
+       HEnd = CommentHandlers.end();
+       H != HEnd; ++H) {
+    if ((*H)->HandleComment(*this, Comment))
+      AnyPendingTokens = true;
+  }
+  if (!AnyPendingTokens || getCommentRetentionState())
+    return false;
+  Lex(result);
+  return true;
+}
+
+ModuleLoader::~ModuleLoader() = default;
+
+CommentHandler::~CommentHandler() = default;
+
+CodeCompletionHandler::~CodeCompletionHandler() = default;
+
+void Preprocessor::createPreprocessingRecord() {
+  if (Record)
+    return;
+
+  Record = new PreprocessingRecord(getSourceManager());
+  addPPCallbacks(std::unique_ptr<PPCallbacks>(Record));
+}