clang-format: [JS] sort ES6 imports.

Summary:
This change automatically sorts ES6 imports and exports into four groups:
absolute imports, parent imports, relative imports, and then exports. Exports
are sorted in the same order, but not grouped further.

To keep JS import sorting out of Format.cpp, this required extracting the
TokenAnalyzer infrastructure to separate header and implementation files.

Reviewers: djasper

Subscribers: cfe-commits, klimek

Differential Revision: http://reviews.llvm.org/D20198

llvm-svn: 270203
diff --git a/clang/lib/Format/FormatTokenLexer.cpp b/clang/lib/Format/FormatTokenLexer.cpp
new file mode 100644
index 0000000..9778f84
--- /dev/null
+++ b/clang/lib/Format/FormatTokenLexer.cpp
@@ -0,0 +1,597 @@
+//===--- FormatTokenLexer.cpp - Lex FormatTokens -------------*- C++ ----*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief This file implements FormatTokenLexer, which tokenizes a source file
+/// into a FormatToken stream suitable for ClangFormat.
+///
+//===----------------------------------------------------------------------===//
+
+#include "FormatTokenLexer.h"
+#include "FormatToken.h"
+#include "clang/Basic/SourceLocation.h"
+#include "clang/Basic/SourceManager.h"
+#include "clang/Format/Format.h"
+#include "llvm/Support/Regex.h"
+
+namespace clang {
+namespace format {
+
+FormatTokenLexer::FormatTokenLexer(const SourceManager &SourceMgr, FileID ID,
+                                   const FormatStyle &Style,
+                                   encoding::Encoding Encoding)
+    : FormatTok(nullptr), IsFirstToken(true), GreaterStashed(false),
+      LessStashed(false), Column(0), TrailingWhitespace(0),
+      SourceMgr(SourceMgr), ID(ID), Style(Style),
+      IdentTable(getFormattingLangOpts(Style)), Keywords(IdentTable),
+      Encoding(Encoding), FirstInLineIndex(0), FormattingDisabled(false),
+      MacroBlockBeginRegex(Style.MacroBlockBegin),
+      MacroBlockEndRegex(Style.MacroBlockEnd) {
+  Lex.reset(new Lexer(ID, SourceMgr.getBuffer(ID), SourceMgr,
+                      getFormattingLangOpts(Style)));
+  Lex->SetKeepWhitespaceMode(true);
+
+  for (const std::string &ForEachMacro : Style.ForEachMacros)
+    ForEachMacros.push_back(&IdentTable.get(ForEachMacro));
+  std::sort(ForEachMacros.begin(), ForEachMacros.end());
+}
+
+ArrayRef<FormatToken *> FormatTokenLexer::lex() {
+  assert(Tokens.empty());
+  assert(FirstInLineIndex == 0);
+  do {
+    Tokens.push_back(getNextToken());
+    if (Style.Language == FormatStyle::LK_JavaScript) {
+      tryParseJSRegexLiteral();
+      tryParseTemplateString();
+    }
+    tryMergePreviousTokens();
+    if (Tokens.back()->NewlinesBefore > 0 || Tokens.back()->IsMultiline)
+      FirstInLineIndex = Tokens.size() - 1;
+  } while (Tokens.back()->Tok.isNot(tok::eof));
+  return Tokens;
+}
+
+void FormatTokenLexer::tryMergePreviousTokens() {
+  if (tryMerge_TMacro())
+    return;
+  if (tryMergeConflictMarkers())
+    return;
+  if (tryMergeLessLess())
+    return;
+
+  if (Style.Language == FormatStyle::LK_JavaScript) {
+    static const tok::TokenKind JSIdentity[] = {tok::equalequal, tok::equal};
+    static const tok::TokenKind JSNotIdentity[] = {tok::exclaimequal,
+                                                   tok::equal};
+    static const tok::TokenKind JSShiftEqual[] = {tok::greater, tok::greater,
+                                                  tok::greaterequal};
+    static const tok::TokenKind JSRightArrow[] = {tok::equal, tok::greater};
+    // FIXME: Investigate what token type gives the correct operator priority.
+    if (tryMergeTokens(JSIdentity, TT_BinaryOperator))
+      return;
+    if (tryMergeTokens(JSNotIdentity, TT_BinaryOperator))
+      return;
+    if (tryMergeTokens(JSShiftEqual, TT_BinaryOperator))
+      return;
+    if (tryMergeTokens(JSRightArrow, TT_JsFatArrow))
+      return;
+  }
+}
+
+bool FormatTokenLexer::tryMergeLessLess() {
+  // Merge X,less,less,Y into X,lessless,Y unless X or Y is less.
+  if (Tokens.size() < 3)
+    return false;
+
+  bool FourthTokenIsLess = false;
+  if (Tokens.size() > 3)
+    FourthTokenIsLess = (Tokens.end() - 4)[0]->is(tok::less);
+
+  auto First = Tokens.end() - 3;
+  if (First[2]->is(tok::less) || First[1]->isNot(tok::less) ||
+      First[0]->isNot(tok::less) || FourthTokenIsLess)
+    return false;
+
+  // Only merge if there currently is no whitespace between the two "<".
+  if (First[1]->WhitespaceRange.getBegin() !=
+      First[1]->WhitespaceRange.getEnd())
+    return false;
+
+  First[0]->Tok.setKind(tok::lessless);
+  First[0]->TokenText = "<<";
+  First[0]->ColumnWidth += 1;
+  Tokens.erase(Tokens.end() - 2);
+  return true;
+}
+
+bool FormatTokenLexer::tryMergeTokens(ArrayRef<tok::TokenKind> Kinds,
+                                      TokenType NewType) {
+  if (Tokens.size() < Kinds.size())
+    return false;
+
+  SmallVectorImpl<FormatToken *>::const_iterator First =
+      Tokens.end() - Kinds.size();
+  if (!First[0]->is(Kinds[0]))
+    return false;
+  unsigned AddLength = 0;
+  for (unsigned i = 1; i < Kinds.size(); ++i) {
+    if (!First[i]->is(Kinds[i]) ||
+        First[i]->WhitespaceRange.getBegin() !=
+            First[i]->WhitespaceRange.getEnd())
+      return false;
+    AddLength += First[i]->TokenText.size();
+  }
+  Tokens.resize(Tokens.size() - Kinds.size() + 1);
+  First[0]->TokenText = StringRef(First[0]->TokenText.data(),
+                                  First[0]->TokenText.size() + AddLength);
+  First[0]->ColumnWidth += AddLength;
+  First[0]->Type = NewType;
+  return true;
+}
+
+// Returns \c true if \p Tok can only be followed by an operand in JavaScript.
+bool FormatTokenLexer::precedesOperand(FormatToken *Tok) {
+  // NB: This is not entirely correct, as an r_paren can introduce an operand
+  // location in e.g. `if (foo) /bar/.exec(...);`. That is a rare enough
+  // corner case to not matter in practice, though.
+  return Tok->isOneOf(tok::period, tok::l_paren, tok::comma, tok::l_brace,
+                      tok::r_brace, tok::l_square, tok::semi, tok::exclaim,
+                      tok::colon, tok::question, tok::tilde) ||
+         Tok->isOneOf(tok::kw_return, tok::kw_do, tok::kw_case, tok::kw_throw,
+                      tok::kw_else, tok::kw_new, tok::kw_delete, tok::kw_void,
+                      tok::kw_typeof, Keywords.kw_instanceof, Keywords.kw_in) ||
+         Tok->isBinaryOperator();
+}
+
+bool FormatTokenLexer::canPrecedeRegexLiteral(FormatToken *Prev) {
+  if (!Prev)
+    return true;
+
+  // Regex literals can only follow after prefix unary operators, not after
+  // postfix unary operators. If the '++' is followed by a non-operand
+  // introducing token, the slash here is the operand and not the start of a
+  // regex.
+  if (Prev->isOneOf(tok::plusplus, tok::minusminus))
+    return (Tokens.size() < 3 || precedesOperand(Tokens[Tokens.size() - 3]));
+
+  // The previous token must introduce an operand location where regex
+  // literals can occur.
+  if (!precedesOperand(Prev))
+    return false;
+
+  return true;
+}
+
+// Tries to parse a JavaScript Regex literal starting at the current token,
+// if that begins with a slash and is in a location where JavaScript allows
+// regex literals. Changes the current token to a regex literal and updates
+// its text if successful.
+void FormatTokenLexer::tryParseJSRegexLiteral() {
+  FormatToken *RegexToken = Tokens.back();
+  if (!RegexToken->isOneOf(tok::slash, tok::slashequal))
+    return;
+
+  FormatToken *Prev = nullptr;
+  for (auto I = Tokens.rbegin() + 1, E = Tokens.rend(); I != E; ++I) {
+    // NB: Because previous pointers are not initialized yet, this cannot use
+    // Token.getPreviousNonComment.
+    if ((*I)->isNot(tok::comment)) {
+      Prev = *I;
+      break;
+    }
+  }
+
+  if (!canPrecedeRegexLiteral(Prev))
+    return;
+
+  // 'Manually' lex ahead in the current file buffer.
+  const char *Offset = Lex->getBufferLocation();
+  const char *RegexBegin = Offset - RegexToken->TokenText.size();
+  StringRef Buffer = Lex->getBuffer();
+  bool InCharacterClass = false;
+  bool HaveClosingSlash = false;
+  for (; !HaveClosingSlash && Offset != Buffer.end(); ++Offset) {
+    // Regular expressions are terminated with a '/', which can only be
+    // escaped using '\' or a character class between '[' and ']'.
+    // See http://www.ecma-international.org/ecma-262/5.1/#sec-7.8.5.
+    switch (*Offset) {
+    case '\\':
+      // Skip the escaped character.
+      ++Offset;
+      break;
+    case '[':
+      InCharacterClass = true;
+      break;
+    case ']':
+      InCharacterClass = false;
+      break;
+    case '/':
+      if (!InCharacterClass)
+        HaveClosingSlash = true;
+      break;
+    }
+  }
+
+  RegexToken->Type = TT_RegexLiteral;
+  // Treat regex literals like other string_literals.
+  RegexToken->Tok.setKind(tok::string_literal);
+  RegexToken->TokenText = StringRef(RegexBegin, Offset - RegexBegin);
+  RegexToken->ColumnWidth = RegexToken->TokenText.size();
+
+  resetLexer(SourceMgr.getFileOffset(Lex->getSourceLocation(Offset)));
+}
+
+void FormatTokenLexer::tryParseTemplateString() {
+  FormatToken *BacktickToken = Tokens.back();
+  if (!BacktickToken->is(tok::unknown) || BacktickToken->TokenText != "`")
+    return;
+
+  // 'Manually' lex ahead in the current file buffer.
+  const char *Offset = Lex->getBufferLocation();
+  const char *TmplBegin = Offset - BacktickToken->TokenText.size(); // at "`"
+  for (; Offset != Lex->getBuffer().end() && *Offset != '`'; ++Offset) {
+    if (*Offset == '\\')
+      ++Offset; // Skip the escaped character.
+  }
+
+  StringRef LiteralText(TmplBegin, Offset - TmplBegin + 1);
+  BacktickToken->Type = TT_TemplateString;
+  BacktickToken->Tok.setKind(tok::string_literal);
+  BacktickToken->TokenText = LiteralText;
+
+  // Adjust width for potentially multiline string literals.
+  size_t FirstBreak = LiteralText.find('\n');
+  StringRef FirstLineText = FirstBreak == StringRef::npos
+                                ? LiteralText
+                                : LiteralText.substr(0, FirstBreak);
+  BacktickToken->ColumnWidth = encoding::columnWidthWithTabs(
+      FirstLineText, BacktickToken->OriginalColumn, Style.TabWidth, Encoding);
+  size_t LastBreak = LiteralText.rfind('\n');
+  if (LastBreak != StringRef::npos) {
+    BacktickToken->IsMultiline = true;
+    unsigned StartColumn = 0; // The template tail spans the entire line.
+    BacktickToken->LastLineColumnWidth = encoding::columnWidthWithTabs(
+        LiteralText.substr(LastBreak + 1, LiteralText.size()), StartColumn,
+        Style.TabWidth, Encoding);
+  }
+
+  resetLexer(SourceMgr.getFileOffset(Lex->getSourceLocation(Offset + 1)));
+}
+
+bool FormatTokenLexer::tryMerge_TMacro() {
+  if (Tokens.size() < 4)
+    return false;
+  FormatToken *Last = Tokens.back();
+  if (!Last->is(tok::r_paren))
+    return false;
+
+  FormatToken *String = Tokens[Tokens.size() - 2];
+  if (!String->is(tok::string_literal) || String->IsMultiline)
+    return false;
+
+  if (!Tokens[Tokens.size() - 3]->is(tok::l_paren))
+    return false;
+
+  FormatToken *Macro = Tokens[Tokens.size() - 4];
+  if (Macro->TokenText != "_T")
+    return false;
+
+  const char *Start = Macro->TokenText.data();
+  const char *End = Last->TokenText.data() + Last->TokenText.size();
+  String->TokenText = StringRef(Start, End - Start);
+  String->IsFirst = Macro->IsFirst;
+  String->LastNewlineOffset = Macro->LastNewlineOffset;
+  String->WhitespaceRange = Macro->WhitespaceRange;
+  String->OriginalColumn = Macro->OriginalColumn;
+  String->ColumnWidth = encoding::columnWidthWithTabs(
+      String->TokenText, String->OriginalColumn, Style.TabWidth, Encoding);
+  String->NewlinesBefore = Macro->NewlinesBefore;
+  String->HasUnescapedNewline = Macro->HasUnescapedNewline;
+
+  Tokens.pop_back();
+  Tokens.pop_back();
+  Tokens.pop_back();
+  Tokens.back() = String;
+  return true;
+}
+
+bool FormatTokenLexer::tryMergeConflictMarkers() {
+  if (Tokens.back()->NewlinesBefore == 0 && Tokens.back()->isNot(tok::eof))
+    return false;
+
+  // Conflict lines look like:
+  // <marker> <text from the vcs>
+  // For example:
+  // >>>>>>> /file/in/file/system at revision 1234
+  //
+  // We merge all tokens in a line that starts with a conflict marker
+  // into a single token with a special token type that the unwrapped line
+  // parser will use to correctly rebuild the underlying code.
+
+  FileID ID;
+  // Get the position of the first token in the line.
+  unsigned FirstInLineOffset;
+  std::tie(ID, FirstInLineOffset) = SourceMgr.getDecomposedLoc(
+      Tokens[FirstInLineIndex]->getStartOfNonWhitespace());
+  StringRef Buffer = SourceMgr.getBuffer(ID)->getBuffer();
+  // Calculate the offset of the start of the current line.
+  auto LineOffset = Buffer.rfind('\n', FirstInLineOffset);
+  if (LineOffset == StringRef::npos) {
+    LineOffset = 0;
+  } else {
+    ++LineOffset;
+  }
+
+  auto FirstSpace = Buffer.find_first_of(" \n", LineOffset);
+  StringRef LineStart;
+  if (FirstSpace == StringRef::npos) {
+    LineStart = Buffer.substr(LineOffset);
+  } else {
+    LineStart = Buffer.substr(LineOffset, FirstSpace - LineOffset);
+  }
+
+  TokenType Type = TT_Unknown;
+  if (LineStart == "<<<<<<<" || LineStart == ">>>>") {
+    Type = TT_ConflictStart;
+  } else if (LineStart == "|||||||" || LineStart == "=======" ||
+             LineStart == "====") {
+    Type = TT_ConflictAlternative;
+  } else if (LineStart == ">>>>>>>" || LineStart == "<<<<") {
+    Type = TT_ConflictEnd;
+  }
+
+  if (Type != TT_Unknown) {
+    FormatToken *Next = Tokens.back();
+
+    Tokens.resize(FirstInLineIndex + 1);
+    // We do not need to build a complete token here, as we will skip it
+    // during parsing anyway (as we must not touch whitespace around conflict
+    // markers).
+    Tokens.back()->Type = Type;
+    Tokens.back()->Tok.setKind(tok::kw___unknown_anytype);
+
+    Tokens.push_back(Next);
+    return true;
+  }
+
+  return false;
+}
+
+FormatToken *FormatTokenLexer::getStashedToken() {
+  // Create a synthesized second '>' or '<' token.
+  Token Tok = FormatTok->Tok;
+  StringRef TokenText = FormatTok->TokenText;
+
+  unsigned OriginalColumn = FormatTok->OriginalColumn;
+  FormatTok = new (Allocator.Allocate()) FormatToken;
+  FormatTok->Tok = Tok;
+  SourceLocation TokLocation =
+      FormatTok->Tok.getLocation().getLocWithOffset(Tok.getLength() - 1);
+  FormatTok->Tok.setLocation(TokLocation);
+  FormatTok->WhitespaceRange = SourceRange(TokLocation, TokLocation);
+  FormatTok->TokenText = TokenText;
+  FormatTok->ColumnWidth = 1;
+  FormatTok->OriginalColumn = OriginalColumn + 1;
+
+  return FormatTok;
+}
+
+FormatToken *FormatTokenLexer::getNextToken() {
+  if (GreaterStashed) {
+    GreaterStashed = false;
+    return getStashedToken();
+  }
+  if (LessStashed) {
+    LessStashed = false;
+    return getStashedToken();
+  }
+
+  FormatTok = new (Allocator.Allocate()) FormatToken;
+  readRawToken(*FormatTok);
+  SourceLocation WhitespaceStart =
+      FormatTok->Tok.getLocation().getLocWithOffset(-TrailingWhitespace);
+  FormatTok->IsFirst = IsFirstToken;
+  IsFirstToken = false;
+
+  // Consume and record whitespace until we find a significant token.
+  unsigned WhitespaceLength = TrailingWhitespace;
+  while (FormatTok->Tok.is(tok::unknown)) {
+    StringRef Text = FormatTok->TokenText;
+    auto EscapesNewline = [&](int pos) {
+      // A '\r' here is just part of '\r\n'. Skip it.
+      if (pos >= 0 && Text[pos] == '\r')
+        --pos;
+      // See whether there is an odd number of '\' before this.
+      unsigned count = 0;
+      for (; pos >= 0; --pos, ++count)
+        if (Text[pos] != '\\')
+          break;
+      return count & 1;
+    };
+    // FIXME: This miscounts tok:unknown tokens that are not just
+    // whitespace, e.g. a '`' character.
+    for (int i = 0, e = Text.size(); i != e; ++i) {
+      switch (Text[i]) {
+      case '\n':
+        ++FormatTok->NewlinesBefore;
+        FormatTok->HasUnescapedNewline = !EscapesNewline(i - 1);
+        FormatTok->LastNewlineOffset = WhitespaceLength + i + 1;
+        Column = 0;
+        break;
+      case '\r':
+        FormatTok->LastNewlineOffset = WhitespaceLength + i + 1;
+        Column = 0;
+        break;
+      case '\f':
+      case '\v':
+        Column = 0;
+        break;
+      case ' ':
+        ++Column;
+        break;
+      case '\t':
+        Column += Style.TabWidth - Column % Style.TabWidth;
+        break;
+      case '\\':
+        if (i + 1 == e || (Text[i + 1] != '\r' && Text[i + 1] != '\n'))
+          FormatTok->Type = TT_ImplicitStringLiteral;
+        break;
+      default:
+        FormatTok->Type = TT_ImplicitStringLiteral;
+        break;
+      }
+      if (FormatTok->Type == TT_ImplicitStringLiteral)
+        break;
+    }
+
+    if (FormatTok->is(TT_ImplicitStringLiteral))
+      break;
+    WhitespaceLength += FormatTok->Tok.getLength();
+
+    readRawToken(*FormatTok);
+  }
+
+  // In case the token starts with escaped newlines, we want to
+  // take them into account as whitespace - this pattern is quite frequent
+  // in macro definitions.
+  // FIXME: Add a more explicit test.
+  while (FormatTok->TokenText.size() > 1 && FormatTok->TokenText[0] == '\\' &&
+         FormatTok->TokenText[1] == '\n') {
+    ++FormatTok->NewlinesBefore;
+    WhitespaceLength += 2;
+    FormatTok->LastNewlineOffset = 2;
+    Column = 0;
+    FormatTok->TokenText = FormatTok->TokenText.substr(2);
+  }
+
+  FormatTok->WhitespaceRange = SourceRange(
+      WhitespaceStart, WhitespaceStart.getLocWithOffset(WhitespaceLength));
+
+  FormatTok->OriginalColumn = Column;
+
+  TrailingWhitespace = 0;
+  if (FormatTok->Tok.is(tok::comment)) {
+    // FIXME: Add the trimmed whitespace to Column.
+    StringRef UntrimmedText = FormatTok->TokenText;
+    FormatTok->TokenText = FormatTok->TokenText.rtrim(" \t\v\f");
+    TrailingWhitespace = UntrimmedText.size() - FormatTok->TokenText.size();
+  } else if (FormatTok->Tok.is(tok::raw_identifier)) {
+    IdentifierInfo &Info = IdentTable.get(FormatTok->TokenText);
+    FormatTok->Tok.setIdentifierInfo(&Info);
+    FormatTok->Tok.setKind(Info.getTokenID());
+    if (Style.Language == FormatStyle::LK_Java &&
+        FormatTok->isOneOf(tok::kw_struct, tok::kw_union, tok::kw_delete,
+                           tok::kw_operator)) {
+      FormatTok->Tok.setKind(tok::identifier);
+      FormatTok->Tok.setIdentifierInfo(nullptr);
+    } else if (Style.Language == FormatStyle::LK_JavaScript &&
+               FormatTok->isOneOf(tok::kw_struct, tok::kw_union,
+                                  tok::kw_operator)) {
+      FormatTok->Tok.setKind(tok::identifier);
+      FormatTok->Tok.setIdentifierInfo(nullptr);
+    }
+  } else if (FormatTok->Tok.is(tok::greatergreater)) {
+    FormatTok->Tok.setKind(tok::greater);
+    FormatTok->TokenText = FormatTok->TokenText.substr(0, 1);
+    GreaterStashed = true;
+  } else if (FormatTok->Tok.is(tok::lessless)) {
+    FormatTok->Tok.setKind(tok::less);
+    FormatTok->TokenText = FormatTok->TokenText.substr(0, 1);
+    LessStashed = true;
+  }
+
+  // Now FormatTok is the next non-whitespace token.
+
+  StringRef Text = FormatTok->TokenText;
+  size_t FirstNewlinePos = Text.find('\n');
+  if (FirstNewlinePos == StringRef::npos) {
+    // FIXME: ColumnWidth actually depends on the start column, we need to
+    // take this into account when the token is moved.
+    FormatTok->ColumnWidth =
+        encoding::columnWidthWithTabs(Text, Column, Style.TabWidth, Encoding);
+    Column += FormatTok->ColumnWidth;
+  } else {
+    FormatTok->IsMultiline = true;
+    // FIXME: ColumnWidth actually depends on the start column, we need to
+    // take this into account when the token is moved.
+    FormatTok->ColumnWidth = encoding::columnWidthWithTabs(
+        Text.substr(0, FirstNewlinePos), Column, Style.TabWidth, Encoding);
+
+    // The last line of the token always starts in column 0.
+    // Thus, the length can be precomputed even in the presence of tabs.
+    FormatTok->LastLineColumnWidth = encoding::columnWidthWithTabs(
+        Text.substr(Text.find_last_of('\n') + 1), 0, Style.TabWidth, Encoding);
+    Column = FormatTok->LastLineColumnWidth;
+  }
+
+  if (Style.Language == FormatStyle::LK_Cpp) {
+    if (!(Tokens.size() > 0 && Tokens.back()->Tok.getIdentifierInfo() &&
+          Tokens.back()->Tok.getIdentifierInfo()->getPPKeywordID() ==
+              tok::pp_define) &&
+        std::find(ForEachMacros.begin(), ForEachMacros.end(),
+                  FormatTok->Tok.getIdentifierInfo()) != ForEachMacros.end()) {
+      FormatTok->Type = TT_ForEachMacro;
+    } else if (FormatTok->is(tok::identifier)) {
+      if (MacroBlockBeginRegex.match(Text)) {
+        FormatTok->Type = TT_MacroBlockBegin;
+      } else if (MacroBlockEndRegex.match(Text)) {
+        FormatTok->Type = TT_MacroBlockEnd;
+      }
+    }
+  }
+
+  return FormatTok;
+}
+
+void FormatTokenLexer::readRawToken(FormatToken &Tok) {
+  Lex->LexFromRawLexer(Tok.Tok);
+  Tok.TokenText = StringRef(SourceMgr.getCharacterData(Tok.Tok.getLocation()),
+                            Tok.Tok.getLength());
+  // For formatting, treat unterminated string literals like normal string
+  // literals.
+  if (Tok.is(tok::unknown)) {
+    if (!Tok.TokenText.empty() && Tok.TokenText[0] == '"') {
+      Tok.Tok.setKind(tok::string_literal);
+      Tok.IsUnterminatedLiteral = true;
+    } else if (Style.Language == FormatStyle::LK_JavaScript &&
+               Tok.TokenText == "''") {
+      Tok.Tok.setKind(tok::string_literal);
+    }
+  }
+
+  if (Style.Language == FormatStyle::LK_JavaScript &&
+      Tok.is(tok::char_constant)) {
+    Tok.Tok.setKind(tok::string_literal);
+  }
+
+  if (Tok.is(tok::comment) && (Tok.TokenText == "// clang-format on" ||
+                               Tok.TokenText == "/* clang-format on */")) {
+    FormattingDisabled = false;
+  }
+
+  Tok.Finalized = FormattingDisabled;
+
+  if (Tok.is(tok::comment) && (Tok.TokenText == "// clang-format off" ||
+                               Tok.TokenText == "/* clang-format off */")) {
+    FormattingDisabled = true;
+  }
+}
+
+void FormatTokenLexer::resetLexer(unsigned Offset) {
+  StringRef Buffer = SourceMgr.getBufferData(ID);
+  Lex.reset(new Lexer(SourceMgr.getLocForStartOfFile(ID),
+                      getFormattingLangOpts(Style), Buffer.begin(),
+                      Buffer.begin() + Offset, Buffer.end()));
+  Lex->SetKeepWhitespaceMode(true);
+  TrailingWhitespace = 0;
+}
+
+} // namespace format
+} // namespace clang