Add YAML parser to Support.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153977 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2115 insertions, 0 deletions

diff --git a/lib/Support/YAMLParser.cpp b/lib/Support/YAMLParser.cpp
new file mode 100644
index 0000000000..3e302d0eb1
--- /dev/null
+++ b/lib/Support/YAMLParser.cpp
@@ -0,0 +1,2115 @@
+//===--- YAMLParser.cpp - Simple YAML parser ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements a YAML parser.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/YAMLParser.h"
+
+#include "llvm/ADT/ilist.h"
+#include "llvm/ADT/ilist_node.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/SourceMgr.h"
+
+using namespace llvm;
+using namespace yaml;
+
+enum UnicodeEncodingForm {
+  UEF_UTF32_LE, //< UTF-32 Little Endian
+  UEF_UTF32_BE, //< UTF-32 Big Endian
+  UEF_UTF16_LE, //< UTF-16 Little Endian
+  UEF_UTF16_BE, //< UTF-16 Big Endian
+  UEF_UTF8,     //< UTF-8 or ascii.
+  UEF_Unknown   //< Not a valid Unicode encoding.
+};
+
+/// EncodingInfo - Holds the encoding type and length of the byte order mark if
+///                it exists. Length is in {0, 2, 3, 4}.
+typedef std::pair<UnicodeEncodingForm, unsigned> EncodingInfo;
+
+/// getUnicodeEncoding - Reads up to the first 4 bytes to determine the Unicode
+///                      encoding form of \a Input.
+///
+/// @param Input A string of length 0 or more.
+/// @returns An EncodingInfo indicating the Unicode encoding form of the input
+///          and how long the byte order mark is if one exists.
+static EncodingInfo getUnicodeEncoding(StringRef Input) {
+  if (Input.size() == 0)
+    return std::make_pair(UEF_Unknown, 0);
+
+  switch (uint8_t(Input[0])) {
+  case 0x00:
+    if (Input.size() >= 4) {
+      if (  Input[1] == 0
+         && uint8_t(Input[2]) == 0xFE
+         && uint8_t(Input[3]) == 0xFF)
+        return std::make_pair(UEF_UTF32_BE, 4);
+      if (Input[1] == 0 && Input[2] == 0 && Input[3] != 0)
+        return std::make_pair(UEF_UTF32_BE, 0);
+    }
+
+    if (Input.size() >= 2 && Input[1] != 0)
+      return std::make_pair(UEF_UTF16_BE, 0);
+    return std::make_pair(UEF_Unknown, 0);
+  case 0xFF:
+    if (  Input.size() >= 4
+       && uint8_t(Input[1]) == 0xFE
+       && Input[2] == 0
+       && Input[3] == 0)
+      return std::make_pair(UEF_UTF32_LE, 4);
+
+    if (Input.size() >= 2 && uint8_t(Input[1]) == 0xFE)
+      return std::make_pair(UEF_UTF16_LE, 2);
+    return std::make_pair(UEF_Unknown, 0);
+  case 0xFE:
+    if (Input.size() >= 2 && uint8_t(Input[1]) == 0xFF)
+      return std::make_pair(UEF_UTF16_BE, 2);
+    return std::make_pair(UEF_Unknown, 0);
+  case 0xEF:
+    if (  Input.size() >= 3
+       && uint8_t(Input[1]) == 0xBB
+       && uint8_t(Input[2]) == 0xBF)
+      return std::make_pair(UEF_UTF8, 3);
+    return std::make_pair(UEF_Unknown, 0);
+  }
+
+  // It could still be utf-32 or utf-16.
+  if (Input.size() >= 4 && Input[1] == 0 && Input[2] == 0 && Input[3] == 0)
+    return std::make_pair(UEF_UTF32_LE, 0);
+
+  if (Input.size() >= 2 && Input[1] == 0)
+    return std::make_pair(UEF_UTF16_LE, 0);
+
+  return std::make_pair(UEF_UTF8, 0);
+}
+
+namespace llvm {
+namespace yaml {
+/// Token - A single YAML token.
+struct Token : ilist_node<Token> {
+  enum TokenKind {
+    TK_Error, // Uninitialized token.
+    TK_StreamStart,
+    TK_StreamEnd,
+    TK_VersionDirective,
+    TK_TagDirective,
+    TK_DocumentStart,
+    TK_DocumentEnd,
+    TK_BlockEntry,
+    TK_BlockEnd,
+    TK_BlockSequenceStart,
+    TK_BlockMappingStart,
+    TK_FlowEntry,
+    TK_FlowSequenceStart,
+    TK_FlowSequenceEnd,
+    TK_FlowMappingStart,
+    TK_FlowMappingEnd,
+    TK_Key,
+    TK_Value,
+    TK_Scalar,
+    TK_Alias,
+    TK_Anchor,
+    TK_Tag
+  } Kind;
+
+  /// A string of length 0 or more whose begin() points to the logical location
+  /// of the token in the input.
+  StringRef Range;
+
+  Token() : Kind(TK_Error) {}
+};
+}
+}
+
+template<>
+struct ilist_sentinel_traits<Token> {
+  Token *createSentinel() const {
+    return &Sentinel;
+  }
+  static void destroySentinel(Token*) {}
+
+  Token *provideInitialHead() const { return createSentinel(); }
+  Token *ensureHead(Token*) const { return createSentinel(); }
+  static void noteHead(Token*, Token*) {}
+
+private:
+  mutable Token Sentinel;
+};
+
+template<>
+struct ilist_node_traits<Token> {
+  Token *createNode(const Token &V) {
+    return new (Alloc.Allocate<Token>()) Token(V);
+  }
+  static void deleteNode(Token *V) {}
+
+  void addNodeToList(Token *) {}
+  void removeNodeFromList(Token *) {}
+  void transferNodesFromList(ilist_node_traits &    /*SrcTraits*/,
+                             ilist_iterator<Token> /*first*/,
+                             ilist_iterator<Token> /*last*/) {}
+
+  BumpPtrAllocator Alloc;
+};
+
+typedef ilist<Token> TokenQueueT;
+
+namespace {
+/// @brief This struct is used to track simple keys.
+///
+/// Simple keys are handled by creating an entry in SimpleKeys for each Token
+/// which could legally be the start of a simple key. When peekNext is called,
+/// if the Token To be returned is referenced by a SimpleKey, we continue
+/// tokenizing until that potential simple key has either been found to not be
+/// a simple key (we moved on to the next line or went further than 1024 chars).
+/// Or when we run into a Value, and then insert a Key token (and possibly
+/// others) before the SimpleKey's Tok.
+struct SimpleKey {
+  TokenQueueT::iterator Tok;
+  unsigned Column;
+  unsigned Line;
+  unsigned FlowLevel;
+  bool IsRequired;
+
+  bool operator ==(const SimpleKey &Other) {
+    return Tok == Other.Tok;
+  }
+};
+}
+
+/// @brief The Unicode scalar value of a UTF-8 minimal well-formed code unit
+///        subsequence and the subsequence's length in code units (uint8_t).
+///        A length of 0 represents an error.
+typedef std::pair<uint32_t, unsigned> UTF8Decoded;
+
+static UTF8Decoded decodeUTF8(StringRef Range) {
+  StringRef::iterator Position= Range.begin();
+  StringRef::iterator End = Range.end();
+  // 1 byte: [0x00, 0x7f]
+  // Bit pattern: 0xxxxxxx
+  if ((*Position & 0x80) == 0) {
+     return std::make_pair(*Position, 1);
+  }
+  // 2 bytes: [0x80, 0x7ff]
+  // Bit pattern: 110xxxxx 10xxxxxx
+  if (Position + 1 != End &&
+      ((*Position & 0xE0) == 0xC0) &&
+      ((*(Position + 1) & 0xC0) == 0x80)) {
+    uint32_t codepoint = ((*Position & 0x1F) << 6) |
+                          (*(Position + 1) & 0x3F);
+    if (codepoint >= 0x80)
+      return std::make_pair(codepoint, 2);
+  }
+  // 3 bytes: [0x8000, 0xffff]
+  // Bit pattern: 1110xxxx 10xxxxxx 10xxxxxx
+  if (Position + 2 != End &&
+      ((*Position & 0xF0) == 0xE0) &&
+      ((*(Position + 1) & 0xC0) == 0x80) &&
+      ((*(Position + 2) & 0xC0) == 0x80)) {
+    uint32_t codepoint = ((*Position & 0x0F) << 12) |
+                         ((*(Position + 1) & 0x3F) << 6) |
+                          (*(Position + 2) & 0x3F);
+    // Codepoints between 0xD800 and 0xDFFF are invalid, as
+    // they are high / low surrogate halves used by UTF-16.
+    if (codepoint >= 0x800 &&
+        (codepoint < 0xD800 || codepoint > 0xDFFF))
+      return std::make_pair(codepoint, 3);
+  }
+  // 4 bytes: [0x10000, 0x10FFFF]
+  // Bit pattern: 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
+  if (Position + 3 != End &&
+      ((*Position & 0xF8) == 0xF0) &&
+      ((*(Position + 1) & 0xC0) == 0x80) &&
+      ((*(Position + 2) & 0xC0) == 0x80) &&
+      ((*(Position + 3) & 0xC0) == 0x80)) {
+    uint32_t codepoint = ((*Position & 0x07) << 18) |
+                         ((*(Position + 1) & 0x3F) << 12) |
+                         ((*(Position + 2) & 0x3F) << 6) |
+                          (*(Position + 3) & 0x3F);
+    if (codepoint >= 0x10000 && codepoint <= 0x10FFFF)
+      return std::make_pair(codepoint, 4);
+  }
+  return std::make_pair(0, 0);
+}
+
+namespace llvm {
+namespace yaml {
+/// @brief Scans YAML tokens from a MemoryBuffer.
+class Scanner {
+public:
+  Scanner(const StringRef Input, SourceMgr &SM);
+
+  /// @brief Parse the next token and return it without popping it.
+  Token &peekNext();
+
+  /// @brief Parse the next token and pop it from the queue.
+  Token getNext();
+
+  void printError(SMLoc Loc, SourceMgr::DiagKind Kind, const Twine &Message,
+                  ArrayRef<SMRange> Ranges = ArrayRef<SMRange>()) {
+    SM.PrintMessage(Loc, Kind, Message, Ranges);
+  }
+
+  void setError(const Twine &Message, StringRef::iterator Position) {
+    if (Current >= End)
+      Current = End - 1;
+
+    // Don't print out more errors after the first one we encounter. The rest
+    // are just the result of the first, and have no meaning.
+    if (!Failed)
+      printError(SMLoc::getFromPointer(Current), SourceMgr::DK_Error, Message);
+    Failed = true;
+  }
+
+  void setError(const Twine &Message) {
+    setError(Message, Current);
+  }
+
+  /// @brief Returns true if an error occurred while parsing.
+  bool failed() {
+    return Failed;
+  }
+
+private:
+  StringRef currentInput() {
+    return StringRef(Current, End - Current);
+  }
+
+  /// @brief Decode a UTF-8 minimal well-formed code unit subsequence starting
+  ///        at \a Position.
+  ///
+  /// If the UTF-8 code units starting at Position do not form a well-formed
+  /// code unit subsequence, then the Unicode scalar value is 0, and the length
+  /// is 0.
+  UTF8Decoded decodeUTF8(StringRef::iterator Position) {
+    return ::decodeUTF8(StringRef(Position, End - Position));
+  }
+
+  // The following functions are based on the gramar rules in the YAML spec. The
+  // style of the function names it meant to closely match how they are written
+  // in the spec. The number within the [] is the number of the grammar rule in
+  // the spec.
+  //
+  // See 4.2 [Production Naming Conventions] for the meaning of the prefixes.
+  //
+  // c-
+  //   A production starting and ending with a special character.
+  // b-
+  //   A production matching a single line break.
+  // nb-
+  //   A production starting and ending with a non-break character.
+  // s-
+  //   A production starting and ending with a white space character.
+  // ns-
+  //   A production starting and ending with a non-space character.
+  // l-
+  //   A production matching complete line(s).
+
+  /// @brief Skip a single nb-char[27] starting at Position.
+  ///
+  /// A nb-char is 0x9 | [0x20-0x7E] | 0x85 | [0xA0-0xD7FF] | [0xE000-0xFEFE]
+  ///                  | [0xFF00-0xFFFD] | [0x10000-0x10FFFF]
+  ///
+  /// @returns The code unit after the nb-char, or Position if it's not an
+  ///          nb-char.
+  StringRef::iterator skip_nb_char(StringRef::iterator Position);
+
+  /// @brief Skip a single b-break[28] starting at Position.
+  ///
+  /// A b-break is 0xD 0xA | 0xD | 0xA
+  ///
+  /// @returns The code unit after the b-break, or Position if it's not a
+  ///          b-break.
+  StringRef::iterator skip_b_break(StringRef::iterator Position);
+
+  /// @brief Skip a single s-white[33] starting at Position.
+  ///
+  /// A s-white is 0x20 | 0x9
+  ///
+  /// @returns The code unit after the s-white, or Position if it's not a
+  ///          s-white.
+  StringRef::iterator skip_s_white(StringRef::iterator Position);
+
+  /// @brief Skip a single ns-char[34] starting at Position.
+  ///
+  /// A ns-char is nb-char - s-white
+  ///
+  /// @returns The code unit after the ns-char, or Position if it's not a
+  ///          ns-char.
+  StringRef::iterator skip_ns_char(StringRef::iterator Position);
+
+  typedef StringRef::iterator (Scanner::*SkipWhileFunc)(StringRef::iterator);
+  /// @brief Skip minimal well-formed code unit subsequences until Func
+  ///        returns its input.
+  ///
+  /// @returns The code unit after the last minimal well-formed code unit
+  ///          subsequence that Func accepted.
+  StringRef::iterator skip_while( SkipWhileFunc Func
+                                , StringRef::iterator Position);
+
+  /// @brief Scan ns-uri-char[39]s starting at Cur.
+  ///
+  /// This updates Cur and Column while scanning.
+  ///
+  /// @returns A StringRef starting at Cur which covers the longest contiguous
+  ///          sequence of ns-uri-char.
+  StringRef scan_ns_uri_char();
+
+  /// @brief Scan ns-plain-one-line[133] starting at \a Cur.
+  StringRef scan_ns_plain_one_line();
+
+  /// @brief Consume a minimal well-formed code unit subsequence starting at
+  ///        \a Cur. Return false if it is not the same Unicode scalar value as
+  ///        \a Expected. This updates \a Column.
+  bool consume(uint32_t Expected);
+
+  /// @brief Skip \a Distance UTF-8 code units. Updates \a Cur and \a Column.
+  void skip(uint32_t Distance);
+
+  /// @brief Return true if the minimal well-formed code unit subsequence at
+  ///        Pos is whitespace or a new line
+  bool isBlankOrBreak(StringRef::iterator Position);
+
+  /// @brief If IsSimpleKeyAllowed, create and push_back a new SimpleKey.
+  void saveSimpleKeyCandidate( TokenQueueT::iterator Tok
+                             , unsigned AtColumn
+                             , bool IsRequired);
+
+  /// @brief Remove simple keys that can no longer be valid simple keys.
+  ///
+  /// Invalid simple keys are not on the current line or are further than 1024
+  /// columns back.
+  void removeStaleSimpleKeyCandidates();
+
+  /// @brief Remove all simple keys on FlowLevel \a Level.
+  void removeSimpleKeyCandidatesOnFlowLevel(unsigned Level);
+
+  /// @brief Unroll indentation in \a Indents back to \a Col. Creates BlockEnd
+  ///        tokens if needed.
+  bool unrollIndent(int ToColumn);
+
+  /// @brief Increase indent to \a Col. Creates \a Kind token at \a InsertPoint
+  ///        if needed.
+  bool rollIndent( int ToColumn
+                 , Token::TokenKind Kind
+                 , TokenQueueT::iterator InsertPoint);
+
+  /// @brief Skip whitespace and comments until the start of the next token.
+  void scanToNextToken();
+
+  /// @brief Must be the first token generated.
+  bool scanStreamStart();
+
+  /// @brief Generate tokens needed to close out the stream.
+  bool scanStreamEnd();
+
+  /// @brief Scan a %BLAH directive.
+  bool scanDirective();
+
+  /// @brief Scan a ... or ---.
+  bool scanDocumentIndicator(bool IsStart);
+
+  /// @brief Scan a [ or { and generate the proper flow collection start token.
+  bool scanFlowCollectionStart(bool IsSequence);
+
+  /// @brief Scan a ] or } and generate the proper flow collection end token.
+  bool scanFlowCollectionEnd(bool IsSequence);
+
+  /// @brief Scan the , that separates entries in a flow collection.
+  bool scanFlowEntry();
+
+  /// @brief Scan the - that starts block sequence entries.
+  bool scanBlockEntry();
+
+  /// @brief Scan an explicit ? indicating a key.
+  bool scanKey();
+
+  /// @brief Scan an explicit : indicating a value.
+  bool scanValue();
+
+  /// @brief Scan a quoted scalar.
+  bool scanFlowScalar(bool IsDoubleQuoted);
+
+  /// @brief Scan an unquoted scalar.
+  bool scanPlainScalar();
+
+  /// @brief Scan an Alias or Anchor starting with * or &.
+  bool scanAliasOrAnchor(bool IsAlias);
+
+  /// @brief Scan a block scalar starting with | or >.
+  bool scanBlockScalar(bool IsLiteral);
+
+  /// @brief Scan a tag of the form !stuff.
+  bool scanTag();
+
+  /// @brief Dispatch to the next scanning function based on \a *Cur.
+  bool fetchMoreTokens();
+
+  /// @brief The SourceMgr used for diagnostics and buffer management.
+  SourceMgr &SM;
+
+  /// @brief The original input.
+  MemoryBuffer *InputBuffer;
+
+  /// @brief The current position of the scanner.
+  StringRef::iterator Current;
+
+  /// @brief The end of the input (one past the last character).
+  StringRef::iterator End;
+
+  /// @brief Current YAML indentation level in spaces.
+  int Indent;
+
+  /// @brief Current column number in Unicode code points.
+  unsigned Column;
+
+  /// @brief Current line number.
+  unsigned Line;
+
+  /// @brief How deep we are in flow style containers. 0 Means at block level.
+  unsigned FlowLevel;
+
+  /// @brief Are we at the start of the stream?
+  bool IsStartOfStream;
+
+  /// @brief Can the next token be the start of a simple key?
+  bool IsSimpleKeyAllowed;
+
+  /// @brief Is the next token required to start a simple key?
+  bool IsSimpleKeyRequired;
+
+  /// @brief True if an error has occurred.
+  bool Failed;
+
+  /// @brief Queue of tokens. This is required to queue up tokens while looking
+  ///        for the end of a simple key. And for cases where a single character
+  ///        can produce multiple tokens (e.g. BlockEnd).
+  TokenQueueT TokenQueue;
+
+  /// @brief Indentation levels.
+  SmallVector<int, 4> Indents;
+
+  /// @brief Potential simple keys.
+  SmallVector<SimpleKey, 4> SimpleKeys;
+};
+
+} // end namespace yaml
+} // end namespace llvm
+
+/// encodeUTF8 - Encode \a UnicodeScalarValue in UTF-8 and append it to result.
+static void encodeUTF8( uint32_t UnicodeScalarValue
+                      , SmallVectorImpl<char> &Result) {
+  if (UnicodeScalarValue <= 0x7F) {
+    Result.push_back(UnicodeScalarValue & 0x7F);
+  } else if (UnicodeScalarValue <= 0x7FF) {
+    uint8_t FirstByte = 0xC0 | ((UnicodeScalarValue & 0x7C0) >> 6);
+    uint8_t SecondByte = 0x80 | (UnicodeScalarValue & 0x3F);
+    Result.push_back(FirstByte);
+    Result.push_back(SecondByte);
+  } else if (UnicodeScalarValue <= 0xFFFF) {
+    uint8_t FirstByte = 0xE0 | ((UnicodeScalarValue & 0xF000) >> 12);
+    uint8_t SecondByte = 0x80 | ((UnicodeScalarValue & 0xFC0) >> 6);
+    uint8_t ThirdByte = 0x80 | (UnicodeScalarValue & 0x3F);
+    Result.push_back(FirstByte);
+    Result.push_back(SecondByte);
+    Result.push_back(ThirdByte);
+  } else if (UnicodeScalarValue <= 0x10FFFF) {
+    uint8_t FirstByte = 0xF0 | ((UnicodeScalarValue & 0x1F0000) >> 18);
+    uint8_t SecondByte = 0x80 | ((UnicodeScalarValue & 0x3F000) >> 12);
+    uint8_t ThirdByte = 0x80 | ((UnicodeScalarValue & 0xFC0) >> 6);
+    uint8_t FourthByte = 0x80 | (UnicodeScalarValue & 0x3F);
+    Result.push_back(FirstByte);
+    Result.push_back(SecondByte);
+    Result.push_back(ThirdByte);
+    Result.push_back(FourthByte);
+  }
+}
+
+bool yaml::dumpTokens(StringRef Input, raw_ostream &OS) {
+  SourceMgr SM;
+  Scanner scanner(Input, SM);
+  while (true) {
+    Token T = scanner.getNext();
+    switch (T.Kind) {
+    case Token::TK_StreamStart:
+      OS << "Stream-Start: ";
+      break;
+    case Token::TK_StreamEnd:
+      OS << "Stream-End: ";
+      break;
+    case Token::TK_VersionDirective:
+      OS << "Version-Directive: ";
+      break;
+    case Token::TK_TagDirective:
+      OS << "Tag-Directive: ";
+      break;
+    case Token::TK_DocumentStart:
+      OS << "Document-Start: ";
+      break;
+    case Token::TK_DocumentEnd:
+      OS << "Document-End: ";
+      break;
+    case Token::TK_BlockEntry:
+      OS << "Block-Entry: ";
+      break;
+    case Token::TK_BlockEnd:
+      OS << "Block-End: ";
+      break;
+    case Token::TK_BlockSequenceStart:
+      OS << "Block-Sequence-Start: ";
+      break;
+    case Token::TK_BlockMappingStart:
+      OS << "Block-Mapping-Start: ";
+      break;
+    case Token::TK_FlowEntry:
+      OS << "Flow-Entry: ";
+      break;
+    case Token::TK_FlowSequenceStart:
+      OS << "Flow-Sequence-Start: ";
+      break;
+    case Token::TK_FlowSequenceEnd:
+      OS << "Flow-Sequence-End: ";
+      break;
+    case Token::TK_FlowMappingStart:
+      OS << "Flow-Mapping-Start: ";
+      break;
+    case Token::TK_FlowMappingEnd:
+      OS << "Flow-Mapping-End: ";
+      break;
+    case Token::TK_Key:
+      OS << "Key: ";
+      break;
+    case Token::TK_Value:
+      OS << "Value: ";
+      break;
+    case Token::TK_Scalar:
+      OS << "Scalar: ";
+      break;
+    case Token::TK_Alias:
+      OS << "Alias: ";
+      break;
+    case Token::TK_Anchor:
+      OS << "Anchor: ";
+      break;
+    case Token::TK_Tag:
+      OS << "Tag: ";
+      break;
+    case Token::TK_Error:
+      break;
+    }
+    OS << T.Range << "\n";
+    if (T.Kind == Token::TK_StreamEnd)
+      break;
+    else if (T.Kind == Token::TK_Error)
+      return false;
+  }
+  return true;
+}
+
+bool yaml::scanTokens(StringRef Input) {
+  llvm::SourceMgr SM;
+  llvm::yaml::Scanner scanner(Input, SM);
+  for (;;) {
+    llvm::yaml::Token T = scanner.getNext();
+    if (T.Kind == Token::TK_StreamEnd)
+      break;
+    else if (T.Kind == Token::TK_Error)
+      return false;
+  }
+  return true;
+}
+
+std::string yaml::escape(StringRef Input) {
+  std::string EscapedInput;
+  for (StringRef::iterator i = Input.begin(), e = Input.end(); i != e; ++i) {
+    if (*i == '\\')
+      EscapedInput += "\\\\";
+    else if (*i == '"')
+      EscapedInput += "\\\"";
+    else if (*i == 0)
+      EscapedInput += "\\0";
+    else if (*i == 0x07)
+      EscapedInput += "\\a";
+    else if (*i == 0x08)
+      EscapedInput += "\\b";
+    else if (*i == 0x09)
+      EscapedInput += "\\t";
+    else if (*i == 0x0A)
+      EscapedInput += "\\n";
+    else if (*i == 0x0B)
+      EscapedInput += "\\v";
+    else if (*i == 0x0C)
+      EscapedInput += "\\f";
+    else if (*i == 0x0D)
+      EscapedInput += "\\r";
+    else if (*i == 0x1B)
+      EscapedInput += "\\e";
+    else if (*i >= 0 && *i < 0x20) { // Control characters not handled above.
+      std::string HexStr = utohexstr(*i);
+      EscapedInput += "\\x" + std::string(2 - HexStr.size(), '0') + HexStr;
+    } else if (*i & 0x80) { // UTF-8 multiple code unit subsequence.
+      UTF8Decoded UnicodeScalarValue
+        = decodeUTF8(StringRef(i, Input.end() - i));
+      if (UnicodeScalarValue.second == 0) {
+        // Found invalid char.
+        SmallString<4> Val;
+        encodeUTF8(0xFFFD, Val);
+        EscapedInput.insert(EscapedInput.end(), Val.begin(), Val.end());
+        // FIXME: Error reporting.
+        return EscapedInput;
+      }
+      if (UnicodeScalarValue.first == 0x85)
+        EscapedInput += "\\N";
+      else if (UnicodeScalarValue.first == 0xA0)
+        EscapedInput += "\\_";
+      else if (UnicodeScalarValue.first == 0x2028)
+        EscapedInput += "\\L";
+      else if (UnicodeScalarValue.first == 0x2029)
+        EscapedInput += "\\P";
+      else {
+        std::string HexStr = utohexstr(UnicodeScalarValue.first);
+        if (HexStr.size() <= 2)
+          EscapedInput += "\\x" + std::string(2 - HexStr.size(), '0') + HexStr;
+        else if (HexStr.size() <= 4)
+          EscapedInput += "\\u" + std::string(4 - HexStr.size(), '0') + HexStr;
+        else if (HexStr.size() <= 8)
+          EscapedInput += "\\U" + std::string(8 - HexStr.size(), '0') + HexStr;
+      }
+      i += UnicodeScalarValue.second - 1;
+    } else
+      EscapedInput.push_back(*i);
+  }
+  return EscapedInput;
+}
+
+Scanner::Scanner(StringRef Input, SourceMgr &sm)
+  : SM(sm)
+  , Indent(-1)
+  , Column(0)
+  , Line(0)
+  , FlowLevel(0)
+  , IsStartOfStream(true)
+  , IsSimpleKeyAllowed(true)
+  , IsSimpleKeyRequired(false)
+  , Failed(false) {
+  InputBuffer = MemoryBuffer::getMemBuffer(Input, "YAML");
+  SM.AddNewSourceBuffer(InputBuffer, SMLoc());
+  Current = InputBuffer->getBufferStart();
+  End = InputBuffer->getBufferEnd();
+}
+
+Token &Scanner::peekNext() {
+  // If the current token is a possible simple key, keep parsing until we
+  // can confirm.
+  bool NeedMore = false;
+  while (true) {
+    if (TokenQueue.empty() || NeedMore) {
+      if (!fetchMoreTokens()) {
+        TokenQueue.clear();
+        TokenQueue.push_back(Token());
+        return TokenQueue.front();
+      }
+    }
+    assert(!TokenQueue.empty() &&
+            "fetchMoreTokens lied about getting tokens!");
+
+    removeStaleSimpleKeyCandidates();
+    SimpleKey SK;
+    SK.Tok = TokenQueue.front();
+    if (std::find(SimpleKeys.begin(), SimpleKeys.end(), SK)
+        == SimpleKeys.end())
+      break;
+    else
+      NeedMore = true;
+  }
+  return TokenQueue.front();
+}
+
+Token Scanner::getNext() {
+  Token Ret = peekNext();
+  // TokenQueue can be empty if there was an error getting the next token.
+  if (!TokenQueue.empty())
+    TokenQueue.pop_front();
+
+  // There cannot be any referenced Token's if the TokenQueue is empty. So do a
+  // quick deallocation of them all.
+  if (TokenQueue.empty()) {
+    TokenQueue.Alloc.Reset();
+  }
+
+  return Ret;
+}
+
+StringRef::iterator Scanner::skip_nb_char(StringRef::iterator Position) {
+  // Check 7 bit c-printable - b-char.
+  if (   *Position == 0x09
+      || (*Position >= 0x20 && *Position <= 0x7E))
+    return Position + 1;
+
+  // Check for valid UTF-8.
+  if (uint8_t(*Position) & 0x80) {
+    UTF8Decoded u8d = decodeUTF8(Position);
+    if (   u8d.second != 0
+        && u8d.first != 0xFEFF
+        && ( u8d.first == 0x85
+          || ( u8d.first >= 0xA0
+            && u8d.first <= 0xD7FF)
+          || ( u8d.first >= 0xE000
+            && u8d.first <= 0xFFFD)
+          || ( u8d.first >= 0x10000
+            && u8d.first <= 0x10FFFF)))
+      return Position + u8d.second;
+  }
+  return Position;
+}
+
+StringRef::iterator Scanner::skip_b_break(StringRef::iterator Position) {
+  if (*Position == 0x0D) {
+    if (Position + 1 != End && *(Position + 1) == 0x0A)
+      return Position + 2;
+    return Position + 1;
+  }
+
+  if (*Position == 0x0A)
+    return Position + 1;
+  return Position;
+}
+
+
+StringRef::iterator Scanner::skip_s_white(StringRef::iterator Position) {
+  if (Position == End)
+    return Position;
+  if (*Position == ' ' || *Position == '\t')
+    return Position + 1;
+  return Position;
+}
+
+StringRef::iterator Scanner::skip_ns_char(StringRef::iterator Position) {
+  if (Position == End)
+    return Position;
+  if (*Position == ' ' || *Position == '\t')
+    return Position;
+  return skip_nb_char(Position);
+}
+
+StringRef::iterator Scanner::skip_while( SkipWhileFunc Func
+                                       , StringRef::iterator Position) {
+  while (true) {
+    StringRef::iterator i = (this->*Func)(Position);
+    if (i == Position)
+      break;
+    Position = i;
+  }
+  return Position;
+}
+
+static bool is_ns_hex_digit(const char C) {
+  return    (C >= '0' && C <= '9')
+         || (C >= 'a' && C <= 'z')
+         || (C >= 'A' && C <= 'Z');
+}
+
+static bool is_ns_word_char(const char C) {
+  return    C == '-'
+         || (C >= 'a' && C <= 'z')
+         || (C >= 'A' && C <= 'Z');
+}
+
+StringRef Scanner::scan_ns_uri_char() {
+  StringRef::iterator Start = Current;
+  while (true) {
+    if (Current == End)
+      break;
+    if ((   *Current == '%'
+          && Current + 2 < End
+          && is_ns_hex_digit(*(Current + 1))
+          && is_ns_hex_digit(*(Current + 2)))
+        || is_ns_word_char(*Current)
+        || StringRef(Current, 1).find_first_of("#;/?:@&=+$,_.!~*'()[]")
+          != StringRef::npos) {
+      ++Current;
+      ++Column;
+    } else
+      break;
+  }
+  return StringRef(Start, Current - Start);
+}
+
+StringRef Scanner::scan_ns_plain_one_line() {
+  StringRef::iterator start = Current;
+  // The first character must already be verified.
+  ++Current;
+  while (true) {
+    if (Current == End) {
+      break;
+    } else if (*Current == ':') {
+      // Check if the next character is a ns-char.
+      if (Current + 1 == End)
+        break;
+      StringRef::iterator i = skip_ns_char(Current + 1);
+      if (Current + 1 != i) {
+        Current = i;
+        Column += 2; // Consume both the ':' and ns-char.
+      } else
+        break;
+    } else if (*Current == '#') {
+      // Check if the previous character was a ns-char.
+      // The & 0x80 check is to check for the trailing byte of a utf-8
+      if (*(Current - 1) & 0x80 || skip_ns_char(Current - 1) == Current) {
+        ++Current;
+        ++Column;
+      } else
+        break;
+    } else {
+      StringRef::iterator i = skip_nb_char(Current);
+      if (i == Current)
+        break;
+      Current = i;
+      ++Column;
+    }
+  }
+  return StringRef(start, Current - start);
+}
+
+bool Scanner::consume(uint32_t Expected) {
+  if (Expected >= 0x80)
+    report_fatal_error("Not dealing with this yet");
+  if (Current == End)
+    return false;
+  if (uint8_t(*Current) >= 0x80)
+    report_fatal_error("Not dealing with this yet");
+  if (uint8_t(*Current) == Expected) {
+    ++Current;
+    ++Column;
+    return true;
+  }
+  return false;
+}
+
+void Scanner::skip(uint32_t Distance) {
+  Current += Distance;
+  Column += Distance;
+}
+
+bool Scanner::isBlankOrBreak(StringRef::iterator Position) {
+  if (Position == End)
+    return false;
+  if (   *Position == ' ' || *Position == '\t'
+      || *Position == '\r' || *Position == '\n')
+    return true;
+  return false;
+}
+
+void Scanner::saveSimpleKeyCandidate( TokenQueueT::iterator Tok
+                                    , unsigned AtColumn
+                                    , bool IsRequired) {
+  if (IsSimpleKeyAllowed) {
+    SimpleKey SK;
+    SK.Tok = Tok;
+    SK.Line = Line;
+    SK.Column = AtColumn;
+    SK.IsRequired = IsRequired;
+    SK.FlowLevel = FlowLevel;
+    SimpleKeys.push_back(SK);
+  }
+}
+
+void Scanner::removeStaleSimpleKeyCandidates() {
+  for (SmallVectorImpl<SimpleKey>::iterator i = SimpleKeys.begin();
+                                            i != SimpleKeys.end();) {
+    if (i->Line != Line || i->Column + 1024 < Column) {
+      if (i->IsRequired)
+        setError( "Could not find expected : for simple key"
+                , i->Tok->Range.begin());
+      i = SimpleKeys.erase(i);
+    } else
+      ++i;
+  }
+}
+
+void Scanner::removeSimpleKeyCandidatesOnFlowLevel(unsigned Level) {
+  if (!SimpleKeys.empty() && (SimpleKeys.end() - 1)->FlowLevel == Level)
+    SimpleKeys.pop_back();
+}
+
+bool Scanner::unrollIndent(int ToColumn) {
+  Token T;
+  // Indentation is ignored in flow.
+  if (FlowLevel != 0)
+    return true;
+
+  while (Indent > ToColumn) {
+    T.Kind = Token::TK_BlockEnd;
+    T.Range = StringRef(Current, 1);
+    TokenQueue.push_back(T);
+    Indent = Indents.pop_back_val();
+  }
+
+  return true;
+}
+
+bool Scanner::rollIndent( int ToColumn
+                        , Token::TokenKind Kind
+                        , TokenQueueT::iterator InsertPoint) {
+  if (FlowLevel)
+    return true;
+  if (Indent < ToColumn) {
+    Indents.push_back(Indent);
+    Indent = ToColumn;
+
+    Token T;
+    T.Kind = Kind;
+    T.Range = StringRef(Current, 0);
+    TokenQueue.insert(InsertPoint, T);
+  }
+  return true;
+}
+
+void Scanner::scanToNextToken() {
+  while (true) {
+    while (*Current == ' ' || *Current == '\t') {
+      skip(1);
+    }
+
+    // Skip comment.
+    if (*Current == '#') {
+      while (true) {
+        // This may skip more than one byte, thus Column is only incremented
+        // for code points.
+        StringRef::iterator i = skip_nb_char(Current);
+        if (i == Current)
+          break;
+        Current = i;
+        ++Column;
+      }
+    }
+
+    // Skip EOL.
+    StringRef::iterator i = skip_b_break(Current);
+    if (i == Current)
+      break;
+    Current = i;
+    ++Line;
+    Column = 0;
+    // New lines may start a simple key.
+    if (!FlowLevel)
+      IsSimpleKeyAllowed = true;
+  }
+}
+
+bool Scanner::scanStreamStart() {
+  IsStartOfStream = false;
+
+  EncodingInfo EI = getUnicodeEncoding(currentInput());
+
+  Token T;
+  T.Kind = Token::TK_StreamStart;
+  T.Range = StringRef(Current, EI.second);
+  TokenQueue.push_back(T);
+  Current += EI.second;
+  return true;
+}
+
+bool Scanner::scanStreamEnd() {
+  // Force an ending new line if one isn't present.
+  if (Column != 0) {
+    Column = 0;
+    ++Line;
+  }
+
+  unrollIndent(-1);
+  SimpleKeys.clear();
+  IsSimpleKeyAllowed = false;
+
+  Token T;
+  T.Kind = Token::TK_StreamEnd;
+  T.Range = StringRef(Current, 0);
+  TokenQueue.push_back(T);
+  return true;
+}
+
+bool Scanner::scanDirective() {
+  // Reset the indentation level.
+  unrollIndent(-1);
+  SimpleKeys.clear();
+  IsSimpleKeyAllowed = false;
+
+  StringRef::iterator Start = Current;
+  consume('%');
+  StringRef::iterator NameStart = Current;
+  Current = skip_while(&Scanner::skip_ns_char, Current);
+  StringRef Name(NameStart, Current - NameStart);
+  Current = skip_while(&Scanner::skip_s_white, Current);
+
+  if (Name == "YAML") {
+    Current = skip_while(&Scanner::skip_ns_char, Current);
+    Token T;
+    T.Kind = Token::TK_VersionDirective;
+    T.Range = StringRef(Start, Current - Start);
+    TokenQueue.push_back(T);
+    return true;
+  }
+  return false;
+}
+
+bool Scanner::scanDocumentIndicator(bool IsStart) {
+  unrollIndent(-1);
+  SimpleKeys.clear();
+  IsSimpleKeyAllowed = false;
+
+  Token T;
+  T.Kind = IsStart ? Token::TK_DocumentStart : Token::TK_DocumentEnd;
+  T.Range = StringRef(Current, 3);
+  skip(3);
+  TokenQueue.push_back(T);
+  return true;
+}
+
+bool Scanner::scanFlowCollectionStart(bool IsSequence) {
+  Token T;
+  T.Kind = IsSequence ? Token::TK_FlowSequenceStart
+                      : Token::TK_FlowMappingStart;
+  T.Range = StringRef(Current, 1);
+  skip(1);
+  TokenQueue.push_back(T);
+
+  // [ and { may begin a simple key.
+  saveSimpleKeyCandidate(TokenQueue.back(), Column - 1, false);
+
+  // And may also be followed by a simple key.
+  IsSimpleKeyAllowed = true;
+  ++FlowLevel;
+  return true;
+}
+
+bool Scanner::scanFlowCollectionEnd(bool IsSequence) {
+  removeSimpleKeyCandidatesOnFlowLevel(FlowLevel);
+  IsSimpleKeyAllowed = false;
+  Token T;
+  T.Kind = IsSequence ? Token::TK_FlowSequenceEnd
+                      : Token::TK_FlowMappingEnd;
+  T.Range = StringRef(Current, 1);
+  skip(1);
+  TokenQueue.push_back(T);
+  if (FlowLevel)
+    --FlowLevel;
+  return true;
+}
+
+bool Scanner::scanFlowEntry() {
+  removeSimpleKeyCandidatesOnFlowLevel(FlowLevel);
+  IsSimpleKeyAllowed = true;
+  Token T;
+  T.Kind = Token::TK_FlowEntry;
+  T.Range = StringRef(Current, 1);
+  skip(1);
+  TokenQueue.push_back(T);
+  return true;
+}
+
+bool Scanner::scanBlockEntry() {
+  rollIndent(Column, Token::TK_BlockSequenceStart, TokenQueue.end());
+  removeSimpleKeyCandidatesOnFlowLevel(FlowLevel);
+  IsSimpleKeyAllowed = true;
+  Token T;
+  T.Kind = Token::TK_BlockEntry;
+  T.Range = StringRef(Current, 1);
+  skip(1);
+  TokenQueue.push_back(T);
+  return true;
+}
+
+bool Scanner::scanKey() {
+  if (!FlowLevel)
+    rollIndent(Column, Token::TK_BlockMappingStart, TokenQueue.end());
+
+  removeSimpleKeyCandidatesOnFlowLevel(FlowLevel);
+  IsSimpleKeyAllowed = !FlowLevel;
+
+  Token T;
+  T.Kind = Token::TK_Key;
+  T.Range = StringRef(Current, 1);
+  skip(1);
+  TokenQueue.push_back(T);
+  return true;
+}
+
+bool Scanner::scanValue() {
+  // If the previous token could have been a simple key, insert the key token
+  // into the token queue.
+  if (!SimpleKeys.empty()) {
+    SimpleKey SK = SimpleKeys.pop_back_val();
+    Token T;
+    T.Kind = Token::TK_Key;
+    T.Range = SK.Tok->Range;
+    TokenQueueT::iterator i, e;
+    for (i = TokenQueue.begin(), e = TokenQueue.end(); i != e; ++i) {
+      if (i == SK.Tok)
+        break;
+    }
+    assert(i != e && "SimpleKey not in token queue!");
+    i = TokenQueue.insert(i, T);
+
+    // We may also need to add a Block-Mapping-Start token.
+    rollIndent(SK.Column, Token::TK_BlockMappingStart, i);
+
+    IsSimpleKeyAllowed = false;
+  } else {
+    if (!FlowLevel)
+      rollIndent(Column, Token::TK_BlockMappingStart, TokenQueue.end());
+    IsSimpleKeyAllowed = !FlowLevel;
+  }
+
+  Token T;
+  T.Kind = Token::TK_Value;
+  T.Range = StringRef(Current, 1);
+  skip(1);
+  TokenQueue.push_back(T);
+  return true;
+}
+
+// Forbidding inlining improves performance by roughly 20%.
+// FIXME: Remove once llvm optimizes this to the faster version without hints.
+LLVM_ATTRIBUTE_NOINLINE static bool
+wasEscaped(StringRef::iterator First, StringRef::iterator Position);
+
+// Returns whether a character at 'Position' was escaped with a leading '\'.
+// 'First' specifies the position of the first character in the string.
+static bool wasEscaped(StringRef::iterator First,
+                       StringRef::iterator Position) {
+  assert(Position - 1 >= First);
+  StringRef::iterator I = Position - 1;
+  // We calculate the number of consecutive '\'s before the current position
+  // by iterating backwards through our string.
+  while (I >= First && *I == '\\') --I;
+  // (Position - 1 - I) now contains the number of '\'s before the current
+  // position. If it is odd, the character at 'Position' was escaped.
+  return (Position - 1 - I) % 2 == 1;
+}
+
+bool Scanner::scanFlowScalar(bool IsDoubleQuoted) {
+  StringRef::iterator Start = Current;
+  unsigned ColStart = Column;
+  if (IsDoubleQuoted) {
+    do {
+      ++Current;
+      while (Current != End && *Current != '"')
+        ++Current;
+      // Repeat until the previous character was not a '\' or was an escaped
+      // backslash.
+    } while (*(Current - 1) == '\\' && wasEscaped(Start + 1, Current));
+  } else {
+    skip(1);
+    while (true) {
+      // Skip a ' followed by another '.
+      if (Current + 1 < End && *Current == '\'' && *(Current + 1) == '\'') {
+        skip(2);
+        continue;
+      } else if (*Current == '\'')
+        break;
+      StringRef::iterator i = skip_nb_char(Current);
+      if (i == Current) {
+        i = skip_b_break(Current);
+        if (i == Current)
+          break;
+        Current = i;
+        Column = 0;
+        ++Line;
+      } else {
+        if (i == End)
+          break;
+        Current = i;
+        ++Column;
+      }
+    }
+  }
+  skip(1); // Skip ending quote.
+  Token T;
+  T.Kind = Token::TK_Scalar;
+  T.Range = StringRef(Start, Current - Start);
+  TokenQueue.push_back(T);
+
+  saveSimpleKeyCandidate(TokenQueue.back(), ColStart, false);
+
+  IsSimpleKeyAllowed = false;
+
+  return true;
+}
+
+bool Scanner::scanPlainScalar() {
+  StringRef::iterator Start = Current;
+  unsigned ColStart = Column;
+  unsigned LeadingBlanks = 0;
+  assert(Indent >= -1 && "Indent must be >= -1 !");
+  unsigned indent = static_cast<unsigned>(Indent + 1);
+  while (true) {
+    if (*Current == '#')
+      break;
+
+    while (!isBlankOrBreak(Current)) {
+      if (  FlowLevel && *Current == ':'
+          && !(isBlankOrBreak(Current + 1) || *(Current + 1) == ',')) {
+        setError("Found unexpected ':' while scanning a plain scalar", Current);
+        return false;
+      }
+
+      // Check for the end of the plain scalar.
+      if (  (*Current == ':' && isBlankOrBreak(Current + 1))
+          || (  FlowLevel
+          && (StringRef(Current, 1).find_first_of(",:?[]{}")
+              != StringRef::npos)))
+        break;
+
+      StringRef::iterator i = skip_nb_char(Current);
+      if (i == Current)
+        break;
+      Current = i;
+      ++Column;
+    }
+
+    // Are we at the end?
+    if (!isBlankOrBreak(Current))
+      break;
+
+    // Eat blanks.
+    StringRef::iterator Tmp = Current;
+    while (isBlankOrBreak(Tmp)) {
+      StringRef::iterator i = skip_s_white(Tmp);
+      if (i != Tmp) {
+        if (LeadingBlanks && (Column < indent) && *Tmp == '\t') {
+          setError("Found invalid tab character in indentation", Tmp);
+          return false;
+        }
+        Tmp = i;
+        ++Column;
+      } else {
+        i = skip_b_break(Tmp);
+        if (!LeadingBlanks)
+          LeadingBlanks = 1;
+        Tmp = i;
+        Column = 0;
+        ++Line;
+      }
+    }
+
+    if (!FlowLevel && Column < indent)
+      break;
+
+    Current = Tmp;
+  }
+  if (Start == Current) {
+    setError("Got empty plain scalar", Start);
+    return false;
+  }
+  Token T;
+  T.Kind = Token::TK_Scalar;
+  T.Range = StringRef(Start, Current - Start);
+  TokenQueue.push_back(T);
+
+  // Plain scalars can be simple keys.
+  saveSimpleKeyCandidate(TokenQueue.back(), ColStart, false);
+
+  IsSimpleKeyAllowed = false;
+
+  return true;
+}
+
+bool Scanner::scanAliasOrAnchor(bool IsAlias) {
+  StringRef::iterator Start = Current;
+  unsigned ColStart = Column;
+  skip(1);
+  while(true) {
+    if (   *Current == '[' || *Current == ']'
+        || *Current == '{' || *Current == '}'
+        || *Current == ','
+        || *Current == ':')
+      break;
+    StringRef::iterator i = skip_ns_char(Current);
+    if (i == Current)
+      break;
+    Current = i;
+    ++Column;
+  }
+
+  if (Start == Current) {
+    setError("Got empty alias or anchor", Start);
+    return false;
+  }
+
+  Token T;
+  T.Kind = IsAlias ? Token::TK_Alias : Token::TK_Anchor;
+  T.Range = StringRef(Start, Current - Start);
+  TokenQueue.push_back(T);
+
+  // Alias and anchors can be simple keys.
+  saveSimpleKeyCandidate(TokenQueue.back(), ColStart, false);
+
+  IsSimpleKeyAllowed = false;
+
+  return true;
+}
+
+bool Scanner::scanBlockScalar(bool IsLiteral) {
+  StringRef::iterator Start = Current;
+  skip(1); // Eat | or >
+  while(true) {
+    StringRef::iterator i = skip_nb_char(Current);
+    if (i == Current) {
+      if (Column == 0)
+        break;
+      i = skip_b_break(Current);
+      if (i != Current) {
+        // We got a line break.
+        Column = 0;
+        ++Line;
+        Current = i;
+        continue;
+      } else {
+        // There was an error, which should already have been printed out.
+        return false;
+      }
+    }
+    Current = i;
+    ++Column;
+  }
+
+  if (Start == Current) {
+    setError("Got empty block scalar", Start);
+    return false;
+  }
+
+  Token T;
+  T.Kind = Token::TK_Scalar;
+  T.Range = StringRef(Start, Current - Start);
+  TokenQueue.push_back(T);
+  return true;
+}
+
+bool Scanner::scanTag() {
+  StringRef::iterator Start = Current;
+  unsigned ColStart = Column;
+  skip(1); // Eat !.
+  if (Current == End || isBlankOrBreak(Current)); // An empty tag.
+  else if (*Current == '<') {
+    skip(1);
+    scan_ns_uri_char();
+    if (!consume('>'))
+      return false;
+  } else {
+    // FIXME: Actually parse the c-ns-shorthand-tag rule.
+    Current = skip_while(&Scanner::skip_ns_char, Current);
+  }
+
+  Token T;
+  T.Kind = Token::TK_Tag;
+  T.Range = StringRef(Start, Current - Start);
+  TokenQueue.push_back(T);
+
+  // Tags can be simple keys.
+  saveSimpleKeyCandidate(TokenQueue.back(), ColStart, false);
+
+  IsSimpleKeyAllowed = false;
+
+  return true;
+}
+
+bool Scanner::fetchMoreTokens() {
+  if (IsStartOfStream)
+    return scanStreamStart();
+
+  scanToNextToken();
+
+  if (Current == End)
+    return scanStreamEnd();
+
+  removeStaleSimpleKeyCandidates();
+
+  unrollIndent(Column);
+
+  if (Column == 0 && *Current == '%')
+    return scanDirective();
+
+  if (Column == 0 && Current + 4 <= End
+      && *Current == '-'
+      && *(Current + 1) == '-'
+      && *(Current + 2) == '-'
+      && (Current + 3 == End || isBlankOrBreak(Current + 3)))
+    return scanDocumentIndicator(true);
+
+  if (Column == 0 && Current + 4 <= End
+      && *Current == '.'
+      && *(Current + 1) == '.'
+      && *(Current + 2) == '.'
+      && (Current + 3 == End || isBlankOrBreak(Current + 3)))
+    return scanDocumentIndicator(false);
+
+  if (*Current == '[')
+    return scanFlowCollectionStart(true);
+
+  if (*Current == '{')
+    return scanFlowCollectionStart(false);
+
+  if (*Current == ']')
+    return scanFlowCollectionEnd(true);
+
+  if (*Current == '}')
+    return scanFlowCollectionEnd(false);
+
+  if (*Current == ',')
+    return scanFlowEntry();
+
+  if (*Current == '-' && isBlankOrBreak(Current + 1))
+    return scanBlockEntry();
+
+  if (*Current == '?' && (FlowLevel || isBlankOrBreak(Current + 1)))
+    return scanKey();
+
+  if (*Current == ':' && (FlowLevel || isBlankOrBreak(Current + 1)))
+    return scanValue();
+
+  if (*Current == '*')
+    return scanAliasOrAnchor(true);
+
+  if (*Current == '&')
+    return scanAliasOrAnchor(false);
+
+  if (*Current == '!')
+    return scanTag();
+
+  if (*Current == '|' && !FlowLevel)
+    return scanBlockScalar(true);
+
+  if (*Current == '>' && !FlowLevel)
+    return scanBlockScalar(false);
+
+  if (*Current == '\'')
+    return scanFlowScalar(false);
+
+  if (*Current == '"')
+    return scanFlowScalar(true);
+
+  // Get a plain scalar.
+  StringRef FirstChar(Current, 1);
+  if (!(isBlankOrBreak(Current)
+        || FirstChar.find_first_of("-?:,[]{}#&*!|>'\"%@`") != StringRef::npos)
+      || (*Current == '-' && !isBlankOrBreak(Current + 1))
+      || (!FlowLevel && (*Current == '?' || *Current == ':')
+          && isBlankOrBreak(Current + 1))
+      || (!FlowLevel && *Current == ':'
+                      && Current + 2 < End
+                      && *(Current + 1) == ':'
+                      && !isBlankOrBreak(Current + 2)))
+    return scanPlainScalar();
+
+  setError("Unrecognized character while tokenizing.");
+  return false;
+}
+
+Stream::Stream(StringRef Input, SourceMgr &SM)
+  : scanner(new Scanner(Input, SM))
+  , CurrentDoc(0) {}
+
+bool Stream::failed() { return scanner->failed(); }
+
+void Stream::printError(Node *N, const Twine &Msg) {
+  SmallVector<SMRange, 1> Ranges;
+  Ranges.push_back(N->getSourceRange());
+  scanner->printError( N->getSourceRange().Start
+                     , SourceMgr::DK_Error
+                     , Msg
+                     , Ranges);
+}
+
+void Stream::handleYAMLDirective(const Token &t) {
+  // TODO: Ensure version is 1.x.
+}
+
+document_iterator Stream::begin() {
+  if (CurrentDoc)
+    report_fatal_error("Can only iterate over the stream once");
+
+  // Skip Stream-Start.
+  scanner->getNext();
+
+  CurrentDoc.reset(new Document(*this));
+  return document_iterator(CurrentDoc);
+}
+
+document_iterator Stream::end() {
+  return document_iterator();
+}
+
+void Stream::skip() {
+  for (document_iterator i = begin(), e = end(); i != e; ++i)
+    i->skip();
+}
+
+Node::Node(unsigned int Type, OwningPtr<Document> &D, StringRef A)
+  : Doc(D)
+  , TypeID(Type)
+  , Anchor(A) {
+  SMLoc Start = SMLoc::getFromPointer(peekNext().Range.begin());
+  SourceRange = SMRange(Start, Start);
+}
+
+Node::~Node() {}
+
+Token &Node::peekNext() {
+  return Doc->peekNext();
+}
+
+Token Node::getNext() {
+  return Doc->getNext();
+}
+
+Node *Node::parseBlockNode() {
+  return Doc->parseBlockNode();
+}
+
+BumpPtrAllocator &Node::getAllocator() {
+  return Doc->NodeAllocator;
+}
+
+void Node::setError(const Twine &Msg, Token &Tok) const {
+  Doc->setError(Msg, Tok);
+}
+
+bool Node::failed() const {
+  return Doc->failed();
+}
+
+
+
+StringRef ScalarNode::getValue(SmallVectorImpl<char> &Storage) const {
+  // TODO: Handle newlines properly. We need to remove leading whitespace.
+  if (Value[0] == '"') { // Double quoted.
+    // Pull off the leading and trailing "s.
+    StringRef UnquotedValue = Value.substr(1, Value.size() - 2);
+    // Search for characters that would require unescaping the value.
+    StringRef::size_type i = UnquotedValue.find_first_of("\\\r\n");
+    if (i != StringRef::npos)
+      return unescapeDoubleQuoted(UnquotedValue, i, Storage);
+    return UnquotedValue;
+  } else if (Value[0] == '\'') { // Single quoted.
+    // Pull off the leading and trailing 's.
+    StringRef UnquotedValue = Value.substr(1, Value.size() - 2);
+    StringRef::size_type i = UnquotedValue.find('\'');
+    if (i != StringRef::npos) {
+      // We're going to need Storage.
+      Storage.clear();
+      Storage.reserve(UnquotedValue.size());
+      for (; i != StringRef::npos; i = UnquotedValue.find('\'')) {
+        StringRef Valid(UnquotedValue.begin(), i);
+        Storage.insert(Storage.end(), Valid.begin(), Valid.end());
+        Storage.push_back('\'');
+        UnquotedValue = UnquotedValue.substr(i + 2);
+      }
+      Storage.insert(Storage.end(), UnquotedValue.begin(), UnquotedValue.end());
+      return StringRef(Storage.begin(), Storage.size());
+    }
+    return UnquotedValue;
+  }
+  // Plain or block.
+  size_t trimtrail = Value.rfind(' ');
+  return Value.drop_back(
+    trimtrail == StringRef::npos ? 0 : Value.size() - trimtrail);
+}
+
+StringRef ScalarNode::unescapeDoubleQuoted( StringRef UnquotedValue
+                                          , StringRef::size_type i
+                                          , SmallVectorImpl<char> &Storage)
+                                          const {
+  // Use Storage to build proper value.
+  Storage.clear();
+  Storage.reserve(UnquotedValue.size());
+  for (; i != StringRef::npos; i = UnquotedValue.find_first_of("\\\r\n")) {
+    // Insert all previous chars into Storage.
+    StringRef Valid(UnquotedValue.begin(), i);
+    Storage.insert(Storage.end(), Valid.begin(), Valid.end());
+    // Chop off inserted chars.
+    UnquotedValue = UnquotedValue.substr(i);
+
+    assert(!UnquotedValue.empty() && "Can't be empty!");
+
+    // Parse escape or line break.
+    switch (UnquotedValue[0]) {
+    case '\r':
+    case '\n':
+      Storage.push_back('\n');
+      if (   UnquotedValue.size() > 1
+          && (UnquotedValue[1] == '\r' || UnquotedValue[1] == '\n'))
+        UnquotedValue = UnquotedValue.substr(1);
+      UnquotedValue = UnquotedValue.substr(1);
+      break;
+    default:
+      if (UnquotedValue.size() == 1)
+        // TODO: Report error.
+        break;
+      UnquotedValue = UnquotedValue.substr(1);
+      switch (UnquotedValue[0]) {
+      default: {
+          Token T;
+          T.Range = StringRef(UnquotedValue.begin(), 1);
+          setError("Unrecognized escape code!", T);
+          return "";
+        }
+      case '\r':
+      case '\n':
+        // Remove the new line.
+        if (   UnquotedValue.size() > 1
+            && (UnquotedValue[1] == '\r' || UnquotedValue[1] == '\n'))
+          UnquotedValue = UnquotedValue.substr(1);
+        // If this was just a single byte newline, it will get skipped
+        // below.
+        break;
+      case '0':
+        Storage.push_back(0x00);
+        break;
+      case 'a':
+        Storage.push_back(0x07);
+        break;
+      case 'b':
+        Storage.push_back(0x08);
+        break;
+      case 't':
+      case 0x09:
+        Storage.push_back(0x09);
+        break;
+      case 'n':
+        Storage.push_back(0x0A);
+        break;
+      case 'v':
+        Storage.push_back(0x0B);
+        break;
+      case 'f':
+        Storage.push_back(0x0C);
+        break;
+      case 'r':
+        Storage.push_back(0x0D);
+        break;
+      case 'e':
+        Storage.push_back(0x1B);
+        break;
+      case ' ':
+        Storage.push_back(0x20);
+        break;
+      case '"':
+        Storage.push_back(0x22);
+        break;
+      case '/':
+        Storage.push_back(0x2F);
+        break;
+      case '\\':
+        Storage.push_back(0x5C);
+        break;
+      case 'N':
+        encodeUTF8(0x85, Storage);
+        break;
+      case '_':
+        encodeUTF8(0xA0, Storage);
+        break;
+      case 'L':
+        encodeUTF8(0x2028, Storage);
+        break;
+      case 'P':
+        encodeUTF8(0x2029, Storage);
+        break;
+      case 'x': {
+          if (UnquotedValue.size() < 3)
+            // TODO: Report error.
+            break;
+          unsigned int UnicodeScalarValue;
+          UnquotedValue.substr(1, 2).getAsInteger(16, UnicodeScalarValue);
+          encodeUTF8(UnicodeScalarValue, Storage);
+          UnquotedValue = UnquotedValue.substr(2);
+          break;
+        }
+      case 'u': {
+          if (UnquotedValue.size() < 5)
+            // TODO: Report error.
+            break;
+          unsigned int UnicodeScalarValue;
+          UnquotedValue.substr(1, 4).getAsInteger(16, UnicodeScalarValue);
+          encodeUTF8(UnicodeScalarValue, Storage);
+          UnquotedValue = UnquotedValue.substr(4);
+          break;
+        }
+      case 'U': {
+          if (UnquotedValue.size() < 9)
+            // TODO: Report error.
+            break;
+          unsigned int UnicodeScalarValue;
+          UnquotedValue.substr(1, 8).getAsInteger(16, UnicodeScalarValue);
+          encodeUTF8(UnicodeScalarValue, Storage);
+          UnquotedValue = UnquotedValue.substr(8);
+          break;
+        }
+      }
+      UnquotedValue = UnquotedValue.substr(1);
+    }
+  }
+  Storage.insert(Storage.end(), UnquotedValue.begin(), UnquotedValue.end());
+  return StringRef(Storage.begin(), Storage.size());
+}
+
+Node *KeyValueNode::getKey() {
+  if (Key)
+    return Key;
+  // Handle implicit null keys.
+  {
+    Token &t = peekNext();
+    if (   t.Kind == Token::TK_BlockEnd
+        || t.Kind == Token::TK_Value
+        || t.Kind == Token::TK_Error) {
+      return Key = new (getAllocator()) NullNode(Doc);
+    }
+    if (t.Kind == Token::TK_Key)
+      getNext(); // skip TK_Key.
+  }
+
+  // Handle explicit null keys.
+  Token &t = peekNext();
+  if (t.Kind == Token::TK_BlockEnd || t.Kind == Token::TK_Value) {
+    return Key = new (getAllocator()) NullNode(Doc);
+  }
+
+  // We've got a normal key.
+  return Key = parseBlockNode();
+}
+
+Node *KeyValueNode::getValue() {
+  if (Value)
+    return Value;
+  getKey()->skip();
+  if (failed())
+    return Value = new (getAllocator()) NullNode(Doc);
+
+  // Handle implicit null values.
+  {
+    Token &t = peekNext();
+    if (   t.Kind == Token::TK_BlockEnd
+        || t.Kind == Token::TK_FlowMappingEnd
+        || t.Kind == Token::TK_Key
+        || t.Kind == Token::TK_FlowEntry
+        || t.Kind == Token::TK_Error) {
+      return Value = new (getAllocator()) NullNode(Doc);
+    }
+
+    if (t.Kind != Token::TK_Value) {
+      setError("Unexpected token in Key Value.", t);
+      return Value = new (getAllocator()) NullNode(Doc);
+    }
+    getNext(); // skip TK_Value.
+  }
+
+  // Handle explicit null values.
+  Token &t = peekNext();
+  if (t.Kind == Token::TK_BlockEnd || t.Kind == Token::TK_Key) {
+    return Value = new (getAllocator()) NullNode(Doc);
+  }
+
+  // We got a normal value.
+  return Value = parseBlockNode();
+}
+
+void MappingNode::increment() {
+  if (failed()) {
+    IsAtEnd = true;
+    CurrentEntry = 0;
+    return;
+  }
+  if (CurrentEntry) {
+    CurrentEntry->skip();
+    if (Type == MT_Inline) {
+      IsAtEnd = true;
+      CurrentEntry = 0;
+      return;
+    }
+  }
+  Token T = peekNext();
+  if (T.Kind == Token::TK_Key || T.Kind == Token::TK_Scalar) {
+    // KeyValueNode eats the TK_Key. That way it can detect null keys.
+    CurrentEntry = new (getAllocator()) KeyValueNode(Doc);
+  } else if (Type == MT_Block) {
+    switch (T.Kind) {
+    case Token::TK_BlockEnd:
+      getNext();
+      IsAtEnd = true;
+      CurrentEntry = 0;
+      break;
+    default:
+      setError("Unexpected token. Expected Key or Block End", T);
+    case Token::TK_Error:
+      IsAtEnd = true;
+      CurrentEntry = 0;
+    }
+  } else {
+    switch (T.Kind) {
+    case Token::TK_FlowEntry:
+      // Eat the flow entry and recurse.
+      getNext();
+      return increment();
+    case Token::TK_FlowMappingEnd:
+      getNext();
+    case Token::TK_Error:
+      // Set this to end iterator.
+      IsAtEnd = true;
+      CurrentEntry = 0;
+      break;
+    default:
+      setError( "Unexpected token. Expected Key, Flow Entry, or Flow "
+                "Mapping End."
+              , T);
+      IsAtEnd = true;
+      CurrentEntry = 0;
+    }
+  }
+}
+
+void SequenceNode::increment() {
+  if (failed()) {
+    IsAtEnd = true;
+    CurrentEntry = 0;
+    return;
+  }
+  if (CurrentEntry)
+    CurrentEntry->skip();
+  Token T = peekNext();
+  if (SeqType == ST_Block) {
+    switch (T.Kind) {
+    case Token::TK_BlockEntry:
+      getNext();
+      CurrentEntry = parseBlockNode();
+      if (CurrentEntry == 0) { // An error occurred.
+        IsAtEnd = true;
+        CurrentEntry = 0;
+      }
+      break;
+    case Token::TK_BlockEnd:
+      getNext();
+      IsAtEnd = true;
+      CurrentEntry = 0;
+      break;
+    default:
+      setError( "Unexpected token. Expected Block Entry or Block End."
+              , T);
+    case Token::TK_Error:
+      IsAtEnd = true;
+      CurrentEntry = 0;
+    }
+  } else if (SeqType == ST_Indentless) {
+    switch (T.Kind) {
+    case Token::TK_BlockEntry:
+      getNext();
+      CurrentEntry = parseBlockNode();
+      if (CurrentEntry == 0) { // An error occurred.
+        IsAtEnd = true;
+        CurrentEntry = 0;
+      }
+      break;
+    default:
+    case Token::TK_Error:
+      IsAtEnd = true;
+      CurrentEntry = 0;
+    }
+  } else if (SeqType == ST_Flow) {
+    switch (T.Kind) {
+    case Token::TK_FlowEntry:
+      // Eat the flow entry and recurse.
+      getNext();
+      WasPreviousTokenFlowEntry = true;
+      return increment();
+    case Token::TK_FlowSequenceEnd:
+      getNext();
+    case Token::TK_Error:
+      // Set this to end iterator.
+      IsAtEnd = true;
+      CurrentEntry = 0;
+      break;
+    case Token::TK_StreamEnd:
+    case Token::TK_DocumentEnd:
+    case Token::TK_DocumentStart:
+      setError("Could not find closing ]!", T);
+      // Set this to end iterator.
+      IsAtEnd = true;
+      CurrentEntry = 0;
+      break;
+    default:
+      if (!WasPreviousTokenFlowEntry) {
+        setError("Expected , between entries!", T);
+        IsAtEnd = true;
+        CurrentEntry = 0;
+        break;
+      }
+      // Otherwise it must be a flow entry.
+      CurrentEntry = parseBlockNode();
+      if (!CurrentEntry) {
+        IsAtEnd = true;
+      }
+      WasPreviousTokenFlowEntry = false;
+      break;
+    }
+  }
+}
+
+Document::Document(Stream &S) : stream(S), Root(0) {
+  if (parseDirectives())
+    expectToken(Token::TK_DocumentStart);
+  Token &T = peekNext();
+  if (T.Kind == Token::TK_DocumentStart)
+    getNext();
+}
+
+bool Document::skip()  {
+  if (stream.scanner->failed())
+    return false;
+  if (!Root)
+    getRoot();
+  Root->skip();
+  Token &T = peekNext();
+  if (T.Kind == Token::TK_StreamEnd)
+    return false;
+  if (T.Kind == Token::TK_DocumentEnd) {
+    getNext();
+    return skip();
+  }
+  return true;
+}
+
+Token &Document::peekNext() {
+  return stream.scanner->peekNext();
+}
+
+Token Document::getNext() {
+  return stream.scanner->getNext();
+}
+
+void Document::setError(const Twine &Message, Token &Location) const {
+  stream.scanner->setError(Message, Location.Range.begin());
+}
+
+bool Document::failed() const {
+  return stream.scanner->failed();
+}
+
+Node *Document::parseBlockNode() {
+  Token T = peekNext();
+  // Handle properties.
+  Token AnchorInfo;
+parse_property:
+  switch (T.Kind) {
+  case Token::TK_Alias:
+    getNext();
+    return new (NodeAllocator) AliasNode(stream.CurrentDoc, T.Range.substr(1));
+  case Token::TK_Anchor:
+    if (AnchorInfo.Kind == Token::TK_Anchor) {
+      setError("Already encountered an anchor for this node!", T);
+      return 0;
+    }
+    AnchorInfo = getNext(); // Consume TK_Anchor.
+    T = peekNext();
+    goto parse_property;
+  case Token::TK_Tag:
+    getNext(); // Skip TK_Tag.
+    T = peekNext();
+    goto parse_property;
+  default:
+    break;
+  }
+
+  switch (T.Kind) {
+  case Token::TK_BlockEntry:
+    // We got an unindented BlockEntry sequence. This is not terminated with
+    // a BlockEnd.
+    // Don't eat the TK_BlockEntry, SequenceNode needs it.
+    return new (NodeAllocator) SequenceNode( stream.CurrentDoc
+                                           , AnchorInfo.Range.substr(1)
+                                           , SequenceNode::ST_Indentless);
+  case Token::TK_BlockSequenceStart:
+    getNext();
+    return new (NodeAllocator)
+      SequenceNode( stream.CurrentDoc
+                  , AnchorInfo.Range.substr(1)
+                  , SequenceNode::ST_Block);
+  case Token::TK_BlockMappingStart:
+    getNext();
+    return new (NodeAllocator)
+      MappingNode( stream.CurrentDoc
+                 , AnchorInfo.Range.substr(1)
+                 , MappingNode::MT_Block);
+  case Token::TK_FlowSequenceStart:
+    getNext();
+    return new (NodeAllocator)
+      SequenceNode( stream.CurrentDoc
+                  , AnchorInfo.Range.substr(1)
+                  , SequenceNode::ST_Flow);
+  case Token::TK_FlowMappingStart:
+    getNext();
+    return new (NodeAllocator)
+      MappingNode( stream.CurrentDoc
+                 , AnchorInfo.Range.substr(1)
+                 , MappingNode::MT_Flow);
+  case Token::TK_Scalar:
+    getNext();
+    return new (NodeAllocator)
+      ScalarNode( stream.CurrentDoc
+                , AnchorInfo.Range.substr(1)
+                , T.Range);
+  case Token::TK_Key:
+    // Don't eat the TK_Key, KeyValueNode expects it.
+    return new (NodeAllocator)
+      MappingNode( stream.CurrentDoc
+                 , AnchorInfo.Range.substr(1)
+                 , MappingNode::MT_Inline);
+  case Token::TK_DocumentStart:
+  case Token::TK_DocumentEnd:
+  case Token::TK_StreamEnd:
+  default:
+    // TODO: Properly handle tags. "[!!str ]" should resolve to !!str "", not
+    //       !!null null.
+    return new (NodeAllocator) NullNode(stream.CurrentDoc);
+  case Token::TK_Error:
+    return 0;
+  }
+  llvm_unreachable("Control flow shouldn't reach here.");
+  return 0;
+}
+
+bool Document::parseDirectives() {
+  bool isDirective = false;
+  while (true) {
+    Token T = peekNext();
+    if (T.Kind == Token::TK_TagDirective) {
+      handleTagDirective(getNext());
+      isDirective = true;
+    } else if (T.Kind == Token::TK_VersionDirective) {
+      stream.handleYAMLDirective(getNext());
+      isDirective = true;
+    } else
+      break;
+  }
+  return isDirective;
+}
+
+bool Document::expectToken(int TK) {
+  Token T = getNext();
+  if (T.Kind != TK) {
+    setError("Unexpected token", T);
+    return false;
+  }
+  return true;
+}
+
+OwningPtr<Document> document_iterator::NullDoc;