summaryrefslogtreecommitdiff
path: root/deps/v8/src/regexp/regexp-ast.h
blob: 3de29512ea12b0446777a7d66e289bf2743bf694 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
// Copyright 2016 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_REGEXP_REGEXP_AST_H_
#define V8_REGEXP_REGEXP_AST_H_

#include "src/objects/js-regexp.h"
#include "src/objects/objects.h"
#include "src/objects/string.h"
#include "src/utils/utils.h"
#include "src/zone/zone-containers.h"
#include "src/zone/zone.h"

namespace v8 {
namespace internal {

#define FOR_EACH_REG_EXP_TREE_TYPE(VISIT) \
  VISIT(Disjunction)                      \
  VISIT(Alternative)                      \
  VISIT(Assertion)                        \
  VISIT(CharacterClass)                   \
  VISIT(Atom)                             \
  VISIT(Quantifier)                       \
  VISIT(Capture)                          \
  VISIT(Group)                            \
  VISIT(Lookaround)                       \
  VISIT(BackReference)                    \
  VISIT(Empty)                            \
  VISIT(Text)

#define FORWARD_DECLARE(Name) class RegExp##Name;
FOR_EACH_REG_EXP_TREE_TYPE(FORWARD_DECLARE)
#undef FORWARD_DECLARE

class RegExpCompiler;
class RegExpNode;
class RegExpTree;

class RegExpVisitor {
 public:
  virtual ~RegExpVisitor() = default;
#define MAKE_CASE(Name) \
  virtual void* Visit##Name(RegExp##Name*, void* data) = 0;
  FOR_EACH_REG_EXP_TREE_TYPE(MAKE_CASE)
#undef MAKE_CASE
};


// A simple closed interval.
class Interval {
 public:
  Interval() : from_(kNone), to_(kNone - 1) {}  // '- 1' for branchless size().
  Interval(int from, int to) : from_(from), to_(to) {}
  Interval Union(Interval that) {
    if (that.from_ == kNone)
      return *this;
    else if (from_ == kNone)
      return that;
    else
      return Interval(Min(from_, that.from_), Max(to_, that.to_));
  }

  bool Contains(int value) { return (from_ <= value) && (value <= to_); }
  bool is_empty() { return from_ == kNone; }
  int from() const { return from_; }
  int to() const { return to_; }
  int size() const { return to_ - from_ + 1; }

  static Interval Empty() { return Interval(); }

  static constexpr int kNone = -1;

 private:
  int from_;
  int to_;
};


// Represents code units in the range from from_ to to_, both ends are
// inclusive.
class CharacterRange {
 public:
  CharacterRange() : from_(0), to_(0) {}
  // For compatibility with the CHECK_OK macro
  CharacterRange(void* null) { DCHECK_NULL(null); }  // NOLINT
  V8_EXPORT_PRIVATE static void AddClassEscape(char type,
                                               ZoneList<CharacterRange>* ranges,
                                               Zone* zone);
  // Add class escapes. Add case equivalent closure for \w and \W if necessary.
  V8_EXPORT_PRIVATE static void AddClassEscape(
      char type, ZoneList<CharacterRange>* ranges,
      bool add_unicode_case_equivalents, Zone* zone);
  static Vector<const int> GetWordBounds();
  static inline CharacterRange Singleton(uc32 value) {
    return CharacterRange(value, value);
  }
  static inline CharacterRange Range(uc32 from, uc32 to) {
    DCHECK(0 <= from && to <= String::kMaxCodePoint);
    DCHECK(static_cast<uint32_t>(from) <= static_cast<uint32_t>(to));
    return CharacterRange(from, to);
  }
  static inline CharacterRange Everything() {
    return CharacterRange(0, String::kMaxCodePoint);
  }
  static inline ZoneList<CharacterRange>* List(Zone* zone,
                                               CharacterRange range) {
    ZoneList<CharacterRange>* list =
        new (zone) ZoneList<CharacterRange>(1, zone);
    list->Add(range, zone);
    return list;
  }
  bool Contains(uc32 i) { return from_ <= i && i <= to_; }
  uc32 from() const { return from_; }
  void set_from(uc32 value) { from_ = value; }
  uc32 to() const { return to_; }
  void set_to(uc32 value) { to_ = value; }
  bool is_valid() { return from_ <= to_; }
  bool IsEverything(uc32 max) { return from_ == 0 && to_ >= max; }
  bool IsSingleton() { return (from_ == to_); }
  V8_EXPORT_PRIVATE static void AddCaseEquivalents(
      Isolate* isolate, Zone* zone, ZoneList<CharacterRange>* ranges,
      bool is_one_byte);
  // Whether a range list is in canonical form: Ranges ordered by from value,
  // and ranges non-overlapping and non-adjacent.
  V8_EXPORT_PRIVATE static bool IsCanonical(ZoneList<CharacterRange>* ranges);
  // Convert range list to canonical form. The characters covered by the ranges
  // will still be the same, but no character is in more than one range, and
  // adjacent ranges are merged. The resulting list may be shorter than the
  // original, but cannot be longer.
  static void Canonicalize(ZoneList<CharacterRange>* ranges);
  // Negate the contents of a character range in canonical form.
  static void Negate(ZoneList<CharacterRange>* src,
                     ZoneList<CharacterRange>* dst, Zone* zone);
  static const int kStartMarker = (1 << 24);
  static const int kPayloadMask = (1 << 24) - 1;

 private:
  CharacterRange(uc32 from, uc32 to) : from_(from), to_(to) {}

  uc32 from_;
  uc32 to_;
};

class CharacterSet final {
 public:
  explicit CharacterSet(uc16 standard_set_type)
      : ranges_(nullptr), standard_set_type_(standard_set_type) {}
  explicit CharacterSet(ZoneList<CharacterRange>* ranges)
      : ranges_(ranges), standard_set_type_(0) {}
  ZoneList<CharacterRange>* ranges(Zone* zone);
  uc16 standard_set_type() const { return standard_set_type_; }
  void set_standard_set_type(uc16 special_set_type) {
    standard_set_type_ = special_set_type;
  }
  bool is_standard() { return standard_set_type_ != 0; }
  V8_EXPORT_PRIVATE void Canonicalize();

 private:
  ZoneList<CharacterRange>* ranges_;
  // If non-zero, the value represents a standard set (e.g., all whitespace
  // characters) without having to expand the ranges.
  uc16 standard_set_type_;
};

class TextElement final {
 public:
  enum TextType { ATOM, CHAR_CLASS };

  static TextElement Atom(RegExpAtom* atom);
  static TextElement CharClass(RegExpCharacterClass* char_class);

  int cp_offset() const { return cp_offset_; }
  void set_cp_offset(int cp_offset) { cp_offset_ = cp_offset; }
  int length() const;

  TextType text_type() const { return text_type_; }

  RegExpTree* tree() const { return tree_; }

  RegExpAtom* atom() const {
    DCHECK(text_type() == ATOM);
    return reinterpret_cast<RegExpAtom*>(tree());
  }

  RegExpCharacterClass* char_class() const {
    DCHECK(text_type() == CHAR_CLASS);
    return reinterpret_cast<RegExpCharacterClass*>(tree());
  }

 private:
  TextElement(TextType text_type, RegExpTree* tree)
      : cp_offset_(-1), text_type_(text_type), tree_(tree) {}

  int cp_offset_;
  TextType text_type_;
  RegExpTree* tree_;
};


class RegExpTree : public ZoneObject {
 public:
  static const int kInfinity = kMaxInt;
  virtual ~RegExpTree() = default;
  virtual void* Accept(RegExpVisitor* visitor, void* data) = 0;
  virtual RegExpNode* ToNode(RegExpCompiler* compiler,
                             RegExpNode* on_success) = 0;
  virtual bool IsTextElement() { return false; }
  virtual bool IsAnchoredAtStart() { return false; }
  virtual bool IsAnchoredAtEnd() { return false; }
  virtual int min_match() = 0;
  virtual int max_match() = 0;
  // Returns the interval of registers used for captures within this
  // expression.
  virtual Interval CaptureRegisters() { return Interval::Empty(); }
  virtual void AppendToText(RegExpText* text, Zone* zone);
  V8_EXPORT_PRIVATE std::ostream& Print(std::ostream& os,
                                        Zone* zone);  // NOLINT
#define MAKE_ASTYPE(Name)           \
  virtual RegExp##Name* As##Name(); \
  virtual bool Is##Name();
  FOR_EACH_REG_EXP_TREE_TYPE(MAKE_ASTYPE)
#undef MAKE_ASTYPE
};


class RegExpDisjunction final : public RegExpTree {
 public:
  explicit RegExpDisjunction(ZoneList<RegExpTree*>* alternatives);
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpDisjunction* AsDisjunction() override;
  Interval CaptureRegisters() override;
  bool IsDisjunction() override;
  bool IsAnchoredAtStart() override;
  bool IsAnchoredAtEnd() override;
  int min_match() override { return min_match_; }
  int max_match() override { return max_match_; }
  ZoneList<RegExpTree*>* alternatives() { return alternatives_; }

 private:
  bool SortConsecutiveAtoms(RegExpCompiler* compiler);
  void RationalizeConsecutiveAtoms(RegExpCompiler* compiler);
  void FixSingleCharacterDisjunctions(RegExpCompiler* compiler);
  ZoneList<RegExpTree*>* alternatives_;
  int min_match_;
  int max_match_;
};


class RegExpAlternative final : public RegExpTree {
 public:
  explicit RegExpAlternative(ZoneList<RegExpTree*>* nodes);
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpAlternative* AsAlternative() override;
  Interval CaptureRegisters() override;
  bool IsAlternative() override;
  bool IsAnchoredAtStart() override;
  bool IsAnchoredAtEnd() override;
  int min_match() override { return min_match_; }
  int max_match() override { return max_match_; }
  ZoneList<RegExpTree*>* nodes() { return nodes_; }

 private:
  ZoneList<RegExpTree*>* nodes_;
  int min_match_;
  int max_match_;
};


class RegExpAssertion final : public RegExpTree {
 public:
  enum AssertionType {
    START_OF_LINE = 0,
    START_OF_INPUT = 1,
    END_OF_LINE = 2,
    END_OF_INPUT = 3,
    BOUNDARY = 4,
    NON_BOUNDARY = 5,
    LAST_TYPE = NON_BOUNDARY,
  };
  RegExpAssertion(AssertionType type, JSRegExp::Flags flags)
      : assertion_type_(type), flags_(flags) {}
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpAssertion* AsAssertion() override;
  bool IsAssertion() override;
  bool IsAnchoredAtStart() override;
  bool IsAnchoredAtEnd() override;
  int min_match() override { return 0; }
  int max_match() override { return 0; }
  AssertionType assertion_type() const { return assertion_type_; }
  JSRegExp::Flags flags() const { return flags_; }

 private:
  const AssertionType assertion_type_;
  const JSRegExp::Flags flags_;
};


class RegExpCharacterClass final : public RegExpTree {
 public:
  // NEGATED: The character class is negated and should match everything but
  //     the specified ranges.
  // CONTAINS_SPLIT_SURROGATE: The character class contains part of a split
  //     surrogate and should not be unicode-desugared (crbug.com/641091).
  enum Flag {
    NEGATED = 1 << 0,
    CONTAINS_SPLIT_SURROGATE = 1 << 1,
  };
  using CharacterClassFlags = base::Flags<Flag>;

  RegExpCharacterClass(
      Zone* zone, ZoneList<CharacterRange>* ranges, JSRegExp::Flags flags,
      CharacterClassFlags character_class_flags = CharacterClassFlags())
      : set_(ranges),
        flags_(flags),
        character_class_flags_(character_class_flags) {
    // Convert the empty set of ranges to the negated Everything() range.
    if (ranges->is_empty()) {
      ranges->Add(CharacterRange::Everything(), zone);
      character_class_flags_ ^= NEGATED;
    }
  }
  RegExpCharacterClass(uc16 type, JSRegExp::Flags flags)
      : set_(type),
        flags_(flags),
        character_class_flags_(CharacterClassFlags()) {}
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpCharacterClass* AsCharacterClass() override;
  bool IsCharacterClass() override;
  bool IsTextElement() override { return true; }
  int min_match() override { return 1; }
  // The character class may match two code units for unicode regexps.
  // TODO(yangguo): we should split this class for usage in TextElement, and
  //                make max_match() dependent on the character class content.
  int max_match() override { return 2; }
  void AppendToText(RegExpText* text, Zone* zone) override;
  CharacterSet character_set() { return set_; }
  // TODO(lrn): Remove need for complex version if is_standard that
  // recognizes a mangled standard set and just do { return set_.is_special(); }
  bool is_standard(Zone* zone);
  // Returns a value representing the standard character set if is_standard()
  // returns true.
  // Currently used values are:
  // s : unicode whitespace
  // S : unicode non-whitespace
  // w : ASCII word character (digit, letter, underscore)
  // W : non-ASCII word character
  // d : ASCII digit
  // D : non-ASCII digit
  // . : non-newline
  // * : All characters, for advancing unanchored regexp
  uc16 standard_type() const { return set_.standard_set_type(); }
  ZoneList<CharacterRange>* ranges(Zone* zone) { return set_.ranges(zone); }
  bool is_negated() const { return (character_class_flags_ & NEGATED) != 0; }
  JSRegExp::Flags flags() const { return flags_; }
  bool contains_split_surrogate() const {
    return (character_class_flags_ & CONTAINS_SPLIT_SURROGATE) != 0;
  }

 private:
  CharacterSet set_;
  const JSRegExp::Flags flags_;
  CharacterClassFlags character_class_flags_;
};


class RegExpAtom final : public RegExpTree {
 public:
  explicit RegExpAtom(Vector<const uc16> data, JSRegExp::Flags flags)
      : data_(data), flags_(flags) {}
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpAtom* AsAtom() override;
  bool IsAtom() override;
  bool IsTextElement() override { return true; }
  int min_match() override { return data_.length(); }
  int max_match() override { return data_.length(); }
  void AppendToText(RegExpText* text, Zone* zone) override;
  Vector<const uc16> data() { return data_; }
  int length() { return data_.length(); }
  JSRegExp::Flags flags() const { return flags_; }
  bool ignore_case() const { return (flags_ & JSRegExp::kIgnoreCase) != 0; }

 private:
  Vector<const uc16> data_;
  const JSRegExp::Flags flags_;
};


class RegExpText final : public RegExpTree {
 public:
  explicit RegExpText(Zone* zone) : elements_(2, zone), length_(0) {}
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpText* AsText() override;
  bool IsText() override;
  bool IsTextElement() override { return true; }
  int min_match() override { return length_; }
  int max_match() override { return length_; }
  void AppendToText(RegExpText* text, Zone* zone) override;
  void AddElement(TextElement elm, Zone* zone) {
    elements_.Add(elm, zone);
    length_ += elm.length();
  }
  ZoneList<TextElement>* elements() { return &elements_; }

 private:
  ZoneList<TextElement> elements_;
  int length_;
};


class RegExpQuantifier final : public RegExpTree {
 public:
  enum QuantifierType { GREEDY, NON_GREEDY, POSSESSIVE };
  RegExpQuantifier(int min, int max, QuantifierType type, RegExpTree* body)
      : body_(body),
        min_(min),
        max_(max),
        quantifier_type_(type) {
    if (min > 0 && body->min_match() > kInfinity / min) {
      min_match_ = kInfinity;
    } else {
      min_match_ = min * body->min_match();
    }
    if (max > 0 && body->max_match() > kInfinity / max) {
      max_match_ = kInfinity;
    } else {
      max_match_ = max * body->max_match();
    }
  }
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  static RegExpNode* ToNode(int min, int max, bool is_greedy, RegExpTree* body,
                            RegExpCompiler* compiler, RegExpNode* on_success,
                            bool not_at_start = false);
  RegExpQuantifier* AsQuantifier() override;
  Interval CaptureRegisters() override;
  bool IsQuantifier() override;
  int min_match() override { return min_match_; }
  int max_match() override { return max_match_; }
  int min() { return min_; }
  int max() { return max_; }
  bool is_possessive() { return quantifier_type_ == POSSESSIVE; }
  bool is_non_greedy() { return quantifier_type_ == NON_GREEDY; }
  bool is_greedy() { return quantifier_type_ == GREEDY; }
  RegExpTree* body() { return body_; }

 private:
  RegExpTree* body_;
  int min_;
  int max_;
  int min_match_;
  int max_match_;
  QuantifierType quantifier_type_;
};


class RegExpCapture final : public RegExpTree {
 public:
  explicit RegExpCapture(int index)
      : body_(nullptr), index_(index), name_(nullptr) {}
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  static RegExpNode* ToNode(RegExpTree* body, int index,
                            RegExpCompiler* compiler, RegExpNode* on_success);
  RegExpCapture* AsCapture() override;
  bool IsAnchoredAtStart() override;
  bool IsAnchoredAtEnd() override;
  Interval CaptureRegisters() override;
  bool IsCapture() override;
  int min_match() override { return body_->min_match(); }
  int max_match() override { return body_->max_match(); }
  RegExpTree* body() { return body_; }
  void set_body(RegExpTree* body) { body_ = body; }
  int index() const { return index_; }
  const ZoneVector<uc16>* name() const { return name_; }
  void set_name(const ZoneVector<uc16>* name) { name_ = name; }
  static int StartRegister(int index) { return index * 2; }
  static int EndRegister(int index) { return index * 2 + 1; }

 private:
  RegExpTree* body_;
  int index_;
  const ZoneVector<uc16>* name_;
};

class RegExpGroup final : public RegExpTree {
 public:
  explicit RegExpGroup(RegExpTree* body) : body_(body) {}
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler,
                     RegExpNode* on_success) override {
    return body_->ToNode(compiler, on_success);
  }
  RegExpGroup* AsGroup() override;
  bool IsAnchoredAtStart() override { return body_->IsAnchoredAtStart(); }
  bool IsAnchoredAtEnd() override { return body_->IsAnchoredAtEnd(); }
  bool IsGroup() override;
  int min_match() override { return body_->min_match(); }
  int max_match() override { return body_->max_match(); }
  Interval CaptureRegisters() override { return body_->CaptureRegisters(); }
  RegExpTree* body() { return body_; }

 private:
  RegExpTree* body_;
};

class RegExpLookaround final : public RegExpTree {
 public:
  enum Type { LOOKAHEAD, LOOKBEHIND };

  RegExpLookaround(RegExpTree* body, bool is_positive, int capture_count,
                   int capture_from, Type type)
      : body_(body),
        is_positive_(is_positive),
        capture_count_(capture_count),
        capture_from_(capture_from),
        type_(type) {}

  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpLookaround* AsLookaround() override;
  Interval CaptureRegisters() override;
  bool IsLookaround() override;
  bool IsAnchoredAtStart() override;
  int min_match() override { return 0; }
  int max_match() override { return 0; }
  RegExpTree* body() { return body_; }
  bool is_positive() { return is_positive_; }
  int capture_count() { return capture_count_; }
  int capture_from() { return capture_from_; }
  Type type() { return type_; }

  class Builder {
   public:
    Builder(bool is_positive, RegExpNode* on_success,
            int stack_pointer_register, int position_register,
            int capture_register_count = 0, int capture_register_start = 0);
    RegExpNode* on_match_success() { return on_match_success_; }
    RegExpNode* ForMatch(RegExpNode* match);

   private:
    bool is_positive_;
    RegExpNode* on_match_success_;
    RegExpNode* on_success_;
    int stack_pointer_register_;
    int position_register_;
  };

 private:
  RegExpTree* body_;
  bool is_positive_;
  int capture_count_;
  int capture_from_;
  Type type_;
};


class RegExpBackReference final : public RegExpTree {
 public:
  explicit RegExpBackReference(JSRegExp::Flags flags)
      : capture_(nullptr), name_(nullptr), flags_(flags) {}
  RegExpBackReference(RegExpCapture* capture, JSRegExp::Flags flags)
      : capture_(capture), name_(nullptr), flags_(flags) {}
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpBackReference* AsBackReference() override;
  bool IsBackReference() override;
  int min_match() override { return 0; }
  // The back reference may be recursive, e.g. /(\2)(\1)/. To avoid infinite
  // recursion, we give up. Ignorance is bliss.
  int max_match() override { return kInfinity; }
  int index() { return capture_->index(); }
  RegExpCapture* capture() { return capture_; }
  void set_capture(RegExpCapture* capture) { capture_ = capture; }
  const ZoneVector<uc16>* name() const { return name_; }
  void set_name(const ZoneVector<uc16>* name) { name_ = name; }

 private:
  RegExpCapture* capture_;
  const ZoneVector<uc16>* name_;
  const JSRegExp::Flags flags_;
};


class RegExpEmpty final : public RegExpTree {
 public:
  RegExpEmpty() = default;
  void* Accept(RegExpVisitor* visitor, void* data) override;
  RegExpNode* ToNode(RegExpCompiler* compiler, RegExpNode* on_success) override;
  RegExpEmpty* AsEmpty() override;
  bool IsEmpty() override;
  int min_match() override { return 0; }
  int max_match() override { return 0; }
};

}  // namespace internal
}  // namespace v8

#endif  // V8_REGEXP_REGEXP_AST_H_