about summary refs log tree commit diff
path: root/absl/base/internal/exception_safety_testing.h
blob: d2742456fec32b3022e463e72bc6a592d1234a0f (plain) (blame)
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
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
// Utilities for testing exception-safety

#ifndef ABSL_BASE_INTERNAL_EXCEPTION_SAFETY_TESTING_H_
#define ABSL_BASE_INTERNAL_EXCEPTION_SAFETY_TESTING_H_

#include <cstddef>
#include <cstdint>
#include <functional>
#include <iosfwd>
#include <string>
#include <unordered_map>

#include "gtest/gtest.h"
#include "absl/base/config.h"
#include "absl/base/internal/pretty_function.h"
#include "absl/meta/type_traits.h"
#include "absl/strings/string_view.h"
#include "absl/strings/substitute.h"

namespace absl {
struct AllocInspector;

// A configuration enum for Throwing*.  Operations whose flags are set will
// throw, everything else won't.  This isn't meant to be exhaustive, more flags
// can always be made in the future.
enum class NoThrow : uint8_t {
  kNone = 0,
  kMoveCtor = 1,
  kMoveAssign = 1 << 1,
  kAllocation = 1 << 2,
  kIntCtor = 1 << 3,
  kNoThrow = static_cast<uint8_t>(-1)
};

constexpr NoThrow operator|(NoThrow a, NoThrow b) {
  using T = absl::underlying_type_t<NoThrow>;
  return static_cast<NoThrow>(static_cast<T>(a) | static_cast<T>(b));
}

constexpr NoThrow operator&(NoThrow a, NoThrow b) {
  using T = absl::underlying_type_t<NoThrow>;
  return static_cast<NoThrow>(static_cast<T>(a) & static_cast<T>(b));
}

namespace exceptions_internal {
constexpr bool ThrowingAllowed(NoThrow flags, NoThrow flag) {
  return !static_cast<bool>(flags & flag);
}

// A simple exception class.  We throw this so that test code can catch
// exceptions specifically thrown by ThrowingValue.
class TestException {
 public:
  explicit TestException(absl::string_view msg) : msg_(msg) {}
  absl::string_view what() const { return msg_; }

 private:
  std::string msg_;
};

extern int countdown;

void MaybeThrow(absl::string_view msg);

testing::AssertionResult FailureMessage(const TestException& e,
                                        int countdown) noexcept;

class TrackedObject {
 protected:
  explicit TrackedObject(absl::string_view child_ctor) {
    if (!GetAllocs().emplace(this, child_ctor).second) {
      ADD_FAILURE() << "Object at address " << static_cast<void*>(this)
                    << " re-constructed in ctor " << child_ctor;
    }
  }

  TrackedObject(const TrackedObject&) = delete;
  TrackedObject(TrackedObject&&) = delete;

  static std::unordered_map<TrackedObject*, absl::string_view>& GetAllocs() {
    static auto* m =
        new std::unordered_map<TrackedObject*, absl::string_view>();
    return *m;
  }

  ~TrackedObject() noexcept {
    if (GetAllocs().erase(this) == 0) {
      ADD_FAILURE() << "Object at address " << static_cast<void*>(this)
                    << " destroyed improperly";
    }
  }

  friend struct ::absl::AllocInspector;
};
}  // namespace exceptions_internal

// A test class which is contextually convertible to bool.  The conversion can
// be instrumented to throw at a controlled time.
class ThrowingBool {
 public:
  ThrowingBool(bool b) noexcept : b_(b) {}  // NOLINT(runtime/explicit)
  explicit operator bool() const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return b_;
  }

 private:
  bool b_;
};

// A testing class instrumented to throw an exception at a controlled time.
//
// ThrowingValue implements a slightly relaxed version of the Regular concept --
// that is it's a value type with the expected semantics.  It also implements
// arithmetic operations.  It doesn't implement member and pointer operators
// like operator-> or operator[].
//
// ThrowingValue can be instrumented to have certain operations be noexcept by
// using compile-time bitfield flag template arguments.  That is, to make an
// ThrowingValue which has a noexcept move constructor and noexcept move
// assignment, use
// ThrowingValue<absl::NoThrow::kMoveCtor | absl::NoThrow::kMoveAssign>.
template <NoThrow Flags = NoThrow::kNone>
class ThrowingValue : private exceptions_internal::TrackedObject {
 public:
  ThrowingValue() : TrackedObject(ABSL_PRETTY_FUNCTION) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ = 0;
  }

  ThrowingValue(const ThrowingValue& other)
      : TrackedObject(ABSL_PRETTY_FUNCTION) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ = other.dummy_;
  }

  ThrowingValue(ThrowingValue&& other) noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kMoveCtor))
      : TrackedObject(ABSL_PRETTY_FUNCTION) {
    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kMoveCtor)) {
      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    }
    dummy_ = other.dummy_;
  }

  explicit ThrowingValue(int i) noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kIntCtor))
      : TrackedObject(ABSL_PRETTY_FUNCTION) {
    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kIntCtor)) {
      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    }
    dummy_ = i;
  }

  // absl expects nothrow destructors
  ~ThrowingValue() noexcept = default;

  ThrowingValue& operator=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ = other.dummy_;
    return *this;
  }

  ThrowingValue& operator=(ThrowingValue&& other) noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kMoveAssign)) {
    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kMoveAssign)) {
      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    }
    dummy_ = other.dummy_;
    return *this;
  }

  // Arithmetic Operators
  ThrowingValue operator+(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ + other.dummy_, NoThrowTag{});
  }

  ThrowingValue operator+() const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_, NoThrowTag{});
  }

  ThrowingValue operator-(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ - other.dummy_, NoThrowTag{});
  }

  ThrowingValue operator-() const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(-dummy_, NoThrowTag{});
  }

  ThrowingValue& operator++() {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    ++dummy_;
    return *this;
  }

  ThrowingValue operator++(int) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    auto out = ThrowingValue(dummy_, NoThrowTag{});
    ++dummy_;
    return out;
  }

  ThrowingValue& operator--() {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    --dummy_;
    return *this;
  }

  ThrowingValue operator--(int) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    auto out = ThrowingValue(dummy_, NoThrowTag{});
    --dummy_;
    return out;
  }

  ThrowingValue operator*(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ * other.dummy_, NoThrowTag{});
  }

  ThrowingValue operator/(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ / other.dummy_, NoThrowTag{});
  }

  ThrowingValue operator%(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ % other.dummy_, NoThrowTag{});
  }

  ThrowingValue operator<<(int shift) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ << shift, NoThrowTag{});
  }

  ThrowingValue operator>>(int shift) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ >> shift, NoThrowTag{});
  }

  // Comparison Operators
  friend ThrowingBool operator==(const ThrowingValue& a,
                                 const ThrowingValue& b) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return a.dummy_ == b.dummy_;
  }
  friend ThrowingBool operator!=(const ThrowingValue& a,
                                 const ThrowingValue& b) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return a.dummy_ != b.dummy_;
  }
  friend ThrowingBool operator<(const ThrowingValue& a,
                                const ThrowingValue& b) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return a.dummy_ < b.dummy_;
  }
  friend ThrowingBool operator<=(const ThrowingValue& a,
                                 const ThrowingValue& b) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return a.dummy_ <= b.dummy_;
  }
  friend ThrowingBool operator>(const ThrowingValue& a,
                                const ThrowingValue& b) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return a.dummy_ > b.dummy_;
  }
  friend ThrowingBool operator>=(const ThrowingValue& a,
                                 const ThrowingValue& b) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return a.dummy_ >= b.dummy_;
  }

  // Logical Operators
  ThrowingBool operator!() const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return !dummy_;
  }

  ThrowingBool operator&&(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return dummy_ && other.dummy_;
  }

  ThrowingBool operator||(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return dummy_ || other.dummy_;
  }

  // Bitwise Logical Operators
  ThrowingValue operator~() const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(~dummy_, NoThrowTag{});
  }

  ThrowingValue operator&(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ & other.dummy_, NoThrowTag{});
  }

  ThrowingValue operator|(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ | other.dummy_, NoThrowTag{});
  }

  ThrowingValue operator^(const ThrowingValue& other) const {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return ThrowingValue(dummy_ ^ other.dummy_, NoThrowTag{});
  }

  // Compound Assignment operators
  ThrowingValue& operator+=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ += other.dummy_;
    return *this;
  }

  ThrowingValue& operator-=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ -= other.dummy_;
    return *this;
  }

  ThrowingValue& operator*=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ *= other.dummy_;
    return *this;
  }

  ThrowingValue& operator/=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ /= other.dummy_;
    return *this;
  }

  ThrowingValue& operator%=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ %= other.dummy_;
    return *this;
  }

  ThrowingValue& operator&=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ &= other.dummy_;
    return *this;
  }

  ThrowingValue& operator|=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ |= other.dummy_;
    return *this;
  }

  ThrowingValue& operator^=(const ThrowingValue& other) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ ^= other.dummy_;
    return *this;
  }

  ThrowingValue& operator<<=(int shift) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ <<= shift;
    return *this;
  }

  ThrowingValue& operator>>=(int shift) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ >>= shift;
    return *this;
  }

  // Pointer operators
  void operator&() const = delete;  // NOLINT(runtime/operator)

  // Stream operators
  friend std::ostream& operator<<(std::ostream& os, const ThrowingValue&) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return os;
  }

  friend std::istream& operator>>(std::istream& is, const ThrowingValue&) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    return is;
  }

  // Memory management operators
  // Args.. allows us to overload regular and placement new in one shot
  template <typename... Args>
  static void* operator new(size_t s, Args&&... args) noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kAllocation)) {
    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kAllocation)) {
      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    }
    return ::operator new(s, std::forward<Args>(args)...);
  }

  template <typename... Args>
  static void* operator new[](size_t s, Args&&... args) noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kAllocation)) {
    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kAllocation)) {
      exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    }
    return ::operator new[](s, std::forward<Args>(args)...);
  }

  // Abseil doesn't support throwing overloaded operator delete.  These are
  // provided so a throwing operator-new can clean up after itself.
  //
  // We provide both regular and templated operator delete because if only the
  // templated version is provided as we did with operator new, the compiler has
  // no way of knowing which overload of operator delete to call. See
  // http://en.cppreference.com/w/cpp/memory/new/operator_delete and
  // http://en.cppreference.com/w/cpp/language/delete for the gory details.
  void operator delete(void* p) noexcept { ::operator delete(p); }

  template <typename... Args>
  void operator delete(void* p, Args&&... args) noexcept {
    ::operator delete(p, std::forward<Args>(args)...);
  }

  void operator delete[](void* p) noexcept { return ::operator delete[](p); }

  template <typename... Args>
  void operator delete[](void* p, Args&&... args) noexcept {
    return ::operator delete[](p, std::forward<Args>(args)...);
  }

  // Non-standard access to the actual contained value.  No need for this to
  // throw.
  int& Get() noexcept { return dummy_; }
  const int& Get() const noexcept { return dummy_; }

 private:
  struct NoThrowTag {};
  ThrowingValue(int i, NoThrowTag) noexcept
      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(i) {}

  int dummy_;
};
// While not having to do with exceptions, explicitly delete comma operator, to
// make sure we don't use it on user-supplied types.
template <NoThrow N, typename T>
void operator,(const ThrowingValue<N>& ef, T&& t) = delete;
template <NoThrow N, typename T>
void operator,(T&& t, const ThrowingValue<N>& ef) = delete;

// An allocator type which is instrumented to throw at a controlled time, or not
// to throw, using NoThrow.  The supported settings are the default of every
// function which is allowed to throw in a conforming allocator possibly
// throwing, or nothing throws, in line with the ABSL_ALLOCATOR_THROWS
// configuration macro.
template <typename T, NoThrow Flags = NoThrow::kNone>
class ThrowingAllocator : private exceptions_internal::TrackedObject {
  static_assert(Flags == NoThrow::kNone || Flags == NoThrow::kNoThrow,
                "Invalid flag");

 public:
  using pointer = T*;
  using const_pointer = const T*;
  using reference = T&;
  using const_reference = const T&;
  using void_pointer = void*;
  using const_void_pointer = const void*;
  using value_type = T;
  using size_type = size_t;
  using difference_type = ptrdiff_t;

  using is_nothrow = std::integral_constant<bool, Flags == NoThrow::kNoThrow>;
  using propagate_on_container_copy_assignment = std::true_type;
  using propagate_on_container_move_assignment = std::true_type;
  using propagate_on_container_swap = std::true_type;
  using is_always_equal = std::false_type;

  ThrowingAllocator() : TrackedObject(ABSL_PRETTY_FUNCTION) {
    exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
    dummy_ = std::make_shared<const int>(next_id_++);
  }

  template <typename U>
  ThrowingAllocator(  // NOLINT
      const ThrowingAllocator<U, Flags>& other) noexcept
      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(other.State()) {}

  ThrowingAllocator(const ThrowingAllocator& other) noexcept
      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(other.State()) {}

  template <typename U>
  ThrowingAllocator(  // NOLINT
      ThrowingAllocator<U, Flags>&& other) noexcept
      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(std::move(other.State())) {}

  ThrowingAllocator(ThrowingAllocator&& other) noexcept
      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(std::move(other.State())) {}

  ~ThrowingAllocator() noexcept = default;

  template <typename U>
  ThrowingAllocator& operator=(
      const ThrowingAllocator<U, Flags>& other) noexcept {
    dummy_ = other.State();
    return *this;
  }

  template <typename U>
  ThrowingAllocator& operator=(ThrowingAllocator<U, Flags>&& other) noexcept {
    dummy_ = std::move(other.State());
    return *this;
  }

  template <typename U>
  struct rebind {
    using other = ThrowingAllocator<U, Flags>;
  };

  pointer allocate(size_type n) noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
    ReadStateAndMaybeThrow(ABSL_PRETTY_FUNCTION);
    return static_cast<pointer>(::operator new(n * sizeof(T)));
  }
  pointer allocate(size_type n, const_void_pointer) noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
    return allocate(n);
  }

  void deallocate(pointer ptr, size_type) noexcept {
    ReadState();
    ::operator delete(static_cast<void*>(ptr));
  }

  template <typename U, typename... Args>
  void construct(U* ptr, Args&&... args) noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
    ReadStateAndMaybeThrow(ABSL_PRETTY_FUNCTION);
    ::new (static_cast<void*>(ptr)) U(std::forward<Args>(args)...);
  }

  template <typename U>
  void destroy(U* p) noexcept {
    ReadState();
    p->~U();
  }

  size_type max_size() const
      noexcept(!exceptions_internal::ThrowingAllowed(Flags,
                                                     NoThrow::kNoThrow)) {
    ReadStateAndMaybeThrow(ABSL_PRETTY_FUNCTION);
    return std::numeric_limits<difference_type>::max() / sizeof(value_type);
  }

  ThrowingAllocator select_on_container_copy_construction() noexcept(
      !exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
    auto& out = *this;
    ReadStateAndMaybeThrow(ABSL_PRETTY_FUNCTION);
    return out;
  }

  template <typename U>
  bool operator==(const ThrowingAllocator<U, Flags>& other) const noexcept {
    return dummy_ == other.dummy_;
  }

  template <typename U>
  bool operator!=(const ThrowingAllocator<U, Flags>& other) const noexcept {
    return dummy_ != other.dummy_;
  }

  template <typename U, NoThrow B>
  friend class ThrowingAllocator;

 private:
  const std::shared_ptr<const int>& State() const { return dummy_; }
  std::shared_ptr<const int>& State() { return dummy_; }

  void ReadState() {
    // we know that this will never be true, but the compiler doesn't, so this
    // should safely force a read of the value.
    if (*dummy_ < 0) std::abort();
  }

  void ReadStateAndMaybeThrow(absl::string_view msg) const {
    if (exceptions_internal::ThrowingAllowed(Flags, NoThrow::kNoThrow)) {
      exceptions_internal::MaybeThrow(
          absl::Substitute("Allocator id $0 threw from $1", *dummy_, msg));
    }
  }

  static int next_id_;
  std::shared_ptr<const int> dummy_;
};

template <typename T, NoThrow Throws>
int ThrowingAllocator<T, Throws>::next_id_ = 0;

// Inspects the constructions and destructions of anything inheriting from
// TrackedObject.  Place this as a member variable in a test fixture to ensure
// that every ThrowingValue was constructed and destroyed correctly.
struct AllocInspector {
  AllocInspector() = default;
  ~AllocInspector() {
    auto& allocs = exceptions_internal::TrackedObject::GetAllocs();
    for (const auto& kv : allocs) {
      ADD_FAILURE() << "Object at address " << static_cast<void*>(kv.first)
                    << " constructed from " << kv.second << " not destroyed";
    }
    allocs.clear();
  }
};

// Tests that performing operation Op on a T follows the basic exception safety
// guarantee.
//
// Parameters:
//   * T: the type under test.
//   * FunctionFromTPtrToVoid: A functor exercising the function under test.  It
//     should take a T* and return void.
//
//  There must also be a function named `AbslCheckInvariants` in an associated
//  namespace of T which takes a const T& and returns true if the T's class
//  invariants hold, and false if they don't.
template <typename T, typename FunctionFromTPtrToVoid>
testing::AssertionResult TestBasicGuarantee(T* t, FunctionFromTPtrToVoid&& op) {
  for (int countdown = 0;; ++countdown) {
    exceptions_internal::countdown = countdown;
    try {
      op(t);
      break;
    } catch (const exceptions_internal::TestException& e) {
      if (!AbslCheckInvariants(*t)) {
        return exceptions_internal::FailureMessage(e, countdown)
               << " broke invariants.";
      }
    }
  }
  exceptions_internal::countdown = -1;
  return testing::AssertionSuccess();
}

// Tests that performing operation Op on a T follows the strong exception safety
// guarantee.
//
// Parameters:
//   * T: the type under test. T must be copy-constructable and
//   equality-comparible.
//   * FunctionFromTPtrToVoid: A functor exercising the function under test.  It
//     should take a T* and return void.
//
//  There must also be a function named `AbslCheckInvariants` in an associated
//  namespace of T which takes a const T& and returns true if the T's class
//  invariants hold, and false if they don't.
template <typename T, typename FunctionFromTPtrToVoid>
testing::AssertionResult TestStrongGuarantee(T* t,
                                             FunctionFromTPtrToVoid&& op) {
  exceptions_internal::countdown = -1;
  for (auto countdown = 0;; ++countdown) {
    T dup = *t;
    exceptions_internal::countdown = countdown;
    try {
      op(t);
      break;
    } catch (const exceptions_internal::TestException& e) {
      if (!AbslCheckInvariants(*t)) {
        return exceptions_internal::FailureMessage(e, countdown)
               << " broke invariants.";
      }
      if (dup != *t)
        return exceptions_internal::FailureMessage(e, countdown)
               << " changed state.";
    }
  }
  exceptions_internal::countdown = -1;
  return testing::AssertionSuccess();
}

}  // namespace absl

#endif  // ABSL_BASE_INTERNAL_EXCEPTION_SAFETY_TESTING_H_