aboutsummaryrefslogtreecommitdiff
path: root/absl/hash/hash_testing.h
blob: 1e1c5741491eaf7c3334e10f590625e839514e1e (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
// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef ABSL_HASH_HASH_TESTING_H_
#define ABSL_HASH_HASH_TESTING_H_

#include <initializer_list>
#include <tuple>
#include <type_traits>
#include <vector>

#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include "absl/hash/internal/spy_hash_state.h"
#include "absl/meta/type_traits.h"
#include "absl/strings/str_cat.h"
#include "absl/types/variant.h"

namespace absl {
ABSL_NAMESPACE_BEGIN

// Run the absl::Hash algorithm over all the elements passed in and verify that
// their hash expansion is congruent with their `==` operator.
//
// It is used in conjunction with EXPECT_TRUE. Failures will output information
// on what requirement failed and on which objects.
//
// Users should pass a collection of types as either an initializer list or a
// container of cases.
//
//   EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(
//       {v1, v2, ..., vN}));
//
//   std::vector<MyType> cases;
//   // Fill cases...
//   EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(cases));
//
// Users can pass a variety of types for testing heterogeneous lookup with
// `std::make_tuple`:
//
//   EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(
//       std::make_tuple(v1, v2, ..., vN)));
//
//
// Ideally, the values passed should provide enough coverage of the `==`
// operator and the AbslHashValue implementations.
// For dynamically sized types, the empty state should usually be included in
// the values.
//
// The function accepts an optional comparator function, in case that `==` is
// not enough for the values provided.
//
// Usage:
//
//   EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(
//       std::make_tuple(v1, v2, ..., vN), MyCustomEq{}));
//
// It checks the following requirements:
//   1. The expansion for a value is deterministic.
//   2. For any two objects `a` and `b` in the sequence, if `a == b` evaluates
//      to true, then their hash expansion must be equal.
//   3. If `a == b` evaluates to false their hash expansion must be unequal.
//   4. If `a == b` evaluates to false neither hash expansion can be a
//      suffix of the other.
//   5. AbslHashValue overloads should not be called by the user. They are only
//      meant to be called by the framework. Users should call H::combine() and
//      H::combine_contiguous().
//   6. No moved-from instance of the hash state is used in the implementation
//      of AbslHashValue.
//
// The values do not have to have the same type. This can be useful for
// equivalent types that support heterogeneous lookup.
//
// A possible reason for breaking (2) is combining state in the hash expansion
// that was not used in `==`.
// For example:
//
// struct Bad2 {
//   int a, b;
//   template <typename H>
//   friend H AbslHashValue(H state, Bad2 x) {
//     // Uses a and b.
//     return H::combine(std::move(state), x.a, x.b);
//   }
//   friend bool operator==(Bad2 x, Bad2 y) {
//     // Only uses a.
//     return x.a == y.a;
//   }
// };
//
// As for (3), breaking this usually means that there is state being passed to
// the `==` operator that is not used in the hash expansion.
// For example:
//
// struct Bad3 {
//   int a, b;
//   template <typename H>
//   friend H AbslHashValue(H state, Bad3 x) {
//     // Only uses a.
//     return H::combine(std::move(state), x.a);
//   }
//   friend bool operator==(Bad3 x, Bad3 y) {
//     // Uses a and b.
//     return x.a == y.a && x.b == y.b;
//   }
// };
//
// Finally, a common way to break 4 is by combining dynamic ranges without
// combining the size of the range.
// For example:
//
// struct Bad4 {
//   int *p, size;
//   template <typename H>
//   friend H AbslHashValue(H state, Bad4 x) {
//     return H::combine_contiguous(std::move(state), x.p, x.p + x.size);
//   }
//   friend bool operator==(Bad4 x, Bad4 y) {
//    // Compare two ranges for equality. C++14 code can instead use std::equal.
//     return absl::equal(x.p, x.p + x.size, y.p, y.p + y.size);
//   }
// };
//
// An easy solution to this is to combine the size after combining the range,
// like so:
// template <typename H>
// friend H AbslHashValue(H state, Bad4 x) {
//   return H::combine(
//       H::combine_contiguous(std::move(state), x.p, x.p + x.size), x.size);
// }
//
template <int&... ExplicitBarrier, typename Container>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(const Container& values);

template <int&... ExplicitBarrier, typename Container, typename Eq>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(const Container& values, Eq equals);

template <int&..., typename T>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(std::initializer_list<T> values);

template <int&..., typename T, typename Eq>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(std::initializer_list<T> values,
                                      Eq equals);

namespace hash_internal {

struct PrintVisitor {
  size_t index;
  template <typename T>
  std::string operator()(const T* value) const {
    return absl::StrCat("#", index, "(", testing::PrintToString(*value), ")");
  }
};

template <typename Eq>
struct EqVisitor {
  Eq eq;
  template <typename T, typename U>
  bool operator()(const T* t, const U* u) const {
    return eq(*t, *u);
  }
};

struct ExpandVisitor {
  template <typename T>
  SpyHashState operator()(const T* value) const {
    return SpyHashState::combine(SpyHashState(), *value);
  }
};

template <typename Container, typename Eq>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(const Container& values, Eq equals) {
  using V = typename Container::value_type;

  struct Info {
    const V& value;
    size_t index;
    std::string ToString() const {
      return absl::visit(PrintVisitor{index}, value);
    }
    SpyHashState expand() const { return absl::visit(ExpandVisitor{}, value); }
  };

  using EqClass = std::vector<Info>;
  std::vector<EqClass> classes;

  // Gather the values in equivalence classes.
  size_t i = 0;
  for (const auto& value : values) {
    EqClass* c = nullptr;
    for (auto& eqclass : classes) {
      if (absl::visit(EqVisitor<Eq>{equals}, value, eqclass[0].value)) {
        c = &eqclass;
        break;
      }
    }
    if (c == nullptr) {
      classes.emplace_back();
      c = &classes.back();
    }
    c->push_back({value, i});
    ++i;

    // Verify potential errors captured by SpyHashState.
    if (auto error = c->back().expand().error()) {
      return testing::AssertionFailure() << *error;
    }
  }

  if (classes.size() < 2) {
    return testing::AssertionFailure()
           << "At least two equivalence classes are expected.";
  }

  // We assume that equality is correctly implemented.
  // Now we verify that AbslHashValue is also correctly implemented.

  for (const auto& c : classes) {
    // All elements of the equivalence class must have the same hash
    // expansion.
    const SpyHashState expected = c[0].expand();
    for (const Info& v : c) {
      if (v.expand() != v.expand()) {
        return testing::AssertionFailure()
               << "Hash expansion for " << v.ToString()
               << " is non-deterministic.";
      }
      if (v.expand() != expected) {
        return testing::AssertionFailure()
               << "Values " << c[0].ToString() << " and " << v.ToString()
               << " evaluate as equal but have an unequal hash expansion.";
      }
    }

    // Elements from other classes must have different hash expansion.
    for (const auto& c2 : classes) {
      if (&c == &c2) continue;
      const SpyHashState c2_hash = c2[0].expand();
      switch (SpyHashState::Compare(expected, c2_hash)) {
        case SpyHashState::CompareResult::kEqual:
          return testing::AssertionFailure()
                 << "Values " << c[0].ToString() << " and " << c2[0].ToString()
                 << " evaluate as unequal but have an equal hash expansion.";
        case SpyHashState::CompareResult::kBSuffixA:
          return testing::AssertionFailure()
                 << "Hash expansion of " << c2[0].ToString()
                 << " is a suffix of the hash expansion of " << c[0].ToString()
                 << ".";
        case SpyHashState::CompareResult::kASuffixB:
          return testing::AssertionFailure()
                 << "Hash expansion of " << c[0].ToString()
                 << " is a suffix of the hash expansion of " << c2[0].ToString()
                 << ".";
        case SpyHashState::CompareResult::kUnequal:
          break;
      }
    }
  }
  return testing::AssertionSuccess();
}

template <typename... T>
struct TypeSet {
  template <typename U, bool = disjunction<std::is_same<T, U>...>::value>
  struct Insert {
    using type = TypeSet<U, T...>;
  };
  template <typename U>
  struct Insert<U, true> {
    using type = TypeSet;
  };

  template <template <typename...> class C>
  using apply = C<T...>;
};

template <typename... T>
struct MakeTypeSet : TypeSet<> {};
template <typename T, typename... Ts>
struct MakeTypeSet<T, Ts...> : MakeTypeSet<Ts...>::template Insert<T>::type {};

template <typename... T>
using VariantForTypes = typename MakeTypeSet<
    const typename std::decay<T>::type*...>::template apply<absl::variant>;

template <typename Container>
struct ContainerAsVector {
  using V = absl::variant<const typename Container::value_type*>;
  using Out = std::vector<V>;

  static Out Do(const Container& values) {
    Out out;
    for (const auto& v : values) out.push_back(&v);
    return out;
  }
};

template <typename... T>
struct ContainerAsVector<std::tuple<T...>> {
  using V = VariantForTypes<T...>;
  using Out = std::vector<V>;

  template <size_t... I>
  static Out DoImpl(const std::tuple<T...>& tuple, absl::index_sequence<I...>) {
    return Out{&std::get<I>(tuple)...};
  }

  static Out Do(const std::tuple<T...>& values) {
    return DoImpl(values, absl::index_sequence_for<T...>());
  }
};

template <>
struct ContainerAsVector<std::tuple<>> {
  static std::vector<VariantForTypes<int>> Do(std::tuple<>) { return {}; }
};

struct DefaultEquals {
  template <typename T, typename U>
  bool operator()(const T& t, const U& u) const {
    return t == u;
  }
};

}  // namespace hash_internal

template <int&..., typename Container>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(const Container& values) {
  return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
      hash_internal::ContainerAsVector<Container>::Do(values),
      hash_internal::DefaultEquals{});
}

template <int&..., typename Container, typename Eq>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(const Container& values, Eq equals) {
  return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
      hash_internal::ContainerAsVector<Container>::Do(values), equals);
}

template <int&..., typename T>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(std::initializer_list<T> values) {
  return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
      hash_internal::ContainerAsVector<std::initializer_list<T>>::Do(values),
      hash_internal::DefaultEquals{});
}

template <int&..., typename T, typename Eq>
ABSL_MUST_USE_RESULT testing::AssertionResult
VerifyTypeImplementsAbslHashCorrectly(std::initializer_list<T> values,
                                      Eq equals) {
  return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
      hash_internal::ContainerAsVector<std::initializer_list<T>>::Do(values),
      equals);
}

ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_HASH_HASH_TESTING_H_