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+// 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 {
+
+// 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);
+}
+
+} // namespace absl
+
+#endif // ABSL_HASH_HASH_TESTING_H_
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