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Diffstat (limited to 'absl/hash/internal/spy_hash_state.h')
-rw-r--r-- | absl/hash/internal/spy_hash_state.h | 220 |
1 files changed, 220 insertions, 0 deletions
diff --git a/absl/hash/internal/spy_hash_state.h b/absl/hash/internal/spy_hash_state.h new file mode 100644 index 00000000..1886d2ef --- /dev/null +++ b/absl/hash/internal/spy_hash_state.h @@ -0,0 +1,220 @@ +// 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 +// +// http://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_INTERNAL_SPY_HASH_STATE_H_ +#define ABSL_HASH_INTERNAL_SPY_HASH_STATE_H_ + +#include <ostream> +#include <string> +#include <vector> + +#include "absl/hash/hash.h" +#include "absl/strings/match.h" +#include "absl/strings/str_format.h" +#include "absl/strings/str_join.h" + +namespace absl { +inline namespace lts_2018_12_18 { +namespace hash_internal { + +// SpyHashState is an implementation of the HashState API that simply +// accumulates all input bytes in an internal buffer. This makes it useful +// for testing AbslHashValue overloads (so long as they are templated on the +// HashState parameter), since it can report the exact hash representation +// that the AbslHashValue overload produces. +// +// Sample usage: +// EXPECT_EQ(SpyHashState::combine(SpyHashState(), foo), +// SpyHashState::combine(SpyHashState(), bar)); +template <typename T> +class SpyHashStateImpl : public HashStateBase<SpyHashStateImpl<T>> { + public: + SpyHashStateImpl() + : error_(std::make_shared<absl::optional<std::string>>()) { + static_assert(std::is_void<T>::value, ""); + } + + // Move-only + SpyHashStateImpl(const SpyHashStateImpl&) = delete; + SpyHashStateImpl& operator=(const SpyHashStateImpl&) = delete; + + SpyHashStateImpl(SpyHashStateImpl&& other) noexcept { + *this = std::move(other); + } + + SpyHashStateImpl& operator=(SpyHashStateImpl&& other) noexcept { + hash_representation_ = std::move(other.hash_representation_); + error_ = other.error_; + moved_from_ = other.moved_from_; + other.moved_from_ = true; + return *this; + } + + template <typename U> + SpyHashStateImpl(SpyHashStateImpl<U>&& other) { // NOLINT + hash_representation_ = std::move(other.hash_representation_); + error_ = other.error_; + moved_from_ = other.moved_from_; + other.moved_from_ = true; + } + + template <typename A, typename... Args> + static SpyHashStateImpl combine(SpyHashStateImpl s, const A& a, + const Args&... args) { + // Pass an instance of SpyHashStateImpl<A> when trying to combine `A`. This + // allows us to test that the user only uses this instance for combine calls + // and does not call AbslHashValue directly. + // See AbslHashValue implementation at the bottom. + s = SpyHashStateImpl<A>::HashStateBase::combine(std::move(s), a); + return SpyHashStateImpl::combine(std::move(s), args...); + } + static SpyHashStateImpl combine(SpyHashStateImpl s) { + if (direct_absl_hash_value_error_) { + *s.error_ = "AbslHashValue should not be invoked directly."; + } else if (s.moved_from_) { + *s.error_ = "Used moved-from instance of the hash state object."; + } + return s; + } + + static void SetDirectAbslHashValueError() { + direct_absl_hash_value_error_ = true; + } + + // Two SpyHashStateImpl objects are equal if they hold equal hash + // representations. + friend bool operator==(const SpyHashStateImpl& lhs, + const SpyHashStateImpl& rhs) { + return lhs.hash_representation_ == rhs.hash_representation_; + } + + friend bool operator!=(const SpyHashStateImpl& lhs, + const SpyHashStateImpl& rhs) { + return !(lhs == rhs); + } + + enum class CompareResult { + kEqual, + kASuffixB, + kBSuffixA, + kUnequal, + }; + + static CompareResult Compare(const SpyHashStateImpl& a, + const SpyHashStateImpl& b) { + const std::string a_flat = absl::StrJoin(a.hash_representation_, ""); + const std::string b_flat = absl::StrJoin(b.hash_representation_, ""); + if (a_flat == b_flat) return CompareResult::kEqual; + if (absl::EndsWith(a_flat, b_flat)) return CompareResult::kBSuffixA; + if (absl::EndsWith(b_flat, a_flat)) return CompareResult::kASuffixB; + return CompareResult::kUnequal; + } + + // operator<< prints the hash representation as a hex and ASCII dump, to + // facilitate debugging. + friend std::ostream& operator<<(std::ostream& out, + const SpyHashStateImpl& hash_state) { + out << "[\n"; + for (auto& s : hash_state.hash_representation_) { + size_t offset = 0; + for (char c : s) { + if (offset % 16 == 0) { + out << absl::StreamFormat("\n0x%04x: ", offset); + } + if (offset % 2 == 0) { + out << " "; + } + out << absl::StreamFormat("%02x", c); + ++offset; + } + out << "\n"; + } + return out << "]"; + } + + // The base case of the combine recursion, which writes raw bytes into the + // internal buffer. + static SpyHashStateImpl combine_contiguous(SpyHashStateImpl hash_state, + const unsigned char* begin, + size_t size) { + hash_state.hash_representation_.emplace_back( + reinterpret_cast<const char*>(begin), size); + return hash_state; + } + + using SpyHashStateImpl::HashStateBase::combine_contiguous; + + absl::optional<std::string> error() const { + if (moved_from_) { + return "Returned a moved-from instance of the hash state object."; + } + return *error_; + } + + private: + template <typename U> + friend class SpyHashStateImpl; + + // This is true if SpyHashStateImpl<T> has been passed to a call of + // AbslHashValue with the wrong type. This detects that the user called + // AbslHashValue directly (because the hash state type does not match). + static bool direct_absl_hash_value_error_; + + + std::vector<std::string> hash_representation_; + // This is a shared_ptr because we want all instances of the particular + // SpyHashState run to share the field. This way we can set the error for + // use-after-move and all the copies will see it. + std::shared_ptr<absl::optional<std::string>> error_; + bool moved_from_ = false; +}; + +template <typename T> +bool SpyHashStateImpl<T>::direct_absl_hash_value_error_; + +template <bool& B> +struct OdrUse { + constexpr OdrUse() {} + bool& b = B; +}; + +template <void (*)()> +struct RunOnStartup { + static bool run; + static constexpr OdrUse<run> kOdrUse{}; +}; + +template <void (*f)()> +bool RunOnStartup<f>::run = (f(), true); + +template < + typename T, typename U, + // Only trigger for when (T != U), + absl::enable_if_t<!std::is_same<T, U>::value, int> = 0, + // This statement works in two ways: + // - First, it instantiates RunOnStartup and forces the initialization of + // `run`, which set the global variable. + // - Second, it triggers a SFINAE error disabling the overload to prevent + // compile time errors. If we didn't disable the overload we would get + // ambiguous overload errors, which we don't want. + int = RunOnStartup<SpyHashStateImpl<T>::SetDirectAbslHashValueError>::run> +void AbslHashValue(SpyHashStateImpl<T>, const U&); + +using SpyHashState = SpyHashStateImpl<void>; + +} // namespace hash_internal +} // inline namespace lts_2018_12_18 +} // namespace absl + +#endif // ABSL_HASH_INTERNAL_SPY_HASH_STATE_H_ |