chore(3p/abseil_cpp): unvendor abseil_cpp r/3786

we weren't actually using these sources anymore, okay?

Change-Id: If701571d9716de308d3512e1eb22c35db0877a66
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5248
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>
Autosubmit: tazjin <tazjin@tvl.su>

1 files changed, 0 insertions, 1003 deletions

diff --git a/third_party/abseil_cpp/absl/hash/internal/hash.h b/third_party/abseil_cpp/absl/hash/internal/hash.h
deleted file mode 100644
index b0132da2069d..000000000000
--- a/third_party/abseil_cpp/absl/hash/internal/hash.h
+++ /dev/null
@@ -1,1003 +0,0 @@
-// 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.
-//
-// -----------------------------------------------------------------------------
-// File: hash.h
-// -----------------------------------------------------------------------------
-//
-#ifndef ABSL_HASH_INTERNAL_HASH_H_
-#define ABSL_HASH_INTERNAL_HASH_H_
-
-#include <algorithm>
-#include <array>
-#include <cmath>
-#include <cstring>
-#include <deque>
-#include <forward_list>
-#include <functional>
-#include <iterator>
-#include <limits>
-#include <list>
-#include <map>
-#include <memory>
-#include <set>
-#include <string>
-#include <tuple>
-#include <type_traits>
-#include <utility>
-#include <vector>
-
-#include "absl/base/internal/endian.h"
-#include "absl/base/port.h"
-#include "absl/container/fixed_array.h"
-#include "absl/meta/type_traits.h"
-#include "absl/numeric/int128.h"
-#include "absl/strings/string_view.h"
-#include "absl/types/optional.h"
-#include "absl/types/variant.h"
-#include "absl/utility/utility.h"
-#include "absl/hash/internal/city.h"
-
-namespace absl {
-ABSL_NAMESPACE_BEGIN
-namespace hash_internal {
-
-// Internal detail: Large buffers are hashed in smaller chunks.  This function
-// returns the size of these chunks.
-constexpr size_t PiecewiseChunkSize() { return 1024; }
-
-// PiecewiseCombiner
-//
-// PiecewiseCombiner is an internal-only helper class for hashing a piecewise
-// buffer of `char` or `unsigned char` as though it were contiguous.  This class
-// provides two methods:
-//
-//   H add_buffer(state, data, size)
-//   H finalize(state)
-//
-// `add_buffer` can be called zero or more times, followed by a single call to
-// `finalize`.  This will produce the same hash expansion as concatenating each
-// buffer piece into a single contiguous buffer, and passing this to
-// `H::combine_contiguous`.
-//
-//  Example usage:
-//    PiecewiseCombiner combiner;
-//    for (const auto& piece : pieces) {
-//      state = combiner.add_buffer(std::move(state), piece.data, piece.size);
-//    }
-//    return combiner.finalize(std::move(state));
-class PiecewiseCombiner {
- public:
-  PiecewiseCombiner() : position_(0) {}
-  PiecewiseCombiner(const PiecewiseCombiner&) = delete;
-  PiecewiseCombiner& operator=(const PiecewiseCombiner&) = delete;
-
-  // PiecewiseCombiner::add_buffer()
-  //
-  // Appends the given range of bytes to the sequence to be hashed, which may
-  // modify the provided hash state.
-  template <typename H>
-  H add_buffer(H state, const unsigned char* data, size_t size);
-  template <typename H>
-  H add_buffer(H state, const char* data, size_t size) {
-    return add_buffer(std::move(state),
-                      reinterpret_cast<const unsigned char*>(data), size);
-  }
-
-  // PiecewiseCombiner::finalize()
-  //
-  // Finishes combining the hash sequence, which may may modify the provided
-  // hash state.
-  //
-  // Once finalize() is called, add_buffer() may no longer be called. The
-  // resulting hash state will be the same as if the pieces passed to
-  // add_buffer() were concatenated into a single flat buffer, and then provided
-  // to H::combine_contiguous().
-  template <typename H>
-  H finalize(H state);
-
- private:
-  unsigned char buf_[PiecewiseChunkSize()];
-  size_t position_;
-};
-
-// HashStateBase
-//
-// A hash state object represents an intermediate state in the computation
-// of an unspecified hash algorithm. `HashStateBase` provides a CRTP style
-// base class for hash state implementations. Developers adding type support
-// for `absl::Hash` should not rely on any parts of the state object other than
-// the following member functions:
-//
-//   * HashStateBase::combine()
-//   * HashStateBase::combine_contiguous()
-//
-// A derived hash state class of type `H` must provide a static member function
-// with a signature similar to the following:
-//
-//    `static H combine_contiguous(H state, const unsigned char*, size_t)`.
-//
-// `HashStateBase` will provide a complete implementation for a hash state
-// object in terms of this method.
-//
-// Example:
-//
-//   // Use CRTP to define your derived class.
-//   struct MyHashState : HashStateBase<MyHashState> {
-//       static H combine_contiguous(H state, const unsigned char*, size_t);
-//       using MyHashState::HashStateBase::combine;
-//       using MyHashState::HashStateBase::combine_contiguous;
-//   };
-template <typename H>
-class HashStateBase {
- public:
-  // HashStateBase::combine()
-  //
-  // Combines an arbitrary number of values into a hash state, returning the
-  // updated state.
-  //
-  // Each of the value types `T` must be separately hashable by the Abseil
-  // hashing framework.
-  //
-  // NOTE:
-  //
-  //   state = H::combine(std::move(state), value1, value2, value3);
-  //
-  // is guaranteed to produce the same hash expansion as:
-  //
-  //   state = H::combine(std::move(state), value1);
-  //   state = H::combine(std::move(state), value2);
-  //   state = H::combine(std::move(state), value3);
-  template <typename T, typename... Ts>
-  static H combine(H state, const T& value, const Ts&... values);
-  static H combine(H state) { return state; }
-
-  // HashStateBase::combine_contiguous()
-  //
-  // Combines a contiguous array of `size` elements into a hash state, returning
-  // the updated state.
-  //
-  // NOTE:
-  //
-  //   state = H::combine_contiguous(std::move(state), data, size);
-  //
-  // is NOT guaranteed to produce the same hash expansion as a for-loop (it may
-  // perform internal optimizations).  If you need this guarantee, use the
-  // for-loop instead.
-  template <typename T>
-  static H combine_contiguous(H state, const T* data, size_t size);
-
-  using AbslInternalPiecewiseCombiner = PiecewiseCombiner;
-};
-
-// is_uniquely_represented
-//
-// `is_uniquely_represented<T>` is a trait class that indicates whether `T`
-// is uniquely represented.
-//
-// A type is "uniquely represented" if two equal values of that type are
-// guaranteed to have the same bytes in their underlying storage. In other
-// words, if `a == b`, then `memcmp(&a, &b, sizeof(T))` is guaranteed to be
-// zero. This property cannot be detected automatically, so this trait is false
-// by default, but can be specialized by types that wish to assert that they are
-// uniquely represented. This makes them eligible for certain optimizations.
-//
-// If you have any doubt whatsoever, do not specialize this template.
-// The default is completely safe, and merely disables some optimizations
-// that will not matter for most types. Specializing this template,
-// on the other hand, can be very hazardous.
-//
-// To be uniquely represented, a type must not have multiple ways of
-// representing the same value; for example, float and double are not
-// uniquely represented, because they have distinct representations for
-// +0 and -0. Furthermore, the type's byte representation must consist
-// solely of user-controlled data, with no padding bits and no compiler-
-// controlled data such as vptrs or sanitizer metadata. This is usually
-// very difficult to guarantee, because in most cases the compiler can
-// insert data and padding bits at its own discretion.
-//
-// If you specialize this template for a type `T`, you must do so in the file
-// that defines that type (or in this file). If you define that specialization
-// anywhere else, `is_uniquely_represented<T>` could have different meanings
-// in different places.
-//
-// The Enable parameter is meaningless; it is provided as a convenience,
-// to support certain SFINAE techniques when defining specializations.
-template <typename T, typename Enable = void>
-struct is_uniquely_represented : std::false_type {};
-
-// is_uniquely_represented<unsigned char>
-//
-// unsigned char is a synonym for "byte", so it is guaranteed to be
-// uniquely represented.
-template <>
-struct is_uniquely_represented<unsigned char> : std::true_type {};
-
-// is_uniquely_represented for non-standard integral types
-//
-// Integral types other than bool should be uniquely represented on any
-// platform that this will plausibly be ported to.
-template <typename Integral>
-struct is_uniquely_represented<
-    Integral, typename std::enable_if<std::is_integral<Integral>::value>::type>
-    : std::true_type {};
-
-// is_uniquely_represented<bool>
-//
-//
-template <>
-struct is_uniquely_represented<bool> : std::false_type {};
-
-// hash_bytes()
-//
-// Convenience function that combines `hash_state` with the byte representation
-// of `value`.
-template <typename H, typename T>
-H hash_bytes(H hash_state, const T& value) {
-  const unsigned char* start = reinterpret_cast<const unsigned char*>(&value);
-  return H::combine_contiguous(std::move(hash_state), start, sizeof(value));
-}
-
-// -----------------------------------------------------------------------------
-// AbslHashValue for Basic Types
-// -----------------------------------------------------------------------------
-
-// Note: Default `AbslHashValue` implementations live in `hash_internal`. This
-// allows us to block lexical scope lookup when doing an unqualified call to
-// `AbslHashValue` below. User-defined implementations of `AbslHashValue` can
-// only be found via ADL.
-
-// AbslHashValue() for hashing bool values
-//
-// We use SFINAE to ensure that this overload only accepts bool, not types that
-// are convertible to bool.
-template <typename H, typename B>
-typename std::enable_if<std::is_same<B, bool>::value, H>::type AbslHashValue(
-    H hash_state, B value) {
-  return H::combine(std::move(hash_state),
-                    static_cast<unsigned char>(value ? 1 : 0));
-}
-
-// AbslHashValue() for hashing enum values
-template <typename H, typename Enum>
-typename std::enable_if<std::is_enum<Enum>::value, H>::type AbslHashValue(
-    H hash_state, Enum e) {
-  // In practice, we could almost certainly just invoke hash_bytes directly,
-  // but it's possible that a sanitizer might one day want to
-  // store data in the unused bits of an enum. To avoid that risk, we
-  // convert to the underlying type before hashing. Hopefully this will get
-  // optimized away; if not, we can reopen discussion with c-toolchain-team.
-  return H::combine(std::move(hash_state),
-                    static_cast<typename std::underlying_type<Enum>::type>(e));
-}
-// AbslHashValue() for hashing floating-point values
-template <typename H, typename Float>
-typename std::enable_if<std::is_same<Float, float>::value ||
-                            std::is_same<Float, double>::value,
-                        H>::type
-AbslHashValue(H hash_state, Float value) {
-  return hash_internal::hash_bytes(std::move(hash_state),
-                                   value == 0 ? 0 : value);
-}
-
-// Long double has the property that it might have extra unused bytes in it.
-// For example, in x86 sizeof(long double)==16 but it only really uses 80-bits
-// of it. This means we can't use hash_bytes on a long double and have to
-// convert it to something else first.
-template <typename H, typename LongDouble>
-typename std::enable_if<std::is_same<LongDouble, long double>::value, H>::type
-AbslHashValue(H hash_state, LongDouble value) {
-  const int category = std::fpclassify(value);
-  switch (category) {
-    case FP_INFINITE:
-      // Add the sign bit to differentiate between +Inf and -Inf
-      hash_state = H::combine(std::move(hash_state), std::signbit(value));
-      break;
-
-    case FP_NAN:
-    case FP_ZERO:
-    default:
-      // Category is enough for these.
-      break;
-
-    case FP_NORMAL:
-    case FP_SUBNORMAL:
-      // We can't convert `value` directly to double because this would have
-      // undefined behavior if the value is out of range.
-      // std::frexp gives us a value in the range (-1, -.5] or [.5, 1) that is
-      // guaranteed to be in range for `double`. The truncation is
-      // implementation defined, but that works as long as it is deterministic.
-      int exp;
-      auto mantissa = static_cast<double>(std::frexp(value, &exp));
-      hash_state = H::combine(std::move(hash_state), mantissa, exp);
-  }
-
-  return H::combine(std::move(hash_state), category);
-}
-
-// AbslHashValue() for hashing pointers
-template <typename H, typename T>
-H AbslHashValue(H hash_state, T* ptr) {
-  auto v = reinterpret_cast<uintptr_t>(ptr);
-  // Due to alignment, pointers tend to have low bits as zero, and the next few
-  // bits follow a pattern since they are also multiples of some base value.
-  // Mixing the pointer twice helps prevent stuck low bits for certain alignment
-  // values.
-  return H::combine(std::move(hash_state), v, v);
-}
-
-// AbslHashValue() for hashing nullptr_t
-template <typename H>
-H AbslHashValue(H hash_state, std::nullptr_t) {
-  return H::combine(std::move(hash_state), static_cast<void*>(nullptr));
-}
-
-// -----------------------------------------------------------------------------
-// AbslHashValue for Composite Types
-// -----------------------------------------------------------------------------
-
-// is_hashable()
-//
-// Trait class which returns true if T is hashable by the absl::Hash framework.
-// Used for the AbslHashValue implementations for composite types below.
-template <typename T>
-struct is_hashable;
-
-// AbslHashValue() for hashing pairs
-template <typename H, typename T1, typename T2>
-typename std::enable_if<is_hashable<T1>::value && is_hashable<T2>::value,
-                        H>::type
-AbslHashValue(H hash_state, const std::pair<T1, T2>& p) {
-  return H::combine(std::move(hash_state), p.first, p.second);
-}
-
-// hash_tuple()
-//
-// Helper function for hashing a tuple. The third argument should
-// be an index_sequence running from 0 to tuple_size<Tuple> - 1.
-template <typename H, typename Tuple, size_t... Is>
-H hash_tuple(H hash_state, const Tuple& t, absl::index_sequence<Is...>) {
-  return H::combine(std::move(hash_state), std::get<Is>(t)...);
-}
-
-// AbslHashValue for hashing tuples
-template <typename H, typename... Ts>
-#if defined(_MSC_VER)
-// This SFINAE gets MSVC confused under some conditions. Let's just disable it
-// for now.
-H
-#else  // _MSC_VER
-typename std::enable_if<absl::conjunction<is_hashable<Ts>...>::value, H>::type
-#endif  // _MSC_VER
-AbslHashValue(H hash_state, const std::tuple<Ts...>& t) {
-  return hash_internal::hash_tuple(std::move(hash_state), t,
-                                   absl::make_index_sequence<sizeof...(Ts)>());
-}
-
-// -----------------------------------------------------------------------------
-// AbslHashValue for Pointers
-// -----------------------------------------------------------------------------
-
-// AbslHashValue for hashing unique_ptr
-template <typename H, typename T, typename D>
-H AbslHashValue(H hash_state, const std::unique_ptr<T, D>& ptr) {
-  return H::combine(std::move(hash_state), ptr.get());
-}
-
-// AbslHashValue for hashing shared_ptr
-template <typename H, typename T>
-H AbslHashValue(H hash_state, const std::shared_ptr<T>& ptr) {
-  return H::combine(std::move(hash_state), ptr.get());
-}
-
-// -----------------------------------------------------------------------------
-// AbslHashValue for String-Like Types
-// -----------------------------------------------------------------------------
-
-// AbslHashValue for hashing strings
-//
-// All the string-like types supported here provide the same hash expansion for
-// the same character sequence. These types are:
-//
-//  - `absl::Cord`
-//  - `std::string` (and std::basic_string<char, std::char_traits<char>, A> for
-//      any allocator A)
-//  - `absl::string_view` and `std::string_view`
-//
-// For simplicity, we currently support only `char` strings. This support may
-// be broadened, if necessary, but with some caution - this overload would
-// misbehave in cases where the traits' `eq()` member isn't equivalent to `==`
-// on the underlying character type.
-template <typename H>
-H AbslHashValue(H hash_state, absl::string_view str) {
-  return H::combine(
-      H::combine_contiguous(std::move(hash_state), str.data(), str.size()),
-      str.size());
-}
-
-// Support std::wstring, std::u16string and std::u32string.
-template <typename Char, typename Alloc, typename H,
-          typename = absl::enable_if_t<std::is_same<Char, wchar_t>::value ||
-                                       std::is_same<Char, char16_t>::value ||
-                                       std::is_same<Char, char32_t>::value>>
-H AbslHashValue(
-    H hash_state,
-    const std::basic_string<Char, std::char_traits<Char>, Alloc>& str) {
-  return H::combine(
-      H::combine_contiguous(std::move(hash_state), str.data(), str.size()),
-      str.size());
-}
-
-// -----------------------------------------------------------------------------
-// AbslHashValue for Sequence Containers
-// -----------------------------------------------------------------------------
-
-// AbslHashValue for hashing std::array
-template <typename H, typename T, size_t N>
-typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
-    H hash_state, const std::array<T, N>& array) {
-  return H::combine_contiguous(std::move(hash_state), array.data(),
-                               array.size());
-}
-
-// AbslHashValue for hashing std::deque
-template <typename H, typename T, typename Allocator>
-typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
-    H hash_state, const std::deque<T, Allocator>& deque) {
-  // TODO(gromer): investigate a more efficient implementation taking
-  // advantage of the chunk structure.
-  for (const auto& t : deque) {
-    hash_state = H::combine(std::move(hash_state), t);
-  }
-  return H::combine(std::move(hash_state), deque.size());
-}
-
-// AbslHashValue for hashing std::forward_list
-template <typename H, typename T, typename Allocator>
-typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
-    H hash_state, const std::forward_list<T, Allocator>& list) {
-  size_t size = 0;
-  for (const T& t : list) {
-    hash_state = H::combine(std::move(hash_state), t);
-    ++size;
-  }
-  return H::combine(std::move(hash_state), size);
-}
-
-// AbslHashValue for hashing std::list
-template <typename H, typename T, typename Allocator>
-typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
-    H hash_state, const std::list<T, Allocator>& list) {
-  for (const auto& t : list) {
-    hash_state = H::combine(std::move(hash_state), t);
-  }
-  return H::combine(std::move(hash_state), list.size());
-}
-
-// AbslHashValue for hashing std::vector
-//
-// Do not use this for vector<bool>. It does not have a .data(), and a fallback
-// for std::hash<> is most likely faster.
-template <typename H, typename T, typename Allocator>
-typename std::enable_if<is_hashable<T>::value && !std::is_same<T, bool>::value,
-                        H>::type
-AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) {
-  return H::combine(H::combine_contiguous(std::move(hash_state), vector.data(),
-                                          vector.size()),
-                    vector.size());
-}
-
-// -----------------------------------------------------------------------------
-// AbslHashValue for Ordered Associative Containers
-// -----------------------------------------------------------------------------
-
-// AbslHashValue for hashing std::map
-template <typename H, typename Key, typename T, typename Compare,
-          typename Allocator>
-typename std::enable_if<is_hashable<Key>::value && is_hashable<T>::value,
-                        H>::type
-AbslHashValue(H hash_state, const std::map<Key, T, Compare, Allocator>& map) {
-  for (const auto& t : map) {
-    hash_state = H::combine(std::move(hash_state), t);
-  }
-  return H::combine(std::move(hash_state), map.size());
-}
-
-// AbslHashValue for hashing std::multimap
-template <typename H, typename Key, typename T, typename Compare,
-          typename Allocator>
-typename std::enable_if<is_hashable<Key>::value && is_hashable<T>::value,
-                        H>::type
-AbslHashValue(H hash_state,
-              const std::multimap<Key, T, Compare, Allocator>& map) {
-  for (const auto& t : map) {
-    hash_state = H::combine(std::move(hash_state), t);
-  }
-  return H::combine(std::move(hash_state), map.size());
-}
-
-// AbslHashValue for hashing std::set
-template <typename H, typename Key, typename Compare, typename Allocator>
-typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue(
-    H hash_state, const std::set<Key, Compare, Allocator>& set) {
-  for (const auto& t : set) {
-    hash_state = H::combine(std::move(hash_state), t);
-  }
-  return H::combine(std::move(hash_state), set.size());
-}
-
-// AbslHashValue for hashing std::multiset
-template <typename H, typename Key, typename Compare, typename Allocator>
-typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue(
-    H hash_state, const std::multiset<Key, Compare, Allocator>& set) {
-  for (const auto& t : set) {
-    hash_state = H::combine(std::move(hash_state), t);
-  }
-  return H::combine(std::move(hash_state), set.size());
-}
-
-// -----------------------------------------------------------------------------
-// AbslHashValue for Wrapper Types
-// -----------------------------------------------------------------------------
-
-// AbslHashValue for hashing std::reference_wrapper
-template <typename H, typename T>
-typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
-    H hash_state, std::reference_wrapper<T> opt) {
-  return H::combine(std::move(hash_state), opt.get());
-}
-
-// AbslHashValue for hashing absl::optional
-template <typename H, typename T>
-typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
-    H hash_state, const absl::optional<T>& opt) {
-  if (opt) hash_state = H::combine(std::move(hash_state), *opt);
-  return H::combine(std::move(hash_state), opt.has_value());
-}
-
-// VariantVisitor
-template <typename H>
-struct VariantVisitor {
-  H&& hash_state;
-  template <typename T>
-  H operator()(const T& t) const {
-    return H::combine(std::move(hash_state), t);
-  }
-};
-
-// AbslHashValue for hashing absl::variant
-template <typename H, typename... T>
-typename std::enable_if<conjunction<is_hashable<T>...>::value, H>::type
-AbslHashValue(H hash_state, const absl::variant<T...>& v) {
-  if (!v.valueless_by_exception()) {
-    hash_state = absl::visit(VariantVisitor<H>{std::move(hash_state)}, v);
-  }
-  return H::combine(std::move(hash_state), v.index());
-}
-
-// -----------------------------------------------------------------------------
-// AbslHashValue for Other Types
-// -----------------------------------------------------------------------------
-
-// AbslHashValue for hashing std::bitset is not defined, for the same reason as
-// for vector<bool> (see std::vector above): It does not expose the raw bytes,
-// and a fallback to std::hash<> is most likely faster.
-
-// -----------------------------------------------------------------------------
-
-// hash_range_or_bytes()
-//
-// Mixes all values in the range [data, data+size) into the hash state.
-// This overload accepts only uniquely-represented types, and hashes them by
-// hashing the entire range of bytes.
-template <typename H, typename T>
-typename std::enable_if<is_uniquely_represented<T>::value, H>::type
-hash_range_or_bytes(H hash_state, const T* data, size_t size) {
-  const auto* bytes = reinterpret_cast<const unsigned char*>(data);
-  return H::combine_contiguous(std::move(hash_state), bytes, sizeof(T) * size);
-}
-
-// hash_range_or_bytes()
-template <typename H, typename T>
-typename std::enable_if<!is_uniquely_represented<T>::value, H>::type
-hash_range_or_bytes(H hash_state, const T* data, size_t size) {
-  for (const auto end = data + size; data < end; ++data) {
-    hash_state = H::combine(std::move(hash_state), *data);
-  }
-  return hash_state;
-}
-
-#if defined(ABSL_INTERNAL_LEGACY_HASH_NAMESPACE) && \
-    ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_
-#define ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ 1
-#else
-#define ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ 0
-#endif
-
-// HashSelect
-//
-// Type trait to select the appropriate hash implementation to use.
-// HashSelect::type<T> will give the proper hash implementation, to be invoked
-// as:
-//   HashSelect::type<T>::Invoke(state, value)
-// Also, HashSelect::type<T>::value is a boolean equal to `true` if there is a
-// valid `Invoke` function. Types that are not hashable will have a ::value of
-// `false`.
-struct HashSelect {
- private:
-  struct State : HashStateBase<State> {
-    static State combine_contiguous(State hash_state, const unsigned char*,
-                                    size_t);
-    using State::HashStateBase::combine_contiguous;
-  };
-
-  struct UniquelyRepresentedProbe {
-    template <typename H, typename T>
-    static auto Invoke(H state, const T& value)
-        -> absl::enable_if_t<is_uniquely_represented<T>::value, H> {
-      return hash_internal::hash_bytes(std::move(state), value);
-    }
-  };
-
-  struct HashValueProbe {
-    template <typename H, typename T>
-    static auto Invoke(H state, const T& value) -> absl::enable_if_t<
-        std::is_same<H,
-                     decltype(AbslHashValue(std::move(state), value))>::value,
-        H> {
-      return AbslHashValue(std::move(state), value);
-    }
-  };
-
-  struct LegacyHashProbe {
-#if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
-    template <typename H, typename T>
-    static auto Invoke(H state, const T& value) -> absl::enable_if_t<
-        std::is_convertible<
-            decltype(ABSL_INTERNAL_LEGACY_HASH_NAMESPACE::hash<T>()(value)),
-            size_t>::value,
-        H> {
-      return hash_internal::hash_bytes(
-          std::move(state),
-          ABSL_INTERNAL_LEGACY_HASH_NAMESPACE::hash<T>{}(value));
-    }
-#endif  // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
-  };
-
-  struct StdHashProbe {
-    template <typename H, typename T>
-    static auto Invoke(H state, const T& value)
-        -> absl::enable_if_t<type_traits_internal::IsHashable<T>::value, H> {
-      return hash_internal::hash_bytes(std::move(state), std::hash<T>{}(value));
-    }
-  };
-
-  template <typename Hash, typename T>
-  struct Probe : Hash {
-   private:
-    template <typename H, typename = decltype(H::Invoke(
-                              std::declval<State>(), std::declval<const T&>()))>
-    static std::true_type Test(int);
-    template <typename U>
-    static std::false_type Test(char);
-
-   public:
-    static constexpr bool value = decltype(Test<Hash>(0))::value;
-  };
-
- public:
-  // Probe each implementation in order.
-  // disjunction provides short circuiting wrt instantiation.
-  template <typename T>
-  using Apply = absl::disjunction<         //
-      Probe<UniquelyRepresentedProbe, T>,  //
-      Probe<HashValueProbe, T>,            //
-      Probe<LegacyHashProbe, T>,           //
-      Probe<StdHashProbe, T>,              //
-      std::false_type>;
-};
-
-template <typename T>
-struct is_hashable
-    : std::integral_constant<bool, HashSelect::template Apply<T>::value> {};
-
-// CityHashState
-class ABSL_DLL CityHashState
-    : public HashStateBase<CityHashState> {
-  // absl::uint128 is not an alias or a thin wrapper around the intrinsic.
-  // We use the intrinsic when available to improve performance.
-#ifdef ABSL_HAVE_INTRINSIC_INT128
-  using uint128 = __uint128_t;
-#else   // ABSL_HAVE_INTRINSIC_INT128
-  using uint128 = absl::uint128;
-#endif  // ABSL_HAVE_INTRINSIC_INT128
-
-  static constexpr uint64_t kMul =
-      sizeof(size_t) == 4 ? uint64_t{0xcc9e2d51}
-                          : uint64_t{0x9ddfea08eb382d69};
-
-  template <typename T>
-  using IntegralFastPath =
-      conjunction<std::is_integral<T>, is_uniquely_represented<T>>;
-
- public:
-  // Move only
-  CityHashState(CityHashState&&) = default;
-  CityHashState& operator=(CityHashState&&) = default;
-
-  // CityHashState::combine_contiguous()
-  //
-  // Fundamental base case for hash recursion: mixes the given range of bytes
-  // into the hash state.
-  static CityHashState combine_contiguous(CityHashState hash_state,
-                                          const unsigned char* first,
-                                          size_t size) {
-    return CityHashState(
-        CombineContiguousImpl(hash_state.state_, first, size,
-                              std::integral_constant<int, sizeof(size_t)>{}));
-  }
-  using CityHashState::HashStateBase::combine_contiguous;
-
-  // CityHashState::hash()
-  //
-  // For performance reasons in non-opt mode, we specialize this for
-  // integral types.
-  // Otherwise we would be instantiating and calling dozens of functions for
-  // something that is just one multiplication and a couple xor's.
-  // The result should be the same as running the whole algorithm, but faster.
-  template <typename T, absl::enable_if_t<IntegralFastPath<T>::value, int> = 0>
-  static size_t hash(T value) {
-    return static_cast<size_t>(Mix(Seed(), static_cast<uint64_t>(value)));
-  }
-
-  // Overload of CityHashState::hash()
-  template <typename T, absl::enable_if_t<!IntegralFastPath<T>::value, int> = 0>
-  static size_t hash(const T& value) {
-    return static_cast<size_t>(combine(CityHashState{}, value).state_);
-  }
-
- private:
-  // Invoked only once for a given argument; that plus the fact that this is
-  // move-only ensures that there is only one non-moved-from object.
-  CityHashState() : state_(Seed()) {}
-
-  // Workaround for MSVC bug.
-  // We make the type copyable to fix the calling convention, even though we
-  // never actually copy it. Keep it private to not affect the public API of the
-  // type.
-  CityHashState(const CityHashState&) = default;
-
-  explicit CityHashState(uint64_t state) : state_(state) {}
-
-  // Implementation of the base case for combine_contiguous where we actually
-  // mix the bytes into the state.
-  // Dispatch to different implementations of the combine_contiguous depending
-  // on the value of `sizeof(size_t)`.
-  static uint64_t CombineContiguousImpl(uint64_t state,
-                                        const unsigned char* first, size_t len,
-                                        std::integral_constant<int, 4>
-                                        /* sizeof_size_t */);
-  static uint64_t CombineContiguousImpl(uint64_t state,
-                                        const unsigned char* first, size_t len,
-                                        std::integral_constant<int, 8>
-                                        /* sizeof_size_t*/);
-
-  // Slow dispatch path for calls to CombineContiguousImpl with a size argument
-  // larger than PiecewiseChunkSize().  Has the same effect as calling
-  // CombineContiguousImpl() repeatedly with the chunk stride size.
-  static uint64_t CombineLargeContiguousImpl32(uint64_t state,
-                                               const unsigned char* first,
-                                               size_t len);
-  static uint64_t CombineLargeContiguousImpl64(uint64_t state,
-                                               const unsigned char* first,
-                                               size_t len);
-
-  // Reads 9 to 16 bytes from p.
-  // The first 8 bytes are in .first, the rest (zero padded) bytes are in
-  // .second.
-  static std::pair<uint64_t, uint64_t> Read9To16(const unsigned char* p,
-                                                 size_t len) {
-    uint64_t high = little_endian::Load64(p + len - 8);
-    return {little_endian::Load64(p), high >> (128 - len * 8)};
-  }
-
-  // Reads 4 to 8 bytes from p. Zero pads to fill uint64_t.
-  static uint64_t Read4To8(const unsigned char* p, size_t len) {
-    return (static_cast<uint64_t>(little_endian::Load32(p + len - 4))
-            << (len - 4) * 8) |
-           little_endian::Load32(p);
-  }
-
-  // Reads 1 to 3 bytes from p. Zero pads to fill uint32_t.
-  static uint32_t Read1To3(const unsigned char* p, size_t len) {
-    return static_cast<uint32_t>((p[0]) |                         //
-                                 (p[len / 2] << (len / 2 * 8)) |  //
-                                 (p[len - 1] << ((len - 1) * 8)));
-  }
-
-  ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Mix(uint64_t state, uint64_t v) {
-    using MultType =
-        absl::conditional_t<sizeof(size_t) == 4, uint64_t, uint128>;
-    // We do the addition in 64-bit space to make sure the 128-bit
-    // multiplication is fast. If we were to do it as MultType the compiler has
-    // to assume that the high word is non-zero and needs to perform 2
-    // multiplications instead of one.
-    MultType m = state + v;
-    m *= kMul;
-    return static_cast<uint64_t>(m ^ (m >> (sizeof(m) * 8 / 2)));
-  }
-
-  // Seed()
-  //
-  // A non-deterministic seed.
-  //
-  // The current purpose of this seed is to generate non-deterministic results
-  // and prevent having users depend on the particular hash values.
-  // It is not meant as a security feature right now, but it leaves the door
-  // open to upgrade it to a true per-process random seed. A true random seed
-  // costs more and we don't need to pay for that right now.
-  //
-  // On platforms with ASLR, we take advantage of it to make a per-process
-  // random value.
-  // See https://en.wikipedia.org/wiki/Address_space_layout_randomization
-  //
-  // On other platforms this is still going to be non-deterministic but most
-  // probably per-build and not per-process.
-  ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Seed() {
-#if (!defined(__clang__) || __clang_major__ > 11) && \
-    !defined(__apple_build_version__)
-    return static_cast<uint64_t>(reinterpret_cast<uintptr_t>(&kSeed));
-#else
-    // Workaround the absence of
-    // https://github.com/llvm/llvm-project/commit/bc15bf66dcca76cc06fe71fca35b74dc4d521021.
-    return static_cast<uint64_t>(reinterpret_cast<uintptr_t>(kSeed));
-#endif
-  }
-  static const void* const kSeed;
-
-  uint64_t state_;
-};
-
-// CityHashState::CombineContiguousImpl()
-inline uint64_t CityHashState::CombineContiguousImpl(
-    uint64_t state, const unsigned char* first, size_t len,
-    std::integral_constant<int, 4> /* sizeof_size_t */) {
-  // For large values we use CityHash, for small ones we just use a
-  // multiplicative hash.
-  uint64_t v;
-  if (len > 8) {
-    if (ABSL_PREDICT_FALSE(len > PiecewiseChunkSize())) {
-      return CombineLargeContiguousImpl32(state, first, len);
-    }
-    v = absl::hash_internal::CityHash32(reinterpret_cast<const char*>(first), len);
-  } else if (len >= 4) {
-    v = Read4To8(first, len);
-  } else if (len > 0) {
-    v = Read1To3(first, len);
-  } else {
-    // Empty ranges have no effect.
-    return state;
-  }
-  return Mix(state, v);
-}
-
-// Overload of CityHashState::CombineContiguousImpl()
-inline uint64_t CityHashState::CombineContiguousImpl(
-    uint64_t state, const unsigned char* first, size_t len,
-    std::integral_constant<int, 8> /* sizeof_size_t */) {
-  // For large values we use CityHash, for small ones we just use a
-  // multiplicative hash.
-  uint64_t v;
-  if (len > 16) {
-    if (ABSL_PREDICT_FALSE(len > PiecewiseChunkSize())) {
-      return CombineLargeContiguousImpl64(state, first, len);
-    }
-    v = absl::hash_internal::CityHash64(reinterpret_cast<const char*>(first), len);
-  } else if (len > 8) {
-    auto p = Read9To16(first, len);
-    state = Mix(state, p.first);
-    v = p.second;
-  } else if (len >= 4) {
-    v = Read4To8(first, len);
-  } else if (len > 0) {
-    v = Read1To3(first, len);
-  } else {
-    // Empty ranges have no effect.
-    return state;
-  }
-  return Mix(state, v);
-}
-
-struct AggregateBarrier {};
-
-// HashImpl
-
-// Add a private base class to make sure this type is not an aggregate.
-// Aggregates can be aggregate initialized even if the default constructor is
-// deleted.
-struct PoisonedHash : private AggregateBarrier {
-  PoisonedHash() = delete;
-  PoisonedHash(const PoisonedHash&) = delete;
-  PoisonedHash& operator=(const PoisonedHash&) = delete;
-};
-
-template <typename T>
-struct HashImpl {
-  size_t operator()(const T& value) const { return CityHashState::hash(value); }
-};
-
-template <typename T>
-struct Hash
-    : absl::conditional_t<is_hashable<T>::value, HashImpl<T>, PoisonedHash> {};
-
-template <typename H>
-template <typename T, typename... Ts>
-H HashStateBase<H>::combine(H state, const T& value, const Ts&... values) {
-  return H::combine(hash_internal::HashSelect::template Apply<T>::Invoke(
-                        std::move(state), value),
-                    values...);
-}
-
-// HashStateBase::combine_contiguous()
-template <typename H>
-template <typename T>
-H HashStateBase<H>::combine_contiguous(H state, const T* data, size_t size) {
-  return hash_internal::hash_range_or_bytes(std::move(state), data, size);
-}
-
-// HashStateBase::PiecewiseCombiner::add_buffer()
-template <typename H>
-H PiecewiseCombiner::add_buffer(H state, const unsigned char* data,
-                                size_t size) {
-  if (position_ + size < PiecewiseChunkSize()) {
-    // This partial chunk does not fill our existing buffer
-    memcpy(buf_ + position_, data, size);
-    position_ += size;
-    return state;
-  }
-
-  // If the buffer is partially filled we need to complete the buffer
-  // and hash it.
-  if (position_ != 0) {
-    const size_t bytes_needed = PiecewiseChunkSize() - position_;
-    memcpy(buf_ + position_, data, bytes_needed);
-    state = H::combine_contiguous(std::move(state), buf_, PiecewiseChunkSize());
-    data += bytes_needed;
-    size -= bytes_needed;
-  }
-
-  // Hash whatever chunks we can without copying
-  while (size >= PiecewiseChunkSize()) {
-    state = H::combine_contiguous(std::move(state), data, PiecewiseChunkSize());
-    data += PiecewiseChunkSize();
-    size -= PiecewiseChunkSize();
-  }
-  // Fill the buffer with the remainder
-  memcpy(buf_, data, size);
-  position_ = size;
-  return state;
-}
-
-// HashStateBase::PiecewiseCombiner::finalize()
-template <typename H>
-H PiecewiseCombiner::finalize(H state) {
-  // Hash the remainder left in the buffer, which may be empty
-  return H::combine_contiguous(std::move(state), buf_, position_);
-}
-
-}  // namespace hash_internal
-ABSL_NAMESPACE_END
-}  // namespace absl
-
-#endif  // ABSL_HASH_INTERNAL_HASH_H_