Export of internal Abseil changes

--
2130ba98c8359b08d97fb16d84dfd05687005dcf by Abseil Team <absl-team@google.com>:

Tweaking the documentation of c_all_of to state the effect more directly.

PiperOrigin-RevId: 410557900

--
4732289bf4b56123fed113e36be4710b55c6a6c7 by Greg Falcon <gfalcon@google.com>:

Improve the quality of absl::Hash<std::vector<bool>>.

This previously dispatched to std::hash<vector<bool>>, which suffers from trivial collisions on many platforms.  (They often hash the internal words but no size info, so that, e.g., {1, 1} and {1, 1, 0} collide.)

Also extended the unit test to exercise this.

PiperOrigin-RevId: 410329943

--
1c5f3934230a7669f74c96b305251786a265e235 by Greg Falcon <gfalcon@google.com>:

Add broader testing of absl hash contracts in the hash unit test.

In particular, test that the hash erasure mechanism works.

PiperOrigin-RevId: 410312738

--
5e1923f527ed3d02f6752a5b38d5e1c17a4a146f by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 410290663

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8c74bc962b3b98a5908017c345efc592393048ea by Martijn Vels <mvels@google.com>:

Add Cord::CreateFlat() function

PiperOrigin-RevId: 410260776

--
bd0de4e94c85620d3b8dd60fae367b730fc4cb34 by Evan Brown <ezb@google.com>:

Rename node_hash_policy to node_slot_policy.

Motivation: we can potentially reuse this code for node_btree_*.
PiperOrigin-RevId: 410082271
GitOrigin-RevId: 2130ba98c8359b08d97fb16d84dfd05687005dcf
Change-Id: Ie052084cf992dee250d8b2f388d39c4de0dcff40

2 files changed, 170 insertions, 44 deletions

diff --git a/absl/hash/hash_test.cc b/absl/hash/hash_test.cc
index b3ddebdd..dbfacb2d 100644
--- a/absl/hash/hash_test.cc
+++ b/absl/hash/hash_test.cc
@@ -14,12 +14,14 @@
 
 #include "absl/hash/hash.h"
 
+#include <algorithm>
 #include <array>
 #include <bitset>
 #include <cstring>
 #include <deque>
 #include <forward_list>
 #include <functional>
+#include <initializer_list>
 #include <iterator>
 #include <limits>
 #include <list>
@@ -46,6 +48,56 @@
 
 namespace {
 
+// Utility wrapper of T for the purposes of testing the `AbslHash` type erasure
+// mechanism.  `TypeErasedValue<T>` can be constructed with a `T`, and can
+// be compared and hashed.  However, all hashing goes through the hashing
+// type-erasure framework.
+template <typename T>
+class TypeErasedValue {
+ public:
+  TypeErasedValue() = default;
+  TypeErasedValue(const TypeErasedValue&) = default;
+  TypeErasedValue(TypeErasedValue&&) = default;
+  explicit TypeErasedValue(const T& n) : n_(n) {}
+
+  template <typename H>
+  friend H AbslHashValue(H hash_state, const TypeErasedValue& v) {
+    v.HashValue(absl::HashState::Create(&hash_state));
+    return hash_state;
+  }
+
+  void HashValue(absl::HashState state) const {
+    absl::HashState::combine(std::move(state), n_);
+  }
+
+  bool operator==(const TypeErasedValue& rhs) const { return n_ == rhs.n_; }
+  bool operator!=(const TypeErasedValue& rhs) const { return !(*this == rhs); }
+
+ private:
+  T n_;
+};
+
+// A TypeErasedValue refinement, for containers.  It exposes the wrapped
+// `value_type` and is constructible from an initializer list.
+template <typename T>
+class TypeErasedContainer : public TypeErasedValue<T> {
+ public:
+  using value_type = typename T::value_type;
+  TypeErasedContainer() = default;
+  TypeErasedContainer(const TypeErasedContainer&) = default;
+  TypeErasedContainer(TypeErasedContainer&&) = default;
+  explicit TypeErasedContainer(const T& n) : TypeErasedValue<T>(n) {}
+  TypeErasedContainer(std::initializer_list<value_type> init_list)
+      : TypeErasedContainer(T(init_list.begin(), init_list.end())) {}
+  // one-argument constructor of value type T, to appease older toolchains that
+  // get confused by one-element initializer lists in some contexts
+  explicit TypeErasedContainer(const value_type& v)
+      : TypeErasedContainer(T(&v, &v + 1)) {}
+};
+
+template <typename T>
+using TypeErasedVector = TypeErasedContainer<std::vector<T>>;
+
 using absl::Hash;
 using absl::hash_internal::SpyHashState;
 
@@ -389,23 +441,60 @@ TYPED_TEST_SUITE_P(HashValueSequenceTest);
 TYPED_TEST_P(HashValueSequenceTest, BasicUsage) {
   EXPECT_TRUE((is_hashable<TypeParam>::value));
 
-  using ValueType = typename TypeParam::value_type;
-  auto a = static_cast<ValueType>(0);
-  auto b = static_cast<ValueType>(23);
-  auto c = static_cast<ValueType>(42);
-
-  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(
-      std::make_tuple(TypeParam(), TypeParam{}, TypeParam{a, b, c},
-                      TypeParam{a, b}, TypeParam{b, c})));
+  using IntType = typename TypeParam::value_type;
+  auto a = static_cast<IntType>(0);
+  auto b = static_cast<IntType>(23);
+  auto c = static_cast<IntType>(42);
+
+  std::vector<TypeParam> exemplars = {
+      TypeParam(),        TypeParam(),        TypeParam{a, b, c},
+      TypeParam{a, c, b}, TypeParam{c, a, b}, TypeParam{a},
+      TypeParam{a, a},    TypeParam{a, a, a}, TypeParam{a, a, b},
+      TypeParam{a, b, a}, TypeParam{b, a, a}, TypeParam{a, b},
+      TypeParam{b, c}};
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(exemplars));
 }
 
 REGISTER_TYPED_TEST_CASE_P(HashValueSequenceTest, BasicUsage);
 using IntSequenceTypes =
     testing::Types<std::deque<int>, std::forward_list<int>, std::list<int>,
-                   std::vector<int>, std::vector<bool>, std::set<int>,
-                   std::multiset<int>>;
+                   std::vector<int>, std::vector<bool>, TypeErasedVector<int>,
+                   TypeErasedVector<bool>, std::set<int>, std::multiset<int>>;
 INSTANTIATE_TYPED_TEST_CASE_P(My, HashValueSequenceTest, IntSequenceTypes);
 
+template <typename T>
+class HashValueNestedSequenceTest : public testing::Test {};
+TYPED_TEST_SUITE_P(HashValueNestedSequenceTest);
+
+TYPED_TEST_P(HashValueNestedSequenceTest, BasicUsage) {
+  using T = TypeParam;
+  using V = typename T::value_type;
+  std::vector<T> exemplars = {
+      // empty case
+      T{},
+      // sets of empty sets
+      T{V{}}, T{V{}, V{}}, T{V{}, V{}, V{}},
+      // multisets of different values
+      T{V{1}}, T{V{1, 1}, V{1, 1}}, T{V{1, 1, 1}, V{1, 1, 1}, V{1, 1, 1}},
+      // various orderings of same nested sets
+      T{V{}, V{1, 2}}, T{V{}, V{2, 1}}, T{V{1, 2}, V{}}, T{V{2, 1}, V{}},
+      // various orderings of various nested sets, case 2
+      T{V{1, 2}, V{3, 4}}, T{V{1, 2}, V{4, 3}}, T{V{1, 3}, V{2, 4}},
+      T{V{1, 3}, V{4, 2}}, T{V{1, 4}, V{2, 3}}, T{V{1, 4}, V{3, 2}},
+      T{V{2, 3}, V{1, 4}}, T{V{2, 3}, V{4, 1}}, T{V{2, 4}, V{1, 3}},
+      T{V{2, 4}, V{3, 1}}, T{V{3, 4}, V{1, 2}}, T{V{3, 4}, V{2, 1}}};
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(exemplars));
+}
+
+REGISTER_TYPED_TEST_CASE_P(HashValueNestedSequenceTest, BasicUsage);
+using NestedIntSequenceTypes =
+    testing::Types<std::vector<std::vector<int>>,
+                   std::vector<TypeErasedVector<int>>,
+                   TypeErasedVector<std::vector<int>>,
+                   TypeErasedVector<TypeErasedVector<int>>>;
+INSTANTIATE_TYPED_TEST_CASE_P(My, HashValueNestedSequenceTest,
+                              NestedIntSequenceTypes);
+
 // Private type that only supports AbslHashValue to make sure our chosen hash
 // implementation is recursive within absl::Hash.
 // It uses std::abs() on the value to provide different bitwise representations
@@ -564,23 +653,59 @@ TEST(HashValueTest, Variant) {
 #endif
 }
 
-TEST(HashValueTest, Maps) {
-  EXPECT_TRUE((is_hashable<std::map<int, std::string>>::value));
+template <typename T>
+class HashValueAssociativeMapTest : public testing::Test {};
+TYPED_TEST_SUITE_P(HashValueAssociativeMapTest);
+
+TYPED_TEST_P(HashValueAssociativeMapTest, BasicUsage) {
+  using M = TypeParam;
+  using V = typename M::value_type;
+  std::vector<M> exemplars{M{},
+                           M{V{0, "foo"}},
+                           M{V{1, "foo"}},
+                           M{V{0, "bar"}},
+                           M{V{1, "bar"}},
+                           M{V{0, "foo"}, V{42, "bar"}},
+                           M{V{42, "bar"}, V{0, "foo"}},
+                           M{V{1, "foo"}, V{42, "bar"}},
+                           M{V{1, "foo"}, V{43, "bar"}},
+                           M{V{1, "foo"}, V{43, "baz"}}};
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(exemplars));
+}
 
-  using M = std::map<int, std::string>;
-  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(std::make_tuple(
-      M{}, M{{0, "foo"}}, M{{1, "foo"}}, M{{0, "bar"}}, M{{1, "bar"}},
-      M{{0, "foo"}, {42, "bar"}}, M{{1, "foo"}, {42, "bar"}},
-      M{{1, "foo"}, {43, "bar"}}, M{{1, "foo"}, {43, "baz"}})));
+REGISTER_TYPED_TEST_CASE_P(HashValueAssociativeMapTest, BasicUsage);
+using AssociativeMapTypes = testing::Types<std::map<int, std::string>>;
+INSTANTIATE_TYPED_TEST_CASE_P(My, HashValueAssociativeMapTest,
+                              AssociativeMapTypes);
 
-  using MM = std::multimap<int, std::string>;
-  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(std::make_tuple(
-      MM{}, MM{{0, "foo"}}, MM{{1, "foo"}}, MM{{0, "bar"}}, MM{{1, "bar"}},
-      MM{{0, "foo"}, {0, "bar"}}, MM{{0, "bar"}, {0, "foo"}},
-      MM{{0, "foo"}, {42, "bar"}}, MM{{1, "foo"}, {42, "bar"}},
-      MM{{1, "foo"}, {1, "foo"}, {43, "bar"}}, MM{{1, "foo"}, {43, "baz"}})));
+template <typename T>
+class HashValueAssociativeMultimapTest : public testing::Test {};
+TYPED_TEST_SUITE_P(HashValueAssociativeMultimapTest);
+
+TYPED_TEST_P(HashValueAssociativeMultimapTest, BasicUsage) {
+  using MM = TypeParam;
+  using V = typename MM::value_type;
+  std::vector<MM> exemplars{MM{},
+                            MM{V{0, "foo"}},
+                            MM{V{1, "foo"}},
+                            MM{V{0, "bar"}},
+                            MM{V{1, "bar"}},
+                            MM{V{0, "foo"}, V{0, "bar"}},
+                            MM{V{0, "bar"}, V{0, "foo"}},
+                            MM{V{0, "foo"}, V{42, "bar"}},
+                            MM{V{1, "foo"}, V{42, "bar"}},
+                            MM{V{1, "foo"}, V{1, "foo"}, V{43, "bar"}},
+                            MM{V{1, "foo"}, V{43, "bar"}, V{1, "foo"}},
+                            MM{V{1, "foo"}, V{43, "baz"}}};
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(exemplars));
 }
 
+REGISTER_TYPED_TEST_CASE_P(HashValueAssociativeMultimapTest, BasicUsage);
+using AssociativeMultimapTypes =
+    testing::Types<std::multimap<int, std::string>>;
+INSTANTIATE_TYPED_TEST_CASE_P(My, HashValueAssociativeMultimapTest,
+                              AssociativeMultimapTypes);
+
 TEST(HashValueTest, ReferenceWrapper) {
   EXPECT_TRUE(is_hashable<std::reference_wrapper<Private>>::value);
 
@@ -928,28 +1053,14 @@ TEST(HashTest, SmallValueOn64ByteBoundary) {
   Hash<IntAndString>()(IntAndString{0, std::string(63, '0')});
 }
 
-struct TypeErased {
-  size_t n;
-
-  template <typename H>
-  friend H AbslHashValue(H hash_state, const TypeErased& v) {
-    v.HashValue(absl::HashState::Create(&hash_state));
-    return hash_state;
-  }
-
-  void HashValue(absl::HashState state) const {
-    absl::HashState::combine(std::move(state), n);
-  }
-};
-
 TEST(HashTest, TypeErased) {
-  EXPECT_TRUE((is_hashable<TypeErased>::value));
-  EXPECT_TRUE((is_hashable<std::pair<TypeErased, int>>::value));
+  EXPECT_TRUE((is_hashable<TypeErasedValue<size_t>>::value));
+  EXPECT_TRUE((is_hashable<std::pair<TypeErasedValue<size_t>, int>>::value));
 
-  EXPECT_EQ(SpyHash(TypeErased{7}), SpyHash(size_t{7}));
-  EXPECT_NE(SpyHash(TypeErased{7}), SpyHash(size_t{13}));
+  EXPECT_EQ(SpyHash(TypeErasedValue<size_t>(7)), SpyHash(size_t{7}));
+  EXPECT_NE(SpyHash(TypeErasedValue<size_t>(7)), SpyHash(size_t{13}));
 
-  EXPECT_EQ(SpyHash(std::make_pair(TypeErased{7}, 17)),
+  EXPECT_EQ(SpyHash(std::make_pair(TypeErasedValue<size_t>(7), 17)),
             SpyHash(std::make_pair(size_t{7}, 17)));
 }
 
diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h
index b1e33caf..97b68bad 100644
--- a/absl/hash/internal/hash.h
+++ b/absl/hash/internal/hash.h
@@ -502,10 +502,9 @@ AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) {
                     vector.size());
 }
 
+// AbslHashValue special cases for hashing std::vector<bool>
 #if defined(ABSL_IS_BIG_ENDIAN) && \
     (defined(__GLIBCXX__) || defined(__GLIBCPP__))
-// AbslHashValue for hashing std::vector<bool>
-//
 // std::hash in libstdc++ does not work correctly with vector<bool> on Big
 // Endian platforms therefore we need to implement a custom AbslHashValue for
 // it. More details on the bug:
@@ -521,6 +520,22 @@ AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) {
   }
   return H::combine(combiner.finalize(std::move(hash_state)), vector.size());
 }
+#else
+// When not working around the libstdc++ bug above, we still have to contend
+// with the fact that std::hash<vector<bool>> is often poor quality, hashing
+// directly on the internal words and on no other state.  On these platforms,
+// vector<bool>{1, 1} and vector<bool>{1, 1, 0} hash to the same value.
+//
+// Mixing in the size (as we do in our other vector<> implementations) on top
+// of the library-provided hash implementation avoids this QOI issue.
+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(std::move(hash_state),
+                    std::hash<std::vector<T, Allocator>>{}(vector),
+                    vector.size());
+}
 #endif
 
 // -----------------------------------------------------------------------------