Change the API constraints of erase(const_iterator, const_iterator) so that calling erase(begin(), end()) resets reserved growth.

PiperOrigin-RevId: 551248712
Change-Id: I34755c63e3ee40da4ba7047e0d24eec567d28173

1 files changed, 58 insertions, 0 deletions

diff --git a/absl/container/internal/raw_hash_set_test.cc b/absl/container/internal/raw_hash_set_test.cc
index 66621cf0..f0947b97 100644
--- a/absl/container/internal/raw_hash_set_test.cc
+++ b/absl/container/internal/raw_hash_set_test.cc
@@ -60,6 +60,10 @@ struct RawHashSetTestOnlyAccess {
   static auto GetSlots(const C& c) -> decltype(c.slot_array()) {
     return c.slot_array();
   }
+  template <typename C>
+  static size_t CountTombstones(const C& c) {
+    return c.common().TombstonesCount();
+  }
 };
 
 namespace {
@@ -472,6 +476,28 @@ struct MinimumAlignmentUint8Table
   using Base::Base;
 };
 
+// Allows for freezing the allocator to expect no further allocations.
+template <typename T>
+struct FreezableAlloc : std::allocator<T> {
+  explicit FreezableAlloc(bool* f) : frozen(f) {}
+
+  template <typename U>
+  explicit FreezableAlloc(const FreezableAlloc<U>& other)
+      : frozen(other.frozen) {}
+
+  template <class U>
+  struct rebind {
+    using other = FreezableAlloc<U>;
+  };
+
+  T* allocate(size_t n) {
+    EXPECT_FALSE(*frozen);
+    return std::allocator<T>::allocate(n);
+  }
+
+  bool* frozen;
+};
+
 struct BadFastHash {
   template <class T>
   size_t operator()(const T&) const {
@@ -479,6 +505,13 @@ struct BadFastHash {
   }
 };
 
+struct BadHashFreezableIntTable
+    : raw_hash_set<IntPolicy, BadFastHash, std::equal_to<int64_t>,
+                   FreezableAlloc<int64_t>> {
+  using Base = typename BadHashFreezableIntTable::raw_hash_set;
+  using Base::Base;
+};
+
 struct BadTable : raw_hash_set<IntPolicy, BadFastHash, std::equal_to<int>,
                                std::allocator<int>> {
   using Base = typename BadTable::raw_hash_set;
@@ -512,6 +545,7 @@ TEST(Table, EmptyFunctorOptimization) {
 
   struct GenerationData {
     size_t reserved_growth;
+    size_t reservation_size;
     GenerationType* generation;
   };
 
@@ -2387,6 +2421,30 @@ TEST(Table, ReservedGrowthUpdatesWhenTableDoesntGrow) {
   EXPECT_EQ(*it, 0);
 }
 
+TEST(Table, EraseBeginEndResetsReservedGrowth) {
+  bool frozen = false;
+  BadHashFreezableIntTable t{FreezableAlloc<int64_t>(&frozen)};
+  t.reserve(100);
+  const size_t cap = t.capacity();
+  frozen = true;  // no further allocs allowed
+
+  for (int i = 0; i < 10; ++i) {
+    // Create a long run (hash function returns constant).
+    for (int j = 0; j < 100; ++j) t.insert(j);
+    // Erase elements from the middle of the long run, which creates tombstones.
+    for (int j = 30; j < 60; ++j) t.erase(j);
+    EXPECT_EQ(t.size(), 70);
+    EXPECT_EQ(t.capacity(), cap);
+    ASSERT_EQ(RawHashSetTestOnlyAccess::CountTombstones(t), 30);
+
+    t.erase(t.begin(), t.end());
+
+    EXPECT_EQ(t.size(), 0);
+    EXPECT_EQ(t.capacity(), cap);
+    ASSERT_EQ(RawHashSetTestOnlyAccess::CountTombstones(t), 0);
+  }
+}
+
 TEST(Table, GenerationInfoResetsOnClear) {
   if (!SwisstableGenerationsEnabled()) GTEST_SKIP() << "Generations disabled.";
   if (kMsvc) GTEST_SKIP() << "MSVC doesn't support | in regexp.";