Add assertions to detect reentrance in `IterateOverFullSlots` and `absl::erase_if`.

Since we have potential plans to use this function more widely including `absl::c_for_each`, we need to have good error detection.

PiperOrigin-RevId: 647236725
Change-Id: I5035bfb8cef24f80f1bbed83a42380e57d84e428

2 files changed, 132 insertions, 3 deletions

diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index 724df193..02e389b9 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -1860,8 +1860,8 @@ inline void* SlotAddress(void* slot_array, size_t slot, size_t slot_size) {
 }
 
 // Iterates over all full slots and calls `cb(const ctrl_t*, SlotType*)`.
-// If kAllowRemoveReentrance is false, no erasure from this table allowed during
-// Callback call. This mode is slightly faster.
+// No insertion to the table allowed during Callback call.
+// Erasure is allowed only for the element passed to the callback.
 template <class SlotType, class Callback>
 ABSL_ATTRIBUTE_ALWAYS_INLINE inline void IterateOverFullSlots(
     const CommonFields& c, SlotType* slot, Callback cb) {
@@ -1890,16 +1890,22 @@ ABSL_ATTRIBUTE_ALWAYS_INLINE inline void IterateOverFullSlots(
     return;
   }
   size_t remaining = c.size();
+  ABSL_ATTRIBUTE_UNUSED const size_t original_size_for_assert = remaining;
   while (remaining != 0) {
     for (uint32_t i : GroupFullEmptyOrDeleted(ctrl).MaskFull()) {
+      assert(IsFull(ctrl[i]) && "hash table was modified unexpectedly");
       cb(ctrl + i, slot + i);
       --remaining;
     }
     ctrl += Group::kWidth;
     slot += Group::kWidth;
     assert((remaining == 0 || *(ctrl - 1) != ctrl_t::kSentinel) &&
-            "element was erased from hash table unexpectedly");
+           "hash table was modified unexpectedly");
   }
+  // NOTE: erasure of the current element is allowed in callback for
+  // absl::erase_if specialization. So we use `>=`.
+  assert(original_size_for_assert >= c.size() &&
+         "hash table was modified unexpectedly");
 }
 
 template <typename CharAlloc>
@@ -4049,12 +4055,14 @@ struct HashtableFreeFunctionsAccess {
     if (c->is_soo()) {
       auto it = c->soo_iterator();
       if (!pred(*it)) {
+        assert(c->size() == 1 && "hash table was modified unexpectedly");
         return 0;
       }
       c->destroy(it.slot());
       c->common().set_empty_soo();
       return 1;
     }
+    ABSL_ATTRIBUTE_UNUSED const size_t original_size_for_assert = c->size();
     size_t num_deleted = 0;
     IterateOverFullSlots(
         c->common(), c->slot_array(), [&](const ctrl_t* ctrl, auto* slot) {
@@ -4065,6 +4073,10 @@ struct HashtableFreeFunctionsAccess {
             ++num_deleted;
           }
         });
+    // NOTE: IterateOverFullSlots allow removal of the current element, so we
+    // verify the size additionally here.
+    assert(original_size_for_assert - num_deleted == c->size() &&
+           "hash table was modified unexpectedly");
     return num_deleted;
   }
 
diff --git a/absl/container/internal/raw_hash_set_test.cc b/absl/container/internal/raw_hash_set_test.cc
index ba603d2b..f1257d4b 100644
--- a/absl/container/internal/raw_hash_set_test.cc
+++ b/absl/container/internal/raw_hash_set_test.cc
@@ -3173,6 +3173,54 @@ TEST(Table, ForEachMutate) {
   }
 }
 
+TYPED_TEST(SooTest, EraseIfReentryDeath) {
+  if (!IsAssertEnabled()) GTEST_SKIP() << "Assertions not enabled.";
+
+  auto erase_if_with_removal_reentrance = [](size_t reserve_size) {
+    TypeParam t;
+    t.reserve(reserve_size);
+    int64_t first_value = -1;
+    t.insert(1024);
+    t.insert(5078);
+    auto pred = [&](const auto& x) {
+      if (first_value == -1) {
+        first_value = static_cast<int64_t>(x);
+        return false;
+      }
+      // We erase on second call to `pred` to reduce the chance that assertion
+      // will happen in IterateOverFullSlots.
+      t.erase(first_value);
+      return true;
+    };
+    absl::container_internal::EraseIf(pred, &t);
+  };
+  // Removal will likely happen in a different group.
+  EXPECT_DEATH_IF_SUPPORTED(erase_if_with_removal_reentrance(1024 * 16),
+                            "hash table was modified unexpectedly");
+  // Removal will happen in the same group.
+  EXPECT_DEATH_IF_SUPPORTED(
+      erase_if_with_removal_reentrance(CapacityToGrowth(Group::kWidth - 1)),
+      "hash table was modified unexpectedly");
+}
+
+// This test is useful to test soo branch.
+TYPED_TEST(SooTest, EraseIfReentrySingleElementDeath) {
+  if (!IsAssertEnabled()) GTEST_SKIP() << "Assertions not enabled.";
+
+  auto erase_if_with_removal_reentrance = []() {
+    TypeParam t;
+    t.insert(1024);
+    auto pred = [&](const auto& x) {
+      // We erase ourselves in order to confuse the erase_if.
+      t.erase(static_cast<int64_t>(x));
+      return false;
+    };
+    absl::container_internal::EraseIf(pred, &t);
+  };
+  EXPECT_DEATH_IF_SUPPORTED(erase_if_with_removal_reentrance(),
+                            "hash table was modified unexpectedly");
+}
+
 TEST(Table, EraseBeginEndResetsReservedGrowth) {
   bool frozen = false;
   BadHashFreezableIntTable t{FreezableAlloc<int64_t>(&frozen)};
@@ -3368,6 +3416,75 @@ TEST(Table, IterateOverFullSlotsFull) {
   }
 }
 
+TEST(Table, IterateOverFullSlotsDeathOnRemoval) {
+  if (!IsAssertEnabled()) GTEST_SKIP() << "Assertions not enabled.";
+
+  auto iterate_with_reentrant_removal = [](int64_t size,
+                                           int64_t reserve_size = -1) {
+    if (reserve_size == -1) reserve_size = size;
+    for (int64_t idx = 0; idx < size; ++idx) {
+      NonSooIntTable t;
+      t.reserve(static_cast<size_t>(reserve_size));
+      for (int val = 0; val <= idx; ++val) {
+        t.insert(val);
+      }
+
+      container_internal::IterateOverFullSlots(
+          RawHashSetTestOnlyAccess::GetCommon(t),
+          RawHashSetTestOnlyAccess::GetSlots(t),
+          [&t](const ctrl_t*, auto* i) {
+            int64_t value = **i;
+            // Erase the other element from 2*k and 2*k+1 pair.
+            t.erase(value ^ 1);
+          });
+    }
+  };
+
+  EXPECT_DEATH_IF_SUPPORTED(iterate_with_reentrant_removal(128),
+                            "hash table was modified unexpectedly");
+  // Removal will likely happen in a different group.
+  EXPECT_DEATH_IF_SUPPORTED(iterate_with_reentrant_removal(14, 1024 * 16),
+                            "hash table was modified unexpectedly");
+  // Removal will happen in the same group.
+  EXPECT_DEATH_IF_SUPPORTED(iterate_with_reentrant_removal(static_cast<int64_t>(
+                                CapacityToGrowth(Group::kWidth - 1))),
+                            "hash table was modified unexpectedly");
+}
+
+TEST(Table, IterateOverFullSlotsDeathOnInsert) {
+  if (!IsAssertEnabled()) GTEST_SKIP() << "Assertions not enabled.";
+
+  auto iterate_with_reentrant_insert = [](int64_t reserve_size,
+                                          int64_t size_divisor = 2) {
+    int64_t size = reserve_size / size_divisor;
+    for (int64_t idx = 1; idx <= size; ++idx) {
+      NonSooIntTable t;
+      t.reserve(static_cast<size_t>(reserve_size));
+      for (int val = 1; val <= idx; ++val) {
+        t.insert(val);
+      }
+
+      container_internal::IterateOverFullSlots(
+          RawHashSetTestOnlyAccess::GetCommon(t),
+          RawHashSetTestOnlyAccess::GetSlots(t),
+          [&t](const ctrl_t*, auto* i) {
+            int64_t value = **i;
+            t.insert(-value);
+          });
+    }
+  };
+
+  EXPECT_DEATH_IF_SUPPORTED(iterate_with_reentrant_insert(128),
+                            "hash table was modified unexpectedly");
+  // Insert will likely happen in a different group.
+  EXPECT_DEATH_IF_SUPPORTED(iterate_with_reentrant_insert(1024 * 16, 1024 * 2),
+                            "hash table was modified unexpectedly");
+  // Insert will happen in the same group.
+  EXPECT_DEATH_IF_SUPPORTED(iterate_with_reentrant_insert(static_cast<int64_t>(
+                                CapacityToGrowth(Group::kWidth - 1))),
+                            "hash table was modified unexpectedly");
+}
+
 template <typename T>
 class SooTable : public testing::Test {};
 using FreezableSooTableTypes =