From ec35402ac93f2f010087794d8216a235d5e62b79 Mon Sep 17 00:00:00 2001
From: Vitaly Goldshteyn <goldvitaly@google.com>
Date: Thu, 12 Mar 2026 03:38:48 -0700
Subject: [PATCH] Fix sampling for the insert into a non-SOO table with
 capacity==1.

RecordInsertMiss is where we increment size for hashtablez.
This call was missing, so size was off by one.
We can even end up with negative size if a later erase takes place on the same table.

PiperOrigin-RevId: 882493632
Change-Id: Ifbb58fb2eaa0225d310c919bd0162dc2e0185d58
---
 absl/container/internal/raw_hash_set.cc      |  4 +++
 absl/container/internal/raw_hash_set_test.cc | 33 ++++++++++++++++++--
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/absl/container/internal/raw_hash_set.cc b/absl/container/internal/raw_hash_set.cc
index 15d072a7..048d2ee6 100644
--- a/absl/container/internal/raw_hash_set.cc
+++ b/absl/container/internal/raw_hash_set.cc
@@ -1528,6 +1528,10 @@ std::pair<ctrl_t*, void*> PrepareInsertSmallNonSoo(
   if (common.capacity() == 1) {
     if (common.empty()) {
       IncrementSmallSizeNonSoo(common, policy);
+      if (common.has_infoz()) {
+        common.infoz().RecordInsertMiss(get_hash(common.seed().seed()),
+                                        /*distance_from_desired=*/0);
+      }
       return {SooControl(), common.slot_array()};
     } else {
       return Grow1To3AndPrepareInsert(common, policy, get_hash);
diff --git a/absl/container/internal/raw_hash_set_test.cc b/absl/container/internal/raw_hash_set_test.cc
index 9c33e3c7..952399ab 100644
--- a/absl/container/internal/raw_hash_set_test.cc
+++ b/absl/container/internal/raw_hash_set_test.cc
@@ -2878,8 +2878,9 @@ TYPED_TEST(RawHashSamplerTest, Sample) {
   }
 }
 
-std::vector<const HashtablezInfo*> SampleSooMutation(
-    absl::FunctionRef<void(SooInt32Table&)> mutate_table) {
+template <typename IntTableType>
+std::vector<const HashtablezInfo*> SampleTableMutation(
+    absl::FunctionRef<void(IntTableType&)> mutate_table) {
   // Enable the feature even if the prod default is off.
   SetSamplingRateTo1Percent();
 
@@ -2892,7 +2893,7 @@ std::vector<const HashtablezInfo*> SampleSooMutation(
     ++start_size;
   });
 
-  std::vector<SooInt32Table> tables;
+  std::vector<IntTableType> tables;
   for (int i = 0; i < 1000000; ++i) {
     tables.emplace_back();
     mutate_table(tables.back());
@@ -2911,6 +2912,16 @@ std::vector<const HashtablezInfo*> SampleSooMutation(
   return infos;
 }
 
+std::vector<const HashtablezInfo*> SampleSooMutation(
+    absl::FunctionRef<void(SooInt32Table&)> mutate_table) {
+  return SampleTableMutation<SooInt32Table>(mutate_table);
+}
+
+std::vector<const HashtablezInfo*> SampleNonSooMutation(
+    absl::FunctionRef<void(NonSooIntTable&)> mutate_table) {
+  return SampleTableMutation<NonSooIntTable>(mutate_table);
+}
+
 TEST(RawHashSamplerTest, SooTableInsertToEmpty) {
   if (SooInt32Table().capacity() != SooCapacity()) {
     CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
@@ -2956,6 +2967,22 @@ TEST(RawHashSamplerTest, SooTableRepeatedInsertEraseDoesNotOversample) {
   // instance.
 }
 
+TEST(RawHashSamplerTest, NonSooTableRepeatedInsertEraseCountSizeRight) {
+  ASSERT_EQ(NonSooIntTable().capacity(), 0);
+  std::vector<const HashtablezInfo*> infos =
+      SampleNonSooMutation([](NonSooIntTable& t) {
+        for (int i = 0; i < 10; ++i) {
+          t.insert(1);
+          t.erase(1);
+        }
+      });
+  for (const HashtablezInfo* info : infos) {
+    EXPECT_EQ(info->soo_capacity, 0);
+    ASSERT_EQ(info->capacity, 1);
+    ASSERT_EQ(info->size, 0);
+  }
+}
+
 // Verifies that copy-constructing or copy-assigning an SOO table does not
 // incorrectly trigger new sampling evaluations.
 TEST(RawHashSamplerTest, SooTableCopyDoesNotOversample) {