From 27c00ae4982e8298f511b3f623ee0f48e9b9ee35 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ion=20Gazta=C3=B1aga?= <igaztanaga@gmail.com>
Date: Sat, 25 Jun 2022 18:32:27 +0200
Subject: [PATCH] Fixes #75 ("Bug: Rehashing an empty unordered_set with
 cache_begin set to true hits an assert")

---
 include/boost/intrusive/hashtable.hpp | 20 +++++++++++++-------
 test/unordered_test.hpp               |  8 ++++++++
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/include/boost/intrusive/hashtable.hpp b/include/boost/intrusive/hashtable.hpp
index 2cc54c1..b8bc877 100644
--- a/include/boost/intrusive/hashtable.hpp
+++ b/include/boost/intrusive/hashtable.hpp
@@ -1546,6 +1546,9 @@ struct bucket_hash_equal_t
    BOOST_INTRUSIVE_FORCEINLINE void priv_set_cache(bucket_ptr)
    {}
 
+   BOOST_INTRUSIVE_FORCEINLINE void priv_set_cache_bucket_num(std::size_t)
+   {}
+
    BOOST_INTRUSIVE_FORCEINLINE std::size_t priv_get_cache_bucket_num()
    {  return 0u;  }
 
@@ -1638,6 +1641,12 @@ struct bucket_hash_equal_t<ValueTraits, VoidOrKeyOfValue, VoidOrKeyHash, VoidOrK
    BOOST_INTRUSIVE_FORCEINLINE void priv_set_cache(bucket_ptr p)
    {  cached_begin_ = p;   }
 
+   BOOST_INTRUSIVE_FORCEINLINE void priv_set_cache_bucket_num(std::size_t insertion_bucket)
+   {
+      BOOST_INTRUSIVE_INVARIANT_ASSERT(insertion_bucket <= this->priv_usable_bucket_count());
+      this->cached_begin_ = this->priv_bucket_pointer() + std::ptrdiff_t(insertion_bucket);
+   }
+
    BOOST_INTRUSIVE_FORCEINLINE std::size_t priv_get_cache_bucket_num()
    {  return std::size_t(this->cached_begin_ - this->priv_bucket_pointer());  }
 
@@ -3602,9 +3611,8 @@ class hashtable_impl
             slist_node_ptr old_bucket_node_ptr = old_buckets[difference_type(n)].get_node_ptr();
             slist_node_algorithms::transfer_after(new_bucket_nodeptr, old_bucket_node_ptr);
          }
-         //Put cache to safe position
-         this->priv_init_cache();
-         this->priv_insertion_update_cache(ini_n);
+         //Reset cache to safe position
+         this->priv_set_cache_bucket_num(ini_n);
       }
 
       this->priv_set_sentinel_bucket();
@@ -3759,7 +3767,6 @@ class hashtable_impl
       this->priv_size_traits().set_size(0);
       //Put cache to safe position
       this->priv_init_cache();
-      this->priv_insertion_update_cache(size_type(0u));
       this->priv_unset_sentinel_bucket();
 
       const size_type split = this->rehash_split_from_bucket_count(new_bucket_count);
@@ -3824,8 +3831,7 @@ class hashtable_impl
       if(&new_bucket_traits != &this->priv_bucket_traits())
          this->priv_bucket_traits() = new_bucket_traits;
       this->priv_set_sentinel_bucket();
-      this->priv_init_cache();
-      this->priv_insertion_update_cache(new_first_bucket_num);
+      this->priv_set_cache_bucket_num(new_first_bucket_num);
       rollback1.release();
       rollback2.release();
    }
@@ -3923,7 +3929,7 @@ class hashtable_impl
       rollback.release();
       this->priv_size_traits().set_size(src.priv_size_traits().get_size());
       this->priv_split_traits().set_size(dst_bucket_count);
-      this->priv_insertion_update_cache(0u);
+      this->priv_set_cache_bucket_num(0u);
       this->priv_erasure_update_cache();
    }
 
diff --git a/test/unordered_test.hpp b/test/unordered_test.hpp
index e5c91c0..33a6679 100644
--- a/test/unordered_test.hpp
+++ b/test/unordered_test.hpp
@@ -635,6 +635,14 @@ void test_unordered<ContainerDefiner>::test_rehash(value_cont_type& values, deta
    testset1.full_rehash();
    {  int init_values [] = { 1, 2, 2, 3, 4, 5 };
       TEST_INTRUSIVE_SEQUENCE_MAYBEUNIQUE( init_values, testset1 );  }
+
+   //Test empty rehash
+   testset1.clear();
+   testset1.rehash(bucket_traits(
+      pointer_traits<bucket_ptr>::pointer_to(buckets1[0]), sizeof(buckets1) / sizeof(*buckets1)));
+   BOOST_TEST(testset1.empty());
+   testset1.full_rehash();
+   BOOST_TEST(testset1.empty());
 }
 
 //test: find, equal_range (lower_bound, upper_bound):