From a24e904455aa0bf09f9c7dc4f740ffe00f220907 Mon Sep 17 00:00:00 2001
From: Tessil <tessil@gmx.com>
Date: Sun, 27 Feb 2022 15:56:13 +0000
Subject: [PATCH] Fix USE_STORED_HASH_ON_REHASH to return true when
 bucket_count is 0, STORE_HASH is true and
 is_power_of_two_policy<GrowthPolicy>::value is true

This commit doesn't change the actual behaviour of the map as even when USE_STORED_HASH_ON_REHASH was returning false on empty map rehashes, no stored hashes were used as the map was empty.
---
 include/tsl/robin_hash.h  | 6 +++---
 tests/robin_map_tests.cpp | 8 ++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/tsl/robin_hash.h b/include/tsl/robin_hash.h
index e34eac3..98643e6 100644
--- a/include/tsl/robin_hash.h
+++ b/include/tsl/robin_hash.h
@@ -410,9 +410,9 @@ class robin_hash : private Hash, private KeyEqual, private GrowthPolicy {
       TSL_RH_UNUSED(bucket_count);
       return true;
     } else if (STORE_HASH && is_power_of_two_policy<GrowthPolicy>::value) {
-      tsl_rh_assert(bucket_count > 0);
-      return (bucket_count - 1) <=
-             std::numeric_limits<truncated_hash_type>::max();
+      return bucket_count == 0 ||
+             (bucket_count - 1) <=
+                 std::numeric_limits<truncated_hash_type>::max();
     } else {
       TSL_RH_UNUSED(bucket_count);
       return false;
diff --git a/tests/robin_map_tests.cpp b/tests/robin_map_tests.cpp
index 34cbd26..cfa620e 100644
--- a/tests/robin_map_tests.cpp
+++ b/tests/robin_map_tests.cpp
@@ -140,6 +140,14 @@ BOOST_AUTO_TEST_CASE(test_range_insert) {
   }
 }
 
+BOOST_AUTO_TEST_CASE(test_rehash_0) {
+  tsl::robin_map<int, int, std::hash<int>,
+                   std::equal_to<int>,
+                   std::allocator<std::pair<int, int>>,
+                   true> map;
+  map.rehash(0);
+}
+
 BOOST_AUTO_TEST_CASE(test_insert_with_hint) {
   tsl::robin_map<int, int> map{{1, 0}, {2, 1}, {3, 2}};