From bb00357add2c44d4b2cf4341be963f6bb9bee63f Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Mon, 30 Jan 2023 11:32:59 -0500
Subject: [PATCH 1/4] Make test/fuzz/coins_view exercise
 CCoinsViewCache::Sync()

---
 src/test/fuzz/coins_view.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/test/fuzz/coins_view.cpp b/src/test/fuzz/coins_view.cpp
index 46026d8df3..e75dc3ce91 100644
--- a/src/test/fuzz/coins_view.cpp
+++ b/src/test/fuzz/coins_view.cpp
@@ -74,6 +74,9 @@ FUZZ_TARGET_INIT(coins_view, initialize_coins_view)
             [&] {
                 (void)coins_view_cache.Flush();
             },
+            [&] {
+                (void)coins_view_cache.Sync();
+            },
             [&] {
                 coins_view_cache.SetBestBlock(ConsumeUInt256(fuzzed_data_provider));
             },

From 98db35c2f81098b179136ed6c5f2a8570b3b5900 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Mon, 30 Jan 2023 13:13:20 -0500
Subject: [PATCH 2/4] Follow coding style for named arguments

---
 src/coins.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/coins.cpp b/src/coins.cpp
index ecbd625cd7..e240136576 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -249,7 +249,7 @@ bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn
 }
 
 bool CCoinsViewCache::Flush() {
-    bool fOk = base->BatchWrite(cacheCoins, hashBlock, /*erase=*/ true);
+    bool fOk = base->BatchWrite(cacheCoins, hashBlock, /*erase=*/true);
     cacheCoins.clear();
     cachedCoinsUsage = 0;
     return fOk;
@@ -257,7 +257,7 @@ bool CCoinsViewCache::Flush() {
 
 bool CCoinsViewCache::Sync()
 {
-    bool fOk = base->BatchWrite(cacheCoins, hashBlock, /*erase=*/ false);
+    bool fOk = base->BatchWrite(cacheCoins, hashBlock, /*erase=*/false);
     // Instead of clearing `cacheCoins` as we would in Flush(), just clear the
     // FRESH/DIRTY flags of any coin that isn't spent.
     for (auto it = cacheCoins.begin(); it != cacheCoins.end(); ) {

From 941feb6ca28522806c4710f85ae5673abdbdb0b9 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Mon, 30 Jan 2023 11:42:00 -0500
Subject: [PATCH 3/4] Avoid unclear {it = ++it;}

---
 src/test/coins_tests.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/test/coins_tests.cpp b/src/test/coins_tests.cpp
index 92bad8dd2e..312f417129 100644
--- a/src/test/coins_tests.cpp
+++ b/src/test/coins_tests.cpp
@@ -55,7 +55,7 @@ public:
 
     bool BatchWrite(CCoinsMap& mapCoins, const uint256& hashBlock, bool erase = true) override
     {
-        for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end(); it = erase ? mapCoins.erase(it) : ++it) {
+        for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end(); it = erase ? mapCoins.erase(it) : std::next(it)) {
             if (it->second.flags & CCoinsCacheEntry::DIRTY) {
                 // Same optimization used in CCoinsViewDB is to only write dirty entries.
                 map_[it->first] = it->second.coin;

From 2e16054a66b0576ec93d4032d6b74f0930a44fef Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Mon, 30 Jan 2023 11:45:14 -0500
Subject: [PATCH 4/4] Add assertions that BatchWrite(erase=true) erases

---
 src/coins.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/coins.cpp b/src/coins.cpp
index e240136576..31ac67674a 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -250,7 +250,10 @@ bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn
 
 bool CCoinsViewCache::Flush() {
     bool fOk = base->BatchWrite(cacheCoins, hashBlock, /*erase=*/true);
-    cacheCoins.clear();
+    if (fOk && !cacheCoins.empty()) {
+        /* BatchWrite must erase all cacheCoins elements when erase=true. */
+        throw std::logic_error("Not all cached coins were erased");
+    }
     cachedCoinsUsage = 0;
     return fOk;
 }