merge bitcoin#26999: A few follow-ups to bitcoin#17487

src/coins.cpp

@@ -236,15 +236,18 @@ bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn
 }
 
 bool CCoinsViewCache::Flush() {
-    bool fOk = base->BatchWrite(cacheCoins, hashBlock, /*erase=*/ true);
-    cacheCoins.clear();
+    bool fOk = base->BatchWrite(cacheCoins, hashBlock, /*erase=*/true);
+    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;
 }
 
 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(); ) {

src/test/coins_tests.cpp

@@ -55,7 +55,7 @@ class CCoinsViewTest : public CCoinsView
 
     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;

src/test/fuzz/coins_view.cpp

@@ -76,6 +76,9 @@ 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));
             },