refactor: inline constant return value of CDBWrapper::WriteBatch

`WriteBatch` can only ever return `true` - its errors are handled by throwing a `throw dbwrapper_error` instead.
The boolean return value is quite confusing, especially since it's symmetric with `CDBWrapper::Read`, which catches the exceptions and returns a boolean instead.
We're removing the constant return value and inlining `true` for its usages.

Author: l0rinc

src/dbwrapper.cpp

@@ -274,7 +274,7 @@ CDBWrapper::~CDBWrapper()
     DBContext().options.env = nullptr;
 }
 
-bool CDBWrapper::WriteBatch(CDBBatch& batch, bool fSync)
+void CDBWrapper::WriteBatch(CDBBatch& batch, bool fSync)
 {
     const bool log_memory = LogAcceptCategory(BCLog::LEVELDB, BCLog::Level::Debug);
     double mem_before = 0;
@@ -288,7 +288,6 @@ bool CDBWrapper::WriteBatch(CDBBatch& batch, bool fSync)
         LogDebug(BCLog::LEVELDB, "WriteBatch memory usage: db=%s, before=%.1fMiB, after=%.1fMiB\n",
                  m_name, mem_before, mem_after);
     }
-    return true;
 }
 
 size_t CDBWrapper::DynamicMemoryUsage() const

src/dbwrapper.h

@@ -234,7 +234,8 @@ class CDBWrapper
     {
         CDBBatch batch(*this);
         batch.Write(key, value);
-        return WriteBatch(batch, fSync);
+        WriteBatch(batch, fSync);
+        return true;
     }
 
     //! @returns filesystem path to the on-disk data.
@@ -259,10 +260,11 @@ class CDBWrapper
     {
         CDBBatch batch(*this);
         batch.Erase(key);
-        return WriteBatch(batch, fSync);
+        WriteBatch(batch, fSync);
+        return true;
     }
 
-    bool WriteBatch(CDBBatch& batch, bool fSync = false);
+    void WriteBatch(CDBBatch& batch, bool fSync = false);
 
     // Get an estimate of LevelDB memory usage (in bytes).
     size_t DynamicMemoryUsage() const;

src/index/base.cpp

@@ -262,7 +262,7 @@ bool BaseIndex::Commit()
         ok = CustomCommit(batch);
         if (ok) {
             GetDB().WriteBestBlock(batch, GetLocator(*m_chain, m_best_block_index.load()->GetBlockHash()));
-            ok = GetDB().WriteBatch(batch);
+            GetDB().WriteBatch(batch);
         }
     }
     if (!ok) {

src/index/blockfilterindex.cpp

@@ -338,7 +338,7 @@ bool BlockFilterIndex::CustomRemove(const interfaces::BlockInfo& block)
     // But since this creates new references to the filter, the position should get updated here
     // atomically as well in case Commit fails.
     batch.Write(DB_FILTER_POS, m_next_filter_pos);
-    if (!m_db->WriteBatch(batch)) return false;
+    m_db->WriteBatch(batch);
 
     // Update cached header to the previous block hash
     m_last_header = *Assert(ReadFilterHeader(block.height - 1, *Assert(block.prev_hash)));

src/index/coinstatsindex.cpp

@@ -263,7 +263,7 @@ bool CoinStatsIndex::CustomRemove(const interfaces::BlockInfo& block)
         return false;
     }
 
-    if (!m_db->WriteBatch(batch)) return false;
+    m_db->WriteBatch(batch);
 
     if (!ReverseBlock(block)) {
         return false; // failure cause logged internally

src/index/txindex.cpp

@@ -46,7 +46,8 @@ bool TxIndex::DB::WriteTxs(const std::vector<std::pair<Txid, CDiskTxPos>>& v_pos
     for (const auto& [txid, pos] : v_pos) {
         batch.Write(std::make_pair(DB_TXINDEX, txid.ToUint256()), pos);
     }
-    return WriteBatch(batch);
+    WriteBatch(batch);
+    return true;
 }
 
 TxIndex::TxIndex(std::unique_ptr<interfaces::Chain> chain, size_t n_cache_size, bool f_memory, bool f_wipe)

src/node/blockstorage.cpp

@@ -88,7 +88,8 @@ bool BlockTreeDB::WriteBatchSync(const std::vector<std::pair<int, const CBlockFi
     for (const CBlockIndex* bi : blockinfo) {
         batch.Write(std::make_pair(DB_BLOCK_INDEX, bi->GetBlockHash()), CDiskBlockIndex{bi});
     }
-    return WriteBatch(batch, true);
+    WriteBatch(batch, true);
+    return true;
 }
 
 bool BlockTreeDB::WriteFlag(const std::string& name, bool fValue)

src/test/dbwrapper_tests.cpp

@@ -173,7 +173,7 @@ BOOST_AUTO_TEST_CASE(dbwrapper_batch)
         // Remove key3 before it's even been written
         batch.Erase(key3);
 
-        BOOST_CHECK(dbw.WriteBatch(batch));
+        dbw.WriteBatch(batch);
 
         BOOST_CHECK(dbw.Read(key, res));
         BOOST_CHECK_EQUAL(res.ToString(), in.ToString());

src/txdb.cpp

@@ -149,9 +149,9 @@ bool CCoinsViewDB::BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashB
     batch.Write(DB_BEST_BLOCK, hashBlock);
 
     LogDebug(BCLog::COINDB, "Writing final batch of %.2f MiB\n", batch.ApproximateSize() * (1.0 / 1048576.0));
-    bool ret = m_db->WriteBatch(batch);
+    m_db->WriteBatch(batch);
     LogDebug(BCLog::COINDB, "Committed %u changed transaction outputs (out of %u) to coin database...\n", (unsigned int)changed, (unsigned int)count);
-    return ret;
+    return true;
 }
 
 size_t CCoinsViewDB::EstimateSize() const