state: Delete empty accounts after each tx

Delete empty accounts after each transaction
and after applying withdrawals and block rewards.

Co-authored-by: Paweł Bylica <pawel@ethereum.org>

test/state/state.cpp

@@ -135,6 +135,18 @@ std::variant<int64_t, std::error_code> validate_transaction(const Account& sende
     return execution_gas_limit;
 }
 
+namespace
+{
+/// Deletes "touched" (marked as erasable) empty accounts in the state.
+void delete_empty_accounts(State& state)
+{
+    std::erase_if(state.get_accounts(), [](const std::pair<const address, Account>& p) noexcept {
+        const auto& acc = p.second;
+        return acc.erasable && acc.is_empty();
+    });
+}
+}  // namespace
+
 void finalize(State& state, evmc_revision rev, const address& coinbase,
     std::optional<uint64_t> block_reward, std::span<Ommer> ommers,
     std::span<Withdrawal> withdrawals)
@@ -158,14 +170,9 @@ void finalize(State& state, evmc_revision rev, const address& coinbase,
     for (const auto& withdrawal : withdrawals)
         state.touch(withdrawal.recipient).balance += withdrawal.get_amount();
 
+    // Delete potentially empty block reward recipients.
     if (rev >= EVMC_SPURIOUS_DRAGON)
-    {
-        std::erase_if(
-            state.get_accounts(), [](const std::pair<const address, Account>& p) noexcept {
-                const auto& acc = p.second;
-                return acc.erasable && acc.is_empty();
-            });
-    }
+        delete_empty_accounts(state);
 }
 
 std::variant<TransactionReceipt, std::error_code> transition(State& state, const BlockInfo& block,
@@ -241,6 +248,12 @@ std::variant<TransactionReceipt, std::error_code> transition(State& state, const
     // Cannot put it into constructor call because logs are std::moved from host instance.
     receipt.logs_bloom_filter = compute_bloom_filter(receipt.logs);
 
+    // Delete empty accounts after every transaction. This is strictly required until Byzantium
+    // where intermediate state root hashes are part of the transaction receipt.
+    // TODO: Consider limiting this only to Spurious Dragon.
+    if (rev >= EVMC_SPURIOUS_DRAGON)
+        delete_empty_accounts(state);
+
     // Set accounts and their storage access status to cold in the end of transition process
     for (auto& acc : state.get_accounts())
     {