refactor: resolve code reviews (2)

Cargo.toml

@@ -4,7 +4,6 @@ version = "0.1.0"
 edition = "2021"
 
 [features]
-default = ["optimism"]
 optimism = [
     "revm/optimism",
     "dep:op-alloy-consensus",

src/chain/optimism.rs

@@ -125,6 +125,7 @@ impl PevmChain for PevmOptimism {
         self.id
     }
 
+    // TODO: allow to construct deposit transactions
     fn build_tx_from_alloy_tx(&self, tx: alloy_rpc_types::Transaction) -> Self::Transaction {
         Self::Transaction {
             inner: tx,
@@ -145,9 +146,13 @@ impl PevmChain for PevmOptimism {
         } else if header.timestamp >= 1704992401 {
             Ok(SpecId::CANYON)
         } else if header.number >= 105235063 {
+            // On Optimism Mainnet, Bedrock and Regolith are activated at the same time.
+            // Therefore, this function never returns SpecId::BEDROCK.
+            // The statement above might not be true for other network, e.g. Optimism Goerli.
             Ok(SpecId::REGOLITH)
         } else {
-            // TODO: revm does not support when L1Block is not available
+            // TODO: revm does not support pre-Bedrock blocks.
+            // https://docs.optimism.io/builders/node-operators/architecture#legacy-geth
             Err(OptimismBlockSpecError::UnsupportedSpec)
         }
     }

src/vm.rs

@@ -624,6 +624,7 @@ impl<'a, S: Storage, C: PevmChain> Vm<'a, S, C> {
                     &mut write_set,
                     tx,
                     U256::from(result_and_state.result.gas_used()),
+                    #[cfg(feature = "optimism")]
                     &evm.context.evm,
                 );
 
@@ -689,7 +690,7 @@ impl<'a, S: Storage, C: PevmChain> Vm<'a, S, C> {
         write_set: &mut WriteSet,
         tx: &TxEnv,
         gas_used: U256,
-        #[allow(unused_variables)] evm_context: &EvmContext<DB>,
+        #[cfg(feature = "optimism")] evm_context: &EvmContext<DB>,
     ) {
         let mut gas_price = if let Some(priority_fee) = tx.gas_priority_fee {
             std::cmp::min(tx.gas_price, priority_fee + self.block_env.basefee)