Rename RemoteTxCache as RemoteCommitmentTransaction and document better

We also remove an unecessary build warning.

Author: Antoine Riard

lightning/src/ln/channelmonitor.rs

@@ -418,14 +418,14 @@ struct LocalSignedTx {
 	htlc_outputs: Vec<(HTLCOutputInCommitment, Option<Signature>, Option<HTLCSource>)>,
 }
 
-/// Cache remote basepoint to compute any transaction on
-/// remote outputs, either justice or preimage/timeout transactions.
+/// We use this to track remote commitment transactions and htlcs outputs and
+/// use it to generate any justice or 2nd-stage preimage/timeout transactions.
 #[derive(PartialEq)]
-struct RemoteTxCache {
+struct RemoteCommitmentTransaction {
 	remote_delayed_payment_base_key: PublicKey,
 	remote_htlc_base_key: PublicKey,
 	on_remote_tx_csv: u16,
-	per_htlc: HashMap<Txid, Vec<(HTLCOutputInCommitment)>>
+	per_htlc: HashMap<Txid, Vec<HTLCOutputInCommitment>>
 }
 
 /// When ChannelMonitor discovers an onchain outpoint being a step of a channel and that it needs
@@ -751,7 +751,7 @@ pub struct ChannelMonitor<ChanSigner: ChannelKeys> {
 	current_remote_commitment_txid: Option<Txid>,
 	prev_remote_commitment_txid: Option<Txid>,
 
-	remote_tx_cache: RemoteTxCache,
+	remote_tx_cache: RemoteCommitmentTransaction,
 	funding_redeemscript: Script,
 	channel_value_satoshis: u64,
 	// first is the idx of the first of the two revocation points
@@ -1089,7 +1089,7 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 		let our_channel_close_key_hash = WPubkeyHash::hash(&shutdown_pubkey.serialize());
 		let shutdown_script = Builder::new().push_opcode(opcodes::all::OP_PUSHBYTES_0).push_slice(&our_channel_close_key_hash[..]).into_script();
 
-		let remote_tx_cache = RemoteTxCache { remote_delayed_payment_base_key: *remote_delayed_payment_base_key, remote_htlc_base_key: *remote_htlc_base_key, on_remote_tx_csv, per_htlc: HashMap::new() };
+		let remote_tx_cache = RemoteCommitmentTransaction { remote_delayed_payment_base_key: *remote_delayed_payment_base_key, remote_htlc_base_key: *remote_htlc_base_key, on_remote_tx_csv, per_htlc: HashMap::new() };
 
 		let mut onchain_tx_handler = OnchainTxHandler::new(destination_script.clone(), keys.clone(), on_local_tx_csv, logger.clone());
 
@@ -2299,7 +2299,7 @@ impl<ChanSigner: ChannelKeys + Readable> ReadableArgs<Arc<Logger>> for (BlockHas
 					return Err(DecodeError::InvalidValue);
 				}
 			}
-			RemoteTxCache {
+			RemoteCommitmentTransaction {
 				remote_delayed_payment_base_key,
 				remote_htlc_base_key,
 				on_remote_tx_csv,