f - attempt to move build_commitment_transaction into ScopedChannelContext

Unfortunately, there's lifetime issue with the return value of
build_commitment_transaction. It seems the impl block introduced
prevents knowing the lifetime on the returned CommitmentStats isn't
outlived after the method returns. It should be the same as the
ChannelContext, but it seems that information is lost the compiler.

Is there anyway to fix this without passing in a FundingScope directly?

Author: jkczyz

lightning/src/ln/channel.rs

@@ -2259,7 +2259,7 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 		self.context.holder_signer.as_mut().provide_channel_parameters(&self.context.channel_transaction_parameters);
 
 		self.context.assert_no_commitment_advancement(transaction_number, "initial commitment_signed");
-		let commitment_signed = self.context.get_initial_commitment_signed(logger);
+		let commitment_signed = self.context_mut().get_initial_commitment_signed(logger);
 		let commitment_signed = match commitment_signed {
 			Ok(commitment_signed) => {
 				self.context.funding_transaction = Some(signing_session.unsigned_tx.build_unsigned_tx());
@@ -3424,7 +3424,14 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 		!self.channel_state.is_pre_funded_state() &&
 			!matches!(self.channel_state, ChannelState::AwaitingChannelReady(flags) if flags.is_set(AwaitingChannelReadyFlags::WAITING_FOR_BATCH))
 	}
+}
 
+impl<C, F, SP: Deref> ScopedChannelContext<C, F, SP>
+where
+	C: Deref<Target = ChannelContext<SP>>,
+	F: Deref<Target = FundingScope>,
+	SP::Target: SignerProvider,
+{
 	/// Transaction nomenclature is somewhat confusing here as there are many different cases - a
 	/// transaction is referred to as "a's transaction" implying that a will be able to broadcast
 	/// the transaction. Thus, b will generally be sending a signature over such a transaction to
@@ -3595,7 +3602,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 		// AwaitingRemoteRevokeToRemove or AwaitingRemovedRemoteRevoke) we may have allowed them to
 		// "violate" their reserve value by couting those against it. Thus, we have to convert
 		// everything to i64 before subtracting as otherwise we can overflow.
-		let value_to_remote_msat: i64 = (self.channel_value_satoshis * 1000) as i64 - (self.value_to_self_msat as i64) - (remote_htlc_total_msat as i64) - value_to_self_msat_offset;
+		let value_to_remote_msat: i64 = (self.channel_value_satoshis() * 1000) as i64 - (self.value_to_self_msat as i64) - (remote_htlc_total_msat as i64) - value_to_self_msat_offset;
 		assert!(value_to_remote_msat >= 0);
 
 		#[cfg(debug_assertions)]
@@ -3673,7 +3680,9 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 			outbound_htlc_preimages,
 		}
 	}
+}
 
+impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 	#[inline]
 	/// Creates a set of keys for build_commitment_transaction to generate a transaction which our
 	/// counterparty will sign (ie DO NOT send signatures over a transaction created by this to
@@ -4510,7 +4519,14 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 				msg_name);
 		}
 	}
+}
 
+impl<C, F, SP: Deref> ScopedChannelContext<C, F, SP>
+where
+	C: Deref<Target = ChannelContext<SP>>,
+	F: Deref<Target = FundingScope>,
+	SP::Target: SignerProvider,
+{
 	fn get_initial_counterparty_commitment_signature<L: Deref>(
 		&self, logger: &L
 	) -> Result<Signature, ChannelError>
@@ -4537,7 +4553,14 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 			_ => todo!(),
 		}
 	}
+}
 
+impl<C, F, SP: Deref> ScopedChannelContext<C, F, SP>
+where
+	C: DerefMut<Target = ChannelContext<SP>>,
+	F: DerefMut<Target = FundingScope>,
+	SP::Target: SignerProvider,
+{
 	fn get_initial_commitment_signed<L: Deref>(
 		&mut self, logger: &L
 	) -> Result<msgs::CommitmentSigned, ChannelError>
@@ -5527,7 +5550,8 @@ impl<SP: Deref> FundedChannel<SP> where
 
 		let keys = self.context.build_holder_transaction_keys(self.holder_commitment_point.current_point());
 
-		let commitment_stats = self.context.build_commitment_transaction(self.holder_commitment_point.transaction_number(), &keys, true, false, logger);
+		let funding_context = self.context();
+		let commitment_stats = funding_context.build_commitment_transaction(self.holder_commitment_point.transaction_number(), &keys, true, false, logger);
 		let commitment_txid = {
 			let trusted_tx = commitment_stats.tx.trust();
 			let bitcoin_tx = trusted_tx.built_transaction();
@@ -6279,7 +6303,8 @@ impl<SP: Deref> FundedChannel<SP> where
 		let dust_exposure_limiting_feerate = self.context.get_dust_exposure_limiting_feerate(&fee_estimator);
 		let htlc_stats = self.context.get_pending_htlc_stats(Some(feerate_per_kw), dust_exposure_limiting_feerate);
 		let keys = self.context.build_holder_transaction_keys(self.holder_commitment_point.current_point());
-		let commitment_stats = self.context.build_commitment_transaction(self.holder_commitment_point.transaction_number(), &keys, true, true, logger);
+		let funding_context = self.context();
+		let commitment_stats = funding_context.build_commitment_transaction(self.holder_commitment_point.transaction_number(), &keys, true, true, logger);
 		let buffer_fee_msat = commit_tx_fee_sat(feerate_per_kw, commitment_stats.num_nondust_htlcs + htlc_stats.on_holder_tx_outbound_holding_cell_htlcs_count as usize + CONCURRENT_INBOUND_HTLC_FEE_BUFFER as usize, self.context.get_channel_type()) * 1000;
 		let holder_balance_msat = commitment_stats.local_balance_msat - htlc_stats.outbound_holding_cell_msat;
 		if holder_balance_msat < buffer_fee_msat  + self.context.counterparty_selected_channel_reserve_satoshis.unwrap() * 1000 {
@@ -6580,7 +6605,7 @@ impl<SP: Deref> FundedChannel<SP> where
 		}
 		let funding_signed = if self.context.signer_pending_funding && !self.context.is_outbound() {
 			let counterparty_keys = self.context.build_remote_transaction_keys();
-			let counterparty_initial_commitment_tx = self.context.build_commitment_transaction(self.context.cur_counterparty_commitment_transaction_number + 1, &counterparty_keys, false, false, logger).tx;
+			let counterparty_initial_commitment_tx = self.context().build_commitment_transaction(self.context.cur_counterparty_commitment_transaction_number + 1, &counterparty_keys, false, false, logger).tx;
 			self.context.get_funding_signed_msg(logger, counterparty_initial_commitment_tx)
 		} else { None };
 		// Provide a `channel_ready` message if we need to, but only if we're _not_ still pending
@@ -8506,7 +8531,8 @@ impl<SP: Deref> FundedChannel<SP> where
 	where L::Target: Logger
 	{
 		let counterparty_keys = self.context.build_remote_transaction_keys();
-		let commitment_stats = self.context.build_commitment_transaction(self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, true, logger);
+		let funding_context = self.context();
+		let commitment_stats = funding_context.build_commitment_transaction(self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, true, logger);
 		let counterparty_commitment_tx = commitment_stats.tx;
 
 		#[cfg(any(test, fuzzing))]
@@ -8538,7 +8564,8 @@ impl<SP: Deref> FundedChannel<SP> where
 		self.build_commitment_no_state_update(logger);
 
 		let counterparty_keys = self.context.build_remote_transaction_keys();
-		let commitment_stats = self.context.build_commitment_transaction(self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, true, logger);
+		let funding_context = self.context();
+		let commitment_stats = funding_context.build_commitment_transaction(self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, true, logger);
 		let counterparty_commitment_txid = commitment_stats.tx.trust().txid();
 
 		match &self.context.holder_signer {
@@ -8815,7 +8842,7 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {
 	/// Only allowed after [`ChannelContext::channel_transaction_parameters`] is set.
 	fn get_funding_created_msg<L: Deref>(&mut self, logger: &L) -> Option<msgs::FundingCreated> where L::Target: Logger {
 		let counterparty_keys = self.context.build_remote_transaction_keys();
-		let counterparty_initial_commitment_tx = self.context.build_commitment_transaction(self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, false, logger).tx;
+		let counterparty_initial_commitment_tx = self.context().build_commitment_transaction(self.context.cur_counterparty_commitment_transaction_number, &counterparty_keys, false, false, logger).tx;
 		let signature = match &self.context.holder_signer {
 			// TODO (taproot|arik): move match into calling method for Taproot
 			ChannelSignerType::Ecdsa(ecdsa) => {