Enter FundingNegotiated state after constructing funding tx

The ChannelState::NegotiatingFunding assertion check in
ChannelContext::get_initial_commitment_signed will fail when
implementing splicing's channel_reestablish logic. In order to support
it and channel establishment, enter ChannelState::FundingNegotiated
prior to calling the method and update the assertion accordingly.

Also allows writing a channel in the FundedNegotiated state when an
interactive signing session is active. This is necessary as it indicates
a previously funded channel being spliced.

Author: jkczyz

lightning/src/ln/channel.rs

@@ -5517,6 +5517,9 @@ where
 		funding
 			.channel_transaction_parameters.funding_outpoint = Some(outpoint);
 
+		self.channel_state = ChannelState::FundingNegotiated(FundingNegotiatedFlags::new());
+		self.channel_state.set_interactive_signing();
+
 		if is_splice {
 			debug_assert_eq!(
 				holder_commitment_transaction_number,
@@ -5580,10 +5583,6 @@ where
 			});
 		};
 
-		let mut channel_state = ChannelState::FundingNegotiated(FundingNegotiatedFlags::new());
-		channel_state.set_interactive_signing();
-		self.channel_state = channel_state;
-
 		Ok((commitment_signed, funding_ready_for_sig_event))
 	}
 
@@ -5636,16 +5635,7 @@ where
 		SP::Target: SignerProvider,
 		L::Target: Logger
 	{
-		if !matches!(
-			self.channel_state, ChannelState::NegotiatingFunding(flags)
-			if flags == (NegotiatingFundingFlags::OUR_INIT_SENT | NegotiatingFundingFlags::THEIR_INIT_SENT)
-		) {
-			debug_assert!(false);
-			let msg = "Tried to get an initial commitment_signed messsage at a time other than \
-				immediately after initial handshake completion (or tried to get funding_created twice)";
-			let reason = ClosureReason::ProcessingError { err: msg.to_owned() };
-			return Err(ChannelError::Close((msg.to_owned(), reason)));
-		}
+		assert!(matches!(self.channel_state, ChannelState::FundingNegotiated(flags) if flags.is_interactive_signing()));
 
 		let signature = match self.get_initial_counterparty_commitment_signature(funding, logger) {
 			Ok(res) => res,
@@ -12880,6 +12870,7 @@ where
 					channel_state.clear_remote_stfu_sent();
 					channel_state.clear_quiescent();
 				},
+				ChannelState::FundingNegotiated(flags) if flags.is_interactive_signing() => {},
 				_ => debug_assert!(false, "Pre-funded/shutdown channels should not be written"),
 			}
 			channel_state.set_peer_disconnected();

lightning/src/ln/splicing_tests.rs

@@ -274,29 +274,7 @@ fn test_v1_splice_in() {
 		_ => panic!("Unexpected event {:?}", events[1]),
 	}
 
-	// TODO(splicing): Continue with commitment flow, new tx confirmation
-
-	// === Close channel, cooperatively
-	initiator_node.node.close_channel(&channel_id, &acceptor_node.node.get_our_node_id()).unwrap();
-	let node0_shutdown_message = get_event_msg!(
-		initiator_node,
-		MessageSendEvent::SendShutdown,
-		acceptor_node.node.get_our_node_id()
-	);
-	acceptor_node
-		.node
-		.handle_shutdown(initiator_node.node.get_our_node_id(), &node0_shutdown_message);
-	let nodes_1_shutdown = get_event_msg!(
-		acceptor_node,
-		MessageSendEvent::SendShutdown,
-		initiator_node.node.get_our_node_id()
-	);
-	initiator_node.node.handle_shutdown(acceptor_node.node.get_our_node_id(), &nodes_1_shutdown);
-	let _ = get_event_msg!(
-		initiator_node,
-		MessageSendEvent::SendClosingSigned,
-		acceptor_node.node.get_our_node_id()
-	);
+	// TODO(splicing): Continue with commitment flow, new tx confirmation, and shutdown
 }
 
 #[test]