f - add docs on panic + add more info on expect in channel reestablish

lightning/src/ln/channel.rs

@@ -5629,7 +5629,9 @@ impl<SP: Deref> Channel<SP> where
 
 		let our_commitment_transaction = INITIAL_COMMITMENT_NUMBER - self.context.holder_commitment_point.transaction_number() - 1;
 		if msg.next_remote_commitment_number > 0 {
-			let expected_point = self.context.holder_signer.as_ref().get_per_commitment_point(INITIAL_COMMITMENT_NUMBER - msg.next_remote_commitment_number + 1, &self.context.secp_ctx).expect("TODO");
+			let expected_point = self.context.holder_signer.as_ref()
+				.get_per_commitment_point(INITIAL_COMMITMENT_NUMBER - msg.next_remote_commitment_number + 1, &self.context.secp_ctx)
+				.expect("TODO: async signing is not yet supported for per commitment points upon channel reestablishment");
 			let given_secret = SecretKey::from_slice(&msg.your_last_per_commitment_secret)
 				.map_err(|_| ChannelError::close("Peer sent a garbage channel_reestablish with unparseable secret key".to_owned()))?;
 			if expected_point != PublicKey::from_secret_key(&self.context.secp_ctx, &given_secret) {

lightning/src/sign/mod.rs

@@ -725,6 +725,10 @@ impl HTLCDescriptor {
 
 /// A trait to handle Lightning channel key material without concretizing the channel type or
 /// the signature mechanism.
+///
+/// Several methods allow error types to be returned to support async signing. This feature
+/// is not yet complete, and panics may occur in certain situations when returning errors
+/// for these methods.
 pub trait ChannelSigner {
 	/// Gets the per-commitment point for a specific commitment number
 	///