OfferBuilder for c_bindings

OfferBuilder is currently not exported to bindings because it uses move
semantics and has impl blocks for specific type parameterizations.
Define a macro that defines OfferBuilder methods such that c_bindings
versions can be defined.

Author: jkczyz

lightning/Cargo.toml

@@ -41,6 +41,7 @@ default = ["std", "grind_signatures"]
 
 [dependencies]
 bitcoin = { version = "0.30.2", default-features = false, features = ["secp-recovery"] }
+secp256k1 = { version = "0.27", features = ["global-context", "recovery"] }
 
 hashbrown = { version = "0.8", optional = true }
 hex = { package = "hex-conservative", version = "0.1.1", default-features = false }

lightning/src/ln/channelmanager.rs

@@ -60,7 +60,7 @@ use crate::ln::wire::Encode;
 use crate::offers::invoice::{BlindedPayInfo, Bolt12Invoice, DEFAULT_RELATIVE_EXPIRY, DerivedSigningPubkey, InvoiceBuilder};
 use crate::offers::invoice_error::InvoiceError;
 use crate::offers::merkle::SignError;
-use crate::offers::offer::{DerivedMetadata, Offer, OfferBuilder};
+use crate::offers::offer::Offer;
 use crate::offers::parse::Bolt12SemanticError;
 use crate::offers::refund::{Refund, RefundBuilder};
 use crate::onion_message::messenger::{Destination, MessageRouter, PendingOnionMessage, new_pending_onion_message};
@@ -98,6 +98,12 @@ use core::ops::Deref;
 pub use crate::ln::outbound_payment::{PaymentSendFailure, ProbeSendFailure, Retry, RetryableSendFailure, RecipientOnionFields};
 use crate::ln::script::ShutdownScript;
 
+#[cfg(not(c_bindings))]
+type OfferBuilder<'a> =
+	crate::offers::offer::OfferBuilder<'a, crate::offers::offer::DerivedMetadata, secp256k1::All>;
+#[cfg(c_bindings)]
+type OfferBuilder<'a> = crate::offers::offer::OfferWithDerivedMetadataBuilder;
+
 // We hold various information about HTLC relay in the HTLC objects in Channel itself:
 //
 // Upon receipt of an HTLC from a peer, we'll give it a PendingHTLCStatus indicating if it should
@@ -7550,20 +7556,32 @@ where
 	/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
 	pub fn create_offer_builder(
 		&self, description: String
-	) -> Result<OfferBuilder<DerivedMetadata, secp256k1::All>, Bolt12SemanticError> {
+	) -> Result<OfferBuilder, Bolt12SemanticError> {
 		let node_id = self.get_our_node_id();
 		let expanded_key = &self.inbound_payment_key;
 		let entropy = &*self.entropy_source;
-		let secp_ctx = &self.secp_ctx;
 
 		let path = self.create_blinded_path().map_err(|_| Bolt12SemanticError::MissingPaths)?;
-		let builder = OfferBuilder::deriving_signing_pubkey(
-			description, node_id, expanded_key, entropy, secp_ctx
-		)
-			.chain_hash(self.chain_hash)
-			.path(path);
 
-		Ok(builder)
+		#[cfg(not(c_bindings))] {
+			let builder = OfferBuilder::deriving_signing_pubkey(
+				description, node_id, expanded_key, entropy, &self.secp_ctx
+			)
+				.chain_hash(self.chain_hash)
+				.path(path);
+
+			Ok(builder)
+		}
+
+		#[cfg(c_bindings)] {
+			let mut builder = OfferBuilder::deriving_signing_pubkey(
+				description, node_id, expanded_key, entropy, &self.secp_ctx
+			);
+			builder.chain_hash(self.chain_hash);
+			builder.path(path);
+
+			Ok(builder)
+		}
 	}
 
 	/// Creates a [`RefundBuilder`] such that the [`Refund`] it builds is recognized by the

lightning/src/offers/invoice.rs

@@ -1644,6 +1644,8 @@ mod tests {
 			],
 		};
 
+		#[cfg(c_bindings)]
+		use crate::offers::offer::OfferWithDerivedMetadataBuilder as OfferBuilder;
 		let offer = OfferBuilder
 			::deriving_signing_pubkey(desc, node_id, &expanded_key, &entropy, &secp_ctx)
 			.amount_msats(1000)