Expose `PaidBolt12Invoice` in bindings after UniFFI 0.29+ upgrade

[vincenzopalazzo]

Summary

The bolt12_invoice field in the PaymentSuccessful event is currently not exposed in FFI bindings due to a UniFFI limitation.

Background

PR #733 adds PaidBolt12Invoice to the PaymentSuccessful event to enable proof of payment for BOLT12 transactions. However, UniFFI v0.28 does not support Object types in enum variant data:

Objects cannot currently be used in enum variant data

This limitation was resolved in uniffi-rs#2412, which shipped in UniFFI v0.29.

Why we can't upgrade yet

We currently can't upgrade to UniFFI v0.29 because NordSecurity/uniffi-bindgen-go lags behind and doesn't support newer versions yet. See: NordSecurity/uniffi-bindgen-go#40

Action needed

Once we can upgrade to UniFFI 0.29+:

1. Remove #[cfg(not(feature = "uniffi"))] from bolt12_invoice field in Event::PaymentSuccessful
2. Add PaidBolt12Invoice as an [Enum] interface in bindings/ldk_node.udl
3. Add StaticInvoice interface in bindings/ldk_node.udl
4. Add the field back to PaymentSuccessful in the UDL
5. Remove the duplicated impl_writeable_tlv_based_enum! macro in src/event.rs

Related

• PR [RFC] event: expose BOLT12 invoice in PaymentSuccessful for proof of payment #733

[vincenzopalazzo]

@tnull I am closing this because it is not completed with the other approach that we used in #733