refactor(payment): add _init_and_read_tlv_stream_with_custom_tlv_decode macro

Add a new _init_and_read_tlv_stream_with_custom_tlv_decode macro that
combines _init_tlv_field_var and decode_tlv_stream_with_custom_tlv_decode,
mirroring how _init_and_read_tlv_stream combines init with decode_tlv_stream.
This avoids manually breaking out field var initialization from the TLV
stream decoding in BlindedPaymentTlvs and BlindedTrampolineTlvs.

Signed-off-by: Asish Kumar <officialasishkumar@gmail.com>

Author: officialasishkumar

lightning/src/blinded_path/payment.rs

@@ -632,15 +632,7 @@ impl<'a> Writeable for BlindedPaymentTlvsRef<'a> {
 
 impl Readable for BlindedPaymentTlvs {
 	fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
-		_init_tlv_field_var!(scid, option);
-		_init_tlv_field_var!(next_blinding_override, option);
-		_init_tlv_field_var!(payment_relay, option);
-		_init_tlv_field_var!(payment_constraints, required);
-		_init_tlv_field_var!(features, (option, encoding: (BlindedHopFeatures, WithoutLength)));
-		_init_tlv_field_var!(payment_secret, option);
-		_init_tlv_field_var!(payment_context, option);
-		_init_tlv_field_var!(is_dummy, option);
-		decode_tlv_stream_with_custom_tlv_decode!(r, {
+		_init_and_read_tlv_stream_with_custom_tlv_decode!(r, {
 			// Reasoning: Padding refers to filler data added to a packet to increase
 			// its size and obscure its actual length. Since padding contains no meaningful
 			// information, we can safely omit reading it here.
@@ -701,14 +693,7 @@ impl Readable for BlindedPaymentTlvs {
 
 impl Readable for BlindedTrampolineTlvs {
 	fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
-		_init_tlv_field_var!(next_trampoline, option);
-		_init_tlv_field_var!(next_blinding_override, option);
-		_init_tlv_field_var!(payment_relay, option);
-		_init_tlv_field_var!(payment_constraints, required);
-		_init_tlv_field_var!(features, (option, encoding: (BlindedHopFeatures, WithoutLength)));
-		_init_tlv_field_var!(payment_secret, option);
-		_init_tlv_field_var!(payment_context, option);
-		decode_tlv_stream_with_custom_tlv_decode!(r, {
+		_init_and_read_tlv_stream_with_custom_tlv_decode!(r, {
 			(4, next_trampoline, option),
 			(8, next_blinding_override, option),
 			(10, payment_relay, option),

lightning/src/util/ser_macros.rs

@@ -1015,6 +1015,23 @@ macro_rules! _init_and_read_tlv_stream {
 	}
 }
 
+/// Equivalent to running [`_init_tlv_field_var`] then
+/// [`decode_tlv_stream_with_custom_tlv_decode`].
+///
+/// If any unused values are read, their type MUST be specified or else `rustc` will read them as an
+/// `i64`.
+macro_rules! _init_and_read_tlv_stream_with_custom_tlv_decode {
+	($reader: ident, {$(($type: expr, $field: ident, $fieldty: tt)),* $(,)*}
+	 $(, $decode_custom_tlv: expr)?) => {
+		$(
+			$crate::_init_tlv_field_var!($field, $fieldty);
+		)*
+		decode_tlv_stream_with_custom_tlv_decode!($reader, {
+			$(($type, $field, $fieldty)),*
+		} $(, $decode_custom_tlv)?);
+	}
+}
+
 /// Reads a TLV stream with the given fields to build a struct/enum variant of type `$thing`
 #[doc(hidden)]
 #[macro_export]