Add a required_vec TLV deserialization type

Historically, we used `vec_type` for all TLV Vec reads/writes, but
it is asymmetric and thus somewhat confusing - on the write side it
always writes a TLV entry, even if there are zero elements. On the
read side, it happily accepts a missing TLV, providing a
zero-length vector.

In 85b573d a new `optional_vec`
TLV format was added which was symmetric, but only supports
optional vecs. This adds the corresponding required form, always
writing a TLV and ensuring it is present.

Author: TheBlueMatt

lightning/src/util/ser_macros.rs

@@ -29,6 +29,9 @@ macro_rules! _encode_tlv {
 		BigSize($field.serialized_length() as u64).write($stream)?;
 		$field.write($stream)?;
 	};
+	($stream: expr, $type: expr, $field: expr, required_vec) => {
+		$crate::_encode_tlv!($stream, $type, $crate::util::ser::WithoutLength(&$field), required);
+	};
 	($stream: expr, $type: expr, $field: expr, vec_type) => {
 		$crate::_encode_tlv!($stream, $type, $crate::util::ser::WithoutLength(&$field), required);
 	};
@@ -41,7 +44,7 @@ macro_rules! _encode_tlv {
 	};
 	($stream: expr, $type: expr, $field: expr, optional_vec) => {
 		if !$field.is_empty() {
-			$crate::_encode_tlv!($stream, $type, $field, vec_type);
+			$crate::_encode_tlv!($stream, $type, $field, required_vec);
 		}
 	};
 	($stream: expr, $type: expr, $field: expr, upgradable_required) => {
@@ -159,6 +162,9 @@ macro_rules! _get_varint_length_prefixed_tlv_length {
 		BigSize(field_len as u64).write(&mut $len).expect("No in-memory data may fail to serialize");
 		$len.0 += field_len;
 	};
+	($len: expr, $type: expr, $field: expr, required_vec) => {
+		$crate::_get_varint_length_prefixed_tlv_length!($len, $type, $crate::util::ser::WithoutLength(&$field), required);
+	};
 	($len: expr, $type: expr, $field: expr, vec_type) => {
 		$crate::_get_varint_length_prefixed_tlv_length!($len, $type, $crate::util::ser::WithoutLength(&$field), required);
 	};
@@ -172,7 +178,7 @@ macro_rules! _get_varint_length_prefixed_tlv_length {
 	};
 	($len: expr, $type: expr, $field: expr, optional_vec) => {
 		if !$field.is_empty() {
-			$crate::_get_varint_length_prefixed_tlv_length!($len, $type, $field, vec_type);
+			$crate::_get_varint_length_prefixed_tlv_length!($len, $type, $field, required_vec);
 		}
 	};
 	($len: expr, $type: expr, $field: expr, (option: $trait: ident $(, $read_arg: expr)?)) => {
@@ -236,6 +242,9 @@ macro_rules! _check_decoded_tlv_order {
 	($last_seen_type: expr, $typ: expr, $type: expr, $field: ident, option) => {{
 		// no-op
 	}};
+	($last_seen_type: expr, $typ: expr, $type: expr, $field: ident, required_vec) => {{
+		$crate::_check_decoded_tlv_order!($last_seen_type, $typ, $type, $field, required);
+	}};
 	($last_seen_type: expr, $typ: expr, $type: expr, $field: ident, vec_type) => {{
 		// no-op
 	}};
@@ -281,6 +290,9 @@ macro_rules! _check_missing_tlv {
 	($last_seen_type: expr, $type: expr, $field: ident, (required: $trait: ident $(, $read_arg: expr)?)) => {{
 		$crate::_check_missing_tlv!($last_seen_type, $type, $field, required);
 	}};
+	($last_seen_type: expr, $type: expr, $field: ident, required_vec) => {{
+		$crate::_check_missing_tlv!($last_seen_type, $type, $field, required);
+	}};
 	($last_seen_type: expr, $type: expr, $field: ident, vec_type) => {{
 		// no-op
 	}};
@@ -320,6 +332,10 @@ macro_rules! _decode_tlv {
 	($reader: expr, $field: ident, (required: $trait: ident $(, $read_arg: expr)?)) => {{
 		$field = $trait::read(&mut $reader $(, $read_arg)*)?;
 	}};
+	($reader: expr, $field: ident, required_vec) => {{
+		let f: $crate::util::ser::WithoutLength<Vec<_>> = $crate::util::ser::Readable::read(&mut $reader)?;
+		$field = f.0;
+	}};
 	($reader: expr, $field: ident, vec_type) => {{
 		let f: $crate::util::ser::WithoutLength<Vec<_>> = $crate::util::ser::Readable::read(&mut $reader)?;
 		$field = Some(f.0);
@@ -694,6 +710,9 @@ macro_rules! _init_tlv_based_struct_field {
 	($field: ident, required) => {
 		$field.0.unwrap()
 	};
+	($field: ident, required_vec) => {
+		$field
+	};
 	($field: ident, vec_type) => {
 		$field.unwrap()
 	};
@@ -720,6 +739,9 @@ macro_rules! _init_tlv_field_var {
 	($field: ident, (required: $trait: ident $(, $read_arg: expr)?)) => {
 		$crate::_init_tlv_field_var!($field, required);
 	};
+	($field: ident, required_vec) => {
+		let mut $field = Vec::new();
+	};
 	($field: ident, vec_type) => {
 		let mut $field = Some(Vec::new());
 	};