refactor and doc

substrate/primitives/runtime/src/generic/unchecked_extrinsic.rs

@@ -156,8 +156,10 @@ where
 				.saturating_add(address.size_hint())
 				.saturating_add(signature.size_hint())
 				.saturating_add(ext.size_hint()),
-			Preamble::General(ext) =>
-				EXTRINSIC_FORMAT_VERSION.size_hint().saturating_add(ext.size_hint()),
+			Preamble::General(ext) => EXTRINSIC_FORMAT_VERSION
+				.size_hint()
+				.saturating_add(0u8.size_hint()) // version
+				.saturating_add(ext.size_hint()),
 		}
 	}
 
@@ -388,8 +390,6 @@ impl<Address, Call, Signature, ExtensionV0, ExtensionOtherVersions>
 	}
 
 	/// New instance of an new-school unsigned transaction.
-	///
-	/// This function is only available for `UncheckedExtrinsic` without multi version extension.
 	pub fn new_transaction(function: Call, tx_ext: ExtensionV0) -> Self {
 		Self { preamble: Preamble::General(ExtensionVariant::V0(tx_ext)), function }
 	}
@@ -561,14 +561,14 @@ where
 }
 
 #[cfg(feature = "serde")]
-impl<
-		Address: Encode,
-		Signature: Encode,
-		Call: Encode,
-		ExtensionV0: Encode,
-		ExtensionOtherVersions: Encode + VersTxExtLineVersion,
-	> serde::Serialize
+impl<Address, Signature, Call, ExtensionV0, ExtensionOtherVersions> serde::Serialize
 	for UncheckedExtrinsic<Address, Call, Signature, ExtensionV0, ExtensionOtherVersions>
+where
+	Address: Encode,
+	Signature: Encode,
+	Call: Encode,
+	ExtensionV0: Encode,
+	ExtensionOtherVersions: Encode + VersTxExtLineVersion,
 {
 	fn serialize<S>(&self, seq: S) -> Result<S::Ok, S::Error>
 	where
@@ -579,15 +579,14 @@ impl<
 }
 
 #[cfg(feature = "serde")]
-impl<
-		'a,
-		Address: Decode,
-		Signature: Decode,
-		Call: Decode,
-		ExtensionV0: Decode,
-		ExtensionOtherVersions: DecodeWithVersion,
-	> serde::Deserialize<'a>
+impl<'a, Address, Signature, Call, ExtensionV0, ExtensionOtherVersions> serde::Deserialize<'a>
 	for UncheckedExtrinsic<Address, Call, Signature, ExtensionV0, ExtensionOtherVersions>
+where
+	Address: Decode,
+	Signature: Decode,
+	Call: Decode,
+	ExtensionV0: Decode,
+	ExtensionOtherVersions: DecodeWithVersion,
 {
 	fn deserialize<D>(de: D) -> Result<Self, D::Error>
 	where

substrate/primitives/runtime/src/traits/vers_tx_ext/at_vers.rs

@@ -65,11 +65,10 @@ impl<const VERSION: u8, Extension> VersTxExtLineVersion for TxExtLineAtVers<VERS
 	}
 }
 
-impl<
-		const VERSION: u8,
-		Call: Dispatchable<RuntimeOrigin: AsTransactionAuthorizedOrigin> + Encode,
-		Extension: TransactionExtension<Call>,
-	> VersTxExtLine<Call> for TxExtLineAtVers<VERSION, Extension>
+impl<const VERSION: u8, Call, Extension> VersTxExtLine<Call> for TxExtLineAtVers<VERSION, Extension>
+where
+	Call: Dispatchable<RuntimeOrigin: AsTransactionAuthorizedOrigin> + Encode,
+	Extension: TransactionExtension<Call>,
 {
 	fn build_metadata(builder: &mut VersTxExtLineMetadataBuilder) {
 		builder.push_versioned_extension(VERSION, Extension::metadata());

substrate/primitives/runtime/src/traits/vers_tx_ext/mod.rs

@@ -109,7 +109,7 @@ pub trait DecodeWithVersion: Sized {
 /// A type to build the metadata for the versioned transaction extension pipeline.
 pub struct VersTxExtLineMetadataBuilder {
 	/// The transaction extension pipeline by version and its list of items as vec of index into
-	/// other field `in_versions`.
+	/// the other field `in_versions`.
 	pub by_version: BTreeMap<u8, Vec<u32>>,
 	/// The list of all transaction extension item used.
 	pub in_versions: Vec<TransactionExtensionMetadata>,

substrate/primitives/runtime/src/traits/vers_tx_ext/multi.rs

@@ -35,6 +35,8 @@ use sp_weights::Weight;
 /// single version.
 pub trait MultiVersionItem {
 	/// The version of the transaction extension pipeline.
+	///
+	/// `None` means that the item has no version and can't be decoded.
 	const VERSION: Option<u8>;
 }
 
@@ -145,6 +147,10 @@ macro_rules! declare_multi_version_enum {
 				input: &mut CodecInput,
 			) -> Result<Self, codec::Error> {
 				$(
+					// NOTE: Here we could try all variants without checking for the version,
+					// but the error would be less informative.
+					// Otherwise we could change the trait `DecodeWithVersion` to return an enum of
+					// 3 variants: ok, error and invalid_version.
 					if $variant::VERSION == Some(extension_version) {
 						return Ok(MultiVersion::$variant($variant::decode_with_version(extension_version, input)?));
 					}