Expose information about the extrinsic in the metadata (#4774)

* Expose information about the extrinsic in the metadata

This pr exposes some information about the extrinsic used in the runtime
via metadata. The following information are exposed:

- Version of the extrinsic
- List of all signed extensions used by the extrinsic.

* Increment `spec_version`

substrate/Cargo.lock

@@ -1311,7 +1311,7 @@ dependencies = [
 
 [[package]]
 name = "frame-metadata"
-version = "10.0.0"
+version = "11.0.0"
 dependencies = [
  "parity-scale-codec 1.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1324,7 +1324,7 @@ name = "frame-support"
 version = "2.0.0"
 dependencies = [
  "bitmask 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "frame-metadata 10.0.0",
+ "frame-metadata 11.0.0",
  "frame-support-procedural 2.0.0",
  "frame-system 2.0.0",
  "impl-trait-for-tuples 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",

substrate/bin/node/runtime/src/lib.rs

@@ -80,7 +80,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// and set impl_version to 0. If only runtime
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
-	spec_version: 209,
+	spec_version: 210,
 	impl_version: 0,
 	apis: RUNTIME_API_VERSIONS,
 };

substrate/frame/contracts/src/lib.rs

@@ -1103,6 +1103,7 @@ impl<T: Trait + Send + Sync> sp_std::fmt::Debug for CheckBlockGasLimit<T> {
 }
 
 impl<T: Trait + Send + Sync> SignedExtension for CheckBlockGasLimit<T> {
+	const IDENTIFIER: &'static str = "CheckBlockGasLimit";
 	type AccountId = T::AccountId;
 	type Call = <T as Trait>::Call;
 	type AdditionalSigned = ();

substrate/frame/example/src/lib.rs

@@ -603,6 +603,7 @@ impl<T: Trait + Send + Sync> sp_std::fmt::Debug for WatchDummy<T> {
 }
 
 impl<T: Trait + Send + Sync> SignedExtension for WatchDummy<T> {
+	const IDENTIFIER: &'static str = "WatchDummy";
 	type AccountId = T::AccountId;
 	// Note that this could also be assigned to the top-level call enum. It is passed into the
 	// balances module directly and since `Trait: pallet_balances::Trait`, you could also use `T::Call`.

substrate/frame/metadata/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "frame-metadata"
-version = "10.0.0"
+version = "11.0.0"
 authors = ["Parity Technologies <admin@parity.io>"]
 edition = "2018"
 license = "GPL-3.0"

substrate/frame/metadata/src/lib.rs

@@ -316,11 +316,21 @@ pub struct StorageMetadata {
 	pub entries: DecodeDifferent<&'static [StorageEntryMetadata], Vec<StorageEntryMetadata>>,
 }
 
+/// Metadata prefixed by a u32 for reserved usage
 #[derive(Eq, Encode, PartialEq, RuntimeDebug)]
 #[cfg_attr(feature = "std", derive(Decode, Serialize))]
-/// Metadata prefixed by a u32 for reserved usage
 pub struct RuntimeMetadataPrefixed(pub u32, pub RuntimeMetadata);
 
+/// Metadata of the extrinsic used by the runtime.
+#[derive(Eq, Encode, PartialEq, RuntimeDebug)]
+#[cfg_attr(feature = "std", derive(Decode, Serialize))]
+pub struct ExtrinsicMetadata {
+	/// Extrinsic version.
+	pub version: u8,
+	/// The signed extensions in the order they appear in the extrinsic.
+	pub signed_extensions: Vec<DecodeDifferentStr>,
+}
+
 /// The metadata of a runtime.
 /// The version ID encoded/decoded through
 /// the enum nature of `RuntimeMetadata`.
@@ -347,8 +357,10 @@ pub enum RuntimeMetadata {
 	V8(RuntimeMetadataDeprecated),
 	/// Version 9 for runtime metadata. No longer used.
 	V9(RuntimeMetadataDeprecated),
-	/// Version 10 for runtime metadata.
-	V10(RuntimeMetadataV10),
+	/// Version 10 for runtime metadata. No longer used.
+	V10(RuntimeMetadataDeprecated),
+	/// Version 11 for runtime metadata.
+	V11(RuntimeMetadataV11),
 }
 
 /// Enum that should fail.
@@ -372,12 +384,15 @@ impl Decode for RuntimeMetadataDeprecated {
 /// The metadata of a runtime.
 #[derive(Eq, Encode, PartialEq, RuntimeDebug)]
 #[cfg_attr(feature = "std", derive(Decode, Serialize))]
-pub struct RuntimeMetadataV10 {
+pub struct RuntimeMetadataV11 {
+	/// Metadata of all the modules.
 	pub modules: DecodeDifferentArray<ModuleMetadata>,
+	/// Metadata of the extrinsic.
+	pub extrinsic: ExtrinsicMetadata,
 }
 
 /// The latest version of the metadata.
-pub type RuntimeMetadataLastVersion = RuntimeMetadataV10;
+pub type RuntimeMetadataLastVersion = RuntimeMetadataV11;
 
 /// All metadata about an runtime module.
 #[derive(Clone, PartialEq, Eq, Encode, RuntimeDebug)]
@@ -402,6 +417,6 @@ impl Into<sp_core::OpaqueMetadata> for RuntimeMetadataPrefixed {
 
 impl Into<RuntimeMetadataPrefixed> for RuntimeMetadataLastVersion {
 	fn into(self) -> RuntimeMetadataPrefixed {
-		RuntimeMetadataPrefixed(META_RESERVED, RuntimeMetadata::V10(self))
+		RuntimeMetadataPrefixed(META_RESERVED, RuntimeMetadata::V11(self))
 	}
 }

substrate/frame/support/Cargo.toml

@@ -9,7 +9,7 @@ license = "GPL-3.0"
 log = "0.4"
 serde = { version = "1.0.101", optional = true, features = ["derive"] }
 codec = { package = "parity-scale-codec", version = "1.0.6", default-features = false, features = ["derive"] }
-frame-metadata = { version = "10.0.0", default-features = false, path = "../metadata" }
+frame-metadata = { version = "11.0.0", default-features = false, path = "../metadata" }
 sp-std = { version = "2.0.0", default-features = false, path = "../../primitives/std" }
 sp-io ={ path = "../../primitives/io", default-features = false }
 sp-runtime = { version = "2.0.0", default-features = false, path = "../../primitives/runtime" }

substrate/frame/support/procedural/src/construct_runtime/mod.rs

@@ -22,7 +22,7 @@ use parse::{ModuleDeclaration, RuntimeDefinition, WhereSection};
 use proc_macro::TokenStream;
 use proc_macro2::{Span, TokenStream as TokenStream2};
 use quote::quote;
-use syn::{Ident, Result};
+use syn::{Ident, Result, TypePath};
 
 /// The fixed name of the system module.
 const SYSTEM_MODULE_NAME: &str = "System";
@@ -86,7 +86,7 @@ fn construct_runtime_parsed(definition: RuntimeDefinition) -> Result<TokenStream
 	let module_to_index = decl_module_to_index(modules.iter(), modules.len(), &scrate);
 
 	let dispatch = decl_outer_dispatch(&name, modules.iter(), &scrate);
-	let metadata = decl_runtime_metadata(&name, modules.iter(), &scrate);
+	let metadata = decl_runtime_metadata(&name, modules.iter(), &scrate, &unchecked_extrinsic);
 	let outer_config = decl_outer_config(&name, modules.iter(), &scrate);
 	let inherent = decl_outer_inherent(&block, &unchecked_extrinsic, modules.iter(), &scrate);
 	let validate_unsigned = decl_validate_unsigned(&name, modules.iter(), &scrate);
@@ -211,6 +211,7 @@ fn decl_runtime_metadata<'a>(
 	runtime: &'a Ident,
 	module_declarations: impl Iterator<Item = &'a ModuleDeclaration>,
 	scrate: &'a TokenStream2,
+	extrinsic: &TypePath,
 ) -> TokenStream2 {
 	let modules_tokens = module_declarations
 		.filter_map(|module_declaration| {
@@ -236,7 +237,7 @@ fn decl_runtime_metadata<'a>(
 		});
 	quote!(
 		#scrate::impl_runtime_metadata!{
-			for #runtime with modules
+			for #runtime with modules where Extrinsic = #extrinsic
 				#(#modules_tokens)*
 		}
 	)

substrate/frame/support/src/metadata.rs

@@ -17,7 +17,8 @@
 pub use frame_metadata::{
 	DecodeDifferent, FnEncode, RuntimeMetadata, ModuleMetadata, RuntimeMetadataLastVersion,
 	DefaultByteGetter, RuntimeMetadataPrefixed, StorageEntryMetadata, StorageMetadata,
-	StorageEntryType, StorageEntryModifier, DefaultByte, StorageHasher, ModuleErrorMetadata
+	StorageEntryType, StorageEntryModifier, DefaultByte, StorageHasher, ModuleErrorMetadata,
+	ExtrinsicMetadata,
 };
 
 /// Implements the metadata support for the given runtime and all its modules.
@@ -43,10 +44,12 @@ pub use frame_metadata::{
 ///#     type Origin = u32;
 ///#     type BlockNumber = u32;
 ///# }
+///#
+///# type UncheckedExtrinsic = sp_runtime::generic::UncheckedExtrinsic<(), (), (), ()>;
 ///
 /// struct Runtime;
 /// frame_support::impl_runtime_metadata! {
-///     for Runtime with modules
+///     for Runtime with modules where Extrinsic = UncheckedExtrinsic
 ///         module0::Module as Module0 with,
 ///         module1::Module as Module1 with,
 ///         module2::Module as Module2 with Storage,
@@ -57,13 +60,24 @@ pub use frame_metadata::{
 #[macro_export]
 macro_rules! impl_runtime_metadata {
 	(
-		for $runtime:ident with modules
+		for $runtime:ident with modules where Extrinsic = $ext:ident
 			$( $rest:tt )*
 	) => {
 		impl $runtime {
 			pub fn metadata() -> $crate::metadata::RuntimeMetadataPrefixed {
 				$crate::metadata::RuntimeMetadataLastVersion {
 						modules: $crate::__runtime_modules_to_metadata!($runtime;; $( $rest )*),
+						extrinsic: $crate::metadata::ExtrinsicMetadata {
+							version: <$ext as $crate::sp_runtime::traits::ExtrinsicMetadata>::VERSION,
+							signed_extensions: <
+									<
+										$ext as $crate::sp_runtime::traits::ExtrinsicMetadata
+									>::SignedExtensions as $crate::sp_runtime::traits::SignedExtension
+								>::identifier()
+									.into_iter()
+									.map($crate::metadata::DecodeDifferent::Encode)
+									.collect(),
+						},
 				}.into()
 			}
 		}
@@ -232,10 +246,46 @@ mod tests {
 	use frame_metadata::{
 		EventMetadata, StorageEntryModifier, StorageEntryType, FunctionMetadata, StorageEntryMetadata,
 		ModuleMetadata, RuntimeMetadataPrefixed, DefaultByte, ModuleConstantMetadata, DefaultByteGetter,
-		ErrorMetadata,
+		ErrorMetadata, ExtrinsicMetadata,
 	};
 	use codec::{Encode, Decode};
 	use crate::traits::Get;
+	use sp_runtime::transaction_validity::TransactionValidityError;
+
+	#[derive(Clone, Eq, Debug, PartialEq, Encode, Decode)]
+	struct TestExtension;
+	impl sp_runtime::traits::SignedExtension for TestExtension {
+		type AccountId = u32;
+		type Call = u32;
+		type AdditionalSigned = u32;
+		type DispatchInfo = ();
+		type Pre = ();
+		const IDENTIFIER: &'static str = "testextension";
+		fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
+			Ok(1)
+		}
+	}
+
+	#[derive(Clone, Eq, Debug, PartialEq, Encode, Decode)]
+	struct TestExtension2;
+	impl sp_runtime::traits::SignedExtension for TestExtension2 {
+		type AccountId = u32;
+		type Call = u32;
+		type AdditionalSigned = u32;
+		type DispatchInfo = ();
+		type Pre = ();
+		const IDENTIFIER: &'static str = "testextension2";
+		fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
+			Ok(1)
+		}
+	}
+
+	struct TestExtrinsic;
+
+	impl sp_runtime::traits::ExtrinsicMetadata for TestExtrinsic {
+		const VERSION: u8 = 1;
+		type SignedExtensions = (TestExtension, TestExtension2);
+	}
 
 	mod system {
 		use super::*;
@@ -393,7 +443,7 @@ mod tests {
 	}
 
 	impl_runtime_metadata!(
-		for TestRuntime with modules
+		for TestRuntime with modules where Extrinsic = TestExtrinsic
 			system::Module as System with Event,
 			event_module::Module as Module with Event Call,
 			event_module2::Module as Module2 with Event Storage Call,
@@ -420,131 +470,138 @@ mod tests {
 		}
 	}
 
-	const EXPECTED_METADATA: RuntimeMetadataLastVersion = RuntimeMetadataLastVersion {
-		modules: DecodeDifferent::Encode(&[
-			ModuleMetadata {
-				name: DecodeDifferent::Encode("System"),
-				storage: None,
-				calls: None,
-				event: Some(DecodeDifferent::Encode(
-					FnEncode(||&[
-						EventMetadata {
-							name: DecodeDifferent::Encode("SystemEvent"),
-							arguments: DecodeDifferent::Encode(&[]),
-							documentation: DecodeDifferent::Encode(&[])
-						}
-					])
-				)),
-				constants: DecodeDifferent::Encode(
-					FnEncode(|| &[
-						ModuleConstantMetadata {
-							name: DecodeDifferent::Encode("BlockNumber"),
-							ty: DecodeDifferent::Encode("T::BlockNumber"),
-							value: DecodeDifferent::Encode(
-								DefaultByteGetter(&ConstantBlockNumberByteGetter)
-							),
-							documentation: DecodeDifferent::Encode(&[" Hi, I am a comment."]),
-						},
-						ModuleConstantMetadata {
-							name: DecodeDifferent::Encode("GetType"),
-							ty: DecodeDifferent::Encode("T::AccountId"),
-							value: DecodeDifferent::Encode(
-								DefaultByteGetter(&ConstantGetTypeByteGetter)
-							),
-							documentation: DecodeDifferent::Encode(&[]),
-						},
-						ModuleConstantMetadata {
-							name: DecodeDifferent::Encode("ASSOCIATED_CONST"),
-							ty: DecodeDifferent::Encode("u64"),
-							value: DecodeDifferent::Encode(
-								DefaultByteGetter(&ConstantAssociatedConstByteGetter)
-							),
-							documentation: DecodeDifferent::Encode(&[]),
-						}
-					])
-				),
-				errors: DecodeDifferent::Encode(FnEncode(|| &[])),
-			},
-			ModuleMetadata {
-				name: DecodeDifferent::Encode("Module"),
-				storage: None,
-				calls: Some(
-					DecodeDifferent::Encode(FnEncode(|| &[
-						FunctionMetadata {
-							name: DecodeDifferent::Encode("aux_0"),
-							arguments: DecodeDifferent::Encode(&[]),
-							documentation: DecodeDifferent::Encode(&[]),
-						}
-					]))),
-				event: Some(DecodeDifferent::Encode(
-					FnEncode(||&[
-						EventMetadata {
-							name: DecodeDifferent::Encode("TestEvent"),
-							arguments: DecodeDifferent::Encode(&["Balance"]),
-							documentation: DecodeDifferent::Encode(&[" Hi, I am a comment."])
-						}
-					])
-				)),
-				constants: DecodeDifferent::Encode(FnEncode(|| &[])),
-				errors: DecodeDifferent::Encode(FnEncode(|| &[
-					ErrorMetadata {
-						name: DecodeDifferent::Encode("UserInputError"),
-						documentation: DecodeDifferent::Encode(&[" Some user input error"]),
-					},
-					ErrorMetadata {
-						name: DecodeDifferent::Encode("BadThingHappened"),
-						documentation: DecodeDifferent::Encode(&[
-							" Something bad happened",
-							" this could be due to many reasons",
-						]),
-					},
-				])),
-			},
-			ModuleMetadata {
-				name: DecodeDifferent::Encode("Module2"),
-				storage: Some(DecodeDifferent::Encode(
-					FnEncode(|| StorageMetadata {
-						prefix: DecodeDifferent::Encode("TestStorage"),
-						entries: DecodeDifferent::Encode(
-							&[
-								StorageEntryMetadata {
-									name: DecodeDifferent::Encode("StorageMethod"),
-									modifier: StorageEntryModifier::Optional,
-									ty: StorageEntryType::Plain(DecodeDifferent::Encode("u32")),
-									default: DecodeDifferent::Encode(
-										DefaultByteGetter(
-											&event_module2::__GetByteStructStorageMethod(
-												std::marker::PhantomData::<TestRuntime>
-											)
-										)
-									),
-									documentation: DecodeDifferent::Encode(&[]),
-								}
-							]
-						)
-					}),
-				)),
-				calls: Some(DecodeDifferent::Encode(FnEncode(|| &[]))),
-				event: Some(DecodeDifferent::Encode(
-					FnEncode(||&[
-						EventMetadata {
-							name: DecodeDifferent::Encode("TestEvent"),
-							arguments: DecodeDifferent::Encode(&["Balance"]),
-							documentation: DecodeDifferent::Encode(&[])
-						}
-					])
-				)),
-				constants: DecodeDifferent::Encode(FnEncode(|| &[])),
-				errors: DecodeDifferent::Encode(FnEncode(|| &[])),
-			},
-		])
-	};
-
 	#[test]
 	fn runtime_metadata() {
+		let expected_metadata: RuntimeMetadataLastVersion = RuntimeMetadataLastVersion {
+			modules: DecodeDifferent::Encode(&[
+				ModuleMetadata {
+					name: DecodeDifferent::Encode("System"),
+					storage: None,
+					calls: None,
+					event: Some(DecodeDifferent::Encode(
+						FnEncode(||&[
+							EventMetadata {
+								name: DecodeDifferent::Encode("SystemEvent"),
+								arguments: DecodeDifferent::Encode(&[]),
+								documentation: DecodeDifferent::Encode(&[])
+							}
+						])
+					)),
+					constants: DecodeDifferent::Encode(
+						FnEncode(|| &[
+							ModuleConstantMetadata {
+								name: DecodeDifferent::Encode("BlockNumber"),
+								ty: DecodeDifferent::Encode("T::BlockNumber"),
+								value: DecodeDifferent::Encode(
+									DefaultByteGetter(&ConstantBlockNumberByteGetter)
+								),
+								documentation: DecodeDifferent::Encode(&[" Hi, I am a comment."]),
+							},
+							ModuleConstantMetadata {
+								name: DecodeDifferent::Encode("GetType"),
+								ty: DecodeDifferent::Encode("T::AccountId"),
+								value: DecodeDifferent::Encode(
+									DefaultByteGetter(&ConstantGetTypeByteGetter)
+								),
+								documentation: DecodeDifferent::Encode(&[]),
+							},
+							ModuleConstantMetadata {
+								name: DecodeDifferent::Encode("ASSOCIATED_CONST"),
+								ty: DecodeDifferent::Encode("u64"),
+								value: DecodeDifferent::Encode(
+									DefaultByteGetter(&ConstantAssociatedConstByteGetter)
+								),
+								documentation: DecodeDifferent::Encode(&[]),
+							}
+						])
+					),
+					errors: DecodeDifferent::Encode(FnEncode(|| &[])),
+				},
+				ModuleMetadata {
+					name: DecodeDifferent::Encode("Module"),
+					storage: None,
+					calls: Some(
+						DecodeDifferent::Encode(FnEncode(|| &[
+							FunctionMetadata {
+								name: DecodeDifferent::Encode("aux_0"),
+								arguments: DecodeDifferent::Encode(&[]),
+								documentation: DecodeDifferent::Encode(&[]),
+							}
+						]))),
+					event: Some(DecodeDifferent::Encode(
+						FnEncode(||&[
+							EventMetadata {
+								name: DecodeDifferent::Encode("TestEvent"),
+								arguments: DecodeDifferent::Encode(&["Balance"]),
+								documentation: DecodeDifferent::Encode(&[" Hi, I am a comment."])
+							}
+						])
+					)),
+					constants: DecodeDifferent::Encode(FnEncode(|| &[])),
+					errors: DecodeDifferent::Encode(FnEncode(|| &[
+						ErrorMetadata {
+							name: DecodeDifferent::Encode("UserInputError"),
+							documentation: DecodeDifferent::Encode(&[" Some user input error"]),
+						},
+						ErrorMetadata {
+							name: DecodeDifferent::Encode("BadThingHappened"),
+							documentation: DecodeDifferent::Encode(&[
+								" Something bad happened",
+								" this could be due to many reasons",
+							]),
+						},
+					])),
+				},
+				ModuleMetadata {
+					name: DecodeDifferent::Encode("Module2"),
+					storage: Some(DecodeDifferent::Encode(
+						FnEncode(|| StorageMetadata {
+							prefix: DecodeDifferent::Encode("TestStorage"),
+							entries: DecodeDifferent::Encode(
+								&[
+									StorageEntryMetadata {
+										name: DecodeDifferent::Encode("StorageMethod"),
+										modifier: StorageEntryModifier::Optional,
+										ty: StorageEntryType::Plain(DecodeDifferent::Encode("u32")),
+										default: DecodeDifferent::Encode(
+											DefaultByteGetter(
+												&event_module2::__GetByteStructStorageMethod(
+													std::marker::PhantomData::<TestRuntime>
+												)
+											)
+										),
+										documentation: DecodeDifferent::Encode(&[]),
+									}
+								]
+							)
+						}),
+					)),
+					calls: Some(DecodeDifferent::Encode(FnEncode(|| &[]))),
+					event: Some(DecodeDifferent::Encode(
+						FnEncode(||&[
+							EventMetadata {
+								name: DecodeDifferent::Encode("TestEvent"),
+								arguments: DecodeDifferent::Encode(&["Balance"]),
+								documentation: DecodeDifferent::Encode(&[])
+							}
+						])
+					)),
+					constants: DecodeDifferent::Encode(FnEncode(|| &[])),
+					errors: DecodeDifferent::Encode(FnEncode(|| &[])),
+				},
+			]),
+			extrinsic: ExtrinsicMetadata {
+				version: 1,
+				signed_extensions: vec![
+					DecodeDifferent::Encode("testextension"),
+					DecodeDifferent::Encode("testextension2"),
+				],
+			}
+		};
+
 		let metadata_encoded = TestRuntime::metadata().encode();
 		let metadata_decoded = RuntimeMetadataPrefixed::decode(&mut &metadata_encoded[..]);
-		let expected_metadata: RuntimeMetadataPrefixed = EXPECTED_METADATA.into();
+		let expected_metadata: RuntimeMetadataPrefixed = expected_metadata.into();
 
 		pretty_assertions::assert_eq!(expected_metadata, metadata_decoded.unwrap());
 	}

substrate/frame/system/src/lib.rs

@@ -960,6 +960,7 @@ impl<T: Trait + Send + Sync> SignedExtension for CheckWeight<T> {
 	type AdditionalSigned = ();
 	type DispatchInfo = DispatchInfo;
 	type Pre = ();
+	const IDENTIFIER: &'static str = "CheckWeight";
 
 	fn additional_signed(&self) -> sp_std::result::Result<(), TransactionValidityError> { Ok(()) }
 
@@ -1040,6 +1041,7 @@ impl<T: Trait> SignedExtension for CheckNonce<T> {
 	type AdditionalSigned = ();
 	type DispatchInfo = DispatchInfo;
 	type Pre = ();
+	const IDENTIFIER: &'static str = "CheckNonce";
 
 	fn additional_signed(&self) -> sp_std::result::Result<(), TransactionValidityError> { Ok(()) }
 
@@ -1124,6 +1126,7 @@ impl<T: Trait + Send + Sync> SignedExtension for CheckEra<T> {
 	type AdditionalSigned = T::Hash;
 	type DispatchInfo = DispatchInfo;
 	type Pre = ();
+	const IDENTIFIER: &'static str = "CheckEra";
 
 	fn validate(
 		&self,
@@ -1180,6 +1183,7 @@ impl<T: Trait + Send + Sync> SignedExtension for CheckGenesis<T> {
 	type AdditionalSigned = T::Hash;
 	type DispatchInfo = DispatchInfo;
 	type Pre = ();
+	const IDENTIFIER: &'static str = "CheckGenesis";
 
 	fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
 		Ok(<Module<T>>::block_hash(T::BlockNumber::zero()))
@@ -1215,6 +1219,7 @@ impl<T: Trait + Send + Sync> SignedExtension for CheckVersion<T> {
 	type AdditionalSigned = u32;
 	type DispatchInfo = DispatchInfo;
 	type Pre = ();
+	const IDENTIFIER: &'static str = "CheckVersion";
 
 	fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
 		Ok(<Module<T>>::runtime_version().spec_version)

substrate/frame/transaction-payment/src/lib.rs

@@ -201,6 +201,7 @@ impl<T: Trait + Send + Sync> sp_std::fmt::Debug for ChargeTransactionPayment<T>
 impl<T: Trait + Send + Sync> SignedExtension for ChargeTransactionPayment<T>
 	where BalanceOf<T>: Send + Sync
 {
+	const IDENTIFIER: &'static str = "ChargeTransactionPayment";
 	type AccountId = T::AccountId;
 	type Call = T::Call;
 	type AdditionalSigned = ();

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

@@ -20,7 +20,10 @@ use sp_std::{fmt, prelude::*};
 use sp_io::hashing::blake2_256;
 use codec::{Decode, Encode, EncodeLike, Input, Error};
 use crate::{
-	traits::{self, Member, MaybeDisplay, SignedExtension, Checkable, Extrinsic, IdentifyAccount},
+	traits::{
+		self, Member, MaybeDisplay, SignedExtension, Checkable, Extrinsic, ExtrinsicMetadata,
+		IdentifyAccount,
+	},
 	generic::CheckedExtrinsic, transaction_validity::{TransactionValidityError, InvalidTransaction},
 };
 
@@ -130,6 +133,15 @@ where
 	}
 }
 
+impl<Address, Call, Signature, Extra> ExtrinsicMetadata
+	for UncheckedExtrinsic<Address, Call, Signature, Extra>
+		where
+			Extra: SignedExtension,
+{
+	const VERSION: u8 = TRANSACTION_VERSION;
+	type SignedExtensions = Extra;
+}
+
 /// A payload that has been signed for an unchecked extrinsics.
 ///
 /// Note that the payload that we sign to produce unchecked extrinsic signature
@@ -316,6 +328,7 @@ mod tests {
 	#[derive(Debug, Encode, Decode, Clone, Eq, PartialEq, Ord, PartialOrd)]
 	struct TestExtra;
 	impl SignedExtension for TestExtra {
+		const IDENTIFIER: &'static str = "TestExtra";
 		type AccountId = u64;
 		type Call = ();
 		type AdditionalSigned = ();

substrate/primitives/runtime/src/traits.rs

@@ -608,6 +608,15 @@ pub trait Extrinsic: Sized {
 	fn new(_call: Self::Call, _signed_data: Option<Self::SignaturePayload>) -> Option<Self> { None }
 }
 
+/// Implementor is an [`Extrinsic`] and provides metadata about this extrinsic.
+pub trait ExtrinsicMetadata {
+	/// The version of the `Extrinsic`.
+	const VERSION: u8;
+
+	/// Signed extensions attached to this `Extrinsic`.
+	type SignedExtensions: SignedExtension;
+}
+
 /// Extract the hasher type for a block.
 pub type HasherFor<B> = <HashFor<B> as Hash>::Hasher;
 /// Extract the hashing type for a block.
@@ -668,6 +677,12 @@ pub trait Dispatchable {
 /// Means by which a transaction may be extended. This type embodies both the data and the logic
 /// that should be additionally associated with the transaction. It should be plain old data.
 pub trait SignedExtension: Codec + Debug + Sync + Send + Clone + Eq + PartialEq {
+	/// Unique identifier of this signed extension.
+	///
+	/// This will be exposed in the metadata to identify the signed extension used
+	/// in an extrinsic.
+	const IDENTIFIER: &'static str;
+
 	/// The type which encodes the sender identity.
 	type AccountId;
 
@@ -765,6 +780,17 @@ pub trait SignedExtension: Codec + Debug + Sync + Send + Clone + Eq + PartialEq
 
 	/// Do any post-flight stuff for a transaction.
 	fn post_dispatch(_pre: Self::Pre, _info: Self::DispatchInfo, _len: usize) { }
+
+	/// Returns the list of unique identifier for this signed extension.
+	///
+	/// As a [`SignedExtension`] can be a tuple of [`SignedExtension`]`s we need to return a `Vec`
+	/// that holds all the unique identifiers. Each individual `SignedExtension` must return
+	/// *exactly* one identifier.
+	///
+	/// This method provides a default implementation that returns `vec![SELF::IDENTIFIER]`.
+	fn identifier() -> Vec<&'static str> {
+		sp_std::vec![Self::IDENTIFIER]
+	}
 }
 
 #[impl_for_tuples(1, 12)]
@@ -773,6 +799,7 @@ impl<AccountId, Call, Info: Clone> SignedExtension for Tuple {
 	type AccountId = AccountId;
 	type Call = Call;
 	type DispatchInfo = Info;
+	const IDENTIFIER: &'static str = "You should call `identifier()`!";
 	for_tuples!( type AdditionalSigned = ( #( Tuple::AdditionalSigned ),* ); );
 	for_tuples!( type Pre = ( #( Tuple::Pre ),* ); );
 
@@ -823,6 +850,12 @@ impl<AccountId, Call, Info: Clone> SignedExtension for Tuple {
 	) {
 		for_tuples!( #( Tuple::post_dispatch(pre.Tuple, info.clone(), len); )* )
 	}
+
+	fn identifier() -> Vec<&'static str> {
+		let mut ids = Vec::new();
+		for_tuples!( #( ids.extend(Tuple::identifier()); )* );
+		ids
+	}
 }
 
 /// Only for bare bone testing when you don't care about signed extensions at all.
@@ -833,6 +866,7 @@ impl SignedExtension for () {
 	type Call = ();
 	type Pre = ();
 	type DispatchInfo = ();
+	const IDENTIFIER: &'static str = "UnitSignedExtension";
 	fn additional_signed(&self) -> sp_std::result::Result<(), TransactionValidityError> { Ok(()) }
 }