FRAME: Create TransactionExtension as a replacement for SignedExtension (#2280)

Closes #2160

First part of [Extrinsic
Horizon](https://github.com/paritytech/polkadot-sdk/issues/2415)

Introduces a new trait `TransactionExtension` to replace
`SignedExtension`. Introduce the idea of transactions which obey the
runtime's extensions and have according Extension data (né Extra data)
yet do not have hard-coded signatures.

Deprecate the terminology of "Unsigned" when used for
transactions/extrinsics owing to there now being "proper" unsigned
transactions which obey the extension framework and "old-style" unsigned
which do not. Instead we have __*General*__ for the former and
__*Bare*__ for the latter. (Ultimately, the latter will be phased out as
a type of transaction, and Bare will only be used for Inherents.)

Types of extrinsic are now therefore:
- Bare (no hardcoded signature, no Extra data; used to be known as
"Unsigned")
- Bare transactions (deprecated): Gossiped, validated with
`ValidateUnsigned` (deprecated) and the `_bare_compat` bits of
`TransactionExtension` (deprecated).
  - Inherents: Not gossiped, validated with `ProvideInherent`.
- Extended (Extra data): Gossiped, validated via `TransactionExtension`.
  - Signed transactions (with a hardcoded signature).
  - General transactions (without a hardcoded signature).

`TransactionExtension` differs from `SignedExtension` because:
- A signature on the underlying transaction may validly not be present.
- It may alter the origin during validation.
- `pre_dispatch` is renamed to `prepare` and need not contain the checks
present in `validate`.
- `validate` and `prepare` is passed an `Origin` rather than a
`AccountId`.
- `validate` may pass arbitrary information into `prepare` via a new
user-specifiable type `Val`.
- `AdditionalSigned`/`additional_signed` is renamed to
`Implicit`/`implicit`. It is encoded *for the entire transaction* and
passed in to each extension as a new argument to `validate`. This
facilitates the ability of extensions to acts as underlying crypto.

There is a new `DispatchTransaction` trait which contains only default
function impls and is impl'ed for any `TransactionExtension` impler. It
provides several utility functions which reduce some of the tedium from
using `TransactionExtension` (indeed, none of its regular functions
should now need to be called directly).

Three transaction version discriminator ("versions") are now
permissible:
- 0b000000100: Bare (used to be called "Unsigned"): contains Signature
or Extra (extension data). After bare transactions are no longer
supported, this will strictly identify an Inherents only.
- 0b100000100: Old-school "Signed" Transaction: contains Signature and
Extra (extension data).
- 0b010000100: New-school "General" Transaction: contains Extra
(extension data), but no Signature.

For the New-school General Transaction, it becomes trivial for authors
to publish extensions to the mechanism for authorizing an Origin, e.g.
through new kinds of key-signing schemes, ZK proofs, pallet state,
mutations over pre-authenticated origins or any combination of the
above.

## Code Migration

### NOW: Getting it to build

Wrap your `SignedExtension`s in `AsTransactionExtension`. This should be
accompanied by renaming your aggregate type in line with the new
terminology. E.g. Before:

```rust
/// The SignedExtension to the basic transaction logic.
pub type SignedExtra = (
	/* snip */
	MySpecialSignedExtension,
);
/// Unchecked extrinsic type as expected by this runtime.
pub type UncheckedExtrinsic =
	generic::UncheckedExtrinsic<Address, RuntimeCall, Signature, SignedExtra>;
```

After:

```rust
/// The extension to the basic transaction logic.
pub type TxExtension = (
	/* snip */
	AsTransactionExtension<MySpecialSignedExtension>,
);
/// Unchecked extrinsic type as expected by this runtime.
pub type UncheckedExtrinsic =
	generic::UncheckedExtrinsic<Address, RuntimeCall, Signature, TxExtension>;
```

You'll also need to alter any transaction building logic to add a
`.into()` to make the conversion happen. E.g. Before:

```rust
fn construct_extrinsic(
		/* snip */
) -> UncheckedExtrinsic {
	let extra: SignedExtra = (
		/* snip */
		MySpecialSignedExtension::new(/* snip */),
	);
	let payload = SignedPayload::new(call.clone(), extra.clone()).unwrap();
	let signature = payload.using_encoded(|e| sender.sign(e));
	UncheckedExtrinsic::new_signed(
		/* snip */
		Signature::Sr25519(signature),
		extra,
	)
}
```

After:

```rust
fn construct_extrinsic(
		/* snip */
) -> UncheckedExtrinsic {
	let tx_ext: TxExtension = (
		/* snip */
		MySpecialSignedExtension::new(/* snip */).into(),
	);
	let payload = SignedPayload::new(call.clone(), tx_ext.clone()).unwrap();
	let signature = payload.using_encoded(|e| sender.sign(e));
	UncheckedExtrinsic::new_signed(
		/* snip */
		Signature::Sr25519(signature),
		tx_ext,
	)
}
```

### SOON: Migrating to `TransactionExtension`

Most `SignedExtension`s can be trivially converted to become a
`TransactionExtension`. There are a few things to know.

- Instead of a single trait like `SignedExtension`, you should now
implement two traits individually: `TransactionExtensionBase` and
`TransactionExtension`.
- Weights are now a thing and must be provided via the new function `fn
weight`.

#### `TransactionExtensionBase`

This trait takes care of anything which is not dependent on types
specific to your runtime, most notably `Call`.

- `AdditionalSigned`/`additional_signed` is renamed to
`Implicit`/`implicit`.
- Weight must be returned by implementing the `weight` function. If your
extension is associated with a pallet, you'll probably want to do this
via the pallet's existing benchmarking infrastructure.

#### `TransactionExtension`

Generally:
- `pre_dispatch` is now `prepare` and you *should not reexecute the
`validate` functionality in there*!
- You don't get an account ID any more; you get an origin instead. If
you need to presume an account ID, then you can use the trait function
`AsSystemOriginSigner::as_system_origin_signer`.
- You get an additional ticket, similar to `Pre`, called `Val`. This
defines data which is passed from `validate` into `prepare`. This is
important since you should not be duplicating logic from `validate` to
`prepare`, you need a way of passing your working from the former into
the latter. This is it.
- This trait takes two type parameters: `Call` and `Context`. `Call` is
the runtime call type which used to be an associated type; you can just
move it to become a type parameter for your trait impl. `Context` is not
currently used and you can safely implement over it as an unbounded
type.
- There's no `AccountId` associated type any more. Just remove it.

Regarding `validate`:
- You get three new parameters in `validate`; all can be ignored when
migrating from `SignedExtension`.
- `validate` returns a tuple on success; the second item in the tuple is
the new ticket type `Self::Val` which gets passed in to `prepare`. If
you use any information extracted during `validate` (off-chain and
on-chain, non-mutating) in `prepare` (on-chain, mutating) then you can
pass it through with this. For the tuple's last item, just return the
`origin` argument.

Regarding `prepare`:
- This is renamed from `pre_dispatch`, but there is one change:
- FUNCTIONALITY TO VALIDATE THE TRANSACTION NEED NOT BE DUPLICATED FROM
`validate`!!
- (This is different to `SignedExtension` which was required to run the
same checks in `pre_dispatch` as in `validate`.)

Regarding `post_dispatch`:
- Since there are no unsigned transactions handled by
`TransactionExtension`, `Pre` is always defined, so the first parameter
is `Self::Pre` rather than `Option<Self::Pre>`.

If you make use of `SignedExtension::validate_unsigned` or
`SignedExtension::pre_dispatch_unsigned`, then:
- Just use the regular versions of these functions instead.
- Have your logic execute in the case that the `origin` is `None`.
- Ensure your transaction creation logic creates a General Transaction
rather than a Bare Transaction; this means having to include all
`TransactionExtension`s' data.
- `ValidateUnsigned` can still be used (for now) if you need to be able
to construct transactions which contain none of the extension data,
however these will be phased out in stage 2 of the Transactions Horizon,
so you should consider moving to an extension-centric design.

## TODO

- [x] Introduce `CheckSignature` impl of `TransactionExtension` to
ensure it's possible to have crypto be done wholly in a
`TransactionExtension`.
- [x] Deprecate `SignedExtension` and move all uses in codebase to
`TransactionExtension`.
  - [x] `ChargeTransactionPayment`
  - [x] `DummyExtension`
  - [x] `ChargeAssetTxPayment` (asset-tx-payment)
  - [x] `ChargeAssetTxPayment` (asset-conversion-tx-payment)
  - [x] `CheckWeight`
  - [x] `CheckTxVersion`
  - [x] `CheckSpecVersion`
  - [x] `CheckNonce`
  - [x] `CheckNonZeroSender`
  - [x] `CheckMortality`
  - [x] `CheckGenesis`
  - [x] `CheckOnlySudoAccount`
  - [x] `WatchDummy`
  - [x] `PrevalidateAttests`
  - [x] `GenericSignedExtension`
  - [x] `SignedExtension` (chain-polkadot-bulletin)
  - [x] `RefundSignedExtensionAdapter`
- [x] Implement `fn weight` across the board.
- [ ] Go through all pre-existing extensions which assume an account
signer and explicitly handle the possibility of another kind of origin.
- [x] `CheckNonce` should probably succeed in the case of a non-account
origin.
- [x] `CheckNonZeroSender` should succeed in the case of a non-account
origin.
- [x] `ChargeTransactionPayment` and family should fail in the case of a
non-account origin.
  - [ ] 
- [x] Fix any broken tests.

---------

Signed-off-by: georgepisaltu <george.pisaltu@parity.io>
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polkadot/runtime/common/src/claims.rs

@@ -29,7 +29,11 @@ use scale_info::TypeInfo;
 use serde::{self, Deserialize, Deserializer, Serialize, Serializer};
 use sp_io::{crypto::secp256k1_ecdsa_recover, hashing::keccak_256};
 use sp_runtime::{
-	traits::{CheckedSub, DispatchInfoOf, SignedExtension, Zero},
+	impl_tx_ext_default,
+	traits::{
+		AsSystemOriginSigner, CheckedSub, DispatchInfoOf, Dispatchable, TransactionExtension,
+		TransactionExtensionBase, Zero,
+	},
 	transaction_validity::{
 		InvalidTransaction, TransactionValidity, TransactionValidityError, ValidTransaction,
 	},
@@ -50,6 +54,7 @@ pub trait WeightInfo {
 	fn claim_attest() -> Weight;
 	fn attest() -> Weight;
 	fn move_claim() -> Weight;
+	fn prevalidate_attests() -> Weight;
 }
 
 pub struct TestWeightInfo;
@@ -69,6 +74,9 @@ impl WeightInfo for TestWeightInfo {
 	fn move_claim() -> Weight {
 		Weight::zero()
 	}
+	fn prevalidate_attests() -> Weight {
+		Weight::zero()
+	}
 }
 
 /// The kind of statement an account needs to make for a claim to be valid.
@@ -84,7 +92,7 @@ pub enum StatementKind {
 
 impl StatementKind {
 	/// Convert this to the (English) statement it represents.
-	fn to_text(self) -> &'static [u8] {
+	pub fn to_text(self) -> &'static [u8] {
 		match self {
 			StatementKind::Regular =>
 				&b"I hereby agree to the terms of the statement whose SHA-256 multihash is \
@@ -166,6 +174,13 @@ pub mod pallet {
 	#[pallet::without_storage_info]
 	pub struct Pallet<T>(_);
 
+	#[cfg(feature = "runtime-benchmarks")]
+	/// Helper trait to benchmark the `PrevalidateAttests` transaction extension.
+	pub trait BenchmarkHelperTrait<RuntimeCall, DispatchInfo> {
+		/// `Call` to be used when benchmarking the transaction extension.
+		fn default_call_and_info() -> (RuntimeCall, DispatchInfo);
+	}
+
 	/// Configuration trait.
 	#[pallet::config]
 	pub trait Config: frame_system::Config {
@@ -176,6 +191,12 @@ pub mod pallet {
 		type Prefix: Get<&'static [u8]>;
 		type MoveClaimOrigin: EnsureOrigin<Self::RuntimeOrigin>;
 		type WeightInfo: WeightInfo;
+		#[cfg(feature = "runtime-benchmarks")]
+		/// Benchmark helper
+		type BenchmarkHelper: BenchmarkHelperTrait<
+			Self::RuntimeCall,
+			DispatchInfoOf<Self::RuntimeCall>,
+		>;
 	}
 
 	#[pallet::event]
@@ -402,7 +423,7 @@ pub mod pallet {
 		/// Attest to a statement, needed to finalize the claims process.
 		///
 		/// WARNING: Insecure unless your chain includes `PrevalidateAttests` as a
-		/// `SignedExtension`.
+		/// `TransactionExtension`.
 		///
 		/// Unsigned Validation:
 		/// A call to attest is deemed valid if the sender has a `Preclaim` registered
@@ -612,46 +633,46 @@ impl<T: Config> PrevalidateAttests<T>
 where
 	<T as frame_system::Config>::RuntimeCall: IsSubType<Call<T>>,
 {
-	/// Create new `SignedExtension` to check runtime version.
+	/// Create new `TransactionExtension` to check runtime version.
 	pub fn new() -> Self {
 		Self(sp_std::marker::PhantomData)
 	}
 }
 
-impl<T: Config> SignedExtension for PrevalidateAttests<T>
+impl<T: Config> TransactionExtensionBase for PrevalidateAttests<T>
 where
 	<T as frame_system::Config>::RuntimeCall: IsSubType<Call<T>>,
 {
-	type AccountId = T::AccountId;
-	type Call = <T as frame_system::Config>::RuntimeCall;
-	type AdditionalSigned = ();
-	type Pre = ();
 	const IDENTIFIER: &'static str = "PrevalidateAttests";
+	type Implicit = ();
+}
 
-	fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
-		Ok(())
-	}
-
-	fn pre_dispatch(
-		self,
-		who: &Self::AccountId,
-		call: &Self::Call,
-		info: &DispatchInfoOf<Self::Call>,
-		len: usize,
-	) -> Result<Self::Pre, TransactionValidityError> {
-		self.validate(who, call, info, len).map(|_| ())
-	}
+impl<T: Config, Context> TransactionExtension<T::RuntimeCall, Context> for PrevalidateAttests<T>
+where
+	<T as frame_system::Config>::RuntimeCall: IsSubType<Call<T>>,
+	<<T as frame_system::Config>::RuntimeCall as Dispatchable>::RuntimeOrigin:
+		AsSystemOriginSigner<T::AccountId> + Clone,
+{
+	type Pre = ();
+	type Val = ();
 
 	// <weight>
 	// The weight of this logic is included in the `attest` dispatchable.
 	// </weight>
 	fn validate(
 		&self,
-		who: &Self::AccountId,
-		call: &Self::Call,
-		_info: &DispatchInfoOf<Self::Call>,
+		origin: <T::RuntimeCall as Dispatchable>::RuntimeOrigin,
+		call: &T::RuntimeCall,
+		_info: &DispatchInfoOf<T::RuntimeCall>,
 		_len: usize,
-	) -> TransactionValidity {
+		_context: &mut Context,
+		_self_implicit: Self::Implicit,
+		_inherited_implication: &impl Encode,
+	) -> Result<
+		(ValidTransaction, Self::Val, <T::RuntimeCall as Dispatchable>::RuntimeOrigin),
+		TransactionValidityError,
+	> {
+		let who = origin.as_system_origin_signer().ok_or(InvalidTransaction::BadSigner)?;
 		if let Some(local_call) = call.is_sub_type() {
 			if let Call::attest { statement: attested_statement } = local_call {
 				let signer = Preclaims::<T>::get(who)
@@ -662,8 +683,9 @@ where
 				}
 			}
 		}
-		Ok(ValidTransaction::default())
+		Ok((ValidTransaction::default(), (), origin))
 	}
+	impl_tx_ext_default!(T::RuntimeCall; Context; prepare);
 }
 
 #[cfg(any(test, feature = "runtime-benchmarks"))]
@@ -696,7 +718,7 @@ mod secp_utils {
 }
 
 #[cfg(test)]
-mod tests {
+pub(super) mod tests {
 	use super::*;
 	use hex_literal::hex;
 	use secp_utils::*;
@@ -714,8 +736,11 @@ mod tests {
 	};
 	use pallet_balances;
 	use sp_runtime::{
-		traits::Identity, transaction_validity::TransactionLongevity, BuildStorage,
-		DispatchError::BadOrigin, TokenError,
+		traits::{DispatchTransaction, Identity},
+		transaction_validity::TransactionLongevity,
+		BuildStorage,
+		DispatchError::BadOrigin,
+		TokenError,
 	};
 
 	type Block = frame_system::mocking::MockBlock<Test>;
@@ -790,6 +815,19 @@ mod tests {
 		type Prefix = Prefix;
 		type MoveClaimOrigin = frame_system::EnsureSignedBy<Six, u64>;
 		type WeightInfo = TestWeightInfo;
+		#[cfg(feature = "runtime-benchmarks")]
+		type BenchmarkHelper = ();
+	}
+
+	#[cfg(feature = "runtime-benchmarks")]
+	impl BenchmarkHelperTrait<RuntimeCall, DispatchInfoOf<RuntimeCall>> for () {
+		fn default_call_and_info() -> (RuntimeCall, DispatchInfoOf<RuntimeCall>) {
+			let call = RuntimeCall::Claims(crate::claims::Call::attest {
+				statement: StatementKind::Regular.to_text().to_vec(),
+			});
+			let info = call.get_dispatch_info();
+			(call, info)
+		}
 	}
 
 	fn alice() -> libsecp256k1::SecretKey {
@@ -1071,8 +1109,8 @@ mod tests {
 			});
 			let di = c.get_dispatch_info();
 			assert_eq!(di.pays_fee, Pays::No);
-			let r = p.validate(&42, &c, &di, 20);
-			assert_eq!(r, TransactionValidity::Ok(ValidTransaction::default()));
+			let r = p.validate_only(Some(42).into(), &c, &di, 20);
+			assert_eq!(r.unwrap().0, ValidTransaction::default());
 		});
 	}
 
@@ -1084,13 +1122,13 @@ mod tests {
 				statement: StatementKind::Regular.to_text().to_vec(),
 			});
 			let di = c.get_dispatch_info();
-			let r = p.validate(&42, &c, &di, 20);
+			let r = p.validate_only(Some(42).into(), &c, &di, 20);
 			assert!(r.is_err());
 			let c = RuntimeCall::Claims(ClaimsCall::attest {
 				statement: StatementKind::Saft.to_text().to_vec(),
 			});
 			let di = c.get_dispatch_info();
-			let r = p.validate(&69, &c, &di, 20);
+			let r = p.validate_only(Some(69).into(), &c, &di, 20);
 			assert!(r.is_err());
 		});
 	}
@@ -1444,14 +1482,17 @@ mod tests {
 }
 
 #[cfg(feature = "runtime-benchmarks")]
-mod benchmarking {
+pub(super) mod benchmarking {
 	use super::*;
 	use crate::claims::Call;
 	use frame_benchmarking::{account, benchmarks};
 	use frame_support::traits::UnfilteredDispatchable;
 	use frame_system::RawOrigin;
 	use secp_utils::*;
-	use sp_runtime::{traits::ValidateUnsigned, DispatchResult};
+	use sp_runtime::{
+		traits::{DispatchTransaction, ValidateUnsigned},
+		DispatchResult,
+	};
 
 	const SEED: u32 = 0;
 
@@ -1487,6 +1528,11 @@ mod benchmarking {
 	}
 
 	benchmarks! {
+		where_clause { where <T as frame_system::Config>::RuntimeCall: IsSubType<Call<T>>,
+			<<T as frame_system::Config>::RuntimeCall as Dispatchable>::RuntimeOrigin: AsSystemOriginSigner<T::AccountId> + Clone,
+			<<T as frame_system::Config>::RuntimeCall as Dispatchable>::PostInfo: Default,
+		}
+
 		// Benchmark `claim` including `validate_unsigned` logic.
 		claim {
 			let c = MAX_CLAIMS;
@@ -1665,6 +1711,38 @@ mod benchmarking {
 			}
 		}
 
+		prevalidate_attests {
+			let c = MAX_CLAIMS;
+
+			for i in 0 .. c / 2 {
+				create_claim::<T>(c)?;
+				create_claim_attest::<T>(u32::MAX - c)?;
+			}
+
+			let ext = PrevalidateAttests::<T>::new();
+			let (call, info) = T::BenchmarkHelper::default_call_and_info();
+			let attest_c = u32::MAX - c;
+			let secret_key = libsecp256k1::SecretKey::parse(&keccak_256(&attest_c.encode())).unwrap();
+			let eth_address = eth(&secret_key);
+			let account: T::AccountId = account("user", c, SEED);
+			let vesting = Some((100_000u32.into(), 1_000u32.into(), 100u32.into()));
+			let statement = StatementKind::Regular;
+			let signature = sig::<T>(&secret_key, &account.encode(), statement.to_text());
+			super::Pallet::<T>::mint_claim(RawOrigin::Root.into(), eth_address, VALUE.into(), vesting, Some(statement))?;
+			Preclaims::<T>::insert(&account, eth_address);
+			assert_eq!(Claims::<T>::get(eth_address), Some(VALUE.into()));
+		}: {
+			assert!(ext.test_run(
+				RawOrigin::Signed(account).into(),
+				&call,
+				&info,
+				0,
+				|_| {
+					Ok(Default::default())
+				}
+			).unwrap().is_ok());
+		}
+
 		impl_benchmark_test_suite!(
 			Pallet,
 			crate::claims::tests::new_test_ext(),