Registrar: Deposit covering max code size (#3020)

This PR implements phase 1 of:
https://github.com/paritytech/polkadot-sdk/pull/2372#discussion_r1461873933

NOTE: This means that all the current parachains can upgrade their code
to the maximum size for free.

---------

Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Radha <86818441+DrW3RK@users.noreply.github.com>

polkadot/runtime/common/src/integration_tests.rs

@@ -930,8 +930,18 @@ fn basic_swap_works() {
 
 		// Deposit is appropriately taken
 		// ----------------------------------------- para deposit --- crowdloan
-		assert_eq!(Balances::reserved_balance(&account_id(1)), (500 + 10 * 2 * 1) + 100);
+		let crowdloan_deposit = 100;
-		assert_eq!(Balances::reserved_balance(&account_id(2)), 500 + 20 * 2 * 1);
+		let para_id_deposit = <Test as paras_registrar::Config>::ParaDeposit::get();
+		let code_deposit = configuration::Pallet::<Test>::config().max_code_size *
+			<Test as paras_registrar::Config>::DataDepositPerByte::get();
+
+		// Para 2000 has a genesis head size of 10.
+		assert_eq!(
+			Balances::reserved_balance(&account_id(1)),
+			crowdloan_deposit + para_id_deposit + code_deposit + 10
+		);
+		// Para 2001 has a genesis head size of 20.
+		assert_eq!(Balances::reserved_balance(&account_id(2)), para_id_deposit + code_deposit + 20);
 		assert_eq!(Balances::reserved_balance(&crowdloan_account), total);
 		// Crowdloan is appropriately set
 		assert!(Crowdloan::funds(ParaId::from(2000)).is_some());
@@ -973,8 +983,8 @@ fn basic_swap_works() {
 		// Deregister on-demand parachain
 		assert_ok!(Registrar::deregister(para_origin(2000).into(), ParaId::from(2000)));
 		// Correct deposit is unreserved
-		assert_eq!(Balances::reserved_balance(&account_id(1)), 100); // crowdloan deposit left over
+		assert_eq!(Balances::reserved_balance(&account_id(1)), crowdloan_deposit);
-		assert_eq!(Balances::reserved_balance(&account_id(2)), 500 + 20 * 2 * 1);
+		assert_eq!(Balances::reserved_balance(&account_id(2)), para_id_deposit + code_deposit + 20);
 		// Crowdloan ownership is swapped
 		assert!(Crowdloan::funds(ParaId::from(2000)).is_none());
 		assert!(Crowdloan::funds(ParaId::from(2001)).is_some());
@@ -1005,7 +1015,7 @@ fn basic_swap_works() {
 		// Dissolve returns the balance of the person who put a deposit for crowdloan
 		assert_ok!(Crowdloan::dissolve(signed(1), ParaId::from(2001)));
 		assert_eq!(Balances::reserved_balance(&account_id(1)), 0);
-		assert_eq!(Balances::reserved_balance(&account_id(2)), 500 + 20 * 2 * 1);
+		assert_eq!(Balances::reserved_balance(&account_id(2)), para_id_deposit + code_deposit + 20);
 
 		// Final deregister sets everything back to the start
 		assert_ok!(Registrar::deregister(para_origin(2001).into(), ParaId::from(2001)));

polkadot/runtime/common/src/paras_registrar/mod.rs

@@ -239,7 +239,13 @@ pub mod pallet {
 		/// - `validation_code`: The initial validation code of the parachain/thread.
 		///
 		/// ## Deposits/Fees
-		/// The origin signed account must reserve a corresponding deposit for the registration.
+		/// The account with the originating signature must reserve a deposit.
+		///
+		/// The deposit is required to cover the costs associated with storing the genesis head
+		/// data and the validation code.
+		/// This accounts for the potential to store validation code of a size up to the
+		/// `max_code_size`, as defined in the configuration pallet
+		///
 		/// Anything already reserved previously for this para ID is accounted for.
 		///
 		/// ## Events
@@ -661,7 +667,7 @@ impl<T: Config> Pallet<T> {
 		let per_byte_fee = T::DataDepositPerByte::get();
 		let deposit = T::ParaDeposit::get()
 			.saturating_add(per_byte_fee.saturating_mul((genesis_head.0.len() as u32).into()))
-			.saturating_add(per_byte_fee.saturating_mul((validation_code.0.len() as u32).into()));
+			.saturating_add(per_byte_fee.saturating_mul(config.max_code_size.into()));
 
 		Ok((ParaGenesisArgs { genesis_head, validation_code, para_kind }, deposit))
 	}
@@ -1013,10 +1019,16 @@ mod tests {
 
 			run_to_session(START_SESSION_INDEX + 2);
 			assert!(Parachains::is_parathread(para_id));
+			// Even though the registered validation code has a smaller size than the maximum the
+			// para manager's deposit is reserved as though they registered the maximum-sized code.
+			// Consequently, they can upgrade their code to the maximum size at any point without
+			// additional cost.
+			let validation_code_deposit =
+				max_code_size() as BalanceOf<Test> * <Test as Config>::DataDepositPerByte::get();
+			let head_deposit = 32 * <Test as Config>::DataDepositPerByte::get();
 			assert_eq!(
 				Balances::reserved_balance(&1),
-				<Test as Config>::ParaDeposit::get() +
+				<Test as Config>::ParaDeposit::get() + head_deposit + validation_code_deposit
-					64 * <Test as Config>::DataDepositPerByte::get()
 			);
 		});
 	}

prdoc/pr_3020.prdoc

@@ -0,0 +1,14 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Para registration deposit covering max code size
+
+doc:
+  - audience: Runtime User
+    description: |
+      With this PR all newly registered parachains must pay a deposit equivalent to the cost of 
+      registering validation code of the maximum size. Consequently, they can upgrade their code
+      to the maximum size at any point without additional cost.
+
+crates: 
+  - name: polkadot-runtime-common