Revert "contracts: Don't rely on reserved balances keeping an account alive (#13369)"

This reverts commit c23c308.

Author: Ross Bulat

frame/contracts/fixtures/caller_contract.wat

@@ -16,11 +16,27 @@
 		)
 	)
 
+	(func $current_balance (param $sp i32) (result i64)
+		(i32.store
+			(i32.sub (get_local $sp) (i32.const 16))
+			(i32.const 8)
+		)
+		(call $seal_balance
+			(i32.sub (get_local $sp) (i32.const 8))
+			(i32.sub (get_local $sp) (i32.const 16))
+		)
+		(call $assert
+			(i32.eq (i32.load (i32.sub (get_local $sp) (i32.const 16))) (i32.const 8))
+		)
+		(i64.load (i32.sub (get_local $sp) (i32.const 8)))
+	)
+
 	(func (export "deploy"))
 
 	(func (export "call")
 		(local $sp i32)
 		(local $exit_code i32)
+		(local $balance i64)
 
 		;; Length of the buffer
 		(i32.store (i32.const 20) (i32.const 32))
@@ -38,6 +54,9 @@
 
 		;; Read current balance into local variable.
 		(set_local $sp (i32.const 1024))
+		(set_local $balance
+			(call $current_balance (get_local $sp))
+		)
 
 		;; Fail to deploy the contract since it returns a non-zero exit status.
 		(set_local $exit_code
@@ -63,6 +82,11 @@
 			(i32.eq (get_local $exit_code) (i32.const 2)) ;; ReturnCode::CalleeReverted
 		)
 
+		;; Check that balance has not changed.
+		(call $assert
+			(i64.eq (get_local $balance) (call $current_balance (get_local $sp)))
+		)
+
 		;; Fail to deploy the contract due to insufficient gas.
 		(set_local $exit_code
 			(call $seal_instantiate
@@ -88,6 +112,11 @@
 			(i32.eq (get_local $exit_code) (i32.const 1)) ;; ReturnCode::CalleeTrapped
 		)
 
+		;; Check that balance has not changed.
+		(call $assert
+			(i64.eq (get_local $balance) (call $current_balance (get_local $sp)))
+		)
+
 		;; Length of the output buffer
 		(i32.store
 			(i32.sub (get_local $sp) (i32.const 4))
@@ -124,6 +153,14 @@
 			(i32.eq (i32.load (i32.sub (get_local $sp) (i32.const 4))) (i32.const 32))
 		)
 
+		;; Check that balance has been deducted.
+		(set_local $balance
+			(i64.sub (get_local $balance) (i64.load (i32.const 0)))
+		)
+		(call $assert
+			(i64.eq (get_local $balance) (call $current_balance (get_local $sp)))
+		)
+
 		;; Zero out destination buffer of output
 		(i32.store
 			(i32.sub (get_local $sp) (i32.const 4))
@@ -167,6 +204,11 @@
 			)
 		)
 
+		;; Check that balance has not changed.
+		(call $assert
+			(i64.eq (get_local $balance) (call $current_balance (get_local $sp)))
+		)
+
 		;; Fail to call the contract due to insufficient gas.
 		(set_local $exit_code
 			(call $seal_call
@@ -187,6 +229,11 @@
 			(i32.eq (get_local $exit_code) (i32.const 1)) ;; ReturnCode::CalleeTrapped
 		)
 
+		;; Check that balance has not changed.
+		(call $assert
+			(i64.eq (get_local $balance) (call $current_balance (get_local $sp)))
+		)
+
 		;; Zero out destination buffer of output
 		(i32.store
 			(i32.sub (get_local $sp) (i32.const 4))
@@ -229,6 +276,14 @@
 				(i32.const 0x77665544)
 			)
 		)
+
+		;; Check that balance has been deducted.
+		(set_local $balance
+			(i64.sub (get_local $balance) (i64.load (i32.const 0)))
+		)
+		(call $assert
+			(i64.eq (get_local $balance) (call $current_balance (get_local $sp)))
+		)
 	)
 
 	(data (i32.const 0) "\00\80")		;; The value to transfer on instantiation and calls.

frame/contracts/fixtures/drain.wat

@@ -34,7 +34,8 @@
 		)
 
 		;; Try to self-destruct by sending full balance to the 0 address.
-		;; The call will fail because a contract transfer has a keep alive requirement
+		;; All the *free* balance will be send away, which is a valid thing to do
+		;; because the storage deposits will keep the account alive.
 		(call $assert
 			(i32.eq
 				(call $seal_transfer
@@ -43,7 +44,7 @@
 					(i32.const 0)	;; Pointer to the buffer with value to transfer
 					(i32.const 8)	;; Length of the buffer with value to transfer
 				)
-				(i32.const 5) ;; ReturnCode::TransferFailed
+				(i32.const 0) ;; ReturnCode::Success
 			)
 		)
 	)

frame/contracts/primitives/src/lib.rs

@@ -47,12 +47,10 @@ pub struct ContractResult<R, Balance> {
 	/// Additionally, any `seal_call` or `seal_instantiate` makes use of pre-charging
 	/// when a non-zero `gas_limit` argument is supplied.
 	pub gas_required: Weight,
-	/// How much balance was paid by the origin into the contract's deposit account in order to
-	/// pay for storage.
+	/// How much balance was deposited and reserved during execution in order to pay for storage.
 	///
-	/// The storage deposit is never actually charged from the origin in case of [`Self::result`]
-	/// is `Err`. This is because on error all storage changes are rolled back including the
-	/// payment of the deposit.
+	/// The storage deposit is never actually charged from the caller in case of [`Self::result`]
+	/// is `Err`. This is because on error all storage changes are rolled back.
 	pub storage_deposit: StorageDeposit<Balance>,
 	/// An optional debug message. This message is only filled when explicitly requested
 	/// by the code that calls into the contract. Otherwise it is empty.
@@ -161,12 +159,12 @@ pub enum StorageDeposit<Balance> {
 	/// The transaction reduced storage consumption.
 	///
 	/// This means that the specified amount of balance was transferred from the involved
-	/// deposit accounts to the origin.
+	/// contracts to the call origin.
 	Refund(Balance),
-	/// The transaction increased storage consumption.
+	/// The transaction increased overall storage usage.
 	///
-	/// This means that the specified amount of balance was transferred from the origin
-	/// to the involved deposit accounts.
+	/// This means that the specified amount of balance was transferred from the call origin
+	/// to the contracts involved.
 	Charge(Balance),
 }