Contracts: seal0::balance should return the free balance (#1254)

substrate/frame/contracts/src/exec.rs

@@ -30,7 +30,7 @@ use frame_support::{
 	storage::{with_transaction, TransactionOutcome},
 	traits::{
 		fungible::{Inspect, Mutate},
-		tokens::Preservation,
+		tokens::{Fortitude, Preservation},
 		Contains, OriginTrait, Randomness, Time,
 	},
 	weights::Weight,
@@ -1368,7 +1368,11 @@ where
 	}
 
 	fn balance(&self) -> BalanceOf<T> {
-		T::Currency::balance(&self.top_frame().account_id)
+		T::Currency::reducible_balance(
+			&self.top_frame().account_id,
+			Preservation::Preserve,
+			Fortitude::Polite,
+		)
 	}
 
 	fn value_transferred(&self) -> BalanceOf<T> {

substrate/frame/contracts/src/tests.rs

@@ -5891,3 +5891,53 @@ fn root_cannot_instantiate() {
 		);
 	});
 }
+
+#[test]
+fn balance_api_returns_free_balance() {
+	let (wasm, _code_hash) = compile_module::<Test>("balance").unwrap();
+	ExtBuilder::default().existential_deposit(200).build().execute_with(|| {
+		let _ = <Test as Config>::Currency::set_balance(&ALICE, 1_000_000);
+
+		// Instantiate the BOB contract without any extra balance.
+		let addr = Contracts::bare_instantiate(
+			ALICE,
+			0,
+			GAS_LIMIT,
+			None,
+			Code::Upload(wasm.to_vec()),
+			vec![],
+			vec![],
+			DebugInfo::Skip,
+			CollectEvents::Skip,
+		)
+		.result
+		.unwrap()
+		.account_id;
+
+		let value = 0;
+		// Call BOB which makes it call the balance runtime API.
+		// The contract code asserts that the returned balance is 0.
+		assert_ok!(Contracts::call(
+			RuntimeOrigin::signed(ALICE),
+			addr.clone(),
+			value,
+			GAS_LIMIT,
+			None,
+			vec![]
+		));
+
+		let value = 1;
+		// Calling with value will trap the contract.
+		assert_err_ignore_postinfo!(
+			Contracts::call(
+				RuntimeOrigin::signed(ALICE),
+				addr.clone(),
+				value,
+				GAS_LIMIT,
+				None,
+				vec![]
+			),
+			<Error<Test>>::ContractTrapped
+		);
+	});
+}