bugfix missing byte swap for the create2 salt value (#272)

Found in https://github.com/paritytech/contract-issues/issues/45, thanks
@albertov19 and @sekisamu

---------

Signed-off-by: xermicus <cyrill@parity.io>
Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/integration/src/cases.rs

@@ -250,6 +250,17 @@ sol!(
 );
 case!("Storage.sol", Storage, transientCall, storage_transient, value: U256);
 
+sol!(
+    contract Predicted {
+        constructor(uint _foo);
+    }
+    contract AddressPredictor {
+        constructor(uint _foo, bytes memory _bytecode) payable;
+    }
+);
+case!("AddressPredictor.sol", Predicted, constructorCall, predicted_constructor, salt: U256);
+case!("AddressPredictor.sol", AddressPredictor, constructorCall, address_predictor_constructor, salt: U256, bytecode: Bytes);
+
 impl Contract {
     pub fn build(calldata: Vec<u8>, name: &'static str, code: &str) -> Self {
         Self {

crates/integration/src/tests.rs

@@ -486,3 +486,31 @@ fn transfer_denies_reentrancy() {
     }
     .run();
 }
+
+#[test]
+fn create2_salt() {
+    let salt = U256::from(777);
+    let predicted = Contract::predicted_constructor(salt).pvm_runtime;
+    let predictor = Contract::address_predictor_constructor(salt, predicted.clone().into());
+    Specs {
+        actions: vec![
+            Upload {
+                origin: TestAddress::Alice,
+                code: Code::Bytes(predicted),
+                storage_deposit_limit: None,
+            },
+            Instantiate {
+                origin: TestAddress::Alice,
+                value: 0,
+                gas_limit: Some(GAS_LIMIT),
+                storage_deposit_limit: None,
+                code: Code::Bytes(predictor.pvm_runtime),
+                data: predictor.calldata,
+                salt: OptionalHex::default(),
+            },
+        ],
+        differential: false,
+        ..Default::default()
+    }
+    .run();
+}