implement immutable variables codegen

Signed-off-by: xermicus <cyrill@parity.io>

crates/integration/codesize.json

@@ -1,10 +1,10 @@
 {
-  "Baseline": 912,
-  "Computation": 4413,
-  "DivisionArithmetics": 40689,
-  "ERC20": 54374,
-  "Events": 1726,
-  "FibonacciIterative": 3015,
-  "Flipper": 3612,
-  "SHA1": 32865
+  "Baseline": 962,
+  "Computation": 4463,
+  "DivisionArithmetics": 40756,
+  "ERC20": 54427,
+  "Events": 1792,
+  "FibonacciIterative": 3065,
+  "Flipper": 3665,
+  "SHA1": 32923
 }

crates/integration/contracts/Immutables.sol

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8;
+
+/* runner.json
+{
+  "differential": true,
+  "actions": [
+    {
+      "Instantiate": {
+	    "code": {
+		  "Solidity": {
+		    "contract": "Immutables"
+		  }
+		},
+        "data": "000000000000000000000000000000000000000000000000000000000000007b"
+      }
+    },
+    {
+      "Call": {
+        "dest": {
+          "Instantiated": 0
+        },
+        "data": "c2985578"
+      }
+    },
+    {
+      "Call": {
+        "dest": {
+          "Instantiated": 0
+        },
+        "data": "febb0f7e"
+      }
+    },
+    {
+      "Call": {
+        "dest": {
+          "Instantiated": 0
+        },
+        "data": "7b6a8777"
+      }
+    },
+    {
+      "Call": {
+        "dest": {
+          "Instantiated": 0
+        }
+      }
+    }
+  ]
+}
+*/
+
+contract Immutables {
+    uint public immutable foo;
+    uint public immutable bar;
+    uint public immutable zoo;
+
+    constructor(uint _foo) payable {
+        foo = _foo;
+        bar = foo + 1;
+        zoo = bar + 2;
+    }
+
+    fallback() external {
+        assert(foo > 0);
+        assert(bar > 0);
+        assert(zoo > 0);
+    }
+}

crates/integration/src/tests.rs

@@ -42,6 +42,7 @@ test_spec!(create, "CreateB", "Create.sol");
 test_spec!(call, "Caller", "Call.sol");
 test_spec!(transfer, "Transfer", "Transfer.sol");
 test_spec!(return_data_oob, "ReturnDataOob", "ReturnDataOob.sol");
+test_spec!(immutables, "Immutables", "Immutables.sol");
 
 fn instantiate(path: &str, contract: &str) -> Vec<SpecsAction> {
     vec![Instantiate {