Forkaware structure (#74)

On L2, I think many contracts need to wait after a fork for the first message that will come from the bridge. E.g. our adjudication framework would have to wait for a message which court is removed before it starts to forward any new information of the oracles/courts. Then I think the following contract will be quite helpful.

.solhint.json

@@ -3,6 +3,8 @@
   "plugins": ["prettier"],
   "rules": {
     "compiler-version": "off",
-    "max-states-count": "off"
+    "max-states-count": "off",
+    "no-empty-blocks": "off",
+    "func-visibility": ["warn",{"ignoreConstructors":true}]
   }
 }

development/contracts/mixin/InitializeChain.sol

@@ -0,0 +1,23 @@
+pragma solidity ^0.8.20;
+
+/** This contract can be inherited form any other contrac that needs to be aware of Forks.
+This contract uses the fact that after a fork the chainId changes and thereby detects forks*/
+
+contract InitializeChain {
+    uint256 public chainId;
+
+    modifier onlyChainUninitialized() {
+        require(chainId != block.chainid, "Not on new fork");
+        _;
+        chainId = block.chainid;
+    }
+
+    modifier onlyChainInitialized() {
+        require(chainId == block.chainid, "On new fork");
+        _;
+    }
+
+    constructor() {
+        chainId = block.chainid;
+    }
+}

test/InitializeChain.sol

@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-3.0-only
+pragma solidity ^0.8.17;
+
+import {Test} from "forge-std/Test.sol";
+import {InitializeChainWrapper} from "./testcontract/InitializeChainWrapper.sol";
+
+contract InitializeChainWrapperTest is Test {
+    InitializeChainWrapper public wrapper;
+
+    function setUp() public {
+        wrapper = new InitializeChainWrapper();
+    }
+
+    function testSetChainId() public {
+        assertEq(wrapper.chainId(), block.chainid);
+    }
+
+    function testonlyChainUninitialized() public {
+        // Simulate a chain fork by setting block.chainid to a new value
+        vm.chainId(2);
+        wrapper.onlyChainUninitializedWrapper(); // This should pass since it's the first TX after fork
+
+        // Subsequent calls should fail
+        try wrapper.onlyChainUninitializedWrapper() {
+            fail(
+                "Should have reverted because it's not the first TX after fork."
+            );
+        } catch Error(string memory reason) {
+            assertEq(reason, "Not on new fork");
+        }
+    }
+
+    function testonlyChainInitialized() public {
+        // On the original chain, this call should succeed
+        wrapper.onlyChainInitializedWrapper();
+
+        // Simulate a chain fork by setting block.chainid to a new value
+        vm.chainId(2);
+
+        // This call should fail since it's the first TX after fork
+        try wrapper.onlyChainInitializedWrapper() {
+            fail("Should have reverted because it's the first TX after fork.");
+        } catch Error(string memory reason) {
+            assertEq(reason, "On new fork");
+        }
+
+        // Call a function with onlyChainUninitialized to update chainId
+        wrapper.onlyChainUninitializedWrapper();
+
+        // Now, this call should succeed
+        wrapper.onlyChainInitializedWrapper();
+    }
+
+    function testUpdateChainId() public {
+        // Initially, chainId is 1
+        assertFalse(wrapper.chainId() == 1);
+
+        // Simulate a chain fork by setting block.chainid to a new value
+        vm.chainId(2);
+        wrapper.onlyChainUninitializedWrapper(); // This should update the chainId
+
+        assertEq(wrapper.chainId(), 2);
+    }
+}

test/testcontract/InitializeChainWrapper.sol

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-3.0-only
+pragma solidity ^0.8.17;
+
+import {InitializeChain} from "../../development/contracts/mixin/InitializeChain.sol";
+
+contract InitializeChainWrapper is InitializeChain {
+    constructor() InitializeChain() {}
+
+    function onlyChainUninitializedWrapper() public onlyChainUninitialized {}
+
+    function onlyChainInitializedWrapper()
+        public
+        onlyChainInitialized
+    {}
+}