Improve upgrade initializer call

contracts/src/Gateway.sol

@@ -373,8 +373,8 @@ contract Gateway is IGateway, IInitializable {
             revert InvalidCodeHash();
         }
 
-        // Verify that the code in the implementation contract was not changed
-        // after the upgrade initiated on BridgeHub parachain.
+        // As a sanity check, ensure that the codehash of implementation contract
+        // matches the codehash in the upgrade proposal
         if (params.impl.codehash != params.implCodeHash) {
             revert InvalidCodeHash();
         }
@@ -384,11 +384,9 @@ contract Gateway is IGateway, IInitializable {
 
         // Apply the initialization function of the implementation only if params were provided
         if (params.initParams.length > 0) {
-            (bool success,) =
-                params.impl.delegatecall(abi.encodeWithSelector(this.initialize.selector, params.initParams));
-            if (!success) {
-                revert InitializationFailed();
-            }
+            (bool success, bytes memory returndata) =
+                params.impl.delegatecall(abi.encodeCall(IInitializable.initialize, params.initParams));
+            Call.verifyResult(success, returndata);
         }
 
         emit Upgraded(params.impl);

contracts/src/GatewayProxy.sol

@@ -3,6 +3,7 @@
 pragma solidity 0.8.22;
 
 import {ERC1967} from "./utils/ERC1967.sol";
+import {Call} from "./utils/Call.sol";
 import {IInitializable} from "./interfaces/IInitializable.sol";
 
 contract GatewayProxy is IInitializable {
@@ -14,13 +15,12 @@ contract GatewayProxy is IInitializable {
         ERC1967.store(implementation);
         // Initialize storage by calling the implementation's `initialize(bytes)` function
         // using `delegatecall`.
-        (bool success,) = implementation.delegatecall(abi.encodeCall(IInitializable.initialize, params));
-        if (!success) {
-            revert InitializationFailed();
-        }
+        (bool success, bytes memory returndata) =
+            implementation.delegatecall(abi.encodeCall(IInitializable.initialize, params));
+        Call.verifyResult(success, returndata);
     }
 
-    // Prevent fallback() from calling `initialize(bytes)` on the implementation contract
+    // Prevent fallback() from calling `IInitializable.initialize(bytes)` on the implementation contract
     function initialize(bytes calldata) external pure {
         revert Unauthorized();
     }

contracts/src/interfaces/IInitializable.sol

@@ -3,10 +3,8 @@
 pragma solidity 0.8.22;
 
 /**
- * @title Initialization of gateway contracts
+ * @title Initialization of gateway logic contracts
  */
 interface IInitializable {
-    error InitializationFailed();
-
     function initialize(bytes calldata data) external;
 }

contracts/test/Gateway.t.sol

@@ -486,7 +486,7 @@ contract GatewayTest is Test {
             initParams: abi.encode(666)
         });
 
-        vm.expectRevert(IInitializable.InitializationFailed.selector);
+        vm.expectRevert("initialize failed");
         GatewayMock(address(gateway)).upgradePublic(abi.encode(params));
     }