refactor: make nextNonce implementation common

while the overrides still need to be present to inform the compiler
about the base class whose function should be called, the implementation
can still be made common in the base class.

src/core/BootstrapLzReceiver.sol

@@ -1,7 +1,9 @@
 pragma solidity ^0.8.19;
 
 import {OAppReceiverUpgradeable, Origin} from "../lzApp/OAppReceiverUpgradeable.sol";
+
 import {BootstrapStorage} from "../storage/BootstrapStorage.sol";
+import {GatewayStorage} from "../storage/GatewayStorage.sol";
 import {PausableUpgradeable} from "@openzeppelin-upgradeable/contracts/utils/PausableUpgradeable.sol";
 
 abstract contract BootstrapLzReceiver is PausableUpgradeable, OAppReceiverUpgradeable, BootstrapStorage {
@@ -35,10 +37,10 @@ abstract contract BootstrapLzReceiver is PausableUpgradeable, OAppReceiverUpgrad
         public
         view
         virtual
-        override(OAppReceiverUpgradeable)
+        override(GatewayStorage, OAppReceiverUpgradeable)
         returns (uint64)
     {
-        return inboundNonce[srcEid][sender] + 1;
+        return GatewayStorage.nextNonce(srcEid, sender);
     }
 
 }

src/core/ClientChainGateway.sol

@@ -6,12 +6,15 @@ import {OAppReceiverUpgradeable} from "../lzApp/OAppReceiverUpgradeable.sol";
 import {MessagingFee, OAppSenderUpgradeable} from "../lzApp/OAppSenderUpgradeable.sol";
 
 import {ClientChainGatewayStorage} from "../storage/ClientChainGatewayStorage.sol";
+
+import {GatewayStorage} from "../storage/GatewayStorage.sol";
 import {ClientGatewayLzReceiver} from "./ClientGatewayLzReceiver.sol";
 import {LSTRestakingController} from "./LSTRestakingController.sol";
 import {NativeRestakingController} from "./NativeRestakingController.sol";
 
 import {IOAppCore} from "@layerzero-v2/oapp/contracts/oapp/interfaces/IOAppCore.sol";
 import {OptionsBuilder} from "@layerzero-v2/oapp/contracts/oapp/libs/OptionsBuilder.sol";
+import {ILayerZeroReceiver} from "@layerzero-v2/protocol/contracts/interfaces/ILayerZeroReceiver.sol";
 import {OwnableUpgradeable} from "@openzeppelin-upgradeable/contracts/access/OwnableUpgradeable.sol";
 import {Initializable} from "@openzeppelin-upgradeable/contracts/proxy/utils/Initializable.sol";
 import {PausableUpgradeable} from "@openzeppelin-upgradeable/contracts/utils/PausableUpgradeable.sol";
@@ -167,4 +170,14 @@ contract ClientChainGateway is
         return (SENDER_VERSION, RECEIVER_VERSION);
     }
 
+    function nextNonce(uint32 srcEid, bytes32 sender)
+        public
+        view
+        virtual
+        override(ClientGatewayLzReceiver, GatewayStorage, ILayerZeroReceiver)
+        returns (uint64)
+    {
+        return GatewayStorage.nextNonce(srcEid, sender);
+    }
+
 }

src/core/ClientGatewayLzReceiver.sol

@@ -3,7 +3,9 @@ pragma solidity ^0.8.19;
 import {IExoCapsule} from "../interfaces/IExoCapsule.sol";
 import {IVault} from "../interfaces/IVault.sol";
 import {OAppReceiverUpgradeable, Origin} from "../lzApp/OAppReceiverUpgradeable.sol";
+
 import {ClientChainGatewayStorage} from "../storage/ClientChainGatewayStorage.sol";
+import {GatewayStorage} from "../storage/GatewayStorage.sol";
 
 import {PausableUpgradeable} from "@openzeppelin-upgradeable/contracts/utils/PausableUpgradeable.sol";
 
@@ -69,10 +71,10 @@ abstract contract ClientGatewayLzReceiver is PausableUpgradeable, OAppReceiverUp
         public
         view
         virtual
-        override(OAppReceiverUpgradeable)
+        override(GatewayStorage, OAppReceiverUpgradeable)
         returns (uint64)
     {
-        return inboundNonce[srcEid][sender] + 1;
+        return GatewayStorage.nextNonce(srcEid, sender);
     }
 
     function afterReceiveDepositResponse(bytes memory requestPayload, bytes calldata responsePayload)

src/core/ExocoreGateway.sol

@@ -13,7 +13,9 @@ import {
     OAppUpgradeable,
     Origin
 } from "../lzApp/OAppUpgradeable.sol";
+
 import {ExocoreGatewayStorage} from "../storage/ExocoreGatewayStorage.sol";
+import {GatewayStorage} from "../storage/GatewayStorage.sol";
 
 import {OAppCoreUpgradeable} from "../lzApp/OAppCoreUpgradeable.sol";
 import {IOAppCore} from "@layerzero-v2/oapp/contracts/oapp/interfaces/IOAppCore.sol";
@@ -344,10 +346,12 @@ contract ExocoreGateway is
         public
         view
         virtual
-        override(ILayerZeroReceiver, OAppReceiverUpgradeable)
+        // since there are 3 contracts with this function, it must be defined so that
+        // the compiler knows which one to call
+        override(GatewayStorage, ILayerZeroReceiver, OAppReceiverUpgradeable)
         returns (uint64)
     {
-        return inboundNonce[srcEid][sender] + 1;
+        return GatewayStorage.nextNonce(srcEid, sender);
     }
 
 }

src/storage/GatewayStorage.sol

@@ -35,4 +35,8 @@ contract GatewayStorage {
         inboundNonce[srcChainId][srcAddress] = nonce;
     }
 
+    function nextNonce(uint32 srcEid, bytes32 sender) public view virtual returns (uint64) {
+        return inboundNonce[srcEid][sender] + 1;
+    }
+
 }

test/mocks/ExocoreGatewayMock.sol

@@ -13,7 +13,9 @@ import {
     OAppUpgradeable,
     Origin
 } from "src/lzApp/OAppUpgradeable.sol";
+
 import {ExocoreGatewayStorage} from "src/storage/ExocoreGatewayStorage.sol";
+import {GatewayStorage} from "src/storage/GatewayStorage.sol";
 
 import {IOAppCore} from "@layerzero-v2/oapp/contracts/oapp/interfaces/IOAppCore.sol";
 import {OptionsBuilder} from "@layerzero-v2/oapp/contracts/oapp/libs/OptionsBuilder.sol";
@@ -335,10 +337,10 @@ contract ExocoreGatewayMock is
         public
         view
         virtual
-        override(ILayerZeroReceiver, OAppReceiverUpgradeable)
+        override(GatewayStorage, ILayerZeroReceiver, OAppReceiverUpgradeable)
         returns (uint64)
     {
-        return inboundNonce[srcEid][sender] + 1;
+        return GatewayStorage.nextNonce(srcEid, sender);
     }
 
 }