fix(ctb): solc warnings in Proxy.sol (#2951)

Cleans up a few solc warnings in Proxy.sol.
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

.changeset/spotty-wombats-fetch.md

+---
+'@eth-optimism/contracts-bedrock': patch
+---
+
+Resolve compiler warnings in Proxy.sol

packages/contracts-bedrock/.gas-snapshot

@@ -5,7 +5,7 @@ GasBenchMark_L1StandardBridge_Deposit:test_depositERC20_benchmark_1() (gas: 1181
 GasBenchMark_L1StandardBridge_Deposit:test_depositETH_benchmark_0() (gas: 251901)
 GasBenchMark_L1StandardBridge_Deposit:test_depositETH_benchmark_1() (gas: 118108)
 GasBenchMark_L1StandardBridge_Finalize:test_finalizeETHWithdrawal_benchmark() (gas: 45385)
-GasBenchMark_L2OutputOracle:test_appendL2Output_benchmark() (gas: 68684)
+GasBenchMark_L2OutputOracle:test_appendL2Output_benchmark() (gas: 68695)
 GasBenchMark_OptimismPortal:test_depositTransaction_benchmark() (gas: 75024)
 GasBenchMark_OptimismPortal:test_depositTransaction_benchmark_1() (gas: 35328)
 CrossDomainHashing_Test:test_l2TransactionHash() (gas: 104131)
@@ -67,24 +67,24 @@ L2CrossDomainMessenger_Test:test_L2MessengerSendMessage() (gas: 119682)
 L2CrossDomainMessenger_Test:test_L2MessengerTwiceSendMessage() (gas: 133142)
 L2CrossDomainMessenger_Test:test_L2MessengerXDomainSenderReverts() (gas: 10577)
 L2CrossDomainMessenger_Test:test_L2MessengerxDomainMessageSenderResets() (gas: 54881)
-L2OutputOracleTest:testCannot_AppendWithUnmatchedBlockhash() (gas: 26822)
-L2OutputOracleTest:testCannot_appendEmptyOutput() (gas: 24097)
-L2OutputOracleTest:testCannot_appendFutureTimetamp() (gas: 26086)
-L2OutputOracleTest:testCannot_appendOnWrongFork() (gas: 26371)
-L2OutputOracleTest:testCannot_appendOutputIfNotSequencer() (gas: 23488)
-L2OutputOracleTest:testCannot_appendUnexpectedBlockNumber() (gas: 25995)
-L2OutputOracleTest:testCannot_deleteL2Output_ifNotOwner() (gas: 24777)
-L2OutputOracleTest:testCannot_deleteL2Output_withWrongRoot() (gas: 91069)
-L2OutputOracleTest:testCannot_deleteL2Output_withWrongTime() (gas: 87084)
-L2OutputOracleTest:test_appendWithBlockhashAndHeight() (gas: 75059)
-L2OutputOracleTest:test_appendingAnotherOutput() (gas: 76861)
-L2OutputOracleTest:test_changeSequencer() (gas: 55754)
+L2OutputOracleTest:testCannot_AppendWithUnmatchedBlockhash() (gas: 26833)
+L2OutputOracleTest:testCannot_appendEmptyOutput() (gas: 24108)
+L2OutputOracleTest:testCannot_appendFutureTimetamp() (gas: 26097)
+L2OutputOracleTest:testCannot_appendOnWrongFork() (gas: 26382)
+L2OutputOracleTest:testCannot_appendOutputIfNotSequencer() (gas: 23499)
+L2OutputOracleTest:testCannot_appendUnexpectedBlockNumber() (gas: 26006)
+L2OutputOracleTest:testCannot_deleteL2Output_ifNotOwner() (gas: 24799)
+L2OutputOracleTest:testCannot_deleteL2Output_withWrongRoot() (gas: 91113)
+L2OutputOracleTest:testCannot_deleteL2Output_withWrongTime() (gas: 87128)
+L2OutputOracleTest:test_appendWithBlockhashAndHeight() (gas: 75070)
+L2OutputOracleTest:test_appendingAnotherOutput() (gas: 76883)
+L2OutputOracleTest:test_changeSequencer() (gas: 55809)
 L2OutputOracleTest:test_computeL2Timestamp() (gas: 30200)
-L2OutputOracleTest:test_constructor() (gas: 48801)
-L2OutputOracleTest:test_deleteL2Output() (gas: 76499)
-L2OutputOracleTest:test_getL2Output() (gas: 82924)
-L2OutputOracleTest:test_latestBlockNumber() (gas: 76198)
-L2OutputOracleTest:test_nextBlockNumber() (gas: 15144)
+L2OutputOracleTest:test_constructor() (gas: 48856)
+L2OutputOracleTest:test_deleteL2Output() (gas: 76543)
+L2OutputOracleTest:test_getL2Output() (gas: 82935)
+L2OutputOracleTest:test_latestBlockNumber() (gas: 76220)
+L2OutputOracleTest:test_nextBlockNumber() (gas: 15166)
 L2OutputOracleTest:test_updateOwner() (gas: 34580)
 L2OutputOracleUpgradeable_Test:test_cannotInitImpl() (gas: 8476)
 L2OutputOracleUpgradeable_Test:test_cannotInitProxy() (gas: 13497)
@@ -129,9 +129,9 @@ OptimismPortalUpgradeable_Test:test_cannotInitImpl() (gas: 10936)
 OptimismPortalUpgradeable_Test:test_cannotInitProxy() (gas: 15978)
 OptimismPortalUpgradeable_Test:test_initValuesOnProxy() (gas: 16034)
 OptimismPortalUpgradeable_Test:test_upgrading() (gas: 230843)
-OptimismPortal_Test:test_OptimismPortalConstructor() (gas: 17308)
+OptimismPortal_Test:test_OptimismPortalConstructor() (gas: 17319)
 OptimismPortal_Test:test_OptimismPortalContractCreationReverts() (gas: 14193)
-OptimismPortal_Test:test_OptimismPortalReceiveEth() (gas: 126599)
+OptimismPortal_Test:test_OptimismPortalReceiveEth() (gas: 126614)
 OptimismPortal_Test:test_cannotVerifyRecentWithdrawal() (gas: 31924)
 OptimismPortal_Test:test_depositTransaction_NoValueContract() (gas: 75775)
 OptimismPortal_Test:test_depositTransaction_NoValueEOA() (gas: 76054)
@@ -141,14 +141,14 @@ OptimismPortal_Test:test_depositTransaction_withEthValueAndContractContractCreat
 OptimismPortal_Test:test_depositTransaction_withEthValueAndEOAContractCreation() (gas: 74962)
 OptimismPortal_Test:test_depositTransaction_withEthValueFromContract() (gas: 82505)
 OptimismPortal_Test:test_depositTransaction_withEthValueFromEOA() (gas: 83100)
-OptimismPortal_Test:test_invalidWithdrawalProof() (gas: 45141)
-OptimismPortal_Test:test_isOutputFinalized() (gas: 131766)
-OptimismPortal_Test:test_simple_isOutputFinalized() (gas: 23898)
+OptimismPortal_Test:test_invalidWithdrawalProof() (gas: 45152)
+OptimismPortal_Test:test_isOutputFinalized() (gas: 131876)
+OptimismPortal_Test:test_simple_isOutputFinalized() (gas: 23909)
 Proxy_Test:test_clashingFunctionSignatures() (gas: 101427)
 Proxy_Test:test_implementationKey() (gas: 20942)
 Proxy_Test:test_implementationProxyCallIfNotAdmin() (gas: 30021)
-Proxy_Test:test_implementationZeroAddress() (gas: 47985)
-Proxy_Test:test_itDelegatesToTheImplementation() (gas: 45240)
+Proxy_Test:test_implementationZeroAddress() (gas: 48000)
+Proxy_Test:test_itDelegatesToTheImplementation() (gas: 45251)
 Proxy_Test:test_ownerKey() (gas: 19091)
 Proxy_Test:test_ownerProxyCallIfNotAdmin() (gas: 34711)
 Proxy_Test:test_payableUpgradeToAndCall() (gas: 53865)

packages/contracts-bedrock/contracts/universal/Proxy.sol

@@ -57,6 +57,12 @@ contract Proxy {
         _doProxyCall();
     }
 
+    // slither-disable-next-line locked-ether
+    receive() external payable {
+        // Proxy call by default.
+        _doProxyCall();
+    }
+
     /**
      * @notice A modifier that reverts if not called by the owner or by address(0) to allow
      *         eth_call to interact with this proxy without needing to use low-level storage
@@ -146,11 +152,11 @@ contract Proxy {
      * @return Implementation address.
      */
     function _getImplementation() internal view returns (address) {
-        address implementation;
+        address impl;
         assembly {
-            implementation := sload(IMPLEMENTATION_KEY)
+            impl := sload(IMPLEMENTATION_KEY)
         }
-        return implementation;
+        return impl;
     }
 
     /**
@@ -183,15 +189,15 @@ contract Proxy {
      * @notice Performs the proxy call via a delegatecall.
      */
     function _doProxyCall() internal {
-        address implementation = _getImplementation();
-        require(implementation != address(0), "Proxy: implementation not initialized");
+        address impl = _getImplementation();
+        require(impl != address(0), "Proxy: implementation not initialized");
 
         assembly {
             // Copy calldata into memory at 0x0....calldatasize.
             calldatacopy(0x0, 0x0, calldatasize())
 
             // Perform the delegatecall, make sure to pass all available gas.
-            let success := delegatecall(gas(), implementation, 0x0, calldatasize(), 0x0, 0x0)
+            let success := delegatecall(gas(), impl, 0x0, calldatasize(), 0x0, 0x0)
 
             // Copy returndata into memory at 0x0....returndatasize. Note that this *will*
             // overwrite the calldata that we just copied into memory but that doesn't really