Add Safe to L2 Setup Contract (#759)

This PR introduces a setup contract that can be called from the `Safe`
setup function in order to automatically promote a Safe at setup time if
the code is executing on an L2. Namely, this allows the Safe Proxy
factory to use a single singleton and initializer for all chains, but
end up with different `singleton`s depending on the chain ID.

The expected use of this contract is to use the standard proxy factory:

```solidity
Safe l1Singleton;
SafeL2 l2Singleton;
SafeToL2Setup l2Setup;

proxyFactory.createProxyWithNonce(
    address(l1Singleton),
    abi.encodeCall(
        l1Singleton.setup,
        (
            owners,
            threshold,
            address(l2Setup),
            abi.encodeCall(l2Setup.setupToL2, address(l2Singleton)),
            fallbackHandler,
            paymentToken,
            payment,
            paymentReceiver
        )
    ),
    saltNonce
)
```

On L1 (i.e. Ethereum Mainnet where `chainId == 1`), you would end up
with a Safe where `safe.singleton == l1Singleton` and on any other
chains, you would end up with `safe.singleton == l2Singleton`. This
would happen _before_ the first transaction.

---------

Co-authored-by: Mikhail <16622558+mmv08@users.noreply.github.com>

.env.sample

@@ -15,3 +15,5 @@ SAFE_CONTRACT_UNDER_TEST="Safe"
 SOLIDITY_VERSION= # Example: '0.8.19'
 # For running coverage tests, `details` section of solidity settings are required, else could be removed.
 SOLIDITY_SETTINGS= # Example: '{"viaIR":true,"optimizer":{"enabled":true, "details": {"yul": true, "yulDetails": { "optimizerSteps": ""}}}}'
+# Sets hardhat chain id. In general, you don't need this, it's only used for testing the SafeToL2Setup contract.
+HARDHAT_CHAIN_ID=31337

.github/workflows/ci.yml

@@ -71,7 +71,7 @@ jobs:
                 solidity: ["0.7.6", "0.8.24"]
                 include:
                     - solidity: "0.8.24"
-                      settings: '{"viaIR":true,"optimizer":{"enabled":true,"runs":1000000}}'
+                      settings: '{"viaIR":false,"optimizer":{"enabled":true,"runs":1000000}}'
         env:
             SOLIDITY_VERSION: ${{ matrix.solidity }}
             SOLIDITY_SETTINGS: ${{ matrix.settings }}

benchmark/utils/setup.ts

@@ -27,6 +27,8 @@ const generateTarget = async (owners: number, threshold: number, guardAddress: s
     const safe = await getSafeWithOwners(
         signers.map((owner) => owner.address),
         threshold,
+        ethers.ZeroAddress,
+        "0x",
         fallbackHandlerAddress,
         logGasUsage,
         saltNumber,

contracts/libraries/SafeToL2Setup.sol

@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+pragma solidity >=0.7.0 <0.9.0;
+
+import {SafeStorage} from "../libraries/SafeStorage.sol";
+
+/**
+ * @title Safe to L2 Setup Contract
+ * @dev This contract expects the singleton to be the {Safe} by default. Even if there are more
+ * {SafeL2} proxies deployed, the average gas cost on L2s is significantly lower, making the
+ * current design more economically efficient overall.
+ * @notice This contract facilitates the deployment of a Safe to the same address on all networks by
+ *         automatically changing the singleton to the L2 version when not on chain ID 1.
+ */
+contract SafeToL2Setup is SafeStorage {
+    /**
+     * @notice Address of the contract.
+     * @dev This is used to ensure that the contract is only ever `DELEGATECALL`-ed.
+     */
+    address public immutable _SELF;
+
+    /**
+     * @notice Event indicating a change of master copy address.
+     * @param singleton New master copy address
+     */
+    event ChangedMasterCopy(address singleton);
+
+    /**
+     * @notice Initializes a new {SafeToL2Setup} instance.
+     */
+    constructor() {
+        _SELF = address(this);
+    }
+
+    /**
+     * @notice Modifier ensure a function is only called via `DELEGATECALL`. Will revert otherwise.
+     */
+    modifier onlyDelegateCall() {
+        require(address(this) != _SELF, "SafeToL2Setup should only be called via delegatecall");
+        _;
+    }
+
+    /**
+     * @notice Modifier to prevent using initialized Safes.
+     */
+    modifier onlyNonceZero() {
+        require(nonce == 0, "Safe must have not executed any tx");
+        _;
+    }
+
+    /**
+     * @notice Modifier to ensure that the specified account is a contract.
+     *
+     */
+    modifier onlyContract(address account) {
+        require(_codeSize(account) != 0, "Account doesn't contain code");
+        _;
+    }
+
+    /**
+     * @notice Setup the Safe with the provided L2 singleton if needed.
+     * @dev This function checks that the chain ID is not 1, and if it isn't updates the singleton
+     *      to the provided L2 singleton.
+     */
+    function setupToL2(address l2Singleton) public onlyDelegateCall onlyNonceZero onlyContract(l2Singleton) {
+        if (_chainId() != 1) {
+            singleton = l2Singleton;
+            emit ChangedMasterCopy(l2Singleton);
+        }
+    }
+
+    /**
+     * @notice Returns the current chain ID.
+     */
+    function _chainId() private view returns (uint256 result) {
+        /* solhint-disable no-inline-assembly */
+        /// @solidity memory-safe-assembly
+        assembly {
+            result := chainid()
+        }
+        /* solhint-enable no-inline-assembly */
+    }
+
+    /**
+     * @notice Returns the code size of the specified account.
+     */
+    function _codeSize(address account) internal view returns (uint256 result) {
+        /* solhint-disable no-inline-assembly */
+        /// @solidity memory-safe-assembly
+        assembly {
+            result := extcodesize(account)
+        }
+        /* solhint-enable no-inline-assembly */
+    }
+}

hardhat.config.ts

@@ -16,7 +16,7 @@ const argv = yargs
 
 // Load environment variables.
 dotenv.config();
-const { NODE_URL, INFURA_KEY, MNEMONIC, ETHERSCAN_API_KEY, PK, SOLIDITY_VERSION, SOLIDITY_SETTINGS } = process.env;
+const { NODE_URL, INFURA_KEY, MNEMONIC, ETHERSCAN_API_KEY, PK, SOLIDITY_VERSION, SOLIDITY_SETTINGS, HARDHAT_CHAIN_ID } = process.env;
 
 const DEFAULT_MNEMONIC = "candy maple cake sugar pudding cream honey rich smooth crumble sweet treat";
 
@@ -78,6 +78,7 @@ const userConfig: HardhatUserConfig = {
             allowUnlimitedContractSize: true,
             blockGasLimit: 100000000,
             gas: 100000000,
+            chainId: typeof HARDHAT_CHAIN_ID === "string" && !Number.isNaN(parseInt(HARDHAT_CHAIN_ID)) ? parseInt(HARDHAT_CHAIN_ID) : 31337,
         },
         mainnet: {
             ...sharedNetworkConfig,