ctb: Add events and custom errors to LivenessModule (#10018)

* ctb: Add events and custom errors to LivenessModule

ctb: Use same event as Safe contract

* ctb: Used past tense event name OwnershipTransferredToFallback()

packages/contracts-bedrock/semver-lock.json

@@ -92,8 +92,8 @@
     "sourceCodeHash": "0x9633cea9b66077e222f470439fe3e9a31f3e33b4f7a5618374c44310fd234b24"
   },
   "src/Safe/LivenessModule.sol": {
-    "initCodeHash": "0x0da844fb4dd22f252ff631524f01f45edf43bca7558fe45f71d711b79af01742",
-    "sourceCodeHash": "0x1afb1d392e8f6a58ff86ea7f648e0d1756d4ba8d0d964279d58a390deaa53b7e"
+    "initCodeHash": "0xcd8b76f70634330e242d4ff497bba1f8e0aaa11d7aecf9845090029c43027a7f",
+    "sourceCodeHash": "0x3b358b51fce4f1516191104d2e1f782c8ec3edecee63c502cc301671aa632b93"
   },
   "src/cannon/MIPS.sol": {
     "initCodeHash": "0xaf2ac814f64ccf12e9c6738db7cef865f51f9e39f39105adef9fba11465f6ee1",

packages/contracts-bedrock/snapshots/abi/LivenessModule.json

@@ -163,5 +163,24 @@
     ],
     "stateMutability": "view",
     "type": "function"
+  },
+  {
+    "anonymous": false,
+    "inputs": [],
+    "name": "OwnershipTransferredToFallback",
+    "type": "event"
+  },
+  {
+    "anonymous": false,
+    "inputs": [
+      {
+        "indexed": true,
+        "internalType": "address",
+        "name": "owner",
+        "type": "address"
+      }
+    ],
+    "name": "RemovedOwner",
+    "type": "event"
   }
 ]
\ No newline at end of file

packages/contracts-bedrock/src/Safe/LivenessModule.sol

@@ -14,6 +14,12 @@ import { ISemver } from "src/universal/ISemver.sol";
 ///         If the number of owners falls below the minimum number of owners, the ownership of the
 ///         safe will be transferred to the fallback owner.
 contract LivenessModule is ISemver {
+    /// @notice Emitted when an owner is removed due to insufficient liveness
+    event RemovedOwner(address indexed owner);
+
+    /// @notice Emitted when the fallback owner takes ownership
+    event OwnershipTransferredToFallback();
+
     /// @notice The Safe contract instance
     Safe internal immutable SAFE;
 
@@ -178,6 +184,7 @@ contract LivenessModule is ISemver {
             }),
             "LivenessModule: failed to swap to fallback owner"
         );
+        emit OwnershipTransferredToFallback();
     }
 
     /// @notice Removes the owner `owner` from the Safe and updates the threshold to `_threshold`.
@@ -194,6 +201,7 @@ contract LivenessModule is ISemver {
             }),
             "LivenessModule: failed to remove owner"
         );
+        emit RemovedOwner(_owner);
     }
 
     /// @notice A FREI-PI invariant check enforcing requirements on number of owners and threshold.

packages/contracts-bedrock/test/Safe/LivenessModule.t.sol

@@ -15,7 +15,10 @@ import { LivenessGuard } from "src/Safe/LivenessGuard.sol";
 contract LivenessModule_TestInit is Test, SafeTestTools {
     using SafeTestLib for SafeInstance;
 
+    // LivenessModule events
     event SignersRecorded(bytes32 indexed txHash, address[] signers);
+    event RemovedOwner(address indexed owner);
+    event OwnershipTransferredToFallback();
 
     uint256 initTime = 10;
     uint256 livenessInterval = 30 days;
@@ -286,6 +289,8 @@ contract LivenessModule_RemoveOwners_Test is LivenessModule_TestInit {
         address ownerToRemove = safeInstance.owners[0];
 
         _warpPastLivenessInterval();
+        vm.expectEmit(address(livenessModule));
+        emit RemovedOwner(ownerToRemove);
         _removeAnOwner(ownerToRemove, safeInstance.owners);
 
         assertFalse(safeInstance.safe.isOwner(ownerToRemove));
@@ -303,6 +308,16 @@ contract LivenessModule_RemoveOwners_Test is LivenessModule_TestInit {
         address[] memory prevOwners = safeInstance.getPrevOwners(ownersToRemove);
 
         _warpPastLivenessInterval();
+        for (uint256 i; i < ownersToRemove.length; i++) {
+            if (i != ownersToRemove.length - 1) {
+                vm.expectEmit(address(livenessModule));
+                emit RemovedOwner(ownersToRemove[i]);
+            }
+        }
+
+        vm.expectEmit(address(livenessModule));
+        emit OwnershipTransferredToFallback();
+
         livenessModule.removeOwners(prevOwners, ownersToRemove);
         assertEq(safeInstance.safe.getOwners().length, 1);
         assertEq(safeInstance.safe.getOwners()[0], fallbackOwner);