Dedup code around auto rebasing opt in

snapshots/OUSDTest.json

@@ -1,27 +1,27 @@
 {
   "Transfer Attacker -> Attacker": "24166",
-  "Transfer Attacker -> Collector": "59816",
-  "Transfer Attacker -> Matt": "57833",
-  "Transfer Attacker -> NonRebasing": "62696",
-  "Transfer Attacker -> Pool": "63955",
-  "Transfer Collector -> Attacker": "56948",
+  "Transfer Attacker -> Collector": "59836",
+  "Transfer Attacker -> Matt": "57873",
+  "Transfer Attacker -> NonRebasing": "62736",
+  "Transfer Attacker -> Pool": "63975",
+  "Transfer Collector -> Attacker": "56968",
   "Transfer Collector -> Collector": "24166",
-  "Transfer Collector -> Matt": "56948",
-  "Transfer Collector -> NonRebasing": "67179",
+  "Transfer Collector -> Matt": "56968",
+  "Transfer Collector -> NonRebasing": "67199",
   "Transfer Collector -> Pool": "52838",
-  "Transfer Matt -> Attacker": "52465",
-  "Transfer Matt -> Collector": "54448",
+  "Transfer Matt -> Attacker": "52505",
+  "Transfer Matt -> Collector": "54468",
   "Transfer Matt -> Matt": "24166",
-  "Transfer Matt -> NonRebasing": "62696",
-  "Transfer Matt -> Pool": "63955",
-  "Transfer NonRebasing -> Attacker": "62696",
-  "Transfer NonRebasing -> Collector": "64679",
-  "Transfer NonRebasing -> Matt": "62696",
+  "Transfer Matt -> NonRebasing": "62736",
+  "Transfer Matt -> Pool": "63975",
+  "Transfer NonRebasing -> Attacker": "62736",
+  "Transfer NonRebasing -> Collector": "64699",
+  "Transfer NonRebasing -> Matt": "62736",
   "Transfer NonRebasing -> NonRebasing": "24166",
-  "Transfer NonRebasing -> Pool": "74186",
-  "Transfer Pool -> Attacker": "66455",
+  "Transfer NonRebasing -> Pool": "74206",
+  "Transfer Pool -> Attacker": "66475",
   "Transfer Pool -> Collector": "52838",
-  "Transfer Pool -> Matt": "66455",
-  "Transfer Pool -> NonRebasing": "76686",
+  "Transfer Pool -> Matt": "66475",
+  "Transfer Pool -> NonRebasing": "76706",
   "Transfer Pool -> Pool": "24166"
 }

src/token/OUSD.sol

@@ -433,35 +433,12 @@ contract OUSD is Governable {
      */
     function _isNonRebasingAccount(address _account) internal returns (bool) {
         bool isContract = _account.code.length > 0;
-        if (isContract && rebaseState[_account] == RebaseOptions.NotSet) {
-            _ensureNonRebasingMigration(_account);
+        if (isContract && rebaseState[_account] == RebaseOptions.NotSet && nonRebasingCreditsPerToken[_account] != 0) {
+            _rebaseOptOut(msg.sender);
         }
         return nonRebasingCreditsPerToken[_account] > 0;
     }
 
-    /**
-     * @dev If this is the first time a contract has been seen, migrate it to
-     *      non-rebasing accounting.
-     */
-    function _ensureNonRebasingMigration(address _account) internal {
-        if (nonRebasingCreditsPerToken[_account] != 0) {
-            return; // Account is already non-rebasing
-        }
-        uint256 oldCredits = _creditBalances[_account];
-        uint256 balance = balanceOf(_account);
-
-        // Account
-        rebaseState[_account] = RebaseOptions.OptOut;
-        _creditBalances[_account] = balance;
-        nonRebasingCreditsPerToken[_account] = 1e18;
-
-        // Global
-        nonRebasingSupply += balance;
-        _rebasingCredits -= oldCredits;
-
-        emit AccountRebasingDisabled(_account);
-    }
-
     function _balanceToRebasingCredits(uint256 balance) internal view returns (uint256) {
         // Rounds up, because we need to ensure that accounts allways have
         // at least the balance that they should have.
@@ -513,22 +490,26 @@ contract OUSD is Governable {
     }
 
     function rebaseOptOut() public nonReentrant {
-        require(!_isNonRebasingAccount(msg.sender), "Account has not opted in");
-        require(rebaseState[msg.sender] != RebaseOptions.YieldDelegationSource, "Cannot opt out while receiving yield");
+        _rebaseOptOut(msg.sender);
+    }
+
+    function _rebaseOptOut(address _account) internal {
+        require(!_isNonRebasingAccount(_account), "Account has not opted in");
+        require(rebaseState[_account] != RebaseOptions.YieldDelegationSource, "Cannot opt out while receiving yield");
 
-        uint256 oldCredits = _creditBalances[msg.sender];
-        uint256 balance = balanceOf(msg.sender);
+        uint256 oldCredits = _creditBalances[_account];
+        uint256 balance = balanceOf(_account);
 
         // Account
-        rebaseState[msg.sender] = RebaseOptions.OptOut;
-        nonRebasingCreditsPerToken[msg.sender] = 1e18;
-        _creditBalances[msg.sender] = balance;
+        rebaseState[_account] = RebaseOptions.OptOut;
+        nonRebasingCreditsPerToken[_account] = 1e18;
+        _creditBalances[_account] = balance;
 
         // Globals
         nonRebasingSupply += balance;
         _rebasingCredits -= oldCredits;
 
-        emit AccountRebasingDisabled(msg.sender);
+        emit AccountRebasingDisabled(_account);
     }
 
     /**