Fix bridge contracts upgradeability (#533)

- Change Abs_L1TokenGateway.DEFAULT_FINALIZE_DEPOSIT_L2_GAS and Abs_L2DepositedToken.DEFAULT_FINALIZE_WITHDRAWAL_L1_GAS to internal constants
- Add virtual declaration to Abs_L1TokenGateway.getFinalizeDepositL2Gas fn
- Add virtual declaration to few more bridge gateway fn to improve extensibility

.changeset/curly-tables-behave.md

+---
+"@eth-optimism/contracts": patch
+---
+
+Fix bridge contracts upgradeability by changing `Abs_L1TokenGateway.DEFAULT_FINALIZE_DEPOSIT_L2_GAS` from a storage var to an internal constant.
+Additionally, make some bridge functions virtual so they could be overriden in child contracts.

packages/contracts/contracts/optimistic-ethereum/OVM/bridge/tokens/Abs_L1TokenGateway.sol

 // SPDX-License-Identifier: MIT
-// @unsupported: ovm 
+// @unsupported: ovm
 pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
@@ -16,7 +16,7 @@ import { OVM_CrossDomainEnabled } from "../../../libraries/bridge/OVM_CrossDomai
  * It synchronizes a corresponding L2 representation of the "deposited token", informing it
  * of new deposits and releasing L1 funds when there are newly finalized withdrawals.
  *
- * NOTE: This abstract contract gives all the core functionality of an L1 token gateway, 
+ * NOTE: This abstract contract gives all the core functionality of an L1 token gateway,
  * but provides easy hooks in case developers need extensions in child contracts.
  * In many cases, the default OVM_L1ERC20Gateway will suffice.
  *
@@ -41,7 +41,7 @@ abstract contract Abs_L1TokenGateway is iOVM_L1TokenGateway, OVM_CrossDomainEnab
      */
     constructor(
         address _l2DepositedToken,
-        address _l1messenger 
+        address _l1messenger
     )
         OVM_CrossDomainEnabled(_l1messenger)
     {
@@ -53,7 +53,7 @@ abstract contract Abs_L1TokenGateway is iOVM_L1TokenGateway, OVM_CrossDomainEnab
      ********************************/
 
     // Default gas value which can be overridden if more complex logic runs on L2.
-    uint32 public DEFAULT_FINALIZE_DEPOSIT_L2_GAS = 1200000;
+    uint32 internal constant DEFAULT_FINALIZE_DEPOSIT_L2_GAS = 1200000;
 
     /**
      * @dev Core logic to be performed when a withdrawal is finalized on L1.
@@ -96,10 +96,10 @@ abstract contract Abs_L1TokenGateway is iOVM_L1TokenGateway, OVM_CrossDomainEnab
      * dynamic, and the above public constant does not suffice.
      *
      */
-
     function getFinalizeDepositL2Gas()
         public
         view
+        virtual
         returns(
             uint32
         )
@@ -118,8 +118,9 @@ abstract contract Abs_L1TokenGateway is iOVM_L1TokenGateway, OVM_CrossDomainEnab
     function deposit(
         uint _amount
     )
-        public
+        external
         override
+        virtual
     {
         _initiateDeposit(msg.sender, msg.sender, _amount);
     }
@@ -133,8 +134,9 @@ abstract contract Abs_L1TokenGateway is iOVM_L1TokenGateway, OVM_CrossDomainEnab
         address _to,
         uint _amount
     )
-        public
+        external
         override
+        virtual
     {
         _initiateDeposit(msg.sender, _to, _amount);
     }
@@ -183,9 +185,9 @@ abstract contract Abs_L1TokenGateway is iOVM_L1TokenGateway, OVM_CrossDomainEnab
      *************************/
 
     /**
-     * @dev Complete a withdrawal from L2 to L1, and credit funds to the recipient's balance of the 
-     * L1 ERC20 token. 
-     * This call will fail if the initialized withdrawal from L2 has not been finalized. 
+     * @dev Complete a withdrawal from L2 to L1, and credit funds to the recipient's balance of the
+     * L1 ERC20 token.
+     * This call will fail if the initialized withdrawal from L2 has not been finalized.
      *
      * @param _to L1 address to credit the withdrawal to
      * @param _amount Amount of the ERC20 to withdraw
@@ -195,7 +197,8 @@ abstract contract Abs_L1TokenGateway is iOVM_L1TokenGateway, OVM_CrossDomainEnab
         uint _amount
     )
         external
-        override 
+        override
+        virtual
         onlyFromCrossDomainAccount(l2DepositedToken)
     {
         // Call our withdrawal accounting handler implemented by child contracts.

packages/contracts/contracts/optimistic-ethereum/OVM/bridge/tokens/Abs_L2DepositedToken.sol

@@ -55,7 +55,6 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
      *
      * @param _l1TokenGateway Address of the corresponding L1 gateway deployed to the main chain
      */
-
     function init(
         iOVM_L1TokenGateway _l1TokenGateway
     )
@@ -64,7 +63,7 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
         require(address(l1TokenGateway) == address(0), "Contract has already been initialized");
 
         l1TokenGateway = _l1TokenGateway;
-        
+
         emit Initialized(l1TokenGateway);
     }
 
@@ -81,8 +80,8 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
      * Overridable Accounting logic *
      ********************************/
 
-    // Default gas value which can be overridden if more complex logic runs on L2.
-    uint32 constant DEFAULT_FINALIZE_WITHDRAWAL_L1_GAS = 100000;
+    // Default gas value which can be overridden if more complex logic runs on L1.
+    uint32 internal constant DEFAULT_FINALIZE_WITHDRAWAL_L1_GAS = 100000;
 
     /**
      * @dev Core logic to be performed when a withdrawal from L2 is initialized.
@@ -91,7 +90,6 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
      * param _to Address being withdrawn to
      * param _amount Amount being withdrawn
      */
-
     function _handleInitiateWithdrawal(
         address, // _to,
         uint // _amount
@@ -122,9 +120,7 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
     /**
      * @dev Overridable getter for the *L1* gas limit of settling the withdrawal, in the case it may be
      * dynamic, and the above public constant does not suffice.
-     *
      */
-
     function getFinalizeWithdrawalL1Gas()
         public
         view
@@ -150,6 +146,7 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
     )
         external
         override
+        virtual
         onlyInitialized()
     {
         _initiateWithdrawal(msg.sender, _amount);
@@ -166,6 +163,7 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
     )
         external
         override
+        virtual
         onlyInitialized()
     {
         _initiateWithdrawal(_to, _amount);
@@ -208,9 +206,9 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
      ************************************/
 
     /**
-     * @dev Complete a deposit from L1 to L2, and credits funds to the recipient's balance of this 
-     * L2 token. 
-     * This call will fail if it did not originate from a corresponding deposit in OVM_l1TokenGateway. 
+     * @dev Complete a deposit from L1 to L2, and credits funds to the recipient's balance of this
+     * L2 token.
+     * This call will fail if it did not originate from a corresponding deposit in OVM_l1TokenGateway.
      *
      * @param _to Address to receive the withdrawal at
      * @param _amount Amount of the token to withdraw
@@ -220,7 +218,8 @@ abstract contract Abs_L2DepositedToken is iOVM_L2DepositedToken, OVM_CrossDomain
         uint _amount
     )
         external
-        override 
+        override
+        virtual
         onlyInitialized()
         onlyFromCrossDomainAccount(address(l1TokenGateway))
     {

packages/contracts/test/contracts/OVM/bridge/assets/OVM_L1ERC20Gateway.spec.ts

@@ -66,7 +66,7 @@ describe('OVM_L1ERC20Gateway', () => {
       Mock__OVM_L1CrossDomainMessenger.address
     )
 
-    finalizeDepositGasLimit = await OVM_L1ERC20Gateway.DEFAULT_FINALIZE_DEPOSIT_L2_GAS()
+    finalizeDepositGasLimit = await OVM_L1ERC20Gateway.getFinalizeDepositL2Gas()
   })
 
   describe('finalizeWithdrawal', () => {