Optimism Dai and upgradable token bridge

• l2/dai.sol - Improved DAI contract
• l1/L1ERC20Gateway.sol - L1 side of the bridge. Escrows L1 DAI in a specified address. Unlocks L1 DAI upon withdrawal message from L2DepositedToken
• l2/L2DepositedToken.sol - L2 side of the bridge. Mints new L2 DAI after receiving message from L1ERC20Gateway. Burns L2 DAI tokens when withdrawals happens

This bridge stores funds in an external escrow account rather than on the bridge address itself. To upgrade, deploy new bridge independently and connect to the same escrow. Thanks to this, no bridge will ever run out of funds.

After deploying a new bridge you might consider closing the old one. Procedure is slightly complicated due to async messages like finalizeDeposit and finalizeWithdraw that can be in progress.

An owner calls L2DepositedToken.close() and L1ERC20Gateway.close() so no new async messages can be sent to the other part of the bridge. After all async messages are done processing (can take up to 1 week) bridge is effectively closed. Now, you can consider revoking approval to access funds from escrow on L1 and token minting rights on L2.

yarn
yarn build
yarn test  # runs unit tests

# start optimism-integration
git clone https://github.com/ethereum-optimism/optimism-integration.git
cd optimism-integration
./up.sh

# in other terminal window run this project
yarn build
yarn test-e2e  # runs unit tests

Run yarn test:fix to run linting in fix mode, auto-formatting and unit tests.

Running yarn test makes sure that contracts are compiled. Running yarn test-e2e doesn't.