Liquidating credit accounts

There are two types of liquidation in the system: liquidations by health factor and liquidations by expiration.

Liquidating accounts by health factor

Once a Credit Account's Health Factor goes below 1, the account can be liquidated in order to make the pool whole and prevent any bad debt. In order to liquidate the account, the liquidator would use a Credit Facade function:

function liquidateCreditAccount(
    address borrower,
    address to,
    uint256 skipTokenMask,
    bool convertWETH,
    MultiCall[] calldata calls
) external payable;

liquidateCreditAccount checks that the account's health factor is less than 1 before liquidation, and will revert otherwise.

Note that unlike normal Credit Account closure, liquidations do not require the entire debt to be repaid to the pool. Credit Facade computes the total value of the Credit Account before liquidation, and will set the amount repaid to the pool to be totalValue * (1 - liquidationPremium) if the total value is less than the debt.

The multicall would typically be used to convert all collateral to underlying in order to repay the loan; in case there is less underlying than required (based on above calculation) after performing the multicall, the shortfall will be transferred from the liquidator.

Liquidating accounts by expiration

If a Credit Facade is in Expirable mode (see below) and the expiration date is reached, all still-open accounts can be liquidated. In order to liquidate an expired account, the liquidator would use a Credit Facade function:

function liquidateExpiredCreditAccount(
    address borrower,
    address to,
    uint256 skipTokenMask,
    bool convertWETH,
    MultiCall[] calldata calls
) external payable

The parameters are the same as liquidateCreditAccount.

Liquidations by expiration have lower liquidation premiums, since they are typically less urgent than liquidations of unhealthy positions; the liquidators should consider that when calculating the profitability of a liquidation.

Motivation

Down the line, in addition to standard variable-rate loans, Gearbox will support fixed-term loans.

Fixed term loans in DeFi typically involve zero-coupon bond-like tokens that have a certain maturity date and yield paid out at maturity (this is usually represented by a discount that decreases the closer to maturity the token is).

In order to support this mode of liquidity provision, CreditFacade has an optional Expirable mode, which is enabled when CreditFacade.expirable() == true.

Expiration details

There is a single expiration date (CreditFacade.params().expirationDate) for each expirable Credit Facade that affects all Credit Accounts opened through it. This expiration date would typically be set shortly before the underlying yield token maturity, so that Gearbox is able to collect any outstanding debt and repay its loan to LP's.

It is not possible to open new Credit Accounts past the expiration date, and all accounts that remain open after the expiration date are eligible to liquidation by expiration.

After expiration, the expiration date in the CreditFacade can be moved forward by the DAO, in order to reflect a new maturity date for loans, which allows opening accounts in the CreditFacade once again.