Catch interest accrual and update interest overflow

[prateek105]

Description of change

High level

• Add try catch for interest accrual and update interest method to avoid pool locking.
• Add tearDown to unit tests where overflow was occurring, so that we know pool can be recovered after such overflows.

[brianmcmichael]

Really need to think about the side-effects of this one. If a pool is bust for a high inflator you'd want to allow repay/withdrawal, but avoid allowing further borrows against the pool, which probably should revert.

[prateek105]

Should we similarly wrap the updateInterestState call?

this is already being done here

[prateek105]

While this is a technically elegant solution, I am concerned about impacts to the game theory. Does this incentivize borrowers to intentionally brick the pool, such that they can continue borrowing without paying interest? If so, how could they do so?

Should we only wrap the following calls to catch interest overflow?

• Removal of liquidity and unencumbered collateral from buckets - Lenders should be able to exit.
• Repayment of debt and pulling collateral - Borrowers should be allowed to exit.
• Kicking new liquidations and settlement of liquidations - Borrowers would otherwise not be incentivized to repay.

Unsure of whether we should catch on the following operations:

• Adding liquidity/collateral to buckets - Should arbitrageurs be able to purchase overpriced deposit?

These changes seem to warrant further discussion.

Also should we allow further borrows against the pool or not as mentioned by @brianmcmichael

[prateek105]

I think we should catch all the actions, if lenders are not gaining any interest they will start removing their liquidity from the pool which will lead to kicking of borrower loans. Borrowers will know that the lenders will be moving their liquidity out of the pool so they should also exit the pool and not make any further borrows.