preLiquidate may revert unexpectedly

[colin-morpho]

In the following line

pre-liquidation/src/PreLiquidation.sol

Line 134 in 1fd963d

uint256 collateralQuoted = uint256(position.collateral).mulDivDown(collateralPrice, ORACLE_PRICE_SCALE);

the value colateralQuoted may be equal to zero, thus resulting in a division by zero by zero error.

This is a very niche case and it's OK, it means that the liquidation is not healthy to pre-liquidate and must be done on Morpho. No need to patch the implementation.

However, we should provide some documentation. See related verification run.

[peyha]

Two possibilities:

• acknowledge this in the documentation
• use an UncollateralizedPosition error in the code

I'm leaning for the second option as it seems more understandable for a user

[MathisGD]

I'm leaning towards the acknowledgment in the documentation (liquidators are technical), but not super strong opinion.

[colin-morpho]

It's being tricky to handle in the verification. Using summaries trigger many divisions by zero 😞. I'll report on the PR when I have more results.

[peyha]

I'll implement the second option today, if it eases FV we should do it

[MathisGD]

Fixed by #77