refactor(interests): expose accrued interests and fee

[Rubilmax]

• Fixes Make accrueInterests public ? #129

The goal of this PR is to let integrators be able to query the amount of hypothetically accrued interests (and corresponding fee shares) upon interaction. In solidity, it would look like:

Changes are significant and we lose minimalism, so I am ok to leave the protocol without this "hypothetical interests" getter. Integrators have the possibility to query independently query the variables necessary for this calculation, but it would cost them more than with the corresponding getter built into the protocol, because of the cost of CALLs.

The difference of gas cost between a built-in getter and a reproduced calculation would approximately be:

• 2 CALLs (totalBorrow + lastUpdate) if only interested in the borrow side (don't need to calculate the fee)
• 5 CALLs (totalSupply + totalBorrow + lastUpdate + fee + totalSupplyShares) if interested in the supply side

To address this issue, we could expose a getter for all information related to a state. It could save 4 CALLs in the worst case, which approximately represents 20k gas.

EDIT: actually, just expose extsload with arrays, just like UniV4, and this topic can be closed.

[MerlinEgalite]

EDIT: actually, just expose extsload with arrays, just like UniV4, and this topic can be closed.

Maybe we can do that and write some helpers in the doc help developers?

[MerlinEgalite]

I'm also ok with this solution

[QGarchery]

actually, just expose extsload with arrays, just like UniV4, and this topic can be closed.

I'm for adding a getter like this. It seems like the one of uniswap is not appropriate because it only allows to retrieve contiguous storage (and totalSupply, totalBorrow, .. are not contiguous). I think it can be easily adapted to take an array of slots as input though

[Rubilmax]

I'm for adding a getter like this. It seems like the one of uniswap is not appropriate because it only allows to retrieve contiguous storage (and totalSupply, totalBorrow, .. are not contiguous). I think it can be easily adapted to take an array of slots as input though

Done in #147!

I gave my POV there, but TLDR: I may prefer this solution even though it complexifies Blue, because I believe it has a way higher business value for integrators (including MetaMorpho vaults).

The base branch was changed.

[MathisGD]

which approximately represents 20k gas.

No it's more like 4 x 100 gas

[Rubilmax]

#171 seems to better do the job

[MerlinEgalite]

Well merge conflicts are not really nice. I'll redo the PR