fix(YAUDIT-COVE-6): correct yearn vault v2 preview functions

codecov.yml

@@ -6,3 +6,4 @@ ignore:
   - "src/deps/*"
   - "src/deps/**/*"
   - "src/interfaces/deps/**/*"
+  - "src/libraries/YearnVaultV2Helper.sol"

src/Yearn4626RouterExt.sol

@@ -7,8 +7,8 @@ import { IPermit2 } from "permit2/interfaces/IPermit2.sol";
 import { ISignatureTransfer } from "permit2/interfaces/ISignatureTransfer.sol";
 import { IWETH9 } from "Yearn-ERC4626-Router/external/PeripheryPayments.sol";
 import { IYearn4626RouterExt } from "./interfaces/IYearn4626RouterExt.sol";
-import { IERC20Metadata, IERC20 } from "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";
-import { SafeERC20 } from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
+import { YearnVaultV2Helper } from "./libraries/YearnVaultV2Helper.sol";
+import { SafeERC20, IERC20 } from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
 import { IERC4626 } from "@openzeppelin/contracts/interfaces/IERC4626.sol";
 import { Math } from "@openzeppelin/contracts/utils/math/Math.sol";
 import { Address } from "@openzeppelin/contracts/utils/Address.sol";
@@ -25,6 +25,7 @@ import { IStakeDaoVault } from "./interfaces/deps/stakeDAO/IStakeDaoVault.sol";
  */
 contract Yearn4626RouterExt is IYearn4626RouterExt, Yearn4626Router {
     using SafeERC20 for IERC20;
+    using YearnVaultV2Helper for IYearnVaultV2;
 
     // slither-disable-next-line naming-convention
     IPermit2 private immutable _PERMIT2;
@@ -60,30 +61,6 @@ contract Yearn4626RouterExt is IYearn4626RouterExt, Yearn4626Router {
 
     // ------------- YEARN VAULT V2 FUNCTIONS ------------- //
 
-    /**
-     * @notice Deposits the specified `amount` of tokens into the Yearn Vault V2.
-     * @dev Calls the `deposit` function of the Yearn Vault V2 contract and checks if the returned shares are above the
-     * `minSharesOut`.
-     * Reverts with `InsufficientShares` if the condition is not met.
-     * @param vault The Yearn Vault V2 contract instance.
-     * @param amount The amount of tokens to deposit.
-     * @param to The address to which the shares will be minted.
-     * @param minSharesOut The minimum number of shares expected to be received.
-     * @return sharesOut The actual number of shares minted to the `to` address.
-     */
-    function depositToVaultV2(
-        IYearnVaultV2 vault,
-        uint256 amount,
-        address to,
-        uint256 minSharesOut
-    )
-        public
-        payable
-        returns (uint256 sharesOut)
-    {
-        if ((sharesOut = vault.deposit(amount, to)) < minSharesOut) revert InsufficientShares();
-    }
-
     /**
      * @notice Redeems the specified `shares` from the Yearn Vault V2.
      * @dev The shares must exist in this router before calling this function.
@@ -230,12 +207,7 @@ contract Yearn4626RouterExt is IYearn4626RouterExt, Yearn4626Router {
                 (success, data) = vault.staticcall(abi.encodeCall(IYearnVaultV2.token, ()));
                 if (success) {
                     vaultAsset = abi.decode(data, (address));
-                    sharesOut[i] = Math.mulDiv(
-                        assetsIn,
-                        10 ** IERC20Metadata(vault).decimals(),
-                        IYearnVaultV2(vault).pricePerShare(),
-                        Math.Rounding.Down
-                    ) - 1;
+                    sharesOut[i] = IYearnVaultV2(vault).previewDeposit(assetsIn);
                 } else {
                     revert PreviewNonVaultAddressInPath(vault);
                 }
@@ -289,12 +261,7 @@ contract Yearn4626RouterExt is IYearn4626RouterExt, Yearn4626Router {
                 (success, data) = vault.staticcall(abi.encodeCall(IYearnVaultV2.token, ()));
                 if (success) {
                     vaultAsset = abi.decode(data, (address));
-                    assetsIn[i - 1] = Math.mulDiv(
-                        sharesOut,
-                        IYearnVaultV2(vault).pricePerShare(),
-                        10 ** IERC20Metadata(vault).decimals(),
-                        Math.Rounding.Up
-                    ) + 1;
+                    assetsIn[i - 1] = IYearnVaultV2(vault).previewMint(sharesOut);
                 } else {
                     revert PreviewNonVaultAddressInPath(vault);
                 }
@@ -349,12 +316,7 @@ contract Yearn4626RouterExt is IYearn4626RouterExt, Yearn4626Router {
                 (success, data) = vault.staticcall(abi.encodeCall(IYearnVaultV2.token, ()));
                 if (success) {
                     vaultAsset = abi.decode(data, (address));
-                    sharesIn[i] = Math.mulDiv(
-                        assetsOut,
-                        10 ** IERC20Metadata(vault).decimals(),
-                        IYearnVaultV2(vault).pricePerShare(),
-                        Math.Rounding.Up
-                    );
+                    sharesIn[i] = IYearnVaultV2(vault).previewWithdraw(assetsOut);
                 } else {
                     // StakeDAO gauge token
                     // StakeDaoGauge.staking_token().token() is the yearn vault v2 token
@@ -413,12 +375,7 @@ contract Yearn4626RouterExt is IYearn4626RouterExt, Yearn4626Router {
                 (success, data) = vault.staticcall(abi.encodeCall(IYearnVaultV2.token, ()));
                 if (success) {
                     vaultAsset = abi.decode(data, (address));
-                    assetsOut[i] = Math.mulDiv(
-                        sharesIn,
-                        IYearnVaultV2(vault).pricePerShare(),
-                        10 ** IERC20Metadata(vault).decimals(),
-                        Math.Rounding.Down
-                    );
+                    assetsOut[i] = IYearnVaultV2(vault).previewRedeem(sharesIn);
                 } else {
                     // StakeDAO gauge token
                     // StakeDaoGauge.staking_token().token() is the yearn vault v2 token

src/interfaces/IYearn4626RouterExt.sol

@@ -8,16 +8,6 @@ import { IERC4626 } from "@openzeppelin/contracts/interfaces/IERC4626.sol";
 import { IStakeDaoGauge } from "./deps/stakeDAO/IStakeDaoGauge.sol";
 
 interface IYearn4626RouterExt is IYearn4626Router {
-    function depositToVaultV2(
-        IYearnVaultV2 vault,
-        uint256 amount,
-        address to,
-        uint256 minSharesOut
-    )
-        external
-        payable
-        returns (uint256 sharesOut);
-
     function redeemVaultV2(
         IYearnVaultV2 vault,
         uint256 shares,

src/interfaces/deps/yearn/veYFI/IYearnVaultV2.sol

@@ -8,4 +8,9 @@ interface IYearnVaultV2 {
     function deposit(uint256 amount) external returns (uint256 shares);
     function withdraw(uint256 shares, address recipient) external returns (uint256 amount);
     function pricePerShare() external view returns (uint256);
+    function totalSupply() external view returns (uint256);
+    function totalAssets() external view returns (uint256);
+    function lastReport() external view returns (uint256);
+    function lockedProfitDegradation() external view returns (uint256);
+    function lockedProfit() external view returns (uint256);
 }

src/libraries/YearnVaultV2Helper.sol

@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity 0.8.18;
+
+import { IYearnVaultV2 } from "src/interfaces/deps/yearn/veYFI/IYearnVaultV2.sol";
+import { Math } from "@openzeppelin/contracts/utils/math/Math.sol";
+
+/**
+ * @title YearnVaultV2Helper
+ * @notice Helper functions for Yearn Vault V2 contracts. Since Yearn Vault V2 contracts are not ERC-4626 compliant,
+ * they do not provide `previewDeposit`, `previewMint`, `previewRedeem`, and `previewWithdraw` functions. This library
+ * provides these functions for previewing share based deposit/mint/redeem/withdraw estimations.
+ * @dev These functions are only to be used off-chain for previewing. Due to how Yearn Vault V2 contracts work,
+ * share based withdraw/redeem estimations may not be accurate if the vault incurs a loss, thus share price changes.
+ * Coverage is currently disabled for this library due to forge limitations. TODO: Once the fix PR is merged,
+ * https://github.com/foundry-rs/foundry/pull/7510 coverage should be re-enabled.
+ */
+library YearnVaultV2Helper {
+    /**
+     * @notice Calculates the currently free funds in a Yearn Vault V2 contract.
+     * @param vault The Yearn Vault V2 contract.
+     * @return The free funds in the vault.
+     * @dev This is based on Yearn Vault V2 contract's free funds calculation logic.
+     * https://github.com/yearn/yearn-vaults/blob/97ca1b2e4fcf20f4be0ff456dabd020bfeb6697b/contracts/Vault.vy#L844-L847
+     */
+    function freeFunds(IYearnVaultV2 vault) internal view returns (uint256) {
+        uint256 lockedProfit = vault.lockedProfit();
+        uint256 lockedFundsRatio = (block.timestamp - vault.lastReport()) * vault.lockedProfitDegradation();
+        // slither-disable-next-line timestamp
+        if (lockedFundsRatio < 1e18) {
+            lockedProfit -= (lockedProfit * lockedFundsRatio) / 1e18;
+        } else {
+            lockedProfit = 0;
+        }
+        return vault.totalAssets() - lockedProfit;
+    }
+
+    /**
+     * @notice Preview the amount of shares to be issued for a given deposit amount.
+     * @param vault The Yearn Vault V2 contract.
+     * @param assetsIn The amount of assets to be deposited.
+     * @return The number of shares that would be issued for the deposited assets.
+     */
+    function previewDeposit(IYearnVaultV2 vault, uint256 assetsIn) internal view returns (uint256) {
+        uint256 totalSupply = vault.totalSupply();
+        if (totalSupply > 0) {
+            return Math.mulDiv(assetsIn, totalSupply, freeFunds(vault), Math.Rounding.Down);
+        }
+        return assetsIn;
+    }
+
+    /**
+     * @notice Preview the amount of assets required to mint a given amount of shares.
+     * @param vault The Yearn Vault V2 contract.
+     * @param sharesOut The number of shares to be minted.
+     * @return The amount of assets required to mint the specified number of shares.
+     */
+    function previewMint(IYearnVaultV2 vault, uint256 sharesOut) internal view returns (uint256) {
+        uint256 totalSupply = vault.totalSupply();
+        if (totalSupply > 0) {
+            return Math.mulDiv(sharesOut, freeFunds(vault), totalSupply, Math.Rounding.Up);
+        }
+        return sharesOut;
+    }
+
+    /**
+     * @notice Preview the amount of assets to be received for redeeming a given amount of shares.
+     * @param vault The Yearn Vault V2 contract.
+     * @param sharesIn The number of shares to be redeemed.
+     * @return The amount of assets that would be received for the redeemed shares.
+     */
+    function previewRedeem(IYearnVaultV2 vault, uint256 sharesIn) internal view returns (uint256) {
+        uint256 totalSupply = vault.totalSupply();
+        if (sharesIn > totalSupply) {
+            return freeFunds(vault);
+        }
+        if (totalSupply > 0) {
+            return Math.mulDiv(sharesIn, freeFunds(vault), totalSupply, Math.Rounding.Down);
+        }
+        return 0;
+    }
+
+    /**
+     * @notice Preview the number of shares to be redeemed for a given withdrawal amount of assets.
+     * @param vault The Yearn Vault V2 contract.
+     * @param assetsOut The amount of assets to be withdrawn.
+     * @return The number of shares that would be redeemed for the withdrawn assets.
+     */
+    function previewWithdraw(IYearnVaultV2 vault, uint256 assetsOut) internal view returns (uint256) {
+        uint256 freeFunds_ = freeFunds(vault);
+        // slither-disable-next-line timestamp
+        if (assetsOut > freeFunds_) {
+            return vault.totalSupply();
+        }
+        // slither-disable-next-line timestamp
+        if (freeFunds_ > 0) {
+            return Math.mulDiv(assetsOut, vault.totalSupply(), freeFunds(vault), Math.Rounding.Up);
+        }
+        return 0;
+    }
+}