<WIP> feat: set reserveOf transient

.forge-snapshots/BinPoolManagerTest#testBurnNativeCurrency.snap

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-142035
+137875

.forge-snapshots/BinPoolManagerTest#testGasBurnHalfBin.snap

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-158207
+147818

.forge-snapshots/BinPoolManagerTest#testGasBurnNineBins.snap

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+295519

.forge-snapshots/BinPoolManagerTest#testGasBurnOneBin.snap

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+131085

.forge-snapshots/BinPoolManagerTest#testGasDonate.snap

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+120152

.forge-snapshots/BinPoolManagerTest#testGasMintNneBins-1.snap

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+973898

.forge-snapshots/BinPoolManagerTest#testGasMintNneBins-2.snap

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.forge-snapshots/BinPoolManagerTest#testGasMintOneBin-1.snap

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.forge-snapshots/BinPoolManagerTest#testGasMintOneBin-2.snap

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+144192

.forge-snapshots/BinPoolManagerTest#testGasSwapMultipleBins.snap

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+179604

.forge-snapshots/BinPoolManagerTest#testGasSwapOverBigBinIdGate.snap

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+185589

.forge-snapshots/BinPoolManagerTest#testGasSwapSingleBin.snap

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-145662
+137953

.forge-snapshots/BinPoolManagerTest#testMintNativeCurrency.snap

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-327364
+308921

.forge-snapshots/BinPoolManagerTest#testNoOpGas_Burn.snap

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-76641
+76706

.forge-snapshots/BinPoolManagerTest#testNoOpGas_Donate.snap

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+54199

.forge-snapshots/BinPoolManagerTest#testNoOpGas_Mint.snap

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-69634
+69699

.forge-snapshots/BinPoolManagerTest#testNoOpGas_Swap.snap

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+57628

.forge-snapshots/CLPoolManagerTest#addLiquidity_fromEmpty.snap

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-401866
+362749

.forge-snapshots/CLPoolManagerTest#addLiquidity_fromNonEmpty.snap

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-182854
+177917

.forge-snapshots/CLPoolManagerTest#addLiquidity_nativeToken.snap

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-247993
+249195

.forge-snapshots/CLPoolManagerTest#donateBothTokens.snap

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-175518
+170492

.forge-snapshots/CLPoolManagerTest#gasDonateOneToken.snap

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-116900
+114415

.forge-snapshots/CLPoolManagerTest#removeLiquidity_toNonEmpty.snap

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+124439

.forge-snapshots/CLPoolManagerTest#swap_againstLiquidity.snap

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-148767
+141058

.forge-snapshots/CLPoolManagerTest#swap_leaveSurplusTokenInVault.snap

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-177177
+174695

.forge-snapshots/CLPoolManagerTest#swap_runOutOfLiquidity.snap

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-24940941
+24933275

.forge-snapshots/CLPoolManagerTest#swap_simple.snap

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-78822
+78887

.forge-snapshots/CLPoolManagerTest#swap_useSurplusTokenAsInput.snap

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-158284
+153122

.forge-snapshots/CLPoolManagerTest#swap_withHooks.snap

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-95329
+95394

.forge-snapshots/CLPoolManagerTest#swap_withNative.snap

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-78825
+78890

.forge-snapshots/CLPoolManagerTest#testNoOp_gas_Donate.snap

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-53926
+53991

.forge-snapshots/CLPoolManagerTest#testNoOp_gas_ModifyPosition.snap

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-60244
+60309

.forge-snapshots/CLPoolManagerTest#testNoOp_gas_Swap.snap

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-56919
+56984

.forge-snapshots/VaultTest#Vault.snap

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-7437
+7136

.forge-snapshots/VaultTest#collectFee.snap

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-53360
+25187

.forge-snapshots/VaultTest#lockSettledWhenAddLiquidity.snap

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-159350
+81544

.forge-snapshots/VaultTest#lockSettledWhenFlashloan.snap

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-103575
+121535

.forge-snapshots/VaultTest#lockSettledWhenMultiHopSwap.snap

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+47404

.forge-snapshots/VaultTest#lockSettledWhenSwap.snap

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-118272
+47404

.forge-snapshots/VaultTest#testLock_NoOp.snap

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+32864

src/Vault.sol

@@ -12,18 +12,17 @@ import {Currency, CurrencyLibrary} from "./types/Currency.sol";
 import {BalanceDelta} from "./types/BalanceDelta.sol";
 import {ILockCallback} from "./interfaces/ILockCallback.sol";
 import {SafeCast} from "./libraries/SafeCast.sol";
+import {VaultReserves} from "./libraries/VaultReserves.sol";
 import {VaultToken} from "./VaultToken.sol";
 
 contract Vault is IVault, VaultToken, Ownable {
     using SafeCast for *;
     using PoolIdLibrary for PoolKey;
     using CurrencyLibrary for Currency;
+    using VaultReserves for Currency;
 
     mapping(address => bool) public override isPoolManagerRegistered;
 
-    /// @dev keep track of the reserves of the whole vault
-    mapping(Currency currency => uint256) public override reservesOfVault;
-
     /// @dev keep track of each pool manager's reserves
     mapping(IPoolManager poolManager => mapping(Currency currency => uint256 reserve)) public reservesOfPoolManager;
 
@@ -104,7 +103,6 @@ contract Vault is IVault, VaultToken, Ownable {
     /// @inheritdoc IVault
     function take(Currency currency, address to, uint256 amount) external override isLocked {
         SettlementGuard.accountDelta(msg.sender, currency, amount.toInt128());
-        if (!currency.isNative()) reservesOfVault[currency] -= amount;
         currency.transfer(to, amount);
     }
 
@@ -114,13 +112,18 @@ contract Vault is IVault, VaultToken, Ownable {
         _mint(to, currency, amount);
     }
 
+    function sync(Currency currency) public returns (uint256 balance) {
+        balance = currency.balanceOfSelf();
+        currency.setVaultReserves(balance);
+    }
+
     /// @inheritdoc IVault
     function settle(Currency currency) external payable override isLocked returns (uint256 paid) {
         if (!currency.isNative()) {
             if (msg.value > 0) revert SettleNonNativeCurrencyWithValue();
-            uint256 reservesBefore = reservesOfVault[currency];
-            reservesOfVault[currency] = currency.balanceOfSelf();
-            paid = reservesOfVault[currency] - reservesBefore;
+            uint256 reservesBefore = currency.getVaultReserves();
+            uint256 reservesNow = sync(currency);
+            paid = reservesNow - reservesBefore;
         } else {
             paid = msg.value;
         }
@@ -129,36 +132,6 @@ contract Vault is IVault, VaultToken, Ownable {
         SettlementGuard.accountDelta(msg.sender, currency, -(paid.toInt128()));
     }
 
-    function settleAndMintRefund(Currency currency, address to)
-        external
-        payable
-        override
-        isLocked
-        returns (uint256 paid, uint256 refund)
-    {
-        if (!currency.isNative()) {
-            if (msg.value > 0) revert SettleNonNativeCurrencyWithValue();
-            uint256 reservesBefore = reservesOfVault[currency];
-            reservesOfVault[currency] = currency.balanceOfSelf();
-            paid = reservesOfVault[currency] - reservesBefore;
-        } else {
-            paid = msg.value;
-        }
-
-        int256 currentDelta = SettlementGuard.getCurrencyDelta(msg.sender, currency);
-        if (currentDelta >= 0) {
-            uint256 currentDeltaUint256 = currentDelta.toUint256();
-            if (paid > currentDeltaUint256) {
-                // msg.sender owes vault but paid more than than whats owed
-                refund = paid - currentDeltaUint256;
-                paid = currentDeltaUint256;
-            }
-        }
-
-        SettlementGuard.accountDelta(msg.sender, currency, -(paid.toInt128()));
-        if (refund > 0) _mint(to, currency, refund);
-    }
-
     /// @inheritdoc IVault
     function settleFor(Currency currency, address target, uint256 amount) external isLocked {
         /// @notice settle all outstanding debt if amount is 0
@@ -177,11 +150,14 @@ contract Vault is IVault, VaultToken, Ownable {
     /// @inheritdoc IVault
     function collectFee(Currency currency, uint256 amount, address recipient) external {
         reservesOfPoolManager[IPoolManager(msg.sender)][currency] -= amount;
-        if (!currency.isNative()) reservesOfVault[currency] -= amount;
-
         currency.transfer(recipient, amount);
     }
 
+    /// @inheritdoc IVault
+    function reservesOfVault(Currency currency) external view returns (uint256 amount) {
+        return currency.getVaultReserves();
+    }
+
     function _accountDeltaOfPoolManager(IPoolManager poolManager, Currency currency, int128 delta) internal {
         if (delta == 0) return;
 

src/interfaces/IVault.sol

@@ -32,7 +32,7 @@ interface IVault is IVaultToken {
 
     function isPoolManagerRegistered(address poolManager) external returns (bool);
 
-    /// @notice Returns the reserves for a given ERC20 currency
+    /// @notice Returns the reserves for a currency thats sync in transient storage
     function reservesOfVault(Currency currency) external view returns (uint256);
 
     /// @notice Returns the reserves for a a given pool type and currency
@@ -67,20 +67,12 @@ interface IVault is IVaultToken {
     /// @dev Can also be used as a mechanism for _free_ flash loans
     function take(Currency currency, address to, uint256 amount) external;
 
+    /// @notice Called before erc20 transfer to tstore the current reserve balance
+    function sync(Currency token0) external returns (uint256 balance);
+
     /// @notice Called by the user to pay what is owed
     function settle(Currency token) external payable returns (uint256 paid);
 
-    /// @notice Called by the user to pay what is owed. If the payment is more than the debt, the surplus is refunded by minting
-    /// @dev To claim the refund, caller must eventually call vault.burn() -> vault.take() to take the ERC20 token from vault
-    /// @param currency The currency to settle
-    /// @param to The address to mint the refund
-    /// @return paid The amount paid
-    /// @return refund The amount refunded
-    function settleAndMintRefund(Currency currency, address to)
-        external
-        payable
-        returns (uint256 paid, uint256 refund);
-
     /// @notice move the delta from target to the msg.sender, only payment delta can be moved
     /// @param currency The currency to settle
     /// @param target The address whose delta will be updated

src/libraries/VaultReserves.sol

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+// Copyright (C) 2024 PancakeSwap
+pragma solidity ^0.8.24;
+
+import {Currency} from "../types/Currency.sol";
+
+/// @notice This is a workaround when transient keyword is absent. It manages:
+///  - 0: mapping(currency => uint256) reserveOfVault
+library VaultReserves {
+    /// @notice Thrown when getVaultReserves is called before sync
+    error ReserveNotSync();
+
+    // uint256 constant RESERVE_OF_VAULT_SLOT = uint256(keccak256("reservesOfVault")) - 1;
+    uint256 constant RESERVE_OF_VAULT_SLOT = uint256(0xb54c65c0f448723e3496562a0e878a1341c4dd2511ef542b5fd5f19cebc47663);
+
+    /// @notice Set balance to the max as a sentinel to track that it has been set if amount == 0
+    uint256 constant ZERO_BALANCE = type(uint256).max;
+
+    /// @notice Transient store the currency reserve
+    /// @dev if the amount is 0, the value stored would be ZERO_BALANCE, a sentinel value
+    function setVaultReserves(Currency currency, uint256 amount) internal {
+        if (amount == 0) amount = ZERO_BALANCE;
+
+        bytes32 slotKey = _getCurrencySlotKey(currency);
+        assembly {
+            tstore(slotKey, amount)
+        }
+    }
+
+    /// @notice Transient load the currency reserve
+    /// @dev If this is called before vault.sync, it will be reverted
+    function getVaultReserves(Currency currency) internal view returns (uint256 amount) {
+        bytes32 slotKey = _getCurrencySlotKey(currency);
+        assembly {
+            amount := tload(slotKey)
+        }
+
+        if (amount == 0) revert ReserveNotSync();
+        if (amount == ZERO_BALANCE) return 0;
+    }
+
+    function _getCurrencySlotKey(Currency currency) internal pure returns (bytes32 key) {
+        uint256 slot = RESERVE_OF_VAULT_SLOT;
+        assembly {
+            mstore(0x0, slot)
+            mstore(0x20, currency)
+            key := keccak256(0x0, 0x40)
+        }
+    }
+}