fix(erc4626): make decimals offset adapt

.github/workflows/foundry.yml

@@ -82,7 +82,7 @@ jobs:
       - uses: ./.github/actions/install-cache
 
       - name: Run tests in ${{ matrix.type }} mode
-        run: yarn test:forge
+        run: yarn test:forge -vvv
         env:
           FOUNDRY_FUZZ_RUNS: ${{ matrix.fuzz-runs }}
           FOUNDRY_FUZZ_MAX_TEST_REJECTS: ${{ matrix.max-test-rejects }}

src/MetaMorpho.sol

@@ -58,6 +58,11 @@ contract MetaMorpho is ERC4626, ERC20Permit, Ownable2Step, Multicall, IMetaMorph
     /// @notice The address of the Morpho contract.
     IMorpho public immutable MORPHO;
 
+    /// @notice OpenZeppelin decimals offset used by the ERC4626 implementation.
+    /// @dev Calculated to be max(0, 18 - underlyingDecimals) at construction, so the initial conversion rate maximizes
+    /// precision between shares and assets.
+    uint8 public immutable DECIMALS_OFFSET;
+
     /* STORAGE */
 
     /// @notice The address of the curator.
@@ -126,6 +131,7 @@ contract MetaMorpho is ERC4626, ERC20Permit, Ownable2Step, Multicall, IMetaMorph
         if (morpho == address(0)) revert ErrorsLib.ZeroAddress();
 
         MORPHO = IMorpho(morpho);
+        DECIMALS_OFFSET = uint8(uint256(18).zeroFloorSub(IERC20Metadata(_asset).decimals()));
 
         _checkTimelockBounds(initialTimelock);
         _setTimelock(initialTimelock);
@@ -619,8 +625,8 @@ contract MetaMorpho is ERC4626, ERC20Permit, Ownable2Step, Multicall, IMetaMorph
     /* ERC4626 (INTERNAL) */
 
     /// @inheritdoc ERC4626
-    function _decimalsOffset() internal pure override returns (uint8) {
-        return ConstantsLib.DECIMALS_OFFSET;
+    function _decimalsOffset() internal view override returns (uint8) {
+        return DECIMALS_OFFSET;
     }
 
     /// @dev Returns the maximum amount of asset (`assets`) that the `owner` can withdraw from the vault, as well as the
@@ -675,7 +681,7 @@ contract MetaMorpho is ERC4626, ERC20Permit, Ownable2Step, Multicall, IMetaMorph
         uint256 newTotalSupply,
         uint256 newTotalAssets,
         Math.Rounding rounding
-    ) internal pure returns (uint256) {
+    ) internal view returns (uint256) {
         return assets.mulDiv(newTotalSupply + 10 ** _decimalsOffset(), newTotalAssets + 1, rounding);
     }
 
@@ -686,7 +692,7 @@ contract MetaMorpho is ERC4626, ERC20Permit, Ownable2Step, Multicall, IMetaMorph
         uint256 newTotalSupply,
         uint256 newTotalAssets,
         Math.Rounding rounding
-    ) internal pure returns (uint256) {
+    ) internal view returns (uint256) {
         return shares.mulDiv(newTotalAssets + 1, newTotalSupply + 10 ** _decimalsOffset(), rounding);
     }
 

src/interfaces/IMetaMorpho.sol

@@ -31,6 +31,7 @@ interface IOwnable {
 /// @dev Consider using the IMetaMorpho interface instead of this one.
 interface IMetaMorphoBase {
     function MORPHO() external view returns (IMorpho);
+    function DECIMALS_OFFSET() external view returns (uint8);
 
     function curator() external view returns (address);
     function isAllocator(address target) external view returns (bool);

src/libraries/ConstantsLib.sol

@@ -12,9 +12,6 @@ library ConstantsLib {
     /// @dev The minimum delay of a timelock.
     uint256 internal constant MIN_TIMELOCK = 1 days;
 
-    /// @dev OpenZeppelin's decimals offset used in MetaMorpho's ERC4626 implementation.
-    uint8 internal constant DECIMALS_OFFSET = 6;
-
     /// @dev The maximum number of markets in the supply/withdraw queue.
     uint256 internal constant MAX_QUEUE_LENGTH = 30;
 

test/forge/ERC4626Test.sol

@@ -17,8 +17,14 @@ contract ERC4626Test is IntegrationTest, IMorphoFlashLoanCallback {
         _sortSupplyQueueIdleLast();
     }
 
-    function testDecimals() public {
-        assertEq(vault.decimals(), loanToken.decimals() + ConstantsLib.DECIMALS_OFFSET, "decimals");
+    function testDecimals(uint8 decimals) public {
+        vm.mockCall(address(loanToken), abi.encodeWithSignature("decimals()"), abi.encode(decimals));
+
+        vault = IMetaMorpho(
+            address(new MetaMorpho(OWNER, address(morpho), TIMELOCK, address(loanToken), "MetaMorpho Vault", "MMV"))
+        );
+
+        assertEq(vault.decimals(), Math.max(18, decimals), "decimals");
     }
 
     function testMint(uint256 assets) public {
@@ -116,16 +122,18 @@ contract ERC4626Test is IntegrationTest, IMorphoFlashLoanCallback {
     function testRedeemTooMuch(uint256 deposited) public {
         deposited = bound(deposited, MIN_TEST_ASSETS, MAX_TEST_ASSETS);
 
-        loanToken.setBalance(SUPPLIER, deposited);
+        loanToken.setBalance(SUPPLIER, deposited * 2);
 
-        vm.prank(SUPPLIER);
-        uint256 shares = vault.deposit(deposited, ONBEHALF);
+        vm.startPrank(SUPPLIER);
+        uint256 shares = vault.deposit(deposited, SUPPLIER);
+        vault.deposit(deposited, ONBEHALF);
+        vm.stopPrank();
 
-        vm.prank(ONBEHALF);
+        vm.prank(SUPPLIER);
         vm.expectRevert(
-            abi.encodeWithSelector(IERC20Errors.ERC20InsufficientBalance.selector, ONBEHALF, shares, shares + 1)
+            abi.encodeWithSelector(IERC20Errors.ERC20InsufficientBalance.selector, SUPPLIER, shares, shares + 1)
         );
-        vault.redeem(shares + 1, RECEIVER, ONBEHALF);
+        vault.redeem(shares + 1, RECEIVER, SUPPLIER);
     }
 
     function testWithdrawAll(uint256 assets) public {
@@ -270,7 +278,7 @@ contract ERC4626Test is IntegrationTest, IMorphoFlashLoanCallback {
         vm.prank(SUPPLIER);
         vault.deposit(deposited, ONBEHALF);
 
-        assets = bound(assets, deposited + 1, type(uint256).max / (deposited + 10 ** ConstantsLib.DECIMALS_OFFSET));
+        assets = bound(assets, deposited + 1, type(uint256).max / (deposited + 1));
 
         vm.prank(ONBEHALF);
         vm.expectRevert(ErrorsLib.NotEnoughLiquidity.selector);
@@ -285,7 +293,7 @@ contract ERC4626Test is IntegrationTest, IMorphoFlashLoanCallback {
         vm.prank(SUPPLIER);
         vault.deposit(deposited, ONBEHALF);
 
-        assets = bound(assets, deposited + 1, type(uint256).max / (deposited + 10 ** ConstantsLib.DECIMALS_OFFSET));
+        assets = bound(assets, deposited + 1, type(uint256).max / (deposited + 1));
 
         collateralToken.setBalance(BORROWER, type(uint128).max);
 

test/forge/FeeTest.sol

@@ -55,11 +55,7 @@ contract FeeTest is IntegrationTest {
         uint256 interest = totalAssetsAfter - vault.lastTotalAssets();
         uint256 feeAssets = interest.mulDiv(FEE, WAD);
 
-        return feeAssets.mulDiv(
-            vault.totalSupply() + 10 ** ConstantsLib.DECIMALS_OFFSET,
-            totalAssetsAfter - feeAssets + 1,
-            Math.Rounding.Floor
-        );
+        return feeAssets.mulDiv(vault.totalSupply() + 1, totalAssetsAfter - feeAssets + 1, Math.Rounding.Floor);
     }
 
     function testAccrueFeeWithinABlock(uint256 deposited, uint256 withdrawn) public {
@@ -312,11 +308,8 @@ contract FeeTest is IntegrationTest {
         _forward(blocks);
 
         uint256 feeShares = _feeShares();
-        uint256 expectedShares = assets.mulDiv(
-            vault.totalSupply() + feeShares + 10 ** ConstantsLib.DECIMALS_OFFSET,
-            vault.totalAssets() + 1,
-            Math.Rounding.Floor
-        );
+        uint256 expectedShares =
+            assets.mulDiv(vault.totalSupply() + feeShares + 1, vault.totalAssets() + 1, Math.Rounding.Floor);
         uint256 shares = vault.convertToShares(assets);
 
         assertEq(shares, expectedShares, "shares");
@@ -325,7 +318,7 @@ contract FeeTest is IntegrationTest {
 
     function testConvertToSharesWithFeeAndInterest(uint256 deposited, uint256 shares, uint256 blocks) public {
         deposited = bound(deposited, MIN_TEST_ASSETS, MAX_TEST_ASSETS);
-        shares = bound(shares, 10 ** ConstantsLib.DECIMALS_OFFSET, MAX_TEST_ASSETS);
+        shares = bound(shares, 1, MAX_TEST_ASSETS);
         blocks = _boundBlocks(blocks);
 
         loanToken.setBalance(SUPPLIER, deposited);
@@ -338,11 +331,8 @@ contract FeeTest is IntegrationTest {
         _forward(blocks);
 
         uint256 feeShares = _feeShares();
-        uint256 expectedAssets = shares.mulDiv(
-            vault.totalAssets() + 1,
-            vault.totalSupply() + feeShares + 10 ** ConstantsLib.DECIMALS_OFFSET,
-            Math.Rounding.Floor
-        );
+        uint256 expectedAssets =
+            shares.mulDiv(vault.totalAssets() + 1, vault.totalSupply() + feeShares + 1, Math.Rounding.Floor);
         uint256 assets = vault.convertToAssets(shares);
 
         assertEq(assets, expectedAssets, "assets");