fix: Fix denom exponent checks (cosmos#800)

* Fix denom exponent checks

* Add changelog

Author: Eric-Warehime

CHANGELOG.md

@@ -24,6 +24,7 @@
 - [\#772](https://github.com/cosmos/evm/pull/772) Avoid panic on close if evm mempool not used.
 - [\#774](https://github.com/cosmos/evm/pull/774) Emit proper allowance amount in erc20 event.
 - [\#790](https://github.com/cosmos/evm/pull/790) fix panic in historical query due to missing EvmCoinInfo.
+- [\#800](https://github.com/cosmos/evm/pull/800) Fix denom exponent validation in virtual fee deduct in vm module.
 
 ## v0.5.0
 

x/vm/keeper/fees.go

@@ -139,11 +139,11 @@ func DeductFees(bankKeeper types.BankKeeper, vmKeeper types.VMKeeper, ctx sdk.Co
 			continue
 		}
 		for _, du := range md.DenomUnits {
-			if du.Denom == evmCoinInfo.Denom && du.Exponent != evmCoinInfo.Decimals {
+			if du.Denom == evmCoinInfo.DisplayDenom && du.Exponent != types.EighteenDecimals.Uint32() {
 				panic(
 					fmt.Sprintf(
-						"Cannot use virtual fee collection for denom, %s, which has a different exponent, %d, than the evm coin's %d",
-						du.Denom, du.Exponent, evmCoinInfo.Decimals))
+						"Cannot use virtual fee collection for denom %s, which has a display denom that has %d exponent",
+						du.Denom, du.Exponent))
 			}
 		}
 	}

x/vm/keeper/fees_test.go

@@ -30,26 +30,26 @@ func TestDeductFees(t *testing.T) {
 		expectedErr   error
 	}{
 		{
-			name:          "happy path coins matching",
+			name:          "happy path coins",
 			feeCoin:       sdk.NewCoin("feecoin", sdkmath.NewInt(100)),
 			sdkDenom:      banktypes.DenomUnit{Denom: "feecoin", Exponent: 18},
-			evmCoinInfo:   vmtypes.EvmCoinInfo{Denom: "feecoin", Decimals: 18},
+			evmCoinInfo:   vmtypes.EvmCoinInfo{DisplayDenom: "feecoin"},
 			expectedPanic: false,
 			expectedErr:   nil,
 		},
 		{
-			name:          "panic on decimal mismatch",
+			name:          "panic on exponent mismatch",
 			feeCoin:       sdk.NewCoin("feecoin", sdkmath.NewInt(100)),
 			sdkDenom:      banktypes.DenomUnit{Denom: "feecoin", Exponent: 6},
-			evmCoinInfo:   vmtypes.EvmCoinInfo{Denom: "feecoin", Decimals: 18},
+			evmCoinInfo:   vmtypes.EvmCoinInfo{DisplayDenom: "feecoin"},
 			expectedPanic: true,
 			expectedErr:   nil,
 		},
 		{
 			name:          "error on bank call failure",
 			feeCoin:       sdk.NewCoin("feecoin", sdkmath.NewInt(100)),
 			sdkDenom:      banktypes.DenomUnit{Denom: "feecoin", Exponent: 18},
-			evmCoinInfo:   vmtypes.EvmCoinInfo{Denom: "feecoin", Decimals: 18},
+			evmCoinInfo:   vmtypes.EvmCoinInfo{DisplayDenom: "feecoin"},
 			expectedPanic: false,
 			expectedErr:   errors.New("foo"),
 		},