Don't fail ante handler on simulate tx with no fee (#120) (#121)

(cherry picked from commit d2f4f3b)

Co-authored-by: Eric Warehime <eric.warehime@gmail.com>

Author: mergify[bot]

x/feemarket/ante/fee.go

@@ -95,14 +95,19 @@ func (dfd feeMarketCheckDecorator) anteHandle(ctx sdk.Context, tx sdk.Tx, simula
 	feeCoins := feeTx.GetFee()
 	gas := feeTx.GetGas() // use provided gas limit
 
-	if len(feeCoins) != 1 {
-		if len(feeCoins) == 0 {
-			return ctx, errorsmod.Wrapf(feemarkettypes.ErrNoFeeCoins, "got length %d", len(feeCoins))
-		}
+	if len(feeCoins) == 0 && !simulate {
+		return ctx, errorsmod.Wrapf(feemarkettypes.ErrNoFeeCoins, "got length %d", len(feeCoins))
+	}
+	if len(feeCoins) > 1 {
 		return ctx, errorsmod.Wrapf(feemarkettypes.ErrTooManyFeeCoins, "got length %d", len(feeCoins))
 	}
 
-	feeCoin := feeCoins[0]
+	var feeCoin sdk.Coin
+	if simulate && len(feeCoins) == 0 {
+		feeCoin = sdk.NewCoin(params.FeeDenom, sdkmath.NewInt(0))
+	} else {
+		feeCoin = feeCoins[0]
+	}
 	feeGas := int64(feeTx.GetGas())
 
 	minGasPrice, err := dfd.feemarketKeeper.GetMinGasPrice(ctx, feeCoin.GetDenom())

x/feemarket/ante/fee_test.go

@@ -76,6 +76,23 @@ func TestAnteHandle(t *testing.T) {
 			ExpPass:  false,
 			ExpErr:   sdkerrors.ErrOutOfGas,
 		},
+		{
+			Name: "0 gas given should pass in simulate",
+			Malleate: func(suite *antesuite.TestSuite) antesuite.TestCaseArgs {
+				accs := suite.CreateTestAccounts(1)
+
+				return antesuite.TestCaseArgs{
+					Msgs:      []sdk.Msg{testdata.NewTestMsg(accs[0].Account.GetAddress())},
+					GasLimit:  0,
+					FeeAmount: nil,
+				}
+			},
+			RunAnte:  true,
+			RunPost:  false,
+			Simulate: true,
+			ExpPass:  true,
+			ExpErr:   nil,
+		},
 		{
 			Name: "signer has enough funds, should pass",
 			Malleate: func(suite *antesuite.TestSuite) antesuite.TestCaseArgs {