fix: (v0.45.x) regression in return value of WithdrawDelegationReward…

…s when rewards are zero (cosmos#13588)

CHANGELOG.md

@@ -48,6 +48,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Bug Fixes
 
+* [#13588](https://github.com/cosmos/cosmos-sdk/pull/13588) Fix regression in distrubtion.WithdrawDelegationRewards when rewards are zero
 * [#13564](https://github.com/cosmos/cosmos-sdk/pull/13564) - Fix `make proto-gen`.
 
 ## v0.45.9 - 2022-10-14

x/distribution/keeper/delegation.go

@@ -188,21 +188,22 @@ func (k Keeper) withdrawDelegationRewards(ctx sdk.Context, val stakingtypes.Vali
 	// remove delegator starting info
 	k.DeleteDelegatorStartingInfo(ctx, del.GetValidatorAddr(), del.GetDelegatorAddr())
 
+	emittedRewards := finalRewards
 	if finalRewards.IsZero() {
 		baseDenom, _ := sdk.GetBaseDenom()
 		if baseDenom == "" {
 			baseDenom = sdk.DefaultBondDenom
 		}
 
 		// Note, we do not call the NewCoins constructor as we do not want the zero
-		// coin removed.
-		finalRewards = sdk.Coins{sdk.NewCoin(baseDenom, sdk.ZeroInt())}
+		// coin removed for event emission.
+		emittedRewards = sdk.Coins{sdk.NewCoin(baseDenom, sdk.ZeroInt())}
 	}
 
 	ctx.EventManager().EmitEvent(
 		sdk.NewEvent(
 			types.EventTypeWithdrawRewards,
-			sdk.NewAttribute(sdk.AttributeKeyAmount, finalRewards.String()),
+			sdk.NewAttribute(sdk.AttributeKeyAmount, emittedRewards.String()),
 			sdk.NewAttribute(types.AttributeKeyValidator, val.GetOperator().String()),
 		),
 	)

x/distribution/keeper/delegation_test.go

@@ -332,6 +332,33 @@ func TestWithdrawDelegationRewardsBasic(t *testing.T) {
 	require.Nil(t, err)
 }
 
+func TestWithdrawDelegationZeroRewards(t *testing.T) {
+	app := simapp.Setup(false)
+	ctx := app.BaseApp.NewContext(false, tmproto.Header{})
+
+	balancePower := int64(1000)
+	balanceTokens := app.StakingKeeper.TokensFromConsensusPower(ctx, balancePower)
+	addr := simapp.AddTestAddrs(app, ctx, 1, sdk.NewInt(1000000000))
+	valAddrs := simapp.ConvertAddrsToValAddrs(addr)
+	tstaking := teststaking.NewHelper(t, ctx, app.StakingKeeper)
+
+	// set module account coins
+	distrAcc := app.DistrKeeper.GetDistributionAccount(ctx)
+	require.NoError(t, simapp.FundModuleAccount(app.BankKeeper, ctx, distrAcc.GetName(), sdk.NewCoins(sdk.NewCoin(sdk.DefaultBondDenom, balanceTokens))))
+	app.AccountKeeper.SetModuleAccount(ctx, distrAcc)
+
+	// create validator with 50% commission
+	power := int64(100)
+	tstaking.Commission = stakingtypes.NewCommissionRates(sdk.NewDecWithPrec(5, 1), sdk.NewDecWithPrec(5, 1), sdk.NewDec(0))
+	_ = tstaking.CreateValidatorWithValPower(valAddrs[0], valConsPk1, power, true)
+
+	// withdraw rewards -- should be 0
+	amount, err := app.DistrKeeper.WithdrawDelegationRewards(ctx, sdk.AccAddress(valAddrs[0]), valAddrs[0])
+	require.NoError(t, err)
+	require.True(t, amount.IsZero(), "expected withdraw rewards to be zero")
+	require.True(t, amount.IsValid(), "expected returned coins to be valid")
+}
+
 func TestCalculateRewardsAfterManySlashesInSameBlock(t *testing.T) {
 	app := simapp.Setup(false)
 	ctx := app.BaseApp.NewContext(false, tmproto.Header{})