feat(x/precisebank): Display 0 reserve balance to module consumers (#1958)

Module reserve represents fractional balances, so it should be hidden to consumers to not have a misleading total balance that doubles the fractional balances. This modifies GetBalance() and SpendableCoin() to always return zero coins when fetching the reserve address balance for fractional amounts.

x/precisebank/keeper/burn_integration_test.go

@@ -261,7 +261,7 @@ func (suite *burnIntegrationTestSuite) TestBurnCoins_Remainder() {
 
 	// Burn 0.1 until balance is 0
 	for {
-		reserveBalBefore := suite.Keeper.GetBalance(
+		reserveBalBefore := suite.BankKeeper.GetBalance(
 			suite.Ctx,
 			reserveAddr,
 			types.IntegerCoinDenom,
@@ -291,7 +291,7 @@ func (suite *burnIntegrationTestSuite) TestBurnCoins_Remainder() {
 			moduleAddr,
 			types.ExtendedCoinDenom,
 		)
-		reserveBalAfter := suite.Keeper.GetBalance(
+		reserveBalAfter := suite.BankKeeper.GetBalance(
 			suite.Ctx,
 			reserveAddr,
 			types.IntegerCoinDenom,
@@ -357,7 +357,7 @@ func (suite *burnIntegrationTestSuite) TestBurnCoins_Spread_Remainder() {
 
 	// Burn 0.1 from each account
 	for _, addr := range addrs {
-		reserveBalBefore := suite.Keeper.GetBalance(
+		reserveBalBefore := suite.BankKeeper.GetBalance(
 			suite.Ctx,
 			reserveAddr,
 			types.IntegerCoinDenom,
@@ -395,7 +395,7 @@ func (suite *burnIntegrationTestSuite) TestBurnCoins_Spread_Remainder() {
 			addr,
 			types.ExtendedCoinDenom,
 		)
-		reserveBalAfter := suite.Keeper.GetBalance(
+		reserveBalAfter := suite.BankKeeper.GetBalance(
 			suite.Ctx,
 			reserveAddr,
 			types.IntegerCoinDenom,

x/precisebank/keeper/view.go

@@ -1,6 +1,7 @@
 package keeper
 
 import (
+	sdkmath "cosmossdk.io/math"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/kava-labs/kava/x/precisebank/types"
 )
@@ -13,6 +14,14 @@ func (k Keeper) GetBalance(
 	addr sdk.AccAddress,
 	denom string,
 ) sdk.Coin {
+	// Module balance should display as empty for extended denom. Module
+	// balances are **only** for the reserve which backs the fractional
+	// balances. Returning the backing balances if querying extended denom would
+	// result in a double counting of the fractional balances.
+	if denom == types.ExtendedCoinDenom && addr.Equals(k.ak.GetModuleAddress(types.ModuleName)) {
+		return sdk.NewCoin(denom, sdkmath.ZeroInt())
+	}
+
 	// Pass through to x/bank for denoms except ExtendedCoinDenom
 	if denom != types.ExtendedCoinDenom {
 		return k.bk.GetBalance(ctx, addr, denom)
@@ -41,6 +50,11 @@ func (k Keeper) SpendableCoin(
 	addr sdk.AccAddress,
 	denom string,
 ) sdk.Coin {
+	// Same as GetBalance, extended denom balances are transparent to consumers.
+	if denom == types.ExtendedCoinDenom && addr.Equals(k.ak.GetModuleAddress(types.ModuleName)) {
+		return sdk.NewCoin(denom, sdkmath.ZeroInt())
+	}
+
 	// Pass through to x/bank for denoms except ExtendedCoinDenom
 	if denom != types.ExtendedCoinDenom {
 		return k.bk.SpendableCoin(ctx, addr, denom)

x/precisebank/keeper/view_integration_test.go

@@ -129,3 +129,74 @@ func (suite *viewIntegrationTestSuite) TestKeeper_SpendableCoin() {
 		})
 	}
 }
+
+func (suite *viewIntegrationTestSuite) TestKeeper_HiddenReserve() {
+	// Reserve balances should not be shown to consumers of x/precisebank, as it
+	// represents the fractional balances of accounts.
+
+	moduleAddr := authtypes.NewModuleAddress(types.ModuleName)
+	addr1 := sdk.AccAddress{1}
+
+	// Make the reserve hold a non-zero balance
+	// Mint fractional coins to an account, which should cause a mint of 1
+	// integer coin to the reserve to back it.
+	extCoin := sdk.NewCoin(types.ExtendedCoinDenom, types.ConversionFactor().AddRaw(1000))
+	unrelatedCoin := sdk.NewCoin("unrelated", sdk.NewInt(1000))
+	suite.MintToAccount(
+		addr1,
+		sdk.NewCoins(
+			extCoin,
+			unrelatedCoin,
+		),
+	)
+
+	// Check underlying x/bank balance for reserve
+	reserveIntCoin := suite.BankKeeper.GetBalance(suite.Ctx, moduleAddr, types.IntegerCoinDenom)
+	suite.Require().Equal(
+		sdkmath.NewInt(1),
+		reserveIntCoin.Amount,
+		"reserve should hold 1 integer coin",
+	)
+
+	tests := []struct {
+		name       string
+		giveAddr   sdk.AccAddress
+		giveDenom  string
+		wantAmount sdkmath.Int
+	}{
+		{
+			"reserve account - hidden extended denom",
+			moduleAddr,
+			types.ExtendedCoinDenom,
+			sdkmath.ZeroInt(),
+		},
+		{
+			"reserve account - visible integer denom",
+			moduleAddr,
+			types.IntegerCoinDenom,
+			sdkmath.OneInt(),
+		},
+		{
+			"user account - visible extended denom",
+			addr1,
+			types.ExtendedCoinDenom,
+			extCoin.Amount,
+		},
+		{
+			"user account - visible integer denom",
+			addr1,
+			types.IntegerCoinDenom,
+			extCoin.Amount.Quo(types.ConversionFactor()),
+		},
+	}
+
+	for _, tt := range tests {
+		suite.Run(tt.name, func() {
+			coin := suite.Keeper.GetBalance(suite.Ctx, tt.giveAddr, tt.giveDenom)
+			suite.Require().Equal(tt.wantAmount.Int64(), coin.Amount.Int64())
+
+			spendableCoin := suite.Keeper.SpendableCoin(suite.Ctx, tt.giveAddr, tt.giveDenom)
+			suite.Require().Equal(tt.wantAmount.Int64(), spendableCoin.Amount.Int64())
+		})
+	}
+}

x/precisebank/keeper/view_test.go

@@ -5,6 +5,7 @@ import (
 
 	sdkmath "cosmossdk.io/math"
 	sdk "github.com/cosmos/cosmos-sdk/types"
+	authtypes "github.com/cosmos/cosmos-sdk/x/auth/types"
 	"github.com/kava-labs/kava/x/precisebank/types"
 	"github.com/stretchr/testify/require"
 )
@@ -90,6 +91,13 @@ func TestKeeper_GetBalance(t *testing.T) {
 			// Set fractional balance in store before query
 			tk.keeper.SetFractionalBalance(tk.ctx, addr, tt.giveFractionalBal)
 
+			// Checks address if its a reserve denom
+			if tt.giveDenom == types.ExtendedCoinDenom {
+				tk.ak.EXPECT().GetModuleAddress(types.ModuleName).
+					Return(authtypes.NewModuleAddress(types.ModuleName)).
+					Once()
+			}
+
 			if tt.giveDenom == types.ExtendedCoinDenom {
 				// No balance pass through
 				tk.bk.EXPECT().
@@ -198,6 +206,13 @@ func TestKeeper_SpendableCoin(t *testing.T) {
 			// Set fractional balance in store before query
 			tk.keeper.SetFractionalBalance(tk.ctx, addr, tt.giveFractionalBal)
 
+			// If its a reserve denom, module address is checked
+			if tt.giveDenom == types.ExtendedCoinDenom {
+				tk.ak.EXPECT().GetModuleAddress(types.ModuleName).
+					Return(authtypes.NewModuleAddress(types.ModuleName)).
+					Once()
+			}
+
 			if tt.giveDenom == types.ExtendedCoinDenom {
 				// No balance pass through
 				tk.bk.EXPECT().
@@ -224,3 +239,58 @@ func TestKeeper_SpendableCoin(t *testing.T) {
 		})
 	}
 }
+
+func TestHiddenReserve(t *testing.T) {
+	// Reserve balances should not be shown to consumers of x/precisebank, as it
+	// represents the fractional balances of accounts.
+
+	tk := NewMockedTestData(t)
+
+	moduleAddr := authtypes.NewModuleAddress(types.ModuleName)
+
+	// No mock bankkeeper expectations, which means the zero coin is returned
+	// directly for reserve address. So the mock bankkeeper doesn't need to have
+	// a handler for getting underlying balance.
+
+	tests := []struct {
+		name            string
+		denom           string
+		expectedBalance sdk.Coin
+	}{
+		{"akava", types.ExtendedCoinDenom, sdk.NewCoin(types.ExtendedCoinDenom, sdkmath.ZeroInt())},
+		{"ukava", types.IntegerCoinDenom, sdk.NewCoin(types.IntegerCoinDenom, sdkmath.NewInt(1))},
+		{"unrelated denom", "cat", sdk.NewCoin("cat", sdkmath.ZeroInt())},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// 2 calls for GetBalance and SpendableCoin, only for reserve coins
+			if tt.denom == "akava" {
+				tk.ak.EXPECT().GetModuleAddress(types.ModuleName).
+					Return(moduleAddr).
+					Twice()
+			} else {
+				// Passthrough to x/bank for non-reserve denoms
+				tk.bk.EXPECT().
+					GetBalance(tk.ctx, moduleAddr, tt.denom).
+					Return(sdk.NewCoin(tt.denom, sdkmath.ZeroInt())).
+					Once()
+
+				tk.bk.EXPECT().
+					SpendableCoin(tk.ctx, moduleAddr, tt.denom).
+					Return(sdk.NewCoin(tt.denom, sdkmath.ZeroInt())).
+					Once()
+			}
+
+			// GetBalance should return zero balance for reserve address
+			coin := tk.keeper.GetBalance(tk.ctx, moduleAddr, tt.denom)
+			require.Equal(t, tt.denom, coin.Denom)
+			require.Equal(t, sdkmath.ZeroInt(), coin.Amount)
+
+			// SpendableCoin should return zero balance for reserve address
+			spendableCoin := tk.keeper.SpendableCoin(tk.ctx, moduleAddr, tt.denom)
+			require.Equal(t, tt.denom, spendableCoin.Denom)
+			require.Equal(t, sdkmath.ZeroInt(), spendableCoin.Amount)
+		})
+	}
+}