fix: precision loss in delegation query

CHANGELOG.md

@@ -73,6 +73,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * (x/epochs) [#25087](https://github.com/cosmos/cosmos-sdk/pull/25087) Remove redundant error check in BeginBlocker.
 * [GHSA-p22h-3m2v-cmgh](https://github.com/cosmos/cosmos-sdk/security/advisories/GHSA-p22h-3m2v-cmgh) Fix x/distribution can halt when historical rewards overflow.
 * (x/staking) [#25258](https://github.com/cosmos/cosmos-sdk/pull/25258) Add delegator address to redelegate event.
+* (x/staking) [#25312](https://github.com/cosmos/cosmos-sdk/pull/25312) Fix precision loss in delegation query
 
 ### Deprecated
 

x/staking/keeper/grpc_query.go

@@ -594,7 +594,7 @@ func delegationToDelegationResponse(ctx context.Context, k *Keeper, del types.De
 		del.DelegatorAddress,
 		del.GetValidatorAddr(),
 		del.Shares,
-		sdk.NewCoin(bondDenom, val.TokensFromShares(del.Shares).TruncateInt()),
+		sdk.NewCoin(bondDenom, val.TokensFromSharesRoundUp(del.Shares).TruncateInt()),
 	), nil
 }
 

x/staking/keeper/grpc_query_test.go

@@ -4,6 +4,8 @@ import (
 	gocontext "context"
 	"fmt"
 
+	"cosmossdk.io/math"
+
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/cosmos/cosmos-sdk/x/staking/testutil"
 	"github.com/cosmos/cosmos-sdk/x/staking/types"
@@ -60,3 +62,41 @@ func (s *KeeperTestSuite) TestGRPCQueryValidator() {
 		})
 	}
 }
+
+func (s *KeeperTestSuite) TestGRPCQueryDelegation() {
+	s.Run("test delegation query with custom values", func() {
+		require := s.Require()
+		validatorTokens := "10132421222471611505485287"
+		validatorDelegatorShares := "10142563785454078365766009.473933091465315992"
+		delegationAmount := "2000000000000000000"
+
+		// Arrange
+		ctx, keeper, queryClient := s.ctx, s.stakingKeeper, s.queryClient
+		validator := testutil.NewValidator(s.T(), PKs[0].Address().Bytes(), PKs[0])
+		tokens, ok := math.NewIntFromString(validatorTokens)
+		require.True(ok)
+		shares := math.LegacyMustNewDecFromStr(validatorDelegatorShares)
+		validator.Tokens = tokens
+		validator.DelegatorShares = shares
+		require.NoError(keeper.SetValidator(ctx, validator))
+
+		delegator := sdk.AccAddress(PKs[1].Address().Bytes())
+		amount, ok := math.NewIntFromString(delegationAmount)
+		require.True(ok)
+		shares, err := validator.SharesFromTokens(amount)
+		require.NoError(err)
+		err = keeper.SetDelegation(ctx, types.NewDelegation(delegator.String(), validator.GetOperator(), shares))
+		require.NoError(err)
+
+		// Act
+		res, err := queryClient.Delegation(gocontext.Background(), &types.QueryDelegationRequest{
+			DelegatorAddr: delegator.String(),
+			ValidatorAddr: validator.GetOperator(),
+		})
+
+		// Assert
+		require.NoError(err)
+		require.NotNil(res)
+		require.True(res.DelegationResponse.Balance.Amount.Equal(amount))
+	})
+}