fix(x/staking): dust share

CHANGELOG.md

@@ -93,6 +93,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * (simulation) [#18196](https://github.com/cosmos/cosmos-sdk/pull/18196) Fix the problem of `validator set is empty after InitGenesis` in simulation test.
 * (baseapp) [#18551](https://github.com/cosmos/cosmos-sdk/pull/18551) Fix SelectTxForProposal the calculation method of tx bytes size is inconsistent with CometBFT
 * (baseapp) [#18895](https://github.com/cosmos/cosmos-sdk/pull/18895) Fix de-duplicating vote extensions during validation in ValidateVoteExtensions.
+* (x/staking) [#18841](https://github.com/cosmos/cosmos-sdk/pull/18841) Fix delegation state when it has dust share. Change the condition of unbond to remove delegation with less than minimum share
 
 ### API Breaking Changes
 
@@ -197,6 +198,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 * (x/upgrade) [#16244](https://github.com/cosmos/cosmos-sdk/pull/16244) Upgrade module no longer stores the app version but gets and sets the app version stored in the `ParamStore` of baseapp.
 * (x/staking) [#17655](https://github.com/cosmos/cosmos-sdk/pull/17655) `HistoricalInfo` was replaced with `HistoricalRecord`, it removes the validator set and comet header and only keep what is needed for IBC. 
+* (x/staking) [#18841](https://github.com/cosmos/cosmos-sdk/pull/18841) Delegations with less than the minimum share removed.
 
 ## [v0.50.2](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.50.2) - 2023-12-11
 

x/staking/keeper/delegation.go

@@ -1197,11 +1197,15 @@ func (k Keeper) ValidateUnbondAmount(
 		return shares, errorsmod.Wrap(sdkerrors.ErrInvalidRequest, "invalid shares amount")
 	}
 
-	// Cap the shares at the delegation's shares. Shares being greater could occur
-	// due to rounding, however we don't want to truncate the shares or take the
-	// minimum because we want to allow for the full withdraw of shares from a
-	// delegation.
-	if shares.GT(delShares) {
+	// Depending on the share, amount can be smaller than unit amount(1stake).
+	// If the remain amount after unbonding is smaller than the minimum share,
+	// it's completely unbonded to avoid leaving dust shares.
+	tolerance, err := validator.SharesFromTokens(math.OneInt())
+	if err != nil {
+		return shares, err
+	}
+
+	if delShares.Sub(shares).LT(tolerance) {
 		shares = delShares
 	}
 

x/staking/keeper/delegation_test.go

@@ -1170,3 +1170,51 @@ func (s *KeeperTestSuite) TestSetUnbondingDelegationEntry() {
 	// unbondingID comes from a global counter -> gaps in unbondingIDs are OK as long as every unbondingID is unique
 	require.Equal(uint64(2), resUnbonding.Entries[1].UnbondingId)
 }
+
+func (s *KeeperTestSuite) TestUndelegateWithDustShare() {
+	ctx, keeper := s.ctx, s.stakingKeeper
+	require := s.Require()
+
+	addrDels, valAddrs := createValAddrs(2)
+
+	s.accountKeeper.EXPECT().AddressCodec().Return(address.NewBech32Codec("cosmos")).AnyTimes()
+
+	// construct the validators[0] & slash 1stake
+	amt := math.NewInt(100)
+	validator := testutil.NewValidator(s.T(), valAddrs[0], PKs[0])
+	validator, _ = validator.AddTokensFromDel(amt)
+	validator = validator.RemoveTokens(math.NewInt(1))
+	validator = stakingkeeper.TestingUpdateValidator(keeper, ctx, validator, true)
+
+	// first add a validators[0] to delegate too
+	bond1to1 := stakingtypes.NewDelegation(addrDels[0].String(), valAddrs[0].String(), math.LegacyNewDec(100))
+	require.NoError(keeper.SetDelegation(ctx, bond1to1))
+	resBond, err := keeper.Delegations.Get(ctx, collections.Join(addrDels[0], valAddrs[0]))
+	require.NoError(err)
+	require.Equal(bond1to1, resBond)
+
+	// second delegators[1] add a validators[0] to delegate
+	bond2to1 := stakingtypes.NewDelegation(addrDels[1].String(), valAddrs[0].String(), math.LegacyNewDec(1))
+	validator, delegatorShare := validator.AddTokensFromDel(math.NewInt(1))
+	bond2to1.Shares = delegatorShare
+	_ = stakingkeeper.TestingUpdateValidator(keeper, ctx, validator, true)
+	require.NoError(keeper.SetDelegation(ctx, bond2to1))
+	resBond, err = keeper.Delegations.Get(ctx, collections.Join(addrDels[1], valAddrs[0]))
+	require.NoError(err)
+	require.Equal(bond2to1, resBond)
+
+	// check delegation state
+	delegations, err := keeper.GetValidatorDelegations(ctx, valAddrs[0])
+	require.NoError(err)
+	require.Equal(2, len(delegations))
+
+	// undelegate all delegator[0]'s delegate
+	_, err = s.msgServer.Undelegate(ctx, stakingtypes.NewMsgUndelegate(addrDels[0].String(), valAddrs[0].String(), sdk.NewCoin(sdk.DefaultBondDenom, math.NewInt(99))))
+	require.NoError(err)
+
+	// remain only delegator[1]'s delegate
+	delegations, err = keeper.GetValidatorDelegations(ctx, valAddrs[0])
+	require.NoError(err)
+	require.Equal(1, len(delegations))
+	require.Equal(delegations[0].DelegatorAddress, addrDels[1].String())
+}