refactor(x/distribution)!: remove PreviousProposer and return early i…

…f there are no fees to distribute (#20735)

tests/integration/distribution/keeper/msg_server_test.go

@@ -216,7 +216,6 @@ func TestMsgWithdrawDelegatorReward(t *testing.T) {
 	require.NoError(t, f.distrKeeper.Params.Set(f.sdkCtx, distrtypes.DefaultParams()))
 
 	delAddr := sdk.AccAddress(PKS[1].Address())
-	valConsAddr := sdk.ConsAddress(valConsPk0.Address())
 
 	valCommission := sdk.DecCoins{
 		sdk.NewDecCoinFromDec("mytoken", math.LegacyNewDec(5).Quo(math.LegacyNewDec(4))),
@@ -325,9 +324,6 @@ func TestMsgWithdrawDelegatorReward(t *testing.T) {
 	}
 	height := f.app.LastBlockHeight()
 
-	_, err = f.distrKeeper.PreviousProposer.Get(f.sdkCtx)
-	assert.ErrorIs(t, err, collections.ErrNotFound)
-
 	for _, tc := range testCases {
 		tc := tc
 		t.Run(tc.name, func(t *testing.T) {
@@ -358,10 +354,6 @@ func TestMsgWithdrawDelegatorReward(t *testing.T) {
 				assert.Assert(t, initBalance.IsAllLTE(curBalance))
 			}
 
-			prevProposerConsAddr, err := f.distrKeeper.PreviousProposer.Get(f.sdkCtx)
-			assert.NilError(t, err)
-			assert.Assert(t, prevProposerConsAddr.Empty() == false)
-			assert.DeepEqual(t, prevProposerConsAddr, valConsAddr)
 			var previousTotalPower int64
 			for _, vote := range f.sdkCtx.CometInfo().LastCommit.Votes {
 				previousTotalPower += vote.Validator.Power

x/distribution/CHANGELOG.md

@@ -66,6 +66,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### State Machine Breaking
 
+* [#20735](https://github.com/cosmos/cosmos-sdk/pull/20735) Remove PreviousProposer from the state machine.
 * [#17657](https://github.com/cosmos/cosmos-sdk/pull/17657) Migrate community pool funds from `x/distribution` to `x/protocolpool`.
 * [#17115](https://github.com/cosmos/cosmos-sdk/pull/17115) Migrate `PreviousProposer` to collections.
 * [#18539](https://github.com/cosmos/cosmos-sdk/pull/18539) Introduce `FeePool.DecimalPool` to replace `FeePool.CommunityPool`, which temporarily holds fractional rewards until they are distributed to the community pool every 1000 blocks.

x/distribution/keeper/abci.go

@@ -6,7 +6,6 @@ import (
 	"cosmossdk.io/x/distribution/types"
 
 	"github.com/cosmos/cosmos-sdk/telemetry"
-	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
 // BeginBlocker sets the proposer for determining distribution during endblock
@@ -38,7 +37,5 @@ func (k Keeper) BeginBlocker(ctx context.Context) error {
 		}
 	}
 
-	// record the proposer for when we payout on the next block
-	consAddr := sdk.ConsAddress(ci.ProposerAddress)
-	return k.PreviousProposer.Set(ctx, consAddr)
+	return nil
 }

x/distribution/keeper/allocation.go

@@ -21,6 +21,10 @@ func (k Keeper) AllocateTokens(ctx context.Context, totalPreviousPower int64, bo
 	// (and distributed to the previous proposer)
 	feeCollector := k.authKeeper.GetModuleAccount(ctx, k.feeCollectorName)
 	feesCollectedInt := k.bankKeeper.GetAllBalances(ctx, feeCollector.GetAddress())
+	// return early if no fees to distribute
+	if feesCollectedInt.Empty() {
+		return nil
+	}
 	feesCollected := sdk.NewDecCoinsFromCoins(feesCollectedInt...)
 
 	// transfer collected fees to the distribution module account

x/distribution/keeper/genesis.go

@@ -37,19 +37,6 @@ func (k Keeper) InitGenesis(ctx context.Context, data types.GenesisState) error
 		}
 	}
 
-	var previousProposer sdk.ConsAddress
-	if data.PreviousProposer != "" {
-		var err error
-		previousProposer, err = k.stakingKeeper.ConsensusAddressCodec().StringToBytes(data.PreviousProposer)
-		if err != nil {
-			return err
-		}
-	}
-
-	if err := k.PreviousProposer.Set(ctx, previousProposer); err != nil {
-		return err
-	}
-
 	for _, rew := range data.OutstandingRewards {
 		valAddr, err := k.stakingKeeper.ValidatorAddressCodec().StringToBytes(rew.ValidatorAddress)
 		if err != nil {
@@ -177,11 +164,6 @@ func (k Keeper) ExportGenesis(ctx context.Context) (*types.GenesisState, error)
 		return nil, err
 	}
 
-	pp, err := k.PreviousProposer.Get(ctx)
-	if err != nil {
-		return nil, err
-	}
-
 	outstanding := make([]types.ValidatorOutstandingRewardsRecord, 0)
 
 	err = k.ValidatorOutstandingRewards.Walk(ctx, nil, func(addr sdk.ValAddress, rewards types.ValidatorOutstandingRewards) (stop bool, err error) {
@@ -303,9 +285,5 @@ func (k Keeper) ExportGenesis(ctx context.Context) (*types.GenesisState, error)
 		return nil, err
 	}
 
-	ppAddr, err := k.stakingKeeper.ConsensusAddressCodec().BytesToString(pp)
-	if err != nil {
-		return nil, err
-	}
-	return types.NewGenesisState(params, feePool, dwi, ppAddr, outstanding, acc, his, cur, dels, slashes), nil
+	return types.NewGenesisState(params, feePool, dwi, outstanding, acc, his, cur, dels, slashes), nil
 }

x/distribution/keeper/keeper.go

@@ -51,7 +51,6 @@ type Keeper struct {
 	ValidatorOutstandingRewards collections.Map[sdk.ValAddress, types.ValidatorOutstandingRewards]
 	// ValidatorHistoricalRewards key: valAddr+period | value: ValidatorHistoricalRewards
 	ValidatorHistoricalRewards collections.Map[collections.Pair[sdk.ValAddress, uint64], types.ValidatorHistoricalRewards]
-	PreviousProposer           collections.Item[sdk.ConsAddress]
 	// ValidatorSlashEvents key: valAddr+height+period | value: ValidatorSlashEvent
 	ValidatorSlashEvents collections.Map[collections.Triple[sdk.ValAddress, uint64, uint64], types.ValidatorSlashEvent]
 
@@ -130,7 +129,6 @@ func NewKeeper(
 			collections.PairKeyCodec(sdk.LengthPrefixedAddressKey(sdk.ValAddressKey), sdk.LEUint64Key), //nolint: staticcheck // sdk.LengthPrefixedAddressKey is needed to retain state compatibility
 			codec.CollValue[types.ValidatorHistoricalRewards](cdc),
 		),
-		PreviousProposer: collections.NewItem(sb, types.ProposerKey, "previous_proposer", collcodec.KeyToValueCodec(sdk.ConsAddressKey)),
 		ValidatorSlashEvents: collections.NewMap(
 			sb,
 			types.ValidatorSlashEventPrefix,

x/distribution/migrations/v4/migrate.go

@@ -6,46 +6,19 @@ import (
 
 	gogotypes "github.com/cosmos/gogoproto/types"
 
-	"cosmossdk.io/collections"
-	collcodec "cosmossdk.io/collections/codec"
 	"cosmossdk.io/core/appmodule"
 	"cosmossdk.io/core/store"
 
 	"github.com/cosmos/cosmos-sdk/codec"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
-var (
-	OldProposerKey = []byte{0x01}
-	NewProposerKey = collections.NewPrefix(1)
-)
+var OldProposerKey = []byte{0x01}
 
+// MigrateStore removes the last proposer from store.
 func MigrateStore(ctx context.Context, env appmodule.Environment, cdc codec.BinaryCodec) error {
 	store := env.KVStoreService.OpenKVStore(ctx)
-	bz, err := store.Get(OldProposerKey)
-	if err != nil {
-		return err
-	}
-
-	if bz == nil {
-		// previous proposer not set, nothing to do
-		return nil
-	}
-
-	addrValue := gogotypes.BytesValue{}
-	err = cdc.Unmarshal(bz, &addrValue)
-	if err != nil {
-		return err
-	}
-
-	sb := collections.NewSchemaBuilder(env.KVStoreService)
-	prevProposer := collections.NewItem(sb, NewProposerKey, "previous_proposer", collcodec.KeyToValueCodec(sdk.ConsAddressKey))
-	_, err = sb.Build()
-	if err != nil {
-		return err
-	}
-
-	return prevProposer.Set(ctx, addrValue.GetValue())
+	return store.Delete(OldProposerKey)
 }
 
 // GetPreviousProposerConsAddr returns the proposer consensus address for the

x/distribution/migrations/v4/migrate_test.go

@@ -5,8 +5,6 @@ import (
 
 	"github.com/stretchr/testify/require"
 
-	"cosmossdk.io/collections"
-	collcodec "cosmossdk.io/collections/codec"
 	"cosmossdk.io/core/log"
 	storetypes "cosmossdk.io/store/types"
 	"cosmossdk.io/x/distribution"
@@ -32,6 +30,7 @@ func TestMigration(t *testing.T) {
 	addr1 := secp256k1.GenPrivKey().PubKey().Address()
 	consAddr1 := sdk.ConsAddress(addr1)
 
+	// Set and check the previous proposer
 	err := v4.SetPreviousProposerConsAddr(ctx, storeService, cdc, consAddr1)
 	require.NoError(t, err)
 
@@ -42,13 +41,7 @@ func TestMigration(t *testing.T) {
 	err = v4.MigrateStore(ctx, env, cdc)
 	require.NoError(t, err)
 
-	sb := collections.NewSchemaBuilder(storeService)
-	prevProposer := collections.NewItem(sb, v4.NewProposerKey, "previous_proposer", collcodec.KeyToValueCodec(sdk.ConsAddressKey))
-	_, err = sb.Build()
-	require.NoError(t, err)
-
-	newAddr, err := prevProposer.Get(ctx)
-	require.NoError(t, err)
-
-	require.Equal(t, consAddr1, newAddr)
+	// Check that the previous proposer has been removed
+	_, err = v4.GetPreviousProposerConsAddr(ctx, storeService, cdc)
+	require.ErrorContains(t, err, "previous proposer not set")
 }

x/distribution/proto/cosmos/distribution/v1beta1/genesis.proto

@@ -126,9 +126,6 @@ message GenesisState {
   repeated DelegatorWithdrawInfo delegator_withdraw_infos = 3
       [(gogoproto.nullable) = false, (amino.dont_omitempty) = true];
 
-  // fee_pool defines the previous proposer at genesis.
-  string previous_proposer = 4 [(cosmos_proto.scalar) = "cosmos.AddressString"];
-
   // fee_pool defines the outstanding rewards of all validators at genesis.
   repeated ValidatorOutstandingRewardsRecord outstanding_rewards = 5
       [(gogoproto.nullable) = false, (amino.dont_omitempty) = true];
@@ -152,4 +149,6 @@ message GenesisState {
   // fee_pool defines the validator slash events at genesis.
   repeated ValidatorSlashEventRecord validator_slash_events = 10
       [(gogoproto.nullable) = false, (amino.dont_omitempty) = true];
+
+  reserved 4; // previous_proposer
 }

x/distribution/simulation/decoder.go

@@ -22,9 +22,6 @@ func NewDecodeStore(cdc codec.Codec) func(kvA, kvB kv.Pair) string {
 			cdc.MustUnmarshal(kvB.Value, &feePoolB)
 			return fmt.Sprintf("%v\n%v", feePoolA, feePoolB)
 
-		case bytes.Equal(kvA.Key[:1], types.ProposerKey):
-			return fmt.Sprintf("%v\n%v", sdk.ConsAddress(kvA.Value), sdk.ConsAddress(kvB.Value))
-
 		case bytes.Equal(kvA.Key[:1], types.ValidatorOutstandingRewardsPrefix):
 			var rewardsA, rewardsB types.ValidatorOutstandingRewards
 			cdc.MustUnmarshal(kvA.Value, &rewardsA)

x/distribution/simulation/decoder_test.go

@@ -19,9 +19,8 @@ import (
 )
 
 var (
-	delPk1    = ed25519.GenPrivKey().PubKey()
-	valAddr1  = sdk.ValAddress(delPk1.Address())
-	consAddr1 = sdk.ConsAddress(delPk1.Address().Bytes())
+	delPk1   = ed25519.GenPrivKey().PubKey()
+	valAddr1 = sdk.ValAddress(delPk1.Address())
 )
 
 func TestDecodeDistributionStore(t *testing.T) {
@@ -38,7 +37,6 @@ func TestDecodeDistributionStore(t *testing.T) {
 	kvPairs := kv.Pairs{
 		Pairs: []kv.Pair{
 			{Key: types.FeePoolKey, Value: cdc.MustMarshal(&feePool)},
-			{Key: types.ProposerKey, Value: consAddr1.Bytes()},
 			{Key: types.GetValidatorSlashEventKeyPrefix(valAddr1, 13), Value: cdc.MustMarshal(&slashEvent)},
 			{Key: []byte{0x99}, Value: []byte{0x99}},
 		},
@@ -49,7 +47,6 @@ func TestDecodeDistributionStore(t *testing.T) {
 		expectedLog string
 	}{
 		{"FeePool", fmt.Sprintf("%v\n%v", feePool, feePool)},
-		{"Proposer", fmt.Sprintf("%v\n%v", consAddr1, consAddr1)},
 		{"ValidatorSlashEvent", fmt.Sprintf("%v\n%v", slashEvent, slashEvent)},
 		{"other", ""},
 	}

x/distribution/types/genesis.go

@@ -1,15 +1,14 @@
 package types
 
 func NewGenesisState(
-	params Params, fp FeePool, dwis []DelegatorWithdrawInfo, pp string, r []ValidatorOutstandingRewardsRecord,
+	params Params, fp FeePool, dwis []DelegatorWithdrawInfo, r []ValidatorOutstandingRewardsRecord,
 	acc []ValidatorAccumulatedCommissionRecord, historical []ValidatorHistoricalRewardsRecord,
 	cur []ValidatorCurrentRewardsRecord, dels []DelegatorStartingInfoRecord, slashes []ValidatorSlashEventRecord,
 ) *GenesisState {
 	return &GenesisState{
 		Params:                          params,
 		FeePool:                         fp,
 		DelegatorWithdrawInfos:          dwis,
-		PreviousProposer:                pp,
 		OutstandingRewards:              r,
 		ValidatorAccumulatedCommissions: acc,
 		ValidatorHistoricalRewards:      historical,
@@ -25,7 +24,6 @@ func DefaultGenesisState() *GenesisState {
 		FeePool:                         InitialFeePool(),
 		Params:                          DefaultParams(),
 		DelegatorWithdrawInfos:          []DelegatorWithdrawInfo{},
-		PreviousProposer:                "",
 		OutstandingRewards:              []ValidatorOutstandingRewardsRecord{},
 		ValidatorAccumulatedCommissions: []ValidatorAccumulatedCommissionRecord{},
 		ValidatorHistoricalRewards:      []ValidatorHistoricalRewardsRecord{},