revert: Turn staking power reduction into an on-chain param (#9495)

<!--
The default pull request template is for types feat, fix, or refactor.
For other templates, add one of the following parameters to the url:
- template=docs.md
- template=other.md
-->

## Description

Closes: #9447

This PR partially reverts #8505. Namely:
- it removes PowerReduction as a staking on-chain param
- however, it keeps #8505's API changes regarding adding a `powerReduction` function argument to staking functions. This allows us to rely less on global variables in said functions.

<!-- Add a description of the changes that this PR introduces and the files that
are the most critical to review. -->

---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

CHANGELOG.md

@@ -86,6 +86,7 @@ if input key is empty, or input data contains empty key.
 * (x/gov) [\#8473](https://github.com/cosmos/cosmos-sdk/pull/8473) On genesis init, if the gov module account balance, coming from bank module state, does not match the one in gov module state, the initialization will panic.
 * (x/distribution) [\#8473](https://github.com/cosmos/cosmos-sdk/pull/8473) On genesis init, if the distribution module account balance, coming from bank module state, does not match the one in distribution module state, the initialization will panic.
 * (client/keys) [\#8500](https://github.com/cosmos/cosmos-sdk/pull/8500) `InfoImporter` interface is removed from legacy keybase.
+* (x/staking) [\#8505](https://github.com/cosmos/cosmos-sdk/pull/8505) `sdk.PowerReduction` has been renamed to `sdk.DefaultPowerReduction`, and most staking functions relying on power reduction take a new function argument, instead of relying on that global variable.
 * [\#8629](https://github.com/cosmos/cosmos-sdk/pull/8629) Deprecated `SetFullFundraiserPath` from `Config` in favor of `SetPurpose` and `SetCoinType`.
 * (x/upgrade) [\#8673](https://github.com/cosmos/cosmos-sdk/pull/8673) Remove IBC logic from x/upgrade. Deprecates IBC fields in an Upgrade Plan. IBC upgrade logic moved to 02-client and an IBC UpgradeProposal is added.
 * (x/bank) [\#8517](https://github.com/cosmos/cosmos-sdk/pull/8517) `SupplyI` interface and `Supply` are removed and uses `sdk.Coins` for supply tracking
@@ -126,7 +127,6 @@ if input key is empty, or input data contains empty key.
 * (x/bank) [\#8656](https://github.com/cosmos/cosmos-sdk/pull/8656) balance and supply are now correctly tracked via `coin_spent`, `coin_received`, `coinbase` and `burn` events.
 * (x/bank) [\#8517](https://github.com/cosmos/cosmos-sdk/pull/8517) Supply is now stored and tracked as `sdk.Coins`
 * (store) [\#8790](https://github.com/cosmos/cosmos-sdk/pull/8790) Reduce gas costs by 10x for transient store operations.
-* (x/staking) [\#8505](https://github.com/cosmos/cosmos-sdk/pull/8505) Convert staking power reduction into an on-chain parameter rather than a hardcoded in-code variable.
 * (x/bank) [\#9051](https://github.com/cosmos/cosmos-sdk/pull/9051) Supply value is stored as `sdk.Int` rather than `string`.
 
 ### Improvements

docs/core/proto-docs.md

@@ -6394,7 +6394,6 @@ Params defines the parameters for the staking module.
 | `max_entries` | [uint32](#uint32) |  | max_entries is the max entries for either unbonding delegation or redelegation (per pair/trio). |
 | `historical_entries` | [uint32](#uint32) |  | historical_entries is the number of historical entries to persist. |
 | `bond_denom` | [string](#string) |  | bond_denom defines the bondable coin denomination. |
-| `power_reduction` | [string](#string) |  | power_reduction is the amount of staking tokens required for 1 unit of consensus-engine power |
 
 
 

proto/cosmos/staking/v1beta1/staking.proto

@@ -282,12 +282,6 @@ message Params {
   uint32 historical_entries = 4 [(gogoproto.moretags) = "yaml:\"historical_entries\""];
   // bond_denom defines the bondable coin denomination.
   string bond_denom = 5 [(gogoproto.moretags) = "yaml:\"bond_denom\""];
-  // power_reduction is the amount of staking tokens required for 1 unit of consensus-engine power
-  string power_reduction = 6 [
-    (gogoproto.moretags)   = "yaml:\"power_reduction\"",
-    (gogoproto.customtype) = "github.com/cosmos/cosmos-sdk/types.Int",
-    (gogoproto.nullable)   = false
-  ];
 }
 
 // DelegationResponse is equivalent to Delegation except that it contains a

x/staking/client/testutil/suite.go

@@ -867,13 +867,12 @@ func (s *IntegrationTestSuite) TestGetCmdQueryParams() {
 historical_entries: 10000
 max_entries: 7
 max_validators: 100
-power_reduction: "1000000"
 unbonding_time: 1814400s`,
 		},
 		{
 			"with json output",
 			[]string{fmt.Sprintf("--%s=json", tmcli.OutputFlag)},
-			`{"unbonding_time":"1814400s","max_validators":100,"max_entries":7,"historical_entries":10000,"bond_denom":"stake","power_reduction":"1000000"}`,
+			`{"unbonding_time":"1814400s","max_validators":100,"max_entries":7,"historical_entries":10000,"bond_denom":"stake"}`,
 		},
 	}
 	for _, tc := range testCases {

x/staking/handler_test.go

@@ -42,51 +42,6 @@ func bootstrapHandlerGenesisTest(t *testing.T, power int64, numAddrs int, accAmo
 	return app, ctx, addrDels, addrVals
 }
 
-func TestPowerReductionChangeValidatorSetUpdates(t *testing.T) {
-	initPower := int64(1000000)
-	app, ctx, _, valAddrs := bootstrapHandlerGenesisTest(t, initPower, 10, sdk.TokensFromConsensusPower(initPower, sdk.DefaultPowerReduction))
-	validatorAddr, validatorAddr3 := valAddrs[0], valAddrs[1]
-	tstaking := teststaking.NewHelper(t, ctx, app.StakingKeeper)
-
-	// create validator
-	tstaking.CreateValidatorWithValPower(validatorAddr, PKs[0], initPower, true)
-
-	// must end-block
-	updates, err := app.StakingKeeper.ApplyAndReturnValidatorSetUpdates(ctx)
-	require.NoError(t, err)
-	require.Equal(t, 1, len(updates))
-
-	// create a second validator keep it bonded
-	tstaking.CreateValidatorWithValPower(validatorAddr3, PKs[2], initPower, true)
-
-	// must end-block
-	updates, err = app.StakingKeeper.ApplyAndReturnValidatorSetUpdates(ctx)
-	require.NoError(t, err)
-	require.Equal(t, 1, len(updates))
-
-	// modify power reduction to 10 times bigger one
-	params := app.StakingKeeper.GetParams(ctx)
-	params.PowerReduction = sdk.DefaultPowerReduction.Mul(sdk.NewInt(10))
-	app.StakingKeeper.SetParams(ctx, params)
-
-	// validator updates for tendermint power
-	updates, err = app.StakingKeeper.ApplyAndReturnValidatorSetUpdates(ctx)
-	require.NoError(t, err)
-	require.Equal(t, 2, len(updates))
-	require.Equal(t, updates[0].Power, initPower/10)
-	require.Equal(t, updates[1].Power, initPower/10)
-
-	// power reduction back to default
-	params = app.StakingKeeper.GetParams(ctx)
-	params.PowerReduction = sdk.DefaultPowerReduction
-	app.StakingKeeper.SetParams(ctx, params)
-
-	// validator updates for tendermint power
-	updates, err = app.StakingKeeper.ApplyAndReturnValidatorSetUpdates(ctx)
-	require.NoError(t, err)
-	require.Equal(t, 2, len(updates))
-}
-
 func TestValidatorByPowerIndex(t *testing.T) {
 	initPower := int64(1000000)
 	app, ctx, _, valAddrs := bootstrapHandlerGenesisTest(t, initPower, 10, sdk.TokensFromConsensusPower(initPower, sdk.DefaultPowerReduction))

x/staking/keeper/migrations.go

@@ -17,5 +17,5 @@ func NewMigrator(keeper Keeper) Migrator {
 
 // Migrate1to2 migrates from version 1 to 2.
 func (m Migrator) Migrate1to2(ctx sdk.Context) error {
-	return v043.MigrateStore(ctx, m.keeper.storeKey, m.keeper.paramstore)
+	return v043.MigrateStore(ctx, m.keeper.storeKey)
 }

x/staking/keeper/params.go

@@ -39,11 +39,12 @@ func (k Keeper) BondDenom(ctx sdk.Context) (res string) {
 	return
 }
 
-// PowerReduction - is the amount of staking tokens required for 1 unit of consensus-engine power
-// governance can update it on a running chain
-func (k Keeper) PowerReduction(ctx sdk.Context) (res sdk.Int) {
-	k.paramstore.Get(ctx, types.KeyPowerReduction, &res)
-	return
+// PowerReduction - is the amount of staking tokens required for 1 unit of consensus-engine power.
+// Currently, this returns a global variable that the app developer can tweak.
+// TODO: we might turn this into an on-chain param:
+// https://github.com/cosmos/cosmos-sdk/issues/8365
+func (k Keeper) PowerReduction(ctx sdk.Context) sdk.Int {
+	return sdk.DefaultPowerReduction
 }
 
 // Get all parameteras as types.Params
@@ -54,7 +55,6 @@ func (k Keeper) GetParams(ctx sdk.Context) types.Params {
 		k.MaxEntries(ctx),
 		k.HistoricalEntries(ctx),
 		k.BondDenom(ctx),
-		k.PowerReduction(ctx),
 	)
 }
 

x/staking/keeper/power_reduction_test.go

@@ -1,22 +1,9 @@
 package keeper_test
 
 import (
-	"math/big"
-
 	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
-func (suite *KeeperTestSuite) TestPowerReductionChange() {
-	// modify power reduction
-	newPowerReduction := sdk.NewIntFromBigInt(new(big.Int).Exp(big.NewInt(10), big.NewInt(12), nil))
-	params := suite.app.StakingKeeper.GetParams(suite.ctx)
-	params.PowerReduction = newPowerReduction
-	suite.app.StakingKeeper.SetParams(suite.ctx, params)
-
-	// check power reduction change
-	suite.Require().Equal(newPowerReduction, suite.app.StakingKeeper.PowerReduction(suite.ctx))
-}
-
 func (suite *KeeperTestSuite) TestTokensToConsensusPower() {
 	suite.Require().Equal(int64(0), suite.app.StakingKeeper.TokensToConsensusPower(suite.ctx, sdk.DefaultPowerReduction.Sub(sdk.NewInt(1))))
 	suite.Require().Equal(int64(1), suite.app.StakingKeeper.TokensToConsensusPower(suite.ctx, sdk.DefaultPowerReduction))

x/staking/keeper/val_state_change.go

@@ -112,7 +112,7 @@ func (k Keeper) BlockValidatorUpdates(ctx sdk.Context) []abci.ValidatorUpdate {
 func (k Keeper) ApplyAndReturnValidatorSetUpdates(ctx sdk.Context) (updates []abci.ValidatorUpdate, err error) {
 	params := k.GetParams(ctx)
 	maxValidators := params.MaxValidators
-	powerReduction := params.PowerReduction
+	powerReduction := k.PowerReduction(ctx)
 	totalPower := sdk.ZeroInt()
 	amtFromBondedToNotBonded, amtFromNotBondedToBonded := sdk.ZeroInt(), sdk.ZeroInt()