feat: add coins burned to slash event (#9458)

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## Description

Adds the amount of coins slashed from the validator to the `Slash` event. Additionally, before this PR, the jail/slash events were emitted **BEFORE** the slash/jail functions were even ran, which could result in a false positive event if an error occurred in these functions. ~~These events were moved to the end of the functions that implement the logic for them instead.~~ This PR moves the events to be emitted after the logic is executed. 

Closes: #9138 

<!-- Add a description of the changes that this PR introduces and the files that
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- +Add `amount_slashed` to slash event
- +Slash now returns the amount of tokens burned
- +Events moved to be emitted after the logic is executed
- +Add test to test the slash return amount
~~- +Add EventType `Jail` to separate it from the `Slash` event~~
~~- +Move slash/jail events into the functions that execute the logic for it~~
~~- -Remove `Reason` attribute from slash event (didn't appear to be consistent with what was happening in code)~~

### 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...

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

- [x] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title - @ryanchristo 
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [x] reviewed state machine logic - not applicable
- [x] reviewed API design and naming - @ryanchristo 
- [x] reviewed documentation is accurate - @ryanchristo 
- [x] reviewed tests and test coverage - @ryanchristo 
- [ ] manually tested (if applicable)

CHANGELOG.md

@@ -48,6 +48,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * [\#9427](https://github.com/cosmos/cosmos-sdk/pull/9427) Move simapp `FundAccount` and `FundModuleAccount` to `x/bank/testutil`
 * (client/tx) [\#9421](https://github.com/cosmos/cosmos-sdk/pull/9421/) `BuildUnsignedTx`, `BuildSimTx`, `PrintUnsignedStdTx` functions are moved to
   the Tx Factory as methods.
+* (x/slashing) [\#9458](https://github.com/cosmos/cosmos-sdk/pull/9458) Coins burned from slashing is now returned from Slash function and included in Slash event.
 * [\#9246](https://github.com/cosmos/cosmos-sdk/pull/9246) The `New` method for the network package now returns an error.
 * (codec) [\#9521](https://github.com/cosmos/cosmos-sdk/pull/9521) Removed deprecated `clientCtx.JSONCodec` from `client.Context`.
 * (codec) [\#9521](https://github.com/cosmos/cosmos-sdk/pull/9521) Rename `EncodingConfig.Marshaler` to `Codec`.

x/distribution/types/expected_keepers.go

@@ -47,7 +47,7 @@ type StakingKeeper interface {
 	ValidatorByConsAddr(sdk.Context, sdk.ConsAddress) stakingtypes.ValidatorI // get a particular validator by consensus address
 
 	// slash the validator and delegators of the validator, specifying offence height, offence power, and slash fraction
-	Slash(sdk.Context, sdk.ConsAddress, int64, int64, sdk.Dec)
+	Slash(sdk.Context, sdk.ConsAddress, int64, int64, sdk.Dec) sdk.Int
 	Jail(sdk.Context, sdk.ConsAddress)   // jail a validator
 	Unjail(sdk.Context, sdk.ConsAddress) // unjail a validator
 

x/slashing/keeper/infractions.go

@@ -84,16 +84,17 @@ func (k Keeper) HandleValidatorSignature(ctx sdk.Context, addr cryptotypes.Addre
 			// That's fine since this is just used to filter unbonding delegations & redelegations.
 			distributionHeight := height - sdk.ValidatorUpdateDelay - 1
 
+			coinsBurned := k.sk.Slash(ctx, consAddr, distributionHeight, power, k.SlashFractionDowntime(ctx))
 			ctx.EventManager().EmitEvent(
 				sdk.NewEvent(
 					types.EventTypeSlash,
 					sdk.NewAttribute(types.AttributeKeyAddress, consAddr.String()),
 					sdk.NewAttribute(types.AttributeKeyPower, fmt.Sprintf("%d", power)),
 					sdk.NewAttribute(types.AttributeKeyReason, types.AttributeValueMissingSignature),
 					sdk.NewAttribute(types.AttributeKeyJailed, consAddr.String()),
+					sdk.NewAttribute(types.AttributeKeyBurnedCoins, coinsBurned.String()),
 				),
 			)
-			k.sk.Slash(ctx, consAddr, distributionHeight, power, k.SlashFractionDowntime(ctx))
 			k.sk.Jail(ctx, consAddr)
 
 			signInfo.JailedUntil = ctx.BlockHeader().Time.Add(k.DowntimeJailDuration(ctx))

x/slashing/keeper/keeper.go

@@ -65,29 +65,28 @@ func (k Keeper) GetPubkey(ctx sdk.Context, a cryptotypes.Address) (cryptotypes.P
 // Slash attempts to slash a validator. The slash is delegated to the staking
 // module to make the necessary validator changes.
 func (k Keeper) Slash(ctx sdk.Context, consAddr sdk.ConsAddress, fraction sdk.Dec, power, distributionHeight int64) {
+	coinsBurned := k.sk.Slash(ctx, consAddr, distributionHeight, power, fraction)
 	ctx.EventManager().EmitEvent(
 		sdk.NewEvent(
 			types.EventTypeSlash,
 			sdk.NewAttribute(types.AttributeKeyAddress, consAddr.String()),
 			sdk.NewAttribute(types.AttributeKeyPower, fmt.Sprintf("%d", power)),
 			sdk.NewAttribute(types.AttributeKeyReason, types.AttributeValueDoubleSign),
+			sdk.NewAttribute(types.AttributeKeyBurnedCoins, coinsBurned.String()),
 		),
 	)
-
-	k.sk.Slash(ctx, consAddr, distributionHeight, power, fraction)
 }
 
 // Jail attempts to jail a validator. The slash is delegated to the staking module
 // to make the necessary validator changes.
 func (k Keeper) Jail(ctx sdk.Context, consAddr sdk.ConsAddress) {
+	k.sk.Jail(ctx, consAddr)
 	ctx.EventManager().EmitEvent(
 		sdk.NewEvent(
 			types.EventTypeSlash,
 			sdk.NewAttribute(types.AttributeKeyJailed, consAddr.String()),
 		),
 	)
-
-	k.sk.Jail(ctx, consAddr)
 }
 
 func (k Keeper) deleteAddrPubkeyRelation(ctx sdk.Context, addr cryptotypes.Address) {

x/slashing/spec/06_events.md

@@ -2,9 +2,9 @@
 order: 6
 -->
 
-# Tags
+# Events
 
-The slashing module emits the following events/tags:
+The slashing module emits the following events:
 
 ## MsgServer
 
@@ -25,6 +25,7 @@ The slashing module emits the following events/tags:
 | slash | power         | {validatorPower}            |
 | slash | reason        | {slashReason}               |
 | slash | jailed [0]    | {validatorConsensusAddress} |
+| slash | burned coins  | {sdk.Int}                   |
 
 - [0] Only included if the validator is jailed.
 

x/slashing/types/events.go

@@ -11,6 +11,7 @@ const (
 	AttributeKeyReason       = "reason"
 	AttributeKeyJailed       = "jailed"
 	AttributeKeyMissedBlocks = "missed_blocks"
+	AttributeKeyBurnedCoins  = "burned_coins"
 
 	AttributeValueDoubleSign       = "double_sign"
 	AttributeValueMissingSignature = "missing_signature"

x/slashing/types/expected_keepers.go

@@ -42,7 +42,7 @@ type StakingKeeper interface {
 	ValidatorByConsAddr(sdk.Context, sdk.ConsAddress) stakingtypes.ValidatorI // get a particular validator by consensus address
 
 	// slash the validator and delegators of the validator, specifying offence height, offence power, and slash fraction
-	Slash(sdk.Context, sdk.ConsAddress, int64, int64, sdk.Dec)
+	Slash(sdk.Context, sdk.ConsAddress, int64, int64, sdk.Dec) sdk.Int
 	Jail(sdk.Context, sdk.ConsAddress)   // jail a validator
 	Unjail(sdk.Context, sdk.ConsAddress) // unjail a validator
 

x/staking/keeper/slash.go

@@ -21,7 +21,7 @@ import (
 // CONTRACT:
 //    Infraction was committed at the current height or at a past height,
 //    not at a height in the future
-func (k Keeper) Slash(ctx sdk.Context, consAddr sdk.ConsAddress, infractionHeight int64, power int64, slashFactor sdk.Dec) {
+func (k Keeper) Slash(ctx sdk.Context, consAddr sdk.ConsAddress, infractionHeight int64, power int64, slashFactor sdk.Dec) sdk.Int {
 	logger := k.Logger(ctx)
 
 	if slashFactor.IsNegative() {
@@ -45,7 +45,7 @@ func (k Keeper) Slash(ctx sdk.Context, consAddr sdk.ConsAddress, infractionHeigh
 			"WARNING: ignored attempt to slash a nonexistent validator; we recommend you investigate immediately",
 			"validator", consAddr.String(),
 		)
-		return
+		return sdk.NewInt(0)
 	}
 
 	// should not be slashing an unbonded validator
@@ -140,6 +140,7 @@ func (k Keeper) Slash(ctx sdk.Context, consAddr sdk.ConsAddress, infractionHeigh
 		"slash_factor", slashFactor.String(),
 		"burned", tokensToBurn,
 	)
+	return tokensToBurn
 }
 
 // jail a validator

x/staking/keeper/slash_test.go

@@ -605,3 +605,16 @@ func TestSlashBoth(t *testing.T) {
 	// power not decreased, all stake was bonded since
 	require.Equal(t, int64(10), validator.GetConsensusPower(app.StakingKeeper.PowerReduction(ctx)))
 }
+
+func TestSlashAmount(t *testing.T) {
+	app, ctx, _, _ := bootstrapSlashTest(t, 10)
+	consAddr := sdk.ConsAddress(PKs[0].Address())
+	fraction := sdk.NewDecWithPrec(5, 1)
+	burnedCoins := app.StakingKeeper.Slash(ctx, consAddr, ctx.BlockHeight(), 10, fraction)
+	require.True(t, burnedCoins.GT(sdk.ZeroInt()))
+
+	// test the case where the validator was not found, which should return no coins
+	_, addrVals := generateAddresses(app, ctx, 100)
+	noBurned := app.StakingKeeper.Slash(ctx, sdk.ConsAddress(addrVals[0]), ctx.BlockHeight(), 10, fraction)
+	require.True(t, sdk.NewInt(0).Equal(noBurned))
+}

x/staking/types/expected_keepers.go

@@ -59,7 +59,7 @@ type ValidatorSet interface {
 	StakingTokenSupply(sdk.Context) sdk.Int                      // total staking token supply
 
 	// slash the validator and delegators of the validator, specifying offence height, offence power, and slash fraction
-	Slash(sdk.Context, sdk.ConsAddress, int64, int64, sdk.Dec)
+	Slash(sdk.Context, sdk.ConsAddress, int64, int64, sdk.Dec) sdk.Int
 	Jail(sdk.Context, sdk.ConsAddress)   // jail a validator
 	Unjail(sdk.Context, sdk.ConsAddress) // unjail a validator