Call incentive hooks before CDPs are modified in begin blocker (#897)

* call hook before cdp changed

* test that risky cdps accrue rewards accurately

* fix typos

* clarify test comments

x/cdp/keeper/interest.go

@@ -159,6 +159,7 @@ func (k Keeper) CalculateNewInterest(ctx sdk.Context, cdp types.CDP) sdk.Coin {
 func (k Keeper) SynchronizeInterestForRiskyCDPs(ctx sdk.Context, slice sdk.Int, targetRatio sdk.Dec, collateralType string) error {
 	cdps := k.GetSliceOfCDPsByRatioAndType(ctx, slice, targetRatio, collateralType)
 	for _, cdp := range cdps {
+		k.hooks.BeforeCDPModified(ctx, cdp)
 		k.SynchronizeInterest(ctx, cdp)
 	}
 	return nil

x/incentive/keeper/cdp_test.go

@@ -0,0 +1,70 @@
+package keeper_test
+
+import (
+	"time"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	abci "github.com/tendermint/tendermint/abci/types"
+
+	cdptypes "github.com/kava-labs/kava/x/cdp/types"
+	"github.com/kava-labs/kava/x/incentive/types"
+)
+
+func (suite *KeeperTestSuite) TestRiskyCDPsAccumulateRewards() {
+	suite.SetupWithGenState()
+	initialTime := suite.ctx.BlockTime()
+
+	// Setup incentive state
+	collateralType := "bnb-a"
+	rewardsPerSecond := c(types.USDXMintingRewardDenom, 1_000_000)
+	params := types.NewParams(
+		types.RewardPeriods{types.NewRewardPeriod(true, collateralType, initialTime, initialTime.Add(4*oneYear), rewardsPerSecond)},
+		nil, // hard rewards not needed
+		nil,
+		nil, // delegator rewards not needed
+		types.Multipliers{types.NewMultiplier(types.MultiplierName("small"), 1, d("0.25")), types.NewMultiplier(types.MultiplierName("large"), 12, d("1.0"))},
+		initialTime.Add(5*oneYear),
+	)
+	suite.keeper.SetParams(suite.ctx, params)
+	suite.keeper.SetPreviousUSDXMintingAccrualTime(suite.ctx, collateralType, initialTime)
+	suite.keeper.SetUSDXMintingRewardFactor(suite.ctx, collateralType, sdk.ZeroDec())
+
+	// Setup cdp state containing one CDP
+	cdpKeeper := suite.app.GetCDPKeeper()
+	initialCollateral := c("bnb", 1_000_000_000)
+	initialPrincipal := c("usdx", 100_000_000)
+	cdpKeeper.SetPreviousAccrualTime(suite.ctx, collateralType, suite.ctx.BlockTime())
+	cdpKeeper.SetInterestFactor(suite.ctx, collateralType, sdk.OneDec())
+	// add coins to user's address // TODO move this to auth genesis setup
+	sk := suite.app.GetSupplyKeeper()
+	sk.MintCoins(suite.ctx, cdptypes.ModuleName, cs(initialCollateral))
+	sk.SendCoinsFromModuleToAccount(suite.ctx, cdptypes.ModuleName, suite.addrs[0], cs(initialCollateral))
+
+	err := cdpKeeper.AddCdp(suite.ctx, suite.addrs[0], initialCollateral, initialPrincipal, collateralType)
+	suite.Require().NoError(err)
+
+	// Skip ahead two blocks to accumulate both interest and usdx reward for the cdp
+	// Two blocks are required because the cdp begin blocker runs before incentive begin blocker.
+	// In the first begin block the cdp is synced, which triggers its claim to sync. But no global rewards have accumulated yet so the sync does nothing.
+	// Global rewards accumulate immediately after during the incentive begin blocker.
+	// Rewards are added to the cdp's claim in the next block when the cdp is synced.
+	_ = suite.app.EndBlocker(suite.ctx, abci.RequestEndBlock{})
+	suite.ctx = suite.ctx.WithBlockTime(suite.ctx.BlockTime().Add(10 * time.Minute))
+	_ = suite.app.BeginBlocker(suite.ctx, abci.RequestBeginBlock{}) // height and time in header are ignored by module begin blockers
+
+	_ = suite.app.EndBlocker(suite.ctx, abci.RequestEndBlock{})
+	suite.ctx = suite.ctx.WithBlockTime(suite.ctx.BlockTime().Add(10 * time.Minute))
+	_ = suite.app.BeginBlocker(suite.ctx, abci.RequestBeginBlock{})
+
+	// check cdp rewards
+	cdp, found := cdpKeeper.GetCdpByOwnerAndCollateralType(suite.ctx, suite.addrs[0], collateralType)
+	suite.Require().True(found)
+	// This additional sync adds the rewards accumulated at the end of the last begin block.
+	// They weren't added during the begin blocker as the incentive BB runs after the CDP BB.
+	suite.keeper.SynchronizeUSDXMintingReward(suite.ctx, cdp)
+	claim, found := suite.keeper.GetUSDXMintingClaim(suite.ctx, suite.addrs[0])
+	suite.Require().True(found)
+
+	// rewards are roughly rewardsPerSecond * secondsElapsed (10mins) * num blocks (2)
+	suite.Require().Equal(c(types.USDXMintingRewardDenom, 1_200_001_671), claim.Reward)
+}