custom inflation calculation function

app/app.go

@@ -839,7 +839,7 @@ func NewApp(
 		// earn.NewAppModule(app.earnKeeper, app.accountKeeper, app.bankKeeper),
 		// router.NewAppModule(app.routerKeeper),
 		// nil InflationCalculationFn, use SDK's default inflation function
-		mint.NewAppModule(appCodec, app.mintKeeper, app.accountKeeper, nil, mintSubspace),
+		mint.NewAppModule(appCodec, app.mintKeeper, app.accountKeeper, chaincfg.CustomInflationCalculateFn, mintSubspace),
 		// community.NewAppModule(app.communityKeeper, app.accountKeeper),
 		metrics.NewAppModule(options.TelemetryOptions),
 

chaincfg/mint.go

@@ -0,0 +1,48 @@
+package chaincfg
+
+import (
+	"github.com/cometbft/cometbft/libs/log"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	minttypes "github.com/cosmos/cosmos-sdk/x/mint/types"
+)
+
+func CustomInflationCalculateFn(ctx sdk.Context, minter minttypes.Minter, params minttypes.Params, bondedRatio sdk.Dec, _ sdk.Dec) sdk.Dec {
+	logger := ctx.Logger()
+	if logger == nil {
+		panic("logger is nil")
+	}
+	return customInflationCalculateFn(logger, minter, params, bondedRatio)
+}
+
+func customInflationCalculateFn(logger log.Logger, minter minttypes.Minter, params minttypes.Params, bondedRatio sdk.Dec) sdk.Dec {
+	// The target annual inflation rate is recalculated for each previsions cycle. The
+	// inflation is also subject to a rate change (positive or negative) depending on
+	// the distance from the desired ratio (67%). The maximum rate change possible is
+	// defined to be 13% per year, however the annual inflation is capped as between
+	// 7% and 20%.
+
+	// (1 - bondedRatio/GoalBonded) * InflationRateChange
+	inflationRateChangePerYear := sdk.OneDec().
+		Sub(bondedRatio.Quo(params.GoalBonded)).
+		Mul(params.InflationRateChange)
+	inflationRateChange := inflationRateChangePerYear.Quo(sdk.NewDec(int64(params.BlocksPerYear)))
+
+	// adjust the new annual inflation for this next cycle
+	inflation := minter.Inflation.Add(inflationRateChange) // note inflationRateChange may be negative
+	if inflation.GT(params.InflationMax) {
+		inflation = params.InflationMax
+	}
+	if inflation.LT(params.InflationMin) {
+		inflation = params.InflationMin
+	}
+
+	logger.Info(
+		"calculated new annual inflation",
+		"bondedRatio", bondedRatio,
+		"inflation", inflation,
+		"params", params,
+		"minter", minter,
+	)
+	return inflation
+}