feat(mint): add optional inflation bounds params

docs/proto/mint.md

@@ -74,6 +74,8 @@ Params defines the parameters for the mint module.
 | `mint_denom` | [string](#string) |  | Denomination of the coin to be minted. |
 | `inflation_coef` | [string](#string) |  | Annual inflation coefficient, influencing the inflation rate based on the bonded ratio. Values range from 0 to 1, with higher values indicating higher inflation. |
 | `blocks_per_year` | [uint64](#uint64) |  | Estimated number of blocks per year. |
+| `inflation_max` | [string](#string) |  | Maximum annual inflation rate. |
+| `inflation_min` | [string](#string) |  | Minimum annual inflation rate. |
 
  [//]: # (end messages)
 

proto/mint/v1beta1/mint.proto

@@ -37,6 +37,21 @@ message Params {
     (gogoproto.customtype) = "cosmossdk.io/math.LegacyDec",
     (gogoproto.nullable) = false
   ];
+
   // Estimated number of blocks per year.
   uint64 blocks_per_year = 3;
+
+  // Maximum annual inflation rate.
+  string inflation_max = 4 [
+    (cosmos_proto.scalar) = "cosmos.Dec",
+    (gogoproto.customtype) = "cosmossdk.io/math.LegacyDec",
+    (gogoproto.nullable) = true
+  ];
+
+  // Minimum annual inflation rate.
+  string inflation_min = 5 [
+    (cosmos_proto.scalar) = "cosmos.Dec",
+    (gogoproto.customtype) = "cosmossdk.io/math.LegacyDec",
+    (gogoproto.nullable) = true
+  ];
 }

x/mint/abci.go

@@ -28,7 +28,7 @@ func BeginBlocker(ctx context.Context, k keeper.Keeper) error {
 		return err
 	}
 
-	minter, err := types.NewMinterWithInflationCoef(params.InflationCoef, bondedRatio, totalSupply)
+	minter, err := types.NewMinterWithInflationCoef(params.InflationCoef, bondedRatio, params.InflationMin, params.InflationMax, totalSupply)
 	if err != nil {
 		panic(err)
 	}

x/mint/types/minter.go

@@ -26,8 +26,8 @@ func NewMinterWithInitialInflation(inflation math.LegacyDec) Minter {
 }
 
 // NewMinterWithInflationCoef returns a new Minter with updated inflation and annual provisions values.
-func NewMinterWithInflationCoef(inflationCoef math.LegacyDec, bondedRatio math.LegacyDec, totalSupply math.Int) (Minter, error) {
-	inflationRate, err := inflationRate(inflationCoef, bondedRatio)
+func NewMinterWithInflationCoef(inflationCoef, bondedRatio math.LegacyDec, minBound, maxBound *math.LegacyDec, totalSupply math.Int) (Minter, error) {
+	inflationRate, err := inflationRate(inflationCoef, bondedRatio, minBound, maxBound)
 	if err != nil {
 		return Minter{}, err
 	}
@@ -55,12 +55,20 @@ func (m Minter) Validate() error {
 
 // inflationRate returns the inflation rate computed from the current bonded ratio
 // and the inflation parameter.
-func inflationRate(inflationCoef math.LegacyDec, bondedRatio math.LegacyDec) (math.LegacyDec, error) {
+func inflationRate(inflationCoef, bondedRatio math.LegacyDec, minBound, maxBound *math.LegacyDec) (math.LegacyDec, error) {
 	if bondedRatio.IsZero() {
 		return math.LegacyZeroDec(), ErrBondedRatioIsZero
 	}
 
-	return inflationCoef.Quo(bondedRatio), nil
+	rate := inflationCoef.Quo(bondedRatio)
+	if minBound != nil {
+		rate = math.LegacyMaxDec(rate, *minBound)
+	}
+	if maxBound != nil {
+		rate = math.LegacyMinDec(rate, *maxBound)
+	}
+
+	return rate, nil
 }
 
 // BlockProvision returns the provisions for a block based on the annual

x/mint/types/minter_test.go

@@ -12,11 +12,16 @@ import (
 )
 
 func TestNextInflation(t *testing.T) {
+	infMin := math.LegacyNewDecWithPrec(7, 2)
+	infMax := math.LegacyNewDecWithPrec(10, 2)
+
 	Convey("Given a test cases", t, func() {
 		cases := []struct {
 			name                     string
 			inflationRatio           math.LegacyDec
 			bondedRatio              math.LegacyDec
+			minBound                 *math.LegacyDec
+			maxBound                 *math.LegacyDec
 			totalSupply              math.Int
 			expectedInflation        math.LegacyDec
 			expectedAnnualProvisions math.LegacyDec
@@ -26,6 +31,8 @@ func TestNextInflation(t *testing.T) {
 				name:                     "inflation ratio is 0",
 				inflationRatio:           math.LegacyNewDec(0),
 				bondedRatio:              math.LegacyNewDecWithPrec(20, 2),
+				minBound:                 nil,
+				maxBound:                 nil,
 				totalSupply:              math.NewInt(1000),
 				expectedInflation:        math.LegacyNewDec(0),
 				expectedAnnualProvisions: math.LegacyNewDec(0),
@@ -34,21 +41,47 @@ func TestNextInflation(t *testing.T) {
 				name:                     "inflation ratio is 0.03",
 				inflationRatio:           math.LegacyNewDecWithPrec(3, 2),
 				bondedRatio:              math.LegacyNewDecWithPrec(2, 1),
+				minBound:                 nil,
+				maxBound:                 nil,
 				totalSupply:              math.NewInt(1000),
 				expectedInflation:        math.LegacyNewDecWithPrec(15, 2),
 				expectedAnnualProvisions: math.LegacyNewDec(150),
 			},
+			{
+				name:                     "inflation max is 0.1",
+				inflationRatio:           math.LegacyNewDecWithPrec(3, 2),
+				bondedRatio:              math.LegacyNewDecWithPrec(2, 1),
+				minBound:                 nil,
+				maxBound:                 &infMax,
+				totalSupply:              math.NewInt(1000),
+				expectedInflation:        math.LegacyNewDecWithPrec(10, 2),
+				expectedAnnualProvisions: math.LegacyNewDec(100),
+			},
+			{
+				name:                     "inflation min is 0.07",
+				inflationRatio:           math.LegacyNewDecWithPrec(3, 2),
+				bondedRatio:              math.LegacyNewDecWithPrec(7, 1),
+				minBound:                 &infMin,
+				maxBound:                 &infMax,
+				totalSupply:              math.NewInt(1000),
+				expectedInflation:        math.LegacyNewDecWithPrec(7, 2),
+				expectedAnnualProvisions: math.LegacyNewDec(70),
+			},
 			{
 				name:           "bonded ratio is 0",
 				inflationRatio: math.LegacyNewDecWithPrec(3, 2),
 				bondedRatio:    math.LegacyNewDec(0),
+				minBound:       nil,
+				maxBound:       nil,
 				totalSupply:    math.NewInt(1000),
 				expectedErr:    fmt.Errorf("bonded ratio is zero"),
 			},
 			{
 				name:           "negative inflation ratio",
 				inflationRatio: math.LegacyNewDecWithPrec(3, 2),
 				bondedRatio:    math.LegacyNewDecWithPrec(-2, 1),
+				minBound:       nil,
+				maxBound:       nil,
 				totalSupply:    math.NewInt(1000),
 				expectedErr:    fmt.Errorf("mint parameter Inflation should be positive, is -0.150000000000000000"),
 			},
@@ -58,7 +91,7 @@ func TestNextInflation(t *testing.T) {
 			Convey(
 				fmt.Sprintf("Given test case #%d: %v", nc, tc.name), func() {
 					Convey("when calling NewMinterWithInflationCoef function", func() {
-						minter, err := NewMinterWithInflationCoef(tc.inflationRatio, tc.bondedRatio, tc.totalSupply)
+						minter, err := NewMinterWithInflationCoef(tc.inflationRatio, tc.bondedRatio, tc.minBound, tc.maxBound, tc.totalSupply)
 						if tc.expectedErr != nil {
 							Convey("then an error should occur", func() {
 								So(err, ShouldNotBeNil)
@@ -109,7 +142,7 @@ func BenchmarkNextInflation(b *testing.B) {
 
 	// run the NextInflationRate function b.N times
 	for n := 0; n < b.N; n++ {
-		_, err := NewMinterWithInflationCoef(params.InflationCoef, bondedRatio, totalSupply)
+		_, err := NewMinterWithInflationCoef(params.InflationCoef, bondedRatio, nil, nil, totalSupply)
 		if err != nil {
 			panic(err)
 		}