refactor(x/mint): initialize inflation decimals once (backport #2407) (…

…#2513)

This is an automatic backport of pull request #2407 done by
[Mergify](https://mergify.com).


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Co-authored-by: Rootul P <[email protected]>

x/mint/types/constants.go

@@ -22,14 +22,20 @@ const (
 	TargetInflationRate = 0.015
 )
 
+var (
+	initialInflationRateAsDec = sdk.NewDecWithPrec(InitialInflationRate*1000, 3)
+	disinflationRateAsDec     = sdk.NewDecWithPrec(DisinflationRate*1000, 3)
+	targetInflationRateAsDec  = sdk.NewDecWithPrec(TargetInflationRate*1000, 3)
+)
+
 func InitialInflationRateAsDec() sdk.Dec {
-	return sdk.NewDecWithPrec(InitialInflationRate*1000, 3)
+	return initialInflationRateAsDec
 }
 
 func DisinflationRateAsDec() sdk.Dec {
-	return sdk.NewDecWithPrec(DisinflationRate*1000, 3)
+	return disinflationRateAsDec
 }
 
 func TargetInflationRateAsDec() sdk.Dec {
-	return sdk.NewDecWithPrec(TargetInflationRate*1000, 3)
+	return targetInflationRateAsDec
 }

x/mint/types/minter.go

@@ -20,9 +20,8 @@ func NewMinter(inflationRate sdk.Dec, annualProvisions sdk.Dec, bondDenom string
 
 // DefaultMinter returns a Minter object with default values.
 func DefaultMinter() Minter {
-	inflationRate := InitialInflationRateAsDec()
 	annualProvisions := sdk.NewDec(0)
-	return NewMinter(inflationRate, annualProvisions, DefaultBondDenom)
+	return NewMinter(InitialInflationRateAsDec(), annualProvisions, DefaultBondDenom)
 }
 
 // Validate returns an error if the minter is invalid.
@@ -44,13 +43,10 @@ func (m Minter) Validate() error {
 // decrease every year according to the schedule specified in the README.
 func (m Minter) CalculateInflationRate(ctx sdk.Context, genesis time.Time) sdk.Dec {
 	years := yearsSinceGenesis(genesis, ctx.BlockTime())
-	initialInflationRate := InitialInflationRateAsDec()
-	disinflationRate := DisinflationRateAsDec()
-	inflationRate := initialInflationRate.Mul(sdk.OneDec().Sub(disinflationRate).Power(uint64(years)))
-	targetInflationRate := TargetInflationRateAsDec()
+	inflationRate := InitialInflationRateAsDec().Mul(sdk.OneDec().Sub(DisinflationRateAsDec()).Power(uint64(years)))
 
-	if inflationRate.LT(targetInflationRate) {
-		return targetInflationRate
+	if inflationRate.LT(TargetInflationRateAsDec()) {
+		return TargetInflationRateAsDec()
 	}
 	return inflationRate
 }

x/mint/types/minter_test.go

@@ -80,9 +80,8 @@ func TestCalculateBlockProvision(t *testing.T) {
 	minter := DefaultMinter()
 	current := time.Date(2023, 1, 2, 0, 0, 0, 0, time.UTC)
 	blockInterval := 15 * time.Second
-	initialInflationRate := InitialInflationRateAsDec()
-	totalSupply := sdk.NewDec(1_000_000_000_000)              // 1 trillion utia
-	annualProvisions := totalSupply.Mul(initialInflationRate) // 80 billion utia
+	totalSupply := sdk.NewDec(1_000_000_000_000)                     // 1 trillion utia
+	annualProvisions := totalSupply.Mul(InitialInflationRateAsDec()) // 80 billion utia
 
 	type testCase struct {
 		name             string
@@ -138,9 +137,8 @@ func TestCalculateBlockProvisionError(t *testing.T) {
 	oneYear := time.Duration(NanosecondsPerYear)
 	end := current.Add(oneYear)
 
-	initialInflationRate := InitialInflationRateAsDec()
-	totalSupply := sdk.NewDec(1_000_000_000_000)              // 1 trillion utia
-	annualProvisions := totalSupply.Mul(initialInflationRate) // 80 billion utia
+	totalSupply := sdk.NewDec(1_000_000_000_000)                     // 1 trillion utia
+	annualProvisions := totalSupply.Mul(InitialInflationRateAsDec()) // 80 billion utia
 	minter.AnnualProvisions = annualProvisions
 	totalBlockProvisions := sdk.NewDec(0)
 	for current.Before(end) {