fix: math: add LegacyNewDecFromStr fuzzers + remove unnecessary error wrapping (#14252)

math/dec.go

@@ -143,19 +143,15 @@ func LegacyNewDecFromIntWithPrec(i Int, prec int64) LegacyDec {
 //
 // CONTRACT - This function does not mutate the input str.
 func LegacyNewDecFromStr(str string) (LegacyDec, error) {
-	if len(str) == 0 {
-		return LegacyDec{}, fmt.Errorf("%s: %w", str, ErrLegacyEmptyDecimalStr)
-	}
-
 	// first extract any negative symbol
 	neg := false
-	if str[0] == '-' {
+	if len(str) > 0 && str[0] == '-' {
 		neg = true
 		str = str[1:]
 	}
 
 	if len(str) == 0 {
-		return LegacyDec{}, fmt.Errorf("%s: %w", str, ErrLegacyEmptyDecimalStr)
+		return LegacyDec{}, ErrLegacyEmptyDecimalStr
 	}
 
 	strs := strings.Split(str, ".")

math/fuzz_test.go

@@ -0,0 +1,30 @@
+package math
+
+import (
+	"testing"
+)
+
+func FuzzLegacyNewDecFromStr(f *testing.F) {
+	if testing.Short() {
+		f.Skip("running in -short mode")
+	}
+
+	f.Add("-123.456")
+	f.Add("123.456789")
+	f.Add("123456789")
+	f.Add("0.12123456789")
+	f.Add("-12123456789")
+
+	f.Fuzz(func(t *testing.T, input string) {
+		dec, err := LegacyNewDecFromStr(input)
+		if err != nil && !dec.IsNil() {
+			t.Fatalf("Inconsistency: dec.notNil=%v yet err=%v", dec, err)
+		}
+	})
+}
+
+func TestDecNegativePrecision(t *testing.T) {
+	t.Skip("https://github.com/cosmos/cosmos-sdk/issues/14004 is not yet addressed")
+
+	LegacyNewDecWithPrec(10, -1)
+}