fix(toDecimal): preserve negative sign for leading zeros

Change #690 fixed the general case of formatting negative unit values, but was one remaining case where formatting was still incorrect: when the first unit is -0, the resulting string didn't include the leading negative sign. This change identifies that exact case (negative value, leading zero) and pads the resulting string with a leading negative sign. Fixes #692
dinerojs · Dec 10, 2022 · 5e78040 · 5e78040
1 parent c5b9173
commit 5e78040
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Showing 2 changed files with 47 additions and 2 deletions.
diff --git a/packages/core/src/api/toDecimal.ts b/packages/core/src/api/toDecimal.ts
@@ -1,7 +1,14 @@
 import { NON_DECIMAL_CURRENCY_MESSAGE } from '../checks';
 import { assert } from '../helpers';
 import type { Calculator, Dinero, Formatter, Transformer } from '../types';
-import { absolute, computeBase, equal, isArray } from '../utils';
+import {
+  absolute,
+  computeBase,
+  equal,
+  isArray,
+  lessThan,
+  sign,
+} from '../utils';
 
 import { toUnits } from './toUnits';
 
@@ -14,6 +21,8 @@ export function toDecimal<TAmount, TOutput>(calculator: Calculator<TAmount>) {
   const toUnitsFn = toUnits<TAmount, readonly TAmount[]>(calculator);
   const computeBaseFn = computeBase(calculator);
   const equalFn = equal(calculator);
+  const lessThanFn = lessThan(calculator);
+  const signFn = sign(calculator);
 
   return function toDecimalFn(
     ...[dineroObject, transformer]: ToDecimalParams<TAmount, TOutput>
@@ -32,9 +41,15 @@ export function toDecimal<TAmount, TOutput>(calculator: Calculator<TAmount>) {
     assert(isDecimal, NON_DECIMAL_CURRENCY_MESSAGE);
 
     const units = toUnitsFn(dineroObject);
+    const isNegative = units.some((unit) => lessThanFn(signFn(unit), zero));
 
     const getDecimalFn = getDecimal(calculator, dineroObject.formatter);
-    const value = getDecimalFn(units, scale);
+    const decimalValue = getDecimalFn(units, scale);
+
+    // A leading negative zero is a special case because the toString
+    // formatter (generally String) won't preserve its negative sign.
+    const value =
+      isNegative && equalFn(units[0], zero) ? `-${decimalValue}` : decimalValue;
 
     if (!transformer) {
       return value;

diff --git a/packages/dinero.js/src/api/__tests__/toDecimal.test.ts b/packages/dinero.js/src/api/__tests__/toDecimal.test.ts
@@ -45,6 +45,16 @@ describe('toDecimal', () => {
 
         expect(toDecimal(d)).toEqual('-10.50');
       });
+      it('returns the negative amount with a leading zero in decimal format', () => {
+        const d = dinero({ amount: -1, currency: USD });
+
+        expect(toDecimal(d)).toEqual('-0.01');
+      });
+      it('returns negative zero amount as a positive value in decimal format', () => {
+        const d = dinero({ amount: -0, currency: USD });
+
+        expect(toDecimal(d)).toEqual('0.00');
+      });
       it('uses a custom transformer', () => {
         const d = dinero({ amount: 1050, currency: USD });
 
@@ -118,6 +128,16 @@ describe('toDecimal', () => {
 
         expect(toDecimal(d)).toEqual('-10.50');
       });
+      it('returns the negative amount with a leading zero in decimal format', () => {
+        const d = dinero({ amount: -1n, currency: bigintUSD });
+
+        expect(toDecimal(d)).toEqual('-0.01');
+      });
+      it('returns negative zero amount as a positive value in decimal format', () => {
+        const d = dinero({ amount: -0n, currency: bigintUSD });
+
+        expect(toDecimal(d)).toEqual('0.00');
+      });
       it('uses a custom transformer', () => {
         const d = dinero({ amount: 1050n, currency: bigintUSD });
 
@@ -198,6 +218,16 @@ describe('toDecimal', () => {
 
         expect(toDecimal(d)).toEqual('-10.05');
       });
+      it('returns the negative amount with a leading zero in decimal format', () => {
+        const d = dinero({ amount: new Big(-1), currency: bigjsUSD });
+
+        expect(toDecimal(d)).toEqual('-0.01');
+      });
+      it('returns negative zero amount as a positive value in decimal format', () => {
+        const d = dinero({ amount: new Big(-0), currency: bigjsUSD });
+
+        expect(toDecimal(d)).toEqual('0.00');
+      });
       it('uses a custom transformer', () => {
         const d = dinero({ amount: new Big(1050), currency: bigjsUSD });