fix: keep the source of numbers that overflow to Infinity

src/schema/core/float.ts

@@ -13,7 +13,7 @@ export const floatNaN: ScalarTag = {
       : str[0] === '-'
         ? Number.NEGATIVE_INFINITY
         : Number.POSITIVE_INFINITY,
-  stringify: stringifyNumber
+  stringify: node => stringifyNumber(node)
 }
 
 export const floatExp: ScalarTag = {
@@ -41,5 +41,5 @@ export const float: ScalarTag = {
       node.minFractionDigits = str.length - dot - 1
     return node
   },
-  stringify: stringifyNumber
+  stringify: node => stringifyNumber(node)
 }

src/schema/core/int.ts

@@ -35,7 +35,7 @@ export const int: ScalarTag = {
   tag: 'tag:yaml.org,2002:int',
   test: /^[-+]?[0-9]+$/,
   resolve: (str, _onError, opt) => intResolve(str, 0, 10, opt),
-  stringify: stringifyNumber
+  stringify: node => stringifyNumber(node)
 }
 
 export const intHex: ScalarTag = {

src/schema/yaml-1.1/float.ts

@@ -13,7 +13,7 @@ export const floatNaN: ScalarTag = {
       : str[0] === '-'
         ? Number.NEGATIVE_INFINITY
         : Number.POSITIVE_INFINITY,
-  stringify: stringifyNumber
+  stringify: node => stringifyNumber(node, '1.1')
 }
 
 export const floatExp: ScalarTag = {
@@ -25,7 +25,7 @@ export const floatExp: ScalarTag = {
   resolve: (str: string) => parseFloat(str.replace(/_/g, '')),
   stringify(node) {
     const num = Number(node.value)
-    return isFinite(num) ? num.toExponential() : stringifyNumber(node)
+    return isFinite(num) ? num.toExponential() : stringifyNumber(node, '1.1')
   }
 }
 
@@ -43,5 +43,5 @@ export const float: ScalarTag = {
     }
     return node
   },
-  stringify: stringifyNumber
+  stringify: node => stringifyNumber(node, '1.1')
 }

src/schema/yaml-1.1/int.ts

@@ -72,7 +72,7 @@ export const int: ScalarTag = {
   test: /^[-+]?[0-9][0-9_]*$/,
   resolve: (str: string, _onError: unknown, opt: ParseOptions) =>
     intResolve(str, 0, 10, opt),
-  stringify: stringifyNumber
+  stringify: node => stringifyNumber(node, '1.1')
 }
 
 export const intHex: ScalarTag = {

src/stringify/stringifyNumber.ts

@@ -1,14 +1,18 @@
 import type { Scalar } from '../nodes/Scalar.ts'
 
-export function stringifyNumber({
-  format,
-  minFractionDigits,
-  tag,
-  value
-}: Scalar): string {
+export function stringifyNumber(
+  { format, minFractionDigits, source, tag, value }: Scalar,
+  version: '1.1' | '1.2' = '1.2'
+): string {
   if (typeof value === 'bigint') return String(value)
   const num = typeof value === 'number' ? value : Number(value)
-  if (!isFinite(num)) return isNaN(num) ? '.nan' : num < 0 ? '-.inf' : '.inf'
+  if (!isFinite(num)) {
+    if (typeof value === 'number' && source) {
+      const source_ = version === '1.1' ? source.replace(/_/g, '') : source
+      if (parseFloat(source_) === num) return source
+    }
+    return isNaN(num) ? '.nan' : num < 0 ? '-.inf' : '.inf'
+  }
   let n = Object.is(value, -0) ? '-0' : JSON.stringify(value)
   if (
     !format &&

tests/doc/types.ts

@@ -14,7 +14,7 @@ import {
   YAMLMap,
   YAMLSeq
 } from 'yaml'
-import { seqTag, stringifyString, stringTag } from 'yaml/util'
+import { seqTag, stringifyNumber, stringifyString, stringTag } from 'yaml/util'
 import { source } from '../_utils.ts'
 
 const parseDocument = <T extends DocValue = DocValue>(
@@ -262,6 +262,48 @@ describe('number types', () => {
       expect(doc.value[5]).not.toHaveProperty('minFractionDigits')
     })
   })
+
+  describe('overflowing values keep their source (#660)', () => {
+    test('float overflowing to Infinity round-trips via its source', () => {
+      expect(String(parseDocument('gitsha: 61e9540'))).toBe('gitsha: 61e9540\n')
+    })
+
+    test('negative overflow keeps its source', () => {
+      expect(String(parseDocument('n: -61e9540'))).toBe('n: -61e9540\n')
+    })
+
+    test('literal .inf / .nan are still emitted as such', () => {
+      expect(String(parseDocument('n: .inf'))).toBe('n: .inf\n')
+      expect(String(parseDocument('n: -.inf'))).toBe('n: -.inf\n')
+      expect(String(parseDocument('n: .nan'))).toBe('n: .nan\n')
+    })
+
+    test('a programmatic Infinity with finite source is emitted as .inf', () => {
+      const doc = parseDocument('n: 1')
+      doc.set('n', Infinity)
+      expect(String(doc)).toBe('n: .inf\n')
+    })
+
+    test('editing the value of a node parsed from a non-finite source is reflected', () => {
+      const doc = parseDocument('n: 61e9540')
+      const node = doc.get('n') as Scalar
+      node.value = -Infinity
+      expect(String(doc)).toBe('n: -.inf\n')
+    })
+
+    test('the source is used only while it still resolves to the value', () => {
+      const node = new Scalar(Infinity)
+      node.source = '61e9540'
+      expect(stringifyNumber(node)).toBe('61e9540')
+      node.source = '5'
+      expect(stringifyNumber(node)).toBe('.inf')
+    })
+
+    test('a YAML 1.1 float with underscores that overflows keeps its source', () => {
+      const doc = parseDocument('n: 6_1e9540', { version: '1.1' })
+      expect(String(doc)).toBe('n: 6_1e9540\n')
+    })
+  })
 })
 
 test('Indented sequence with sequence values (#2)', () => {