fix: Quote top-level map keys containing document markers (fixes #431)

Author: eemeli

src/stringify/stringifyString.ts

@@ -266,7 +266,7 @@ function plainString(
   onChompKeep?: () => void
 ) {
   const { type, value } = item
-  const { actualString, implicitKey, indent, inFlow } = ctx
+  const { actualString, implicitKey, indent, indentStep, inFlow } = ctx
   if (
     (implicitKey && /[\n[\]{},]/.test(value)) ||
     (inFlow && /[[\]{},]/.test(value))
@@ -298,9 +298,13 @@ function plainString(
     // Where allowed & type not set explicitly, prefer block style for multiline strings
     return blockString(item, ctx, onComment, onChompKeep)
   }
-  if (indent === '' && containsDocumentMarker(value)) {
-    ctx.forceBlockIndent = true
-    return blockString(item, ctx, onComment, onChompKeep)
+  if (containsDocumentMarker(value)) {
+    if (indent === '') {
+      ctx.forceBlockIndent = true
+      return blockString(item, ctx, onComment, onChompKeep)
+    } else if (implicitKey && indent === indentStep) {
+      return quotedString(value, ctx)
+    }
   }
   const str = value.replace(/\n+/g, `$&\n${indent}`)
   // Verify that output will be parsed as a string, as e.g. plain numbers and

tests/doc/stringify.js

@@ -1118,6 +1118,20 @@ describe('Document markers in top-level scalars', () => {
   })
 })
 
+describe('Document markers in top-level map keys (eemeli/yaml#431)', () => {
+  test('---', () => {
+    const str = YAML.stringify({ '--- x': 42 })
+    expect(str).toBe('"--- x": 42\n')
+    expect(YAML.parse(str)).toEqual({ '--- x': 42 })
+  })
+
+  test('...', () => {
+    const str = YAML.stringify({ '... x': 42 })
+    expect(str).toBe('"... x": 42\n')
+    expect(YAML.parse(str)).toEqual({ '... x': 42 })
+  })
+})
+
 describe('undefined values', () => {
   test('undefined', () => {
     expect(YAML.stringify(undefined)).toBeUndefined()