From c8551ebca947c0fcd7a5cbd5b7b2636d4bd6925c Mon Sep 17 00:00:00 2001
From: Eemeli Aro <eemeli@gmail.com>
Date: Fri, 30 Dec 2022 11:30:16 +0200
Subject: [PATCH] fix: Quote top-level map keys containing document markers
 (fixes #431)

---
 src/stringify/stringifyString.ts | 12 ++++++++----
 tests/doc/stringify.js           | 14 ++++++++++++++
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/stringify/stringifyString.ts b/src/stringify/stringifyString.ts
index c71a848d..942b2d1a 100644
--- a/src/stringify/stringifyString.ts
+++ b/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
diff --git a/tests/doc/stringify.js b/tests/doc/stringify.js
index 2e33bfa1..b973e96f 100644
--- a/tests/doc/stringify.js
+++ b/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()