fix: Do not require quotes for implicit keys with flow indicators (#494)

Author: eemeli

src/stringify/stringifyString.ts

@@ -280,7 +280,7 @@ function plainString(
   const { type, value } = item
   const { actualString, implicitKey, indent, indentStep, inFlow } = ctx
   if (
-    (implicitKey && /[\n[\]{},]/.test(value)) ||
+    (implicitKey && value.includes('\n')) ||
     (inFlow && /[[\]{},]/.test(value))
   ) {
     return quotedString(value, ctx)

tests/doc/stringify.ts

@@ -336,6 +336,11 @@ z:
     expect(String(doc)).toBe('a: 1\n? b: 2\n  c: 3\n')
   })
 
+  test('plain key containing flow indicators', () => {
+    const doc = YAML.parseDocument('foo[{}]: bar')
+    expect(doc.toString()).toBe('foo[{}]: bar\n')
+  })
+
   describe('No extra whitespace for empty values', () => {
     const getDoc = () =>
       new YAML.Document<YAML.YAMLMap<YAML.Scalar, YAML.Scalar>, false>({