fix: quote flow scalars where a colon precedes a flow indicator (#773)

Author: spokodev

src/ast/presenter.ts

@@ -257,7 +257,14 @@ function isPlainSafe (c: number, prev: number, inblock: boolean) {
     !(prev === CHAR_COLON && !cIsNsChar)
   ) || // false on ': '
   (isNsCharOrWhitespace(prev) && !isWhitespace(prev) && c === CHAR_SHARP) || // change to true on '[^ ]#'
-  (prev === CHAR_COLON && cIsNsChar) // change to true on ':[^ ]'
+  (prev === CHAR_COLON && cIsNsChar &&
+    // outside block context a following c-flow-indicator is not ns-plain-safe
+    (inblock ||
+      (c !== CHAR_COMMA &&
+       c !== CHAR_LEFT_SQUARE_BRACKET &&
+       c !== CHAR_RIGHT_SQUARE_BRACKET &&
+       c !== CHAR_LEFT_CURLY_BRACKET &&
+       c !== CHAR_RIGHT_CURLY_BRACKET))) // change to true on ':[^ ]'
 }
 
 // Simplified test for values allowed as the first character in plain style.

test/core/units/dump-options.test.mjs

@@ -1,6 +1,6 @@
 import { describe, it } from 'node:test'
 import assert from 'node:assert/strict'
-import { dump, JSON_SCHEMA, CORE_SCHEMA, defineMappingTag, realMapTag, YAMLException } from 'js-yaml'
+import { dump, load, JSON_SCHEMA, CORE_SCHEMA, defineMappingTag, realMapTag, YAMLException } from 'js-yaml'
 
 describe('dump options', () => {
   it('schema — decides which plain scalars need quoting', () => {
@@ -96,6 +96,16 @@ describe('dump options', () => {
     assert.equal(dump({ a: [1, 2] }, { flowLevel: 1 }), 'a: [1, 2]\n')
   })
 
+  it('flowLevel — quotes a colon followed by a flow indicator', () => {
+    // In flow context a `:` followed by a flow indicator ({ } [ ] ,) is not
+    // plain-safe (ns-plain-safe-in excludes c-flow-indicator), so the value
+    // must be quoted for the output to re-parse.
+    for (const value of [':{', ':[', ':,', ':}', ':]', 'x:{']) {
+      assert.deepStrictEqual(load(dump([value], { flowLevel: 0 })), [value])
+      assert.deepStrictEqual(load(dump({ k: value }, { flowLevel: 0 })), { k: value })
+    }
+  })
+
   it('transform — mutates the generated documents before presentation', () => {
     const output = dump({ values: [1, 2] }, {
       flowLevel: 1,