fix: reject a raw string whose comment marker follows a byte-order mark

Author: johannschopplich

packages/toon/src/encode/raw-string.ts

@@ -1,8 +1,9 @@
 import type { JsonPrimitive } from '../types.ts'
-import { COMMENT_MARKER } from '../constants.ts'
+import { BYTE_ORDER_MARK, COMMENT_MARKER } from '../constants.ts'
 
-// Decoders silently strip a line whose first non-space character is the comment marker.
-const COMMENT_LINE_PATTERN = new RegExp(`(?:^|\\n) *${COMMENT_MARKER}`)
+// Decoders silently strip a line whose first non-space character is the comment marker,
+// and they remove a leading byte-order mark before making that test.
+const COMMENT_LINE_PATTERN = new RegExp(`(?:^${BYTE_ORDER_MARK}?|\\n) *${COMMENT_MARKER}`)
 
 /**
  * Pre-formatted string that the encoder emits verbatim at a primitive value

packages/toon/test/raw-string.test.ts

@@ -87,6 +87,10 @@ describe('rawString', () => {
       expect(() => rawString('note\n# hidden')).toThrowError(TypeError)
     })
 
+    it('throws when a byte-order mark precedes the comment marker', () => {
+      expect(() => rawString('\u{FEFF}#hi')).toThrowError(TypeError)
+    })
+
     it('allows the comment marker after other content on the same line', () => {
       expect(encode({ tag: rawString('a #tag') })).toBe('tag: a #tag')
     })