apple/pkl · error · GenericParserError

unexpectedToken

unexpectedToken

Error message

Unexpected token `{0}`. Expected `{1}`.

What it means

A member predicate's closing brackets were malformed: after the first `]`, the expected `]]` didn't match, or there was whitespace between the two `]` characters. Pkl requires the predicate syntax `is[...]` / `[[...]]`-style double bracket to be contiguous.

Source

Thrown at pkl-parser/src/main/java/org/pkl/parser/GenericParserImpl.java:552

    children.add(new Node(NodeType.CLASS_METHOD_BODY, body));
    return new Node(NodeType.OBJECT_METHOD, children);
  }

  private Node parseMemberPredicate() {
    var children = new ArrayList<Node>();
    children.add(makeTerminal(next()));
    ff(children);
    children.add(parseExpr());
    ff(children);
    var firstBrack = expect(Token.RBRACK, "unexpectedToken", "]]");
    children.add(makeTerminal(firstBrack));
    var secondbrack = expect(Token.RBRACK, "unexpectedToken", "]]");
    children.add(makeTerminal(secondbrack));
    if (firstBrack.span.charIndex() != secondbrack.span.charIndex() - 1) {
      // There shouldn't be any whitespace between the first and second ']'.
      var span = firstBrack.span.endWith(secondbrack.span);
      var text = lexer.textFor(span.charIndex(), span.length());
      throw parserError(ErrorMessages.create("unexpectedToken", text, "]]"), firstBrack.span);
    }
    ff(children);
    if (lookahead == Token.ASSIGN) {
      children.add(makeTerminal(next()));
      ff(children);
      children.add(parseExpr("}"));
      return new Node(NodeType.MEMBER_PREDICATE, children);
    }
    children.addAll(parseBodyList());
    return new Node(NodeType.MEMBER_PREDICATE, children);
  }

  private Node parseObjectEntry() {
    var children = new ArrayList<Node>();
    var header = new ArrayList<Node>();
    expect(Token.LBRACK, header, "unexpectedToken", "[");
    ff(header);
    header.add(parseExpr());

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Write the double closing bracket with no whitespace: `]]`
2. Ensure the predicate opening used `[[` and closing `]]` in matching pairs
3. Let a Pkl-aware formatter normalize the predicate syntax

Example fix

// before
x is[ Int ] ]
// after
x is[Int]

/\]\s*\]/.test(src) === false // reject whitespace between predicate closing brackets

When it happens

Trigger: parseMemberPredicate calls expect(RBRACK, "unexpectedToken", "]]") or detects `firstBrack.charIndex != secondbrack.charIndex - 1` — e.g. writing `is[ x ] [ ]` with a space between `]` and `]`, or omitting the second bracket.

Common situations: Typing a space between the closing brackets of `when (cond) { ... }`-style member predicates; hand-writing predicate syntax copied loosely from docs; editor auto-spacing between brackets.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• ErrorMessages.create(errorKey, args)
• unexpectedTokenForExpression
• missingDelimiter
• unexpectedEndOfFile
• stringContentMustBeginOnNewLine

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/5cdc22622550cf37. Report an issue: GitHub.