oracle/graal · error · RuleParseError

Out of tokens looking for %s

Error message

Out of tokens looking for %s

What it means

Thrown by RuleParser.peek(name) when tokens run out while the parser was specifically expecting something (a node type, a name, ')', etc.). Unlike the plain 'Out of tokens' variant, it names what was being looked for, which pinpoints the missing element of the match pattern.

Source

Thrown at compiler/src/jdk.graal.compiler.processor/src/jdk/graal/compiler/core/match/processor/MatchProcessor.java:147

            matchDescriptor = parseExpression();
            if (!done()) {
                throw new RuleParseError("didn't consume all tokens");
            }
            capturedNames.add(0, "root");
            capturedTypes.add(0, matchDescriptor.nodeType);
        }

        String next() {
            return tokens[current++];
        }

        String peek(String name) {
            if (current >= tokens.length) {
                if (name == null) {
                    throw new RuleParseError("Out of tokens");
                }
                throw new RuleParseError("Out of tokens looking for %s", name);
            }
            return tokens[current];
        }

        boolean done() {
            return current == tokens.length;
        }

        private MatchDescriptor parseExpression() {
            if (peek("(").equals("(")) {
                next();
                MatchDescriptor descriptor = parseType(true);
                for (int n = 0; n < descriptor.nodeType.inputs.size(); n++) {
                    if (peek("(").equals("(")) {
                        descriptor.inputs[n] = parseExpression();
                    } else {
                        descriptor.inputs[n] = parseType(false);
                    }

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Supply the token named in the message — usually a closing ')' or the node type/name it says it was looking for.
2. Re-balance parentheses by counting opens/closes in the rule string.
3. Use the message's 'looking for %s' field literally: it tells you the exact grammar element to append.

Example fix

// before
@MatchRule("Add(x = ")

// after
@MatchRule("Add(x = value, y)")

Compile-time error only. Parse the 'looking for %s' field from the javac diagnostic in developer tooling to auto-suggest the missing token.

When it happens

Trigger: Rules such as "Add(x, " (looking for ')' or a node type/name), "Add(x = " (looking for a captured name after '='), or any construct left half-finished. Every peek(String) call site passes its expectation, e.g. peek("node type or name"), peek(")"), peek("=").

Common situations: Interrupted edits to @MatchRule strings; renaming nodes and dropping a token; copy-paste that loses the tail of a long pattern.

Related errors

• Unexpected tokens :${rule.substring(m.end(), m.regionEnd())}
• didn't consume all tokens
• Out of tokens
• not enough inputs for ${descriptor.name}
• Too many arguments to ${descriptor.nodeType.nodeClass}

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/7285ccd02e3d7494. Report an issue: GitHub.