antlr/antlr4 · error · IllegalArgumentException

ruleName cannot be null or empty.

Error message

ruleName cannot be null or empty.

What it means

Error "ruleName cannot be null or empty." thrown in antlr/antlr4.

Source

Thrown at runtime/Java/src/org/antlr/v4/runtime/tree/pattern/RuleTagToken.java:61

	public RuleTagToken(String ruleName, int bypassTokenType) {
		this(ruleName, bypassTokenType, null);
	}

	/**
	 * Constructs a new instance of {@link RuleTagToken} with the specified rule
	 * name, bypass token type, and label.
	 *
	 * @param ruleName The name of the parser rule this rule tag matches.
	 * @param bypassTokenType The bypass token type assigned to the parser rule.
	 * @param label The label associated with the rule tag, or {@code null} if
	 * the rule tag is unlabeled.
	 *
	 * @exception IllegalArgumentException if {@code ruleName} is {@code null}
	 * or empty.
	 */
	public RuleTagToken(String ruleName, int bypassTokenType, String label) {
		if (ruleName == null || ruleName.isEmpty()) {
			throw new IllegalArgumentException("ruleName cannot be null or empty.");
		}

		this.ruleName = ruleName;
		this.bypassTokenType = bypassTokenType;
		this.label = label;
	}

	/**
	 * Gets the name of the rule associated with this rule tag.
	 *
	 * @return The name of the parser rule associated with this rule tag.
	 */

	public final String getRuleName() {
		return ruleName;
	}

	/**

View on GitHub (pinned to 7d5770395b)

Solutions

1. Pass a non-null, non-empty rule name to the RuleTagToken constructor.
2. Let ParseTreePatternMatcher.compile build tag tokens for you rather than constructing RuleTagToken manually.

Example fix

RuleTagToken t = new RuleTagToken("expr", MyParser.RULE_expr);

When it happens

Trigger: RuleTagToken constructed with a null or empty ruleName.

Common situations: Supply a valid parser rule name when creating RuleTagToken; empty tags like <> are rejected.

AI-assisted analysis of antlr/antlr4@7d5770395b (2026-08-14). Data as JSON: /api/errors/cbdfb6237199964f. Report an issue: GitHub.