antlr/antlr4 · error · IllegalArgumentException

stop cannot be null or empty

Error message

stop cannot be null or empty

What it means

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

Source

Thrown at runtime/Java/src/org/antlr/v4/runtime/tree/pattern/ParseTreePatternMatcher.java:141

	/**
	 * Set the delimiters used for marking rule and token tags within concrete
	 * syntax used by the tree pattern parser.
	 *
	 * @param start The start delimiter.
	 * @param stop The stop delimiter.
	 * @param escapeLeft The escape sequence to use for escaping a start or stop delimiter.
	 *
	 * @exception IllegalArgumentException if {@code start} is {@code null} or empty.
	 * @exception IllegalArgumentException if {@code stop} is {@code null} or empty.
	 */
	public void setDelimiters(String start, String stop, String escapeLeft) {
		if (start == null || start.isEmpty()) {
			throw new IllegalArgumentException("start cannot be null or empty");
		}

		if (stop == null || stop.isEmpty()) {
			throw new IllegalArgumentException("stop cannot be null or empty");
		}

		this.start = start;
		this.stop = stop;
		this.escape = escapeLeft;
	}

	/** Does {@code pattern} matched as rule {@code patternRuleIndex} match {@code tree}? */
	public boolean matches(ParseTree tree, String pattern, int patternRuleIndex) {
		ParseTreePattern p = compile(pattern, patternRuleIndex);
		return matches(tree, p);
	}

	/** Does {@code pattern} matched as rule patternRuleIndex match tree? Pass in a
	 *  compiled pattern instead of a string representation of a tree pattern.
	 */
	public boolean matches(ParseTree tree, ParseTreePattern pattern) {
		MultiMap<String, ParseTree> labels = new MultiMap<String, ParseTree>();

View on GitHub (pinned to 7d5770395b)

Solutions

1. Pass a non-null, non-empty stop tag name to ParseTreePatternMatcher.setDelimiters(...).
2. Ensure the stop delimiter differs from the start delimiter.

Example fix

matcher.setDelimiters("<", ">", "$");

When it happens

Trigger: ParseTreePatternMatcher.setStop() called with null or empty string.

Common situations: Use a non-empty delimiter such as '>' for setStop; validate delimiters differ and are non-empty.

AI-assisted analysis of antlr/antlr4@7d5770395b (2026-08-14). Data as JSON: /api/errors/2324ec3dd60d42db. Report an issue: GitHub.