antlr/antlr4 · error · IllegalArgumentException

Missing path element at end of path

Error message

Missing path element at end of path

What it means

XPath.getXPathElement expects a word token (wildcard, token ref, rule ref, or string literal) but received EOF, meaning the path ended right where an element was required. Typical trigger: a trailing '/' or '//' with nothing after it.

Source

Thrown at runtime/Java/src/org/antlr/v4/runtime/tree/xpath/XPath.java:159

				case Token.EOF :
					break loop;

				default :
					throw new IllegalArgumentException("Unknowth path element "+el);
			}
		}
		return elements.toArray(new XPathElement[0]);
	}

	/**
	 * Convert word like {@code *} or {@code ID} or {@code expr} to a path
	 * element. {@code anywhere} is {@code true} if {@code //} precedes the
	 * word.
	 */
	protected XPathElement getXPathElement(Token wordToken, boolean anywhere) {
		if ( wordToken.getType()==Token.EOF ) {
			throw new IllegalArgumentException("Missing path element at end of path");
		}
		String word = wordToken.getText();
		int ttype = parser.getTokenType(word);
		int ruleIndex = parser.getRuleIndex(word);
		switch ( wordToken.getType() ) {
			case XPathLexer.WILDCARD :
				return anywhere ?
					new XPathWildcardAnywhereElement() :
					new XPathWildcardElement();
			case XPathLexer.TOKEN_REF :
			case XPathLexer.STRING :
				if ( ttype==Token.INVALID_TYPE ) {
					throw new IllegalArgumentException(word+
													   " at index "+
													   wordToken.getStartIndex()+
													   " isn't a valid token name");
				}
				return anywhere ?

View on GitHub (pinned to 7d5770395b)

Solutions

1. Remove the trailing '/' or '//' or complete it with a rule name, token name, '*', or 'name:"literal"'
2. When concatenating path segments, join with '/' and trim trailing separators: path.replaceAll("/+$", "")

Example fix

// before
String xpath = base + "/"; // ends with separator
XPath.findAll(tree, xpath, parser);

// after
String xpath = base.replaceAll("/+$", "");
XPath.findAll(tree, xpath, parser);

String cleaned = path.replaceAll("/+$", "");
boolean endsWithSeparator = path.endsWith("/") || path.endsWith("//");

try { XPath.findAll(tree, path, parser); } catch (IllegalArgumentException e) { if (e.getMessage().contains("Missing path element")) { /* fix trailing separator */ } }

When it happens

Trigger: new XPath(parser, "/expr//") or XPath.findAll(tree, "/statement/", parser) — any path whose last step is empty.

Common situations: Concatenating path fragments dynamically so a separator is appended without the following element name; trailing-slip typos in hand-written queries.

Related errors

• Invalid tokens or characters at index "+pos+" in path '"+pat
• Could not read path: "+path
• Unknowth path element "+el
• {word} at index {startIndex} isn't a valid token name
• {word} at index {startIndex} isn't a valid rule name

AI-assisted analysis of antlr/antlr4@7d5770395b (2026-08-14). Data as JSON: /api/errors/6e1d6c828c4984b5. Report an issue: GitHub.