public int getRuleIndex(String ruleName) {
		Integer ruleIndex = getRuleIndexMap().get(ruleName);
		if ( ruleIndex!=null ) return ruleIndex;
		return -1;
	}
Get a rule's index (i.e., {@code RULE_ruleName} field) or -1 if not found.
runtime/Java/src/org/antlr/v4/runtime/Parser.java