@Override
	public String getSourceName() {
		if (name == null || name.isEmpty()) {
			return UNKNOWN_SOURCE_NAME;
		}

		return name;
	}
consume() ahead until p==index; can't just set p=index as we must
 update line and charPositionInLine. If we seek backwards, just set p
runtime/Java/src/org/antlr/v4/runtime/ANTLRInputStream.java