public void panic(ErrorType errorType, Object... args) {
		ToolMessage msg = new ToolMessage(errorType, args);
		ST msgST = getMessageTemplate(msg);
		String outputMsg = msgST.render();
		if ( formatWantsSingleLineMessage() ) {
			outputMsg = outputMsg.replace('\n', ' ');
		}
		panic(outputMsg);
	}
If there are errors during ErrorManager init, we have no choice
 but to go to System.err.
tool/src/org/antlr/v4/tool/ErrorManager.java