protected boolean verifyFormat() {
        boolean ok = true;
        if (!format.isDefined("location")) {
            System.err.println("Format template 'location' not found in " + formatName);
            ok = false;
        }
        if (!format.isDefined("message")) {
            System.err.println("Format template 'message' not found in " + formatName);
            ok = false;
        }
        if (!format.isDefined("report")) {
            System.err.println("Format template 'report' not found in " + formatName);
            ok = false;
        }
        return ok;
    }
Verify the message format template group
tool/src/org/antlr/v4/tool/ErrorManager.java