Can we set log filter level at runtime

[Yaoxiao1]

Hi, I read the docs and find that the log filter level can only be set at complie time, I tested the set_max_level()function, can only find the max_level changed, but the filter still remain as the original setup. Here is my test code

fn main() {
    let mut logger = env_logger::Builder::new();
    logger.format(|buf, record| {
        writeln!(
            buf,
            "[{}] {} {}:{} - {}",
            record.level(),
            chrono::Local::now().format("%Y-%m-%dT%H:%M:%S.%3f"),
            record.file().unwrap_or("unknown"),
            record.line().unwrap_or(0),
            record.args()
        )
    })
    .filter(None, log::LevelFilter::Info);
    logger.init();
    println!("current max log level is : {:?}", log::max_level());
    log::trace!("this is a trace log");
    log::debug!("this is a debug log");
    log::info!("this is a info log");
    log::warn!("this is a warn log");
    log::error!("this is a error log");
    // logger.filter(None, log::LevelFilter::Debug);
    log::set_max_level(log::LevelFilter::Debug);
    sleep(Duration::from_secs(3));
    println!("current max log level is : {:?}", log::max_level());
    log::trace!("this is a trace log");
    log::debug!("this is a debug log");
    log::info!("this is a info log");
    log::warn!("this is a warn log");
    log::error!("this is a error log");
}

So my issue is, is it possible to change the log filter at runtime? I have met such situation in my development work. Thank you.

[Thomasdezeeuw]

You can use set_max_level to change the log level at runtime.

[Yaoxiao1]

You can use set_max_level to change the log level at runtime.

@Thomasdezeeuw Hi, I ran the test code above, the max_level did changed, but the filter remains the same, here is the output there should be a line like "[DEBUG] YYYY-MM-DD - this is a debug log", but there wasn't, which means set_max_level() only changed a static variable but filter didn't change.

[Thomasdezeeuw]

Have you set either the max_level_* or release_max_level_* features? Because those can't be lowered as they remove all the logs at compile time. For example setting the max_level_warn feature removes all trace, debug and info logs.

If not it might depend on the env_logger crate, e.g. try using env_logger::Builder::filter_level.

[Yaoxiao1]

For example setting the max_level_warn feature removes all trace, debug and info logs.

yes, that's correct, I changed the filter level at compile time, then the runtime level can alter as I need. Thank you!