flexi_logger 0.20.1

An easy-to-configure and flexible logger that writes logs to stderr or stdout and/or to files. It allows custom logline formats, and it allows changing the log specification at runtime. It also allows defining additional log streams, e.g. for alert or security messages.
Documentation 
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mod test_utils;

#[cfg(feature = "specfile_without_notification")]
mod a {
    use flexi_logger::{detailed_format, FileSpec, Logger};
    use log::*;
    use std::io::Write;

    const WAIT_MILLIS: u64 = 2000;

    /// Test of the specfile feature
    #[test]
    fn test_specfile() {
        let specfile = super::test_utils::file("logspec.toml");

        std::fs::remove_file(&specfile).ok();
        assert!(!specfile.exists());

        let logger = Logger::try_with_str("info")
            .unwrap()
            .log_to_file(
                FileSpec::default()
                    .directory(super::test_utils::dir())
                    .suppress_timestamp(),
            )
            .format(detailed_format)
            .start_with_specfile(&specfile)
            .unwrap_or_else(|e| panic!("Logger initialization failed because: {}", e));

        error!("This is an error-0");
        warn!("This is a warning-0");
        info!("This is an info-0");
        debug!("This is a debug-0");
        trace!("This is a trace-0");

        eprintln!(
            "[{}] ===== behave like many editors: rename and recreate, as warn",
            super::test_utils::now_local()
        );
        {
            let mut old_name = specfile.clone();
            old_name.set_file_name("old_logspec.toml");
            std::fs::rename(&specfile, old_name).unwrap();
            let mut file = std::fs::OpenOptions::new()
                .create(true)
                .write(true)
                .open(&specfile)
                .unwrap();
            file.write_all(
                b"
                global_level = 'warn'
                [modules]
                ",
            )
            .unwrap();
        }

        std::thread::sleep(std::time::Duration::from_millis(WAIT_MILLIS));

        error!("This is an error-1");
        warn!("This is a warning-1");
        info!("This is an info-1");
        debug!("This is a debug-1");
        trace!("This is a trace-1");

        eprintln!(
            "[{}] ===== truncate and rewrite, update to error",
            super::test_utils::now_local()
        );
        {
            let mut file = std::fs::OpenOptions::new()
                .truncate(true)
                .write(true)
                .open(&specfile)
                .unwrap();
            file.write_all(
                b"
                global_level = 'error'
                [modules]
                ",
            )
            .unwrap();
        }

        std::thread::sleep(std::time::Duration::from_millis(WAIT_MILLIS));

        error!("This is an error-2");
        warn!("This is a warning-2");
        info!("This is an info-2");
        debug!("This is a debug-2");
        trace!("This is a trace-2");

        if cfg!(feature = "specfile") {
            eprintln!("feature is: specfile!");
            logger.validate_logs(&[
                ("ERROR", "test_specfile::a", "error-0"),
                ("WARN", "test_specfile::a", "warning-0"),
                ("INFO", "test_specfile::a", "info-0"),
                ("ERROR", "test_specfile::a", "error-1"),
                ("WARN", "test_specfile::a", "warning-1"),
                ("ERROR", "test_specfile::a", "error-2"),
            ]);
        } else {
            eprintln!("feature is: specfile_without_notification!");
            logger.validate_logs(&[
                ("ERROR", "test_specfile::a", "error-0"),
                ("WARN", "test_specfile::a", "warning-0"),
                ("INFO", "test_specfile::a", "info-0"),
                ("ERROR", "test_specfile::a", "error-1"),
                ("WARN", "test_specfile::a", "warning-1"),
                ("INFO", "test_specfile::a", "info-1"),
                ("ERROR", "test_specfile::a", "error-2"),
                ("WARN", "test_specfile::a", "warning-2"),
                ("INFO", "test_specfile::a", "info-2"),
            ]);
        }
    }
}