Consider using "WARNING" instead of "WARN" for the log level.

[josecelano]

Feature Request

I was setting up Datadog for a project I'm working on, and I realized log lines containing "WARN" were categorised as "INFO".

Datadog uses the severity levels described here:

https://en.wikipedia.org/wiki/Syslog#Severity_level

"WARN" is deprecated in favour of "WARNING." It's not a problem because you can remap the status. However, I've seen some libraries also encourage using the whole word "WARNING."

I guess that change would be a breaking change even if you only change the Display implementation:

impl fmt::Display for Level {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            Level::TRACE => f.pad("TRACE"),
            Level::DEBUG => f.pad("DEBUG"),
            Level::INFO => f.pad("INFO"),
            Level::WARN => f.pad("WARN"),
            Level::ERROR => f.pad("ERROR"),
        }
    }
}

Crates

tracing-core

Motivation

It potentially improves the user experience when parsing the logs generated by the tracing crate by providing a smooth integration with other services that parse logs.

I've asked ChatGPT which languages/packages are recommending this change:

The deprecation of "WARN" in favor of "WARNING" is typically seen in logging frameworks and libraries rather than in programming languages themselves. Some examples include:

1. Java Logging (java.util.logging): In Java's built-in logging framework, using "WARN" has been discouraged in favor of "WARNING."

2. Log4j: Log4j, a popular logging library for Java, has historically used "WARN" as a logging level. However, it's recommended to use "WARN" as an alias for "WARNING" for consistency.

3. Python logging module: Python's logging module uses "WARNING" instead of "WARN" to represent log levels indicating potential issues or warnings.

4. Syslog: As you mentioned, in the syslog standard, "WARN" has been deprecated in favor of "WARNING."

In general, this deprecation is part of a broader trend towards clearer and more consistent logging practices, making log messages easier to understand and analyze across different systems and programming languages.

Proposal

Allow users to remap/overwrite these keywords. And keep the current ones as defaults.

Alternatives

I guess you could just change it in the next big release if there is consensus. To be honest, I don't see "WARN" as a big problem. Datadog is just one provider, and others may keep using it.

[davidbarsky]

We're going to stick with WARN in order to be closer to the log crate, I'm afraid: https://docs.rs/log/latest/log/enum.Level.html.

If you're running into issue with DataDog, I'd consider defining your own formatters for tracing_subscriber::fmt (which I assume you're doing) similar to what I did in tracing-glog: https://github.com/davidbarsky/tracing-glog/blob/main/src/format.rs#L15