Struct tracing::Level[][src]

pub struct Level(_);
Expand description

Describes the level of verbosity of a span or event.

Comparing Levels

Level implements the PartialOrd and Ord traits, allowing two Levels to be compared to determine which is considered more or less verbose. Levels which are more verbose are considered “greater than” levels which are less verbose, with Level::ERROR considered the lowest, and Level::TRACE considered the highest.

For example:

use tracing_core::Level;

assert!(Level::TRACE > Level::DEBUG);
assert!(Level::ERROR < Level::WARN);
assert!(Level::INFO <= Level::DEBUG);
assert_eq!(Level::TRACE, Level::TRACE);

Filtering

Levels are typically used to implement filtering that determines which spans and events are enabled. Depending on the use case, more or less verbose diagnostics may be desired. For example, when running in development, DEBUG-level traces may be enabled by default. When running in production, only INFO-level and lower traces might be enabled. Libraries may include very verbose diagnostics at the DEBUG and/or TRACE levels. Applications using those libraries typically chose to ignore those traces. However, when debugging an issue involving said libraries, it may be useful to temporarily enable the more verbose traces.

The LevelFilter type is provided to enable filtering traces by verbosity. Levels can be compared against LevelFilters, and LevelFilter has a variant for each Level, which compares analogously to that level. In addition, LevelFilter adds a LevelFilter::OFF variant, which is considered “less verbose” than every other `Level. This is intended to allow filters to completely disable tracing in a particular context.

For example:

use tracing_core::{Level, LevelFilter};

assert!(LevelFilter::OFF < Level::TRACE);
assert!(LevelFilter::TRACE > Level::DEBUG);
assert!(LevelFilter::ERROR < Level::WARN);
assert!(LevelFilter::INFO <= Level::DEBUG);
assert!(LevelFilter::INFO >= Level::INFO);

Examples

Below is a simple example of how a collector could implement filtering through a LevelFilter. When a span or event is recorded, the Collect::enabled method compares the span or event’s Level against the configured LevelFilter. The optional Collect::max_level_hint method can also be implemented to allow spans and events above a maximum verbosity level to be skipped more efficiently, often improving performance in short-lived programs.

use tracing_core::{span, Event, Level, LevelFilter, Collect, Metadata};

#[derive(Debug)]
pub struct MyCollector {
    /// The most verbose level that this collector will enable.
    max_level: LevelFilter,

    // ...
}

impl MyCollector {
    /// Returns a new `MyCollector` which will record spans and events up to
    /// `max_level`.
    pub fn with_max_level(max_level: LevelFilter) -> Self {
        Self {
            max_level,
            // ...
        }
    }
}
impl Collect for MyCollector {
    fn enabled(&self, meta: &Metadata<'_>) -> bool {
        // A span or event is enabled if it is at or below the configured
        // maximum level.
        meta.level() <= &self.max_level
    }

    // This optional method returns the most verbose level that this
    // collector will enable. Although implementing this method is not
    // *required*, it permits additional optimizations when it is provided,
    // allowing spans and events above the max level to be skipped
    // more efficiently.
    fn max_level_hint(&self) -> Option<LevelFilter> {
        Some(self.max_level)
    }

    // Implement the rest of the collector...
    fn new_span(&self, span: &span::Attributes<'_>) -> span::Id {
        // ...
    }
    fn event(&self, event: &Event<'_>) {
        // ...
    }

    // ...
}

It is worth noting that the tracing-subscriber crate provides additional APIs for performing more sophisticated filtering, such as enabling different levels based on which module or crate a span or event is recorded in.

Implementations

The “error” level.

Designates very serious errors.

The “warn” level.

Designates hazardous situations.

The “info” level.

Designates useful information.

The “debug” level.

Designates lower priority information.

The “trace” level.

Designates very low priority, often extremely verbose, information.

Returns the string representation of the Level.

This returns the same string as the fmt::Display implementation.

Trait Implementations

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Formats the value using the given formatter. Read more

Performs the conversion.

The associated error which can be returned from parsing.

Parses a string s to return a value of this type. Read more

Feeds this value into the given Hasher. Read more

Feeds a slice of this type into the given Hasher. Read more

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Performs the conversion.

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more

Instruments this type with the current Span, returning an Instrumented wrapper. Read more

Performs the conversion.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

Converts the given value to a String. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

This is supported on crate feature std only.

Attaches the provided collector to this type, returning a WithDispatch wrapper. Read more

This is supported on crate feature std only.

Attaches the current default collector to this type, returning a WithDispatch wrapper. Read more