🛈 Note: This is pre-release documentation for the upcoming tracing 0.2.0 ecosystem.

For the release documentation, please see docs.rs, instead.

Struct tracing_core::metadata::Level

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pub struct Level(/* private fields */);
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§

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impl Level

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pub const ERROR: Level = _

The “error” level.

Designates very serious errors.

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pub const WARN: Level = _

The “warn” level.

Designates hazardous situations.

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pub const INFO: Level = _

The “info” level.

Designates useful information.

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pub const DEBUG: Level = _

The “debug” level.

Designates lower priority information.

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pub const TRACE: Level = _

The “trace” level.

Designates very low priority, often extremely verbose, information.

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pub fn as_str(&self) -> &'static str

Returns the string representation of the Level.

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

Trait Implementations§

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impl Clone for Level

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fn clone(&self) -> Level

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for Level

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl Display for Level

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl From<Level> for LevelFilter

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fn from(level: Level) -> Self

Converts to this type from the input type.
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impl FromStr for Level

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type Err = ParseLevelError

The associated error which can be returned from parsing.
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fn from_str(s: &str) -> Result<Self, ParseLevelError>

Parses a string s to return a value of this type. Read more
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impl Hash for Level

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fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl Ord for Level

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fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other. Read more
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fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
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fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
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fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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impl PartialEq<Level> for LevelFilter

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fn eq(&self, other: &Level) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl PartialEq<LevelFilter> for Level

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fn eq(&self, other: &LevelFilter) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl PartialEq for Level

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fn eq(&self, other: &Level) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl PartialOrd<Level> for LevelFilter

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fn partial_cmp(&self, other: &Level) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Level) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Level) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Level) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Level) -> bool

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

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fn partial_cmp(&self, other: &LevelFilter) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &LevelFilter) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &LevelFilter) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &LevelFilter) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &LevelFilter) -> bool

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

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fn partial_cmp(&self, other: &Level) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Level) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Level) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Level) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Level) -> bool

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

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impl Eq for Level

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impl StructuralPartialEq for Level

Auto Trait Implementations§

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impl Freeze for Level

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impl RefUnwindSafe for Level

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impl Send for Level

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impl Sync for Level

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impl Unpin for Level

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impl UnwindSafe for Level

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T> ToString for T
where T: Display + ?Sized,

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default fn to_string(&self) -> String

Converts the given value to a String. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.