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//! Metadata describing trace data.
use super::{callsite, field};
use crate::stdlib::{
cmp, fmt,
str::FromStr,
sync::atomic::{AtomicUsize, Ordering},
};
/// Metadata describing a [span] or [event].
///
/// All spans and events have the following metadata:
/// - A [name], represented as a static string.
/// - A [target], a string that categorizes part of the system where the span
/// or event occurred. The `tracing` macros default to using the module
/// path where the span or event originated as the target, but it may be
/// overridden.
/// - A [verbosity level]. This determines how verbose a given span or event
/// is, and allows enabling or disabling more verbose diagnostics
/// situationally. See the documentation for the [`Level`] type for details.
/// - The names of the [fields] defined by the span or event.
/// - Whether the metadata corresponds to a span or event.
///
/// In addition, the following optional metadata describing the source code
/// location where the span or event originated _may_ be provided:
/// - The [file name]
/// - The [line number]
/// - The [module path]
///
/// Metadata is used by [`Subscriber`]s when filtering spans and events, and it
/// may also be used as part of their data payload.
///
/// When created by the `event!` or `span!` macro, the metadata describing a
/// particular event or span is constructed statically and exists as a single
/// static instance. Thus, the overhead of creating the metadata is
/// _significantly_ lower than that of creating the actual span. Therefore,
/// filtering is based on metadata, rather than on the constructed span.
///
/// ## Equality
///
/// In well-behaved applications, two `Metadata` with equal
/// [callsite identifiers] will be equal in all other ways (i.e., have the same
/// `name`, `target`, etc.). Consequently, in release builds, [`Metadata::eq`]
/// *only* checks that its arguments have equal callsites. However, the equality
/// of `Metadata`'s other fields is checked in debug builds.
///
/// [span]: super::span
/// [event]: super::event
/// [name]: Self::name
/// [target]: Self::target
/// [fields]: Self::fields
/// [verbosity level]: Self::level
/// [file name]: Self::file
/// [line number]: Self::line
/// [module path]: Self::module_path
/// [`Subscriber`]: super::subscriber::Subscriber
/// [callsite identifiers]: Self::callsite
pub struct Metadata<'a> {
/// The name of the span described by this metadata.
name: &'static str,
/// The part of the system that the span that this metadata describes
/// occurred in.
target: &'a str,
/// The level of verbosity of the described span.
level: Level,
/// The name of the Rust module where the span occurred, or `None` if this
/// could not be determined.
module_path: Option<&'a str>,
/// The name of the source code file where the span occurred, or `None` if
/// this could not be determined.
file: Option<&'a str>,
/// The line number in the source code file where the span occurred, or
/// `None` if this could not be determined.
line: Option<u32>,
/// The names of the key-value fields attached to the described span or
/// event.
fields: field::FieldSet,
/// The kind of the callsite.
kind: Kind,
}
/// Indicates whether the callsite is a span or event.
#[derive(Clone, Eq, PartialEq)]
pub struct Kind(u8);
/// Describes the level of verbosity of a span or event.
///
/// # Comparing Levels
///
/// `Level` implements the [`PartialOrd`] and [`Ord`] traits, allowing two
/// `Level`s 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
///
/// `Level`s 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. `Level`s can be compared against [`LevelFilter`]s, 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 [`Subscriber`] could implement filtering through
/// a [`LevelFilter`]. When a span or event is recorded, the [`Subscriber::enabled`] method
/// compares the span or event's `Level` against the configured [`LevelFilter`].
/// The optional [`Subscriber::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, Subscriber, Metadata};
/// # use tracing_core::span::{Id, Record, Current};
///
/// #[derive(Debug)]
/// pub struct MySubscriber {
/// /// The most verbose level that this subscriber will enable.
/// max_level: LevelFilter,
///
/// // ...
/// }
///
/// impl MySubscriber {
/// /// Returns a new `MySubscriber` which will record spans and events up to
/// /// `max_level`.
/// pub fn with_max_level(max_level: LevelFilter) -> Self {
/// Self {
/// max_level,
/// // ...
/// }
/// }
/// }
/// impl Subscriber for MySubscriber {
/// 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
/// // subscriber 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 subscriber...
/// fn new_span(&self, span: &span::Attributes<'_>) -> span::Id {
/// // ...
/// # drop(span); Id::from_u64(1)
/// }
/// fn event(&self, event: &Event<'_>) {
/// // ...
/// # drop(event);
/// }
///
/// // ...
/// # fn enter(&self, _: &Id) {}
/// # fn exit(&self, _: &Id) {}
/// # fn record(&self, _: &Id, _: &Record<'_>) {}
/// # fn record_follows_from(&self, _: &Id, _: &Id) {}
/// }
/// ```
///
/// It is worth noting that the `tracing-subscriber` crate provides [additional
/// APIs][envfilter] for performing more sophisticated filtering, such as
/// enabling different levels based on which module or crate a span or event is
/// recorded in.
///
/// [`DEBUG`]: Level::DEBUG
/// [`INFO`]: Level::INFO
/// [`TRACE`]: Level::TRACE
/// [`Subscriber::enabled`]: crate::subscriber::Subscriber::enabled
/// [`Subscriber::max_level_hint`]: crate::subscriber::Subscriber::max_level_hint
/// [`Subscriber`]: crate::subscriber::Subscriber
/// [envfilter]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/filter/struct.EnvFilter.html
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
pub struct Level(LevelInner);
/// A filter comparable to a verbosity [`Level`].
///
/// If a [`Level`] is considered less than a `LevelFilter`, it should be
/// considered enabled; if greater than or equal to the `LevelFilter`,
/// that level is disabled. See [`LevelFilter::current`] for more
/// details.
///
/// Note that this is essentially identical to the `Level` type, but with the
/// addition of an [`OFF`] level that completely disables all trace
/// instrumentation.
///
/// See the documentation for the [`Level`] type to see how `Level`s
/// and `LevelFilter`s interact.
///
/// [`OFF`]: LevelFilter::OFF
#[repr(transparent)]
#[derive(Copy, Clone, Eq, PartialEq, Hash)]
pub struct LevelFilter(Option<Level>);
/// Indicates that a string could not be parsed to a valid level.
#[derive(Clone, Debug)]
pub struct ParseLevelFilterError(());
static MAX_LEVEL: AtomicUsize = AtomicUsize::new(LevelFilter::OFF_USIZE);
// ===== impl Metadata =====
impl<'a> Metadata<'a> {
/// Construct new metadata for a span or event, with a name, target, level, field
/// names, and optional source code location.
pub const fn new(
name: &'static str,
target: &'a str,
level: Level,
file: Option<&'a str>,
line: Option<u32>,
module_path: Option<&'a str>,
fields: field::FieldSet,
kind: Kind,
) -> Self {
Metadata {
name,
target,
level,
module_path,
file,
line,
fields,
kind,
}
}
/// Returns the names of the fields on the described span or event.
pub fn fields(&self) -> &field::FieldSet {
&self.fields
}
/// Returns the level of verbosity of the described span or event.
pub fn level(&self) -> &Level {
&self.level
}
/// Returns the name of the span.
pub fn name(&self) -> &'static str {
self.name
}
/// Returns a string describing the part of the system where the span or
/// event that this metadata describes occurred.
///
/// Typically, this is the module path, but alternate targets may be set
/// when spans or events are constructed.
pub fn target(&self) -> &'a str {
self.target
}
/// Returns the path to the Rust module where the span occurred, or
/// `None` if the module path is unknown.
pub fn module_path(&self) -> Option<&'a str> {
self.module_path
}
/// Returns the name of the source code file where the span
/// occurred, or `None` if the file is unknown
pub fn file(&self) -> Option<&'a str> {
self.file
}
/// Returns the line number in the source code file where the span
/// occurred, or `None` if the line number is unknown.
pub fn line(&self) -> Option<u32> {
self.line
}
/// Returns an opaque `Identifier` that uniquely identifies the callsite
/// this `Metadata` originated from.
#[inline]
pub fn callsite(&self) -> callsite::Identifier {
self.fields.callsite()
}
/// Returns true if the callsite kind is `Event`.
pub fn is_event(&self) -> bool {
self.kind.is_event()
}
/// Return true if the callsite kind is `Span`.
pub fn is_span(&self) -> bool {
self.kind.is_span()
}
}
impl<'a> fmt::Debug for Metadata<'a> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let mut meta = f.debug_struct("Metadata");
meta.field("name", &self.name)
.field("target", &self.target)
.field("level", &self.level);
if let Some(path) = self.module_path() {
meta.field("module_path", &path);
}
match (self.file(), self.line()) {
(Some(file), Some(line)) => {
meta.field("location", &format_args!("{}:{}", file, line));
}
(Some(file), None) => {
meta.field("file", &format_args!("{}", file));
}
// Note: a line num with no file is a kind of weird case that _probably_ never occurs...
(None, Some(line)) => {
meta.field("line", &line);
}
(None, None) => {}
};
meta.field("fields", &format_args!("{}", self.fields))
.field("callsite", &self.callsite())
.field("kind", &self.kind)
.finish()
}
}
impl Kind {
const EVENT_BIT: u8 = 1 << 0;
const SPAN_BIT: u8 = 1 << 1;
const HINT_BIT: u8 = 1 << 2;
/// `Event` callsite
pub const EVENT: Kind = Kind(Self::EVENT_BIT);
/// `Span` callsite
pub const SPAN: Kind = Kind(Self::SPAN_BIT);
/// `enabled!` callsite. [`Subscriber`][`crate::subscriber::Subscriber`]s can assume
/// this `Kind` means they will never recieve a
/// full event with this [`Metadata`].
pub const HINT: Kind = Kind(Self::HINT_BIT);
/// Return true if the callsite kind is `Span`
pub fn is_span(&self) -> bool {
self.0 & Self::SPAN_BIT == Self::SPAN_BIT
}
/// Return true if the callsite kind is `Event`
pub fn is_event(&self) -> bool {
self.0 & Self::EVENT_BIT == Self::EVENT_BIT
}
/// Return true if the callsite kind is `Hint`
pub fn is_hint(&self) -> bool {
self.0 & Self::HINT_BIT == Self::HINT_BIT
}
/// Sets that this `Kind` is a [hint](Self::HINT).
///
/// This can be called on [`SPAN`](Self::SPAN) and [`EVENT`](Self::EVENT)
/// kinds to construct a hint callsite that also counts as a span or event.
pub const fn hint(self) -> Self {
Self(self.0 | Self::HINT_BIT)
}
}
impl fmt::Debug for Kind {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("Kind(")?;
let mut has_bits = false;
let mut write_bit = |name: &str| {
if has_bits {
f.write_str(" | ")?;
}
f.write_str(name)?;
has_bits = true;
Ok(())
};
if self.is_event() {
write_bit("EVENT")?;
}
if self.is_span() {
write_bit("SPAN")?;
}
if self.is_hint() {
write_bit("HINT")?;
}
// if none of the expected bits were set, something is messed up, so
// just print the bits for debugging purposes
if !has_bits {
write!(f, "{:#b}", self.0)?;
}
f.write_str(")")
}
}
impl<'a> Eq for Metadata<'a> {}
impl<'a> PartialEq for Metadata<'a> {
#[inline]
fn eq(&self, other: &Self) -> bool {
if core::ptr::eq(&self, &other) {
true
} else if cfg!(not(debug_assertions)) {
// In a well-behaving application, two `Metadata` can be assumed to
// be totally equal so long as they share the same callsite.
self.callsite() == other.callsite()
} else {
// However, when debug-assertions are enabled, do not assume that
// the application is well-behaving; check every field of `Metadata`
// for equality.
// `Metadata` is destructured here to ensure a compile-error if the
// fields of `Metadata` change.
let Metadata {
name: lhs_name,
target: lhs_target,
level: lhs_level,
module_path: lhs_module_path,
file: lhs_file,
line: lhs_line,
fields: lhs_fields,
kind: lhs_kind,
} = self;
let Metadata {
name: rhs_name,
target: rhs_target,
level: rhs_level,
module_path: rhs_module_path,
file: rhs_file,
line: rhs_line,
fields: rhs_fields,
kind: rhs_kind,
} = &other;
// The initial comparison of callsites is purely an optimization;
// it can be removed without affecting the overall semantics of the
// expression.
self.callsite() == other.callsite()
&& lhs_name == rhs_name
&& lhs_target == rhs_target
&& lhs_level == rhs_level
&& lhs_module_path == rhs_module_path
&& lhs_file == rhs_file
&& lhs_line == rhs_line
&& lhs_fields == rhs_fields
&& lhs_kind == rhs_kind
}
}
}
// ===== impl Level =====
impl Level {
/// The "error" level.
///
/// Designates very serious errors.
pub const ERROR: Level = Level(LevelInner::Error);
/// The "warn" level.
///
/// Designates hazardous situations.
pub const WARN: Level = Level(LevelInner::Warn);
/// The "info" level.
///
/// Designates useful information.
pub const INFO: Level = Level(LevelInner::Info);
/// The "debug" level.
///
/// Designates lower priority information.
pub const DEBUG: Level = Level(LevelInner::Debug);
/// The "trace" level.
///
/// Designates very low priority, often extremely verbose, information.
pub const TRACE: Level = Level(LevelInner::Trace);
/// Returns the string representation of the `Level`.
///
/// This returns the same string as the `fmt::Display` implementation.
pub fn as_str(&self) -> &'static str {
match *self {
Level::TRACE => "TRACE",
Level::DEBUG => "DEBUG",
Level::INFO => "INFO",
Level::WARN => "WARN",
Level::ERROR => "ERROR",
}
}
}
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"),
}
}
}
#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl crate::stdlib::error::Error for ParseLevelError {}
impl FromStr for Level {
type Err = ParseLevelError;
fn from_str(s: &str) -> Result<Self, ParseLevelError> {
s.parse::<usize>()
.map_err(|_| ParseLevelError { _p: () })
.and_then(|num| match num {
1 => Ok(Level::ERROR),
2 => Ok(Level::WARN),
3 => Ok(Level::INFO),
4 => Ok(Level::DEBUG),
5 => Ok(Level::TRACE),
_ => Err(ParseLevelError { _p: () }),
})
.or_else(|_| match s {
s if s.eq_ignore_ascii_case("error") => Ok(Level::ERROR),
s if s.eq_ignore_ascii_case("warn") => Ok(Level::WARN),
s if s.eq_ignore_ascii_case("info") => Ok(Level::INFO),
s if s.eq_ignore_ascii_case("debug") => Ok(Level::DEBUG),
s if s.eq_ignore_ascii_case("trace") => Ok(Level::TRACE),
_ => Err(ParseLevelError { _p: () }),
})
}
}
#[repr(usize)]
#[derive(Copy, Clone, Debug, Hash, Eq, PartialEq)]
enum LevelInner {
/// The "trace" level.
///
/// Designates very low priority, often extremely verbose, information.
Trace = 0,
/// The "debug" level.
///
/// Designates lower priority information.
Debug = 1,
/// The "info" level.
///
/// Designates useful information.
Info = 2,
/// The "warn" level.
///
/// Designates hazardous situations.
Warn = 3,
/// The "error" level.
///
/// Designates very serious errors.
Error = 4,
}
// === impl LevelFilter ===
impl From<Level> for LevelFilter {
#[inline]
fn from(level: Level) -> Self {
Self::from_level(level)
}
}
impl From<Option<Level>> for LevelFilter {
#[inline]
fn from(level: Option<Level>) -> Self {
Self(level)
}
}
impl From<LevelFilter> for Option<Level> {
#[inline]
fn from(filter: LevelFilter) -> Self {
filter.into_level()
}
}
impl LevelFilter {
/// The "off" level.
///
/// Designates that trace instrumentation should be completely disabled.
pub const OFF: LevelFilter = LevelFilter(None);
/// The "error" level.
///
/// Designates very serious errors.
pub const ERROR: LevelFilter = LevelFilter::from_level(Level::ERROR);
/// The "warn" level.
///
/// Designates hazardous situations.
pub const WARN: LevelFilter = LevelFilter::from_level(Level::WARN);
/// The "info" level.
///
/// Designates useful information.
pub const INFO: LevelFilter = LevelFilter::from_level(Level::INFO);
/// The "debug" level.
///
/// Designates lower priority information.
pub const DEBUG: LevelFilter = LevelFilter::from_level(Level::DEBUG);
/// The "trace" level.
///
/// Designates very low priority, often extremely verbose, information.
pub const TRACE: LevelFilter = LevelFilter(Some(Level::TRACE));
/// Returns a `LevelFilter` that enables spans and events with verbosity up
/// to and including `level`.
pub const fn from_level(level: Level) -> Self {
Self(Some(level))
}
/// Returns the most verbose [`Level`] that this filter accepts, or `None`
/// if it is [`OFF`].
///
/// [`OFF`]: LevelFilter::OFF
pub const fn into_level(self) -> Option<Level> {
self.0
}
// These consts are necessary because `as` casts are not allowed as
// match patterns.
const ERROR_USIZE: usize = LevelInner::Error as usize;
const WARN_USIZE: usize = LevelInner::Warn as usize;
const INFO_USIZE: usize = LevelInner::Info as usize;
const DEBUG_USIZE: usize = LevelInner::Debug as usize;
const TRACE_USIZE: usize = LevelInner::Trace as usize;
// Using the value of the last variant + 1 ensures that we match the value
// for `Option::None` as selected by the niche optimization for
// `LevelFilter`. If this is the case, converting a `usize` value into a
// `LevelFilter` (in `LevelFilter::current`) will be an identity conversion,
// rather than generating a lookup table.
const OFF_USIZE: usize = LevelInner::Error as usize + 1;
/// Returns a `LevelFilter` that matches the most verbose [`Level`] that any
/// currently active [`Subscriber`] will enable.
///
/// User code should treat this as a *hint*. If a given span or event has a
/// level *higher* than the returned `LevelFilter`, it will not be enabled.
/// However, if the level is less than or equal to this value, the span or
/// event is *not* guaranteed to be enabled; the subscriber will still
/// filter each callsite individually.
///
/// Therefore, comparing a given span or event's level to the returned
/// `LevelFilter` **can** be used for determining if something is
/// *disabled*, but **should not** be used for determining if something is
/// *enabled*.
///
/// [`Level`]: super::Level
/// [`Subscriber`]: super::Subscriber
#[inline(always)]
pub fn current() -> Self {
match MAX_LEVEL.load(Ordering::Relaxed) {
Self::ERROR_USIZE => Self::ERROR,
Self::WARN_USIZE => Self::WARN,
Self::INFO_USIZE => Self::INFO,
Self::DEBUG_USIZE => Self::DEBUG,
Self::TRACE_USIZE => Self::TRACE,
Self::OFF_USIZE => Self::OFF,
#[cfg(debug_assertions)]
unknown => unreachable!(
"/!\\ `LevelFilter` representation seems to have changed! /!\\ \n\
This is a bug (and it's pretty bad). Please contact the `tracing` \
maintainers. Thank you and I'm sorry.\n \
The offending repr was: {:?}",
unknown,
),
#[cfg(not(debug_assertions))]
_ => unsafe {
// Using `unreachable_unchecked` here (rather than
// `unreachable!()`) is necessary to ensure that rustc generates
// an identity conversion from integer -> discriminant, rather
// than generating a lookup table. We want to ensure this
// function is a single `mov` instruction (on x86) if at all
// possible, because it is called *every* time a span/event
// callsite is hit; and it is (potentially) the only code in the
// hottest path for skipping a majority of callsites when level
// filtering is in use.
//
// safety: This branch is only truly unreachable if we guarantee
// that no values other than the possible enum discriminants
// will *ever* be present. The `AtomicUsize` is initialized to
// the `OFF` value. It is only set by the `set_max` function,
// which takes a `LevelFilter` as a parameter. This restricts
// the inputs to `set_max` to the set of valid discriminants.
// Therefore, **as long as `MAX_VALUE` is only ever set by
// `set_max`**, this is safe.
crate::stdlib::hint::unreachable_unchecked()
},
}
}
pub(crate) fn set_max(LevelFilter(level): LevelFilter) {
let val = match level {
Some(Level(level)) => level as usize,
None => Self::OFF_USIZE,
};
// using an AcqRel swap ensures an ordered relationship of writes to the
// max level.
MAX_LEVEL.swap(val, Ordering::AcqRel);
}
}
impl fmt::Display for LevelFilter {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match *self {
LevelFilter::OFF => f.pad("off"),
LevelFilter::ERROR => f.pad("error"),
LevelFilter::WARN => f.pad("warn"),
LevelFilter::INFO => f.pad("info"),
LevelFilter::DEBUG => f.pad("debug"),
LevelFilter::TRACE => f.pad("trace"),
}
}
}
impl fmt::Debug for LevelFilter {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match *self {
LevelFilter::OFF => f.pad("LevelFilter::OFF"),
LevelFilter::ERROR => f.pad("LevelFilter::ERROR"),
LevelFilter::WARN => f.pad("LevelFilter::WARN"),
LevelFilter::INFO => f.pad("LevelFilter::INFO"),
LevelFilter::DEBUG => f.pad("LevelFilter::DEBUG"),
LevelFilter::TRACE => f.pad("LevelFilter::TRACE"),
}
}
}
impl FromStr for LevelFilter {
type Err = ParseLevelFilterError;
fn from_str(from: &str) -> Result<Self, Self::Err> {
from.parse::<usize>()
.ok()
.and_then(|num| match num {
0 => Some(LevelFilter::OFF),
1 => Some(LevelFilter::ERROR),
2 => Some(LevelFilter::WARN),
3 => Some(LevelFilter::INFO),
4 => Some(LevelFilter::DEBUG),
5 => Some(LevelFilter::TRACE),
_ => None,
})
.or_else(|| match from {
"" => Some(LevelFilter::ERROR),
s if s.eq_ignore_ascii_case("error") => Some(LevelFilter::ERROR),
s if s.eq_ignore_ascii_case("warn") => Some(LevelFilter::WARN),
s if s.eq_ignore_ascii_case("info") => Some(LevelFilter::INFO),
s if s.eq_ignore_ascii_case("debug") => Some(LevelFilter::DEBUG),
s if s.eq_ignore_ascii_case("trace") => Some(LevelFilter::TRACE),
s if s.eq_ignore_ascii_case("off") => Some(LevelFilter::OFF),
_ => None,
})
.ok_or(ParseLevelFilterError(()))
}
}
/// Returned if parsing a `Level` fails.
#[derive(Debug)]
pub struct ParseLevelError {
_p: (),
}
impl fmt::Display for ParseLevelError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad(
"error parsing level: expected one of \"error\", \"warn\", \
\"info\", \"debug\", \"trace\", or a number 1-5",
)
}
}
impl fmt::Display for ParseLevelFilterError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad(
"error parsing level filter: expected one of \"off\", \"error\", \
\"warn\", \"info\", \"debug\", \"trace\", or a number 0-5",
)
}
}
#[cfg(feature = "std")]
impl std::error::Error for ParseLevelFilterError {}
// ==== Level and LevelFilter comparisons ====
// /!\ BIG, IMPORTANT WARNING /!\
// Do NOT mess with these implementations! They are hand-written for a reason!
//
// Since comparing `Level`s and `LevelFilter`s happens in a *very* hot path
// (potentially, every time a span or event macro is hit, regardless of whether
// or not is enabled), we *need* to ensure that these comparisons are as fast as
// possible. Therefore, we have some requirements:
//
// 1. We want to do our best to ensure that rustc will generate integer-integer
// comparisons wherever possible.
//
// The derived `Ord`/`PartialOrd` impls for `LevelFilter` will not do this,
// because `LevelFilter`s are represented by `Option<Level>`, rather than as
// a separate `#[repr(usize)]` enum. This was (unfortunately) necessary for
// backwards-compatibility reasons, as the `tracing` crate's original
// version of `LevelFilter` defined `const fn` conversions between `Level`s
// and `LevelFilter`, so we're stuck with the `Option<Level>` repr.
// Therefore, we need hand-written `PartialOrd` impls that cast both sides of
// the comparison to `usize`s, to force the compiler to generate integer
// compares.
//
// 2. The hottest `Level`/`LevelFilter` comparison, the one that happens every
// time a callsite is hit, occurs *within the `tracing` crate's macros*.
// This means that the comparison is happening *inside* a crate that
// *depends* on `tracing-core`, not in `tracing-core` itself. The compiler
// will only inline function calls across crate boundaries if the called
// function is annotated with an `#[inline]` attribute, and we *definitely*
// want the comparison functions to be inlined: as previously mentioned, they
// should compile down to a single integer comparison on release builds, and
// it seems really sad to push an entire stack frame to call a function
// consisting of one `cmp` instruction!
//
// Therefore, we need to ensure that all the comparison methods have
// `#[inline]` or `#[inline(always)]` attributes. It's not sufficient to just
// add the attribute to `partial_cmp` in a manual implementation of the
// trait, since it's the comparison operators (`lt`, `le`, `gt`, and `ge`)
// that will actually be *used*, and the default implementation of *those*
// methods, which calls `partial_cmp`, does not have an inline annotation.
//
// 3. We need the comparisons to be inverted. The discriminants for the
// `LevelInner` enum are assigned in "backwards" order, with `TRACE` having
// the *lowest* value. However, we want `TRACE` to compare greater-than all
// other levels.
//
// Why are the numeric values inverted? In order to ensure that `LevelFilter`
// (which, as previously mentioned, *has* to be internally represented by an
// `Option<Level>`) compiles down to a single integer value. This is
// necessary for storing the global max in an `AtomicUsize`, and for ensuring
// that we use fast integer-integer comparisons, as mentioned previously. In
// order to ensure this, we exploit the niche optimization. The niche
// optimization for `Option<{enum with a numeric repr}>` will choose
// `(HIGHEST_DISCRIMINANT_VALUE + 1)` as the representation for `None`.
// Therefore, the integer representation of `LevelFilter::OFF` (which is
// `None`) will be the number 5. `OFF` must compare higher than every other
// level in order for it to filter as expected. Since we want to use a single
// `cmp` instruction, we can't special-case the integer value of `OFF` to
// compare higher, as that will generate more code. Instead, we need it to be
// on one end of the enum, with `ERROR` on the opposite end, so we assign the
// value 0 to `ERROR`.
//
// This *does* mean that when parsing `LevelFilter`s or `Level`s from
// `String`s, the integer values are inverted, but that doesn't happen in a
// hot path.
//
// Note that we manually invert the comparisons by swapping the left-hand and
// right-hand side. Using `Ordering::reverse` generates significantly worse
// code (per Matt Godbolt's Compiler Explorer).
//
// Anyway, that's a brief history of why this code is the way it is. Don't
// change it unless you know what you're doing.
impl PartialEq<LevelFilter> for Level {
#[inline(always)]
fn eq(&self, other: &LevelFilter) -> bool {
self.0 as usize == filter_as_usize(&other.0)
}
}
impl PartialOrd for Level {
#[inline(always)]
fn partial_cmp(&self, other: &Level) -> Option<cmp::Ordering> {
Some(self.cmp(other))
}
#[inline(always)]
fn lt(&self, other: &Level) -> bool {
(other.0 as usize) < (self.0 as usize)
}
#[inline(always)]
fn le(&self, other: &Level) -> bool {
(other.0 as usize) <= (self.0 as usize)
}
#[inline(always)]
fn gt(&self, other: &Level) -> bool {
(other.0 as usize) > (self.0 as usize)
}
#[inline(always)]
fn ge(&self, other: &Level) -> bool {
(other.0 as usize) >= (self.0 as usize)
}
}
impl Ord for Level {
#[inline(always)]
fn cmp(&self, other: &Self) -> cmp::Ordering {
(other.0 as usize).cmp(&(self.0 as usize))
}
}
impl PartialOrd<LevelFilter> for Level {
#[inline(always)]
fn partial_cmp(&self, other: &LevelFilter) -> Option<cmp::Ordering> {
Some(filter_as_usize(&other.0).cmp(&(self.0 as usize)))
}
#[inline(always)]
fn lt(&self, other: &LevelFilter) -> bool {
filter_as_usize(&other.0) < (self.0 as usize)
}
#[inline(always)]
fn le(&self, other: &LevelFilter) -> bool {
filter_as_usize(&other.0) <= (self.0 as usize)
}
#[inline(always)]
fn gt(&self, other: &LevelFilter) -> bool {
filter_as_usize(&other.0) > (self.0 as usize)
}
#[inline(always)]
fn ge(&self, other: &LevelFilter) -> bool {
filter_as_usize(&other.0) >= (self.0 as usize)
}
}
#[inline(always)]
fn filter_as_usize(x: &Option<Level>) -> usize {
match x {
Some(Level(f)) => *f as usize,
None => LevelFilter::OFF_USIZE,
}
}
impl PartialEq<Level> for LevelFilter {
#[inline(always)]
fn eq(&self, other: &Level) -> bool {
filter_as_usize(&self.0) == other.0 as usize
}
}
impl PartialOrd for LevelFilter {
#[inline(always)]
fn partial_cmp(&self, other: &LevelFilter) -> Option<cmp::Ordering> {
Some(self.cmp(other))
}
#[inline(always)]
fn lt(&self, other: &LevelFilter) -> bool {
filter_as_usize(&other.0) < filter_as_usize(&self.0)
}
#[inline(always)]
fn le(&self, other: &LevelFilter) -> bool {
filter_as_usize(&other.0) <= filter_as_usize(&self.0)
}
#[inline(always)]
fn gt(&self, other: &LevelFilter) -> bool {
filter_as_usize(&other.0) > filter_as_usize(&self.0)
}
#[inline(always)]
fn ge(&self, other: &LevelFilter) -> bool {
filter_as_usize(&other.0) >= filter_as_usize(&self.0)
}
}
impl Ord for LevelFilter {
#[inline(always)]
fn cmp(&self, other: &Self) -> cmp::Ordering {
filter_as_usize(&other.0).cmp(&filter_as_usize(&self.0))
}
}
impl PartialOrd<Level> for LevelFilter {
#[inline(always)]
fn partial_cmp(&self, other: &Level) -> Option<cmp::Ordering> {
Some((other.0 as usize).cmp(&filter_as_usize(&self.0)))
}
#[inline(always)]
fn lt(&self, other: &Level) -> bool {
(other.0 as usize) < filter_as_usize(&self.0)
}
#[inline(always)]
fn le(&self, other: &Level) -> bool {
(other.0 as usize) <= filter_as_usize(&self.0)
}
#[inline(always)]
fn gt(&self, other: &Level) -> bool {
(other.0 as usize) > filter_as_usize(&self.0)
}
#[inline(always)]
fn ge(&self, other: &Level) -> bool {
(other.0 as usize) >= filter_as_usize(&self.0)
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::stdlib::mem;
#[test]
fn level_from_str() {
assert_eq!("error".parse::<Level>().unwrap(), Level::ERROR);
assert_eq!("4".parse::<Level>().unwrap(), Level::DEBUG);
assert!("0".parse::<Level>().is_err())
}
#[test]
fn filter_level_conversion() {
let mapping = [
(LevelFilter::OFF, None),
(LevelFilter::ERROR, Some(Level::ERROR)),
(LevelFilter::WARN, Some(Level::WARN)),
(LevelFilter::INFO, Some(Level::INFO)),
(LevelFilter::DEBUG, Some(Level::DEBUG)),
(LevelFilter::TRACE, Some(Level::TRACE)),
];
for (filter, level) in mapping.iter() {
assert_eq!(filter.into_level(), *level);
match level {
Some(level) => {
let actual: LevelFilter = (*level).into();
assert_eq!(actual, *filter);
}
None => {
let actual: LevelFilter = None.into();
assert_eq!(actual, *filter);
}
}
}
}
#[test]
fn level_filter_is_usize_sized() {
assert_eq!(
mem::size_of::<LevelFilter>(),
mem::size_of::<usize>(),
"`LevelFilter` is no longer `usize`-sized! global MAX_LEVEL may now be invalid!"
)
}
#[test]
fn level_filter_reprs() {
let mapping = [
(LevelFilter::OFF, LevelInner::Error as usize + 1),
(LevelFilter::ERROR, LevelInner::Error as usize),
(LevelFilter::WARN, LevelInner::Warn as usize),
(LevelFilter::INFO, LevelInner::Info as usize),
(LevelFilter::DEBUG, LevelInner::Debug as usize),
(LevelFilter::TRACE, LevelInner::Trace as usize),
];
for &(filter, expected) in &mapping {
let repr = unsafe {
// safety: The entire purpose of this test is to assert that the
// actual repr matches what we expect it to be --- we're testing
// that *other* unsafe code is sound using the transmuted value.
// We're not going to do anything with it that might be unsound.
mem::transmute::<LevelFilter, usize>(filter)
};
assert_eq!(expected, repr, "repr changed for {:?}", filter)
}
}
}