tracing_capture/predicates/
parent.rs

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//! `parent()` predicate factory.

use predicates::{
    reflection::{Case, PredicateReflection, Product},
    Predicate,
};

use std::{fmt, iter};

use crate::{Captured, CapturedSpan};

/// Creates a predicate for the direct parent [`CapturedSpan`] of a span or a [`CapturedEvent`].
///
/// [`CapturedEvent`]: crate::CapturedEvent
///
/// # Examples
///
/// ```
/// # use predicates::ord::eq;
/// # use tracing_core::Level;
/// # use tracing_subscriber::{layer::SubscriberExt, Registry};
/// # use tracing_capture::{predicates::*, CaptureLayer, SharedStorage};
/// let storage = SharedStorage::default();
/// let subscriber = Registry::default().with(CaptureLayer::new(&storage));
/// tracing::subscriber::with_default(subscriber, || {
///     tracing::info_span!("compute").in_scope(|| {
///         tracing::info!(answer = 42, "done");
///     });
/// });
///
/// let storage = storage.lock();
/// let parent_pred = level(Level::INFO) & name(eq("compute"));
/// let _ = storage.scan_events().single(&parent(parent_pred));
/// ```
pub fn parent<P>(matches: P) -> ParentPredicate<P>
where
    P: for<'a> Predicate<CapturedSpan<'a>>,
{
    ParentPredicate { matches }
}

/// Predicate for the parent of a [`CapturedSpan`] or [`CapturedEvent`] returned
/// by the [`parent()`] function.
///
/// [`CapturedEvent`]: crate::CapturedEvent
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ParentPredicate<P> {
    matches: P,
}

impl_bool_ops!(ParentPredicate<P>);

impl<P> fmt::Display for ParentPredicate<P>
where
    P: for<'a> Predicate<CapturedSpan<'a>>,
{
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(formatter, "parent({})", self.matches)
    }
}

impl<P> PredicateReflection for ParentPredicate<P> where P: for<'a> Predicate<CapturedSpan<'a>> {}

impl<'a, P, T> Predicate<T> for ParentPredicate<P>
where
    T: Captured<'a>,
    P: for<'p> Predicate<CapturedSpan<'p>>,
{
    fn eval(&self, variable: &T) -> bool {
        let parent = variable.parent();
        parent.map_or(false, |parent| self.matches.eval(&parent))
    }

    fn find_case(&self, expected: bool, variable: &T) -> Option<Case<'_>> {
        let Some(parent) = variable.parent() else {
            return if expected {
                None // was expecting a parent, but there is none
            } else {
                let product = Product::new("parent", "None");
                Some(Case::new(Some(self), expected).add_product(product))
            };
        };

        let child = self.matches.find_case(expected, &parent)?;
        Some(Case::new(Some(self), expected).add_child(child))
    }
}

/// Creates a predicate for ancestor [`CapturedSpan`]s of a span or a [`CapturedEvent`].
/// The predicate is true iff the wrapped span predicate holds true for *any* of the ancestors.
///
/// [`CapturedEvent`]: crate::CapturedEvent
///
/// # Examples
///
/// ```
/// # use predicates::ord::eq;
/// # use tracing_core::Level;
/// # use tracing_subscriber::{layer::SubscriberExt, Registry};
/// # use tracing_capture::{predicates::*, CaptureLayer, SharedStorage};
/// let storage = SharedStorage::default();
/// let subscriber = Registry::default().with(CaptureLayer::new(&storage));
/// tracing::subscriber::with_default(subscriber, || {
///     let _entered = tracing::info_span!("wrapper").entered();
///     tracing::info_span!("compute").in_scope(|| {
///         tracing::info!(answer = 42, "done");
///     });
/// });
///
/// let storage = storage.lock();
/// let parent_pred = level(Level::INFO) & name(eq("wrapper"));
/// let _ = storage.scan_events().single(&ancestor(parent_pred));
/// ```
pub fn ancestor<P>(matches: P) -> AncestorPredicate<P>
where
    P: for<'a> Predicate<CapturedSpan<'a>>,
{
    AncestorPredicate { matches }
}

/// Predicate for the ancestors of a [`CapturedSpan`] or [`CapturedEvent`] returned
/// by the [`ancestor()`] function.
///
/// [`CapturedEvent`]: crate::CapturedEvent
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct AncestorPredicate<P> {
    matches: P,
}

impl_bool_ops!(AncestorPredicate<P>);

impl<P> fmt::Display for AncestorPredicate<P>
where
    P: for<'a> Predicate<CapturedSpan<'a>>,
{
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(formatter, "ancestor({})", self.matches)
    }
}

impl<P> PredicateReflection for AncestorPredicate<P> where P: for<'a> Predicate<CapturedSpan<'a>> {}

impl<'a, P, T> Predicate<T> for AncestorPredicate<P>
where
    T: Captured<'a>,
    P: for<'p> Predicate<CapturedSpan<'p>>,
{
    fn eval(&self, variable: &T) -> bool {
        let mut ancestors = iter::successors(variable.parent(), CapturedSpan::parent);
        ancestors.any(|span| self.matches.eval(&span))
    }

    fn find_case(&self, expected: bool, variable: &T) -> Option<Case<'_>> {
        let mut ancestors = iter::successors(variable.parent(), CapturedSpan::parent);
        if expected {
            // Return the first of ancestor cases.
            let child = ancestors.find_map(|span| self.matches.find_case(expected, &span))?;
            Some(Case::new(Some(self), expected).add_child(child))
        } else {
            // Need all ancestor cases.
            let case = Case::new(Some(self), expected);
            ancestors.try_fold(case, |case, span| {
                let child = self.matches.find_case(expected, &span)?;
                Some(case.add_child(child))
            })
        }
    }
}