vectordotdev/vector · error

Failed type coercion

Error message

Failed type coercion, {self:?} is not a metric reference

What it means

EventRef::as_metric downcasts the EventRef enum to its Metric variant and panics if the reference actually holds a LogEvent or TraceEvent. Like the other coercions in this file it encodes a caller assertion rather than a recoverable Result. The Debug repr of the real variant is embedded in the panic.

Solutions

1. Match on EventRef and only call as_metric for EventRef::Metric
2. Filter or route non-metric events before reaching this code
3. Guard with matches!(r, EventRef::Metric(_)) prior to coercion

Example fix

// before
let metric = EventRef::from(&event).as_metric();
// after
if let EventRef::Metric(metric) = EventRef::from(&event) {
    // use metric
}

assert!(matches!(event_ref, EventRef::Metric(_)), "expected metric, got {:?}", event_ref);

fn as_metric_ref(r: EventRef<'_>) -> Option<&Metric> {
    match r {
        EventRef::Metric(m) => Some(m),
        _ => None,
    }
}

When it happens

Trigger: Calling as_metric on an EventRef built from Event::Log or Event::Trace, e.g. EventRef::from(&event).as_metric() in a metric sink receiving log events.

Common situations: Metric-processing code (transforms writing custom metric logic, metric sinks) hooked into a pipeline where log-producing sources (file, stdin, kafka) also route into it.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Failed type coercion
• Failed type coercion
• Failed type coercion
• Failed type coercion
• Failed type coercion

AI-assisted analysis of vectordotdev/vector@bdb87aeaa4 (2026-09-16). Data as JSON: /api/errors/b9ba9b942102c0fb. Report an issue: GitHub.

Appendix: source

Thrown at lib/vector-core/src/event/ref.rs:52

    /// # Panics
    ///
    /// This will panic if this is not a `LogEvent` reference.
    pub fn into_log(self) -> LogEvent {
        match self {
            Self::Log(log) => log.clone(),
            _ => panic!("Failed type coercion, {self:?} is not a log reference"),
        }
    }

    /// Extract the `Metric` reference in this.
    ///
    /// # Panics
    ///
    /// This will panic if this is not a `Metric` reference.
    pub fn as_metric(self) -> &'a Metric {
        match self {
            Self::Metric(metric) => metric,
            _ => panic!("Failed type coercion, {self:?} is not a metric reference"),
        }
    }

    /// Convert this reference into a new `Metric` by cloning.
    ///
    /// # Panics
    ///
    /// This will panic if this is not a `Metric` reference.
    pub fn into_metric(self) -> Metric {
        match self {
            Self::Metric(metric) => metric.clone(),
            _ => panic!("Failed type coercion, {self:?} is not a metric reference"),
        }
    }
}

impl<'a> From<&'a Event> for EventRef<'a> {
    fn from(event: &'a Event) -> Self {

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