Pumpkin-MC/Pumpkin · error

unexpected event

Error message

unexpected event

What it means

This panic fires inside `FromIntoEvent::data_from_event` for `ChunkPopulateEvent` when the passed `Event` variant is anything other than `Event::ChunkPopulateEvent`. The conversion exists to unwrap typed data after `EVENT_TYPE`-based routing; a foreign variant indicates the event bus misrouted the event or someone constructed the `Event` manually, and the handler panics.

Solutions

1. Ensure the bus dispatches only `Event::ChunkPopulateEvent` to this handler.
2. Synchronize plugin API and host builds to the same revision.
3. Wrap payload as `Event::ChunkPopulateEvent(data)` in custom dispatch code.
4. Add an integration test asserting each handler receives exactly its registered event type.

Example fix

// before
if is_chunk_event(&ev) { populate_handler(ev) } // any chunk event passes
// after
if matches!(ev, Event::ChunkPopulateEvent(_)) { populate_handler(ev) }

assert!(matches!(event, Event::ChunkPopulateEvent(_)), "handler requires Event::ChunkPopulateEvent");

fn as_chunk_populate(ev: &Event) -> Option<&ChunkPopulateEventData> {
    if let Event::ChunkPopulateEvent(d) = ev { Some(d) } else { None }
}

// guard before dispatch:
if let Event::ChunkPopulateEvent(data) = event { handle(data) } else { log::warn!("mismatched event at chunk-populate handler") }

When it happens

Trigger: Delivering any other world event to a `ChunkPopulateEvent` handler, or invoking the macro-generated conversion with a mismatched `Event` in a custom harness.

Common situations: Alternate plugin hosts with incorrect event-to-handler keying; host/plugin version skew changing the `Event` enum; tests sharing one event across multiple registered handlers.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• unexpected event
• unexpected event
• unexpected event
• unexpected event
• unexpected event

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/0100df039a3e6b8e. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-plugin-api/src/events/world/chunk_populate.rs:13

use super::super::FromIntoEvent;
use crate::wit::pumpkin::plugin::event::{ChunkPopulateEventData, Event, EventType};

/// Event triggered when a chunk is populated.
pub struct ChunkPopulateEvent;
impl FromIntoEvent for ChunkPopulateEvent {
    const EVENT_TYPE: EventType = EventType::ChunkPopulateEvent;
    type Data = ChunkPopulateEventData;

    fn data_from_event(event: Event) -> Self::Data {
        match event {
            Event::ChunkPopulateEvent(data) => data,
            _ => panic!("unexpected event"),
        }
    }

    fn data_into_event(data: Self::Data) -> Event {
        Event::ChunkPopulateEvent(data)
    }
}

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