Pumpkin-MC/Pumpkin · error

unexpected event

Error message

unexpected event

What it means

This panic fires inside `FromIntoEvent::data_from_event` for `ChunkSaveEvent` when the passed `Event` is not `Event::ChunkSaveEvent`. This impl unwraps the typed save payload after type-keyed routing; any other variant violates the library invariant that handlers only see their registered event type and causes a panic in the plugin thread.

Solutions

1. Correct the dispatcher mapping so save handlers receive only `Event::ChunkSaveEvent`.
2. Rebuild plugin and host from one API version to remove `Event` enum drift.
3. Construct `Event::ChunkSaveEvent(data)` explicitly before invoking handlers in a harness.
4. Add a debug assertion that `ev.event_type() == EventType::ChunkSaveEvent` prior to conversion.

Example fix

// before
Event::ChunkSaveEvent(data) => data,
_ => panic!("unexpected event"),
// after (diagnostic)
Event::ChunkSaveEvent(data) => data,
other => unreachable!("ChunkSave handler got {:?}", other.event_type()),

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

fn as_chunk_save(ev: &Event) -> Option<&ChunkSaveEventData> {
    if let Event::ChunkSaveEvent(d) = ev { Some(d) } else { None }
}

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

When it happens

Trigger: Routing e.g. `Event::ChunkLoadEvent` into a `ChunkSaveEvent` handler, or calling the generated conversion directly with a mismatched `Event` in custom dispatch infrastructure.

Common situations: Custom hosts with swapped chunk event registrations; host/plugin ABI or WIT version skew after enum changes; test harnesses reusing a single `Event` value across 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/f75340f8e2b51b2f. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-plugin-api/src/events/world/chunk_save.rs:15

use crate::wit::pumpkin::plugin::event::{ChunkSaveEventData, Event, EventType};

use super::super::FromIntoEvent;

/// An event that occurs when a chunk is saved in a world.
pub struct ChunkSaveEvent;

impl FromIntoEvent for ChunkSaveEvent {
    const EVENT_TYPE: EventType = EventType::ChunkSaveEvent;
    type Data = ChunkSaveEventData;

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

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

View on GitHub (pinned to 8d4639e25a)