Pumpkin-MC/Pumpkin · error

unexpected event

Error message

unexpected event

What it means

This panic fires inside `FromIntoEvent::data_from_event` for `AsyncStructureSpawnEvent` when the passed `Event` variant is anything other than `Event::AsyncStructureSpawnEvent`. The conversion unwraps typed payload after type-based routing; receiving any other variant violates the invariant that the event bus delivers only matching events and results in a panic inside the plugin handler.

Solutions

1. Correct routing so only `Event::AsyncStructureSpawnEvent` reaches this handler.
2. Align plugin API versions between host and plugin to eliminate enum drift.
3. Construct `Event::AsyncStructureSpawnEvent(data)` explicitly in custom harnesses.
4. Add a debug assertion comparing `event.event_type()` with `EventType::AsyncStructureSpawnEvent` before conversion.

Example fix

// before
handler(Event::ChunkLoadEvent(data)) // wrong variant
// after
handler(Event::AsyncStructureSpawnEvent(data))

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

fn as_async_structure_spawn(ev: &Event) -> Option<&AsyncStructureSpawnEventData> {
    if let Event::AsyncStructureSpawnEvent(d) = ev { Some(d) } else { None }
}

// guard before dispatch:
if let Event::AsyncStructureSpawnEvent(data) = event { handle(data) } else { log::warn!("non-spawn event in structure-spawn handler") }

When it happens

Trigger: Dispatching a foreign event variant to an `AsyncStructureSpawnEvent` handler, or a custom plugin harness invoking the generated conversion with a mismatched `Event`.

Common situations: Hand-written dispatch tables in alternate hosts; host/plugin ABI skew where `Event` variants changed; test fixtures passing one shared event to multiple 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/cbad2619e92ebd89. Report an issue: GitHub.

Appendix: source

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

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

/// Event triggered when a structure is asynchronously spawned.
pub struct AsyncStructureSpawnEvent;
impl FromIntoEvent for AsyncStructureSpawnEvent {
    const EVENT_TYPE: EventType = EventType::AsyncStructureSpawnEvent;
    type Data = AsyncStructureSpawnEventData;

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

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

View on GitHub (pinned to 8d4639e25a)