bevyengine/bevy · error

{e}

Error message

{e}

What it means

Forwarding panic (panic_on_err) in World::entity_mut: mutable entity fetching failed; the underlying error (e.g. EntityMutableFetchError for despawned or doubly-borrowed entities) is rendered into this message.

Source

Thrown at crates/bevy_ecs/src/world/mod.rs:884

    /// let e3 = world.spawn(Position { x: 0.0, y: 1.0 }).id();
    ///
    /// let ids = EntityHashSet::from_iter([e1, e2, e3]);
    /// for (_id, mut eref) in world.entity_mut(&ids) {
    ///     let mut pos = eref.get_mut::<Position>().unwrap();
    ///     pos.y = 2.0;
    ///     assert_eq!(pos.y, 2.0);
    /// }
    /// ```
    ///
    /// [`EntityHashSet`]: crate::entity::EntityHashSet
    #[inline]
    #[track_caller]
    pub fn entity_mut<F: WorldEntityFetch>(&mut self, entities: F) -> F::Mut<'_> {
        #[inline(never)]
        #[cold]
        #[track_caller]
        fn panic_on_err(e: EntityMutableFetchError) -> ! {
            panic!("{e}");
        }

        match self.get_entity_mut(entities) {
            Ok(fetched) => fetched,
            Err(e) => panic_on_err(e),
        }
    }

    /// Returns the components of an [`Entity`] through [`ComponentInfo`].
    #[inline]
    pub fn inspect_entity(
        &self,
        entity: Entity,
    ) -> Result<impl Iterator<Item = &ComponentInfo>, EntityNotSpawnedError> {
        let entity_location = self.entities().get_spawned(entity)?;

        let archetype = self
            .archetypes()

View on GitHub (pinned to 396ca72708)

Solutions

1. Use world.get_entity_mut(...) to handle missing entities as an Option
2. Avoid requesting the same entity mutably twice in one fetch
3. Check entity validity after any operation that may despawn entities

When it happens

Trigger: Thrown at crates/bevy_ecs/src/world/mod.rs:884 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/f9cc9024b4b0c65c. Report an issue: GitHub.