What causes "Expected {after:?} to exist" in bevyengine/bevy?

Insert relative to a label guaranteed to exist, e.g. `Render` or `First`

Expected {after:?} to exist

Error message

Expected {after:?} to exist

What it means

`RenderScheduleOrder` holds the ordered list of schedule labels the RenderApp executes (starting from First and Render in the default setup). `insert_after(after, schedule)` panics with "Expected {after:?} to exist" when the anchor label is not in that list — insertion is only possible relative to an already-present schedule.

Source

Thrown at crates/bevy_render/src/lib.rs:302

    pub labels: Vec<InternedScheduleLabel>,
}

impl Default for RenderScheduleOrder {
    fn default() -> Self {
        Self {
            labels: vec![First.intern(), Render.intern()],
        }
    }
}

impl RenderScheduleOrder {
    /// Adds the given `schedule` after the `after` schedule
    pub fn insert_after(&mut self, after: impl ScheduleLabel, schedule: impl ScheduleLabel) {
        let index = self
            .labels
            .iter()
            .position(|current| (**current).eq(&after))
            .unwrap_or_else(|| panic!("Expected {after:?} to exist"));
        self.labels.insert(index + 1, schedule.intern());
    }

    /// Adds the given `schedule` before the `before` schedule
    pub fn insert_before(&mut self, before: impl ScheduleLabel, schedule: impl ScheduleLabel) {
        let index = self
            .labels
            .iter()
            .position(|current| (**current).eq(&before))
            .unwrap_or_else(|| panic!("Expected {before:?} to exist"));
        self.labels.insert(index, schedule.intern());
    }
}

/// The main render schedule.
///
/// See also [`RenderGraph`] for more details.
#[derive(ScheduleLabel, Debug, Hash, PartialEq, Eq, Clone, Default)]

View on GitHub (pinned to 396ca72708)

Solutions

Insert relative to a label guaranteed to exist, e.g. `Render` or `First`
Ensure the anchor schedule was inserted earlier (inspect `order.labels`)
Insert your schedule standalone first, then reorder it relative to known labels

Example fix

// before
order.insert_after(MyCustomSchedule, MyNewSchedule); // MyCustomSchedule not inserted yet

// after
order.insert_after(Render, MyNewSchedule); // or insert MyCustomSchedule first

Defensive patterns

Strategy: validation

Validate before calling

// RenderScheduleOrder stores Box<dyn ScheduleLabel>
let exists = order.labels.iter().any(|l| (**l).eq(&MySchedule));
if exists {
    order.insert_after(MySchedule, MyNewSchedule);
} else {
    order.insert_after(Render, MyNewSchedule); // safe anchor
}

Prevention

Anchor insert_after calls to Render or First, which always exist
Insert custom labels before other plugins order against them
Log order.labels once at startup to see the actual order

When it happens

Trigger: Calling `render_schedule_order.insert_after(MySchedule, NewSchedule)` when `MySchedule` was never inserted into the order, was removed, or the label type is misspelled/different.

Common situations: Plugins inserting a custom sub-schedule relative to their own label before that label is registered; hand-written ordering code using the wrong label type.

Related errors

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/a60f8376ac7970eb. Report an issue: GitHub.