Creating a bundle complains about mem::forget

[SUPERCILEX]

Bevy version

0.7.0

What you did

#[derive(Component, Default)]
pub struct NominoMarker;

#[derive(Component, Deref)]
pub struct BoundingBoxes(&'static [Rect<f32>]);

#[derive(Bundle)]
pub struct NominoBundle {
    #[bundle]
    shape: bevy_prototype_lyon::entity::ShapeBundle,
    bounding_boxes: BoundingBoxes,
    _marker: NominoMarker,
}

What you expected to happen

No warnings

What actually happened

warning: call to `std::mem::forget` with a value that does not implement `Drop`. Forgetting such a type is the same as dropping it
   --> src/nominos.rs:106:10
    |
106 | #[derive(Bundle)]
    |          ^^^^^^
    |
    = note: `#[warn(clippy::forget_non_drop)]` on by default
note: argument has type `nominos::BoundingBoxes`
   --> src/nominos.rs:106:10
    |
106 | #[derive(Bundle)]
    |          ^^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#forget_non_drop
    = note: this warning originates in the derive macro `Bundle` (in Nightly builds, run with -Z macro-backtrace for more info)

[alice-i-cecile]

Are you on Rust nightly? Can you reproduce this with a simpler bundle?

[SUPERCILEX]

Yeah: rustc 1.62.0-nightly (18f314e70 2022-04-24). Simpler:

#[derive(Component, Default)]
pub struct NominoMarker;

#[derive(Bundle)]
pub struct TestBundle {
    _marker: NominoMarker,
}

[DJMcNab]

The std::mem::forget version of the bundle code is slightly suspect anyway; we need to migrate it to MaybeUninit (maybe ManuallyDrop is sufficient). (I suspect there are at least 2 open PRs which make this change.)

A temporary workaround is just to allow that lint for your entire crate.

[SUPERCILEX]

Seems like these two: #3634 and #2975

[alice-i-cecile]

Running into this on nightly too for my own projects, which breaks my clippy-checking CI. For those looking for a workaround, add #![allow(clippy::forget_non_drop)] to the top of your main.rs to silence the warning for now.

[ghost]

This problem seems to be fixed in main by #3001 because of the removal of the std::mem::forget call in bevy_ecs/src/bundle.rs (see https://github.com/bevyengine/bevy/pull/3001/files#diff-0e94997025571f709abd7cac97f03bb4e8ec8bf29650068a7e5ec07170011892L121-R126).

This code generates a warning when running cargo clippy with bevy 0.7but doesn't in bevy main:

use bevy::prelude::*;

#[derive(Bundle)]
pub struct Foo {
    bar: Bar,
}

#[derive(Component)]
struct Bar;

fn main() {}