Use an opaque type for EntityCommand::with_entity

[JoJoJet]

Objective

The trait method with_entity is used to add an EntityCommand to the command queue. Currently this method returns WithEntity<C> which pairs a command with an Entity. By replacing this explicit type with an opaque type, implementors can override this default implementation by returning a custom command or closure that does the same thing with a lower memory footprint.

Solution

Return an opaque type from the method. As a bonus this file is now cleaner without the WithEntity boilerplate

[github-actions]

It looks like your PR is a breaking change, but you didn't provide a migration guide.

Could you add some context on what users should update when this change get released in a new version of Bevy?
It will be used to help writing the migration guide for the version. Putting it after a ## Migration Guide will help it get automatically picked up by our tooling.

[github-actions]

Your PR increases Bevy Minimum Supported Rust Version. Please update the rust-version field in the root Cargo.toml file.

[github-actions]

Your PR increases Bevy Minimum Supported Rust Version. Please update the rust-version field in the root Cargo.toml file.

[Nilirad]

Just wanted to know if it is ok to use impl Command as a return type in this case, as the release notes generally discourage using this syntax in public traits.

[JoJoJet]

Just wanted to know if it is ok to use impl Command as a return type in this case, as the release notes generally discourage using this syntax in public traits.

I think the main reason this use is discouraged is due to weirdness surrounding Send bounds and other auto traits. Command already has a Send bound so I think this should be fine.

[JoJoJet]

On further consideration I don't think this is a breaking change. It was not possible to construct or use the WithEntity type in any way other than as a Command, so it was effectively an opaque type