Fully qualify crate paths in BevyManifest

[jnhyatt]

Objective

Subtle, very minor issue. The following code fails to compile on main:

struct bevy;
#[derive(::bevy::ecs::component::Component)]
struct MyComponent;

The derive proc macro is pasting in essentially:

impl bevy::ecs::component::Component for MyComponent

...which normally works, but I've added struct bevy, which makes the proc macro spit out incorrect code.

Very cursed, but to my knowledge has never been encountered in practice. All the same, it's technically incorrect and should be fixed.

Solution

The solution is simply to prepend :: to crate names. Specifically, all (all?) Bevy's derive macros determine the root crate name using BevyManifest, which does some toml-parsing witchcraft to figure out whether to qualify names using the umbrella bevy crate or individual bevy_xxx crates. I just added a :: to the spot where we parse the syn::Path. The above example compiles properly after that.

Testing

• CI should catch any errors since this change should cause compile errors if for some reason they're being used in a cursed way somewhere that would make this break something.

Note

If this does break something for someone, this really needs a comment in BevyManifest::maybe_get_path explaining why we can't make this change.

[SpecificProtagonist]

I haven't found a way to break this (apart from renaming crates of course, but that's broken already anyways).

[dj-blume9]

I don't have anything breaking for me with this change. Looks good.