bevy_lint: Add zst_query lint

[MrGVSV]

Resolves #130

[janhohenheim]

Just making sure, this still allows Query<(), With<Foo>>, right? :)

[MrGVSV]

Just making sure, this still allows Query<(), With<Foo>>, right? :)

Good question! I just tested it and it seems like it does! I added a test for this case specifically.

[BD103]

Is there ever a case where there may be generics before the final path segment? If so we could do this:

Suggested change

	path.segments.last()?.args().args.get(index)
	path.segments.iter().flat_map(|segment| segment.args().args).nth(index)

This implementation joins all of the generics in a path together, then finds the GenericArg at the index. This may have undesired effects, though I haven't tested it.

[MrGVSV]

Yeah there could be like Foo::<i32>::baz::<usize> for a function signature type or something. So it could be useful. I don't think it would break things for our purposes here since Query doesn't look like that haha.

I'll try it out!

[MrGVSV]

On second thought, this might break in cases like:

trait Queryable {
    type Query<'w, 's, D: QueryData + 'static, F: QueryFilter + 'static>;
}

struct MyQueryable<T>(T);

impl<T> Queryable for MyQueryable<T> {
    type Query<'w, 's, D: QueryData + 'static, F: QueryFilter + 'static> = Query<'w, 's, D, F>;
}

fn system<'w, 's>(query: <MyQueryable<f32> as Queryable>::Query<'w, 's, &'static Foo, ()>) {}

Although, to be fair, I just tested this and we don't currently catch associated types like this.

[MrGVSV]

Maybe we save adding this functionality for the future when it's needed? It might at that point even make sense to be a separate function depending on the edge cases.

[BD103]

Maybe we save adding this functionality for the future when it's needed?

I'm fine with that, but would you mind adding a comment to the function docs do users know that it only indexes the generics in the final path segment? (Non-blocking, though)

[BD103]

Thank you, let's get this merged!