Probably it should be possible to have "holes" in the colorAttachments array (e.g. have attachments 0 and 2, but not 1).

I know we discussed this a VERY long time ago, but right now in the API this is not expressible. We should make sure it's possible and change the API to support it (e.g. sequence of nullable, or put the attachment location inside the GPURenderPassColorAttachmentDescriptor like with GPUBindGroupLayoutEntry).