Function wgpu_render_bundle_set_vertex_buffer 

pub fn wgpu_render_bundle_set_vertex_buffer(
    bundle: &mut RenderBundleEncoder,
    slot: u32,
    buffer_id: Id<Buffer>,
    offset: u64,
    size: Option<NonZero<u64>>,
)

Available on crate feature unstable-wgpu-27 only.