Function format_opencl 

pub fn format_opencl(
    version: &str,
    platform: &str,
    device: Option<&str>,
) -> String

Render the OpenCL field, distinguishing “usable” from “present but inert”.

A platform that advertises a version while exposing no device cannot run anything, so saying so is the whole point of the field. See the module docs for why this does not simply enable rusticl for itself and report the better-looking answer.