Function rustc_verbose_version 

pub async fn rustc_verbose_version(
    host: &Host,
    toolchain: &str,
) -> Result<String>

The rustc -vV identity of toolchain — what a cached -Zbuild-std artifact pins to, because a channel name like nightly outlives the compiler it resolves to after rustup update.

Errors

Returns an error when rustup cannot run the toolchain’s rustc.