im 8.0.0

Assorted immutable collection datatypes
Documentation 
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extern crate rustc_version;

use rustc_version::{version_meta, Channel};

fn main() {
    println!("cargo:rerun-if-changed=build.rs");
    match version_meta().unwrap().channel {
        Channel::Nightly => println!("cargo:rustc-cfg=has_specialisation"),
        _ => (),
    }
}