output.txt

> multirust run 1.9.0 $PWD/rust-unstable.sh                                                                                                                                     logic@chaos
warning: 'multirust' is being renamed to 'rustup'. this command is deprecated. use 'rustup' instead
rustc 1.9.0 (e4e8b6668 2016-05-18)

Compiling without bootstrapt key:
code.rs:1:1: 1:27 error: #[feature] may not be used on the stable release channel
code.rs:1 #![feature(rustc_private)]
          ^~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error

Compiling with bootstrapt key:
code.rs:1:12: 1:25 warning: unused or unknown feature, #[warn(unused_features)] on by default
code.rs:1 #![feature(rustc_private)]
                     ^~~~~~~~~~~~~
> multirust run stable $PWD/rust-unstable.sh                                                                                                                                    logic@chaos
warning: 'multirust' is being renamed to 'rustup'. this command is deprecated. use 'rustup' instead
rustc 1.10.0 (cfcb716cf 2016-07-03)

Compiling without bootstrapt key:
code.rs:1:1: 1:27 error: #[feature] may not be used on the stable release channel
code.rs:1 #![feature(rustc_private)]
          ^~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error

Compiling with bootstrapt key:
code.rs:1:12: 1:25 warning: unused or unknown feature, #[warn(unused_features)] on by default
code.rs:1 #![feature(rustc_private)]
                     ^~~~~~~~~~~~~

rust-unstable.sh

#!/bin/bash

set -e

rustc --version

cat << EOF > code.rs
#![feature(rustc_private)]
#![crate_type = "lib"]
EOF

echo ""
echo "Compiling without bootstrapt key:"
rustc  code.rs || true

export RUSTC_BOOTSTRAP_KEY=`rustc --version | cut -f2 -d' ' | tr -d "\n" | md5sum | cut -c-8`

echo ""
echo "Compiling with bootstrapt key:"
rustc code.rs