Bootstrap a working native aarch64-apple-darwin Rust toolchain

install-rust-aarch64-apple-darwin.sh

#!/bin/bash

# "Bash Strict Mode with logging"
set -eux -o pipefail
IFS=$'\n\t'

case $(uname -p) in
arm)
  ;;
*)
  echo This has only been tested with a native ARM shell.
  exit 1
  ;;
esac

if (file $(which rustup) | grep "arm64"); then
  exit 0
fi

# Adapted from
# https://github.com/rust-lang/rustup/issues/2413#issuecomment-729140037

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | arch --x86_64 sh -s -- \
  -y  \
  --default-host aarch64-apple-darwin \
  --default-toolchain nightly-2020-11-18

rustup_tempdir=$(mktemp -d)

pushd $rustup_tempdir

source ~/.cargo/env

# Adapted from
# https://github.com/rust-lang/rustup/issues/2413#issuecomment-729173518 and
# https://github.com/rust-lang/rustup/issues/2413#issuecomment-729216870
git clone https://github.com/rust-lang/rustup/ .
git checkout 5674652a45ecf9066128df32fbc51e965586e4b2
RUSTC=$(rustup which rustc) $(rustup which cargo) build
RUSTC=$(rustup which rustc) $(rustup which cargo) dev-install

popd

rm -Rf $rustup_tempdir

if ! (file $(which rustup) | grep -q "arm64"); then
  echo rustup did not get converted to ARM64 for some reason.
  exit 1
fi