message: test for rustup-toolchain-install-master
diff: @@ -13,6 +13,12 @@ set -e
  #
  # ./rustup-toolchain $COMMIT: Update "miri" toolchain and `rust-version` file to match that commit.
  +# Make sure rustup-toolchain-install-master is installed.
  +if ! which rustup-toolchain-install-master >/dev/null; then
  + echo "Please install rustup-toolchain-install-master by running 'cargo install rustup-toolchain-install-master'"
  + exit 1
  +fi
  +
  # Determine new commit.
  if [[ "$1" == "" ]]; then
  NEW_COMMIT=$(cat rust-version)
  