old_contents: {
      'packages': {
          'brew': {
              'bundle': 'conf/Brewfile',
              'post_install': (
                  'HOME/bin/update_shell.sh `brew --prefix`/bin/zsh',  # set shell to homebrew'd shell
                  'ln -sf `brew --prefix`/share/zsh-autosuggestions/zsh-autosuggestions.zsh HOME/bin/shell_sources/3rdparty',
                  'perl -pi -e \'s/fc -rl 1/fc -rli 1/\' "$(brew --prefix fzf)/shell/key-bindings.zsh"',
                  # https://docs.docker.com/docker-for-mac/#zsh
                  """
                      etc=/Applications/Docker.app/Contents/Resources/etc;
                      sf=`brew --prefix`/share/zsh/site-functions;
                      ln -sf $etc/docker.zsh-completion $sf/_docker;
                      ln -sf $etc/docker-machine.zsh-completion $sf/_docker-machine;
                      ln -sf $etc/docker-compose.zsh-completion $sf/_docker-compose;
                  """,
              ),
          },
          'python': {
              'cmd': ['pip3', 'install', '--upgrade', '-r', 'conf/requirements.txt'],
              'post_install': (
                  'poetry completions zsh > `brew --prefix`/share/zsh/site-functions/_poetry',
              )
          },
          'node': {
              'cmd': "cat conf/npm.txt | xargs -t npm install -g",
          },
          'rust': {
              'cmd': (
                  ['rustup', 'update'],
                  ['cargo', '+nightly', 'install', 'pyoxidizer', '-Z', 'install-upgrade'],
              ),
          },
          'mac': {
              'skip_if_not_requested': True,
              'path': 'conf/mac.py'
          },
          'vscode': {
              'extensions': 'conf/vscode.txt',
          },
      },
  }
  
new_contents: {
      'packages': {
          'brew': {
              'bundle': 'conf/Brewfile',
              'post_install': (
                  'HOME/bin/update_shell.sh `brew --prefix`/bin/zsh',  # set shell to homebrew'd shell
                  'ln -sf `brew --prefix`/share/zsh-autosuggestions/zsh-autosuggestions.zsh HOME/bin/shell_sources/3rdparty',
                  'perl -pi -e \'s/fc -rl 1/fc -rli 1/\' "$(brew --prefix fzf)/shell/key-bindings.zsh"',
                  # https://docs.docker.com/docker-for-mac/#zsh
                  """
                      etc=/Applications/Docker.app/Contents/Resources/etc;
                      sf=`brew --prefix`/share/zsh/site-functions;
                      ln -sf $etc/docker.zsh-completion $sf/_docker;
                      ln -sf $etc/docker-machine.zsh-completion $sf/_docker-machine;
                      ln -sf $etc/docker-compose.zsh-completion $sf/_docker-compose;
                  """,
              ),
          },
          'python': {
              'cmd': ['pip3', 'install', '--upgrade', '-r', 'conf/requirements.txt'],
              'post_install': (
                  'poetry completions zsh > `brew --prefix`/share/zsh/site-functions/_poetry',
              )
          },
          'node': {
              'cmd': "cat conf/npm.txt | xargs -t npm install -g",
          },
          'rust': {
              'skip_if_not_requested': True,
              'cmd': (
                  ['rustup', 'update'],
                  ['rustup', 'install', 'nightly'],
                  ['cargo', '+nightly', 'install', 'pyoxidizer', '-Z', 'install-upgrade'],
              ),
          },
          'mac': {
              'skip_if_not_requested': True,
              'path': 'conf/mac.py'
          },
          'vscode': {
              'extensions': 'conf/vscode.txt',
          },
      },
  }
  
subject: Add rust nightly install to rust packages and skip it by default