title: Why does a clean yarn install delete modules from yarn.lock?
body: <p>In a React Native project: when I delete everything in my node_modules directory, then run yarn v 1.22 against my yarn.lock, modules are deleted from the text of yarn.lock and, consequently, my node_modules install is incomplete.</p>
  <p>This is inconvenient when the yarn.lock is committed, then another developer does a pull, tries to run yarn, and gets the results I described.</p>
  <p>Is there a way to run yarn so that all files in the module are installed, and nothing is deleted from yarn.lock?</p>