Caching Yarn workspaces on CircleCI

Yarn workspaces make it easy to share packages within the same monorepo but I found that something wasn’t quite working with CircleCI’s caching — the correct cache was found and used but it didn’t seem to be enough because yarn install continued for 30 seconds.

Yarn workspaces use a single yarn.lock at the root of the project along with a node_modules directory. However, even though the individual workspace node_modules directories may look empty you’ll probably see that they contain a .bin directory if you list hidden files — and this was the clue to fix my caching issue.

To ensure the cache is properly populated you must specify that each workspace’s node_modules directory is included in the cache along with the main one:

- save_cache:
    key: yarn-{{ checksum "yarn.lock" }}
    paths:
      - node_modules
      - workspace-a/node_modules
      - workspace-b/node_modules