Caching both the store and the node_modules folders with pnpm

[jgoux]

Hey 👋,

We're trying to migrate our monorepo from yarn to pnpm, and we have one last blocker: the caching story in the CI.

Our action is quite simple:

name: Bootstrap

runs:
  using: composite
  steps:
    - uses: pnpm/action-setup@v2
    - uses: actions/setup-node@v3
      with:
        node-version: 18
    - name: Get pnpm store directory
      id: pnpm-store-path
      shell: bash
      run: |
        echo "STORE_PATH=$(pnpm store path)" >> $GITHUB_OUTPUT
    - uses: actions/cache@v3
      with:
        path: |
          ${{ steps.pnpm-store-path.outputs.STORE_PATH }}
          **/node_modules
        key: ${{ runner.os }}-pnpm-${{ hashFiles('**/pnpm-lock.yaml') }}
        restore-keys: |
          ${{ runner.os }}-pnpm-
    - run: pnpm install
      shell: bash

The cache saving does work:

/usr/bin/tar --posix -cf cache.tzst --exclude cache.tzst -P -C /home/runner/work/snaplet/snaplet --files-from manifest.txt --use-compress-program zstdmt
Cache Size: ~530 MB (555679482 B)
Cache saved successfully
Cache saved with key: Linux-pnpm-f79d92af2bdd42e612381ad72adf9da1e03aa2d7c04802bd0b8dc4760eb3707c 

But the restoration is broken: https://gist.github.com/jgoux/f85685b3b9ad513115a0897331e9ef6f

pnpm uses hardlinks, but I looked up and hardlinks are supported by tar, so I don't understand why it's not able to restore the cache correctly 🤔

It's important for us to cache both the store and the node_modules, as it allows for near-instant dependencies restoration instead of waiting for ~40s per job for pnpm to recreate the node_modules hierarchy if we only cache the store.

We don't want to switch to node-linker=hoisted as it will erase most of the benefits of pnpm.