Another option might be to use pnpm instead of Yarn and cache your pnpm dependencies. pnpm actually works a bit like Nix in that it creates a pnpm-lock.yaml file with content-based hashes for the full package.json dependency tree. This enables it to quickly determine which parts of the dependency tree it needs to build and which are already available.

[1]: https://github.com/NixOS/nixpkgs/blob/master/doc/languages-f...

Node packages sometimes pull additional files from the internet in a postinstall script, or do other funky stuff that's incompatible with Nix. So the idea that you can construct a pure derivation from a package-lock.json or yarn.lock file is a pipe dream.

That means that node_modules (as created by a package-lock.json) can't really be cached or be built from caches since it depends on the particular version solution found by npm for a particular project.

So there's only so much that Nix can do. It can cache it about as well as using a naive caching scheme with actions/upload-artifact or similar (create a tarball of your node_modules and just cache it across runs, update when you need to).

Basically node_modules is inherently large. If you want better performance for caching dependencies use a better programming language environment.

  - uses: actions/cache@v3
    with:
      # npm cache files are stored in `~/.npm` on Linux/macOS
      path: ~/.npm
      key: ${{ runner.os }}-${{ hashFiles('**/package-lock.json') }}