Cache with gh action `ocaml/setup-ocaml@v2`

Ecosystem
7

Did you manage to get the caching to improve the performance of your actions?

On a project I’ve been working on recently (to be open sourced soon hopefully), we were able to get our action times to drop from 30+minutes to 5minutes by making use of the cache.

I’ve included the relevant snippet from the action we used:

      - name: Cache
        id: cache-opam
        uses: actions/cache@v3
        env:
          cache-name: cache-opam
        with:
          path: |
            /home/runner/work/proof-repair/proof-repair/_opam/
          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/*.opam') }}

      - name: Opam & Coq
        if: steps.cache-opam.outputs.cache-hit != 'true'
        run: |
           opam repository add default https://github.com/ocaml/opam-repository.git --all-switches --set-default
           opam repository add coq-released https://coq.inria.fr/opam/released --all-switches --set-default
      - name: Install Dune
        if: steps.cache-opam.outputs.cache-hit != 'true'
        run: |
          opam install dune
      - name: Install
        if: steps.cache-opam.outputs.cache-hit != 'true'
        run: |
          opam install . --deps-only

Actually, the hard work was done by an undergrad @mayank working with me, so I can’t really comment on whether this is actually a robust way of improving performance times.

I think the key step in reducing build times was to add the if check to the install steps to avoid running them when the cache was hit.