Add a parameter to ignore the existing cache but still store the cache at the end

Feature Request

Description

Add a parameter “no-restore” that will ignore the existing cache but still store the cache at the end of the job.

Use Case

I’m building a Rust project and I try to keep a cache “main” that is used in fallback of PR if there is no pre-existing cache for that PR. In other words, newly created PR use this cache as “base”.

Unfortunately the dependencies can change, the version of the compiler too, and the target (build) directory gets bigger over time.

I don’t need a cache on the main branch, I only use it to accelerate the first build of the PR. So it would be nice to have a flag “no-restore” that would ignore the existing cache but still save and replace the cache at the end.

Workaround

In the workflow that builds the main branch:

      - name: Get main commit hash
        id: main_commit
        run: echo "::set-output name=hash::$(git rev-parse origin/main)"

      - name: Cache target, rustup and cargo registry
        id: cache-target
        uses: actions/cache@v2
        with:
          path: |
            ~/.rustup
            ~/.cargo/registry
            ~/.cargo/bin
            target
          key: main-${{ steps.main_commit.outputs.hash }}

In the workflow that builds the PR:

      - name: Get main commit hash
        id: main_commit
        run: echo "::set-output name=hash::$(git rev-parse origin/main)"

      - name: Cache target, rustup and cargo registry
        id: cache-target
        uses: actions/cache@v2
        with:
          path: |
            ~/.rustup
            ~/.cargo/registry
            ~/.cargo/bin
            target
          key: ${{ github.event.issue.number }}-${{ runner.os }}-pr
          restore-keys: main-${{ steps.main_commit.outputs.hash }}

[eyal0]

Putting the git SHA hash into the key means that you will be saving a new cache each time. That’s way too often! Because the cache is limited in size, old stuff will expire too frequently!

Think about what functions we’d actually like from a cache:

1. Fetch from cache, possibly not finding a hit.
2. Save to cache if there is no entry.
3. Save to cache overwriting an entry.

This GitHub action does the first two but there is no way to do the third. If the entry exists, you can’t overwrite it. That’s why you need a way to force an overwrite. That’s what I did in my PR linked above.

You can mess around with the cache key and restore-keys but you’ll not find a way to update an existing key. So either you can’t refresh or you get a solution that will churn the cache entries.

[b-onc]

We also have a need for this: In our iOS project, we cache Carthage folder, but sometimes the cache becomes invalid even if it was a hit. In that case, we’d like to be able to invalidate cache.