Answer by TrinitronX for Clear cache in GitHub Actions

Here's another automated solution similar to @beatngu13's cache key invalidation method. This one uses a generated timestamp file that gets committed and then used in a hashFiles(...) prefix to the cache key.

Included is a set of GNU Makefile targets to make using this method very easy: make clear-github-cache

Note: Make sure each Makefile"recipe" section is indented with 1 tab character! StackOverflow converts tabs to spaces in the code block.

.github/clear_github_actions_cache:    date  +%s > .github/clear_github_actions_cache.PHONY: clean-github-cache-file clear-github-cacheclear-github-cache: clean-github-cache-file .github/clear_github_actions_cache ## Force GitHub Actions Cache key to change for fresh CI run    git add .github/clear_github_actions_cache    git commit -m "Clear GitHub Actions Cache @ $$(cat .github/clear_github_actions_cache)"clean-github-cache-file: ## Remove GitHub Actions Cache timestamp invalidator file.    [ -f '.github/clear_github_actions_cache' ] && rm -f '.github/clear_github_actions_cache' || true

Then, inside the GitHub Actions workflow YAML, add a cache key prefix that uses the hash of this file:

      - name: Cache R packages        if: runner.os != 'Windows'        uses: actions/cache@v2        with:          path: ${{ env.R_LIBS_USER }}          key: ${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('.github/clear_github_actions_cache') }}-${{ hashFiles('.github/R-version') }}-${{ hashFiles('.github/depends.Rds') }}          restore-keys: |            ${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('.github/clear_github_actions_cache') }}-${{ hashFiles('.github/R-version') }}-${{ hashFiles('.github/depends.Rds') }}            ${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('.github/clear_github_actions_cache') }}-${{ hashFiles('.github/R-version') }}-            ${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('.github/clear_github_actions_cache') }}-

Now just run:

make clear-github-cache

This generates and commits a file, .github/clear_github_actions_cache, with Unix timestamp as contents. The hashFiles(...) cache key prefix uses this and will generate a unique hash of this file as a prefix to the rest of the cache / restore-key.

Next time you use git push, the cache key will be invalidated... effectively running GitHub Actions with an empty cache.