How do I cache steps in GitHub actions?

Question

Say I have a GitHub actions workflow with 2 steps.

1. Download and compile my application\'s dependencies.
2. Compile and test my application

My

Answer 1

The cache action can only cache the contents of a folder. So if there is such a folder, you may win some time by caching it.

For instance, if you use some imaginary package-installer (like Python's pip or virtualenv, or NodeJS' npm, or anything else that puts its files into a folder), you can win some time by doing it like this:

    - uses: actions/cache@v2
      id: cache-packages  # give it a name for checking the cache hit-or-not
      with:
        path: ./packages/  # what we cache: the folder
        key: ${{ runner.os }}-packages-${{ hashFiles('**/packages*.txt') }}
        restore-keys: |
          ${{ runner.os }}-packages-
    - run: package-installer packages.txt
      if: steps.cache-packages.outputs.cache-hit != 'true'

So what's important here:

1. We give this step a name, cache-packages
2. Later, we use this name for conditional execution: if, steps.cache-packages.outputs.cache-hit != 'true'
3. Give the cache action a path to the folder you want to cache: ./packages/
4. Cache key: something that depends on the hash of your input files. That is, if any packages.txt file changes, the cache will be rebuilt.
5. The second step, package installer, will only be run if there was no cache

For users of virtualenv: if you need to activate some shell environment, you have to do it in every step. Like this:

- run: . ./environment/activate && command