Enable cache clear by adding a version prefix to the key

[yutannihilation]

Unlike Travis CI and AppVeyor, GitHub Actions doesn't provide a way to clear cache. In such a situation, it seems it's a common practice to add a version prefix to the key as Circle CI suggests so:

Tip: Caches are immutable so it is useful to start all your cache keys with a version prefix, for example v1-.... This enables you to regenerate all of your caches by incrementing the version in this prefix.
(https://circleci.com/docs/2.0/caching/#clearing-cache)

I followed this on ggplot2: tidyverse/ggplot2@644c436

[lcolladotor]

Hi @yutannihilation,

I found that if you edit the if condition for the step that caches, you can skip the cache step. That way you can test things without your cached R packages. However, you can't clear the cache. Clearing seems to be a highly requested feature upstream of r-lib/actions at actions/cache#2.

That is, edit check-standard.yaml#L45-L46 from

- name: Cache R packages
  if: runner.os != 'Windows'

to something like this (you can keep the Windows part inside the if statement if you want):

- name: Cache R packages
  if: "!contains(github.event.head_commit.message, '/nocache')"

which is what I did at check-bioc.yml#L91. You can see at the GHA logs here that on a commit with the word /nocache on the commit message (such as LieberInstitute/recount3@0cb70fa) correctly skipped the caching step.

I ran into the need for something like this myself to avoid making mistakes like at r-lib/xml2#296 (comment) where I thought I had resolved my macOS issue with compiling xml2, but it was simply due to having the package already cached (after using Rscript -e "remotes::install_github('r-lib/xml2')" successfully in a previous run). I discovered the issue when I copied the GHA workflow to a new package which I initially suspected would be an issue after discovering this r-lib/xml2#296 (comment). Hence my family of commits like leekgroup/derfinderHelper@0a7f5e7.

Best,
Leo

[jimhester]

Bumping the cache by adding a number like @yutannihilation suggests is the correct solution. I normally just append a -2- to the cache myself, e.g. this is how I bumped the cache recently in xml2 r-lib/xml2@6baece5.

[hadley]

I think clearing the cache is such an important action that GitHub is bound to implement it in the near future, so I think it's premature to design anything into r-lib/actions at this point.

[yutannihilation]

GitHub is bound to implement it in the near future

Not allowing cache clear can be a design choice (as I described above, Circle CI is an example). That said, I'm not sure how GitHub will handle this popular feature request, so I agree it's better to wait for some months before considering implementing this on r-lib/actions' side.

Anyway, in the meantime, we can use this issue to share the tips like @lcolladotor's one. Hope this helps those who struggle with cache.

[jimhester]

The workflows now have a -1- suffix to hopefully make it more clear what you have to bump (if needed).

[github-actions]

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