Cache R installation on Windows

[wch]

On Windows, it would be useful to cache the R installation. I've been informed that the r-lib/actions/setup-r action doesn't just install R (and Rtools); it also sets up environment variables and PATH.

[jimhester]

Another possible way to handle this might be making a Windows container with R + Rtools preinstalled, though that would require someone to maintain them, and who knows if it would actually be any faster to start up.

[wch]

This is only tangentially related, but for package caching on Windows (or anything that uses actions/cache), I found that you have to fix the path so that actions/cache doesn't try to use C:/Rtools/bin/tar.exe when it saves the cache. (I've filed this at actions/cache#125)

Adding this to the end of a script will fix the problem, by pointing actions/cache to the tar.exe that it would normally use:

      - name: Fix path for Windows caching
        if: runner.os == 'Windows'
        run: echo "::add-path::C:/Program Files/Git/usr/bin"

https://github.com/wch/gha/blob/4c9a1a0b92c17c1af0d5c8a95418b979add88447/.github/workflows/hello.yml#L90-L96

UPDATE:
Github has made some changes for security reasons, so now you have to do the following:

      - name: Fix path for Windows caching
        if: runner.os == 'Windows'
        run: echo "C:/Program Files/Git/usr/bin" >> $GITHUB_PATH

Info here: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

[jimhester]

That is a good way to fix it, #13 was the issue for that problem. It seems like partially a bug in the tar implementation shipped with RTools, it doesn't find the gzip executable also in RTools even though it is on the windows PATH.

[jennybc]

In my hands, it seems to be very important to specify the shell on Windows, which defaults to powershell. So here's the snippet I ended up using:

      - name: Fix path for Windows caching
        if: runner.os == 'Windows'
        shell: bash
        run: echo "C:/Program Files/Git/usr/bin" >> $GITHUB_PATH

[jennybc]

Where this echo "{path}" >> $GITHUB_PATH syntax is documented:

https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-commands-for-github-actions#adding-a-system-path

[benthecoder]

Is there a way to cache setting up R on github actions for mac os as well? The time fluctuates a lot, from a few seconds to 4 minutes.

[jennybc]

@benthecoder Caching on macOS works for me in our standard workflows "out of the box". Not sure what you're seeing and why, but in any case, I'm going to hide your (and this) comment as off-topic for this specific thread.

[jennybc]

Just re-confirmed that for "windows-latest + R 3.6" you really do need shell: bash if you want caching. I find this is not necessary for later versions of R (more specifically, the associated Rtools).