On windows, short path name (or 8.3 filename) are still used on GHA. This path can cause issue with some tools - specifically we encounter error on windows with LaTeX when rendering from a tempfile()

As nothing is done specifically in setup-r, R will look at %TEMP% which contains a short filename - this has been reported already and it is normal. (actions/runner-images#712)

What about setting TEMPDIR, TMP or TEMP to the runner temp directory by default? (RUNNER_TEMP, runner.temp, process.env["RUNNER_TEMP"]). This is already use to place the R user library (R_LIBS_USER). This folder has the advantage to not have space on Windows, so no short file name with ~.

It could also be a parameter to pass to the action to set the R temp dir to a different location

      - uses: r-lib/actions/setup-r@v1
        with:
          temp_directory: ${{ runner.temp }}

Currently to make the test pass, I set this environment for the step

      - name: Check
        env:
          _R_CHECK_CRAN_INCOMING_: false
          TMPDIR: ${{ runner.temp }}
        run: rcmdcheck::rcmdcheck(args = c("--no-manual", "--as-cran"), error_on = "warning", check_dir = "check")
        shell: Rscript {0}

I could also do it for the job by setting globally using a custom step

      - name: change temp dir
        run: echo "TMPDIR=${{ runner.temp }}" >> $GITHUB_ENV
        shell: bash

it seems this variable can't be define in env: at the job level, as it is done with secrets (no access to ${{ runner.temp }} there it seems)

Would it be something to consider ?