Install SBT on self-hosted gha runners

[zarthross]

The $HOME/work directory may not always exist on runners if they are self hosted for instance (our work folder was $HOME/_work).

Github has a $RUNNER_TEMP location though that gets cleaned up between jobs and will exist.

Instead of using a location like $HOME/work that might not exist we can use $RUNNER_TEMP that will.

[eed3si9n]

https://github.com/actions/toolkit/blob/main/packages/tool-cache/src/tool-cache.ts#L747
Maybe I'm supposed to use RUNNER_TOOL_CACHE?

[zarthross]

Looking closer at the tool-cache, it does look like the RUNNER_TEMP is the right place to download the zip file tool, and RUNNER_TOOL_CACHE is the correct place to extract the zip to and add to the path. It would appear doing a check that its not already in the RUNNER_TOOL_CACHE before doing those things would be a wise idea.

[eed3si9n]

It would appear doing a check that its not already in the RUNNER_TOOL_CACHE before doing those things would be a wise idea.

The action is using actions/cache to check if it needs to be downloaded or not:

    - name: Cache sbt distribution
      id: cache-dir
      uses: actions/cache@v4
      with:
        path: ${{ steps.cache-paths.outputs.setupsbt_path }}
        key: ${{ runner.os }}-sbt-${{ inputs.sbt-runner-version }}-1.1.1

[zarthross]

Yes, the download is cached in the github cache... but i think the tool cache is different on self-hosted runners and persists after each run. So if you leave the extracted zip file in the tool runner folder, you might be able to just check that its there and not even have to pull from the cache, or download the zip again.

I'm trying some experiments to look into this.

[zarthross]

A bit more of an involved change, but here is an alternative approach to the one here: #11