Trying this now.

Unless I specified the action version incorrectly (I've never tried using a git rev before, but I'm pretty certain it's right), this does not fix the issue. The error is the same (/etc/bashrc.backup-before-nix exists and the installer aborts).

The log is here:

https://gist.github.com/dhess/86d3bf8c3310c688013fe5105de0cf00

Sorry, I posted the raw logs rather than the gist I created for them. Fixed.

Same problem with take 2:

https://gist.github.com/dhess/1344497ff8ad3cf9e43af26bb7e3a2ea

I don't know much about how the runner works, but is it possible that it's cleaning up things like the runner home dir and even /nix, but not /etc? This should be easy to test by just adding an rm -rf /etc/bashrc.backup-before-nix near the beginning of the action and seeing how far it gets, even if that's not the proper fix that you want to commit to the main branch.

FYI, I added this block to the workflow before the uses: cachix/install-nix-action@712fbc2bf94f397a90c5cf7ef2e4e5f159fbebab step and now it works fine:

    - name: Clean up in case this is a reused runner.
      run: |
        sudo rm -rf /etc/bashrc.backup-before-nix
        sudo rm -rf /etc/profile.d/nix.sh.backup-before-nix
        sudo rm -rf /etc/zshenv.backup-before-nix
        sudo rm -rf /etc/bash.bashrc.backup-before-nix

Logs: https://gist.github.com/dhess/e1ed3b0d08f422ebd66113d616a21f47

Take 3 thinks that Nix is already installed, but either the path isn't set correctly, or Nix isn't actually installed:

https://gist.github.com/dhess/24b98976465d9db55b185a3a774df18f

Closing this as it didn't fix the issue, will experiment further