@actions/cache fails on Windows when GNU tar from MSYS2 is in PATH

[eregon]

Describe the bug

When C:\msys64\usr\bin is in the path on Windows, and using @actions/cache, I noticed that cache saving always fails:
ruby/setup-ruby#102

https://github.com/ruby/setup-ruby/runs/1370892940?check_suite_focus=true

  Saving cache
  C:\msys64\usr\bin\tar.exe --posix --use-compress-program "zstd -T0" -cf cache.tzst -P -C D:/a/setup-ruby/setup-ruby --files-from manifest.txt --force-local
  /usr/bin/tar: vendor\bundle: Cannot stat: No such file or directory
  /usr/bin/tar: Exiting with failure status due to previous errors
  Warning: Tar failed with error: The process 'C:\msys64\usr\bin\tar.exe' failed with exit code 2

The problem seems to be that the cache paths written to manifest.txt use \\ and not /, which I would think GNU tar expects.
On https://github.com/eregon/setup-ruby/runs/1392737782?check_suite_focus=true#step:3:100 we can see the cache paths written to manifest.txt is ["vendor\\bundle"] but it should most likely uses / as separator for GNU tar.

To Reproduce

Minimal repro using actions/cache:

name: Test
on: [push]
jobs:
  build:
    strategy:
      fail-fast: false
      matrix:
        os: [ ubuntu, macos, windows ]
    runs-on: ${{ matrix.os }}-latest
    steps:
      - run: echo "C:\msys64\usr\bin" >> $GITHUB_PATH
        shell: bash

      - uses: actions/cache@v2
        with:
          path: top/foo
          key: ${{ runner.os }}-debug-cache1

      - run: ls -l
        shell: bash

      - name: Generate files
        run: |
          mkdir -p top/foo
          echo hello > top/foo/bar.txt
        shell: bash

https://github.com/eregon/setup-ruby-test/runs/1392827825?check_suite_focus=true#step:10:3

C:\msys64\usr\bin\tar.exe --posix --use-compress-program "zstd -T0" -cf cache.tzst -P -C D:/a/setup-ruby-test/setup-ruby-test --files-from manifest.txt --force-local
/usr/bin/tar: top\foo: Cannot stat: No such file or directory
/usr/bin/tar: Exiting with failure status due to previous errors
Warning: Tar failed with error: The process 'C:\msys64\usr\bin\tar.exe' failed with exit code 2

Full repro using the @actions/cache package:

    - runs-on: windows-latest
    - uses: ruby/setup-ruby@v1
      with:
        ruby-version: 2.7
        bundler-cache: true

Expand the bundle install group of ruby/setup-ruby@v1.

Expected behavior
It should save the cache successfully.

[eine]

See related discussion in November 24, 2020 3:28 PM:

well, calling cygwin tools with Windows paths is a bit of a luck thing.. they weren't programmed for that and none of those scenarios are tested
From what I understand if the paths aren't touched and passed through to the "posix API" then things work fine.. if there is any path processing otherwise your best bet is to use /, relative paths etc..
tar also has a --force-local option which disables some paths checks, see msys2/MSYS2-packages#1286 (comment)
So I'd try using "/" only in the input file and "--force-local"

using cygpath for writting processed path to a file which is then to be read by tar; but not having any issue with CLI args

---

they could just download it in the action
If I were github I'd look into libarchive/libarchive#1419

[eregon]

I think replacing \ by / in cache paths would work fine. I would have tested it myself, but not quite sure how to pick my changes as an npm package (either in the ruby/setup-ruby or actions/cache action).

[eregon]

Thank you for fixing this, @aiqiaoy, I can confirm it works now :)