Restoring cache on Windows created on Linux silently fails if GNU tar is not on Windows Path

I setup a CI pipeline where a linux job downloads files from a remote repository and puts them into a cache. Then jobs on different platforms (linux, macos, windows) are started that reference the cache. All jobs receive a cache hit but on Windows the downloaded cache archive is empty.

It looks like on Windows the filename cache.tgz is expected but on Linux and MacOS cache.tzst is used.

These are the logs I get for the jobs using the cache:

Linux:
------
Run actions/cache@v2
  with:
    path: .extensions
    key: extensions-802592892
    restore-keys: extensions-
Received 129569068 of 129569068 (100.0%), 136.2 MBs/sec
Cache Size: ~124 MB (129569068 B)
/usr/bin/tar --use-compress-program zstd -d -xf /home/runner/work/_temp/8f4a3549-d2e9-4b85-a044-4c0d37f47d60/cache.tzst -P -C /home/runner/work/vitcode/vitcode
Cache restored successfully
Cache restored from key: extensions-802592892

MacOS:
------
Run actions/cache@v2
  with:
    path: .extensions
    key: extensions-802592892
    restore-keys: extensions-
Received 129569068 of 129569068 (100.0%),  45.9 MBs/sec
Cache Size: ~124 MB (129569068 B)
/usr/local/bin/gtar --use-compress-program zstd -d -xf /Users/runner/work/_temp/d133514d-3d07-4e10-8844-14d51d463fff/cache.tzst -P -C /Users/runner/work/vitcode/vitcode --delay-directory-restore
Cache restored successfully
Cache restored from key: extensions-802592892

Windows:
--------
Run actions/cache@v2
  with:
    path: .extensions
    key: extensions-802592892
    restore-keys: extensions-
Received 30 of 30 (100.0%), 0.0 MBs/sec
Cache Size: ~0 MB (30 B)
C:\Windows\System32\tar.exe -z -xf D:/a/_temp/7133fe6d-5fa6-462d-a494-8faa9cdd0b31/cache.tgz -P -C D:/a/vitcode/vitcode
Cache restored successfully
Cache restored from key: extensions-802592892

Pseudo pipeline config:

name: Build

jobs:
  download-extensions:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v2
    - uses: actions/cache@v2
      with:
        path: .extensions
        key: extensions-${{ github.run_id }}
        restore-keys: extensions-
    - name: "Downloading Extensions"
      shell: bash
      run: ... # execute commands that download files to ./.extensions

  build-on-linux:
    runs-on: ubuntu-latest
    needs: [ download-extensions ]
    steps:
    - uses: actions/checkout@v2
    - uses: actions/cache@v2
      with:
        path: .extensions
        key: extensions-${{ github.run_id }}
    - name: "Build"
      # ... build software

  build-on-macos:
    runs-on: macos-latest
    needs: [ download-extensions ]
    steps:
    - uses: actions/checkout@v2
    - uses: actions/cache@v2
      with:
        path: .extensions
        key: extensions-${{ github.run_id }}
    - name: "Build"
      # ... build software

  windows-amd64:
    runs-on: macos-latest
    needs: [ download-extensions ]
    steps:
    - uses: actions/checkout@v2
    - uses: actions/cache@v2
      with:
        path: .extensions
        key: extensions-${{ github.run_id }}
    - name: "Build"
      # ... build software

[rfay]

Since this hasn’t been addressed… it needs to stay alive.

[rfay]

Thanks for this. My solution (on self-hosted Windows runner) was to put C:\Program Files\Git\usr\bin early in the system path on the Windows machine and restart the runner service.

I also had to install zstd.exe in C:\Program Files\Git\usr\bin to get it to work.

@sebthom since you sorted this out, could you please retitle and add to the OP what you learned? A title like “restoring cache fails if GNU tar is not the default tar in $PATH” would help people sort this out.