Tar cannot overwrite read-only files on Windows

[mzabaluev]

Describe the bug
C:\Windows\System32\tar.exe fails to remove existing files that need to be overwritten by an archive extraction, but have the read-only attribute.

Area for Triage:
Scripting and command line

Question, Bug, or Feature?:
Bug

Virtual environments affected

• macOS 10.15
• Ubuntu 16.04 LTS
• Ubuntu 18.04 LTS
• Windows Server 2016 R2
• Windows Server 2019

Expected behavior
This workflow should succeed despite read-only object files present in the .git directory.

jobs:
  test:
    runs-on: windows-latest
    steps:

      - uses: actions/checkout@v2

      - name: List read-only files
        run: Get-ChildItem .git -Recurse -Attributes ReadOnly

      - name: Pack and unpack
        run: |
          C:\windows\System32\tar.exe -cz -f ${{ runner.temp }}\repo.tgz .
          C:\windows\System32\tar.exe -xzv -f ${{ runner.temp }}\repo.tgz

The cache action uses this tar executable in this way. tar works with these options on the Unix OSes where git also makes its object/pack files read-only, and I haven't found any tar options that could be used to force removal of read-only files specifically on Windows.

Actual behavior
Failure with "Can't unlink already-existing object" errors referring to the read-only files.

[Darleev]

Hello @mzabaluev,
I have reproduced the issue on agent machine, and it seems the issue in bsdtar installed on agent machine( C:\windows\System32\tar.exe ).
As a workaround for the issue, you can use tar from git directory like in an example below:

C:\"Program Files"\Git\usr\bin\tar.exe -cz -f ${{ runner.temp }}\repo.tgz .
C:\"Program Files"\Git\usr\bin\tar.exe -xzv -f ${{ runner.temp }}\repo.tgz

We will consider changing default tar directory in Windows 2019 image.

[Darleev]

Current implementation of actions/cache uses tar from system32 directory.

const systemTar = ${process.env['windir']}\\System32\\tar.exe

Windows2019 image contain bsdtar 3.3.2 in this folder.
"C:\ProgramFiles\Git" folder contains tar (GNU tar) 1.32 that works for this cases.
Unfortunately, we can't replace system32 tar with GNU version because previously, it caused huge regression for a lot of customers.
I suggest to improve actions/cache to use tar that come from Git or place own tar.exe binary in Action
Also, it is possible to remove tar from C:\Windows\System32\ directory. In this case, git tar will be automatically used as default one.
If additional information or assistance is required, do not hesitate to contact us.

[mzabaluev]

Hello @mzabaluev,
As a workaround for the issue, you can use tar from git directory like in an example below:

C:\"Program Files"\Git\usr\bin\tar.exe -cz -f ${{ runner.temp }}\repo.tgz .
C:\"Program Files"\Git\usr\bin\tar.exe -xzv -f ${{ runner.temp }}\repo.tgz

This fails because the tar in Git distribution does not interpret Windows path names as such. This has not changed since #480, so I guess it's not an option for the time being.

[Darleev]

@mzabaluev I have tested in your test repository on a separate branch the behavior you have mentioned. I have changed a little bit your workflow file, and it works fine with the following configuration:

      - name: Pack and unpack
        run: |
          C:\"Program Files"\Git\usr\bin\tar.exe --force-local -cz -f ${{ runner.temp }}\repo.tgz .
          C:\"Program Files"\Git\usr\bin\tar.exe --force-local -xzv -f ${{ runner.temp }}\repo.tgz

Could you please verify on your side and provide a result?

[mzabaluev]

@Darleev Thank you, the --force-local option makes it work.

Closing, as it's not reasonable to expect the Windows-provided tool in its standard location to be replaced with something that behaves differently.