Wily fails when enabled on GitHub workflow

[edmondop]

Describe the bug
I have added a specific job to my Github Workflow without installing wily locally and Wily fails with a git error:

Failed to setup archiver: '<class 'git.exc.GitCommandError'> - Cmd('git') failed due to: exit code(128)
  cmdline: git diff --numstat 4b2122317b4775a75d30403fc158ea89bac3d204 ce16aee57f19e7e948a4794779d5aa5135b64e8f --
  stderr: 'fatal: bad object 4b2122317b4775a75d30403fc158ea89bac3d204''

To Reproduce
Add a job to a Github pipeline to your code like so:

  evaluate-complexity:
    name: Evaluate code complexity
    runs-on: ubuntu-latest
    steps:
    - name: Checkout repository
      uses: actions/checkout@v2
    - name: Set up Python
      uses: actions/setup-python@v2
      with:
        python-version: 3.10.0
    - name: Install Wily and compile cache
      run: |
            pip install wily
            wily build my_proj
    - name: Compute code complexity diff with main
      run: "wily diff my_proj/ -r main"
      id: run_wily

Expected behavior
Build would succeed

Additional context
It's interesting that the git diff command copy-pasted on my machine works correctly

[skarzi]

Hi 👋

that's probably because actions/checkout fetches only a single commit by default.
Try to use: fetch-depth: 0 to checkout the full history or write some custom script to fetch only needed commits

[edmondop]

Thanks a lot for your help. That resolves the problem with the bad object, but not Wily fails elsewhere

Run wily build my_pkg/ test/
Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/wily/commands/build.py", line 30, in build
    archiver = archiver.cls(config)
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/wily/archivers/git.py", line 38, in __init__
    self.current_branch = self.repo.active_branch
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/git/repo/base.py", line [7](https://github.com/edmondo1984/my-pkg/pull/19/checks#step:5:7)97, in active_branch
    return self.head.reference
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/git/refs/symbolic.py", line 294, in _get_reference
    raise TypeError("%s is a detached symbolic reference as it points to %r" % (self, sha))
TypeError: HEAD is a detached symbolic reference as it points to '7e0196a45590b167123caab43179b6f2d[8](https://github.com/edmondo1984/my-pkg/pull/19/checks#step:5:8)b3303e'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.10.0/x64/bin/wily", line 8, in <module>
    sys.exit(cli())
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/click/core.py", line 1128, in __call__
    return self.main(*args, **kwargs)
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/click/core.py", line 1053, in main
    rv = self.invoke(ctx)
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/click/core.py", line 165[9](https://github.com/edmondo1984/my-pkg/pull/19/checks#step:5:9), in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/opt/hostedtoolcache/Python/3.[10](https://github.com/edmondo1984/my-pkg/pull/19/checks#step:5:10).0/x64/lib/python3.10/site-packages/click/core.py", line [13](https://github.com/edmondo1984/my-pkg/pull/19/checks#step:5:13)95, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/click/core.py", line 754, in invoke
    return __callback(*args, **kwargs)
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/click/decorators.py", line [26](https://github.com/edmondo1984/my-pkg/pull/19/checks#step:5:26), in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/wily/__main__.py", line 99, in build
    build(
  File "/opt/hostedtoolcache/Python/3.10.0/x64/lib/python3.10/site-packages/wily/commands/build.py", line [33](https://github.com/edmondo1984/my-pkg/pull/19/checks#step:5:33), in build
    logger.error(f"Failed to setup archiver: '{e.message}'")
AttributeError: 'TypeError' object has no attribute 'message'

[skarzi]

Are you running your action on the pull_request event?

The problem is you are in a detached HEAD state, see this StackOverflow post for reference

[edmondop]

Correct, why is the pull request in detached HEAD?

[tonybaloney]

PR will copy the code at the commit hash instead of checking out the particular branch.
Wily needs to use the git API to checkout previous revisions and build a history.

IIRC you can use wily build <path> -a filesystem to make it only run the analytics on the current changes.

[tonybaloney]

checkout the build docs for more https://wily.readthedocs.io/en/latest/commands/build.html#wily

[edmondop]

I think it is desirable to run Wily on a PR to compare with the previous result, can you please suggest how to do it?

[edmondop]

#143