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Error in `repo.active_branch` if branch is in DETACHED HEAD state #633

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cgi1 opened this issue May 29, 2017 · 5 comments
Open

Error in `repo.active_branch` if branch is in DETACHED HEAD state #633

cgi1 opened this issue May 29, 2017 · 5 comments
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@cgi1
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@cgi1 cgi1 commented May 29, 2017 •
edited

Error in repo.active_branch if branch is in DETACHED HEAD state:

{TypeError}HEAD is a detached symbolic reference as it points to '0fa1f2a7d9dd9fb63fa775d2d97ad72f56f1d819'

The branch is None in def _get_ref_info(cls, repo, ref_path): because of

# its a commit
        if repo.re_hexsha_only.match(tokens[0]):
            return (tokens[0], None)

def active_branch(self) could return HEAD-{commit-hash} instead like:

    try:
        active_branch = repo.active_branch
    except:
        active_branch = 'DETACHED_' + repo.head.object.hexsha
@cgi1
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@cgi1 cgi1 commented May 30, 2017

Looks similar to #629
@Byron
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@Byron Byron commented Jun 10, 2017

I am not sure it would be right to return a commit instead. The function is called active_branch, and I would assume people expect it to return a branch, never a commit. If HEAD is detached, there is no branch to return.
What do you think?
@cgi1
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@cgi1 cgi1 commented Jun 13, 2017

Hm good point, I don´t have a pefect answer.. To return no branch seems to be ok.
@Byron
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@Byron Byron commented Jun 17, 2017

I think returning no branch would break existing code which expects an exception. On the other hand, the exception is not documented, so in a way it's running under the radar anyway.

Maybe it could be adjusted to return None if there is no active branch instead, which would make the calling code a little less cumbersome and safer, as it could start to expect that.

Would you like to contribute a respective PR?
@peterbe
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@peterbe peterbe commented Aug 16, 2019

I stumbled on this too. With submodules.
My solution wasn't to try to rely on a try: except: ... but I made it always check out at least some branch first before it started switching to the branch I ultimately wanted to. I.e. always start with repo.heads[config["master_branch"]].checkout()
akinnane added a commit to alphagov/gds-pre-commit that referenced this issue Mar 31, 2020
@akinnane @detnon
Use hexsha instead of active_branch to work around detached head
9dc2f8d 
When concourse checks out a repo it leaves it in a detached head
state. This was causing errors as python git has slightly undefined
behaviour in this case.

```
File "detect_checker.py", line 125, in _load_repo
    self.parent_branch = self.repo.active_branch
File "/home/a/venv/local/lib/python3.7/site-packages/git/repo/base.py", line 703, in active_branch
    return self.head.reference
File "/home/a/venv/local/lib/python3.7/site-packages/git/refs/symbolic.py", line 272, 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 '6e589de2864ee310a46a343ae9d656405e6b8c84'
```

gitpython-developers/GitPython#633

This PR changes it use the hexsha instead which works correctly with
detached heads and normal branches.

Co-authored-by: detnon <sam.detnon@digital.cabinet-office.gov.uk>
Co-authored-by: Alex Kinnane <17098249+akinnane@users.noreply.github.com>
@akinnane akinnane mentioned this issue Mar 31, 2020
Merged
akinnane added a commit to alphagov/gds-pre-commit that referenced this issue Mar 31, 2020
@akinnane @detnon
Use hexsha instead of active_branch to work around detached head
0a4ff88 
When concourse checks out a repo it leaves it in a detached head
state. This was causing errors as python git has slightly undefined
behaviour in this case.

```
File "detect_checker.py", line 125, in _load_repo
    self.parent_branch = self.repo.active_branch
File "/home/a/venv/local/lib/python3.7/site-packages/git/repo/base.py", line 703, in active_branch
    return self.head.reference
File "/home/a/venv/local/lib/python3.7/site-packages/git/refs/symbolic.py", line 272, 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 '6e589de2864ee310a46a343ae9d656405e6b8c84'
```

gitpython-developers/GitPython#633

This PR changes it use the hexsha instead which works correctly with
detached heads and normal branches.

Co-authored-by: detnon <sam.detnon@digital.cabinet-office.gov.uk>
Co-authored-by: Alex Kinnane <17098249+akinnane@users.noreply.github.com>
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