Support scanning bare repos

[tarkatronic]

Currently, attempting to scan a bare git repo, using --repo_path, produces an error along the lines of:

Traceback (most recent call last):
  File "/home/jwilhelm/Documents/workspace/tartufo/.venv/bin/tartufo", line 11, in <module>
    load_entry_point('tartufo', 'console_scripts', 'tartufo')()
  File "/home/jwilhelm/Documents/workspace/tartufo/tartufo/cli.py", line 58, in main
    path_exclusions=path_exclusions,
  File "/home/jwilhelm/Documents/workspace/tartufo/tartufo/scanner.py", line 287, in find_strings
    for curr_commit in repo.iter_commits(branch_name, max_count=max_depth):
  File "/home/jwilhelm/Documents/workspace/tartufo/.venv/lib64/python3.7/site-packages/git/objects/commit.py", line 278, in _iter_from_process_or_stream
    finalize_process(proc_or_stream)
  File "/home/jwilhelm/Documents/workspace/tartufo/.venv/lib64/python3.7/site-packages/git/util.py", line 332, in finalize_process
    proc.wait(**kwargs)
  File "/home/jwilhelm/Documents/workspace/tartufo/.venv/lib64/python3.7/site-packages/git/cmd.py", line 414, in wait
    raise GitCommandError(self.args, status, errstr)
git.exc.GitCommandError: Cmd('git') failed due to: exit code(128)
  cmdline: git rev-list --max-count=1000000 1/head --
  stderr: 'fatal: bad revision '1/head'

This is because a bare repo is a wholly different structure from a normal clone, and produces different results from git operations. The specific problem causing the error here is this:

>>> repo = git.Repo('tartufo.git')
>>> for branch in repo.remotes.origin.fetch():
...     print(branch.name)
... 
master
split_tests
1/head
10/head
11/head
16/head
19/head
2/head
20/head
21/head
22/head
23/head
24/head
25/head
3/head
8/head
9/head
v0.0.1
v0.0.2
>>> repo = git.Repo('../tartufo')
>>> for branch in repo.remotes.origin.fetch():
...     print(branch.name)
... 
origin/master
origin/split_tests
>>>

All of the X/head references are not actual valid git revisions, and so tartufo chokes on them.

We should figure out a way to either scan all refs, or only scan actual branches.

[sjacoby-godaddy]

Just a note, processing --mirror repos seems to work
ex:

git clone --mirror git@github.com:username/myrepo.git
tartufo --regex --json --cleanup myrepo.git

[jolinger-godaddy]

Just to note @sjacoby-godaddy suggestion did not work in my case and this still fails even on mirror repos.

git clone --mirror git@github.com:org/repo.git

tartufo --regex --json scan-local-repo ${GITHUBREPO}.git | \    
          jq -r '.found_issues[].matched_string' | \
          sort -u > ${GITHUBREPO}-remove.txt

Fatal error

Traceback (most recent call last):
  File "/usr/local/bin/tartufo", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.8/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.8/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.8/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/click/decorators.py", line 33, in new_func
    return f(get_current_context().obj, *args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/click/decorators.py", line 21, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/tartufo/commands/scan_local_repo.py", line 39, in main
    issues = scanner.scan()
  File "/usr/local/lib/python3.8/site-packages/tartufo/scanner.py", line 258, in scan
    for chunk in self.chunks:
  File "/usr/local/lib/python3.8/site-packages/tartufo/scanner.py", line 477, in chunks
    for curr_commit, prev_commit in self._iter_branch_commits(
  File "/usr/local/lib/python3.8/site-packages/tartufo/scanner.py", line 438, in _iter_branch_commits
    for curr_commit in repo.iter_commits(
  File "/usr/local/lib/python3.8/site-packages/git/objects/commit.py", line 277, in _iter_from_process_or_stream
    finalize_process(proc_or_stream)
  File "/usr/local/lib/python3.8/site-packages/git/util.py", line 329, in finalize_process
    proc.wait(**kwargs)
  File "/usr/local/lib/python3.8/site-packages/git/cmd.py", line 408, in wait
    raise GitCommandError(self.args, status, errstr)
git.exc.GitCommandError: Cmd('git') failed due to: exit code(128)
  cmdline: git rev-list --max-count=1000000 1/head --
  stderr: 'fatal: bad revision '1/head'