➜ pre-commit try-repo .git -vvv
[WARNING] Creating temporary repo with uncommitted changes...
An unexpected error has occurred: CalledProcessError: Command: ('/usr/bin/git', 'add', '-u')
Return code: 128
Expected return code: 0
Output: (none)
Errors: 
    fatal: this operation must be run in a work tree
    

Check the log at ~/.cache/pre-commit/pre-commit.log

An unexpected error has occurred: CalledProcessError: Command: ('/usr/bin/git', 'add', '-u')
Return code: 128
Expected return code: 0
Output: (none)
Errors: 
    fatal: this operation must be run in a work tree
    

Traceback (most recent call last):
  File "~/.pyenv/versions/3.7.1/lib/python3.7/site-packages/pre_commit/error_handler.py", line 46, in error_handler
    yield
  File "~/.pyenv/versions/3.7.1/lib/python3.7/site-packages/pre_commit/main.py", line 296, in main
    return try_repo(args)
  File "~/.pyenv/versions/3.7.1/lib/python3.7/site-packages/pre_commit/commands/try_repo.py", line 55, in try_repo
    repo, ref = _repo_ref(tempdir, args.repo, args.ref)
  File "~/.pyenv/versions/3.7.1/lib/python3.7/site-packages/pre_commit/commands/try_repo.py", line 45, in _repo_ref
    cmd_output('git', 'add', '-u', cwd=repo, env=env)
  File "~/.pyenv/versions/3.7.1/lib/python3.7/site-packages/pre_commit/util.py", line 153, in cmd_output
    returncode, cmd, retcode, output=(stdout, stderr),
pre_commit.util.CalledProcessError: Command: ('/usr/bin/git', 'add', '-u')
Return code: 128
Expected return code: 0
Output: (none)
Errors: 
    fatal: this operation must be run in a work tree