How to test updating from a dirty repository?

[anjos]

I'm new to copier. I'm trying to develop test units so that I can test changes I'm implementing.

Project generation (aka. copy) works well. My problem relates to testing changes from a dirty git repo, with uncommitted changes, and potentially new files.

In my first test, I'm trying to run an update using the same state of the (dirty) git repo that generated a copy. Here is a sketch of I'm trying to do:

1. Create a git repo called foo, with the following contents:

a) A file called copier.yml:

_min_copier_version: '9'

_exclude:
  - .git
  - copier.yml

project_name:
  type: str
  default: new-foo
  help: A short (slug-style) name for your project

b) a file called {{ _copier_conf.answers_file}}.jinja:

_min_copier_version: '9'

_exclude:
  - .git
  - copier.yml

project_name:
  type: str
  default: new-foo
  help: Help for project-name

2. Initialize a git repo on foo and commit all files.
3. Slightly modify a file, say copier.yml so that the repository becomes dirty.
4. Go back to the parent directory cd ..
5. Create a new copy by calling copier copy --defaults $(PWD)/foo --vcs-ref=HEAD new-foo, observe that Dirty template changes included automatically. correctly appears indicating copier is aware of the dirty repo.
6. Change dir to new-foo and initialize a git repo: git init . && git add . && git commit -m 'Initial commit' -a
7. Go back to the parent directory and try an update with: copier update --defaults --vcs-ref=HEAD new-foo (that should result in no changes as the dirty changes where not modified). I observe that Dirty template changes included automatically. appears, however, this exercise results in the following exception being raised:

/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/vcs.py:209: DirtyLocalWarning: Dirty template changes included automatically.
  warn(
No git tags found in template; using HEAD as ref
Traceback (most recent call last):
  File "/Users/andre/.local/share/pixi/envs/python/bin/copier", line 10, in <module>
    sys.exit(CopierApp.run())
             ~~~~~~~~~~~~~^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/plumbum/cli/application.py", line 640, in run
    inst, retcode = subapp.run(argv, exit=False)
                    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/plumbum/cli/application.py", line 635, in run
    retcode = inst.main(*tailargs)
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/cli.py", line 425, in main
    return _handle_exceptions(inner)
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/cli.py", line 70, in _handle_exceptions
    method()
    ~~~~~~^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/cli.py", line 415, in inner
    with self._worker(
         ~~~~~~~~~~~~^
        dst_path=destination_path,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<4 lines>...
        overwrite=True,
        ^^^^^^^^^^^^^^^
    ) as worker:
    ^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/main.py", line 237, in __exit__
    raise value
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/cli.py", line 423, in inner
    worker.run_update()
    ~~~~~~~~~~~~~~~~~^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/main.py", line 872, in run_update
    self._check_unsafe("update")
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/main.py", line 256, in _check_unsafe
    if self.subproject.template.jinja_extensions:
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/functools.py", line 1039, in __get__
    val = self.func(instance)
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/template.py", line 337, in jinja_extensions
    return tuple(self.config_data.get("jinja_extensions", ()))
                 ^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/functools.py", line 1039, in __get__
    val = self.func(instance)
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/template.py", line 300, in config_data
    result = filter_config(self._raw_config)[0]
                           ^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/functools.py", line 1039, in __get__
    val = self.func(instance)
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/template.py", line 257, in _raw_config
    for p in self.local_abspath.glob("copier.*")
             ^^^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/functools.py", line 1039, in __get__
    val = self.func(instance)
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/template.py", line 555, in local_abspath
    result = Path(clone(self.url_expanded, self.ref))
                  ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/copier/vcs.py", line 215, in clone
    git("checkout", "-f", ref or "HEAD")
    ~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/plumbum/commands/base.py", line 115, in __call__
    return self.run(args, **kwargs)[1]
           ~~~~~~~~^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/plumbum/commands/base.py", line 254, in run
    return p.run()
           ~~~~~^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/plumbum/commands/base.py", line 217, in runner
    return run_proc(p, retcode, timeout)
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/plumbum/commands/processes.py", line 330, in run_proc
    return _check_process(proc, retcode, timeout, stdout, stderr)
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/plumbum/commands/processes.py", line 19, in _check_process
    proc.verify(retcode, timeout, stdout, stderr)
    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andre/.local/share/pixi/envs/python/lib/python3.13/site-packages/plumbum/machines/base.py", line 29, in verify
    raise ProcessExecutionError(
        getattr(self, "argv", None), self.returncode, stdout, stderr
    )
plumbum.commands.processes.ProcessExecutionError: Unexpected exit code: 1
Command line: | /Users/andre/.local/share/pixi/envs/python/bin/git checkout -f bce5732
Stderr:       | error: pathspec 'bce5732' did not match any file(s) known to git

Of course, the commit bce5732 does not exist, but I guess copier created that on a separate clone. The problem I'm observing is that, somehow, it cannot "re-create" that commit/hash upon an update.

How can I make the update from a dirty repo work as described above?