bug: ContextHook is executed for before each question since copier 9.4

[noirbizarre]

Description of the bug

Since copier 9.4, since copier-org/copier#1840 more precisely (I think), ContextHoook.hook is called before each question during the update phase.

This is due to _copier_conf being already present during update questions, cf. https://github.com/copier-org/copier-templates-extensions/blob/main/src/copier_templates_extensions/extensions/context.py#L46

To Reproduce

• ensure you have copier>=9.4.0
• create a template with a question
• use ContextUpdater as extension
• access ctx["the_question"] in the ContextHook.hook method
• run copier copy on the template
• run copier update on the generated project
• it fails with a KeyError

Full traceback

Full traceback

copier update --trust --skip-tasks
Updating to template version 0.12.1
Traceback (most recent call last):
  File "/home/noirbizarre/.local/bin/copier", line 8, in <module>
    sys.exit(copier_app_run())
             ^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/plumbum/cli/application.py", line 640, in run
    inst, retcode = subapp.run(argv, exit=False)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/plumbum/cli/application.py", line 635, in run
    retcode = inst.main(*tailargs)
              ^^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/cli.py", line 425, in main
    return _handle_exceptions(inner)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/cli.py", line 70, in _handle_exceptions
    method()
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/cli.py", line 415, in inner
    with self._worker(
         ^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/main.py", line 237, in __exit__
    raise value
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/cli.py", line 423, in inner
    worker.run_update()
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/main.py", line 914, in run_update
    self._apply_update()
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/main.py", line 970, in _apply_update
    set(self.exclude).union(
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/main.py", line 978, in <genexpr>
    if not self.match_skip(path)
           ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/functools.py", line 993, in __get__
    val = self.func(instance)
          ^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/main.py", line 596, in match_skip
    return self._path_matcher(
           ^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/main.py", line 363, in _path_matcher
    spec = PathSpec.from_lines("gitwildmatch", normalized_patterns)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/pathspec/pathspec.py", line 212, in from_lines
    patterns = [pattern_factory(line) for line in lines if line]
                                                  ^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/main.py", line 362, in <genexpr>
    normalized_patterns = (normalize("NFD", pattern) for pattern in patterns)
                                                                    ^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier/main.py", line 768, in _render_string
    return tpl.render(**self._render_context(), **(extra_context or {}))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/jinja2/environment.py", line 1299, in render
    ctx = self.new_context(dict(*args, **kwargs))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/jinja2/environment.py", line 1391, in new_context
    return new_context(
           ^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/jinja2/runtime.py", line 117, in new_context
    return environment.context_class(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/noirbizarre/.local/pipx/venvs/copier/lib/python3.12/site-packages/copier_templates_extensions/extensions/context.py", line 23, in __init__
    parent.update(extension_self.hook(parent))
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/copier.vcs.clone.uqdq9im4/extensions/context.py", line 103, in hook
KeyError: 'project_slug

Expected behavior

One of:

• ContextHook only run in the project rendering phase (was the case for copier<9.4)
• ContextHook has a way to know all questions have been answered

Additional context

I fill this issue for tracking, but I am also filling a feature request/proposal on copier to have a stable solution: copier-org/copier#1883

[pawamoy]

Thanks for the report @noirbizarre, I was able to reproduce the issue with my own template.

I suppose we have to find a new way to detect when is the right time to run then 🤔

EDIT: ah, that's exactly what you say in the other issue 👍

As a consequence, they have to guess which context variable is available and safe for them to use.

[pawamoy]

I have trouble replicating the bug programmatically 🤔 Not providing data to run_update fails with EOF. Providing data to run_update injects the answer early (I believe), preventing the bug to trigger. I'll try with stdin.

[pawamoy]

Erm I can't reproduce this issue anymore 🤔 Could you provide a script/zip that does?