Fix admin import without django-stubs runtime monkeypatch

[samiashi]

Fix import-time admin crash when Django generic types are not runtime-subscriptable

Description

This PR fixes an import-time crash in django_fsm.admin introduced by the 4.2.0 typing/admin integration changes.

At module import time, django_fsm.admin evaluated typed Django generics such as ModelForm[...] and ModelAdmin[...]. In downstream projects that do not call django_stubs_ext.monkeypatch() before Django admin autodiscovery, those classes are not runtime-subscriptable, which raises:

TypeError: type 'ModelForm' is not subscriptable

This change keeps the precise generic typing under typing.TYPE_CHECKING and uses unsubscripted runtime fallbacks instead. That preserves static typing for type checkers while allowing django_fsm.admin to import cleanly without requiring a runtime monkeypatch in consumer projects.

This PR also adds a regression test that imports django_fsm.admin in a fresh subprocess with only minimal Django settings configured. The test verifies the module can be imported without inheriting the test suite's django_stubs_ext.monkeypatch() setup.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Other (no functional changes)

Checklist

• I have read the CONTRIBUTING.md guide
• Tests added/updated for the changes
• All tests pass locally (uv run pytest or pytest)
• Linting passes (uv run ruff check .)
• Documentation updated (if applicable)
• CHANGELOG.rst updated (for user-facing changes)

Testing

Ran the full test suite and lint locally.

uv run pytest
uvx ruff check .
uvx ruff format --check .

Additionally, the new regression coverage is in:

• tests/testapp/tests/test_admin.py::test_admin_module_imports_without_django_stubs_monkeypatch

This test spawns a fresh Python process, configures minimal Django settings, and verifies import django_fsm.admin succeeds without relying on the test suite's django_stubs_ext monkeypatch.

Related Issues

Related to the import-time runtime typing regression in django_fsm.admin introduced in 4.2.0 admin integration.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
django_fsm/admin.py	100.00% <100.00%> (ø)

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• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[pfouque]

Thanks for the great fix and the regression test — nice catch. 👍

I only moved the test into a dedicated file for consistency with the rest of the suite.

I'll ship this in today's release. ⛵