Add special support for @django.cached_property needed in django-stubs (#18959)

sobolevn · web-flow · commit a3aac7102b5c · 2025-05-10T10:15:04.000+03:00
Hi! We, in `django-stubs`, have a lot of usages of `@cached_property` decorator that is a part of `django`: https://docs.djangoproject.com/en/5.2/ref/utils/#django.utils.functional.cached_property All usages of it we have to add to `subtest/allowlist.txt`, which is not great. In typing we reuse `@functools.cached_property` to have all the benefits of its inference: https://github.com/typeddjango/django-stubs/blob/ee8e8b11c37866969ff0406be20591a067dfa983/django-stubs/utils/functional.pyi#L3-L4 But, `stubtest` is not happy with this move: because in runtime objects have `django.utils.functional.cached_property` type and we see the following error: ``` error: django.http.response.HttpResponse.text is inconsistent, cannot reconcile @Property on stub with runtime object Stub: in file /home/runner/work/django-stubs/django-stubs/django-stubs/http/response.pyi:106 def (self: django.http.response.HttpResponse) -> builtins.str Runtime: <django.utils.functional.cached_property object at 0x7f7ce7704920> ``` So, we add all `@django.utils.functional.cached_property` usages to our `allowlist.txt`. There are LOTS of entries there: https://github.com/typeddjango/django-stubs/blob/ee8e8b11c37866969ff0406be20591a067dfa983/scripts/stubtest/allowlist.txt#L158-L425 Moreover, we have to always tell about this problem to new contributors on review :( That's why I propose to special case this as we do with other `property`-likes. I've tested locally and it works perfectly. I don't want to complicate the CI with `django` installation and special tests. So, I added `# pragma: no cover` to indicate that it is not tested.
diff --git a/mypy/stubtest.py b/mypy/stubtest.py
@@ -1256,6 +1256,19 @@ def verify_paramspecexpr(
         return
 
 
+def _is_django_cached_property(runtime: Any) -> bool:  # pragma: no cover
+    # This is a special case for
+    # https://docs.djangoproject.com/en/5.2/ref/utils/#django.utils.functional.cached_property
+    # This is needed in `django-stubs` project:
+    # https://github.com/typeddjango/django-stubs
+    if type(runtime).__name__ != "cached_property":
+        return False
+    try:
+        return bool(runtime.func)
+    except Exception:
+        return False
+
+
 def _verify_readonly_property(stub: nodes.Decorator, runtime: Any) -> Iterator[str]:
     assert stub.func.is_property
     if isinstance(runtime, property):
@@ -1264,6 +1277,9 @@ def _verify_readonly_property(stub: nodes.Decorator, runtime: Any) -> Iterator[s
     if isinstance(runtime, functools.cached_property):
         yield from _verify_final_method(stub.func, runtime.func, MISSING)
         return
+    if _is_django_cached_property(runtime):
+        yield from _verify_final_method(stub.func, runtime.func, MISSING)
+        return
     if inspect.isdatadescriptor(runtime):
         # It's enough like a property...
         return
