Allow overridable checks to be CheckMessage (#497)

* Allow overridable checks to be CheckMessage

The checks framework expects return types to be "List[CheckMessage]". This
allows all overridable checks-returning methods to return the more general
"CheckMessage", instead of the "Error" subclass.

* Ignore an incorrect usage of the checks API in Django 2.2

django-stubs/contrib/admin/checks.pyi

@@ -1,7 +1,7 @@
 from typing import Any, List, Union, Iterable, Optional
 
 from django.contrib.admin.options import BaseModelAdmin
-from django.core.checks.messages import Error
+from django.core.checks.messages import CheckMessage, Error
 
 from django.apps.config import AppConfig
 
@@ -11,7 +11,7 @@ def check_admin_app(app_configs: Optional[Iterable[AppConfig]], **kwargs: Any) -
 def check_dependencies(**kwargs: Any) -> List[_CheckError]: ...
 
 class BaseModelAdminChecks:
-    def check(self, admin_obj: BaseModelAdmin, **kwargs: Any) -> List[_CheckError]: ...
+    def check(self, admin_obj: BaseModelAdmin, **kwargs: Any) -> List[CheckMessage]: ...
 
 class ModelAdminChecks(BaseModelAdminChecks): ...
 class InlineModelAdminChecks(BaseModelAdminChecks): ...

django-stubs/contrib/admin/options.pyi

@@ -11,7 +11,7 @@ from django.contrib.admin.sites import AdminSite
 from django.contrib.admin.views.main import ChangeList
 from django.contrib.auth.forms import AdminPasswordChangeForm
 from django.contrib.contenttypes.models import ContentType
-from django.core.checks.messages import Error
+from django.core.checks.messages import CheckMessage
 from django.core.paginator import Paginator
 from django.db.models.base import Model
 from django.db.models.fields.related import ForeignKey, ManyToManyField, RelatedField
@@ -75,7 +75,7 @@ class BaseModelAdmin:
     view_on_site: bool = ...
     show_full_result_count: bool = ...
     checks_class: Any = ...
-    def check(self, **kwargs: Any) -> List[Union[str, Error]]: ...
+    def check(self, **kwargs: Any) -> List[CheckMessage]: ...
     def formfield_for_dbfield(
         self, db_field: Field, request: Optional[HttpRequest], **kwargs: Any
     ) -> Optional[Field]: ...

django-stubs/contrib/contenttypes/fields.pyi

@@ -1,7 +1,7 @@
 from typing import Any, Callable, Dict, List, Optional, Tuple, Type, Union
 
 from django.contrib.contenttypes.models import ContentType
-from django.core.checks.messages import Error
+from django.core.checks.messages import CheckMessage
 from django.db.models.base import Model
 from django.db.models.expressions import Combinable
 from django.db.models.fields.mixins import FieldCacheMixin
@@ -41,7 +41,7 @@ class GenericForeignKey(FieldCacheMixin):
     def contribute_to_class(self, cls: Type[Model], name: str, **kwargs: Any) -> None: ...
     def get_filter_kwargs_for_object(self, obj: Model) -> Dict[str, Optional[ContentType]]: ...
     def get_forward_related_filter(self, obj: Model) -> Dict[str, int]: ...
-    def check(self, **kwargs: Any) -> List[Error]: ...
+    def check(self, **kwargs: Any) -> List[CheckMessage]: ...
     def get_cache_name(self) -> str: ...
     def get_content_type(
         self, obj: Optional[Model] = ..., id: Optional[int] = ..., using: Optional[str] = ...

django-stubs/contrib/staticfiles/finders.pyi

@@ -1,13 +1,13 @@
 from typing import Any, Iterable, Iterator, List, Mapping, Optional, Union, overload
 
-from django.core.checks.messages import Error
+from django.core.checks.messages import CheckMessage
 from django.core.files.storage import Storage
 from typing_extensions import Literal
 
 searched_locations: Any
 
 class BaseFinder:
-    def check(self, **kwargs: Any) -> List[Error]: ...
+    def check(self, **kwargs: Any) -> List[CheckMessage]: ...
     def find(self, path: str, all: bool = ...) -> Optional[Any]: ...
     def list(self, ignore_patterns: Any) -> Iterable[Any]: ...
 

django-stubs/db/models/fields/__init__.pyi

@@ -17,7 +17,7 @@ from typing import (
     overload,
 )
 
-from django.core import checks
+from django.core.checks import CheckMessage
 
 from django.db.models import Model
 from django.core.exceptions import FieldDoesNotExist as FieldDoesNotExist
@@ -132,7 +132,7 @@ class Field(RegisterLookupMixin, Generic[_ST, _GT]):
     ) -> Sequence[Union[_Choice, _ChoiceNamedGroup]]: ...
     def has_default(self) -> bool: ...
     def get_default(self) -> Any: ...
-    def check(self, **kwargs: Any) -> List[checks.Error]: ...
+    def check(self, **kwargs: Any) -> List[CheckMessage]: ...
     @property
     def validators(self) -> List[_ValidatorCallable]: ...
     def validate(self, value: Any, model_instance: Model) -> None: ...

scripts/enabled_test_modules.py

@@ -68,6 +68,9 @@ IGNORED_ERRORS = {
         'error: "HttpResponse" has no attribute "streaming_content"',
         'error: "HttpResponse" has no attribute "context_data"',
     ],
+    'admin_checks': [
+        'Argument 1 to "append" of "list" has incompatible type "str"; expected "CheckMessage"'
+    ],
     'admin_inlines': [
         'error: "HttpResponse" has no attribute "rendered_content"',
     ],