Fix used_parameters and params types in admin filter stubs

django-stubs/contrib/admin/filters.pyi

@@ -25,9 +25,9 @@ class ListFilter:
     title: _StrOrPromise | None
     template: str
     request: HttpRequest
-    used_parameters: dict[str, bool | datetime | str]
+    used_parameters: dict[str, list[str] | list[bool]]
     def __init__(
-        self, request: HttpRequest, params: dict[str, str], model: type[Model], model_admin: ModelAdmin
+        self, request: HttpRequest, params: dict[str, list[str]], model: type[Model], model_admin: ModelAdmin
     ) -> None: ...
     def has_output(self) -> bool: ...
     def choices(self, changelist: ChangeList) -> Iterator[_ListFilterChoices]: ...
@@ -39,6 +39,8 @@ class FacetsMixin:
     def get_facet_queryset(self, changelist: ChangeList) -> dict[str, int]: ...
 
 class SimpleListFilter(FacetsMixin, ListFilter):
+    # SimpleListFilter stores scalar str (value[-1]) instead of list, breaking the base class contract
+    used_parameters: dict[str, str]  # type: ignore[assignment]
     parameter_name: str | None
     lookup_choices: list[tuple[str, _StrOrPromise]]
     def value(self) -> str | None: ...
@@ -52,7 +54,7 @@ class FieldListFilter(FacetsMixin, ListFilter):
         self,
         field: Field,
         request: HttpRequest,
-        params: dict[str, str],
+        params: dict[str, list[str]],
         model: type[Model],
         model_admin: ModelAdmin,
         field_path: str,
@@ -66,7 +68,7 @@ class FieldListFilter(FacetsMixin, ListFilter):
         cls,
         field: Field,
         request: HttpRequest,
-        params: dict[str, str],
+        params: dict[str, list[str]],
         model: type[Model],
         model_admin: ModelAdmin,
         field_path: str,

django-stubs/contrib/admin/utils.pyi

@@ -1,4 +1,3 @@
-import datetime
 from collections import defaultdict
 from collections.abc import Callable, Iterable, Sequence
 from typing import Any, Literal, TypeVar, overload, type_check_only
@@ -28,9 +27,14 @@ class FieldIsAForeignKeyColumnName(Exception): ...
 
 def lookup_spawns_duplicates(opts: Options, lookup_path: str) -> bool: ...
 def get_last_value_from_parameters(parameters: dict[str, list[str] | str], key: str) -> str | None: ...
-def prepare_lookup_value(
-    key: str, value: list[bool | datetime.datetime | str] | datetime.datetime | str, separator: str = ...
-) -> list[bool | datetime.datetime | str] | bool | datetime.datetime | str: ...
+
+# The implementation recurses on list inputs, but the contract is list[str] | str
+# input only (lookup parameters are supposed to be flat string lists) — do not type the
+# return as a recursive/deeply-nested type.
+@overload
+def prepare_lookup_value(key: str, value: list[str], separator: str = ...) -> list[str] | list[bool]: ...
+@overload
+def prepare_lookup_value(key: str, value: str, separator: str = ...) -> str | bool | list[str]: ...
 def build_q_object_from_lookup_parameters(parameters: dict[str, list[str]]) -> Q: ...
 def quote(s: int | str | UUID) -> str: ...
 def unquote(s: str) -> str: ...