Fixed #28184 -- Allowed using a callable for FileField and ImageField storage.

django/db/models/fields/files.py

@@ -5,7 +5,7 @@ from django import forms
 from django.core import checks
 from django.core.files.base import File
 from django.core.files.images import ImageFile
-from django.core.files.storage import default_storage
+from django.core.files.storage import Storage, default_storage
 from django.db.models import signals
 from django.db.models.fields import Field
 from django.utils.translation import gettext_lazy as _
@@ -234,6 +234,13 @@ class FileField(Field):
         self._primary_key_set_explicitly = 'primary_key' in kwargs
 
         self.storage = storage or default_storage
+        if callable(self.storage):
+            self.storage = self.storage()
+            if not isinstance(self.storage, Storage):
+                raise TypeError(
+                    "%s.storage must be a subclass/instance of %s.%s"
+                    % (self.__class__.__qualname__, Storage.__module__, Storage.__qualname__)
+                )
         self.upload_to = upload_to
 
         kwargs.setdefault('max_length', 100)