Added warning and test case for it

django/contrib/postgres/fields/array.py

@@ -1,4 +1,5 @@
 import json
+import warnings
 
 from django import forms
 from django.contrib.postgres import lookups
@@ -8,6 +9,7 @@ from django.core import checks, exceptions
 from django.db.models import Field, Func, IntegerField, Transform, Value
 from django.db.models.fields.mixins import CheckFieldDefaultMixin
 from django.db.models.lookups import Exact, In
+from django.utils.deprecation import RemovedInDjango51Warning
 from django.utils.translation import gettext_lazy as _
 
 from ..utils import prefix_validation_error
@@ -204,22 +206,22 @@ class ArrayField(CheckFieldDefaultMixin, Field):
 
     def formfield(self, **kwargs):
         if self.base_field.choices and "choices_form_class" not in kwargs:
+            obj = self.base_field
             defaults = {
                 "choices_form_class": forms.TypedMultipleChoiceField,
-                "coerce": self.base_field.to_python,
             }
-            defaults.update(kwargs)
-            return self.base_field.formfield(**defaults)
-        elif not self.choices:
+        else:
+            obj = super()
             defaults = {
                 "form_class": SimpleArrayField,
                 "base_field": self.base_field.formfield(),
                 "max_length": self.size,
             }
-            defaults.update(kwargs)
-        else:
-            raise NotImplementedError("Choices should be defined in base field.")
-        return super().formfield(**defaults)
+            if self.choices:
+                warnings.warn(
+                    "Choices should be defined in base field.", RemovedInDjango51Warning
+                )
+        return obj.formfield(**{**defaults, **kwargs})
 
 
 class ArrayRHSMixin:

django/db/models/fields/__init__.py

@@ -1024,7 +1024,7 @@ class Field(RegisterLookupMixin):
                 self.has_default() or "initial" in kwargs
             )
             defaults["choices"] = self.get_choices(include_blank=include_blank)
-            defaults["coerce"] = kwargs.get("coerce", self.to_python)
+            defaults["coerce"] = self.to_python
             if self.null:
                 defaults["empty_value"] = None
             if choices_form_class is not None:

tests/postgres_tests/test_array.py

@@ -3,6 +3,7 @@ import enum
 import json
 import unittest
 import uuid
+import warnings
 
 from django import forms
 from django.core import checks, exceptions, serializers, validators
@@ -14,6 +15,7 @@ from django.db.models.functions import Cast, JSONObject, Upper
 from django.test import TransactionTestCase, modify_settings, override_settings
 from django.test.utils import isolate_apps
 from django.utils import timezone
+from django.utils.deprecation import RemovedInDjango51Warning
 
 from . import PostgreSQLSimpleTestCase, PostgreSQLTestCase, PostgreSQLWidgetTestCase
 from .models import (
@@ -1134,12 +1136,15 @@ class TestChoiceFormField(PostgreSQLTestCase):
         )
 
     def test_model_field_formfield_choices(self):
-        with self.assertRaises(NotImplementedError):
         model_field = ArrayField(
             models.CharField(max_length=27), choices=(("a1", "A1"), ("b1", "B1"))
         )
-            form_field = model_field.formfield()
-            form_field.clean(["a1", "b1"])
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            model_field.formfield()
+            assert len(w) == 1
+            assert issubclass(w[-1].category, RemovedInDjango51Warning)
+            assert "Choices should be defined in base field." in str(w[-1].message)
 
 
 class TestSplitFormField(PostgreSQLSimpleTestCase):