Fixed #28577 -- Added checks for ArrayField and JSONField to prevent mutable defaults.

tests/postgres_tests/models.py

@@ -41,7 +41,7 @@ class PostgreSQLModel(models.Model):
 
 
 class IntegerArrayModel(PostgreSQLModel):
-    field = ArrayField(models.IntegerField(), default=[], blank=True)
+    field = ArrayField(models.IntegerField(), default=list, blank=True)
 
 
 class NullableIntegerArrayModel(PostgreSQLModel):

tests/postgres_tests/test_array.py

@@ -4,7 +4,7 @@ import unittest
 import uuid
 
 from django import forms
-from django.core import exceptions, serializers, validators
+from django.core import checks, exceptions, serializers, validators
 from django.core.exceptions import FieldError
 from django.core.management import call_command
 from django.db import IntegrityError, connection, models
@@ -424,6 +424,38 @@ class TestChecks(PostgreSQLTestCase):
         self.assertEqual(len(errors), 1)
         self.assertEqual(errors[0].id, 'postgres.E002')
 
+    def test_invalid_default(self):
+        class MyModel(PostgreSQLModel):
+            field = ArrayField(models.IntegerField(), default=[])
+
+        model = MyModel()
+        self.assertEqual(model.check(), [
+            checks.Warning(
+                msg=(
+                    "ArrayField default should be a callable instead of an "
+                    "instance so that it's not shared between all field "
+                    "instances."
+                ),
+                hint='Use a callable instead, e.g., use `list` instead of `[]`.',
+                obj=MyModel._meta.get_field('field'),
+                id='postgres.E003',
+            )
+        ])
+
+    def test_valid_default(self):
+        class MyModel(PostgreSQLModel):
+            field = ArrayField(models.IntegerField(), default=list)
+
+        model = MyModel()
+        self.assertEqual(model.check(), [])
+
+    def test_valid_default_none(self):
+        class MyModel(PostgreSQLModel):
+            field = ArrayField(models.IntegerField(), default=None)
+
+        model = MyModel()
+        self.assertEqual(model.check(), [])
+
     def test_nested_field_checks(self):
         """
         Nested ArrayFields are permitted.

tests/postgres_tests/test_json.py

@@ -2,13 +2,14 @@ import datetime
 import uuid
 from decimal import Decimal
 
-from django.core import exceptions, serializers
+from django.core import checks, exceptions, serializers
 from django.core.serializers.json import DjangoJSONEncoder
 from django.forms import CharField, Form, widgets
+from django.test.utils import isolate_apps
 from django.utils.html import escape
 
 from . import PostgreSQLTestCase
-from .models import JSONModel
+from .models import JSONModel, PostgreSQLModel
 
 try:
     from django.contrib.postgres import forms
@@ -259,6 +260,42 @@ class TestQuerying(PostgreSQLTestCase):
         self.assertTrue(JSONModel.objects.filter(field__foo__iregex=r'^bAr$').exists())
 
 
+@isolate_apps('postgres_tests')
+class TestChecks(PostgreSQLTestCase):
+
+    def test_invalid_default(self):
+        class MyModel(PostgreSQLModel):
+            field = JSONField(default={})
+
+        model = MyModel()
+        self.assertEqual(model.check(), [
+            checks.Warning(
+                msg=(
+                    "JSONField default should be a callable instead of an "
+                    "instance so that it's not shared between all field "
+                    "instances."
+                ),
+                hint='Use a callable instead, e.g., use `dict` instead of `{}`.',
+                obj=MyModel._meta.get_field('field'),
+                id='postgres.E003',
+            )
+        ])
+
+    def test_valid_default(self):
+        class MyModel(PostgreSQLModel):
+            field = JSONField(default=dict)
+
+        model = MyModel()
+        self.assertEqual(model.check(), [])
+
+    def test_valid_default_none(self):
+        class MyModel(PostgreSQLModel):
+            field = JSONField(default=None)
+
+        model = MyModel()
+        self.assertEqual(model.check(), [])
+
+
 class TestSerialization(PostgreSQLTestCase):
     test_data = (
         '[{"fields": {"field": {"a": "b", "c": null}, "field_custom": null}, '