Fixed #24195 -- Deconstructed the limit_choices_to option of related fields.

Migrations will now be created for changes to limit_choices_to.

AUTHORS

@@ -9,6 +9,7 @@ answer newbie questions, and generally made Django that much better:
     Aaron Swartz <http://www.aaronsw.com/>
     Aaron T. Myers <atmyers@gmail.com>
     Abhishek Gautam <abhishekg1128@yahoo.com>
+    Adam Bogdał <adam@bogdal.pl>
     Adam Johnson <https://github.com/adamchainz>
     Adam Malinowski <http://adammalinowski.co.uk>
     Adam Vandenberg

django/db/models/fields/related.py

@@ -318,6 +318,12 @@ class RelatedField(Field):
                 field.do_related_class(related, model)
             lazy_related_operation(resolve_related_class, cls, self.remote_field.model, field=self)
 
+    def deconstruct(self):
+        name, path, args, kwargs = super().deconstruct()
+        if self.remote_field.limit_choices_to:
+            kwargs['limit_choices_to'] = self.remote_field.limit_choices_to
+        return name, path, args, kwargs
+
     def get_forward_related_filter(self, obj):
         """
         Return the keyword arguments that when supplied to

docs/releases/2.0.txt

@@ -444,6 +444,10 @@ Miscellaneous
 * A model instance's primary key now appears in the default ``Model.__str__()``
   method, e.g. ``Question object (1)``.
 
+* ``makemigrations`` now detects changes to the model field ``limit_choices_to``
+  option. Add this to your existing migrations or accept an auto-generated
+  migration for fields that use it.
+
 .. _deprecated-features-2.0:
 
 Features deprecated in 2.0

tests/field_deconstruction/tests.py

@@ -214,6 +214,15 @@ class FieldDeconstructionTests(SimpleTestCase):
         self.assertEqual(path, "django.db.models.ForeignKey")
         self.assertEqual(args, [])
         self.assertEqual(kwargs, {"to": "auth.Permission", "related_name": "foobar", "on_delete": models.CASCADE})
+        # Test limit_choices_to
+        field = models.ForeignKey("auth.Permission", models.CASCADE, limit_choices_to={'foo': 'bar'})
+        name, path, args, kwargs = field.deconstruct()
+        self.assertEqual(path, "django.db.models.ForeignKey")
+        self.assertEqual(args, [])
+        self.assertEqual(
+            kwargs,
+            {"to": "auth.Permission", "limit_choices_to": {'foo': 'bar'}, "on_delete": models.CASCADE}
+        )
 
     @override_settings(AUTH_USER_MODEL="auth.Permission")
     def test_foreign_key_swapped(self):
@@ -228,6 +237,17 @@ class FieldDeconstructionTests(SimpleTestCase):
         self.assertEqual(kwargs, {"to": "auth.Permission", "on_delete": models.CASCADE})
         self.assertEqual(kwargs['to'].setting_name, "AUTH_USER_MODEL")
 
+    def test_one_to_one(self):
+        # Test limit_choices_to
+        field = models.OneToOneField("auth.Permission", models.CASCADE, limit_choices_to={'foo': 'bar'})
+        name, path, args, kwargs = field.deconstruct()
+        self.assertEqual(path, "django.db.models.OneToOneField")
+        self.assertEqual(args, [])
+        self.assertEqual(
+            kwargs,
+            {"to": "auth.Permission", "limit_choices_to": {'foo': 'bar'}, "on_delete": models.CASCADE}
+        )
+
     def test_image_field(self):
         field = models.ImageField(upload_to="foo/barness", width_field="width", height_field="height")
         name, path, args, kwargs = field.deconstruct()
@@ -294,6 +314,12 @@ class FieldDeconstructionTests(SimpleTestCase):
         self.assertEqual(path, "django.db.models.ManyToManyField")
         self.assertEqual(args, [])
         self.assertEqual(kwargs, {"to": "auth.Permission", "related_name": "custom_table"})
+        # Test limit_choices_to
+        field = models.ManyToManyField("auth.Permission", limit_choices_to={'foo': 'bar'})
+        name, path, args, kwargs = field.deconstruct()
+        self.assertEqual(path, "django.db.models.ManyToManyField")
+        self.assertEqual(args, [])
+        self.assertEqual(kwargs, {"to": "auth.Permission", "limit_choices_to": {'foo': 'bar'}})
 
     @override_settings(AUTH_USER_MODEL="auth.Permission")
     def test_many_to_many_field_swapped(self):