[#31] Do not validate defaults for Django fields with choices

The reason here is that the source of our config values cannot
express complex types such as enum members, and that defaults
for Django fields with choices frequently include such types
(or callables returning such types). We are mainly about the
types of the values provided from outside, not of Django field
defaults (beyond null and blank), so we can leave the validation
of the default to Django.

django_setup_configuration/fields.py

@@ -127,6 +127,17 @@ def __init__(
             else:
                 field_info_creation_kwargs["default"] = inferred_default
 
+        # Defaults for fields with choices often do not map neatly onto the consructed
+        # type used for serialization (e.g. a string) because they may not be a literal
+        # choices but e.g. an enum/Choices member. Inferring the types of the default
+        # can be non-trivial (especially if a default factory is involved), and because
+        # we care about types that can be expressed as simple YAML/JSON scalars, it also
+        # would not make much sense to add complex types to the annotation.
+        validate_defaults = False if self.django_field.choices else True
+        field_info_creation_kwargs["validate_default"] = field_info_creation_kwargs[
+            "validate_return"
+        ] = validate_defaults
+
         return super().__init__(**field_info_creation_kwargs)
 
     @staticmethod

testapp/models.py

@@ -25,6 +25,12 @@ class TestModel(models.Model):
     str_with_choices_and_default = models.CharField(
         max_length=3, choices=StrChoices.choices, default=StrChoices.bar
     )
+    str_with_choices_and_incorrectly_typed_default = models.CharField(
+        max_length=3, choices=StrChoices.choices, default=1974
+    )
+    str_with_choices_and_incorrectly_typed_default_factory = models.CharField(
+        max_length=3, choices=StrChoices.choices, default=lambda: 1985
+    )
     str_with_choices_and_blank = models.CharField(
         max_length=3, choices=StrChoices.choices, blank=True
     )

tests/test_django_model_ref_field.py

@@ -372,3 +372,18 @@ class Config(ConfigurationModel):
     assert field.annotation == Literal[1, 8] | Literal[42]
     assert field.default == 42
     assert field.is_required() is False
+
+
+def test_choices_with_incorrectly_typed_default_is_not_validated():
+
+    class Config(ConfigurationModel):
+        str_with_choices_and_incorrectly_typed_default = DjangoModelRef(
+            TestModel, "str_with_choices_and_incorrectly_typed_default"
+        )
+        str_with_choices_and_incorrectly_typed_default_factory = DjangoModelRef(
+            TestModel, "str_with_choices_and_incorrectly_typed_default_factory"
+        )
+
+    config = Config()
+    assert config.str_with_choices_and_incorrectly_typed_default == 1974
+    assert config.str_with_choices_and_incorrectly_typed_default_factory == 1985