fix: Raise ImproperlyConfigured error when fields provided as a string

Co-authored-by: Willem Van Onsem <[email protected]>

Author: last-partizan

modeltranslation/tests/tests.py

@@ -5,7 +5,7 @@
 import shutil
 import sys
 from decimal import Decimal
-
+from modeltranslation.translator import TranslationOptions
 import pytest
 from django import forms
 from django.apps import apps as django_apps
@@ -2345,6 +2345,12 @@ def test_multi_inheritance(self):
         assert "titlee" in clsb.fields
         assert 5 == len(clsb.fields)  # there are no repetitions
 
+    def test_str_instead_of_tuple(self):
+        with pytest.raises(ImproperlyConfigured):
+
+            class ModelOptions(TranslationOptions):
+                fields = "titlea"
+
 
 class UpdateCommandTest(ModeltranslationTestBase):
     def test_update_command(self):

modeltranslation/translator.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from textwrap import dedent
 from copy import deepcopy
 from functools import partial
 from typing import Any, Callable, ClassVar, cast
@@ -79,7 +80,18 @@ class FieldsAggregationMetaClass(type):
     fields: Sequence[str]
 
     def __new__(cls, name: str, bases: tuple[type, ...], attrs: dict[str, Any]) -> type:
-        attrs["fields"] = set(attrs.get("fields", ()))
+        fields = attrs.get("fields", ())
+        if isinstance(fields, str):
+            raise ImproperlyConfigured(
+                dedent(f"""`fields` property should be list or tuple, received `str`.
+
+                Hint: Replace with:
+
+                    fields = ("{fields}", )
+                """)
+            )
+        else:
+            attrs["fields"] = set(fields)
         for base in bases:
             if isinstance(base, FieldsAggregationMetaClass):
                 attrs["fields"].update(base.fields)