Refs #34899 -- Extracted Field.flatchoices to flatten_choices helper function.

Co-authored-by: Natalia Bidart <124304+nessita@users.noreply.github.com>

3 files changed, 60 insertions, 13 deletions

diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index f15b5856bf..6174b7bc98 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -15,7 +15,11 @@ from django.db import connection, connections, router
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.query_utils import DeferredAttribute, RegisterLookupMixin
 from django.utils import timezone
-from django.utils.choices import CallableChoiceIterator, normalize_choices
+from django.utils.choices import (
+    CallableChoiceIterator,
+    flatten_choices,
+    normalize_choices,
+)
 from django.utils.datastructures import DictWrapper
 from django.utils.dateparse import (
     parse_date,
@@ -1080,19 +1084,10 @@ class Field(RegisterLookupMixin):
         """
         return str(self.value_from_object(obj))
 
-    def _get_flatchoices(self):
+    @property
+    def flatchoices(self):
         """Flattened version of choices tuple."""
-        if self.choices is None:
-            return []
-        flat = []
-        for choice, value in self.choices:
-            if isinstance(value, (list, tuple)):
-                flat.extend(value)
-            else:
-                flat.append((choice, value))
-        return flat
-
-    flatchoices = property(_get_flatchoices)
+        return list(flatten_choices(self.choices))
 
     def save_form_data(self, instance, data):
         setattr(instance, self.name, data)
diff --git a/django/utils/choices.py b/django/utils/choices.py
index 734b9331a1..54dbdcb3aa 100644
--- a/django/utils/choices.py
+++ b/django/utils/choices.py
@@ -6,6 +6,7 @@ from django.utils.functional import Promise
 __all__ = [
     "BaseChoiceIterator",
     "CallableChoiceIterator",
+    "flatten_choices",
     "normalize_choices",
 ]
 
@@ -43,6 +44,15 @@ class CallableChoiceIterator(BaseChoiceIterator):
         yield from normalize_choices(self.func())
 
 
+def flatten_choices(choices):
+    """Flatten choices by removing nested values."""
+    for value_or_group, label_or_nested in choices or ():
+        if isinstance(label_or_nested, (list, tuple)):
+            yield from label_or_nested
+        else:
+            yield value_or_group, label_or_nested
+
+
 def normalize_choices(value, *, depth=0):
     """Normalize choices values consistently for fields and widgets."""
     # Avoid circular import when importing django.forms.
diff --git a/tests/utils_tests/test_choices.py b/tests/utils_tests/test_choices.py
index a2ad5541a4..e3e3766ea9 100644
--- a/tests/utils_tests/test_choices.py
+++ b/tests/utils_tests/test_choices.py
@@ -1,3 +1,4 @@
+import collections.abc
 from unittest import mock
 
 from django.db.models import TextChoices
@@ -5,6 +6,7 @@ from django.test import SimpleTestCase
 from django.utils.choices import (
     BaseChoiceIterator,
     CallableChoiceIterator,
+    flatten_choices,
     normalize_choices,
 )
 from django.utils.translation import gettext_lazy as _
@@ -56,6 +58,46 @@ class ChoiceIteratorTests(SimpleTestCase):
                 self.assertTrue(str(ctx.exception).endswith("index out of range"))
 
 
+class FlattenChoicesTests(SimpleTestCase):
+    def test_empty(self):
+        def generator():
+            yield from ()
+
+        for choices in ({}, [], (), set(), frozenset(), generator(), None, ""):
+            with self.subTest(choices=choices):
+                result = flatten_choices(choices)
+                self.assertIsInstance(result, collections.abc.Generator)
+                self.assertEqual(list(result), [])
+
+    def test_non_empty(self):
+        choices = [
+            ("C", _("Club")),
+            ("D", _("Diamond")),
+            ("H", _("Heart")),
+            ("S", _("Spade")),
+        ]
+        result = flatten_choices(choices)
+        self.assertIsInstance(result, collections.abc.Generator)
+        self.assertEqual(list(result), choices)
+
+    def test_nested_choices(self):
+        choices = [
+            ("Audio", [("vinyl", _("Vinyl")), ("cd", _("CD"))]),
+            ("Video", [("vhs", _("VHS Tape")), ("dvd", _("DVD"))]),
+            ("unknown", _("Unknown")),
+        ]
+        expected = [
+            ("vinyl", _("Vinyl")),
+            ("cd", _("CD")),
+            ("vhs", _("VHS Tape")),
+            ("dvd", _("DVD")),
+            ("unknown", _("Unknown")),
+        ]
+        result = flatten_choices(choices)
+        self.assertIsInstance(result, collections.abc.Generator)
+        self.assertEqual(list(result), expected)
+
+
 class NormalizeFieldChoicesTests(SimpleTestCase):
     expected = [
         ("C", _("Club")),