Fixed #30076 -- Added Model.get_FOO_display() even if field's choices are empty.

3 files changed, 80 insertions, 9 deletions

diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index d0a1324c79..f32ce64629 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -153,7 +153,7 @@ class Field(RegisterLookupMixin):
         self.unique_for_year = unique_for_year
         if isinstance(choices, collections.abc.Iterator):
             choices = list(choices)
-        self.choices = choices or []
+        self.choices = choices
         self.help_text = help_text
         self.db_index = db_index
         self.db_column = db_column
@@ -443,7 +443,7 @@ class Field(RegisterLookupMixin):
             "unique_for_date": None,
             "unique_for_month": None,
             "unique_for_year": None,
-            "choices": [],
+            "choices": None,
             "help_text": '',
             "db_column": None,
             "db_tablespace": None,
@@ -598,7 +598,7 @@ class Field(RegisterLookupMixin):
             # Skip validation for non-editable fields.
             return
 
-        if self.choices and value not in self.empty_values:
+        if self.choices is not None and value not in self.empty_values:
             for option_key, option_value in self.choices:
                 if isinstance(option_value, (list, tuple)):
                     # This is an optgroup, so look inside the group for
@@ -742,7 +742,7 @@ class Field(RegisterLookupMixin):
             # such fields can't be deferred (we don't have a check for this).
             if not getattr(cls, self.attname, None):
                 setattr(cls, self.attname, DeferredAttribute(self.attname))
-        if self.choices:
+        if self.choices is not None:
             setattr(cls, 'get_%s_display' % self.name,
                     partialmethod(cls._get_FIELD_display, field=self))
 
@@ -812,7 +812,7 @@ class Field(RegisterLookupMixin):
         Return choices with a default blank choices included, for use
         as <select> choices for this field.
         """
-        if self.choices:
+        if self.choices is not None:
             choices = list(self.choices)
             if include_blank:
                 blank_defined = any(choice in ('', None) for choice, _ in self.flatchoices)
@@ -840,6 +840,8 @@ class Field(RegisterLookupMixin):
 
     def _get_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)):
@@ -865,7 +867,7 @@ class Field(RegisterLookupMixin):
                 defaults['show_hidden_initial'] = True
             else:
                 defaults['initial'] = self.get_default()
-        if self.choices:
+        if self.choices is not None:
             # Fields with choices get special treatment.
             include_blank = (self.blank or
                              not (self.has_default() or 'initial' in kwargs))
@@ -1018,7 +1020,7 @@ class BooleanField(Field):
         return self.to_python(value)
 
     def formfield(self, **kwargs):
-        if self.choices:
+        if self.choices is not None:
             include_blank = not (self.has_default() or 'initial' in kwargs)
             defaults = {'choices': self.get_choices(include_blank=include_blank)}
         else:
@@ -2080,7 +2082,7 @@ class TextField(Field):
         # the value in the form field (to pass into widget for example).
         return super().formfield(**{
             'max_length': self.max_length,
-            **({} if self.choices else {'widget': forms.Textarea}),
+            **({} if self.choices is not None else {'widget': forms.Textarea}),
             **kwargs,
         })
 
diff --git a/tests/model_fields/models.py b/tests/model_fields/models.py
index 13d4843632..02fea36b31 100644
--- a/tests/model_fields/models.py
+++ b/tests/model_fields/models.py
@@ -50,6 +50,14 @@ class Whiz(models.Model):
     c = models.IntegerField(choices=CHOICES, null=True)
 
 
+class WhizDelayed(models.Model):
+    c = models.IntegerField(choices=(), null=True)
+
+
+# Contrived way of adding choices later.
+WhizDelayed._meta.get_field('c').choices = Whiz.CHOICES
+
+
 class WhizIter(models.Model):
     c = models.IntegerField(choices=iter(Whiz.CHOICES), null=True)
 
@@ -58,6 +66,14 @@ class WhizIterEmpty(models.Model):
     c = models.CharField(choices=iter(()), blank=True, max_length=1)
 
 
+class Choiceful(models.Model):
+    no_choices = models.IntegerField(null=True)
+    empty_choices = models.IntegerField(choices=(), null=True)
+    with_choices = models.IntegerField(choices=[(1, 'A')], null=True)
+    empty_choices_bool = models.BooleanField(choices=())
+    empty_choices_text = models.TextField(choices=())
+
+
 class BigD(models.Model):
     d = models.DecimalField(max_digits=32, decimal_places=30)
 
diff --git a/tests/model_fields/tests.py b/tests/model_fields/tests.py
index 42e784db54..f55175aa9e 100644
--- a/tests/model_fields/tests.py
+++ b/tests/model_fields/tests.py
@@ -1,12 +1,14 @@
 import pickle
 
 from django import forms
+from django.core.exceptions import ValidationError
 from django.db import models
 from django.test import SimpleTestCase, TestCase
 from django.utils.functional import lazy
 
 from .models import (
-    Bar, Foo, RenamedField, VerboseNameField, Whiz, WhizIter, WhizIterEmpty,
+    Bar, Choiceful, Foo, RenamedField, VerboseNameField, Whiz, WhizDelayed,
+    WhizIter, WhizIterEmpty,
 )
 
 
@@ -103,6 +105,51 @@ class BasicFieldTests(SimpleTestCase):
 
 class ChoicesTests(SimpleTestCase):
 
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        cls.no_choices = Choiceful._meta.get_field('no_choices')
+        cls.empty_choices = Choiceful._meta.get_field('empty_choices')
+        cls.empty_choices_bool = Choiceful._meta.get_field('empty_choices_bool')
+        cls.empty_choices_text = Choiceful._meta.get_field('empty_choices_text')
+        cls.with_choices = Choiceful._meta.get_field('with_choices')
+
+    def test_choices(self):
+        self.assertIsNone(self.no_choices.choices)
+        self.assertEqual(self.empty_choices.choices, ())
+        self.assertEqual(self.with_choices.choices, [(1, 'A')])
+
+    def test_flatchoices(self):
+        self.assertEqual(self.no_choices.flatchoices, [])
+        self.assertEqual(self.empty_choices.flatchoices, [])
+        self.assertEqual(self.with_choices.flatchoices, [(1, 'A')])
+
+    def test_check(self):
+        self.assertEqual(Choiceful.check(), [])
+
+    def test_invalid_choice(self):
+        model_instance = None  # Actual model instance not needed.
+        self.no_choices.validate(0, model_instance)
+        msg = "['Value 99 is not a valid choice.']"
+        with self.assertRaisesMessage(ValidationError, msg):
+            self.empty_choices.validate(99, model_instance)
+        with self.assertRaisesMessage(ValidationError, msg):
+            self.with_choices.validate(99, model_instance)
+
+    def test_formfield(self):
+        no_choices_formfield = self.no_choices.formfield()
+        self.assertIsInstance(no_choices_formfield, forms.IntegerField)
+        fields = (
+            self.empty_choices, self.with_choices, self.empty_choices_bool,
+            self.empty_choices_text,
+        )
+        for field in fields:
+            with self.subTest(field=field):
+                self.assertIsInstance(field.formfield(), forms.ChoiceField)
+
+
+class GetFieldDisplayTests(SimpleTestCase):
+
     def test_choices_and_field_display(self):
         """
         get_choices() interacts with get_FIELD_display() to return the expected
@@ -113,6 +160,7 @@ class ChoicesTests(SimpleTestCase):
         self.assertEqual(Whiz(c=9).get_c_display(), 9)          # Invalid value
         self.assertIsNone(Whiz(c=None).get_c_display())         # Blank value
         self.assertEqual(Whiz(c='').get_c_display(), '')        # Empty value
+        self.assertEqual(WhizDelayed(c=0).get_c_display(), 'Other')  # Delayed choices
 
     def test_iterator_choices(self):
         """
@@ -135,6 +183,11 @@ class ChoicesTests(SimpleTestCase):
 
 class GetChoicesTests(SimpleTestCase):
 
+    def test_empty_choices(self):
+        choices = []
+        f = models.CharField(choices=choices)
+        self.assertEqual(f.get_choices(include_blank=False), choices)
+
     def test_blank_in_choices(self):
         choices = [('', '<><>'), ('a', 'A')]
         f = models.CharField(choices=choices)