Fixed #34119 -- Prevented callable default hidden widget value from being overridden.

Thanks to Benjamin Rigaud for the report.

django/forms/boundfield.py

@@ -96,9 +96,17 @@ class BoundField:
             attrs.setdefault(
                 "id", self.html_initial_id if only_initial else self.auto_id
             )
+        if only_initial and self.html_initial_name in self.form.data:
+            # Propagate the hidden initial value.
+            value = self.form._widget_data_value(
+                self.field.hidden_widget(),
+                self.html_initial_name,
+            )
+        else:
+            value = self.value()
         return widget.render(
             name=self.html_initial_name if only_initial else self.html_name,
-            value=self.value(),
+            value=value,
             attrs=attrs,
             renderer=self.form.renderer,
         )

tests/forms_tests/tests/tests.py

@@ -203,6 +203,46 @@ class ModelFormCallableModelDefault(TestCase):
             """,
         )
 
+    def test_callable_default_hidden_widget_value_not_overridden(self):
+        class FieldWithCallableDefaultsModel(models.Model):
+            int_field = models.IntegerField(default=lambda: 1)
+            json_field = models.JSONField(default=dict)
+
+        class FieldWithCallableDefaultsModelForm(ModelForm):
+            class Meta:
+                model = FieldWithCallableDefaultsModel
+                fields = "__all__"
+
+        form = FieldWithCallableDefaultsModelForm(
+            data={
+                "initial-int_field": "1",
+                "int_field": "1000",
+                "initial-json_field": "{}",
+                "json_field": '{"key": "val"}',
+            }
+        )
+        form_html = form.as_p()
+        self.assertHTMLEqual(
+            form_html,
+            """
+            <p>
+            <label for="id_int_field">Int field:</label>
+            <input type="number" name="int_field" value="1000"
+                required id="id_int_field">
+            <input type="hidden" name="initial-int_field" value="1"
+                id="initial-id_int_field">
+            </p>
+            <p>
+            <label for="id_json_field">Json field:</label>
+            <textarea cols="40" id="id_json_field" name="json_field" required rows="10">
+            {&quot;key&quot;: &quot;val&quot;}
+            </textarea>
+            <input id="initial-id_json_field" name="initial-json_field" type="hidden"
+                value="{}">
+            </p>
+            """,
+        )
+
 
 class FormsModelTestCase(TestCase):
     def test_unicode_filename(self):