Fixed #32347 -- Made ModelChoiceField include the value in ValidationError for invalid_choice.

docs/ref/forms/fields.txt

@@ -1219,6 +1219,9 @@ generating choices. See :ref:`iterating-relationship-choices` for details.
     * Validates that the given id exists in the queryset.
     * Error message keys: ``required``, ``invalid_choice``
 
+    The ``invalid_choice`` error message may contain ``%(value)s``, which will
+    be replaced with the selected choice.
+
     Allows the selection of a single model object, suitable for representing a
     foreign key. Note that the default widget for ``ModelChoiceField`` becomes
     impractical when the number of entries increases. You should avoid using it
@@ -1307,6 +1310,11 @@ generating choices. See :ref:`iterating-relationship-choices` for details.
             def label_from_instance(self, obj):
                 return "My Object #%i" % obj.id
 
+    .. versionchanged:: 4.0
+
+        Support for containing ``%(value)s`` in the ``invalid_choice`` error
+        message was added.
+
 ``ModelMultipleChoiceField``
 ----------------------------
 

docs/releases/4.0.txt

@@ -135,7 +135,11 @@ File Uploads
 Forms
 ~~~~~
 
-* ...
+* :class:`~django.forms.ModelChoiceField` now includes the provided value in
+  the ``params`` argument of a raised
+  :exc:`~django.core.exceptions.ValidationError` for the ``invalid_choice``
+  error message. This allows custom error messages to use the ``%(value)s``
+  placeholder.
 
 Generic Views
 ~~~~~~~~~~~~~