Avoided creating default form fields in fields_for_model() when declared on form.

django/forms/models.py

@@ -146,6 +146,7 @@ def fields_for_model(
     field_classes=None,
     *,
     apply_limit_choices_to=True,
+    form_declared_fields=None,
 ):
     """
     Return a dictionary containing form fields for the given model.
@@ -176,7 +177,11 @@ def fields_for_model(
 
     ``apply_limit_choices_to`` is a boolean indicating if limit_choices_to
     should be applied to a field's queryset.
+
+    ``form_declared_fields`` is a dictionary of form fields created directly on
+    a form.
     """
+    form_declared_fields = form_declared_fields or {}
     field_dict = {}
     ignored = []
     opts = model._meta
@@ -204,6 +209,9 @@ def fields_for_model(
             continue
         if exclude and f.name in exclude:
             continue
+        if f.name in form_declared_fields:
+            field_dict[f.name] = form_declared_fields[f.name]
+            continue
 
         kwargs = {}
         if widgets and f.name in widgets:
@@ -310,6 +318,7 @@ class ModelFormMetaclass(DeclarativeFieldsMetaclass):
                 opts.field_classes,
                 # limit_choices_to will be applied during ModelForm.__init__().
                 apply_limit_choices_to=False,
+                form_declared_fields=new_class.declared_fields,
             )
 
             # make sure opts.fields doesn't specify an invalid field
@@ -319,8 +328,7 @@ class ModelFormMetaclass(DeclarativeFieldsMetaclass):
                 message = "Unknown field(s) (%s) specified for %s"
                 message %= (", ".join(missing_fields), opts.model.__name__)
                 raise FieldError(message)
-            # Override default model fields with any custom declared ones
-            # (plus, include all the other declared fields).
+            # Include all the other declared fields.
             fields.update(new_class.declared_fields)
         else:
             fields = new_class.declared_fields

tests/model_forms/tests.py

@@ -236,6 +236,15 @@ class ModelFormBaseTest(TestCase):
         field_dict = fields_for_model(Person, fields=())
         self.assertEqual(len(field_dict), 0)
 
+    def test_fields_for_model_form_fields(self):
+        form_declared_fields = CustomWriterForm.declared_fields
+        field_dict = fields_for_model(
+            Writer,
+            fields=["name"],
+            form_declared_fields=form_declared_fields,
+        )
+        self.assertIs(field_dict["name"], form_declared_fields["name"])
+
     def test_empty_fields_on_modelform(self):
         """
         No fields on a ModelForm should actually result in no fields.