Preserve field description when rebuilding model fields (#11698)

Viicos · web-flow · commit f14b7da9cf7f · 2025-04-08T14:07:57.000+02:00
diff --git a/pydantic/_internal/_fields.py b/pydantic/_internal/_fields.py
@@ -319,18 +319,20 @@ def rebuild_model_fields(
             if field_info._complete:
                 rebuilt_fields[f_name] = field_info
             else:
+                existing_desc = field_info.description
                 ann = _typing_extra.eval_type(
                     field_info._original_annotation,
                     *ns_resolver.types_namespace,
                 )
                 ann = _generics.replace_types(ann, typevars_map)
 
                 if (assign := field_info._original_assignment) is PydanticUndefined:
-                    rebuilt_fields[f_name] = FieldInfo_.from_annotation(ann, _source=AnnotationSource.CLASS)
+                    new_field = FieldInfo_.from_annotation(ann, _source=AnnotationSource.CLASS)
                 else:
-                    rebuilt_fields[f_name] = FieldInfo_.from_annotated_attribute(
-                        ann, assign, _source=AnnotationSource.CLASS
-                    )
+                    new_field = FieldInfo_.from_annotated_attribute(ann, assign, _source=AnnotationSource.CLASS)
+                # The description might come from the docstring if `use_attribute_docstrings` was `True`:
+                new_field.description = new_field.description if new_field.description is not None else existing_desc
+                rebuilt_fields[f_name] = new_field
 
     return rebuilt_fields
 
diff --git a/tests/test_fields.py b/tests/test_fields.py
@@ -170,3 +170,21 @@ class Model(BaseModel):
         field: str = Field(coerce_numbers_to_str=True)
 
     assert Model(field=number).field == str(number)
+
+
+def test_rebuild_model_fields_preserves_description() -> None:
+    """https://github.com/pydantic/pydantic/issues/11696"""
+
+    class Model(BaseModel):
+        model_config = ConfigDict(use_attribute_docstrings=True)
+
+        f: 'Int'
+        """test doc"""
+
+    assert Model.model_fields['f'].description == 'test doc'
+
+    Int = int
+
+    Model.model_rebuild()
+
+    assert Model.model_fields['f'].description == 'test doc'
