🐛 Raise PydanticSerializationUnexpectedValue in root model serializer only if strict check is enabled

src/serializers/type_serializers/model.rs

@@ -166,9 +166,13 @@ impl TypeSerializer for ModelSerializer {
         if self.root_model {
             extra.field_name = Some(ROOT_FIELD);
             let py = value.py();
-            let root = value
-                .getattr(intern!(py, ROOT_FIELD))
-                .map_err(|_| PydanticSerializationUnexpectedValue::new_err(None))?;
+            let root = value.getattr(intern!(py, ROOT_FIELD)).map_err(|original_err| {
+                if extra.check.enabled() {
+                    PydanticSerializationUnexpectedValue::new_err(None)
+                } else {
+                    original_err
+                }
+            })?;
             self.serializer.to_python(root, include, exclude, &extra)
         } else if self.allow_value(value, &extra)? {
             let inner_value = self.get_inner_value(value, &extra)?;

tests/serializers/test_model_root.py

@@ -179,3 +179,29 @@ class Model(RootModel):
 
     assert s.to_python(m) == [1, 2, {'value': 'abc'}]
     assert s.to_json(m) == b'[1,2,{"value":"abc"}]'
+
+
+def test_construct_nested():
+    class RModel(RootModel):
+        root: int
+
+    class BModel(BaseModel):
+        value: RModel
+
+    s = SchemaSerializer(
+        core_schema.model_schema(
+            BModel,
+            core_schema.model_fields_schema(
+                {
+                    'value': core_schema.model_field(
+                        core_schema.model_schema(RModel, core_schema.int_schema(), root_model=True)
+                    )
+                }
+            ),
+        )
+    )
+
+    m = BModel(value=42)
+
+    with pytest.raises(AttributeError, match="'int' object has no attribute 'root'"):
+        s.to_python(m)