feat(DTO): Enable codegen backend by default (#3215)

* Enable DTO codegen backend by default
* Update docs

docs/usage/dto/0-basic-use.rst

@@ -78,11 +78,12 @@ DTOs can similarly be defined on :class:`Routers <litestar.router.Router>` and
 Improving performance with the codegen backend
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. admonition:: Experimental feature
-    :class: danger
+.. note::
 
-    This is an experimental feature and should be approached with caution. It may
-    behave unexpectedly, contain bugs and may disappear again in a future version.
+    This feature was introduced in ``2.2.0`` and hidden behind the ``DTO_CODEGEN``
+    feature flag. As of ``2.8.0`` it is considered stable and enabled by default. It can
+    still be disabled selectively by using the
+    ``DTOConfig(experimental_codegen_backend=True)`` override.
 
 
 The DTO backend is the part that does the heavy lifting for all the DTO features. It

litestar/app.py

@@ -3,6 +3,7 @@
 import inspect
 import logging
 import os
+import warnings
 from contextlib import (
     AbstractAsyncContextManager,
     AsyncExitStack,
@@ -20,12 +21,13 @@
 from litestar._openapi.plugin import OpenAPIPlugin
 from litestar._openapi.schema_generation import openapi_schema_plugins
 from litestar.config.allowed_hosts import AllowedHostsConfig
-from litestar.config.app import AppConfig
+from litestar.config.app import AppConfig, ExperimentalFeatures
 from litestar.config.response_cache import ResponseCacheConfig
 from litestar.connection import Request, WebSocket
 from litestar.datastructures.state import State
 from litestar.events.emitter import BaseEventEmitterBackend, SimpleEventEmitter
 from litestar.exceptions import (
+    LitestarWarning,
     MissingDependencyException,
     NoRouteMatchFoundException,
 )
@@ -55,7 +57,6 @@
 if TYPE_CHECKING:
     from typing_extensions import Self
 
-    from litestar.config.app import ExperimentalFeatures
     from litestar.config.compression import CompressionConfig
     from litestar.config.cors import CORSConfig
     from litestar.config.csrf import CSRFConfig
@@ -396,6 +397,16 @@ def __init__(
             self._lifespan_managers.append(store)
         self._server_lifespan_managers = [p.server_lifespan for p in config.plugins or [] if isinstance(p, CLIPlugin)]
         self.experimental_features = frozenset(config.experimental_features or [])
+        if ExperimentalFeatures.DTO_CODEGEN in self.experimental_features:
+            warnings.warn(
+                "Use of redundant experimental feature flag DTO_CODEGEN. "
+                "DTO codegen backend is enabled by default since Litestar 2.8. The "
+                "DTO_CODEGEN feature flag can be safely removed from the configuration "
+                "and will be removed in version 3.0.",
+                category=LitestarWarning,
+                stacklevel=2,
+            )
+
         self.get_logger: GetLogger = get_logger_placeholder
         self.logger: Logger | None = None
         self.routes: list[HTTPRoute | ASGIRoute | WebSocketRoute] = []

litestar/dto/base_dto.py

@@ -178,9 +178,7 @@ def create_for_field_definition(
                     )
 
             if backend_cls is None:
-                backend_cls = DTOCodegenBackend if cls.config.experimental_codegen_backend else DTOBackend
-            elif backend_cls is DTOCodegenBackend and cls.config.experimental_codegen_backend is False:
-                backend_cls = DTOBackend
+                backend_cls = DTOCodegenBackend if cls.config.experimental_codegen_backend is not False else DTOBackend
 
             backend_context[key] = backend_cls(  # type: ignore[literal-required]
                 dto_factory=cls,

litestar/handlers/base.py

@@ -5,7 +5,6 @@
 from typing import TYPE_CHECKING, Any, Callable, Mapping, Sequence, cast
 
 from litestar._signature import SignatureModel
-from litestar.config.app import ExperimentalFeatures
 from litestar.di import Provide
 from litestar.dto import DTOData
 from litestar.exceptions import ImproperlyConfiguredException
@@ -32,7 +31,6 @@
     from litestar.connection import ASGIConnection
     from litestar.controller import Controller
     from litestar.dto import AbstractDTO
-    from litestar.dto._backend import DTOBackend
     from litestar.params import ParameterKwarg
     from litestar.router import Router
     from litestar.types import AnyCallable, AsyncAnyCallable, ExceptionHandler
@@ -442,13 +440,6 @@ def resolve_signature_namespace(self) -> dict[str, Any]:
             self._resolved_signature_namespace = ns
         return cast("dict[str, Any]", self._resolved_signature_namespace)
 
-    def _get_dto_backend_cls(self) -> type[DTOBackend] | None:
-        if ExperimentalFeatures.DTO_CODEGEN in self.app.experimental_features:
-            from litestar.dto._codegen_backend import DTOCodegenBackend
-
-            return DTOCodegenBackend
-        return None
-
     def resolve_data_dto(self) -> type[AbstractDTO] | None:
         """Resolve the data_dto by starting from the route handler and moving up.
         If a handler is found it is returned, otherwise None is set.
@@ -478,7 +469,6 @@ def resolve_data_dto(self) -> type[AbstractDTO] | None:
                 data_dto.create_for_field_definition(
                     field_definition=self.parsed_data_field,
                     handler_id=self.handler_id,
-                    backend_cls=self._get_dto_backend_cls(),
                 )
 
             self._resolved_data_dto = data_dto
@@ -512,7 +502,6 @@ def resolve_return_dto(self) -> type[AbstractDTO] | None:
                 return_dto.create_for_field_definition(
                     field_definition=self.parsed_return_field,
                     handler_id=self.handler_id,
-                    backend_cls=self._get_dto_backend_cls(),
                 )
                 self._resolved_return_dto = return_dto
             else:

tests/unit/test_app.py

@@ -14,7 +14,7 @@
 from pytest import MonkeyPatch
 
 from litestar import Litestar, MediaType, Request, Response, get
-from litestar.config.app import AppConfig
+from litestar.config.app import AppConfig, ExperimentalFeatures
 from litestar.config.response_cache import ResponseCacheConfig
 from litestar.contrib.sqlalchemy.plugins import SQLAlchemySerializationPlugin
 from litestar.datastructures import MutableScopeHeaders, State
@@ -445,3 +445,8 @@ async def hook_b(app: Litestar) -> None:
     assert events[1] == "ctx_1"
     assert events[2] == "hook_a"
     assert events[3] == "hook_b"
+
+
+def test_use_dto_codegen_feature_flag_warns() -> None:
+    with pytest.warns(LitestarWarning, match="Use of redundant experimental feature flag DTO_CODEGEN"):
+        Litestar(experimental_features=[ExperimentalFeatures.DTO_CODEGEN])

tests/unit/test_dto/test_integration.py

@@ -153,3 +153,16 @@ def handler(data: Model) -> Model:
 
     backend = handler.resolve_data_dto()._dto_backends[handler.handler_id]["data_backend"]  # type: ignore[union-attr]
     assert isinstance(backend, DTOBackend)
+
+
+def test_use_codegen_backend_by_default(ModelDataDTO: type[AbstractDTO]) -> None:
+    ModelDataDTO.config = DTOConfig()
+
+    @post(dto=ModelDataDTO, signature_types=[Model])
+    def handler(data: Model) -> Model:
+        return data
+
+    Litestar(route_handlers=[handler])
+
+    backend = handler.resolve_data_dto()._dto_backends[handler.handler_id]["data_backend"]  # type: ignore[union-attr]
+    assert isinstance(backend, DTOBackend)