fix: quote forward references in recursive RootModel generic parameters (#2720)

Author: koxudaxi

src/datamodel_code_generator/parser/base.py

@@ -1892,11 +1892,11 @@ def __is_new_required_field(self, field: DataModelFieldBase, inherited: set[str]
 
     @classmethod
     def __update_type_aliases(cls, models: list[DataModel]) -> None:
-        """Update type aliases to properly handle forward references per PEP 484."""
+        """Update type aliases and RootModels to properly handle forward references per PEP 484."""
         model_index: dict[str, int] = {m.class_name: i for i, m in enumerate(models)}
 
         for i, model in enumerate(models):
-            if not isinstance(model, TypeAliasBase):
+            if not isinstance(model, (TypeAliasBase, pydantic_model_v2.RootModel)):
                 continue
             if isinstance(model, TypeStatement):
                 continue

tests/data/expected/main/openapi/type_alias_recursive_pydantic_v2.py

@@ -0,0 +1,46 @@
+# generated by datamodel-codegen:
+#   filename:  type_alias_recursive.yaml
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Union
+
+from pydantic import BaseModel, RootModel
+
+
+class File(BaseModel):
+    path: str
+
+
+class Folder(BaseModel):
+    address: str | None = None
+    files: list[File]
+    subfolders: list[Folder] | None = None
+
+
+class ElementaryType(RootModel[bool | str | int | float | None]):
+    root: bool | str | int | float | None = None
+
+
+class JsonType(
+    RootModel[Union[ElementaryType, list["JsonType"], dict[str, "JsonType"]]]
+):
+    root: Union[ElementaryType, list["JsonType"], dict[str, "JsonType"]]
+
+
+class Space(BaseModel):
+    label: str | None = None
+    data: JsonType | None = None
+    dual: DualSpace | None = None
+
+
+class DualSpace(BaseModel):
+    label: str | None = None
+    data: JsonType | None = None
+    predual: Space | None = None
+
+
+Folder.model_rebuild()
+JsonType.model_rebuild()
+Space.model_rebuild()

tests/main/openapi/test_main_openapi.py

@@ -3468,6 +3468,26 @@ def test_main_openapi_type_alias_recursive(output_file: Path) -> None:
     )
 
 
+def test_main_openapi_type_alias_recursive_pydantic_v2(output_file: Path) -> None:
+    """Test recursive RootModel with forward references in Pydantic v2.
+
+    Without --use-type-alias, recursive schemas generate RootModel classes.
+    Forward references in the generic parameter must be quoted to avoid
+    NameError at class definition time.
+    """
+    run_main_and_assert(
+        input_path=OPEN_API_DATA_PATH / "type_alias_recursive.yaml",
+        output_path=output_file,
+        input_file_type="openapi",
+        assert_func=assert_file_content,
+        expected_file="type_alias_recursive_pydantic_v2.py",
+        extra_args=[
+            "--output-model-type",
+            "pydantic_v2.BaseModel",
+        ],
+    )
+
+
 def test_main_openapi_type_alias_cross_module_collision_a(output_file: Path) -> None:
     """Test TypeAlias generation for module A in cross-module collision scenario."""
     run_main_and_assert(