Sync RootModel config before rendering

Author: koxudaxi

src/datamodel_code_generator/model/pydantic_v2/root_model.py

@@ -9,7 +9,11 @@
 
 from datamodel_code_generator import Error
 from datamodel_code_generator.imports import IMPORT_ANY, Import
-from datamodel_code_generator.model.pydantic_v2.base_model import _CONFIG_ITEMS_TEMPLATE_DATA_KEY, BaseModel
+from datamodel_code_generator.model.pydantic_v2.base_model import (
+    _CONFIG_ITEMS_TEMPLATE_DATA_KEY,
+    BaseModel,
+    _config_dict_items,
+)
 from datamodel_code_generator.model.pydantic_v2.imports import IMPORT_CONFIG_DICT
 
 IMPORT_ABC_ITERATOR = Import.from_full_path("collections.abc.Iterator")
@@ -44,15 +48,38 @@ def __init__(
 
         super().__init__(**kwargs)
 
-        config = self.extra_template_data.get("config")
-        has_meaningful_config = config is not None and (
-            getattr(config, "regex_engine", None) is not None or getattr(config, "frozen", None) is not None
-        )
-        if not has_meaningful_config:
+        if not self._has_meaningful_config(self.extra_template_data.get("config")):
             self.extra_template_data.pop("config", None)
             self.extra_template_data.pop(_CONFIG_ITEMS_TEMPLATE_DATA_KEY, None)
             self._additional_imports = [imp for imp in self._additional_imports if imp != IMPORT_CONFIG_DICT]
 
+    @staticmethod
+    def _has_meaningful_config(config: Any) -> bool:
+        match config:
+            case None:
+                return False
+            case dict():
+                return config.get("regex_engine") is not None or config.get("frozen") is not None
+            case _:
+                return getattr(config, "regex_engine", None) is not None or getattr(config, "frozen", None) is not None
+
+    def _sync_config_items(self) -> None:
+        if _CONFIG_ITEMS_TEMPLATE_DATA_KEY in self.extra_template_data:
+            return
+        config = self.extra_template_data.get("config")
+        if not self._has_meaningful_config(config):
+            self.extra_template_data.pop("config", None)
+            return
+        if config_items := _config_dict_items(config):
+            self.extra_template_data[_CONFIG_ITEMS_TEMPLATE_DATA_KEY] = config_items
+            if IMPORT_CONFIG_DICT not in self._additional_imports:
+                self._additional_imports.append(IMPORT_CONFIG_DICT)
+            self.clear_imports_cache()
+            return
+        self.extra_template_data.pop("config", None)
+        self._additional_imports = [imp for imp in self._additional_imports if imp != IMPORT_CONFIG_DICT]
+        self.clear_imports_cache()
+
     def add_sequence_interface(self, item_type: str, slice_type: str) -> None:
         """Add sequence interface helpers that delegate to the wrapped root value."""
         self._additional_imports.append(IMPORT_ABC_ITERATOR)
@@ -68,6 +95,7 @@ def add_sequence_interface(self, item_type: str, slice_type: str) -> None:
 
     def render(self, *, class_name: str | None = None) -> str:
         """Render the RootModel and validate custom sequence templates when needed."""
+        self._sync_config_items()
         rendered = super().render(class_name=class_name)
         self._validate_custom_template_sequence_interface(rendered)
         return rendered

tests/model/pydantic_v2/test_root_model.py

@@ -293,3 +293,24 @@ def test_root_model_renders_existing_config_object() -> None:
     assert "model_config = ConfigDict(" in rendered
     assert 'regex_engine="python-re",' in rendered
     assert _CONFIG_ITEMS_TEMPLATE_DATA_KEY in root_model.extra_template_data
+
+
+def test_root_model_renders_late_config_dict() -> None:
+    """RootModel syncs config_items for config added after initialization."""
+    root_model = RootModel(
+        fields=[
+            DataModelFieldBase(
+                name="a",
+                data_type=DataType(type="str"),
+                required=True,
+            )
+        ],
+        reference=Reference(name="TestRootModel", path="test_root_model"),
+    )
+    root_model.extra_template_data["config"] = {"regex_engine": '"python-re"'}
+
+    rendered = root_model.render()
+
+    assert "model_config = ConfigDict(" in rendered
+    assert 'regex_engine="python-re",' in rendered
+    assert _CONFIG_ITEMS_TEMPLATE_DATA_KEY in root_model.extra_template_data