Add GenerateConfig lazy import from top-level module

Author: koxudaxi

docs/using_as_module.md

@@ -16,6 +16,11 @@ pip install 'datamodel-code-generator[http]'
 
 When the `output` parameter is omitted (or set to `None`), `generate()` returns the generated code directly as a string:
 
+!!! note
+    `GenerateConfig` is only available in Pydantic v2 environments.
+    For Pydantic v1, use `from datamodel_code_generator.config import GenerateConfig`
+    and call `update_forward_refs()` before use.
+
 ```python
 from datamodel_code_generator import InputFileType, generate, GenerateConfig, DataModelType
 

src/datamodel_code_generator/__init__.py

@@ -971,13 +971,21 @@ def infer_input_type(text: str) -> InputFileType:
     "detect_jsonschema_version": "datamodel_code_generator.parser.schema_version",
     "detect_openapi_version": "datamodel_code_generator.parser.schema_version",
     "generate_dynamic_models": "datamodel_code_generator.dynamic",
+    "GenerateConfig": "datamodel_code_generator.config",
 }
 
 
 def __getattr__(name: str) -> Any:
     if name in _LAZY_IMPORTS:
         import importlib  # noqa: PLC0415
 
+        if name == "GenerateConfig" and not is_pydantic_v2():  # pragma: no cover
+            msg = (
+                f"'{name}' is only available in Pydantic v2 environments. "
+                "Use 'from datamodel_code_generator.config import GenerateConfig' instead."
+            )
+            raise ImportError(msg)
+
         module = importlib.import_module(_LAZY_IMPORTS[name])
         return getattr(module, name)
     msg = f"module {__name__!r} has no attribute {name!r}"
@@ -1025,3 +1033,6 @@ def __getattr__(name: str) -> Any:
     "generate",
     "generate_dynamic_models",  # noqa: F822
 ]
+
+if is_pydantic_v2():  # pragma: no cover
+    __all__ += ["GenerateConfig"]

tests/main/test_main_general.py

@@ -28,6 +28,7 @@
 from datamodel_code_generator.format import CodeFormatter, PythonVersion
 from datamodel_code_generator.model.pydantic_v2 import UnionMode
 from datamodel_code_generator.parser.openapi import OpenAPIParser
+from datamodel_code_generator.util import is_pydantic_v2
 from tests.conftest import assert_output, create_assert_file_content, freeze_time
 from tests.main.conftest import (
     DATA_PATH,
@@ -2307,3 +2308,40 @@ def test_use_annotated_no_warning_pydantic_v1(output_file: Path) -> None:
             extra_args=["--output-model-type", "pydantic.BaseModel"],
         )
     assert not any("--use-annotated will be enabled" in str(warning.message) for warning in w)
+
+
+@pytest.mark.skipif(not is_pydantic_v2(), reason="GenerateConfig requires Pydantic v2")
+def test_import_generate_config_from_top_level() -> None:
+    """Test that GenerateConfig can be imported from top-level module."""
+    from datamodel_code_generator import GenerateConfig as TopLevelGenerateConfig
+
+    assert TopLevelGenerateConfig is not None
+    assert TopLevelGenerateConfig is GenerateConfig
+
+
+@pytest.mark.skipif(not is_pydantic_v2(), reason="GenerateConfig requires Pydantic v2")
+def test_generate_with_imported_config_from_top_level() -> None:
+    """Test generate() with GenerateConfig imported from top-level."""
+    from datamodel_code_generator import GenerateConfig as TopLevelGenerateConfig
+
+    config = TopLevelGenerateConfig(class_name="TestModel")
+    result = generate('{"type": "object"}', config=config)
+    assert result is not None
+    assert "class TestModel" in result
+
+
+@pytest.mark.skipif(not is_pydantic_v2(), reason="GenerateConfig requires Pydantic v2")
+def test_all_exports_includes_generate_config() -> None:
+    """Test that __all__ includes GenerateConfig in Pydantic v2."""
+    import datamodel_code_generator
+
+    assert "GenerateConfig" in datamodel_code_generator.__all__
+
+
+@pytest.mark.skipif(is_pydantic_v2(), reason="Test for Pydantic v1 only")
+def test_import_generate_config_fails_on_v1() -> None:
+    """GenerateConfig should not be importable from top-level in Pydantic v1."""
+    import datamodel_code_generator
+
+    with pytest.raises(ImportError, match="only available in Pydantic v2"):
+        _ = datamodel_code_generator.GenerateConfig