Use semantic None default checks

Author: koxudaxi

src/datamodel_code_generator/model/base.py

@@ -315,6 +315,14 @@ def _process_const_as_literal(self) -> None:
         if self.default is None and not self.has_default:
             self.default = const
 
+    def should_strip_default_none(self, *, keep_optional: bool = False) -> bool:
+        """Return whether an actual None default should be omitted."""
+        match (self.strip_default_none, keep_optional and self.data_type.is_optional):
+            case (False, _) | (_, True):
+                return False
+
+        return self.default is None
+
     def self_reference(self) -> bool:
         """Check if field references its parent model.
 

src/datamodel_code_generator/model/dataclass.py

@@ -34,8 +34,7 @@
 def has_field_assignment(field: DataModelFieldBase) -> bool:
     """Check if a dataclass field renders with an assignment or default value."""
     return (bool(field.field) and not field.use_annotated) or not (
-        (field.required and not field.use_default_with_required)
-        or (field.represented_default == "None" and field.strip_default_none)
+        (field.required and not field.use_default_with_required) or field.should_strip_default_none()
     )
 
 

src/datamodel_code_generator/model/msgspec.py

@@ -60,9 +60,7 @@ def __str__(self) -> str:
 
 def has_field_assignment(field: DataModelFieldBase) -> bool:
     """Return whether a msgspec field renders with a default assignment."""
-    return field.use_default_with_required or not (
-        field.required or (field.represented_default == "None" and field.strip_default_none)
-    )
+    return field.use_default_with_required or not (field.required or field.should_strip_default_none())
 
 
 DataModelFieldBaseT = TypeVar("DataModelFieldBaseT", bound=DataModelFieldBase)

src/datamodel_code_generator/model/pydantic_base.py

@@ -235,12 +235,6 @@ def _process_data_in_str(self, data: dict[str, Any]) -> None:  # pragma: no cove
     def _process_annotated_field_arguments(self, field_arguments: list[str]) -> list[str]:  # noqa: PLR6301
         return field_arguments
 
-    def _should_strip_default_none_from_field(self) -> bool:
-        if self.data_type.is_optional:
-            return False
-
-        return self.default is None
-
     def _get_field_data_and_default_factory(self) -> tuple[dict[str, Any], Any]:
         """Build Field() keyword data and the effective default_factory."""
         data: dict[str, Any] = {k: v for k, v in self.extras.items() if k not in self._EXCLUDE_FIELD_KEYS}
@@ -315,7 +309,7 @@ def __str__(self) -> str:
         elif (
             not default_factory
             and (default_repr := represent_python_value(self.default))
-            and (not self.strip_default_none or not self._should_strip_default_none_from_field())
+            and not self.should_strip_default_none(keep_optional=True)
         ):
             field_arguments = [default_repr, *field_arguments]
 

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

@@ -0,0 +1,14 @@
+# generated by datamodel-codegen:
+#   filename:  strip_default_none_semantic.yaml
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+
+@dataclass
+class SemanticNoneModel:
+    implicitNone: str | None
+    stringNoneDefault: str | None = 'None'
+    explicitDefault: str | None = 'active'

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

@@ -0,0 +1,13 @@
+# generated by datamodel-codegen:
+#   filename:  strip_default_none_semantic.yaml
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from msgspec import UNSET, Struct, UnsetType
+
+
+class SemanticNoneModel(Struct):
+    implicitNone: str | UnsetType = UNSET
+    stringNoneDefault: str | UnsetType = 'None'
+    explicitDefault: str | UnsetType = 'active'

tests/data/openapi/strip_default_none_semantic.yaml

@@ -0,0 +1,18 @@
+openapi: 3.0.3
+info:
+  title: strip default none semantic
+  version: 1.0.0
+paths: {}
+components:
+  schemas:
+    SemanticNoneModel:
+      type: object
+      properties:
+        implicitNone:
+          type: string
+        stringNoneDefault:
+          type: string
+          default: "None"
+        explicitDefault:
+          type: string
+          default: active

tests/main/openapi/test_main_openapi.py

@@ -1319,6 +1319,44 @@ def test_main_openapi_pydantic_v2_strip_default_none_field_metadata(output_file:
     )
 
 
+@pytest.mark.parametrize(
+    ("output_model_type", "target_python_version", "expected_file"),
+    [
+        (
+            "dataclasses.dataclass",
+            "3.10",
+            "strip_default_none_semantic_dataclass.py",
+        ),
+        (
+            "msgspec.Struct",
+            "3.10",
+            "strip_default_none_semantic_msgspec.py",
+        ),
+    ],
+)
+def test_main_openapi_strip_default_none_semantic_default(
+    output_model_type: str,
+    target_python_version: str,
+    expected_file: str,
+    output_file: Path,
+) -> None:
+    """Test strip-default-none treats only actual None defaults as None."""
+    run_main_and_assert(
+        input_path=OPEN_API_DATA_PATH / "strip_default_none_semantic.yaml",
+        output_path=output_file,
+        input_file_type="openapi",
+        assert_func=assert_file_content,
+        expected_file=expected_file,
+        extra_args=[
+            "--strip-default-none",
+            "--output-model-type",
+            output_model_type,
+            "--target-python-version",
+            target_python_version,
+        ],
+    )
+
+
 def test_disable_timestamp(output_file: Path) -> None:
     """Test OpenAPI generation with timestamp disabled."""
     run_main_and_assert(