Fix allOf handling to generate class definitions with descriptions instead of aliases (#2643)

Author: koxudaxi

src/datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2

@@ -1,4 +1,4 @@
-{% if base_class != "BaseModel" and "," not in base_class and not fields and not config -%}
+{% if base_class != "BaseModel" and "," not in base_class and not fields and not config and not description -%}
 
 {# if this is just going to be `class Foo(Bar): pass`, then might as well just make Foo
 an alias for Bar: every pydantic model class consumes considerable memory. #}

tests/data/expected/main_kr/main_allof_with_description_only/output.py

@@ -0,0 +1,23 @@
+# generated by datamodel-codegen:
+#   filename:  allof_with_description_only.yaml
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Optional
+
+from pydantic import BaseModel
+
+
+class MyModel(BaseModel):
+    """
+    A model that has a description.
+    """
+
+    name: Optional[str] = None
+
+
+class MyOtherModel(MyModel):
+    """
+    Another model that should also have a description.
+    """

tests/data/openapi/allof_with_description_only.yaml

@@ -0,0 +1,17 @@
+openapi: "3.0.0"
+info:
+  title: Test API
+  version: "1.0.0"
+paths: {}
+components:
+  schemas:
+    MyModel:
+      type: object
+      description: A model that has a description.
+      properties:
+        name:
+          type: string
+    MyOtherModel:
+      allOf:
+        - $ref: "#/components/schemas/MyModel"
+      description: Another model that should also have a description.

tests/test_main_kr.py

@@ -955,3 +955,20 @@ def test_profile_without_pyproject_errors(tmp_path: Path, capsys: pytest.Capture
         assert return_code == Exit.ERROR
         captured = capsys.readouterr()
         assert "no [tool.datamodel-codegen] section found" in captured.err.lower()
+
+
+@freeze_time("2019-07-26")
+def test_allof_with_description_generates_class_not_alias(output_file: Path) -> None:
+    """Test that allOf with description generates class definition, not alias."""
+    run_main_and_assert(
+        input_path=OPEN_API_DATA_PATH / "allof_with_description_only.yaml",
+        output_path=output_file,
+        input_file_type=None,
+        assert_func=assert_file_content,
+        expected_file=EXPECTED_MAIN_KR_PATH / "main_allof_with_description_only" / "output.py",
+        extra_args=[
+            "--output-model-type",
+            "pydantic_v2.BaseModel",
+            "--use-schema-description",
+        ],
+    )