Describe the bug
Generated python code with nested properties causes pydantic v2 to be stuck in infinite loop.

To Reproduce

Example schema:

{
  "title": "Test",
  "type": "object",
  "properties": {
    "TestObject": {
      "title": "TestObject",
      "type": "object",
      "properties": {
        "test_string": {
          "type": "string"
        }
      }
    }
  }
}

Used commandline:

$ datamodel-codegen --input sample.json --output sample.py

then run python -c "from sample import Test"

which throws a RecursionError: maximum recursion depth exceeded

Mind you that this used to work just fine with pydantic v1 , but breaks in v2. Probably related to pydantic/pydantic#6646 (comment).

In the generated python code

[...]
class TestObject(BaseModel):
    test_string: Optional[str] = None


class Test(BaseModel):
    TestObject: Optional[TestObject] = Field(None, title='TestObject')

we could solve the issue by renaming class TestObject(BaseModel) to for example class TestObject_(BaseModel).

Expected behavior
Don't generate output code with namespace collision.

Version:

python==3.12.3
datamodel-code-generator==0.28.2                
pydantic==2.10.6
pydantic_core==2.27.2