[BUG][PYTHON-FASTAPI] Generator specifies path parameter default values

[lvijnck]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

The generator adds default values to path parameters, which FastAPI does not like.

openapi-generator version

v7.0.0-beta

OpenAPI declaration file content or url

{
  "openapi": "3.0.0",
  "paths": {
    "/project/{projectId}/status": {
      "post": {
        "operationId": "ProjectController_projectStatus",
        "summary": "Notify of changes in the project",
        "description": "Synchronous endpoint. Platform Api would call this endpoint to notify any changes made to a project.",
        "parameters": [
          {
            "name": "projectId",
            "required": true,
            "in": "path",
            "description": "Globally unique ID of an project across time",
            "example": "1bd98aa5-5a83-4bf3-97a2-a8a7e444c73e",
            "schema": {
              "type": "string"
            }
          }
        ],
        "requestBody": {
          "required": true,
          "content": {
            "application/json": {
              "schema": {
                "$ref": "#/components/schemas/ProjectStatusRequestBodyDto"
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "OK"
          },
        },
        "tags": [
          "Project related endpoints"
        ]
      }
    }
  },
  "info": {
    "title": "Asset API Specification",
    "description": "API Specification that an asset has to implement in order to integrate with the Platform.",
    "version": "1.0.0",
    "contact": {}
  },
  "tags": [],
  "servers": [
    {
      "url": "dummy"
    }
  ]
}

This yields

# FastAPI does not like the `None` below, it should be `...`
projectId: str = Path(None, description="Globally unique ID of an project across time"),

This check is explicitly codified in the FastAPI source code:

https://github.com/tiangolo/fastapi/blob/master/fastapi/params.py

i.e.,

class Path(Param):
    in_ = ParamTypes.path

    def __init__(
        self,
        default: Any = ...,
        *,
        alias: Optional[str] = None,
        title: Optional[str] = None,
        description: Optional[str] = None,
        gt: Optional[float] = None,
        ge: Optional[float] = None,
        lt: Optional[float] = None,
        le: Optional[float] = None,
        min_length: Optional[int] = None,
        max_length: Optional[int] = None,
        regex: Optional[str] = None,
        examples: Optional[List[Any]] = None,
        example: Annotated[
            Optional[Any],
            deprecated(
                "Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, "
                "although still supported. Use examples instead."
            ),
        ] = Undefined,
        deprecated: Optional[bool] = None,
        include_in_schema: bool = True,
        **extra: Any,
    ):
        assert default is ..., "Path parameters cannot have a default value"
        ...

Generation Details

Steps to reproduce

1. Use config above to generate with FastAPI generator
2. See generated output

Suggest a fix

Ensure default path params are always set to ...

[rockc2020]

I met the same issue when running openapi-generator for python fastapi, and then pytest failed.
After changing None to ... as suggested, all tests passed.
openapi-generator version: 6.6.0

[giulio-opal]

I'm encountering the same issue, even with the latest version:

Traceback (most recent call last):
  File "/venv/bin/uvicorn", line 8, in <module>
    sys.exit(main())
  File "/venv/lib/python3.7/site-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
  File "/venv/lib/python3.7/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
  File "/venv/lib/python3.7/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/venv/lib/python3.7/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
  File "/venv/lib/python3.7/site-packages/uvicorn/main.py", line 456, in main
    h11_max_incomplete_event_size=h11_max_incomplete_event_size,
  File "/venv/lib/python3.7/site-packages/uvicorn/main.py", line 578, in run
    server.run()
  File "/venv/lib/python3.7/site-packages/uvicorn/server.py", line 61, in run
    return asyncio.run(self.serve(sockets=sockets))
  File "/usr/local/lib/python3.7/asyncio/runners.py", line 43, in run
    return loop.run_until_complete(main)
  File "uvloop/loop.pyx", line 1517, in uvloop.loop.Loop.run_until_complete
  File "/venv/lib/python3.7/site-packages/uvicorn/server.py", line 68, in serve
    config.load()
  File "/venv/lib/python3.7/site-packages/uvicorn/config.py", line 473, in load
    self.loaded_app = import_from_string(self.app)
  File "/venv/lib/python3.7/site-packages/uvicorn/importer.py", line 21, in import_from_string
    module = importlib.import_module(module_str)
  File "/usr/local/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/venv/lib/python3.7/site-packages/openapi_server/main.py", line 15, in <module>
    from openapi_server.apis.groups_api import router as GroupsApiRouter
  File "/venv/lib/python3.7/site-packages/openapi_server/apis/groups_api.py", line 53, in <module>
    group_id: str = Path(None, description="The id of the group."),
  File "/venv/lib/python3.7/site-packages/fastapi/param_functions.py", line 85, in Path
    **extra,
  File "/venv/lib/python3.7/site-packages/fastapi/params.py", line 182, in __init__
    assert default is ..., "Path parameters cannot have a default value"
AssertionError: Path parameters cannot have a default value

I can either remove None or replace it with ... but every time I regenerate the schema, that change is overridden. Is there a workaround I can adopt to avoid having to replace it every time? Thank you!

[yoccodog]

i ran into this and used a custom template file to fix the issue. the contents of my custom endpoint_argument_definition.mustache file are:

{{#isPathParam}}{{baseName}}{{/isPathParam}}{{^isPathParam}}{{paramName}}{{/isPathParam}}: {{>param_type}} = {{#isPathParam}}Path{{/isPathParam}}{{#isHeaderParam}}Header{{/isHeaderParam}}{{#isFormParam}}Form{{/isFormParam}}{{#isQueryParam}}Query{{/isQueryParam}}{{#isCookieParam}}Cookie{{/isCookieParam}}{{#isBodyParam}}Body{{/isBodyParam}}({{&defaultValue}}{{^defaultValue}}{{#isPathParam}}...{{/isPathParam}}{{^isPathParam}}None{{/isPathParam}}{{/defaultValue}}, description="{{description}}"{{#isLong}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isLong}}{{#isInteger}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isInteger}}{{#pattern}}, regex=r"{{.}}"{{/pattern}}{{#minLength}}, min_length={{.}}{{/minLength}}{{#maxLength}}, max_length={{.}}{{/maxLength}})

it's hard to see the diff but i changed this:

{{^defaultValue}}None{{/defaultValue}}

to this:

{{^defaultValue}}{{#isPathParam}}...{{/isPathParam}}{{^isPathParam}}None{{/isPathParam}}{{/defaultValue}}