[BUG][python-fastapi] Reordering of path operations can cause issues when path parameters are involved

[zhornback]

Description

The OpenAPI Generator reorders path operations while generating server code. According to https://fastapi.tiangolo.com/tutorial/path-params/?h=path#order-matters, the order of path declaration is important. This can lead to FastAPI incorrectly routing a call to one endpoint to a similar endpoint containing a path parameter.

openapi-generator version

Initially found with v7.12.0, but reproduced with v7.16.0 as well.

OpenAPI declaration file content or url

https://gist.github.com/zhornback/dfd8b93c90907c403bef3af6a5b38c67

Steps to reproduce

• Download yaml file linked above.
• Get most recent openapi-generator-cli.jar
• Generate server using 'java -jar ./openapi-generator-cli.jar generate -i ./petstore/petstore.yaml -g python-fastapi -o ./petstore/python-fastapi'.
• Open petstore/python-fastapi/src/openapi_server/apis/pet_api.py.
• Notice that GET /pet/{petID} is declared prior to GET /pet/latest. If you ran the server, you'd find calls to GET /pet/latest will fail, because 'latest' isn't a valid petID.

Related issues/PRs

#19550 seems like a similar issue for another generator.

Suggest a fix

The configuration for FastAPI should set setSkipSortingOperations to True. I will put together a PR to that effect as soon as I can.

As a short-term workaround, the generator is alphabetically sorting based upon path operationIDs. If you appropriately name your path operationIDs, you can control how the paths are sorted and avoid the issue.